One of the effects of COVID-19 pandemic is a rapidly growing and changing stream of publications to inform clinicians, researchers, policy makers, and patients about the health, socio-economic, and cultural consequences of the pandemic. Managing this information stream manually is not feasible. Automatic Question Answering can quickly bring the most salient points to the user’s attention. Leveraging a collection of scientific articles, government websites, relevant news articles, curated social media posts, and questions asked by researchers, clinicians, and the general public, we developed a dataset to explore automatic Question Answering for multiple stakeholders. Analysis of questions asked by various stakeholders shows that while information needs of experts and the public may overlap, satisfactory answers to these questions often originate from different information sources or benefit from different approaches to answer generation. We believe that this dataset has the potential to support the development of question answering systems not only for epidemic questions, but for other domains with varying expertise such as legal or finance.  The COVID-19 pandemic has highlighted two major problems with access to reliable domain-specific information: (1) information providers are rapidly generating reams of potentially vital information that might never reach their intended audience, and (2) information seekers struggle to find answers to their specific and changing information needs in the rapidly growing and changing body of communications. These two problems are effectively two sides of the same coin, and making information easier to discover reduces the potential for vital information to remain overlooked by its intended audience. Information Retrieval (IR) systems  are now an integral part of information seeking and one of the main tools used to satisfy information needs. The pandemic exposed a major problem when relying on information retrieval systems under stressful and fast-changing circumstances: existing solutions retrieve hundreds or thousands of documents –- many of which may not be relevant to the user’s specific information need. This needlessly increases the time and mental effort required by information seekers who must read through these documents to find answers to their information needs. Question Answering is a research area aiming to alleviate the problem of finding pertinent information from thousands of documents by bringing the most salient points of relevant documents to focus immediately, saving time and highlighting information that may have been overlooked.Epidemic QA (EPIC-QA), intended to evaluate automatic approaches for answering ad-hoc questions about the disease COVID-19, its causal virus SARS-CoV-2, related coronaviruses, and the recommended response to the pandemic. While COVID-19 has been an impetus for a large body of emergent scientific research and inquiry, the response to COVID-19 raises questions for the general public. The rapid increase in coronavirus literature and evolving guidelines on community response creates a challenging burden not only for the scientific and medical communities but also the general public to stay up-to-date on the latest developments. Consequently, the goal of the dataset is to evaluate systems on their ability to provide timely and accurate expert-level answers as expected by the scientific and medical communities as well as answers in suitable language for the general public. The EPIC-QA dataset consists of (a) questions collected from various stakeholders who need information on COVID-19, (b) documents – including scientific research articles suited for experts as well as relevant news, social media, and pages from authoritative websites intended for the general public, and (c) answers to these questions extracted from documents in the dataset and systematically annotated and judged by experts.To this end, we propose a new question answering dataset: 1 is the most widely used document collection, containing documents from PubMed, research articles from the World Health Organization (WHO), pre-prints from bioRxiv, medRxiv, and arXiv, and SemanticScholar. CORD-19, however, does not provide questions or answers. In terms of COVID question answering, CovidQA2 provides 124 question–article–answer triplets from 85 articles; COVID-Q3 consists of 1,690 questions (without answers) annotated into 15 categories and 207 clusters; Medical Question Pairs (MQP)4 contains 3,048 pairs of medical questions annotated as being similar or dissimilar to COVID-19 FAQs; the Synergy Task of the 2021 BioASQ Challenge (http://www.bioasq.org/) included four rounds of binary, factoid, list, and summary questions based on the CORD-19 collection; and the 2021 TREC Health Misinformation Track  includes topics focused on COVID-19 with annotations indicating whether documents contradict the topic’s answer. For a detailed review of additional natural language processing resources for COVID-19, see Chen et al. (2021)5. By contrast, EPIC-QA, which incorporates both public-facing and expert-level documents, is the only dataset exploring the difference between answers suitable for the general public and those appropriate for experts. It is the only dataset designed to include a wide variety of unique possible answers for each question.Only a handful of publicly available health-related QA datasets exist. In terms of information retrieval, CORD-19How does the vaccine work? In the eyes of an expert, an answer should indicate the exact mechanism and pathways involved. By contrast, for a member of the general public, this information is too involved and may cause confusion; instead, a more appropriate answer would provide a more general overview of the role of the vaccine and a high-level description of its mechanism. In the context of the rapidly accelerating knowledge of COVID-19, managing this duality between expert- and general- level information is even more important. It is our hope that the EPIC-QA dataset will stimulate research in automatic question answering not only to support providing high-quality timely information about COVID-19, but also to support the development of generalizable approaches to meeting information needs in the face of varying levels of expertise for other domains, such as general healthcare, finance, or legal.While there is overlap in the types of questions asked by different stakeholders, the answers to such questions should vary based on the background knowledge of the user. For example, consider the simple question illustrated in Fig. information retrieval step, in which relevant documents are retrieved for a given question, and an answer extraction step, in which relevant passages or answers are identified within the retrieved documents and extracted as-is or used to synthesize an answer. Recently, end-to-end question answering systems have been developed in which (deep) neural networks are trained to jointly identify relevant passages and extract answers from those passages. Consequently, the EPIC-QA dataset includes two collections intended to facilitate research on (a) answer extraction or (b) end-to-end question answering, respectively. The questions in the answer-extraction dataset are adapted from the queries of the TREC-COVID retrieval shared task (https://ir.nist.gov/trec-covid), and are associated with the set of relevancy annotations from that task. For the end-to-end dataset, we introduce a novel set of questions, and provide relevant documents and answer annotations without associated retrieval relevance rankings. These two collections can be used separately or in concert to study the relationship between document retrieval and answer extraction. Both collections consist of three components:Two sets of manually-produced questions, one asked by the general public as well as another asked by experts pertaining to COVID-19;A collection of documents relevant to COVID-19 including published and pre-print biomedical research articles as well as documents obtained from government websites, news, and social media, automatically parsed into sentences; andA diverse list of manually-produced answers for each question as well as a set of relevant document excerpts with manual sentence-level annotations indicating which answers, if any, are evidenced by each sentence.Question answering systems traditionally involve two main steps: an To facilitate answer-extraction research, the questions in the answer-extraction dataset are additionally associated with a set of relevant documents as might be retrieved by an optimal search engine, while the questions in the end-to-end dataset are not. We detail the process by which each of these components was produced.https://ir.nist.gov/covidSubmit). The majority of these questions originated from users’ interactions with MedlinePlus. Additional scientific questions were developed based on group discussions from the National Institutes of Health (NIH) special interest group on COVID-19, questions asked by Oregon Health & Science University clinicians, and responses to a public call for questions. The TREC-COVID topics included expert-level background descriptions of the user’s information need; to facilitate public-facing question answering we produced public-friendly backgrounds for each question. We provide the document-level relevance judgments produced during the TREC-COVID evaluation for these questions. The answer extraction collection includes 45 expert questions and 42 general public questions with document-level relevance judgments. For the end-to-end collections, a new set of 30 expert and 30 general public questions were developed, none of which were evaluated in TREC-COVID; consequently, these questions do not come with document-level relevance judgments. Example questions are provided in Fig. Two sets of questions are included: one for expert-level questions and one for the general public. By design, many of the expert and consumer questions overlap in focus to facilitate comparison between both types of stakeholders. For the answer extraction dataset, we adapted the topics evaluated in the fourth round of TREC-COVID  and sentence boundaries. To support both levels of expertise, the document collections consists of two parts: scientific and medical research, and public-facing online documents.Each document in EPIC-QA includes explicitly pre-defined 6. The dataset was created by the Allen Institute for AI in partnership with the Chan Zuckerberg Initiative, Georgetown University’s Center for Security and Emerging Technology, Microsoft Research, and the National Library of Medicine – National Institutes of Health, in coordination with The White House Office of Science and Technology Policy. The CORD-19 collection includes a subset of articles in PubMed Central (PMC) as well as pre-prints from bioRxiv and medRxiv. Contexts in this collection correspond to automatically identified paragraphs in the articles’ abstracts, or main texts. We include two snapshots of CORD-19: a snapshot from June 19, 2020 to be used with the answer extraction collection, and a snapshot from October 22, 2020, to be used for the end-to-end collection.We adapt the collection of biomedical articles released for the COVID-19 Open Research Dataset Challenge (CORD-19)7. This collection includes authoritative articles from the Centers for Disease Control and Prevention (CDC); the Genetic and Rare Disease Information Center (GARD); the Genetics Home Reference (GHR); Medline Plus; the National Institute of Allergy and Infectious Diseases (NIAID); and the World Health Organization (WHO). Contexts in this collection correspond to paragraphs or sections as indicated by the HTML markup of the document. All articles were filtered for COVID-19 content using the terms in Fig. https://trec-health-misinfo.github.io/). To avoid misinformation, we only considered Reddit threats from the heavily-moderated /r/askscience community that were tagged as pertaining to COVID-19, Medicine, Biology, or the Human Body  service of the U.S. National Library of Medicine (NLM)Technical Validation for more details). These contexts were pooled at a depth of five for expert questions and a depth of eight for questions from the general public, resulting in roughly 45–60 contexts per question. Human assessors read these retrieved contexts and judged them. Specifically, 17 medical indexers with five to thirty years of experience at the National Library of Medicine analyzed the pooled contexts in two rounds: (1) an answer-key generation round, followed by (2) a sentence-level answer annotation round. Annotations were performed as part of the medical indexers’ official duties at the National Library of Medicine.When producing answers for the EPIC-QA dataset, our intent was to explore the landscape of answers asserted in the document collection. Thus, we consider any statement that answers the question as an “answer” regardless of whether or not the answer is factually accurate at the time the document was authored or given current information. The answers in this dataset are intended as an intermediary step where-in one would like to explore all answers provided by the document collection – both correct answers as well as incorrect answers that people may have discovered on their own. Answers were produced by applying multiple automatic question answering systems to the questions in EPIC-QA to identify contexts that may answer the question  nuggets that they feel should be included in the answer key based on their understanding of the question.In the first round, assessors had access to a pool of contexts identified for a given question as well as an ad-hoc search engine over the document collection. The role of the answer key generation round was for assessors to explore the contexts identified by automatic question answering systems as well as the document collection to determine a set of atomic “facts” that answer the question based on the question’s information need or background see Fig. . As in VCOVID trial, trial pause, lack of benefit, hydroxychloroquine, patient safety, and review of the data.In the second round, the answer key (list of nuggets) was fixed. Assessors were given the same set of pooled contexts used in round one. This time, they were asked to annotate all sentences in each context indicating which nugget(s) (if any) are addressed by each sentence. For example, for the question “Which COVID-19 vaccine trials were paused and what were the health safety concerns?” the sentence “[I]n the light of a recent publication...on the lack of safety and efficacy of HCQ in the treatment for COVID-19 patients, the Executive Group of the Solidarity Trial decided to implement a temporary pause of the HCQ arm within the trial as a precaution, while the safety data is being reviewed” was annotated as containing the expert nuggets: 12. The questions in the EPIC-QA dataset are provided in four files following the JSON format illustrated in Fig. ae/expert_questions.json contains 45 expert-level questions produced for the answer extraction collection; andae/general_questions.json contains 42 questions from the general public produced for the answer extraction collection.e2e/expert_questions.json contains 30 expert-level questions produced for the end-to-end collection; ande2e/general_questions.json contains 30 questions from the general public produced for the end-to-end collection.The Epidemic Question Answering (EPIC-QA) dataset is available through the Open Science Foundation (OSF) at 10.17605/OSF.IO/VNYK8ae/cord19/ contains 129,069 JSON files, each corresponding to a biomedical research article from a June 19, 2020 snapshot of CORD-19; andae/general/ contains 925 JSON files, each corresponding to a government or health agency website crawled on June 10, 2020.e2e/cord19/ contains 236,035 JSON files, each corresponding to a biomedical research article from an October 22, 2020 snapshot of CORD-19;e2e/ask_science/ is initially empty , however, it can be populated using the Python script scripts/populate_reddit.py to create 263 JSON files, each corresponding to a post made between December 01 2019 and October 29, 2020 to the /r/askscience community on Reddit tagged by community moderators as corresponding to COVID-19, health, medicine, or biology, which contained one of the COVID-19 keywords shown in Fig. 3e2e/ccns_trec/ contains 114,645 JSON files, each corresponding to an HTML-parsed website included in the CommonCrawl News Subset used by the TREC Misinformation Track containing one of the COVID-19 keywords shown in Fig. e2e/chqa contains 2,739 JSON files, each corresponding to an October 9, 2020 HTML-parsed snapshot of a web page affiliated with the NIH, CDC, or WHO containing one of the COVID-19 keywords shown in Fig. The documents included in the EPIC-QA dataset are provided separately for the answer extraction and end-to-end collections. For each collection, each document is provided as a separate JSON file, adhering to the JSON schema illustrated in Fig. https://github.com/usnistgov/trec_eval) format, as illustrated in Fig. Technical Validation for details), as well as an “ideal” ranking of answers based on our assessor’s answer annotations.Finally, answers are provided in four files, corresponding to the answer extraction and end-to-end collections of expert and public questions. For each question: each answer  is associated with the set of sentence-IDs that nugget was identified within, as shown by the JSON schema in Fig. passages for each question, where a passage was defined as a contiguous sequence of sentences from a single context. We first evaluated the answer extraction collection, and provided the judgments produced from that evaluation as additional data for participants of the later end-to-end evaluation.To validate the EPIC-QA dataset, we organized a community evaluation at the 2020 Text Analysis Conference (TAC), in which participants were provided with the dataset (without answers) and asked to submit ranked lists of up to 1,000 relevant 13 (NDCG) which we refer to as the Normalized Discount Novelty Score (NDNS). Importantly, while the cumulative gain in NDCG can be computed for a document independently of the other retrieved documents, the Novelty Score (NS) measures the information in a passage that has not been seen previously in the ranked list of passages. Formally, we define the novelty score, NS, of passage p as:novel answers in passage p and Exact, which prioritizes passages that contain as many novel nuggets in as few sentences as possible, such that Partial, in which the number of sentences used to express novel nuggets is not considered, i.e., Relaxed, in which the number of sentences used to express novel or previously seen nuggets is not considered, i.e., We encouraged teams to explore diversity in their answers rather than returning many passages providing the most common or obvious answer. To this end, we validated EPIC-QA using a modified version of Normalized Discounted Cumulative GainThe evaluation script is included with the dataset.14 fine-tuned on the SQuAD 2.015 general domain question answering data; their second and third runs additionally fine-tuned on QuAC16, a dialogue-based question answering dataset involving crowd workers and a teacher discussing a passage of text. Interestingly, their third and best-performing run relied on their own information retrieval system rather than the relevance labels produced during TREC-COVID. IBM’s three runs ignored the included relevance labels, using three different ensembles of elastic search with passage retrieval and/or neural re-ranking approaches. Their final runs were a combination of their ensemble information retrieval scores and scores from RoBERTa17 fine-tuned on Natural Questions18, a general domain question answering dataset derived from Google search queries and Wikipedia passages. The HLTRI runs relied on a BioBERT19-based neural passage re-ranker applied to sentence shingles (runs of multiple adjacent sentences) using the TREC-COVID relevance labels. Overall, while the relevance judgments did help with answering questions for the general public, their impact was less clear for expert-level questions, suggesting that documents may be relevant from an information retrieval perspective despite not having explicitly extraditable answers to the question.A total of 17 submissions were received from eight teams for the expert questions, and 10 submissions from six teams for the general public questions, as shown in Table 20, followed by a BERT-based21 re-ranker, and a final-step inspired by recognizing question entailment22. The first run from Yastil_R relied on an information retrieval step informed by BM25, DeepCT23, ColBERT24, and docTTTTTquery25, followed by an answer-extraction step relying on BERT fine-tuned on MS-MARCO26. When looking at the general public, the top performance was exhibited by h2loo, whose runs involved a BM25-based retrieval step followed by point-wise and pair-wise re-ranking using T5, and a final sentence-re-ranking step using maximal marginal relevance (MMR) to improve diversity.For the end-to-end questions, a total of 16 submissions were received from seven teams for expert questions, and 12 submissions from five teams were received for questions from the general public, as shown in Table When comparing between the answer extraction and end-to-end validation results, it is clear that teams generally performed better on end-to-end despite end-to-end being a more challenging problem. This is likely explained by the fact that the answer extraction phase of the TAC challenge was designed and promoted as a preliminary data-collection round, while the end-to-end questions were presented as the primary round for evaluation. It is our belief that the higher performance on the end-to-end evaluation suggests that teams spent more of their research effort on that task than on the answer extraction task.Overall, teams were able to produce satisfactory answers using a variety of approaches based on the EPIC-QA data. Interestingly, the changing in ranking between expert and public performance also suggests that one-size does not fit all, and that systems need to better account for varying stakeholders, such as experts and the general public.Fig. We presented the Epidemic Question Answering (EPIC-QA) dataset, designed to evaluate and draw attention to the important problem of answering questions about COVID-19 from emergent literature, as well as to explore the differences between answers expected by different stakeholders. The EPIC-QA dataset consists of two parts, intended to facilitate answer extraction or end-to-end question answering research, respectively, with each part including (a) two sets of questions collected from two types of stakeholders , (b) manually-produced answers to these questions extracted from documents in the dataset and systematically hand-annotated and judged by human experts, and (c) a document collection including scientific research articles suited for experts as well as relevant news, social media, and pages from authoritative websites intended for the general public. Technical validation accomplished through a community evaluation at the Text Analysis Conference (TAC) indicates that systems can discover useful answers in the collections, and that answers (and supporting passages) expected by different stakeholders can vary substantially. We believe that our technical validation demonstrates the importance of exploring the diverse landscape of answers available online for health questions and shows the importance of accounting for varying levels of understanding when identifying satisfactory answers to health questions, and hope that this dataset will be of value to researchers exploring answer diversity, multiple stakeholders, or open-ended healthcare question answering.https://tac.nist.gov.We have provided instructions for how to process this dataset in the README file provided with the dataset. Descriptions of automatic systems developed using this dataset are available at


Although carbon materials, particularly graphene and carbon nanotubes, are widely used to reinforce metal matrix composites, understanding the fabrication process and connection between morphology and mechanical properties is still not understood well. This review discusses the relevant literature concerning the simulation of graphene/metal composites and their mechanical properties. This review demonstrates the promising role of simulation of composite fabrication and their properties. Further, results from the revised studies suggest that morphology and fabrication techniques play the most crucial roles in property improvements. The presented results can open up the way for developing new nanocomposites based on the combination of metal and graphene components. It is shown that computer simulation is a possible and practical way to understand the effect of the morphology of graphene reinforcement and strengthening mechanisms. Metal matrix composites (MMCs) are fundamental structures for the aerospace industry, construction, transportation, and other practical realizations because of their unique properties. The demands for better performances are constantly increasing and one of the essential goals is the search for new composite morphologies with new efficient reinforcement components.Carbon nano-polymorphs, such as graphene, carbon nanotubes (CNTs), fullerenes, and diamond-like carbon, are well-known for their unique mechanical and physical properties. Two-dimensional 2D) graphene is known as the strongest and thinnest material available and even has better properties than CNTs. In recent years, graphene has been widely used as a reinforcing material in MMC ,2,3. SevD graphenThe most-reported metal matrices that can be reinforced by graphene are Al, Cu, Ni, ferrite, and Ti. Aluminum is well-known as a lightweight metal with good corrosion resistance and formability, as well as multifunctional applications, but with low strength. Copper matrix composites are lightweight, low in cost, have good electrical and thermal conductivities, and are resistant to corrosion. Nickel matrix composites have great corrosion and wear resistance associated with superior resistance to thermal oxidation and have the potential for aero-engine applications. The strengths of Fe and Ti are quite high by themselves; however, they can be further increased by graphene reinforcement. Further, for simplicity, if the special metal is not mentioned, it would be abbreviated as Me. To date, the number of works devoted to the fabrication of graphene/Me or graphene/polyethylene composites are presented ,10,11,12One of the key factors for mechanical properties is the homogeneous distribution of graphene . The fabCrumpled graphene is one of the most promising and progressive structural materials; it has a high specific surface area, high porosity, and low weight ,22,23. DThe complexity of the composite structures and the difference in their morphology cause significant difficulties in an experimental indication of the relationships between structure and properties or external treatment and properties. The understanding of the strengthening mechanisms by graphene reinforcement is also quite complicated directly from the experiment. The molecular dynamics (MD) simulation is a suitable tool used to investigate the properties of the nanocarbon-reinforced MMCs and allows the consideration of crystal orientations, interfacial structures, and mechanical treatment in a wide range of working temperatures and strain rates, etc.Several reviews concerning the metal/graphene composites from different points of view have been published ,16,28,29To date, mainly the MMC composites reinforced by graphene are considered by MD. The simplest morphology is a metal matrix with one graphene layer inside, which allows for studying different mechanisms of the composite formations, mechanical behaviors, etc. In As can be seen from For such composites, many different factors affecting the mechanical properties of the composites are distinguished: the size of graphene flakes, their orientation , the number of graphene flakes inside the metal matrix, the distance between graphene sheets. Moreover, planar single-layer graphene is rarely used for MMCs fabrication since it is unstable in the planar form. The graphene tends to agglomerate and stack to multilayered flakes or even to graphene networks .Thus, it was realized that, inside, the metal matrix graphene in its equilibrium state is not planar and can be transformed into a crumpled/rippled state during the fabrication of the composite, especially if the metal matrix is melted. It is much more natural to consider the system of crumpled graphene flakes instead of planar graphene. As can be seen from In real experiments, it is quite complicated to obtain the monocrystal metal matrix. Commonly, there is a polycrystal with different grain sizes. This is one of the main contributing morphology factors affecting the mechanical and physical properties of the composite. Thus, graphene flakes can also be distributed differently and considerably affect the grain size and resulting mechanical properties . In FiguThe same was shown for CNTs, which have a strong pinning effect on grain boundaries, which results in a low ductility of the composites ,32. In tab initio (or first principles), semi-empirical and empirical methods, based on when the data from the experiments are used to determine the parameters of the system. Thus, the obtained results can be further used to understand the MD results or to prepare the parameters of interatomic potential for MD simulations.The deposition of C atoms on different metal sources, along with the diffusion of carbon atoms, and further segregation on the surface were extensively studied both by the experiment and simulation. Commonly, such studies are conducted to analyze the process of graphene or CNT growth, but in terms of composites, more important characteristics can be obtained from such studies pertaining to how actively graphene and metal can interact with each other. Such simulations are often conducted by Different metals have different adhesion energy, solubility, and catalytic properties in contact with carbon . For exad-orbitals, but weakly interacts with Cu [ab initio simulations suggested that the Me/graphene interaction is vdW, rather than a chemical bonding interaction [It was shown that graphene demonstrates strong bonding with metals, such as Ti and Ni due to the coupling between open  with Cu ,36,37,38 with Cu ,40. Amon with Cu ,43,44,45eraction . Althougeraction ,48, thanIt should be noted that the results for the interaction between single or coupled C atoms and the metal surface can differ from the results describing the interaction between the graphene layer and metal surface ,29,49. E2  and 72.72 [2 , compare2 [2 [2 . The adh[2 [2 [2  and 12.7[2 [2 [2 ; calcula[2 [2 [2 . Differe[2 [2 [2 ,54. Thus[2 [2 [2 .To date, different methods were employed to obtain different kinds of graphene hybrids—a mixture of graphene and Me or Si nanoparticles, graphene in a metal matrix, and the metal nanoparticles wrapped by graphene, to name a few. The morphologies of such hybrid structures can be very different depending on the fabrication technique and materials–precursors. One of the main objects of this review is the graphene/metal composites based on a mixture of graphene flakes and metal nanoparticles. Graphene/metal nanoparticle hybrid systems were already obtained for noble metal nanoparticles  ,57 and tA new way to fabricate the composite with controllable morphology where graphene wrapped the nanoparticles has been reported in . The metOne of the well-known methods is the mechanical mixing of graphene and various nanoparticles. Composites based on graphene oxide and nanoparticles were successfully prepared through a simple ball-milling method for different applications ,64. HoweN atoms as the function of their coordinates. The forces acting on each atom are calculated from this potential function:Molecular dynamics simulation is based on the mathematical description of the interaction between atoms. The accuracy of predictions made based on the simulation results depends on the accuracy of this description and application to a specific problem. Classical methods of interaction are described using the potential function The simplest form of the description of the interatomic interaction is the pair potential. Strictly speaking, this potential does not have quantum mechanical justification. However, due to its simplicity, it is often used in modeling. At the approximation of pair potentials, the energy of a system of particles is represented as the sum of potential energy interactions of all pairs of atoms:For the structure, where two types of atoms are considered, it is necessary to choose a potential that will take into account three types of interactions. For graphene/metal composites, the potential should include covalent bonds for graphene, interactions of the metal atoms with graphene, and interactions between metal atoms inside the metal part. Thus, the potential function for the composite can be defined as the sum of three potential energies of carbon–carbon The interaction of C-–Me is at least one order of magnitude smaller than the interactions between Me atoms , while con atoms :(2)UC−C=loped in , UijLJ toperties ,18,28.Understanding how the simulation process itself affects the results is also important for such a complex system. In , it was The other important factor is interatomic potential. The interaction between metal atoms and carbon atoms can be represented by pairing the interatomic potential—LJ or Morse. As it was mentioned before, graphene has strong bonding with Ti and Ni and interacts weakly with Cu ,35 and Aab initio). Some of these methods should be named: the embedded atom method (EAM), effective medium theory, Finnis–Sinclair potential, etc. The Morse potential can also be applied to study various properties of metals.Since the 1980s, several methods have been proposed to describe interatomic interactions in metals. It is quite important to take into account the complex nature of the interaction of atoms. Thus, for metals, potentials are built from quantum theory and the electronic structure of crystals, which is conducted based on first principles  potential can be described asFor metal/graphene composites, the LJ potential is most commonly used for the simulation of the Me–C interaction. It is applied to both strong and weak interactions with graphene metals. As it was shown, nonbonded Me–C interactions can be successfully reproduced by the LJ potential ,114,115.The Morse potential can be written asB of the crystal associated with the slope of the potential near its minimum. This potential is also often used to model metals with f.c.c. and h.p.c. lattices.Three parameters One of the main things that should be reproduced by the potential is the bonding stiffness/hardness for different metals. Such things are usually studied during the simulation of catalytic syntheses of graphene or CNTs ,116, themposites ,125,126.It was shown in  that theThe ‘many-body’ character of the interaction between carbon and such metals as Ni or Ti requires more complex potentials for different problems.ab initio data and it was found that the ReaxFF potential performed poorly.For example, a more general bond order method was designed and called ReaxFF potential for hydrocarbons on Ni ,132,133.ab initio force field and it has been proven to be applicable in the investigation of the mechanical properties of the CNT contact with Cu.In , a forceThe other type of interatomic potential for the simulation of Cu/graphene structures is the charge-optimized many-body potential (COMB) ,141. In Recent progress in computer science has led to an increase in the simulation studies of composite fabrication. MD simulation is a good tool used to study and predict this non-simple process, for example, fabrication mechanisms, structures, and dynamics of surfaces and interfaces. During MD simulations, such processes can be described in detail since various factors can be easily considered: (i) process temperature; (ii) type of the reinforcement and metal matrix; (iii) deformation treatment; (iv) variety of structures.The process of deposition of graphene on the metal surface is one of the most studied by different simulation techniques. It is not exactly the fabrication process but it is very important for understanding how graphene can be introduced to the metal matrix. The interaction of metal nanoparticles with the graphene surface has also been widely studied over the past several decades . The bonWith many metals, graphene interacts by weak vdW forces. Since this interaction can be easily destroyed even at room temperature, it reduces the strength of such layered composites. The weak vdW contact between the graphene and metal matrix significantly reduces the mechanical performance of such composites. In , a new bThe other effective way to obtain the composite is compression of the MMC reinforced by graphene. In , models Powder metallurgy is one of the most important techniques for processing composites at low temperatures with the ability to incorporate high-volume fractions of reinforcements. However, the work of reinforcing phases will be affected by the various dispersing technologies such as ultrasonic dispersion or ball-milling. As it was shown in , the strIn , the Al/It was found ,15 that From this point of view, the idea to create a graphene network in the metal matrix is arise. Such a network can give much more strength to MMC. It was realized in , where tThe other effective way of fabrication of composite with a graphene network is the pressure-temperature treatment, presented in ,19 for gMoreover, the fabrication scheme was developed, as shown in To study the mechanical behavior, tensile deformation can be applied which even allows for comparison of the experiments and simulation results. The mechanical properties and deformation behaviors of different graphene/Me composites can be obtained under different conditions. MD has always been used as an effective way to study graphene coatings under nanoindentation ,149,150 Let us consider the simple laminated structure first: the graphene layer between two layers of metal see a.The next step for further property improvement is to add more graphene layers to the metal matrix. It can be done variously: (i) to add bi- or multi-layer graphene see a, I; iia, II; ia, III. IAs mentioned previously, it is better to consider polycrystalline samples since the interaction between graphene and grain boundaries can significantly affect the resulting mechanical properties. If the crystallization of metal is considered, the content of graphene can affect the uniformity of grain distribution and the final grain size of MMCs . MoreoveIn Composite with the lowest Cu thickness has the lowest stress value among the composites at the time of delamination . The greater the thickness of the Cu layer, the lower the fracture strength. From the snapshots of the structure, it can be seen that for the Cu layer with small thicknesses, fracture took place in a metal part rather than on graphene. For the structure with the average and maximal thickness, the graphene sheet was broken earlier than Cu completely fractured. However, for tension along the armchair direction, slightly different results were obtained: composite with the maximal Cu thickness has the lowest stress value among others at the time of delamination initiation, while the fracture behavior is the same as during tension along zigzag. It was concluded that an increase in Cu thickness reduces the strength of the graphene/Cu composites.In For a better understanding of the strengthening of the metal by graphene, it is interesting to consider nanoindentation of the surface covered by graphene. In , it was The location of the graphene in the metal matrix as well as its orientation will also affect the mechanical properties of the composite. In y-axis (increased by 15% for CG21 and by 23% for CG47).As shown previously, both isotropic and anisotropic structures can be obtained. In In , nanoparFor a big nanoparticle, GF just totally covers it, while for a small one, also the crumpling of the flake and changing of its shape took place. At high temperatures, the interaction is much faster, especially for small nanoclusters which can be also melted. In that case, the nanoparticle is divided to separate atoms and spread over the flake. This results in the formation of bi-layer GF with Ni atoms between two layers. For bigger nanoparticles, GFs work as capsules containing metal. However, if the nanoparticle is big, all the free bonds in the basal plane of graphene are occupied, which makes it difficult to form new covalent bonds with other GFs.In  it was rIn , the nanIn this case, graphene does not affect the strength of Ni mono- or low-angle Ni bi-crystal. Dislocations are not stopped by graphene. Moreover, graphene bend under indentation and does not increase the composite strength. Moreover, in  the dislx- and y-axes are presented for MMC composite reinforced by: (i) graphene; (ii) bilayer graphene, and (iii) diamond sphere. In both cases, the composite containing graphene has the best mechanical properties. In the case of bilayer graphene, there is a difference in tension along different axes, and this composite demonstrates the increase of ductility. It was concluded that a large graphene sheet results in a strength increase, while the addition of bilayer graphene increases the difference in mechanical properties.In Interestingly, this metal type strongly affects the composite behavior under indentation. For example, in  the Al/gThe following issues should be discussed for a better understanding of the mechanical properties of metal/graphene composites: (1) are these composites anisotropic or isotropic and can the anisotropy be controlled by fabrication technique; (2) how to increase the strength of the composite; (3) how the ratio between some metal and C atoms will affect mechanical properties; (4) deformation and strengthening mechanisms should be defined. The other important issue is to define why and how graphene can increase strength: very different mechanisms were found to date. For example, graphene can participate in the load transfer, and affect the dislocation passing mechanisms and dislocation hardening, resulting in the thermal mismatch between the metallic matrix and graphene. The contribution of such strengthening mechanisms of graphene/metal composites is not always clear.One of the main parameters affecting the final properties of the graphene/Me composites is their special morphology. In particular, as described in To summarize the reviewed works, we chose such main characteristics important for the simulation of the mechanical properties of the composites as the Me type, type of the potential function, reinforcement, and studied properties. We do not show the obtained values of, for example, ultimate tensile strength or elastic modulus, but just point out what was done to study the mechanical properties. The investigation into mono- or polycrystals also affects the mechanical properties of the composite. In the literature, the majority of works with graphene are located in a monocrystalline metal matrix, since this allows us to understand the hardening mechanisms in detail. On the other hand, those works that consider a polycrystalline matrix make it possible to understand how graphene will be introduced into real systems. For example, it is shown that if the grain misorientation is low and graphene is located at the boundary then the strength is lower than with a high-angle grain boundary. In addition, graphene affects the grain structure itself. If we consider the fabrication of a composite, it was found that graphene prevents grain growth; therefore, on the one hand, with graphene, it is possible to obtain a nanocrystalline material in which grain growth is limited, but on the other hand, such a structure may have low strength since graphene is located directly at the grain boundaries.This work presents advances in the MD simulation of fabrication and the study of mechanical properties of metal/graphene composites of various morphology. The search for such new composites with improved properties is important in many fields of science and technology. Different aspects of MD simulation studies on the strengthening mechanisms, deformation behaviors, and connections between properties and structures are covered. The present review provides helpful information for future simulation studies on the metal/graphene composite.It can be concluded that the vdW force between the layers of graphene and some metals is weak, which makes it easy to form interlaminar shear and delamination ,155,161.The level of enhancement could be further increased by optimizing the size, volume fraction, and orientation of graphene-based reinforcement materials. One of the perspective ways to further increase strength and mechanical properties is to obtain a graphene network. Moreover, it can be much simpler than reinforcing a metal matrix with a single-layer planar graphene. The understanding of the factors mainly affecting the composite properties can enable one to control the strength of metal/graphene composites by tuning their structure morphologies.


High-quality graphene has demonstrated remarkable mechanical, thermal, electronic, and optical properties. These features have paved the road for the introduction of graphene into numerous applications such as optoelectronics and energy devices, photodegradation, bioimaging, photodetectors, sensors, and biosensors. Due to this, graphene research has accelerated exponentially, with the aim of reaching a sustainable large-scale production process of high-quality graphene that can produce graphene-based technologies at an industrial scale. There exist numerous routes for graphene fabrication; however, pulsed laser ablation in liquids (PLAL) has emerged as a simple, fast, green, and environmentally friendly method as it does not require the use of toxic chemicals. Moreover, it does not involve the use of expensive vacuum chambers or clean rooms. However, the great advantage of PLAL is its ability to control the size, shape, and structure of the produced nanostructures through the choice of laser parameters and liquid used. Consequently, this review will focus on recent research on the synthesis of graphene nanosheets and graphene quantum dots via PLAL and the effect of experimental parameters such as laser wavelength, pulse width, pulse energy, repetition rate, irradiation time, and liquid media on the produced nanostructures. Moreover, it will discuss extended PLAL techniques which incorporate other methods into PLAL. Finally, different applications that utilize nanostructures produced by PLAL will be highlighted. We hope that this review will provide a useful guide for researchers to further develop the PLAL technique and the fabrication of graphene-based materials. The element carbon has many allotropes. These include graphite, diamond, fullerene, carbon nanotubes, and graphene, and other forms are predicted . In grap5 cm2 V−1s−1 at room temperature . T. T45]. TOne of the main factors that has a great effect in laser–matter interaction is the temporal width of the laser pulse. Nano-, pico-, and femtosecond lasers interact differently with materials . For exaOther factors that affect the laser–matter interaction are the laser wavelength and fluence. The ablation rate is higher when shorter wavelengths are used in a PLAL process . HoweverA major concern in nanostructure synthesis in general is the ability to control size and size distribution. In PLAL, this is accomplished by controlling the laser and experimental parameters. Factors such as laser wavelength, pulse duration, laser fluence, and repetition rate are linked to the laser instruments. However, more parameters are involved and can control the size of the produced nanostructures. For example, the focal length of the lens used to focus the laser beam, the liquid medium used, its temperature, height above the target, and the target itself and whether it is bulk or flakes. Therefore, regardless of the simplicity of the setup, its factors and their interdependency need to be optimized to develop a protocol for controlled synthesis . ExtendiGraphite consists of a planar layered structure. Graphene is an individual layer of graphite. Weak Van der Waals bonds are responsible for the bonding between the graphene layers. Due to this, the graphite layers can be easily separated when sufficient energy is provided. The laser energy in the PLAL process can provide such energy to break the weak Van der Waals bonds between the graphite planes to produced graphene nanosheets ,56.In PLAL, the energy transferred from the laser to the material is used to perform different processes. Part of the energy is consumed in melting, evaporating, and ionizing the target material to form the nanoparticles. The other part of the energy can be used to break the Van der Waals bonds . The synAlthough laser energy in the PLAL process can be utilized to produce graphene nanosheets, the choice of liquid media is of high importance. Since graphene is hydrophobic, it tends to agglomerate irreversibly and undergo restacking to form graphite. Hence, the advantages of single- or multi-layer graphene are lost. Therefore, different liquid media that would hinder the stacking of the graphene nanosheets were investigated ,62.PLAL has also been used to directly deposit layers of graphene on the surface of a foil . Figure Graphene and graphene-oxide nanostructures have diverse structural and optical properties. To identify these properties, different analytical techniques are employed. These techniques include X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, UV-Vis absorbance spectroscopy, photoluminescence emission (PL), and Fourier transform infrared spectroscopy (FT-IR). Below, a brief description of these techniques is given with the main features of graphene and graphene-oxide nanostructures yielded by these methods. A summary of these features is listed in X-ray diffraction (XRD) is an analytical technique that is used in the identification of crystalline materials and provides knowledge of their phase. Furthermore, it can give information on the material’s unit cell dimensions. Graphene is identified by five major peaks in an XRD spectrum. These peaks occur at 26.5°, 42.3°, 44.5°, 54.6°, and 77.4°, which are related, respectively, to the hexagonal planes (002), (100), (101), (004), and (110) of graphitic carbon  Figure a. The XRXPS is concerned with the analysis of the surface chemistry of a material. XPS analysis provides information on the elemental composition of the material under investigation as well as its chemical and electronic state of the atoms within it.When analyzing carbon nanostructures through XPS, two major elements are revealed: carbon and oxygen. These are indicated by two peaks positioned at 284 eV and 532 eV, which correspond to the singlet C 1 s and O 1 s peaks, respectively . By deco−1), G-band (1560–1600 cm−1), and 2D-band (2400–1700 cm−1). While the G-band indicates the graphitic nature of the carbon, the D-band signifies any structural disorder or defect. The position and relative intensities of the bands conveys more information about the graphene structure , graphene-oxide nanosheets (GONS), graphene quantum dots (GQDs), graphene-oxide quantum dots (GOQDs), graphene nanotubes (GNTs), nanodiamonds, polyynes, and carbon-encapsulating metal/metal-carbide/metal-oxide nanoparticles (C/M-CNPs) ,70. In tWhile graphene is a zero-band gap semiconductor, and thus does not have photoactive or photoluminescence properties, graphene oxide (GO) might have a tunable band gap depending on its oxidation level and therefore demonstrate broad photoluminescent characteristics. This feature has enabled GO to have many applications ,73. GO hThe product obtained via a PLAL process is highly dependent on the experimental parameters used . Some ofThere are numerous experimental parameters that influence the formation of graphene and graphene-oxide nanosheets during a PLAL process. Below, these parameters are highlighted and their influence is discussed. A summary of the research conducted to investigate the effect of these parameters is listed in For the production of graphene nanosheets through PLAL, it was reported that the properties of the liquid medium are important factors . For exa2 resulted in the production of more graphene and less of other carbon nanostructures. Moreover, the study did not report the observation of graphene oxide; however, there was an indication of the presence of a small amount of oxygen trapped between graphene layers. The graphene layers were of multilayer thickness and were not stacked in an orderly fashion, as indicated by the broad peak of the XRD analysis [At room temperature, graphene has been formed by irradiating a graphite target with a 532 nm Nd:YAG laser when the target was submerged in distilled water . The repanalysis .2 to favor the formation of graphene nanosheets while using different liquid environments. Different liquid environments result in different pressures of the plasma plume on the surface of the target. This pressure is found to affect the structure, size, and morphology of the formulated nanostructures and their aggregation. A decreased plasma plume pressure favors the formation of graphene nanosheets when graphite targets are used in PLAL experiments. To determine the quality of the produced graphene nanosheets when obtained from different liquid environments, Raman spectroscopy was performed. It was found that ID/IG = 0.25 when nitrogen was used as a liquid medium, while ID/IG = 0.94 when distilled water was used. Since the D band is related with structural defects, a lower ID indicates a better quality. Hence, it was concluded that using nitrogen as a liquid environment produced better-quality graphene. The number of graphene layers could also be concluded from Raman spectroscopy by calculating the ratio of the 2D band intensity to that of the G band. The use of liquid nitrogen resulted in the formation of fewer layers of graphene when compared to the use of distilled water. However, when XRD analysis was performed, the samples obtained with distilled water did not show a graphite peak at 26.58°, which is an indication of the presence of graphene. Samples obtained with liquid nitrogen also did not show any peak at 26.58°; however, they showed a sharp peak at 32.1°. This could indicate the presence of a great proportion of other carbon nanostructures in the colloidal solution [To draw a comparison between nitrogen and water as the liquid environment for PLAL, further investigation was done . The lassolution .2 fluence to irradiate a graphite target immersed in liquid nitrogen. The target and liquid nitrogen were contained in a cell with a BK7 window in front of the laser beam. The laser beam was focused using a concave lens to a 1 mm2 spot on the target. After irradiation, the liquid nitrogen was evaporated at room temperature and de-ionized water was added to provide a suspension for the graphene nanosheets. It was suggested in this work that the cryogenic liquid forms a 2D-fluid monolayer which can penetrate the spacing of graphite. When laser exposure takes place, the liquid molecules expand to a gaseous phase where it supports the dissociation of the weak bonds of graphite layers. Hence, graphene nanosheets are formed. Single and bi-layer graphene sheets were found in the suspension along with graphite films and nanodiamonds. The Raman analysis of the D and G bands concluded that the quality of the graphene nanosheets was acceptable (ID/IG ≈ 0.5) [Cryogenic liquids have also been employed for graphene nanosheet production via PLAL. Liquid nitrogen was used to generate graphene nanosheets using PLAL . A 1064 G ≈ 0.5) .2. The PG was six layers thick and had porous dimensions of ~20 nm. When liquid nitrogen was used instead of water, while keeping all other experimental parameters the same, no PG was observed. It was concluded that O2 and H2O2 are key reagents for the formation of PG [Porous graphene (PG) has been synthesized using a highly oriented pyrolytic graphite (HOPG) target submerged in water and irradiated by a 35 fs laser with wavelength of 800 nm and 1 kHz repetition rate. The fluence was set in the range from 20–30 J/cmon of PG .2, and 5000 laser pulses were shot on the target. In each sample, graphene nanosheets and carbon nanoparticles were found but with different percentages. Where CTAB contained the least amount of graphene sheets, this amount increased in alcohol, acetone, and liquid nitrogen, and was the highest in water  of cetyl trimethylammonium bromide (CTAB) were used ,85. By iin water . However2 fluence was focused on a graphite target submerged in CTAB of different concentrations. The main advantage of using CTAB as an ablation medium is that it decreases the aggregation of the produced nanostructures and hence increases their stability. However, it was found that different concentrations of CTAB can affect the properties of the produced graphene. By increasing the concentration of CTAB from 0.02 to 0.1 M, a critical concentration seemed to exist where the quality of the produced graphene was the highest. This critical concentration was about 0.06 M. Above the critical concentration, the liquid medium became denser, causing the pressure on the plasma plume to increase. This increased pressure resulted in the breakage of the produced graphene and increased its aggregation. Below the critical CTAB concentration, the produced graphene nanosheets were less aggregated and the thickness of the graphene nanosheets decreased. However, decreasing the CTAB concentration even more caused the nanosheet to be thicker. A similar investigation was performed using a 0.04 M concentration of CTAB with a 532 nm laser wavelength and a reduced laser fluence of 0.5 J/cm2. It was found that graphene nanosheets obtained had a high level of defects and were smaller in size; the ratio DI/GI reached 1.93, indicating poor quality.Although (0.01 Molar) CTAB, when used as an ablation liquid medium, showed the lowest concentration of graphene nanosheets , the effN-methyl-pyrrolidone (NMP) and sodium dodecylbenzene sulfonate/water were used as ablation liquid media [2. The suspension was left for 24 h and then centrifuged for 20 min at 500 rpm. The upper uniform graphene suspension was characterized and showed the existence of graphene sheets of ~1 nm in thickness (three-layer graphene) and tens of micrometers in size.Pulsed laser exfoliation of HOPG in liquid has also been used with liquids other than water. For example, id media . It was Furthermore, a three-liquid medium was tested to investigate its effect on fabricated graphene nanosheets. Flexible graphite target was submerged in de-ionized (DI) water, acetone, and dimethylformamide (DMF) and was irradiated under a 532 nm wavelength, 50 mJ/pulse energy, and 5 Hz repetition rate for a irradiation time of 5 min . Results2 fluence to a graphite plate immersed in different liquids for 5000 laser pulses, graphene, graphene oxide, and carbon nanoparticles were produced. By keeping the experimental conditions fixed and only changing the ablation medium, it was possible to investigate the best conditions for obtaining graphene-oxide nanosheets. By comparing de-ionized water, liquid nitrogen, and 0.01 M CTAB, it was found that de-ionized water produced better-quality GO nanosheets that are large and least in defects compared to the other liquids [In PLAL, when the ablation medium has plenty of oxygen, there will be a higher probability that the carbon atoms will be oxidized during the production of graphene . Upon ap liquids .To further investigate the optimized conditions for producing GO nanosheets, the effect of different concentrations of CTAB as a liquid medium was investigated . The emp2 and 5000 laser pulses were aimed at the target. Five samples were prepared, where the distilled water of each sample was kept at a different temperature. These temperatures were 0, 20, 35, 50, and 65 °C. All samples showed the formation of graphene and carbon nanostructures with different proportions. The low-temperature samples contained more graphene nanosheets while the high-temperature samples had more carbon spherical nanoparticles. Furthermore, the XRD analysis showed that increasing the temperature of the liquid medium resulted in better crystallinity of the produced nanoparticles and a deviation from the graphene monolayer structure. The absorption peaks of the samples in the UV–Vis and FT-IR analysis were not affected by the change in temperature. However, the intensity of the absorption in both analyses increased as the temperature increased. This was attributed to the increase of the number of nanostructures with increased temperature. This investigation concluded that to obtain large and smooth nanosheets of graphene with few layers, the distilled water must be kept at 0 °C. Liquid temperature in the range of 35 °C gave thicker graphene sheets. When the temperature was increased even more, the graphene sheets became more chopped and more spherical carbon nanoparticles were formed [The effect of liquid temperature on the quality of the production of graphene through PLAL was investigated . A 1064 e formed   and carbon nanoparticles (CNPs). The wavelength of the laser beam affected the size of the produced CNTs: they had an average diameter of 26 nm when the 532 nm laser was used and 35 nm when the laser with a wavelength of 1064 nm was used. Moreover, the concentration of the fabricated CNT was higher for 1064 nm compared to 532 nm. This was attributed to the absorption depth, which was small for 532 nm and high for 1064 nm, hence, smaller-size nanostructures were fabricated with the 532 nm beam , which indicates the level of disorders. As for the thickness of the graphene nanosheets, it is usually found through the ratio of the intensities of the 2D and G bands (I2D/IG). It was concluded that the best quality was achieved when using 532 nm laser beam; however, the sheets were of multilayer thickness. This was also confirmed by other work by the same group [Two more important points that were investigated are the quality of the produced graphene nanosheets and the role of the wavelength on the quality and thickness of the nanosheets . The quame group . Bilayer2 is approximately the borderline between nanosheet and nanoparticle formation when a 1064 nm laser wavelength is used [The effect of laser fluence on the production of graphene nanosheets via PLAL when graphite target is immersed in liquid nitrogen was studied  Figure . It was  is used .2 and 0.8 J/cm2 for a laser wavelength of 532 nm, it was found that increase in laser fluence resulted in the production of more carbon nanostructures in comparison to graphene nanosheets. Moreover, increase in fluence from 0.5 J/cm2 to 0.8 J/cm2 when a 1064 nm laser was employed caused the graphene nanosheets to be torn and fragmented [The quality and thickness of graphene nanosheets under different fluences were investigated . By compagmented .2, 15 min of irradiation time, and ultrasonic wave assistance [2 gave the thinnest nanosheets, ranging from a single layer up to four layers.Another investigation was performed using a 532 nm laser beam focused on a graphite target with laser fluences of 0.5, 2.2, and 3.6 J/cmsistance . It was 2 cannot result in the formation of PG. A fluence in the range of 20–30 J/cm2 is required for the formation of PG layers [In order to determine the threshold fluence for the formation of PG while using a femtosecond laser to irradiate an HOPG target in water, it was found that a laser fluence below 12 J/cmG layers .A pulsed Nd:YAG laser of 1064 nm wavelength and pulse duration of 7 ns was employed in a PLAL process that involved post-irradiation . Two las2 @1064, 3.33 J/cm2 @1064, 1.33 J/cm2 @532, and 0.38 J/cm2 @266 nm) [Most PLAL processes incorporate lasers of wavelength 1064 nm and 532 nm. Rarely, wavelengths of 355 nm and 266 nm are also used. To investigate the effect of wavelength and fluence on the production of graphene oxide, these parameters were changed in four experiments (6.61 J/cm@266 nm) . The pul2 and a pulse width of 7 ns, the laser beam irradiated the graphite target for different time intervals of 10, 20, 30, 40, and 60 s. It was found that the irradiation time has an effect on the produced carbon nanostructures. At 10 s of irradiation, bi-layered graphene was obtained. When the irradiation time was increased to greater than 30 s, the colloidal solution was mainly amorphous carbon and graphite.Using a 532 nm wavelength, a graphite plate submerged in acetone was exfoliated to produce graphene nanosheets . Using a2, while the irradiation time varied from 20 to 50 min. It was found that 20 min of irradiation was not sufficient for graphene exfoliation, while 30 min was the best irradiation interval to obtain bi-layer graphene, which is highly crystalline. Extending the irradiation time to 50 min resulted in the formation of multi-layer graphene  were used as a graphite source . After tgraphene . This wo2, 0.1% K2O, and 0.7% Al2O3), FG2 , and a nuclear graphite (NG), it was found that NG did not produce graphene nanosheets. Moreover, FG1 resulted in fewer defects in the produced graphene nanosheets. The quality of the prepared graphene nanosheets as determined from ID/IG showed that FG1 produced a better quality with a ratio of 0.3 compared to 0.4 when FG2 was used, with the number of layers being less than ten layers [Different graphite targets have shown to have an effect in PLAL . When con layers  , and samples were irradiated for 15 min. When comparing samples that were placed in an ultrasonic bath with those that were not, it was found that the presence of ultrasonic waves had a significant effect. Incorporating ultrasonic waves during the PLAL process assisted in the exfoliation of graphene nanosheets. These sheets were large in size and regularly shaped. Moreover, these nanosheets were single-layer and up to four layers, rarely containing few layers  on a foil using the pulsed ablation in liquid technique. An attempt to directly deposit FLG on a Cu foil using PLAL to study the effect of laser energy on the structure and number of layers of the FLG was performed . Graphit2 substrate using PLAL were accomplished [2 was dipped in the colloidal solution using a tweezer and then taken out and dried naturally. An extensive Raman spectroscopy was employed to confirm the formation of BLG. It is also worth noting that the fluence of the laser beam had a great effect on the number of graphene layers. Increasing the laser fluence increased the number of graphene layers on the substrate. It was found that a BLG was obtained with a fluence of 2.5 J/cm2 [Bilayer graphene (BLG) films on a Si/SiOmplished , where amplished , the sub.5 J/cm2 .As seen above, PLAL can be used to fabricated graphene nanosheets; however, it can also be used to fabricate graphene nanoparticles. It was found that by increasing the laser fluence, nanoparticles can be formed. When it comes to terminology, there seems to be a wide range of names that indicate nano carbon particles. These names include carbon nanoparticles (CNPs), carbon dots (CDs), graphene quantum dots (GQDs), and graphene-oxide quantum dots (GOQDs). The name is usually linked to the type of carbon precursor used and the structure and properties of the produced nanostructure .Graphene quantum dots (GQDs) have emerged as a beneficial derivative of graphene that is more suitable for applications such as photovoltaics, transistors, and light-emitting diodes due to its tunable band gap feature as a result of the quantum confinement effect ,93,94. GCarbon particles with flower-like morphology have been fabricated using 1064 nm laser with 2 Hz repetition rate, 5 ms pulse duration, and 3 J/pulse of energy . A graph2 and the sample was irradiated for 5 min. The nanoparticles that were fabricated with these experimental settings had sizes ranging from 10 nm to 20 nm with a few particles having sizes larger than 20 nm. The selected area diffraction (SAD) showed that the structure of the nanoparticles was amorphous and proved to have optical limiting properties. This investigation was taken further by using a liquid other than water. When tetrahydrofuran was used with laser fluence of 1 J/cm2 and irradiation time of 30 min, the size of the produced carbon nanoparticles was reduced, reaching an average of 6 nm [A pure glassy carbon plate was submerged in de-ionized water and irradiated with a 532 nm Nd:YAG laser . The las of 6 nm . Hence, GQDs were synthesized using PLAL . By usin2. Investigating the colloidal solution obtained showed the existence GQDs. The GQDs were of 2–5 nm size. To investigate the effect of liquid medium on the formation of the GQDs, water was replaced with liquid nitrogen. Although all experimental parameters were kept the same, no GQDs were observed in this case. Hence, it was shown that one of the main factors for the formation of GQDs is the presence of O2 and H2O2 in the liquid medium [Using a femtosecond laser with pulse duration of 35 fs, 800 nm wavelength, and 1 kHz repetition rate, an HOPG target was submerged in water and irradiated for 20 min with laser fluence ranging from 20–30 J/cmd medium .200N, PLAL was performed using a 1064 nm laser with power density of 6.0 × 106 W/cm2. After 2 h irradiation, carbon nanoparticles were obtained. The size of the CNPs were in the range of 3 nm with a narrow size distribution. Moreover, the CNPs prepared in PEG200N displayed photoluminescence properties, irradiating blue light when excited by a 365 nm wavelength. This property was not observed in the CNPs that were prepared in water  in a solution of ethanol and double distilled water [An unfocused beam of an Nd:YAG laser of 532 nm wavelength, 10 ns pulse duration, 10 Hz repetition rate, and fluence of 0.131 J/cmed water . The samed water .2. The obtained N-GQDs had a size of ~14 nm and exhibited PL emission tunability that was dependent on the liquid used. Moreover, these N-GQDs showed the ability to be used as an electrocatalyst [When different nitrogen-containing precursors dissolved in water were used as liquid media in a PLAL process, the synthesis of nitrogen-doped GQDs (N-GQDs) was successful . Carbon catalyst .In order to improve the selectivity production of GQDs and GOQDs, the effect of laser wavelength was investigated . Two wavGraphene-oxide nanostructures have also been fabricated using a 1064 nm and 532 nm lasers. The laser irradiated a graphite target immersed in de-ionized water, and graphene-oxide nanoballs and nanowires were produced  Figure . Althoug2 fluence for 180 s. It was concluded that changing the laser fluence controlled the size and concentration of the CNPs in the colloidal solution. Moreover, these CNPs showed good tunable photoluminescent properties.The laser fluence effect on the production of CNPs was also investigated . Spheric2 resulted in the synthesis of GQDs. When the fluence was reduced below 12 J/cm2, no GQDs were formed. This demonstrated that a threshold fluence is required for the production of GQDs [Laser fluence was found to be an important factor for the formation of GQDs when incorporating a femtosecond laser. Irradiating an HOPG target immersed in water for 20 min with a laser beam of 35 fs pulse duration, 800 nm wavelength, 1 kHz repetition rate, and fluence ranging from 20–30 J/cm of GQDs .200N [2 to 1000 J/cm2, and the resultant CDs were investigated. It was found that as the fluence was increased from 150 J/cm2 to 750 J/cm2, the size of the CDs increased  and longer pulse width (7 ns), which reached an average of 6 nm [Work was done to fabricate CNP with high repetition rate, high fluence, and high number of pulses . Using a of 6 nm . This mi200N using an 800 nm laser, pulse width 150 fs, and repetition rate of 1 kHz [2 with a spot size of 16 μm, the size of the formed CDs was studied. It was observed that with increasing irradiation time, the size of the as-prepared CDs decreased, reaching a size of 1.3 nm after 4 h. Moreover, the size distribution became narrower [More investigations on the effect of irradiation time on the size of fabricated CDs was performed . The irrof 1 kHz . While knarrower .Graphene-oxide nanospheres (GONs) were fabricated using PLAL by starting with graphene nanoplatelets dispersed in ethanol . By irra2, respectively. The change in fluence had a direct effect on the size and morphology of the produced GO nanoparticles, where lower fluence produced spherical particles, while higher fluence gave a more elongated particle (The effect of laser repetition rate on the size and morphology of the GO nanoparticles after a PLAL process was investigated . A 532 nparticle . The repStarting from carbon nano-onions (nCNOs) as a target material immersed in de-ionized water, PLAL was employed to produced GQDs . A 532 nGOQDs were fabricated through PLAL starting from coal as a carbon source . One graStarting with a mixture of nickel (II) oxide powder in benzene as a carbon source, a laser beam of wavelength 1064 nm irradiated the solution for 30 min. The laser beam had 10 ns pulse duration, 10 Hz repetition rate, and laser energy of 30 mJ/pulse. After irradiation, the solution was centrifuged to obtain the GQDs in the supernatant. The benzene was separated from the GQDs through rotor evaporation, and then the GQDs were dissolved in de-ionized water. The size of the fabricated GQDs were in the range of 2–6 nm with a very narrow size distribution . MoreovePLAL was also used with the assistance of high-power sonication . Startin2 fluence irradiated the graphite target. The PLAL processed was followed with a solvothermal treatment where the colloidal dispersion was placed in a sealed glass bottle and heated in an oven at 65, 90, and 120 °C for 72 h. As a result, the PLAL produced GQDs that were doped with nitrogen (N-GQDs). The subsequent solvothermal treatment of the N-GQDs assisted in the reduction of oxygen functional groups and the increase of the nitrogen content of the N-GQDs. At 120 °C, the N-GQDs exhibited the highest photoluminescence intensity, making the product a good candidate for an optical sensor [Doping GQDs with nitrogen (N-GQDs) improved their optical properties, resulting in broadening of their emission band. Furthermore, nitrogen doping enabled the tuning of the N-GQDs luminescence . DMF wasl sensor .Nitrogen-doped GQD production has also been attempted with a focus on the effect of sonication during the PLAL process on the doping process . Using a2 laser, the LIG was obtained. The LIG film was then scrapped to obtain LIG powder, which was mixed with water and ammonia to prepare a suspension. After ultrasonic treatment, a PLAL process was performed where the suspension was irradiated with a 1030 nm femtosecond laser with 100 kHz repetition rate, 8 W power, and 365 fs pulse duration. The colloidal solution had a light brown color, indicating the presence of GQDs. When comparing the produced GQDs and the N-doped GQDs, the N-doped GQDs had a smaller size, in the range of 3 nm, and were more uniform, with 1–3 layers thickness. The PL spectrum of the N-doped GQDs showed higher intensity when compared to undoped GQDs, while fluorescing in the blue-green region [Another method for the production of N-doped GQDs incorporated laser-induced-graphene (LIG) as a carbon precursor in a PLAL process . The LIGn region .Post-treatment of the PLAL process for the production of CNPs was investigated . Startin2 to ablate the graphite target. In the second stage, the graphite target was removed and the colloidal solution was irradiated by a focused beam offering a high fluence, reaching 15 J/cm2, to shred the particles formed in the first stage. Splitting the process into two stages helped meet the conflicting requirements, in terms of fluence, for the ablation and refinement of the fabricated particles. Incorporating urea in stage one or two or both helped in improving the luminescent properties of the CNPs [To improve the production of luminescent carbon nanoparticles, a two-stage PLAL process was suggested . In the the CNPs .4OH solution resulted in the formation of carbon nanoparticles , annealing at high temperature, and laser ablation (LA) in NHarticles . The lasGraphene-based materials have gained great interest since they have features that enable the tunability of their physical, electronic, and mechanical properties ,119. ForImaging in the medical field is of high importance. The ability to label and track living cells will assist in better diagnose of diseases. Semiconductor quantum dots, such as CdSe, HgTe, InAs, and HgCd are good candidates as they fluoresce efficiently and do not photobleach, giving them long stability. However, these semiconductor quantum dots are very toxic to cells, rendering them unsuitable in biomedical applications. GQDs have emerged as a biocompatible material for medical applications and have shown properties of stable fluorescence, making them very suitable for medical imaging ,141,142.GQDs were fabricated using PLAL for the biomedical application of cell tracking and single-cell imaging . The proAn assessment of GOQDs for a bioimaging application has been undertaken . By perf3+ [3+. The system of N-GQDs/Fe3+ was then tested as a sensor for AA and showed excellent properties as an “on-off-on” detector [3+. Such work opens the door for more biocompatible fluorescence sensors.Ascorbic acid (AA) plays an important role in the human body, being involved in processes such as iron absorption and infection protection. Therefore, monitoring AA is of significant importance. Nitrogen-doped GQDs (N-GQDs) were found to have photoluminescence properties that were quenched in the presence of Fe3+ . Hence, detector . A simildetector . StartinGQDs were obtained from irradiating a mixture of nickel (II) oxide powder in benzene, as a carbon source, by a 1064 nm laser for 30 min. The GQDs showed strong fluorescence, reaching a maximum PL emission intensity of 450 nm when excited by a 350 nm wavelength. When bacteria were exposed to the fabricated GQDs and incubated for 3 h, confocal microscopy images showed an enhanced imageability of the bacteria under excitation wavelengths of 405, 488, and 561 nm with high contrast. Since the GQDs were reported to be non-toxic, this makes them highly suitable for biological applications .Platanus biomass as a carbon precursor. The NM-CQDs exhibited high dual wavelength (indigo–blue) photoluminescence emission. Moreover, the NM-CQDs had a stable emission in various conditions such as different temperatures, pH levels, salt ionic concentration, and excitation wavelengths. These features rendered the NM-CQDs suitable for bioimaging applications since they also exhibited good internalization in different cells [N-doped micropore carbon quantum dots (NM-CQDs) were synthesized using PLAL utilizing nt cells .200N using a 1064 nm laser wavelength, 8 ns pulse width, 20 Hz repetition rate, and 100 mJ pulse energy [Tunable broadband fluorescence CDs have been fabricated via PLAL by irradiating carbon powder in PEGe energy . The aveAn investigation of the effectiveness of GO nanosheets when incorporated with metallic NPs for photodegradation was conducted . Startin3-rGO) composites for photocatalytic water decontamination [3 NPs and monolayers of graphene oxide dispersed in de-ionized water was irradiated by a 355 nm laser beam at 280 mJ/pulse energy for 30 min. During the irradiation, the photo-induced electrons in the WO3 reduced GO to rGO and assisted in anchoring the WO3 NPs on the graphene sheets, forming WO3–rGO composite. When the WO3–rGO composite was tested for photodegradation of MB in water, it showed an enhancement in efficiency when compared to pure WO3 NPs.PLAL was also used to fabricate tungsten-oxide/reduced graphene-oxide  photodetectors. C-doped ZnO QDs have been fabricated by irradiating a Zn ethanol  using an12 Jones.PLAL was used to manufacture MWCNTs/Si photodetectors . The MWC3–rGO composite was prepared by PLAL using a 355 nm laser wavelength, which irradiated a mixture of WO3 NPs and monolayers of graphene oxide dispersed in de-ionized water. This composite was examined as an electrode material for supercapacitor application and exhibited an enhanced performance of capacitance when compared with pure WO3 NPs. Hence, such a composite may prove beneficial for energy storage applications [Furthermore, a WOications .Graphene and its derivatives have found their way into many industrial applications sectors, such as optoelectronics, energy devices, and bioimaging, to name a few. Hence, the development of large-scale fabrication methods to synthesize high-quality graphene nanosheets and graphene quantum dots is highly desirable. Although numerous methods have been established, many entail a high cost. One promising method to reduce the cost of graphene nanostructures production is pulsed laser ablation in liquid (PLAL) which has been shown to be single-step, easy, fast, and relatively inexpensive.However, a successful controlled production would require the control of the experimental parameters that are related to all aspects of the process. For example, the laser source used for the ablation entails parameters such as the wavelength of the laser beam, its energy, pulse width, repetition rate, and focusing optics. Furthermore, the liquid medium chosen in the process has great effect on the structure, morphology, and optical properties of the synthesized nanostructures. Moreover, the target which is used as a carbon precursor is also of high importance. All these parameters are interlinked and collectively influence the laser–matter interaction, which form the bases for the fabrication mechanism.In this review, recent developments in the utilization of PLAL techniques for the synthesis of graphene nanosheets and graphene quantum dots have been surveyed. This survey is intended to provide a useful guide for researchers and offer a motivation to invest more work into correlating experimental results with theory. A better understanding of the physical and chemical processes involved in graphene synthesis via PLAL will provide a better control protocol for fabricating final products with specific features.This review discusses the importance of graphene as a product and the advantages of PLAL as a promising technique for its production. The fundamental mechanisms of laser ablation in liquids are summarized, and the influence of experimental parameters on this mechanism is explained. The variety of experimental setups in a PLAL process is also illustrated, along with major characterization methods used to identify produced nanostructures, such as XRD, XPS, and Raman spectroscopy.References covered in this review were largely published in the last five years. They offer diverse experimental conditions for target materials, liquids, and laser parameters. Moreover, some extend the PLAL by integrating it with other techniques to better control the produced nanostructures. Others have investigated the use of biowaste to synthesize graphene in an effort to reduce waste and transform it into useful graphene. All these experimental works offer a pool of information that is necessary to understand the dynamics of the PLAL process in pursuit of a more controllable mechanism.PLAL has exhibited great advancements as a synthesis technique for graphene nanostructures; however, many challenges need to be overcome for it to compete as an industrial production process. Of these challenges, the low ablation rate, which in turn translates to relatively low concentrations of the fabricated particles, hinders scaling-up. Furthermore, although much research has been devoted to synthesizing graphene and its derivatives via PLAL processes, work on their potential applications is still limited. For example, GQDs and GOQDs have demonstrated excellent photo-luminance properties that suit them for bioimaging applications. To better control the products of a PLAL process and tune product properties, more understanding of fundamental process mechanisms is required. This requires more theoretical and computational work to be correlated with experimental results. One of the advantages of graphene production via PLAL is the reduction of contamination, as it is formed in a colloidal solution, guaranteeing its purification. Attempts to deposit graphene films onto substrates through a PLAL process replace the need to transfer the graphene sheets onto substrates and, in turn, reduce the possibility of degrading the graphene during the transfer step.We hope that this review aids in the understanding of PLAL techniques as a tool for the production of graphene nanosheets and graphene quantum dots and that it may serve as a reference for the further development of PLAL as a synthesis technique that can be utilized in diverse applications.


The term graphene was coined using the prefix “graph” taken from graphite and the suffix “-ene” for the C=C bond, by Boehm et al. in 1986. The synthesis of graphene can be done using various methods. The synthesized graphene was further oxidized to graphene oxide (GO) using different methods, to enhance its multitude of applications. Graphene oxide (GO) is the oxidized analogy of graphene, familiar as the only intermediate or precursor for obtaining the latter at a large scale. Graphene oxide has recently obtained enormous popularity in the energy, environment, sensor, and biomedical fields and has been handsomely exploited for water purification membranes. GO is a unique class of mechanically robust, ultrathin, high flux, high-selectivity, and fouling-resistant separation membranes that provide opportunities to advance water desalination technologies. The facile synthesis of GO membranes opens the doors for ideal next-generation membranes as cost-effective and sustainable alternative to long existing thin-film composite membranes for water purification applications. Many types of GO–metal oxide nanocomposites have been used to eradicate the problem of metal ions, halomethanes, other organic pollutants, and different colors from water bodies, making water fit for further use. Furthermore, to enhance the applications of GO/metal oxide nanocomposites, they were deposited on polymeric membranes for water purification due to their relatively low-cost, clear pore-forming mechanism and higher flexibility compared to inorganic membranes. Along with other applications, using these nanocomposites in the preparation of membranes not only resulted in excellent fouling resistance but also could be a possible solution to overcome the trade-off between water permeability and solute selectivity. Hence, a GO/metal oxide nanocomposite could improve overall performance, including antibacterial properties, strength, roughness, pore size, and the surface hydrophilicity of the membrane. In this review, we highlight the structure and synthesis of graphene, as well as graphene oxide, and its decoration with a polymeric membrane for further applications. It is t2 hybridized carbon, and was finally accepted by the International Union for Pure and Applied Chemistry in 1997 [The name graphene was coined by Boehm in 1986 [ in 1997 ,31,32,33 in 1997 . The maiGenerally, graphene can be synthesized using two different routes, viz, bottom-up and top-down ,35,36, aIn this method, graphite is exfoliated or converted into graphene ,37 via m2 substrate. It was first invented by K. Novoselov and Andre Geim in 2004, and they were honored with a Nobel Prize for this invention [This method involves the stripping/peeling of layers of graphite using adhesive tape onto a SiOnvention . Similarnvention . Graphitnvention . Electrochemical exfoliation is a technique in which the graphite as an electrode is exfoliated in an electrochemical cell under the effect of different electrolytes to give pure graphene. When a current is applied to the electrochemical cell, up to three layer of graphene sheets are exfoliated from the graphite, along with the formation of graphene intercalation compounds ,41. Many3PO4 as an electrolyte, and the obtained graphene was not homogeneous, with defects in thickness and size distribution [In other attempts by Parvez et al. in 2013, an electrolytic cell was prepared using graphite as an anode and platinum or other metal as cathode. The electrodes were immersed in an electrolyte solution of sulfuric acid with potential of +10 V for 10 min. The yield of this process was more than 60%, and the obtained graphene had multiple layers . Similarribution . Hence, Liquid phase exfoliation (LPE) is another top-down method in which sonication is performed for the exfoliation of the graphite into graphene layers, as depicted in Further in 2009, Green and Hersam used sodium cholate as a surfactant for the exfoliation of graphite . The advIn this technique, the laser erodes the carbon surface and produces graphene of the required quality. Several parameters, viz., laser beam repetition rate, wavelength, and pulse duration, must be checked during the synthesis process . SecondlThis method is generally a self deposition or self-assembling process of nanoparticles carried out using four subtechniques, such as: arc discharge, chemical vapor deposition, pyrolysis, and plasma-enhanced chemical vapor deposition. In these subtechniques, the deposition of the graphite is carried out under controlled parameters like pressure, temperature, and flow rate . The obtIn CVD, general equipment consists of tube furnace, gas flow, substrates, and tail gas treatment, as depicted in Krastchmer and Hoffman were the first to use the arc discharge method. In this method, an electric arc oven comprises two graphite electrodes with a steel chamber cooled with water, and further direct current arc voltage is applied across these two graphite electrodes immersed in an inert gas, as shown in The PECVD process is commonly designed to produce graphene from a hydrogen/methane gas mixture on copper and nickel samples. It is an additional method for the production of graphene that is similar to the thermal CVD process ,74,75,76The pyrolysis or devolatilization process is the thermal decomposition of materials at high temperature in the atmosphere of inert gases. A change occurs in the chemical onfiguration of the starting material. To fabricate few-layer graphene, carbon atoms were synthesized on a metal surface. One of the familiar techniques to synthesize graphene is the thermal decomposition of silicon carbide (SiC) . At elevThe advantages and disadvantages of the above-mentioned methods used for graphene synthesis are mentioned in In comparison to graphene, graphene oxide is considered a more versatile and advanced material. GO has a broad range of oxygen containing functional groups such as carboxyl, hydroxyl, epoxy, carbonyl, and keto groups on its surface, as shown in GO has shown great potential in a variety of fields by virtue of its high surface area , unique In 1840, German scientist Schafhacutl was given the first report on the synthesis of graphene oxide and graphite intercalated compounds . For the4 (strong oxidizing agent) along with nitric acid and heated the content at 60 °C for 3–4 days [11H4O5. After nearly four decades, in 1898, Staudenmaier and Hoffmann modified Brodie’s method and trimmed down the reaction time of graphene oxide synthesis from 4 days to 2 days [2 or N2O4.The most preferred methods are Brodie , Stauden3–4 days . The GO o 2 days . The nit4 as the oxidizing agent instead of KclO4, followed by the addition of sodium nitrate, but the problem of toxic gases still remains a challenge [4. This improvement made the process eco-friendly, as it completely stops the release of toxic gases such as NO2, N2O4 or ClO2, along with easy temperature control and better yield [2O2) to eliminate all impurities due to permanganate and manganese dioxide.In 1958, Hummer reduced the reaction time from 2 days to 12 h by using KmnOhallenge . Furtherhallenge  replaceder yield . In addiFurthermore, the final color of the product GO varies from army green to light yellow, depending on the carbon-to-oxygen ratios , as depi2SO4 and H2O2 solutions [The post-synthesis treatment or workup of GO is a must, as the synthesized GO contains a noticeable amount of impurities, viz, the starting material (graphite), oxidizing agents, and the acids . The worolutions .2), and titania (TiO2). In conclusion, it can be said that, to further enhance the properties of GO sheets for various applications, it is necessary to control the oxidation of graphite to tune the amount of oxygen functional groups [Various properties of GO, viz, electrical conductivity, band gap energy, transparency, optical properties, and surface charge are deeply influenced by the content of oxygen in carbonyl moieties present in GO after the oxidation of graphene ,123,124.l groups ,127,128.2 to an sp3 hybridized carbon system. Various structural models of GO, as shown in Scholz and Boehm in 1969  proposedAmong the above-discussed models from 1936 to 2018, the L–K model has been accepted the most, due to good interpretability over the majority of experimental observations and the ease of further adaption and modification.In order to authenticate the synthesis of GO and to analyze its chemical configuration, a range of characterization techniques have been employed by numerous research groups. For example, in order to achieve the information of size and surface morphology of graphene oxide, SEM, TEM, and AFM were used abroad ,146,147.Graphene oxide (GO) is no doubt a rising star material for nano-building and has shown great potential in membrane technology for water purification ,165,166.The purification ability of an adsorption process depends on the properties of the adsorbent used. Some functional groups, viz, -C=O, -COOH, -OH, -C-O-C on the graphene oxide surface make GO an excellent adsorbent. Further, due to the huge surface area, a large number of active binding sites and the electron-rich environment of GO nanocomposites have been successfully employed for the adsorption of various pollutants, including pesticides, heavy metals ions, different types of organic dyes, and other organic pollutants ,168,169.2, CO, NO2, and NH3 [In the present time, the fast development of industries even in the countryside causes the contamination of natural water reservoirs through the ejection of poisonous industrial by-products ,165,166. and NH3 .2/GO nanocomposite showed a major improvement in terms of water flux, pollutant rejection, and antifouling tendency in membranes [2/GO also shows a vast performance in different aspects such as hydrophilicity, water permeability, and fouling resistance [The combination of silver–graphene oxide (Ag/GO) nanocomposites has been reported as an excellent antibacterial agent for water disinfection. According to Sun. et al., the Ag/GO nanocomposite has been further developed for an antibacterial water purification membrane . The graembranes . Moreovesistance . BesidesOver the last few decades, enormous efforts were made to synthesize different types of membranes that could be further employed for a number of applications, viz, drinking-water filtration, use in food , the bevDespite the good success in the membrane filtration technology, some difficulties and drawbacks ,200,201 Further, various types of polymers are tried as a core material, along with organic solvents and inorganic metal oxides, as shown in Nanoparticles may be either coated onto the membrane surface or dispersed in the polymer solution before membrane casting, as shown in The graphene-oxide-based nanomaterial, along with metal oxide nanocomposites, deposited on polymeric membranes have achieved excellent appreciation as a water purifier, but there are still few drawbacks and challenges that confine their use at a large scale.Various routes of GO synthesis have been discussed in the research, and each route has given GO that is good quality-wise, but the overall yield is low. An improvement in the overall yield is a major concern. It needs to be addressed sooner, if we want to use GO in large-scale applications.The second challenge is the aggregation of the GO–metal oxide nanomaterials on the membrane surfaces, which diminishes the active surface area, the porosity, and the overall performance of the membrane. Over the last two decade or so, many research ,201,202 The third and the most important challenge is related to membrane strength, membrane-wetting, and membrane-fouling due to colloids and particles present in the feed flow, which tends to significantly reduce membrane performance, increase operating costs, and shorten membrane life.In recent years, many research groups are paying attention towards graphene because of its sole physicochemical properties, viz, high tensile strength, better electrical and thermal conductivity, fast carrier mobility, elasticity, and about 97% optical transparency. In this review article, a brief account on the structure, properties, synthesis, characterizations, and applications of graphene, graphene oxide, and GO–metal oxide-decorated polymeric membranes are discussed. Since its discovery in 2004, graphene has resulted in a wide range of applications in various fields such as solar cells, supercapacitors, sensors, batteries, and water-purification technologies. In addition, the presence of an abundance of oxygenated moieties on the GO nanoparticles imparts a high negative charge density over the GO surface and improves the adsorption quality. The addition of the graphene-based materials in the polymeric membrane-based water-purification processes enhanced the positive impact on the hydrophilicity and the antifouling and antibacterial properties of the membranes. Furthermore, GO–metal oxide nanocomposites with increased antibacterial effects and low toxicity can be employed efficiently as disinfection agents in the surface coatings on numerous membranes to effectively suppress bacterial growth.The aim of this review was to study the development of a novel high-tech membrane using a polymer decorated with a GO–metal nanocomposite to improve the overall membrane performance, including antibacterial properties, antifouling, porosity, and the surface hydrophilicity of the membrane.