The aim of this study was to optimize a Question Prompt List which is designed to improve communication about the heart failure trajectory among patients, family members, and health care professionals.Data were collected in a two-round Delphi survey and a cross-sectional survey, including patients with heart failure, their family members, and health care professionals working in heart failure care in Sweden and the Netherlands. Acceptability for and demand of the Question Prompt List were assessed.A total of 96 patients, 63 family members and 26 health care professionals participated in the study. Regarding acceptability, most of the original questions were found to be relevant by the participants for inclusion in the Question Prompt List but some cultural differences exist, which resulted in two versions of the list: a Swedish version including 33 questions and a Dutch version including 38 questions. Concerning demand, participants reported that they were interested in discussing the questions in the revised Question Prompt List with a physician or a nurse. Few patients and family members reported that they were worried by the questions in the Question Prompt List and hence did not want to discuss the questions.This Question Prompt List has successfully been adapted into a Swedish version and a Dutch version and includes questions about the HF trajectory which patients, their families, and health care professionals perceived to be relevant for discussion in clinical practice. Overall, patients and family members were not worried about the content in the Question Prompt List and if used in accordance with patients’ and family members’ preferences, the Question Prompt List can help to improve communication about the heart failure trajectory. Discussing the Heart Failure (HF) trajectory with patients and their families is recommended in clinical guidelines worldwide –3. HealtOne way to improve communication about sensitive topics in clinical practice is by using a communication tool . A tool heartfailurematters.org, an educational tool provided by the Heart Failure Association of the European Society of Cardiology that has a specific section which intends to help patients and families to discuss living with HF and plan for the end-of-life [Previous research on QPLs are mostly from cancer care where such a tool has helped cancer patients and their families to give cues that they wished to discuss prognosis and end-of-life care with health care professionals . Special-of-life . In othe-of-life , 18 howeRecently, our research group including researchers from Sweden and the Netherlands, developed a QPL with the aim of improving communication about the HF trajectory in HF care. The first version of the QPL was developed in a co-design process  in SwedeTo ensure the QPL is connected to clinical practice and has the potential to be used in the “real world”, further testing among patients, family members and health care professionals is needed. Accordingly, we know from previous studies in cancer care that QPLs developed in one country might need to be adapted for other countries depending on differences in how cultures approach sensitive topics . Also, aThe aim of this study was to optimize a Question Prompt List which is designed to improve communication about the heart failure trajectory among patients, family members, and health care professionals.How do the participants perceive the title, the pictures, and the introductory text in the QPL?Are the questions in the QPL relevant, are they clearly formulated, or do they need to be re-formulated?Are there questions missing in the QPL?Are the participants interested in discussing the questions in the QPL with a physician or a nurse?What are the participants’ reasons for discussing/not discussing the questions in the QPL?This study was conducted in two steps Fig.  with thePurposeful sampling  was usedTo report on the participants’ reactions to and perceived appropriateness of the QPL (acceptability), patients with HF, their family members and health care professionals in HF care in Sweden and the Netherlands were invited to take part in a two-round Delphi survey.In the first round, participants were asked to comment on their reactions to the title, the pictures, and the introductory text in the QPL. They were asked to report on the relevance of each of the 45 questions in the QPL, using a Likert scale from 0 to 4 . They were also asked to report on the clarity (yes/no) and need for re-formulation of each question. Furthermore, they could suggest additional questions to be included in the QPL (Table A revised QPL was developed for the second round with 1) questions which the majority of the participants found relevant and thought should be kept on the list, 2) questions that were suggested for deletion because they were perceived as not relevant, and 3) questions that were added by participants. In the second round, participants were asked to state for each question whether the question should be kept, deleted or added. After this second round, a revised version of the QPL was made by the research group.To test the demand of the QPL, a cross-sectional survey was performed. A questionnaire including the revised questions in the QPL was sent out to a new sample of participants to assess the estimated use of the QPL . The parDescriptive statistics were used to analyse the data in the study. The Delphi technique was used as a tool to receive feed-back on possible areas that could be optimised in the QPL. Round 1 questions that were perceived as not relevant by 25% or more of the participants were specifically discussed in the research group concerning formulations and content. Some of these questions were re-worded and added to round two for participants to comment on; some were suggested for deletion. Questions that were perceived as relevant by 50% or more of the participants in rounds 1- and 2 were kept in the QPL. The opinions of the participants had the biggest impact on the results, but the researchers also took on an active role in the analysis, contributing their knowledge to the optimizing of the QPL. The researchers’ role in the analysis of data concerned i. e. bringing in knowledge from relevant literature when designing the QPL, deciding on the ordering of the questions in the list as well as their final wording, using suggestions from all participants.Ethical approval was granted for this study by the Swedish Ethical Review Authority in Linköping . The Medical Ethical Committee of the University Medical Centre Groningen (UMCG) concluded that no additional approval of the committee was needed (METC 2018/169). Written informed consent was obtained from all patients before commencement of the study.Box 1 An example of one of the questions and the different response alternatives in the cross-sectional surveyA total of 71 participants were approached and 57 responded in the first round . Patients had a mean age of 70 years (± 9), 78% were male and 89% were married or living with a partner. Most of the patients (56%) were in NYHA-class III and 72% of them had an ICD or CRT device. Family members had a mean age of 67 years (± 11), 71% were female and most of them (93%) were living together with the patient. Only one family member was the child of a patient. The professionals  had a mean age of 43 years, 54% were female, and the majority of them (85%) worked at a hospital. In total, 4 patients, 6 family members and 5 health care professionals did not respond in the first round.In the second round, 68 participants who responded in the first round were approached, and 51 participants responded . In total, 5 patients, 6 family members and 6 health care professionals did not respond.Overall, most of the participants in both samples endorsed the title, the two pictures and the introductory text of the QPL. Comments were made such as: the title could be shorter, and the picture on the front page  was found to be “too positive” with a tone that did not correspond with the serious content of the QPL. There were Dutch patients/family members who did not recognise themselves in the couple shown in the picture. There were also smaller changes suggested for the introductory text.Forty-five of the questions in Sweden and thirty-nine in the Netherlands were perceived as relevant and clear by the participants, but for some of the questions, re-formulations were suggested to make them clearer Fig. . Most ofAfter Delphi round 1, the research groups in both countries discussed the results and discussed which questions should be kept, merged and/or re-formulated as they had similar content, which questions could be deleted from the QPL and also which new questions could be added that were found to be missing in the QPL.In the second Delphi round, the Swedish QPL included 49 questions of which the researchers suggested that 33 should be kept, 12 questions deleted, and 4 new questions added. In the second Delphi round in the Netherlands, the QPL included 59 questions of which the researchers suggested that 33 should be kept, 12 questions deleted, and 12 new questions added. The participants were asked to state if they agreed on the suggestions.In round 2, the participants agreed that 38 proposed questions in Sweden and 45 questions in the Netherlands should be kept in the list. In the research group discussions, some questions with similar content were merged or deleted which resulted in a final QPL for Sweden including 33 questions and 38 questions for the Dutch QPL. Based on the participants’ answers questions that that were deleted were for example “is it possible to predict how long someone has left to live?”, “what happens in the body when you die from HF?”, and “how do I reply to the question “Am I going to die now?”.A total of 115 patients .If participants did not want to discuss a question, they most often gave the reason that they already had enough information. If participants reported they did not want to discuss a question because they would be worried or they did not want to think about the future, it was often the same participants reporting this answer on more than one question.In this section Fig. , each quIn this section Fig. , each quIn this section Fig. , each quIn this section Fig. , only thIn this section Fig. , only thPatients and family members in both countries provided additional comments to describe their reasons for why they did or did not want to discuss certain questions in the QPL at this moment. For some it seemed too early to discuss several questions at this point in the HF trajectory but later, it could be important to get more information. Some patients expressed how they wanted to live ‘in the here and now’, not worrying about possible deterioration in the future. On the other hand, participants also commented that it could be too late to have this kind of conversation, if the patient, for example, was very old.This study describes the optimizing of a QPL to improve communication about the HF trajectory in HF care. The QPL was previously developed in a co-design process  togetherThe acceptability testing  focused Our findings show that patients and families in our study were not upset by the idea of discussing the more sensitive questions concerning the HF trajectory. Health care professionals, such as physicians, nurses and other relevant professionals, need to discuss the HF trajectory with patients in order to improve their understanding of their illness and address possible care needs of patients and their families , 2, 29. A QPL needs to be used with care as patients have different approaches to cope with HF and also want different amounts of information depending on their current situation . Some paWe found in our acceptability testing of the QPL that most of the original 45 questions were perceived as appropriate by the participants in both Sweden and the Netherlands and there were no huge differences in the participants’ opinions. Nevertheless, some cultural discrepancies exist in the content and in the amount of questions, resulting in two versions of the QPL: a Swedish version including 33 questions and a Dutch version including 38 questions. The Dutch QPL included more questions in the sections “Heart Failure in daily life”, “Support when deteriorating”, and “End-of-life”. The Swedish QPL included more questions in the section covering “Questions for family members”.We suggest that the questions in the Swedish and the Dutch QPLs can function as a blue-print for others to use. These QPLs can provide possible questions to be included in future QPLs, but we recommend that cultural adaptation of the questions should be done to fit the intended culture optimally and also provide the opportunity for each country to add additional questions that might be missing in the original QPL . AdditioThe participants’ interest in using the QPL in clinical practice was assessed, and participants in both Sweden and the Netherlands reported that they were interested to discuss questions from all the five sections in the QPL. Some participants, particularly those who felt they lacked information, commented that the QPL could help them to select questions and initiate a discussion. This is in line with previous research concluding that providing a QPL in clinical practice can increase the number of questions a patient asks if the QPL is tailored to the patient’s needs , 23, 38.Importantly, few patients and family members reported that they were worried by the questions in the QPL and hence did not want to discuss the questions. This needs to be considered in clinical practice since one commonly reported barrier from health care professionals why they avoid conversations about the HF trajectory is the belief that patients might become worried if they initiate discussions about prognosis or end-of-life issues , 32.For participants who did not want to discuss the questions in the QPL, the most reported reason was because they already had all the information that they wanted about the HF trajectory. Interestingly, all patients included in this study were visiting a HF clinic in Sweden or the Netherlands, where they were provided with dedicated time with professionals specialised in HF care. Nevertheless, around 30% of the participants declared a need for more information about the HF trajectory, indicating that we can do better in providing this kind of information to patients and their families.We found in the open-ended answers from patients and family members that the timepoint at which they wanted to discuss certain questions in the certain sections in the QPL differed. Some participants wanted to discuss, for example end-of-life issues later in the HF trajectory, and perceived that it was too early at the time the questionnaire was administered. Hence, we suggest that there must be repeated opportunities for discussion when the patient and family members want more information. These repeated opportunities for discussion are also important as we know that many HF patients are not aware of their poor prognosis or the severity of HF , 40. ManFamily members reported that they would like to discuss questions in all the sections of the QPL; sometimes they reported even higher needs for information than the patients did. Information needs may change between patients and their family members during the HF trajectory, whereas patients tend to want less information the closer they are to the end-of-life , but theStudy participants were recruited from regions which are seen as average regions for each country. They consisted of a diverse group of patients, their families and health care professionals from Sweden and the Netherlands. Although our study population was selected from HF clinics, we still realise that participants were approached to be in a research study. Maybe only patients, families, and health care professionals with an open approach to discussing the HF trajectory were represented in the samples, but as we included four different samples from two different countries, we believe this risk is minimized.The research team, involving 6 nurses, 1 physician and 1 behavioral scientist, provided their clinical experience and research knowledge of HF- and palliative care to inform the planning and performance of the study.In the cross-sectional survey, the participants were asked if they would like to discuss the questions in the QPL with a physician or a nurse, as these are health care professionals that they in general meet the most. Additionally, we argue that the QPL is suitable for use by several other health care professionals as well, such as social workers, and psychologists. Accordingly, in the cross-sectional survey the participants were asked if they wanted to discuss the questions in the QPL “right now”. This may have affected the results and the final questions in the QPL.There were some differences between the countries in sample sizes and NYHA class in the cross-sectional study. The Dutch samples included more patients and family members compared to the Swedish samples and a bigger proportion of the Dutch patients had more symptomatic patients in NYHA class III.One possible limitation in data analyses in the cross-sectional survey was the use of predetermined answering options in the questionnaire. If only open answers would have been allowed it could have produced a more rich data, possibly providing more important insights into the reasons why or why not patients and their family members wanted to discuss the different questions in the QPL.The QPL, designed for communication about the HF trajectory, has successfully been adapted into one Swedish version and one Dutch version. It includes questions that patients, their families, and health care professionals perceived as relevant to discuss with health care professionals about the HF trajectory. Overall, patients and family members were not worried about the content in the QPL and if used in accordance with patients’ and family members’ preferences, the QPL can help to improve communication about the heart failure trajectory. The QPL is ready to be used in clinical HF care in Sweden and the Netherlands. Further research is needed to examine the optimal way of delivery of the QPL into clinical practice and to examine how patients/family/professionals experience using the QPL in daily practice.Additional file 1. The final questions in the two versions of the QPL. SW, Sweden, NL, The Netherlands.Additional file 2. The questions that were suggested to be deleted or added in the Swedish and Dutch Delphi rounds. SW, Sweden, NL, The Netherlands.


Skin manifestations of sarcoidosis occur in up to 30% of cases, and may be the sentinel sign of the disease, with the skin being sometimes exclusively affected. While this may facilitate an early dermatologic diagnosis, heterogeneity in the cutaneous morphologies of sarcoidosis complicates recognition and affirms its reputation as a “great imitator”. Here, we present a case of a verrucous version of sarcoidosis that may be misdiagnosed because it can mimic other inflammatory and neoplastic skin disorders. Although it is a rare variant, its presence should alert clinicians to the likelihood of systemic involvement of cutaneous sarcoidosis. Skin manifestations of sarcoidosis occur in up to 30% of cases, and may be the sentinel sign of the disease . CutaneoA 63-year-old man presented with a one-year history of progressive and itchy perineal lesions. On physical examination, the patient had extensive verrucous plaques and nodules of the gluteal region, perineum extending to the inner thighs . Skin biSarcoidosis-specific cutaneous lesions are characterized by variable clinical presentations. This fact makes it difficult for dermatologists to appropriately classify this condition on macroscopic evaluation . VerrucoHistologically, these cases showed marked verrucous epidermal hyperplasia with dermal involvement by both typical noncaseating sarcoid granulomas . Only twOur case highlights that verrucous versions of sarcoidosis may be misdiagnosed because it can mimic other inflammatory and neoplastic skin disorders. Although it is a rare variant, its presence should alert clinicians to the likelihood of systemic involvement of cutaneous sarcoidosis.


The presence of traces of heavy metals in wastewater causes adverse health effects on humans and the ecosystem. Adsorption is a low cost and eco-friendly method for the removal of low concentrations of heavy metals from wastewater streams. Over the past several years, graphene-based materials have been researched as exceptional adsorbents. In this review, the applications of graphene oxide (GO), reduce graphene oxide (rGO), and graphene-based nanocomposites (GNCs) for the removal of various metals are analyzed. Firstly, the common synthesis routes for GO, rGO, and GNCs are discussed. Secondly, the available literature on the adsorption of heavy metals including arsenic, lead, cadmium, nickel, mercury, chromium and copper using graphene-based materials are reviewed and analyzed. The adsorption isotherms, kinetics, capacity, and removal efficiency for each metal on different graphene materials, as well as the effects of the synthesis method and the adsorption process conditions on the recyclability of the graphene materials, are discussed. Finally, future perspectives and trends in the field are also highlighted. Both natural and anthropogenic sources linked to industrial activities such as electroplating, metal smelting, fertilizer industries, mining operations, pesticides, and paper manufacturing result in wastewater streams contaminated with various heavy metals. Discharging these streams into the environment leads to the absorption and accumulation of heavy metals into living organisms resulting in severe health complications. Therefore, the current stringent regulations, requires the removal of heavy metal from wastewater streams to extremely low levels. The WHO guideline  for the Several technologies are being used or proposed for removing heavy metals from wastewater streams including chemical precipitation , ion excAlthough graphene can be prepared by bottom up approaches such as CVD, epitaxial growth, templating, and organic synthesis, graphene materials used in adsorption applications are prepared by top-down methods via oxidation of graphite to produced graphene oxide (GO) that can be thermally or chemically reduced to obtain reduced graphene oxide (rGO). Further modification of GO and rGO via the development of nanocomposites with metal oxides and organic molecules enhances their sorption characteristics.This review focuses on the removal of heavy metals from wastewater using various graphene materials. Although there are already few articles that review the adsorption of various metals on graphene materials, this article is more comprehensive and it also accounts for the large number of very recent articles appeared in 2018 and 2019, which represent about 60% of the total number of publications. Moreover, this review includes a concise section on the synthesis of various graphene materials and composites in order to classify the various graphene materials and establish the correlation between the synthesis method, structure, and the adsorption characteristics of the graphene materials. Moreover, the key adsorption parameters associated with each metal on various graphene-based materials are summarized in tables and the performance of the key graphene materials are highlighted and discussed. It is very evident that application of graphene materials as adsorbents for metal removal is a rapidly growing research field as can be seen by the very large increase in number of publications in 2018 and 2019, This review begins with a concise discussion on the synthesis of GO, rGO and their nanocomposites with organic, inorganic, and polymers, which have been used for metal removal. Then an overview of the typical methodology to study adsorption and the models used for analysis of the process thermodynamics and kinetics are provided and a comprehensive analysis of the performance of various graphene-based materials for the adsorption of various metals is carried. Finally, an outline of the major challenges for the commercialization of graphene-based adsorbents for heavy metals and highlights the future research directions are presented. GO and rGO and their foam/aerogel structures andHybrid of GO or rGO with metallic, organic, inorganic, and polymeric materialsThe graphene materials used for the removal of heavy metals are classified into two broad categories that include:While there are few studies on the use GO and rGO in powder, aerogel, and 3D foam structure, most of the reports are on using hybrids of GO and rGO with organic, inorganic, and/or polymers. In this section, we summarize the synthesis methods for GO, rGO and hybrid graphene materials.2 in graphite to a mixture of sp2 and sp3 in GO. The oxygen content of graphite oxide is defined by the C/O ratio which ranges between 1:1 in highly oxidized GO to 4:1 in less oxidized GO depending on the oxidation method and conditions. The presence of these oxygen groups makes graphite oxide very hydrophilic such that it readily exfoliates to GO in aqueous solution. rGO is prepared by thermal, hydrothermal, or chemical reduction of graphite oxide or GO. The reduction of GO to rGO reduced the oxygen content to about C/O ratio of 10. The structure of GO and rGO as well as the schematic for their preparation is shown in Although graphene can be obtained directly from graphite using mechanical cleavage or solution assisted exfoliation, the dominant type of graphene used in adsorption application is prepared via the graphite oxide route not only because its potential for large scale production, but also because it produces a functional form of graphene that is attractive for adsorption applications. In this route, GO is produced by exfoliation of graphite powder, which is produced through solution oxidation/intercalation of graphite using acids and oxidants. The first report on the synthesis of graphite dates back to 1958 by Brodie using nitric acid and potassium chlorate . CurrentAlazmi et al.  investigIn addition to microscopic characterization of GO and rGO, characterization using spectroscopic techniques such as XPS and FTIR and diffraction techniques such as XRD and SAD are commonly used to determine the structure of GO and rGO and the presence of oxygen-containing functional compounds. Other characterization techniques have been performed. The synthesis of the adsorbents was been carried out with a variety of methods and with great rigor and control. Heat treatment at different temperature ranges, vacuum promoted exfoliation, physical incorporation of additives, and surface modifications using oxidative agents are a few techniques used in the synthesis processes . For mor3O4 are very commonly applied not only to enhance the adsorption characteristics, but also to allow the retrieval of the adsorbent for regeneration at the end of the batch adsorption using magnetic recovery. Nevertheless, many studies have further modified the magnetic GO or rGO with other metallic, organic or inorganic materials. A concise review of the synthesis of these different hybrid graphene materials applied for the adsorption of heavy metals is provided.To improve the adsorption characteristics of GO and rGO and to enable their effective application in selective adsorption of heavy metals, a few strategies are applied. These strategies include the formation of hybrid structures of GO or rGO with oxides of transition metals such as iron, Zn, Cu, Ni, and Co, organic materials such as cellulose and chitosan, inorganic materials including metal organic framework (MOF), zeolites, and silica nanostructure, polymers and mixtures of two or more of these groups. Among these strategies, the development of magnetic nanocomposites of GO and rGO with Fe3O4 or Fe3S4. mGO is synthesized via impregnation or co-precipitation methods [3O4, FeSO4, Fe(NO)3, or iron acetate on the surface of dispersed GO under sonication, see One of the significant challenges faced when using nanosorbents is their separation from the treated solution. Centrifugation, sedimentation, filtration, and other traditional separation methods deem to be ineffective and time consuming. On the other hand, magnetic GO (mGO) is synthesized via impregnation or co-precipitation methods ,25,26,27 methods ,25,26,27In the impregnation method, a GO suspension is mixed with pre-synthesized magnetic nanoparticles and sonicated at room temperature until a homogenous suspension is achieved. The mGO is then collected by centrifugation followed by freeze-drying, 4·7H2O to create GO/Brianyoungite GO/BY) composite with hollow spherical and flake-like morphologies. Wen et al. [3O4/GO/Cu-ZEA via solid state dispersion of Cu-ZEA and Fe3O4 into GO suspension followed by sonication. Lingamdinne et al. [Zhu et al. used ZnSOn et al.  incubaten et al.  fabricate et al.  mixed Hy2+, Cu2+, and As3+. Shahzad et al. synthesized EDTA-MCS/GO via 2-step process in which the first step yielded (MCS/GO), which was dried and mixed with Na2EDTA to produce the composite [Graphene-based hybrids have been widely used in the removal of heavy metals. Some of the materials used to make these composites include chitosan and cellulose. Cellulose is combined with GO to form Ethylenediaminetetraacetic acid (EDTA)-functionalized magnetic chitosan (CS) graphene oxide (GO) nanocomposites (EDTA-MCS/GO) through a reduction precipitation method . This coomposite . Yang etomposite  cross-liomposite . 3O4 and adding it to graphene to develop polypyrrole–graphene (PPy–GO) nanocomposites [3O4-encapsulated poly(C3N3S3) polymer/rGO nanocomposite following the method shown in Zhu et al. fabricated a magnetic composite by polymerizing Femposites . Yang etmposites . Tadjaromposites . Sulfurimposites . Najafabmposites . Li et amposites . Zare-Domposites . Nano simposites  on GO tooC, mg/L), equilibrium concentration , maximum adsorption capacity , adsorption percentage (%), the kinetics are studies by measuring the adsorption capacity at a given time t , solution volume , weight of GO , and the final concentration of metal ions . The equations are based on the mass balance of the reaction, as follows:Water solution containing various concentrations of heavy metal ions are used to carry out the adsorption studies typically at pH 5.5 and room temperature. After equilibrium is achieved, the following parameters are measured or calculated: initial concentration  > Cu (II) >> Cd (II) > Zn (II). The adsorption affinity is not dependent on the ionic radius of the heavy metals but more on their relative positions in the electro chemical series. However, the capacity can increase or decrease with temperature depending on heat of adsorption, i.e., exothermicity or endothermicity of the process . tC) and adsorption capacity (tQ) versus adsorption time (t) and various kinetic models are used to regress these data to find the kinetic model that best describes the collected data. For the adsorption of heavy metal ions on GO-based substances, two kinetic models are commonly applied, pseudo-1st-order kinetic model and pseudo-2nd-order kinetic model.Studying the kinetics of the adsorption process is crucial not only to identify the adsorption mechanism but also to ensure the proper design of the adsorption process in terms of the required residence time. In general, experiments are designed to collect data on the change of the adsorbate concentration , more functional groups are available and electrostatic interactions between the heavy metal ions and GO are stronger, but the optimum pH for maximum ion uptake may vary depending on the type of the heavy metal ion. GO modified with metal oxides and organic molecules are among the highest capacities, while inorganic composites (Mg−Al layered double hydroxides GO nanocomposite) when dispersed in water, it swells and forms viscous gel as shown in 0~1 mg/L. The kinetic of the arsenate adsorption on the various graphene materials provided in An important and key aspect for the commercial application of the adsorption processes that are based on costly adsorbent, which is often neglected in research studies, is the regeneration and re-usability of the adsorbent. Few studies have investigated the regeneration and reuse of the graphene adsorbents using either a strong alkali (NaOH) or strong acid (HCl) in the desorption step. For As (III), M-nOG, EDTA-MCS/GO, and GO-f were found to be reusable. M-nOG was observed to retain 94.5% of the first cycle capacity after 5 cycles . Moreove3O4 [Because of the toxicity and abundance of lead in wastewater streams, there are large number of studies focused on the adsorption of Pb (II) on GO with several of studies investigating the regeneration of the graphene adsorbents. The properties of the graphene adsorbents and their lead (II) adsorption properties are summarized in 3O4 ,59,60,613O4 . The trends for the best synthesis method to yield a high capacity adsorbent were very hard to distinguish. The best capacities were achieved by modifying graphene with polymers and inorganics ,64. The The most economic synthesis methods are those using fewer chemicals and production steps. One-pot hydrothermal, dispersion and co-precipitation with few components would serve as a better synthesis option especially when coupled with good performance. For instance, 3D G/chitosan/nickel ferrite NC was synthesized hydrothermally in a few steps utilizing sustainable components like chitosan and is one of the best performing graphene-based adsorbents in the removal of lead from aqueous solutions with a maximum capacity of 957.3 mg/g . 2O4-G, NiFe2O4-G, Fe3O4-GS, EDTA-mGO, EDTA-MCS/GO, DTPA/MGO, GOMCS-IL, and IT-PRGO, Mg−Al LDH / pRGO [3O4-GS and EDTA-mGO maintained more than 80% of their original adsorption capacity [2O4-G and CoFe2O4-G had 98% and 100% desorbing capacity and the adsorption efficiency was almost retained during 3 repeated cycles [The potential for the regeneration of the lead loaded adsorbents has also attracted much attention and several studies have investigated the reusability of the sorbents after regeneration. These include: CoFeH / pRGO ,73,74,75capacity ,77. The capacity . EDTA-MCcapacity . The adscapacity . Similarcapacity . IT-PRGOcapacity . Mg−Al Lcapacity . NiFe2O4d cycles ,66. Basid cycles . It wort4Cl was 17,900 mg/g which is extremely high, although the conditions and results of the study may not be realistic [Despite the large number of adsorption studies for the removal of lead (II) using graphene oxides and derivatives of graphene oxide, almost all the equilibrium adsorption results are best-modeled using the Langmuir isotherm. Most of the kinetic results follows pseudo-second order kinetics with exception of Mg-Al LDH/pRGO and pRGO, which followed Elovich kinetics model , HMO@GO ealistic . The adsorption capacity, removal efficiency, and the isotherm models for the adsorption of Cadmium (II) on different graphene materials are summarized in The most common routes used for synthesis of graphene composites used for Cadmium removal were the solvothermal, hydrothermal, dispersion, and co-precipitation methods. However, nanoscale zero-valent iron-reduced graphene oxide composite was prepared via plasma-reduction method and graphene oxide embedded calcium alginate was prepared via drop-wise formation method to create bead like structures . The bes2O4, G-CoFe2O4, GO-DPA, rGO-NZVI and GO-f are found to be reusable with a slight decrease in capacity with number of cycles. For example, the Cadmium adsorption capacities of DTPA/MGO-based composites synthesized following the route shown in 2O4 and G-CoFe2O4 retained 98% and 100% of their capacity during 3 repeated cycles [Regeneration and reusability of the graphene materials are examined by several groups and mGO- DTPA, G-NiFed cycles . GO-DPA d cycles . rGO-NZVd cycles . The recd cycles . 2O3, GO and DTPA forming a compound with a higher metal binding and electrostatic forces thus improving adsorption capacity [Magnetized DTPA-mGO has been synthesized by combining Fecapacity .4Cl and Zinc [Cadmium is another highly toxic heavy metal, where the kinetics of its adsorption with various conventional adsorbents including Amberlite IR-120 synthetic resin—101 mg/g , modifieand Zinc . The entxR@TiO2 [The adsorption properties of Ni (II) on graphene-based materials are presented in xR@TiO2 . The adsxR@TiO2 .The synthesis process of 2, 20-dipyridylamine (DPA) was a simple precipitation in the presence of nitrogen gas. Dry dichloromethane and phosphorous pentachloride were added to GO and mixed to yield a highly sensitive and stable composite for the adsorption of nickel . The reported capacities of 76, 104, 181 mg Ni (II)/g GO are linked to the high initial adsorbate concentrations of 51, 60, 100 mg/L, respectively . These vThe results of studies on the adsorption characteristics of Hg (II) ions on GO (s) are presented in All studies were on batch experiments. The most common synthesis methods were hydrothermal, solvothermal, and diffusion methods. Some adsorbents were fabricated through a mechanical route whether ultra-sonication , electroHigh adsorption capacities of mercury in the range of 168–700 mg/g have been obtained with different graphene composites ,133,134.The Hg (II) capacities on conventional adsorbents are frequently much lower with adsorption capacities ranging from single digit values to over 200 mg/g. Other reported capacities on conventional adsorbents include walnut shell derived activated carbon—151 mg/g .3O4 to facilitate the decontamination process by simplifying the separation process described in Utilization of the magnetic properties of FeComposite adsorbents have higher adsorption capacities than pure graphene oxide. A novel adsorbent was designed by chemically modifying graphene oxide (GO) with 2-pyridinecarboxaldehyde thiosemicarbazone (2-PTSC) as ligand for removing Hg (II) from aqueous solutions with capacity reaching 555 mg/g. During this experiment the effect of pH, mercury concentrations and time on adsorption capacity were investigated. Moreover, EDTA-mGO, Ag/graphene, GO/2-PTSC, GO/2-PTSC with US, GO-f were identified as reusable adsorbents. Almost half of the studies investigated the regeneration of the adsorbents. Some studies reported excellent regeneration after 6 cycles but had lower maximum capacities in comparison to the rest of the adsorbents ,137. Reu3O4 was a component additive and the resulting adsorbent material had more than one active surface adsorption site. On the other hand, the kinetic data are well represented by the pseudo-2nd order model with two exceptions where the double-exponential and intraparticle diffusion models were followed [The adsorption capacities of Cr (III) and Cr (VI) on various GO-based adsorbents are presented in followed .Ak and Bk, for each step respectively. This model is represented by Equation (4):tq—amount of chromium adsorbed at time t, eq—amount of chromium adsorbed at equilibrium e. Ad and Bd—amounts of rapidly and slowly adsorbed fraction of chromium (mg/L), respectively, m—mass of adsorbent.The double exponential kinetic model assumes the adsorption reaction occurs in two steps comprising a fast stage step 1 and a slow stage step 2, with first order rate constants, 2SO4 which introduces more active sites on the surface of the adsorbents [G-PDAP is a sulfuric acid doped diaminopyridine polymer prepared in-situ on the surface of GO through mutual oxidation-reduction process as detailed in sorbents .Ultrasonication was a popular synthesis route with organic graphene composites with competitive results ,80,141. 3O4/SiO2-GO-PEI was recycled several times without a significant decrease in its adsorption capacity [All these high capacities have the initial adsorbate concentration greater than 200 mg/L. The ability to regenerate and reuse the GO-based adsorbents has been reported. In a few cases, Fecapacity . GONF wacapacity  and rGO-capacity . The moscapacity ,149.th cycle of Cr (VI) removal [GEC’s adsorption capacity decreased slightly from 92.5% to 87.5% after 7 cycles, indicating it is suitable adsorbent for Cr (VI) removal . For chi removal . Moreove removal . DAP–RGO removal . The reg removal . Upon an removal . nd order model. Only one study followed the Double Exponential kinetic model [Removal of copper ions or copper complexes from water are most widely studied among all other metal ions due to its extensive occurrence especially in the microelectronics industry effluents. ic model .The highest copper uptake capacities shown in 3O4, Fe3O4/TiO2, CS-IIP and Fe3O4/HAP/GQDs were found to be reusable. EDTA-mGO retained a 97.6% removal efficiency after five cycles [In addition to high adsorption capacity, it is important for the expensive GO derived adsorbents to have the ability to be regenerated and reused many times, whilst retaining a high capacity. In this regard EDTA-mGO, FA-mGO, EDTA-MCS/GO, DTPA/MGO, GO-DPA, chitosan/GO, GO-CTPy, Fee cycles  and FA-me cycles . i), simple emulsion and Co-precipitation (mGOp) [Magnetic graphene oxide is prepared through the Impregnation Method (mGOn (mGOp) ,71,134. Various methods were used to fabricate or synthesize the graphene composites used for the removal of copper. The three most common were solvothermal, hydrothermal and dispersion methods. In some cases, a combination of the methods was used to synthesize different components of the adsorbents ,70. The th cycle for metal ions [3O4 and FTG were 9% and 7.4% after 5 cycles [EDTA-MCS/GO showed high magnetic sensitivity in the presence of an external magnetic field after 4 cycles, which indicated good reusability status . DTPA/MGtal ions . The adstal ions . It also5 cycles . CS-IIP’5 cycles . The adsorption capacities for copper using the more conventional adsorbents are generally much lower than the high values reported in 5 remained about 95% with both Au(III) and Pd(II) after 3 cycles, showing that it is possible to successfully reuse CSGO5 for the adsorption of both metals [h metals .GO provides an economically viable and efficient method to treat wastewater containing harmful heavy metals. Various methods are available for synthesizing composite GO materials providing materials that are tailored for removal of specific species. The carboxyl, hydroxyl, and epoxy functional oxygen groups on GO facilitate the adsorption of ions by providing active binding sites. This review analyzes the metal adsorption results from over one hundred and eighty recent studies using GO and GO-derived materials for the removal of more than 10 metal ions. The adsorption capacities of different metals are analyzed and compared with the capacity of conventional adsorbents. In almost every case, the metal adsorption capacity using GO materials are considerably higher. Although the production of GOs is expensive at present, these high capacities may lead to lower cost for treatment of wastewater streams polluted with metal ions as not only is the required adsorbent amount lower, but also the size of adsorption equipment will be less and hence the plant capital cost will be less. There are no studies that have considered how to recover the valuable metals for re-use which is an important topic that needs further research.New research directions started in the last few years for GO hybridizations with different organics to enhance the metal uptake and speed the adsorption kinetics. More detailed mechanistic studies have been utilizing UV and ultrasound to facilitate the adsorption process. More research is required on new functional groups and composites that increase the maximum adsorption capacity of GO and improve its reusability. More fixed bed column studies are required and both testing of the graphene materials for selective removal of metals is still absent from the current literature as the current studies focus on testing single metals. Moreover, the effect of water salinity on the adsorption of heavy metals is important for treatment of oil- and gas-produced water, where high concentrations of monovalent salts exist. Another key issue is the ability to regenerate and retain the adsorption capacity of the GO-based adsorbent in an economic manner and recover the desorbed metal  for reuse. There are almost no studies which have utilized the use of fixed bed columns experiments as almost all studies have been on batch experiments. Further studies in this area and scale-up are also required with estimation of the cost of the material and its impact on the economic viability of large-scale adsorption processes.


We review graphene gas sensors functionalized by different materials, including metallic nanoparticles, metal oxides, organic molecules, and conducting polymers. The various sensing mechanism of functionalized graphene gas sensors are explained and compared. Meanwhile, some existing challenges that may hinder the sensor mass production are discussed and several related solutions are proposed. Possible opportunities and perspective applications of the graphene NH3 sensors are also presented.Since the first graphene gas sensor has been reported, functionalized graphene gas sensors have already attracted a lot of research interest due to their potential for high sensitivity, great selectivity, and fast detection of various gases. In this paper, we summarize the recent development and progression of functionalized graphene sensors for ammonia (NH Most of NH3 in our life environment is emitted directly or indirectly by agricultural sector, waste handling, road transportation, industrial applications, and human activities. NH3 plays a decisive role in particulate matter (PM) formation in polluted environments [3 is caustic and hazardous to human health. Specifically, it injures the human eyes, skin, respiratory tract, liver, and kidneys beyond a concentration of 25 parts per million (ppm) [3 sensing and monitoring are essential for industrial emission control, environment conservation, and human safety. Recently, NH3 sensors have found new potential in medical applications, because NH3 is a biomarker for renal and ulcer diseases [3 sensors can be used to diagnose these diseases through detecting NH3 concentration from human breath. For a healthy person, the mean concentration of NH3 in the breath exhalation is about 0.83 ppm [3 concentration in the range from 0.82 to 14.7 ppm  [3 sensors have been investigated in the literature [3 intelligent sensors, which can be integrated with complementary metal-oxide semiconductor (CMOS) circuits and used in the context of the Internet of Things (IoT). Metal oxides, such as SnO2, V2O2, WO3, ZnO, In2O3, TiO2, and Cu2O, are very popular compounds for NH3 sensing [3 sensing are based on conducting polymers such as polypyrrole or polyaniline [Ammonia (NHronments . NH3 is diseases . Therefo.88 ppm) . Althougterature , it is s sensing ,11,12. Hyaniline ,16,17. Dyaniline ,19,20. T2 molecule by using pristine graphene in pure helium or nitrogen at atmospheric pressure. Their results also revealed that pristine graphene sensor responds not only to NO2, but also to NH3, CO, and H2O. Subsequently, graphene-based sensors were widely exploited for detecting various types of gases, for example NH3, CO, O2, NO2, H2, CH4, SO2, H2S, and volatile organic compounds (VOCs) [2 and NH3. The detection limit reached 100 and 500 parts-per-billion (ppb) for NO2 and NH3, respectively. These values are markedly superior to commercially available sensors. However, the full recovery of pristine graphene sensors requires them to be heated at 200 °C in inert gases. Dan et al. [3 at room temperature. The first-principles calculation also predicts that pristine graphene is chemically inert [3 molecules in ambient condition. As a result, interest in the functionalization to generate specific links between pristine graphene and NH3 molecules is highlighted. Generally, graphene functionalization can be accomplished by metallic nanoparticles, metal oxides, organic molecules, or conducting polymers. This article does not review all the functionalization methods presented in the literature but mainly focuses on the graphene functionalized by ultrathin conducting polymers for NH3 sensing. Since the discovery of graphene (G) in 2004, it has been researched and developed as a gas-sensing material because of its extremely large surface-to-volume ratio and high carrier mobility. One adsorbed molecule can cause a notable change in the graphene resistance, allowing the sensing ability to single molecule level ,22. In 2s (VOCs) ,25,26,27s (VOCs)  used chen et al.  found ouly inert . These f3 detection, including mass sensitive, Schottky/semiconductor diode, chemiresistor, and field-effect transistor (FET) sensors. In 3 sensors are first briefly described, followed by the presentation of their main properties and their related sensing mechanisms. The graphene sensors functionalized by ultrathin polymers are presented in detail. In 3 sensors are presented, which may provide future research directions. The article is arranged as follows. In Graphene is one of the most promising materials for gas-sensor applications. In this section, we present the distinctive band structure and outstanding physical properties of graphene. Then, we briefly review the graphene preparation methods.sp2-bonded carbon atoms. Electrons are delocalized and free to move in this 2D sheet. The energy band structure of graphene is illustrated in p-type doping [p-type or n-type semiconductor.Graphene is a two-dimensional (2D) material with a monolayer of e doping . The zere doping . HoweverDue to this structure, graphene is very sensitive to Fermi level changes. Its conductivity can be easily modified by doping or a back gate voltage when the graphene sheet is fabricated as a field effect transistor sensor .2/g [2/s.V) [Single-layer graphene has the largest surface-to-volume ratio of 2630 m2/g  and expo [2/s.V)  and exce [2/s.V)  of graph [2/s.V) . For gra2/Si wafer) is dipped in the acetone and then washed with plenty of water and propanol, which removes mostly thick flakes. In this case, some thin flakes are captured on the target substrate’s surface due to van der Waals and/or capillary forces. Although mechanical exfoliation can provide high-quality single-layer graphene, it is not a scalable technique, and other techniques were proposed.Historical graphene was first prepared by mechanical exfoliation of graphite ,40. For 4) on catalytic metal substrates at high temperature (about 1000 °C) in a controlled atmosphere or atmospheric pressure. Cu, Ni, Ti, Ru, Pd, Pt, Ir, Co, Au, and Rh can be used as the catalytic metal substrates [Chemical vapor deposition (CVD) holds great promises for large-scale production of high-quality graphene ,42. Concbstrates . Among tGraphene has also been grown on the surface of single-crystal silicon carbide (SiC) by thermal decomposition . Namely,4 and NaNO3 in concentrated H2SO4. This method has broadly been used in gas-sensor fabrication because of its high efficiency. However, it still has a few drawbacks. For instance, the oxidation procedure releases toxic gasses and the control of the graphene oxide sheets is difficult. Recently, several modified methods were proposed in the literature to improve the control of the GO and rGO synthesis [For large-scale production of low-cost graphene, one of the most popular approaches is the use of strong oxidizing agents to obtain GO and then convert GO to reduced graphene oxide (rGO) by thermal treatment or chemical reduction. In 1958, Hummers  reportedynthesis ,47. It iynthesis ,49.3. Graphene and rGO can be fabricated by various methods. CVD can provide large-scale production of high-quality graphene. However, high power consumption and waste catalytic metals limit its production cost. The rGO is considered as a more practical method due to its large-scale and low-cost production.In brief, the outstanding properties of graphene make it suitable for developing highly sensitive sensors for NH3 detection. It includes mass sensitive sensors, Schottky/heterojunction diode sensors, chemiresistor sensors, and field-effect transistor (FET) sensors.In this section, we briefly review the working principle and operation mode of various functionalized graphene sensors for NH3 molecules adsorb on the functionalized graphene surface over the quartz crystal surface, the resonant frequency of the resonator varies proportionally with the mass of NH3 adsorbed on the sensing layer. The change in the resonance frequency is used to measure the mass of adsorbed NH3 by using the Sauerbrey equation [3, respectively. A is the surface area of the electrode. According to the chemical equilibrium, one can obtain the 3 adsorption and increases the resonance frequency change, thereby improving the sensitivity of the QCM.Mass sensitive sensor is a transducing device with a sensitive layer. After the sensitive layer adsorbing the target gas, the device gives a signal related to the mass uptake of this layer. The sensors are divided in quartz crystal microbalance (QCM) sensors  and surfequation :(1)Δf=−23 detection. This is attributed to the abundant oxygen-containing groups on the surface of rGO film, which strongly adsorb NH3 molecules and increase the film stiffness.The surface acoustic wave (SAW) sensor is more common than the QCM sensor. Its working principle is based on the elastic loading effect. ψSBH) can lead to a huge difference in the diode current–voltage (I–V) characteristics. n-type silicon interface for the pristine graphene state (middle), the graphene electrode exposed to electron-donor gas (left), and the graphene electrode exposed to electron-acceptor gas (right) [3 molecule is strongly nucleophilic. Once it is attached to graphene, it donates electrons to the latter via coupling π bonds. One NH3 molecule can donate 0.03 electrons onto graphene [3 can be described as follows: when the graphene electrode surface is exposed to NH3, the electron transfer from NH3 to graphene causes a shift of the graphene Fermi level toward the Si conduction band, lowering the ψSBH (as shown in I) across the graphene/n-type Si interface is determined by the ψSBH through formula [V is the applied voltage, A is the area of the Schottky junction, A** is the Richardson constant, T is temperature, q is electric charge, k is the Planck constant, ψSBH is the Schottky barrier height, n is the ideality factor. For the pristine graphene/n-type silicon, n = 1.41 and ψSBH = 0.79 eV. For the pristine graphene/p-type silicon, n = 1.31 and ψSBH = 0.74 B eV [Graphene  and semiconductor Schottky diode sensor is a promising candidate for quickly sensing low concentration gas. When the Schottky diode is exposed to the target gas, a small change in the graphene electrode composition and Schottky barrier height ( (right) . NH3 molgraphene ,57. The  formula :(2)I= AA.74 B eV .3 directly impacts the current of the Schottky diode. More specifically, a small change in the ψSBH caused by NH3 adsorption on the graphene electrode can exponentially change the current of the Schottky diode through Equation (2). As a consequence, the current change can be used to identify various adsorbents and determine their concentration. I–V curves of a graphene/n-type Si Schottky diode sensor before and after exposing to electron-donor gas and electron-acceptor gas.The chemical or physical modification of the graphene electrode by NHn-Si Schottky diode for sensing NH3. Their results indicated that 200 ppm NH3 caused the ψSBH change of 0.1 meV. In order to engender selectivity of the graphene/Si Schottky diode sensor, functionalizing graphene is necessary. Biswas et al. [3 in ambient air. They obtained a detection limit of ppb level with the response and recovery times of 95 and 101 s, respectively.Polichetti et al.  reporteds et al.  used rGO2) layer on top of Si wafer. The SiO2 thickness is 90 or 300 nm for easily observing graphene with an optical microscope [Chemiresistor sensor is popular for the successful detection of a wide range of gases. Chemiresistor sensor is easy to fabricate, has relatively low cost, and enables direct measurement. The typical structure of the graphene chemiresistor sensor is shown in croscope . The usep-type semiconductor containing many holes [3) are adsorbed on the graphene surface, they donate the weakly bonded electrons to graphene, causing the Fermi level to rise by small increments. In this case, the donor electrons deplete the holes in the p-type graphene, resulting in the resistance increase in graphene. Conversely, the electron-acceptor gas molecules (such as NO2) are adsorbed on the graphene surface, they take the electrons from graphene, lowering the Fermi level. The extra holes increase the holes concentration in the p-type graphene, leading to the resistance decrease in graphene. Therefore, the gas concentration can be quantitatively analyzed by directly measuring the change in the sensor resistance under the interaction with the target gas [n-type graphene can be described by only changing sign referred to in In ambient condition, graphene behaves like a ny holes , as showrget gas . The casThe electron-donating or electron-accepting nature of the gas is related to the relative position between the graphene Fermi level and the electron energy level of the highest occupied molecular orbital (HOMO) or the electron energy level of the lowest unoccupied molecular orbital (LUMO).Many research groups used graphene to fabricate field-effect transistors (FET) . Howeverp-type and n-type, for which the current flow is due to electron and hole transport, respectively. Hereafter, we will limit our analysis and discussion to the p-type sensing layer, since the principle is the same for n-type sensing layer but changing sign. When the target gas is off, the current into the sensing layer is only controlled by the back gate voltage (VG). As shown in p-type sensing layer is exposed to the electron-donor gas under the negative gate voltage, three possibilities exist: (i) the channel holes induced by negative gate voltage are equal to the donated electrons by the target gas, the sensing layer current keeps unchanged (keeps on baseline); (ii) the induced channel holes are more than the donated electrons, the sensing layer current decreases; (iii) the induced channel holes are less than the donated electrons, the sensing layer current increases. In the case of the p-type graphene FET sensor with electron-donor gas, it is better to use high positive gate voltage for the measurement. Such choice ensures that the graphene FET sensor would still be with electron conduction under electron-donor exposure. Otherwise, the case will be very complicated. It was reported [3, the p-type graphene FET sensor exhibits superior performance operated at high positive gate voltage rather than at negative gate voltage. On the contrary, for the electron-acceptor gas, it is better to use n-type graphene and high negative gate voltage.The detection mechanism of the graphene FET sensor to gas depends on the synergistic effect: the current of the sensing layer is modified (i) by the field strength through the gate voltage and (ii) the electron transfer with the gas molecules. reported  that forID) of the graphene FET sensor is expressed by [µ is the carrier mobility, W and L are the width and length of the sensing layer, respectively, COX is the unity gate capacitance, VD and VG are the drain voltage and the gate voltage, respectively. When the sensing layer is exposed to the target gas and the modification of the graphene surface is taken into account in the above relationship, the following equation is obtained [Qm (C.cm−2) is the interface charges induced by the gas molecules. Importantly, Qm is not zero when electrons transfer between the gas molecules and graphene channel. This is the reason why the graphene FET sensor can detect the gas concentration when it reacts with an electron-donor or electron-acceptor gas. From Equation (4), we can clearly see the synergistic effect: for a given sensing layer and drain voltage (VD), ID depends on not only the gate voltage (VG), but also the adsorbed gas molecules (Qm).When the target gas is off, the simplified drain current  is applied to the gate of the graphene FET sensor in order to simultaneously excite the perturbation of target molecular dipoles and modulate the channel charge carriers. As discussed above, graphene-based materials are suitable for various mode NH3 detection, because it does not possess any functional groups or defects. Monocrystalline graphene of mechanical exfoliation is well known as pristine graphene. However, it includes few isolated point defects. When NH3 molecules are attached on the isolated point defects, the resistance of the pristine graphene sensor does not significantly change. Since the donor electrons of NH3 can transfer through low resistance pathways around the isolated point defects [3 sensor. Thanks to the abundant defects  and functional groups on it, they strongly adsorb NH3 molecules. Around such defects, no low-resistance pathways exist. So, the resistance change caused by NH3 adsorption is significant, leading to a higher sensitivity.Pristine graphene without bandgap behaves like a semimetal . It is n defects . On the p-type graphene, the adsorption of a reducing gas (either NH3 or H2S) donates electrons to the graphene and depletes the concentration of holes, increasing the graphene resistance. The adsorption of an oxidizing gas (either NO2 or SO2) accepts electrons from the graphene and enhances the concentration of holes, decreasing the graphene resistance. As a consequence, different gases may generate the same sensing signals [3, but also CO, H2O, and NO2 in the same conditions as shown in It is mentioned above that non-functionalized graphene is nonselective to gases . A varie signals . Indeed,sp2 into sp3, disrupting graphene electronic and mechanical properties. Whereas, the latter provides functional groups to the graphene surface by electrostatic or π–π interactions, enhancing the graphene bonding ability and simultaneously preserving the graphene original properties (the high carrier mobility and favorable noise characteristics). It is, thus, important to optimize and improve non-covalent functionalization techniques.The functionalization (generating specific links and increasing the adsorbing sites) is a viable method to improve chemical inert and poor selectivity of graphene. The graphene functionalization can be classified to covalent and non-covalent strategies . The for3 sensing. According to the interaction nature between the target molecule and the receptor attached to graphene (or rGO), sensing reactions are distinguished to physisorption and chemisorption. The physisorption depends on the van der Waals forces of attraction with low binding energy, leading to full and fast recovery, but low sensitivity and poor selectivity. The chemisorption depends on the formation of chemical bonds between NH3 molecules and the sensing layers, resulting in good selectivity, but slow and incomplete recovery. For certain sensing layers, physisorption and chemisorption can happen at the same time. Both adsorptions can cause charge transfer, yielding p-doping or n-doping of the graphene film.Over the past few years, a number of functionalization procedures have been developed. Various materials, from metallic nanoparticles and metal oxides to organic molecules and conducting polymers, are used to accomplish the graphene functionalization for promoting a high sensitivity and great selectivity to NH2) [2 sensors with high performance [One of the strategies is to modify graphene by decorating its surface with metallic nanoparticles (NPs). They were widely used for detecting hydrogen (H2) ,79,80. Rformance .3 at room temperature. While the rGO sensor without Ag nanoparticles only shown a response of 0.2%. Karaduman et al. [3 sensors based on rGO decorated by metallic nanoparticles  by using a single-step chemical reduction. They obtained the highest sensitivity of 6.52%/ppm with Ag-NPs/rGO sensor. This sensor exhibited fast response/recovery of 5 s and great selectivity compared to CO, CO2, and H2 at room temperature. Gautam et al. [3 detection. The other functionalization methods of metallic nanoparticles can be found in reference [Cui et al.  reportedn et al.  fabricatm et al.  and Songm et al.  also preeference .3 sensing mechanism. When the Pt nanoparticles are weakly bonded with graphene by van der Waals force, the electronic structure of graphene is still preserved [p-type graphene is 5.1 [2/Si substrate behaves like a p-type semiconductor. After the Pt nanoparticle decoration, the graphene resistance is decreased, since the work function of Pt is larger than that of the p-type graphene. In the other words, the Fermi level of Pt is lower than that of the p-type graphene. This is beneficial towards the electron transfer from the p-type graphene to Pt nanoparticles, enhancing the hole density in the p-type graphene. When the Pt-decorated graphene sensor is exposed to NH3 at room temperature, NH3 molecules are dissociated at the surface of the Pt nanoparticles to form the Pt-NH3 phase, which exhibits a work function smaller than the Pt one, as shown in 3 phase to the graphene, reducing the hole density in the p-type graphene.Now, we take the Pt-decorated graphene sensor as an example to explain the NHreserved . As showe is 5.1  and 4.7 e is 5.1 , respect3 chemisorption, improving the sensor selectivity. The Pt-decorated graphene surface can be considered as a graphene film with p-type doping. It is equivalent to the hole reservoir and pathway to accelerate the sensor response and recovery. The issue for the functionalization by noble metal NPs, including Pt, Au, Ag, Pd, Ti, and so on [In fact, the Pt nanoparticles act as catalysts to concentrate the reactants by adsorption to increase the probability of interaction, thereby enhancing the sensor sensitivity. Moreover, the Pt nanoparticles may also provide number of specific reaction sites for NHnd so on ,91,92, iIn general, metal-oxide-sensing materials have relatively poor selectivity and need a high operating temperature. To overcome these shortages, heating or illumination is required. This results in a complex fabrication process, high power consumption, high cost, and the size increase in the overall device. It is interesting that the hybrid of metal oxides with graphene can significantly improve the sensing performance, particularly, the selectivity and response/recovery times at room temperature ,94.2 sensor presented a negligible response even for 100 ppm NH3 [2 hybrid sensor yielded a response of 21% for 50 ppm NH3, with response/recovery times of 15/30 s and without the interference of VOCs [2 solution at 70 °C to form C-O-Sn- bonds. When the hybrid sensor was exposed to NH3, the donor electrons of NH3 transferred from Sn to C of graphene through O. High sensitivity of the hybrid sensor is attributed to high electrical conductivity of graphene. Sn is a transition element, and it can easily accept the electron into its “d” orbital. Therefore, the rapid response was obtained in the hybrid sensor during exposure to NH3, while the rapid recovery is due to the weak bonding between NH3 and Sn. Kodu et al. [3 sensors functionalized by V2O5. The response of the epitaxial graphene sensor was one order of magnitude higher than the one of the CVD-G sensor. The authors believed that the adsorption sites provided by V2O5 nanophase were similar for both, but the response difference was due to the larger initial free charge carrier in the CVD-G sensor.At room temperature, a pure SnO ppm NH3 . However of VOCs . The hybu et al.  compared3 at room temperature. Meanwhile, our previous review raised the improved experimental schemes and the future research directions. The functionalization methods of metal oxides are also described in the review paper [More work on graphene mixed by metal oxides can be found in our previous work , which sew paper .3. The combination included a lot of functional groups for selectively binding NH3 molecules. Therefore, the Rose Bengal/rGO sensor exhibited an enhanced response to NH3 compared with the rGO sensor without Rose Bengal. The detection limit of the Rose Bengal/rGO sensor was 0.9 ppm.One of the advantages of graphene is its compatibility with organic molecules . Graphen3 in ambient condition. Their sensor has dual-mode  response to NH3 and high stability under mechanical bending. Their results reveal that BPB aromatic molecules can be anchored and concentrated at the edges and defects of the rGO layer. Interactions between the sensing layer and NH3 molecules can be increased on rough surfaces. This is why the BPB/rGO sensor has an increased sensitivity. On the other hand, the BPB/rGO sensor is similar to pH papers, which can qualitatively measure the presence of NH3. Specifically, when the sensor was exposed to NH3, the color change was clearly observed with naked eyes.Duy et al.  demonstr3 sensors [3 compared to non-functionalized graphene [3 (~2.5% and 45 s for 100 ppb NH3) [3  [Besides, porphyrins and phthalocyanines with different coordinated metals were used to functionalize graphene for improving the performance of the NH sensors . For exagraphene . The Co-ppb NH3) . In addi and CO) .However, most of dye molecules are toxic. In the case of high concentration, Rose Bengal is toxic on the human corneal epithelium , and broThe selectivity of gas sensors can be achieved with conducting polymer/graphene composites at room temperature. The synergistic effect of the conducting polymer/graphene is highly significant towards enhancing the sensor performance. Conducting polymers include polypyrrole (PPy), polyaniline (PANI), polythiophene (PTh), poly (butyl acrylate) (PBuA), and poly (vinylidene fluoride) (PVDF) . Hereaft3 sensor with PPy as sensing material goes back to 1983 by Nylander et al. [3 [2 [2S [3, the high contact resist (Schottky contact) between PANI and electrode materials was an issue. General problems in the use of conducting polymers for gas detection are: (i) sensing response and recovery are usually slow [In fact, pure conducting polymer gas sensors have attracted great interest due to the high sensitivity, repeatable response, and low-cost production . The firr et al. . To datet al. [3 , they cal. [3 [2 , H2S [123 [2 [2S , amines 3 [2 [2S , polar v3 [2 [2S , and so lly slow , (ii) thlly slow .3 sensor was built in 2012 based on PANI/graphene hybrids with a response of 59.2% for 50 ppm NH3 [In 2009, Dan et al.  first fo ppm NH3 .The easily tunable electrical properties of PPy make it a very popular conducting polymer ,128. PPy3 detection by in situ oxidative polymerization. The sensor exhibited a response three times larger than the pure PPy thin film sensor. Wang et al. [3 is nearly consistent with Tiwari’s group research result. Hu et al. [Most of PPy/graphene sensors used the chemical synthesis PPy. Tiwari et al.  preparedg et al.  developeu et al.  reported3 sensors based on the composites of CVD-G or rGO with conducting polymers, operating at room temperature. As we can see from the According to the literature survey, we summarized in the 3 is presented at room temperature. A repeatable response of 12.6 ± 0.8% is obtained after 10 injections. 3 concentrations from 1 to 4 ppm, with a sensitivity of 6.1%/ppm. The key parameters of two sensors are added in 3, high sensitivity, quick and reversible response, good stability, and immunity to humidity. These performances are associated with the synergistic effect of the ultrathin PPy layer and graphene.In 3 is described as follows. The PPy layer behaves like a p-type semiconductor [3, its resistance increases due to the fact that the donor electrons of NH3 molecules deplete the holes in the p-type PPy. The donor electrons can also transfer to p-type CVD-G film through the ultrathin PPy layer, in certain way thereby increasing the p-type CVD-G film resistance. On the other hand, the p-type CVD-G film is not only the growth support of the PPy layer, but also the conductive pathway of the electron transfer. The high conduction of the CVD-G film accelerates the sensor response and recovery. Additionally, the porous nature of the ultrathin PPy layer makes a major contribution to the sensor selectivity, response speed, and immunity to humidity. The synergistic effect of both materials promotes the sensor performance.The sensing mechanism of the PPy/CVD-G sensor for NHonductor . When it3. Nonetheless, the PPy synthesis or growth is more effective on the rGO film than on the CVD-G film. The explanation is that the hydrophilic oxygen groups (hydroxyl and epoxy groups) in the rGO provide more nucleation sites for the PPy layer during the electropolymerization. The PPy/rGO sensor, thus, has a higher availability of the surface activation for NH3. Moreover, the formation of π–π stacking between rGO and PPy results in a faster transport of electrons [The PPy/rGO sensor and the PPy/CVD-G sensor have the same sensing mechanism when exposed to NHlectrons . These f3 at room temperature. Therefore, the study on the functionalization materials is critical to fabricate high performance graphene sensors for NH3 detection. The synergistic effect of graphene and functional materials significantly improves the sensor performance. As discussed above, there is no unified sensing mechanism for the graphene NH3 sensors functionalized by different materials. However, all of the sensor responses depend on their resistance change caused by electrons transfer between NH3 and the related sensing layers. High conductance of graphene provides an efficient pathway for electrons transfer, thereby accelerating response and recovery of the sensor. Each functional material plays a key role in the sensitivity and selectivity of the sensors, as listed in In summary, non-functionalized graphene is chemically inert and nonselective to NH3 sensors have been studied and developed, great challenges still exist for their practical applications. In this section, we will analyze the hindering factors and propose related solutions.Although a lot of graphene-based NH3. They found out that the number of layers of graphene has no obvious influence on the sensor’s sensitivity. On the contrary, Crowther et al. [3 molecules. Therefore, the multiple-layer graphene has poor sensing performance.Hwang et al.  studied r et al.  indicater et al.  explain r et al.  in a rev3 molecules adsorbed on the cluster top cannot influence electric current passing through the cluster bottom. This means that the resistance modulation is not very effective, degrading the sensor performance.Our research results reveal that the PPy/rGO sensor is superior to the PPy/CVD-G in terms of performance. In essence, the PPy/rGO sensor can be produced more easily and at a cheaper cost. However, the PPy/rGO sensor reproducibility is still a key issue. Unlike CVD-G, the size, thickness, and uniformity of the GO dispersions are not well controlled presently. As shown in 3 sensors does not absolutely need high-quality single-layer graphene, such as the CVD-G. However, for the integration of the NH3 sensors with graphene electron devices in CMOS circuits, CVD-G is a good candidate. rGO is an abundant material and it is very easy to be prepared. However, the sensitivity and response time obviously degrade as the rGO thickness increases. For mass production and commercial application, we have to find appropriate methods to well control the thickness of the rGO for improving the sensor reproducibility. Recently, new approaches for large-scale production of high-quality graphene are being developed and studied, such as industrially viable water-phase exfoliation method [Our results suggest that the unique application of the NHn method  and non-n method .3 molecules and graphene. During functionalization, the specific surface area of pristine graphene should be kept unchanged or even increased for obtaining high sensitivity. Tamersit et al. [3 by a factor of 2.The functionalization is the core of the graphene sensor development. It provides specific links and binding sites. The specific links act as bridges to enhance the temporary connection between NHt et al.  establist et al.  also fou3 sensing, phenyl was used. Designing appropriate structures (such as nanomesh or nanoribbon) can also increase the specific surface area of graphene or the edges of graphene. Based on the CVD-G film, Paul et al. [3 with a limit detection of 160 ppb at room temperature. This value is significantly better than its film counterpart due to more edges of the nanomesh graphene. Three-dimensional (3D) structures may be another pathway to increase the specific surface area of graphene [Usually, the specific surface area of thick GO dispersions is degraded. Teradal et al.  proposedl et al.  construcgraphene ,162.3 sensor, which exhibited fast response (30 s) and high sensitivity (3.8%/ppm) at room temperature. The fluorine atoms interact with the graphene matrix to form covalent C−F bonds, which enhance physisorption of NH3 molecules, thereby improving the sensor performance. Kim et al. [3 sensor based on chemically fluorinated GO flakes. The sensor achieved the theoretical detection limit of ~6 ppb at room temperature. The other trends are to synthesis novel multicomponent materials and hybrid nanostructures for improving sensor performance. Su at al. [3 sensing, such as the ternary nanocomposite film of Pd-NPs/SnO2/rGO. Recently, they reported the results of the ternary film (Pd-NPs/TiO2/rGO) for NH3 sensing [3 at room temperature. For 50 ppm NH3, the response of the PPy/TiO2/graphene nanoparticles sensor was 102.2% [Besides the functionalization methods discussed above, the fluorination or fluorine doping is the other functionalization technology to increase the sensitivity and selectivity of the graphene sensors. Zhang et al.  used a pm et al.  exploiteu at al.  proposed sensing . This ses 102.2% , while ts 102.2% ,126. The2, talc (Mg3Si4O10(OH)2), and hexagonal boron nitride (hBN). They found out that for the NH3 detection the FET sensor on G/hBN-substrate exhibited higher response and faster recovery than the FET sensor on G/SiO2-substrate. The electron transfer from NH3 molecules to the graphene sensing layer is strongly dependent on the distance between the sensing layer and substrate. Aziza et al. [2-3T4O10X2) and SiO2 substrates. The sensitivity of the sensor on G/mica-substrate is higher than that of the sensor on G/SiO2-substrate, because the mica substrate induces more p-doping in graphene. Therefore, the substrate engineering should be put under consideration for the further improvement of the sensor performance, particularly, in the choice of the flexible substrates.The sensor substrate also plays an important role for the interaction of the sensing layer with target gas. Cadore et al.  compareda et al.  compared3 sensors are still in the laboratory. To move them from the laboratory level to commercial and practical applications, the following challenges exist.Up to now, the graphene NH3 sensors first needs large-area few-layer graphene with controlled structural quality. CVD-G is the most appropriate choice. However, high growth temperature (above 1000 °C), transferring from metal foils to target substrates, and catalytic metal foil waste make the CVD process complex, expensive, and have a negative impact on the environment. By contrast, rGO can be produced in large quantities and converted from GO by thermal treatment or chemical reduction. Particularly, rGO can be deposited by simple methods such as drop coating, spin coating, and inkjet printing. Although the rGO synthesis is quite easy and cheap, the rGO properties  are difficult to be well controlled. In addition, high contact resistance between rGO and metal electrodes degrades the sensor sensitivity.Mass production of graphene NH3 sensing applications. A detection limit of 1 ppm and response time of 30 min were observed for a typical sensor at room temperature. However, the characterization of the batch sensors has not been reported yet. Our PPy/G and PPy/rGO sensors were fabricated on 3-inch wafers. However, the electropolymerization was a post process step, which was carried out one sensor by one sensor at a time. To move the present process from laboratory concept to industrial application, it is necessary to functionalize all the sensors on one wafer once. In reality, the technique to produce the graphene NH3 sensors with a high yield was not been found due to reproducibility issues. In addition, for the feasibility of a sensing system, uniformity across the batch is a more relevant parameter than the sensor itself [Deokar et al.  synthesir itself ,171. FurFrom what has been discussed above, although CVD-G presents high quality, it requires high growth temperature and catalytic metal foils. The rGO is an easily synthesized, cheap, and defective graphene. However, the properties of the GO dispersions should be well controlled. The suspended graphene and designed structures can increase the specific surface area or the edges of graphene. New and innovative functionalization technologies, such as fluorination and graphene-based ternary composites, are other ways for improving sensing properties. In addition, the substrate choice is also important for the further improvement of the sensor performance. For mass production and practical applications, the sensor reproducibility, uniformity, stability, and immunity to humidity should be further exploited and investigated.3 sensors can be assembled with commercially available electronic devices and modules, as well as previously fabricated chips to build a prototype. With application software, the prototype would wirelessly transfer the measurement data to a mobile phone or computer. Thus, one could continuously and remotely monitor the NH3 concentration in a real-life environment.Graphene NHOur research indicates that the combination of graphene and conducting polymers is very promising as a chemical sensing material. As long as the electropolymerization could be carried out on wafer scale, it could be possible to integrate the conducting polymer/graphene sensors with CMOS circuits onto the same chip for monitoring different gases. The electronic nose consists of a gas-sensor array to detect various gases through multiple sensors. Graphene could be used as the sensing layers in the array. Then, the sensing layer of each sensor is functionalized by different materials or methods according to the requirements of target gases. This could be of great interest for fabricating the electronic nose fully integrated with CMOS circuits for accurately detecting different gases and biochemical and chemical molecules. It also could be of great interest for fabricating lab-on-chip in the field of environmental monitoring. Due to the current boom of IoT and connected devices, there is a growing demand for low-power devices. Graphene-based gas sensors with good performance are more advantageous in this topic than gas sensors based on heated metal oxides in the market, since the former requires less energy than the latter.3) sensing due to its large specific surface area and high carrier mobility. However, the non-functionalized graphene is nonselective and weakly binding with NH3 molecules at room temperature. Fortunately, it can be easily modified by functional groups. Functionalized graphene will occupy an important position in the future of gas-sensing materials. This paper summarizes the graphene sensors functionalized by different materials for NH3 detection, including metallic nanoparticles, metal oxides, organic molecules, and conducting polymers. Among them, the graphene functionalized by conducting polymers has a long lifetime, low cost, operation at room temperature, and compatibility with CMOS technology. Recently, we functionalized graphene and reduced graphene oxide by ultrathin polypyrrole (PPy) through electropolymerization. The synergistic effect of graphene and the ultrathin PPy significantly improves the sensor performance. Graphene increases the conductivity of the polymer film, accelerating the sensor response and recovery. On the other hand, the polymer film provides the specific reaction sites for NH3 adsorption, defining the sensor selectivity and enhancing the sensor sensibility. Overall, the sensor performance is strongly influenced by the charge transfer mechanisms, the functional molecules, and graphene itself. The functionalized graphene NH3 sensors will have a bright perspective due to the advantages of high sensitivity, fast response, great selectivity, low power consumption, cost-effectiveness, and operation in real-life condition. They are expected to be applied in the fields of lab-on-chip, electronic nose, Internet of Things for industrial control, agricultural storage, environmental monitoring, disease diagnosis, wearable health, ecological protection, and public safety.Graphene is a potential material for ammonia (NH


Supercell atomic models of composite films on the basis of graphene and single-wall carbon nanotubes (SWCNTs) with an irregular arrangement of SWCNTs were built. It is revealed that composite films of this type have a semiconducting type of conductivity and are characterized by the presence of an energy gap of 0.43–0.73 eV. It was found that the absorption spectrum of composite films contained specific peaks in a wide range of visible and infrared (IR) wavelengths. On the basis of calculated composite films volt-ampere characteristics (VAC), the dependence of the current flowing through the films on the distance between the nanotubes was identified. For the investigated composites, spectral dependences of the photocurrent were calculated. It was shown that depending on the distance between nanotubes, the maximum photocurrent might shift from the IR to the optical range. An impoficiency .2-hybridized carbon nanostructures and the availability of experimental technologies for the chemical and structural modification of graphene and SWCNTs, it is predicted that an all-carbon graphene/SWCNT hybrid material may become a promising candidate for the creation of phototransistors with tunable bandwidth. In particular, a high-performance photodetector based on graphene/SWCNT van der Waals heterostructures obtained by transferring the CVD-grown graphene onto an ultrathin layer of SWNTs formed on a SiO2/Si substrate has already been implemented in practice. The created device exhibited a photoconductive gain of 105 and a fast response time (~100 μs), which indicates the potential use of the graphene/SWCNT composite for light harvesting applications [Due to the existing electronic coupling between two spications . Liu et ications . The comications . The synications . Based oications . A graphications . This deNevertheless, studies of the photoelectric properties of graphene/SWCNT composite films with covalent bonding of carbon components are currently fragmentary and need further deepening. In this paper, using in silico methods, we predict the electroconductive and photovoltaic properties of composite films based on two graphene monolayers and SWCNTs located irregularly relative to each other between the layers and covalently bonded to them.x and Ly, in the direction of the X (perpendicular to the SWCNT) and Y  axes were introduced, respectively. Optimization of the extended supercell structure geometry in this case was performed by the quantum method. Herewith, the lengths of the translation vectors Lx and Ly, as well as coordinates of atoms, were optimized. Due to the polyatomic nature of the resulting supercells (400–800 atoms), we applied the self-consistent charge density functional tight-binding (SCC DFTB) method [To find supercells of graphene/SWCNTs films with irregular arrangement of nanotubes between graphene monolayers we used the original “magnifying glass method” that was earlier successfully applied for search of supercells of graphene/SWCNTs films with regular arrangement of nanotube graphene monolayers . The “ma) method , which, c—energy of composite graphene/SWCNT, Egr—total energy of graphene monolayers in a composite, Etube—total energy of nanotubes in a composite, and Natom—number of the composite’s atoms. If the value of ∆E was negative, such a topological configuration of the supercell was considered energetically favorable.Using the “magnifying glass method”, we built topological models of supercell of graphene/SWCNT composite films with tubes , where m = 10, 12, 14, 16. Non-chiral zigzag-type SWCNTs were selected since it was previously shown that only tubes of this topological type can form energy-stable covalent bonds with graphene monolayers . The diax and Ly, film thickness h, changes in total energy ∆E, Fermi level Ef, and energy gap Egap of the band structure. According to the data in T(E)—transmission function that determines the total quantum mechanical transparency of the conducting structure over all independent conduction channels for an electron with energy E; f1 and f2—Fermi–Dirac functions that characterize the energy levels of the source and drain corresponding to the energy level of the conducting structure. The VAC was calculated for the direction of current transport along the SWCNTs, since there is no current in the perpendicular direction. Further, in order to identify patterns of current transfer, the volt-ampere characteristics (VAC) were calculated for all the considered models of graphene/SWCNT composite films. For the calculation of current transfer in the structure, the Landauer–Butticker formula was used :(2)I=eh∫αβ(ω)Z0/2 + σαβ(ω)Z0/2—the reflection coefficient, T(ω) = 2/2 + σαβ(ω)Z0/2—transmission coefficient, Z0—wave resistance, and σαβ(ω)—the optical conductivity tensor. The value Z0 was calculated by the formula Z0 = Ex/Hy = ηcosθ—for waves of S-polarization (the electric field vector E was perpendicular to the plane of the wave incidence) and Z0 = Ex/Hy = η/cosθ—for waves of P-polarization . Coefficient η = 120π Ohm expressed the impedance of the vacuum. Note that sunlight is not polarized, so we calculated the average value of a(ω) for S- and P- polarization waves. The incidence of light waves on the film was considered as normal, i.e., θ = 90°. The complex optical conductivity tensor was calculated by the Kubo–Greenwood formula [To study the photovoltaic properties of composite films, it is necessary to know, first of all, the spectrum of the absorption coefficient a(ω). For this purpose, we applied quasi-classical approach, in which the formula for the absorption coefficient and the formulas for the reflection and transmission coefficients were determined based on the classical theory of electrodynamics. To calculate the dynamic conductivity, the quantum theory of irreversible Kubo processes was used. Previously, authors developed the formula for calculating the reflection coefficient of thin films whose thickness was much less than the wavelength of incident radiation . In our  formula .The calculated absorption spectra for different variations of the distances between the SWCNTs are shown in To explain the appearance of peaks at certain wavelengths, we calculated the absorption spectra of films, which are only irregularly arranged nanotubes, and the spectra of films made of curvilinear graphene. in—the power of incident solar radiation, e—electron charge, and hω is the energy of a quantum of solar radiation. Formula (4) allows one to obtain the maximum photocurrent spectrum, since it does not take into account a partial electron–hole recombination. Thus, Formula (4) is applicable for the case of an internal quantum efficiency of 100%, when each absorbed photon generates an electron. Further, on the basis of calculated spectrum, the integral value of the photocurrent was calculated as an integral over the entire considered frequency range. It should be noted that the power of solar radiation is unevenly distributed over the wavelengths. The peak of the maximum intensity of solar radiation is located in the visible light region; then, the intensity decreases exponentially, reaching a minimum in the infrared region [The spectrum of the photocurrent maximum value and the integral value of the photocurrent were calculated on the basis of absorption spectra. The photocurrent spectrum was calculated by the following formula:d region .−2, respectively  has an absorption peak at the wavelength of ~1500 nm (see The spectra of the photocurrent with the distribution of solar radiation power over wavelengths on the earth’s surface (AM1.5) and outside the atmosphere (AM0) (in inserts)  are illuvely see b. These e −2 see c. With a0 nm see c. Howevesum calculated for the range 0.2–2 µm for all film topological models with different distances between tubes H1/H2. The values of the photocurrent for the visible range of the solar spectrum of 380–780 nm and the integral value of the photocurrent for the IR range of 780–2000 nm are also given.To determine the efficiency of the considered composite films as materials for photovoltaic applications, it is necessary to identify the integral value of the photocurrent. 2 (3.9 mA/cm2), MoSe2 (4.6 mA/cm2) and WS2 (2.3 mA/cm2) [The analysis of the obtained data presented in  mA/cm2) . Based oThus, we have shown that all the topological models of graphene/SWCNT composite films considered in this paper are semiconductors with an energy gap in the range of 0.43–0.73 eV, which is an important condition for the potential use of such films in photovoltaic applications. According to the simulation results, the electric current flowing through the nanotubes of graphene/SWCNT composite films can reach values of ~50–65 µA at a voltage of 2 V. In this case, the current value is affected by the regularity of the nanotube locations relative to each other and the distance between them. This fact indicates the possibility of topological controlling the electrophysical properties of the considered graphene/SWCNT composite films. Thus, for example, the change in the distance between the SWNTs by just one hexagon leads to a change in the current by 8–17%. Thus, by regulating the distance between the SWCNTs, one can change the behavior of the current–voltage characteristics and the current value. Controlling the nanotube diameter allows us to control the profile of the absorption spectrum of graphene/SWCNT composite films by shifting the maximum peaks. Controlling the distance between the SWCNTs and the regularity of their location allows us to control the absorption intensity without significantly shift of the peaks. It was found that the integral photocurrent for all the considered graphene/SWCNT composite films with an irregular arrangement of SWCNTs is practically independent of the nanotube diameter and the distance between them, which is important in terms of the potential practical application of such films, since it is practically impossible to achieve the same CNT diameters and the distance between them in a real device.