Physical inactivity is a major risk factor for a population's health, especially among socially disadvantaged groups. Many health promotion projects focus on increasing physical activity among their respective target groups. However, because they are mostly developed and implemented under laboratory conditions, they fail when being scaled to real-world settings. The community-based participatory research projects BIG and GESTALT have demonstrated their effectiveness regarding the physical activity promotion in real-world settings by employing a participatory method.Within the context of the BIG-5 and GET-10 projects, these previously implemented and tested participatory projects are scaled to 15 additional settings in Bavaria, Germany. By applying an overarching mixed-methods evaluation framework, the aim is to gain insights into a) the recruitment of communities for scale-up; b) the specific results of the projects according to the RE-AIM framework. In the recruitment of communities, standardized information on the first contact, the consultation process, the person in charge, and previously implemented health promotion projects are collected. A systematic web search will complete information on each community and their health promotion activities. Results will be compared with information on those communities most in need, here according to the deprivation index of communities in Bavaria, Germany. The scale-up process and its results will be measured using semi-structured interviews with project coordinators. A standardized questionnaire will be used with the course's participants. Applying the RE-AIM framework, the collected data will be analyzed deductively.We expect the results to be highly relevant for the effective scale-up of any health promotion project. The study will enhance the understanding of how to reach those communities most in need of health promotion projects and will identify the barriers coordinators face in reaching socially disadvantaged groups.Although participatory projects are often used as individual projects, little is known about the scaling up of participatory health promotion projects. This cross-cutting evaluation of two projects aims at producing data on the barriers and facilitators for the reach of settings most in need, and those success factors for a durable implementation. As in many other Western nations, physical inactivity is a major public health issue in Germany , 2. PhysTo target these existing health inequalities, and in particular promote PA, the German Federal Ministry of Health has launched a policy initiative (“IN FORM”) in 2008 . While mThese findings make research on how to scale proven PA interventions, and at the same time maintain their efficacy a relevant research topic. Thus far, only few studies have explored such questions in Germany, particularly for projects rooted in community-based participatory health promotion with the goal of promoting PA.Bewegung als Investition in Gesundheit”  and “GEhen, Spielen und Tanzen Als Lebenlange Tätigkeit” , described in this study protocol, lend themselves excellently to increase our understanding on the scale-up of such interventions. Both projects have demonstrated to be effective on the individual, policy, and environmental levels, and have succeeded in increasing PA levels among the socially disadvantaged groups of women in difficult life situations and older people with a risk for dementia  and 10 (GET-10) communities. To the best of our knowledge, this is the first study that includes two separate projects in their evaluation. In doing so, we aim at gaining knowledge on the following key questions, which can be organized into two areas.How do the communities and rural districts receive information on the two projects?Which communities intend to participate in the projects?Which barriers do communities face when applying for state-level funding for implementation?What are the health promotion capacities developed by communities during the project's implementation?What are the barriers and facilitators of communities for implementing the projects and for local capacity building?Do communities succeed in reaching the target population? If so, to what extent?By including two projects, namely GET-10 and BIG-5, with a focus on different audiences, we will be able to compare the data regarding the efforts of communities to implement and maintain projects for the respective target groups. Additionally, it increases the chances to produce generalizable knowledge on scale-up and transfer of health promotion interventions.The previous project BIG, which forms the foundation for BIG-5, was initiated in 2005. Its aim was to develop and implement exercise health promotion programs among women in difficult life situations. These women include low-income earners, ethnic minority members, the unemployed, those unable to work, and single mothers. BIG has been implemented in 17 communities, and its effects, efficiency, and long-term implementation have been evaluated regularly among the different settings . The proTo implement BIG-5, communities receive funding covering a part-time (20 h/week) coordinator position within the communities' administration, and yearly compensation for the voluntary efforts of three peers, to implement the participatory approach, PA classes, and constant advertisement for a period of up to 3.5 years. During funding a total of 18 different PA classes are meant to be implemented in each community. Peers mainly act as social catalysts to help reach out to and involve the target group. Coordinators will be in contact with and receive help from the scientific project team. The first GESTALT project was developed and implemented in 2010 and acts as the foundation of GET-10. The project aimed at the prevention of dementia by enabling sedentary older people (above 65 years of age) to develop an active lifestyle. GESTALT has been previously implemented in 5 communities. The project implements an evidence-based 12-session exercise program  17). Ad. Ad17). The projects receive funding from the Federal Centre for Health Education. Communities located in Bavaria, Germany, with over 5,000 inhabitants can apply for funding for one of the projects by contacting the scientific coordinators. Using a low-threshold application scheme, communities have to send an expression of interest signed by the local major to the funding agency. Based on the expression of interest and some other formal criteria, communities receive funding.During the project work, the 15 communities function as so-called “real-world laboratories” that “contribute to capacity development, new scientific insights and societal learning, building on iterations of experimentation and reflection” . In thisCommunities will implement a predeveloped project plan for one of the two projects, as visualized in Coordinators also receive guidance and attend biannual workshops to share experiences among themselves. The workshops will be organized by the scientific team and cover topics such as (a) the cooperative planning method and coproduction of knowledge, (b) networking and capacity building, and (c) empowerment of the target group. Additional topics will be raised by coordinators. Because both projects follow the same participatory methodology, they work closely together and are connected during workshops and knowledge-exchange meetings.Both projects have been approved by the ethics committee of FAU, Germany (520_20Bc). All participants who are involved will be informed about the voluntary nature of participation in any scientific data collection and their right to withdraw their consent at any time without having to provide a reason.To answer the research questions in the three areas mentioned above, a convergent parallel mixed methods approach  will be To evaluate the recruitment process of the communities, all contact between the researchers and the interested community members will be systematically documented. Interested community members will engage in one-on-one phone calls with researchers. During the call, the researchers will ask standardized questions to gather information on (a) how the communities learned about the projects , (b) who contacted the researchers , (c) why they were interested in the project, and d) if they had previous experience or carried out similar projects in the past.Additionally, data will be collected on all the interactions with the communities until they have made a final decision to take part. This will include (a) the time it took, (b) the number of contacts, and (c) the factors that the communities mentioned as influencing their decision.A systematic web and database search and qualitative content analysis, here according to McMillan et al. , will coThe collected data will be analyzed using qualitative content analysis  to make The analysis will identify the time period needed by communities to reach a decision, barriers and facilitators that led to the decision, number of already existing health-promotion projects in the communities, and whether socioeconomically deprived communities are being reached by the funding scheme.To answer the research questions regarding the effectiveness of the projects, we utilize the RE-AIM framework and its five dimensions: “reach,” “efficacy,” “adoption,” “implementation,” and “maintenance” . Using tn = 45 interviews), as well as annual semi-structured focus groups with peers (n = 30 interviews) in each setting. Additionally, quantitative data will be collected, including an annual evaluation of capacity building using a standardized questionnaire filled out by the projects' coordinators, all attendance lists of the BIG-5 and GET-10 exercise courses, including number of people on the waiting lists, and data on satisfaction using a standardized short feedback questionnaire filled out by the course participants. We will conduct annual semi-structured interviews with the project's coordinators of the 15 communities  and focus group interviews (n = 30) will be audio-recorded, transcribed verbatim, and anonymized. Data will be deductively coded using Mayring's qualitative content analysis  . This frn = 5).Based on the capacity building dimensions and stimulated by a study by Nickel et al. , we haven = 45). Survey data will be analyzed using spider graphs for easy visualization of the data for each community, as suggested by Trojan and Nickel  and women in difficult life situations (BIG-5).n = 45). Therefore, questions will ask for (1) the participation of local stakeholders and the target population during the cooperative planning sessions, (2) the contributions of local leaders , (3) available resources , (4) networking and cooperation , and (5) program offers implemented in the community.To receive further in-depth information on the capacity areas defined by Nickel et al. , semi-stn = 30). Questions will focus on the efforts made to recruit participants, their satisfaction with the program, and their personal opinion on the capacity-building dimension (as mentioned above).To receive information on the effects regarding the empowerment of peers, the latter (three peers per setting) will be asked to participate in annual focus group interviews  featuring high levels of physical inactivity makes the projects valuable from a public health and health equity perspective . At the The limitations of the present study include the following:1) Measurements regarding the reach of the population group and effectiveness of the interventions will use a mixed methods approach and mainly rely on qualitative interviews and surveys. A more robust study design  is not in place, and as such, we will provide only limited information on how effective the two interventions are in generating a public health impact.2) The study duration is 3.5 years. Thus, the projects will not yield results regarding the long-term impacts of the interventions, in particular on the question of whether they are being maintained in the different communities.3) Because of the COVID-19 pandemic, we expect a delay in the implementation of projects, which may influence the outcomes of our scale-up process.Nevertheless, our study also has some strengths:1) We attract a diverse set of communities, ranging from larger cities  to rural counties with around 5,000 to 10,000 inhabitants. As such, the communities will differ greatly in their potential to implement the two interventions, which will give greater insights into the diversity of communitie's implementation capacities.2) Both projects can draw on empirical evidence gathered over 17 (BIG) and 12 (GESTALT) years, respectively. This extensive experience can be used for the successful implementation of the two project's successful implementation in 15 new settings.3) By using a mixed methods approach, we can gain not only insights from a quantitative perspective, but also in-depth qualitative information on all the factors related to the implementation of the interventions in the communities.4) The sample size of 15 communities is quite generous for studying factors that would allow for further scaling of both projects.5) The projects allow us to gather information not only on communities who participate, but also on those who voice some interest but then decide against joining the funding scheme. This provides a unique opportunity to identify the barriers that inhibit the scaling of the two interventions.Scale-up and sustainment of community-based participatory research projects is crucial to reduce health inequalities. The two interventions have already been evaluated and demonstrated effectiveness. The current study can provide additional evidence on the barriers and facilitators of scale-up and sustainability, capacity building within a community setting through health promotion projects, and the project's effects on the target populations. Through a cross-sectional examination of the recruitment process of communities, the current study will be the first to provide evidence on how to reach communities to engage in such projects and the barriers and facilitators for implementation they may face.AH-M, TF, KA-O, HZ, and AR contributed to conception and design of the study. MT wrote the first draft of the manuscript. All authors contributed to manuscript revision, read, and approved the submitted version.This study received funding from the German Federal Center for Health Education . The funder was not involved in the study design, and the writing of this article or the decision to submit it for publication.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.


Evidence suggests that optimism has a positive impact on health status. Attentional bias modification (ABM) may be beneficial for enhancing optimism, but its effective application requires a detailed investigation of the association between attentional bias and optimism. This study aimed to determine the association between attentional bias and optimism based on different task types. Eighty-four participants completed the attentional bias measures using the dot-probe task (DPT), emotional visual search task (EVST) paradigms, and psychological assessments. Optimism was assessed using the Life Orientation Test-Revised with subscales for optimism and pessimism. Pearson’s correlation coefficient and multivariate linear regression analysis were applied to investigate the association between optimism and attentional bias. Neither the attentional bias derived from DPT nor EVST was significantly correlated with optimism total score or subscales. Regression analysis also showed no association between attentional bias and optimism , optimism subscales , or pessimism subscales . Our findings showed no evidence that attentional biases derived from either the DPT or EVST measures are associated with optimism or pessimism. Further studies are needed to effectively adapt the ABM to enhance optimism. There is growing evidence that optimism plays an important role in the successful aging of older adults . OptimisIn recent years, attention bias modification (ABM) has emerged as a potentially effective intervention for enhancing optimism . The ABMThis study aimed to examine whether attentional bias, as measured by the dot-probe and positive-search paradigms, is associated with optimism. We hypothesized that optimism and attentional bias are associated and that their association depends on the type of task that derives attentional bias . Clarifying these relationships may contribute to the development of effective attentional bias training for enhancing optimism.A priori power analysis using G*power software was performed to calculate an adequate sample size for correlation analysis. An effect size of 0.3, a significance level of 0.05, and a power of 0.8 were considered. Eighty-four samples were estimated. We recruited healthy Japanese volunteers from the rehabilitation staff at the hospitals to which the authors (Y.A. and Y.H.) belong and from undergraduate and graduate students at Kagoshima university and Nagasaki University. A total of 87 healthy subjects were enrolled in this study. All the participants had normal or corrected-to-normal vision. None of the participants had a history of neurological or psychiatric disorders. The study was approved by the Ethics Committee on Epidemiological Studies of Kagoshima University (Ref No. 210273) and conducted in accordance with the Declaration of Helsinki. Written informed consent to participate in this investigation was obtained from all participants.Optimism was assessed using the Life Orientation Test-Revised (LOT-R), which has been validated in Japanese samples . The LOTAttentional bias was measured using the dot-probe task (DPT) and emotional visual search task (EVST) ,22,23. Thttps://people.socsci.tau.ac.il/mu/anxietytrauma/research/, accessed on 21 November 2022). We replaced the facial stimuli with images obtained from the Japanese database to adapt to the sample in this study. The DPT comprised 120 trials: 80 threat–neutral and 40 neutral–neutral trials. In the threat–neutral trials, pairs of threat and neutral facial expressions were randomly presented at the top and bottom of the screen, respectively. In the neutral–neutral trials, pairs of neutral facial expressions were randomly presented at the top and bottom of the screen. The trials began with a black fixation cross presented for 500 ms, after which a threat–neutral or neutral–neutral pair was presented for 500 ms. Following the removal of facial images, a probe (“<” or “>”) appeared in either the same location as the threat face  or that of the neutral face . Participants were required to click the left or right mouse button in the direction of the probe. The probe was presented until the response was recorded, and the participants were instructed to respond as quickly and accurately as possible. Ten practice trials were conducted before the assignment to ensure that participants performed correctly.The DPT adapted the facial stimulus-based task from the Tel Aviv University National Institute of Mental Health Attention Bias Measurement Toolbox, which was designed to measure standardized attentional bias (Reaction times (RT) for threat–neutral trials were used to calculate the attentional bias index. The attentional bias index was calculated by subtracting the mean RT of congruent trials from that of incongruent trials. Consistent with standard practice, trials with incorrect responses and extremely short (<150 ms) and extremely long (>2000 ms) RTs were excluded ,23,25. TThe EVST comprised two separate blocks of positive and negative trials, each with 32 trials ,22. PartThe attentional bias index was calculated by subtracting the mean RT of the negative trials from that of the positive trials. Consistent with standard practice, trials with incorrect responses and extremely short RTs (<200 ms) were excluded ,23. TriaWe also assessed participant characteristics, including age (years), sex, education (years), mood, rumination, and personality traits, as potential factors influencing optimism. Participants’ affect was assessed using the Positive and Negative Affect Schedule (PANAS) . The PANAfter signing the informed consent form, participants performed two attentional bias measurement tasks: the DPT and EVST. The order of the DPT or EVST tasks was counterbalanced across participants. After the completion of the attentional bias measurement task, the participants were required to complete four self-reported questionnaires. The assessment took approximately 45 min.Participant characteristics are presented as the mean and standard deviation for each assessment. A one-sample t-test was used to calculate whether the mean attentional bias of all the participants was significantly different from zero. Pearson’s correlation coefficient was used to investigate the association between optimism, attentional bias, and other variables. Attentional biases were also examined in correlation with optimism and pessimism subscales. In addition, we explored the association between optimism and attentional bias using multivariate linear regression analysis adjusted for demographic and psychological variables.All statistical analyses were performed using R version 4.1.2, with a significance level set at 5%.n = 3). p = 0.585). For EVST, incorrect trials and trials with RTs more than two SDs from the individual’s mean were removed (0.9%). A one-sample t-test showed that the participants exhibited an attentional bias toward positive stimuli (p = 0.007).Ultimately, 84 participants  were included in the analysis, except those with missing psychological assessment data . The same was observed for attentional bias derived from the EVST .r = 0.451, p < 0.001), extraversion , and openness  showed significant positive correlations with optimism, whereas rumination  and neuroticism  showed significant negative correlations with optimism.β = 0.12, p = 0.22; optimism subscale: β = 0.09, p = 0.39; pessimism subscale: β = −0.10, p = 0.39) or EVST  task showed no association with optimism total scores, optimism subscale, or pessimism subscale. There were significant associations between positive mood , rumination , and openness  on the optimism total score. In addition, rumination  and openness  showed significant associations with the optimism subscale, and rumination  showed a significant association with pessimism subscale.This study investigated whether attentional biases derived from two different measures are associated with optimism. Our findings showed no evidence of a cross-sectional association between attentional bias and optimism in either task. We hypothesized that attentional biases would be differentially associated with optimism or pessimism depending on the characteristics of the measurement task; however, contrary to expectations, we could not confirm their association. The attentional biases derived from the DPT and EVST are associated with the degree of anxiety and depression symptoms . MeanwhiThe possibility that this result may differ depending on the measure of optimism should be considered. This study used the LOT-R, a widely used measure of trait optimism, to assess both optimism and pessimism. Previous studies have shown that ABM does not increase the state of optimism, showing effects only on comparative optimism related to social comparisons ,32. TheyWe also examined affect, rumination, and personality traits as potential factors influencing optimism. We found that positive affect, rumination, and personality traits including extraversion, neuroticism, and openness were significantly correlated with optimism. Multivariate linear regression analyses suggest that positive affect, rumination, and openness are particularly important factors in optimism. Consistent with the results of previous studies ,35,36,37This study has several limitations. First, this study excluded individuals with psychiatric disorders, but the psychological assessment of depression was not available, so potential depressive effects cannot be ruled out. However, the inclusion of important factors of depression such as rumination and neuroticism as covariates and the very weak association between optimism and each attentional bias in the correlation and linear regression analyses means that the impact on the primary results is unlikely to be significant. Second, this study applied a reaction-time-based measure of attentional bias, which has been the focus of many studies to date. However, attentional bias for negative stimuli derived from reaction times, such as the DPT, has been noted to have poor test–retest reliability ,39 and iOur findings showed no evidence that attentional biases derived from either the DPT or EVST measures are associated with optimism or pessimism. Further studies are needed to effectively adapt the ABM to enhance optimism.


Two carbonaceous (amorphous carbon and graphene) coatings were catalytically grown on bulk Ni plates. It was found that the flame-deposited carbon (FDC) layers exhibited a unique hierarchical structure with the formation of FDC/Ni nano-interlocking interface. The effect of the flame coating time on its corrosion protective efficiency (PE) was studied and compared with that of graphene coating produced via chemical vapor deposition. The FDC grown for 10 min exhibited a PE of 92.7%, which was much greater than that of the graphene coating (75.6%). The anti-corrosive mechanisms of both coatings were revealed and compared. For graphene coatings, the higher reaction temperature than that for FDC resulted in large grain boundaries inherent in the coating. Such boundaries were weak points and easily initiated grain boundary corrosion. In contrast, corrosion started at only certain local defects in FDC layers, whose unique interface structure likely promoted its PE as well. Moreover, after the coating process, the hardness of FDC-coated Ni remained almost unchanged, in contrast to that of graphene-coated samples (reduced by ~30%). This is suggested to be related to the crystal structure evolution of the Ni substrate caused by the heat treatment accompanying the coating process. Graphene coatings have been demonstrated to be highly effective in protecting Cu and Cu/Ni alloy substrates from oxidation [Due to its excellent chemical inertness, high thermal stability, environmental friendliness, and cost effectiveness, carbon-based coating has been investigated as one type of the most important surface protection materials. Various carbon coatings have been developed so far, including the conventional diamond-like carbon ,2,3 and xidation . Researcxidation ,21,22,23xidation . In situxidation . For thexidation . In addixidation . MeanwhiDue to its time-saving, energy-conserving, and eco-friendly characteristics, and its convenience of operation, the flame synthesis of carbon materials has drawn growing attention. Carbonaceous nanomaterials in various forms, including 3D foam, 2D layer and 1D nanotube/nanofiber, have been deposited by this method on various substrates recently, including metals ,25,26, iHerein, graphene coatings will be fabricated via CVD on bulk Ni substrate for surface protection, and FDC layers will be catalytically grown on the same catalytic metal substrate and carbon source as well. Their structure and properties will be investigated in comparison with each other. The FDC layers with unique hierarchical structure were found to be flame-deposited on Ni within a few minutes. The influence of the carbon deposition on the micro-hardness, the scratch, and corrosion resistance of bulk Ni substrate will be investigated based on the comprehensive characterization of the physico-chemical structure of both the FDC and graphene-coated samples. The corrosion mechanisms for both the FDC and graphene coating will be studied and proposed as well, including the role of FDC/Ni interlocking interface and the grain boundaries of graphene-coated Ni substrate.Ni plates were polished with 3.5-micron diamond polishing paste and cleaned in an ultrasonic cleaner. Acetone, alcohol and water were used, respectively, to ultrasonically clean the Ni plates for 10 min in sequence, to ensure the complete removal of diamond abrasive particles. After that, the samples were dried in an oven at 60 °C for 30 min, followed by being cut into small plates with the dimensions of 10 mm × 10 mm. The carbon deposition was carried out by inserting the plates into the flame generated by the alcohol burner. They were treated in the flame zone with a temperature of 400–450 °C for 1 min, 3 min, 5 min, 10 min and 15 min, the respective specimens being labeled as C/Ni-1, C/Ni-3, C/Ni-5, C/Ni-10 and C/Ni-15. In order to characterize the flame-derived carbon coating in detail, the Ni substrate in the C/Ni-3, C/Ni-5 and C/Ni-10 specimens was etched off by HCl, and the obtained carbon layer was labeled as C-3, C-5 and C-10, respectively.2 atmosphere, the graphene-coated Ni sample was obtained and labeled as G/Ni-10. Similarly, a graphene layer was obtained by the removal of the Ni substrate with chemicals, and labeled as G-10.For the CVD deposition of the graphene coating, the polished Ni plates were placed into the tube furnace. After being treated for 10 min at 1000 °C in an ethanol/N−1. ZEISS ultra plus FESEM was used to detect the surface and structure of the carbon coatings. X-ray diffraction (XRD) was conducted on a Rigaku Ultima IV X-ray diffractometer . Transmission electron microscopy (TEM) was performed on a JEOL 2100F . A scratch test was conducted on ZKKH WS-2005 scratch tester together with a KOPPACE KP-200MRT microscope . The C/Ni-10 sample was scratched with a diamond indenter (120° core angle) under an increased normal load from 0 to 50 N, at a loading rate of 50 N min−1, and a scratching speed of 4 mm min−1. Optical photos of the immersion test were taken with a Leica DMI 3000 m inverted microscope. The hardness of bare Ni and coated samples had been measured with a Vickers hardness tester (HXD-1000TMSC/LCD), a load of 0.5 N (HV 0.05) was used to test the hardness of the samples according to the standard GB/T 4340.2-2012.Raman spectrum measurements were obtained under a 633 nm laser light  with the wavenumber range from 800 to 3000 cm2 exposed area as work electrode. Potentiodynamic polarization curves were swept from −0.6 V to 0.4 V (vs. Ag/AgCl). EIS tests were performed at open circuit potential in a range of 105–10−2 Hz, with amplitude of 5 mV.The electrochemical study of the corrosion behavior of the specimens was conducted in 0.1 M HCl. All electrochemical tests were carried out on a CHI 760E electrochemical workstation. The typical three-electrode configuration consists of a Pt foil as counter electrode, an Ag/AgCl reference electrode and specimen with 1 cmA schematic diagram of the flame coating process is presented as −1 and the 2D band at 2706 cm−1, but a very weak peak for the D band at 1352 cm−1. Normally, the D band refers to the defect or disorder structure, whereas G band originates from the in-vibrations of sp2-bonded carbon atoms [2D/IG) of the graphene coating is 0.45, which is much less than 1, implying its multi-layered structure. As calculated by the spectrum in D/IG) of the FDC and graphene coating is 1.3:1 and 0.14:1, respectively. These results indicate the presence of rich defects in the FDC layer, in contrast to the high regularity of the graphene coating fabricated via CVD with the same carbon source. In XRD patterns of C/Ni-10 and G/Ni-10  are shown in corr of C/Ni-10 was only 2.8 μA cm−2, which meant a roughly 13-fold improvement in the corrosion resistance over the bare Ni (38.3 μA cm−2). Additionally, when the flame time exceeded 5 min and the thickness of FDC layer was close to 200 nm, the effect of the flame time on its anti-corrosive performance became insignificant. For instance, either the icorr or CR of C/Ni-5 was close to that of C/Ni-10 (−1) was much larger than that for C/Ni-10 (1.2 mil a−1). This indicates that 10 min is the optimized time for the fabrication of the FDC layer with highest anticorrosion properties. Moreover, it is noted that the polarization curve shifted in a negative direction in comparison with those of both C/Ni-10 and C/Ni-15 /i0corr, where i0corr and iccorr represents bare Ni and the coated Ni plates, respectively. Particularly, the PE of the FDC (92.7%) is much larger than that of G/Ni-10 (75.6%), and those values reported in the literature [The corrosion inhibition performance of the carbon-based coating was characterized by potentiodynamic polarization tests. o 10 min a–c. The  C/Ni-10 . On the  C/Ni-15 b. And bo C/Ni-10 . This interature ,15.s represents the solution resistance. Rct is defined as the electron transfer resistance at the metal/solution interface. Constant phase element (CPE) is an imperfect double-layer capacitance with a constant phase n (−90 × n°) formed by the dispersion effect. The value of n is related to the topography of the substrate surface [p and CPEf in the equivalent circuit of carbon-coated Ni samples represent the coating resistance and film capacitance, respectively  under the same test conditions. The scratch test result confirmed the excellent scratch resistance of the FDC layer and its good bonding to the substrate. The anti-corrosive mechanism of both the FDC and graphene coating were analyzed and explained. Additionally, due to the lower temperature required for growing FDC than that for graphene coating, the micro-hardness of the FDC-coated bulk Ni plate remained unchanged, in contrast to its graphene-coated counterparts (reduced by ~30%). The excellent anti-corrosion of the flame-treated metal substrate is believed to be due to the formation of the homogeneous FDC layer along the metal surface and the unique coating/substrate interlocking interface, in contrast to the evident grain boundary corrosion mechanism in the case of graphene coating.


The appearance of a set of localized states in graphene’s VB related to the molecular orbitals of the introduced functionalities was signified both experimentally and theoretically. Applying the density functional theory calculations, the impact of the localized states corresponding to the molecular orbitals of the hydroxyl and epoxide groups was decomposed. Altogether, these findings unveiled the particular contribution of the epoxide and hydroxyl groups to the core-level spectra and band structure of graphene derivatives, advancing graphene functionalization as a tool to engineer its physical properties.The derivatization of graphene to engineer its band structure is a subject of significant attention nowadays, extending the frames of graphene material applications in the fields of catalysis, sensing, and energy harvesting. Yet, the accurate identification of a certain group and its effect on graphene’s electronic structure is an intricate question. Herein, we propose the advanced fingerprinting of the epoxide and hydroxyl groups on the graphene layers via core-level methods and reveal the modification of their valence band (VB) upon the introduction of these oxygen functionalities. The distinctive contribution of epoxide and hydroxyl groups to the C 1 Engineering two-dimensional materials’ electronic structure has been one of the key issues since their isolation, starting with graphene and followed by metal dichalcogenides layers and elemental two-dimensional materials ,2,3, levp- or n-doping of the graphene layer owing to the electron-donating or electron-withdrawing effect of the modifying functional groups; and (iii) the introduction of local electron states in the valence or conduction bands, related to energy levels corresponding to the molecular orbitals (MOs) of the added moieties. To date, the main results have been achieved within the frame of the first approach. The graphene band gap has been demonstrated to be tuned within the range of 0.05–4.5 eV by means of altering the functionalization of its basal plane with oxygen groups or fluorine [The chemical modification of graphene benefits by engineering its electronic structure due to performing it at multiple levels, namely: (i) the regulation of its local and absolute π-conjugation degree, which determines the material’s band gap; (ii) the management of the Fermi level and, thus, the fluorine ,16,17—thfluorine ,19. Furtfluorine ,21.Conversely, almost no attention has been paid to the question of the effect of molecular-related states of the introduced functional groups on the DOS of graphene. Only a generalized interpretation of the oxygen-related states has been given ,22,23. Os and O 1s X-ray photoelectron spectra hinders the estimation of the absolute and relative concentration of hydroxyls and epoxides. Combined with the absence of an unequivocal equation of the resonances in the X-ray absorption spectra to hydroxyl and epoxide groups, all this challenges further interpretation of the effect of these functionalities on the band structure of the material. Only solid-state 13C nuclear magnetic resonance (NMR) spectroscopy grants the unequivocal discernment of hydroxyls and epoxides and the derivation of their relative concentration [Recently, we have revealed the appearance of a set of localized molecular-related states in graphene’s VB upon its derivatization by carboxyl groups and ketones , as the ntration , althougs XPS and C K XAS spectra, as well as the molecular-related states in the valence band (VB), are revealed via the systematic study of diversely oxidized graphene layers by a set of spectroscopic methods complemented by density functional theory (DFT) modeling. Based on the comparative study of the XPS spectra with the NMR and infrared (IR) spectroscopy data, the distinctive spectral components related to the epoxide and hydroxyl groups were discerned and characterized in the C 1s spectra. Furthermore, the corresponding fingerprints in the C K XAS spectra were identified. Given this data on the chemistry of the studied graphene derivatives, contributions of the hydroxyl and epoxide groups to the VB structure were decomposed both experimentally and theoretically. The origin of each molecular state in the epoxide and hydroxyl groups was revealed by the theoretical calculations of both the DOS of the whole CMG layer and its projection solely on the modifying group. As a net result, these findings unveiled the particular contribution of epoxide and hydroxyl groups to the core-level spectra and band structure of graphene derivatives, advancing chemical derivatization as a tool to engineer their physical properties.Herein, taking advantage of our recent advances in XPS and theoretical studies of other graphene derivatives ,35, the www.graphtechrus.com (accessed on 30 October 2022)). Sodium hydroxide (NaOH) and hydrochloric acid (HCl) were purchased from Merck KGaA .An aqueous dispersion of GO was purchased from Graphene Technologies . All the chemicals were of analytical purity grade and were commercially available. The materials were used as received without any additional purification.pH value of 8.5. The pH values of the suspensions were evaluated with a Fisher Scientific Accumet Basic AB15 pH meter . Thus, the acquired reaction mixture was stored under heating at T = 50 °C for 48 h in the air, while continuously stirring. Upon the end of heating, the mixture was cooled down to room temperature (RT) and copiously washed by means of centrifugation  at 18,200× g for 15 min with sequential rinsing of the obtained sediment by distilled water (30 mL). The ascribed washing procedure was repeated five times to obtain an aqueous suspension of H-xy graphene platelets.H-xy and E-xy graphene were derived by the liquid-phase modification of the pristine GO. In brief, to synthesize H-xy graphene, 50 mL of a GO aqueous suspension of 0.1 wt.% concentration was poured into a Teflon reaction vessel and mixed with NaOH while stirring to reach a g for 15 min with sequential rinsing of the obtained sediment with DMSO, repeating the ascribed procedure 5 times to almost completely eliminate water from the GO. Afterward, 10 mL of 0.05 M HCl was poured into the GO suspension in DMSO, and the Teflon reaction vessel was placed in the oven to be heated to 50 °C for 48 h. At the expiry time, the mixture was cooled down to RT and copiously purified analogously to the H-xy graphene, except for replacing the water with ethanol.E-xy graphene was derived from GO by substituting aqueous media with dimethyl sulfoxide (DMSO) via sequential centrifugation and the following treatment with an HCl solution. In brief, 50 mL of a GO aqueous suspension of 0.1 wt.% concentration was centrifuged at 18,200× T = 600 °C in an ultra-high vacuum chamber (p = 10−9 Torr) for 3 h: first, 1.5 h to reach the temperature, and secondly, 1.5 h at the maintained temperature.The rGO layers were fabricated by the thermal annealing of GO at The composition of functional groups in the synthesized graphene derivatives was examined via a set of core-level techniques and spectroscopic methods, namely XPS, XAS, Fourier-transform infrared (FTIR), and NMR spectroscopies.s, and VB XPS spectra along with C K-edge XAS spectra were collected at the ultra-high vacuum experimental station of the Russian–German beamline of the electron storage ring BESSY-II at Helmholtz-Zentrum Berlin (HZB) [p ~ 10−9 Torr for 20 h at room temperature (ca. T = 25 ± 2 °C) to remove the adsorbates. The measurements were performed in three distinct spots of the sample, of ca. 200 × 100 µm in size, to consider the possible spatial heterogeneity of the materials’ chemistry. The difference in the C 1s and VB spectra did not exceed 5%, thus verifying the pertinence of the acquired data. For further processing, the recorded spectra were averaged.The survey, C 1in (HZB) . Prior thv = 736 eV. Conversely, the C 1s and VB spectra were acquired at the excitation energies of hv = 400 eV and hv = 130 eV, respectively. For the latter case, the cross-sections of the 2p and 2s states were almost equal, allowing the precise derivation of the effect of these states on the structure of the material’s VB. At the same time, the choice of an excitation energy of hv = 400 eV for the C 1s spectra guaranteed that the probing depths for these spectra and VB ones almost coincided. As a net result, the C 1s data accurately reflected the impact of the functional groups on the measured DOS in the VB.The survey spectra were collected with the excitation energy of s spectra were deconvoluted into a sum of the Shirley background and five model functions by means of CasaXPS@ software . Four functions related to the oxygen functional groups were simulated by symmetrical Gaussian–Lorentzian lineshape functions (GL(n)), where parameter n was chosen as equal to 90 in our case. The full width at half maximum (FWHM) for all functions was chosen not to exceed 1.8 to adequately restrict the possible level of deviations in the binding energy of oxygen functionalities due to their interaction. The fifth function, associated with the contribution of carbon atoms occupying nonfunctionalized sites of graphene lattice (peak C=C), was simulated using a special CasaXPS function LF  ), representing a Lorentzian asymmetric lineshape with tail damping [s line corresponding to domains of the π-conjugated carbon atoms of the graphene network.To extract quantitative information on the chemical composition of the examined materials, the collected C 1 damping , which sK near-edge X-ray absorption fine-structure spectra were collected in the Auger electron yield (AEY) mode; that is, the collected spectra reflect how the yield of CKKV Auger electrons with a kinetic energy of ~250 eV depends on the energy of the SR photons irradiating the respective sample. The angle between the incident beam and the surface normal of the sample was equal to the “magic” angle, α = 54.7°, providing a nearly equal excitation of the π and σ states. The as-recorded XAS spectra were normalized and smoothed by following a processing algorithm described elsewhere [The C lsewhere .−3 wt.% concentration, with subsequent drying at room temperature (ca. 25 °C) for 12 h. In the case of rGO, the GO suspension was deposited with the subsequent thermal reduction according to the procedure presented in The FTIR spectra were acquired using an Infralum-08 spectrometer  equipped with an attenuation of total reflectance attachment. For the XPS, XAS, and FTIR measurements, films of the E-xy graphene, H-xy graphene, and rGO were placed over Si wafers by the drop-casting of 25 μL of the corresponding aqueous suspension, of 5 × 1013C nuclei were collected in the magic angle spinning cross polarization pulse sequence (CPMAS) mode with a magnetic field of 9.4 T and a spinning rate of 8 kHz. Prior to the measurements, the samples were milled from the films into a powder and subsequently loaded into 4 mm-diameter zirconia rotors. To achieve an optimal signal-to-noise ratio, the number of scans for each experiment was chosen to be 8192. All the measurements were carried out at room temperature.NMR spectra for the k-mesh [−3 eV and 10−4 eV, respectively. In self-consistent calculations, the electronic convergence criterion was 10−5 eV. At the same time, the plane-wave cutoff energy was set as 500 eV in all calculations.DFT modeling was carried out using supercomputers at the Joint Supercomputer Center of the Russian Academy of Sciences (JSCC RAS)  and the k-mesh  of 3 × 3Z-axis to minimize the interaction between periodical images. Both models were fully optimized. The acquired E-xy and H-xy graphene supercells are displayed in For the calculation of the electron structure of the E-xy and H-xy graphene derivatives, model systems based on a graphene supercell with the size of 19.7 Å × 19.7 Å in the XY and an angle between the X and Y axes of 60° were employed. Three-dimensional periodical boundary conditions were used with 15 Å of vacuum along the As test calculations, the GGA, PAW, PBE, and LDA ultrasoft levels of approximations were used and compared. LDA was shown to be more accurate at predicting bond lengths during geometry optimization, with no significant differences in the calculated DOS for the modeled systems. Thus, only the results with LDA are presented.v = 3000–3700 cm−1,comprising a set of absorption bands of the O–H stretching vibrations in hydroxyl groups, carboxyls, and mainly water molecules [v = 41,620 cm−1, attributed to the bending vibrations of the water molecules [v = 1620 cm−1 and v = 3000–3700 cm−1 were of enhanced intensity in the case of H-xy graphene, asserting a higher amount of adsorbed water in this material due to its higher hydrophilicity.olecules . The higolecules . Notablyv = 1050 cm−1, v = 1280 cm−1, and v = 1720 cm−1, corresponding to edge-located hydroxyls (denoted hereinafter as C-OH(e)), ketone groups, and carboxyls, respectively [v = 1105 cm−1 and v = 1365 cm−1 related to basal-plane hydroxyls (denoted hereinafter C-OH(b)) on one hand, and the absorption band at v = 1225 cm−1 of epoxide groups on the other [Besides water-related absorption bands, both spectra comprised almost equally pronounced absorption bands at ectively . Convershe other , substan13C NMR solid-state spectra of the E-xy and H-xy graphenes displayed in δ= 58 ppm, δ= 68 ppm, δ= 95 ppm, δ= 133 ppm, δ= 167 ppm, and δ= 191 ppm corresponding to hydroxyls, epoxides, ethers (O-C-O), 2sp-hybridized carbon atoms of the unfunctionalized graphene network, carboxyl groups, and ketone groups, respectively [δ= 40–80 ppm by Lorentzian functions allowed an estimation of the relationship between the number of epoxide and hydroxyl groups in both derivatives. For the E-xy graphene, the relation was found to be 68% to 32% in favor of epoxides, whereas for the H-xy graphene, these values were 73% to 27% in favor of hydroxyls.This assertion was further verified by the ectively ,50. Appas and O 1s core-level signals at the binding energies (BEs) of 284.7 eV and 532.5 eV, respectively, were distinguished. Besides, only negligible peaks at the BEs of 168.2 eV and 400.1 eV were discerned, indicating the presence of trace amounts of ammonium sulfate adsorbates retained after the GO synthesis and its following derivatization into H-xy and E-xy graphenes. The concentration of ammonium sulfate was estimated to be less than 0.2 at.%, and we assert that it had a negligible effect on the VB of the graphene layer, which was verified by corresponding studies in the subsequent section.Given the results of the FTIR and NMR analyses, the H-xy and E-xy graphenes were examined by means of X-ray photoelectron and X-ray absorption spectroscopies. s spectra of E-xy graphene, H-xy graphene, and rGO after the deconvolution routine. All spectra comprised a dominant asymmetric C=C line centered at a BE of 284.6 eV, which was related to the pristine graphene network of sp2-hybridized π-conjugated carbon atoms [BEs of 288.2 eV and 288.9 eV corresponded to edge-located ketone and carboxyl groups, as has been signified by a number of synchrotron studies of GO and other graphene derivatives [s spectral components derived during deconvolution, which as a rule noticeably exceeded 1.0 eV, and (ii) a relatively small difference in the predicted BEs of the C-OH and C-O-C components in the C 1s spectra, commonly estimated to be less than 0.2–0.3 eV [on atoms . On the ivatives ,53. Moviivatives ,51,52. T2–0.3 eV ,55,56.s spectrum was indicated, owing to the redistribution of the relative integral intensity of the corresponding components. This could be clearly seen in the acquired C 1s spectra of the E-xy and H-xy graphene, with the peak at the BEs of 286.1–288.1 eV moving to lower BEs, from 287.0 eV to 286.7 eV, upon transition from the dominance of epoxides (E-xy graphene) to the enhanced relative concentration of hydroxyls (H-xy graphene), given the discussed FTIR and NMR data. Considering this fact, BEs of 287.0 eV and 286.7 eV for the spectral components of the epoxide and hydroxyl groups, respectively, were accepted.Nevertheless, in the case of the dominance of one of these groups, an observable shift in the second maximum of the C 1s spectra. The respective values of these groups’ relative concentrations are collected in s spectra of graphene derivatives with the determined BEs of the C-O-C and C-OH peaks allowed one to assess the absolute and relative concentrations of the epoxide and hydroxyl groups.To justify the proposed deconvolution procedure, data on the relative concentration of all oxygen functionalities were acquired via common quantitative processing of the integral intensities of the corresponding spectral features in the C 1p orbitals. This is due to these features having sufficiently large half-widths and similar intensities, along with the fact that the features inherent to carbonyl edge groups are mainly located between the features inherent to carboxyl ones [Despite the difference in the basal-plane oxygen groups, the relative concentrations of the ketone and carboxyl groups are comparable. This assumes that the possible difference in the DOS of E-xy and H-xy graphenes arises from the effect of the basal-plane epoxide and hydroxyl groups. Furthermore, the almost-equal relative concentrations of ketones and carboxyls results in the effective smoothing of those VB features that arise from oxygen 2xyl ones .K-edge XAS spectra of the materials under study were collected, being displayed in hv = 285.1–285.3 eV, which matured from the electron transitions in the C=C bonds at pristine sp2 domains [hv = 291.65 eV, which was excited sufficiently and reliably only if the size of the respective graphene domain exceeded ~five periods of its lattice and signified the complete recuperation of the conjugated graphene network [To further figure out the fingerprints of the epoxide and hydroxyl groups in the XPS and XAS spectra, C  domains . In rGO, network ,59. The hv = 286.2 and hv = 288.4 eV could be distinguished, which are commonly attributed to the C 1s-π* resonances of the electronic transitions in C-O bonds in the edge-located hydroxyls and C=O bonds in the ketone and carboxyl groups, respectively [hv = 287.3 eV and hv = 289.6 eV, respectively. The assignment of the peak at hv = 287.3 eV to the π*(C-O-C) resonances is generally accepted [2 groups [v = 2750–2900 cm−1 even at low concentrations of C-H/C-H2 [hv = 287.3 eV in the H-xy spectrum, the discussed spectral feature was assumed to arise from C 1s-π* electronic transitions in the epoxide groups.In turn, in the E-xy and H-xy graphene spectra, a set of resonances at ectively ,57,60. Baccepted ,60,61, a2 groups . HoweverC-H/C-H2 ,63. Combhv = 289.6 eV exclusively presented in the pre-edge region of the H-xy spectrum was more unambiguous. Some authors assign it to the π* resonance corresponding to carboxyl groups [K-Edge XAS spectra obtained for carboxylated graphenes [hv = 289.6 eV was assigned to correspond to the σ* resonance of the hydroxyl groups on the graphene basal plane, fingerprinting this oxygen group in the C K-Edge XAS spectra.The nature of the π*-resonance-like maximum with an energy of l groups , which iraphenes ,53,57; oraphenes . Howeverraphenes . Given thv = 130 eV and acquired at the normal angle of the photoelectron escape. All three spectra were quantitatively processed by the method of second derivatives, which allowed the significant refinement of the energy position of VB features that were only slightly visible in the original PES spectra of E-xy and H-xy graphene , the order of which corresponds to the direction of increasing binding energies. Only two peaks, with the lowest one, having a BE ~ 31 eV, visible in all three spectra and the highest one, centered at a BE of 3.2 eV, defined only in the VB spectrum of the rGO sample, were labeled in a distinct way. The former one, denoted as Na 2p, corresponded to trace amounts of sodium ions adsorbed on the studied graphene derivatives. In turn, the latter one was related to the highest critical point of the graphene band structure and is discussed below.By figuring out the chemistry of E-xy and H-xy graphene and verifying the predominance of either epoxide or hydroxyl groups in the synthesized derivatives, the examination of the VB of the acquired materials becomes feasible. graphene b. The reГ, M, and K) of its hexagonal Brillouin zone and are commonly referred to as critical points of the graphene electron band structure [VASP-DFT calculations of the graphene DOS [Furthermore, owing to the high degree of reduction, all the features in the rGO VB spectrum and its second derivative were related to the local maxima of the graphene DOS, which are located in certain high-symmetry points , B (BE ~ 7.8 eV), D (BE ~ 13.5 eV), E (BE ~ 17.0 eV), and F (BE ~ 19.3 eV), can be resolved in all three spectra, suggesting their possible dual nature. Particularly, these spectral bands probably comprise both states of the π-conjugated carbon atoms forming domains of the pure graphene DOS maxima and the molecular-related states of the epoxide and hydroxyl groups, that is, the energy levels of molecular orbitals formed upon the covalent bonding of the carbon and oxygen atoms. Conversely, the features C, G’, and G, with BEs of 10.6 eV, 24.7 eV, and 26.9 eV, respectively, were absent in the VB spectrum of rGO and revealed themselves only in the spectra of the E-xy and H-xy graphenes. Hence, they can be unambiguously identified as oxygen-related ones.Accordingly, the ectively ,66. A seG is related to the O 2s shallow core level, participating in the formation of σ-type C-O orbitals of the presented oxygen functional groups. Owing to the difference in the composition and geometry of groups, the BE of this core level varied from one functionality to other, resulting in a broad peak summarizing the impact from the states of the C-O orbitals of all oxygen groups. This was reflected by the identification of its sub-component G’, revealing itself only in the second-derivative spectra, which corresponded to the C-O orbitals of carboxyl groups and was almost undetectable due to the low relative concentration of these oxygen moieties in the H-xy and E-xy graphene [The origin of the prominent and broad feature graphene .A–C features, the rGO VB spectrum was normalized in such a way that the intensity of its high-energy tail (BE > 25 eV) became approximately equal to the intensities of the corresponding tails of spectra 1 and 2 (after the respective subtraction of an intensity coming from peak G). Thus, the acquired spectrum was overlaid on the VB spectra of E-xy and H-xy graphene (dotted line). Such an approach allowed the identification that the DOS in the region of BEs 5–11 eV was much higher in the VB spectra of E-xy and H-xy graphene compared to the rGO one. Since the probing depth and lateral dimensions of the X-ray beam were the same for all the samples, such a difference in the VB intensities points out that the A-C features were predominantly contributed to by electrons localized on the occupied oxygen 2p atomic orbitals (AOs), comprising MOs of the basal-plane hydroxyl and epoxide groups. This assertion is supported by the fact that the photon energy of 130 eV 2p subshell photoionization cross-section in the case of oxygen was about 7.5 times larger than one of carbon [To further perform an accurate analysis of the f carbon . Thus, tD, E, and F features, a contrary situation was observed: the relative intensity of these peaks in the E-xy and H-xy spectra were either almost equal (feature D) or even noticeably lower (features E and F) than in the rGO VB spectrum. This evidenced that the main contribution to the intensity of these features was provided by photoelectrons emitted from the carbon atoms of the pristine graphene network. Thus, the features D, E, and F were assumed to be associated with electronic states of such critical points of the graphene band structure in this energy range as In the case of the on GO VB ,18,66, aBEs, the relative intensities and FWHM of the same features differed. Most obviously, this was illustrated by the A and B features.A further comparison of the E-xy and H-xy spectra, both in their original forms and in the form of second derivatives, also revealed differences in the DOS of these derivatives. Despite comprising the same sets of spectral features with almost identical A-G features in the experimental spectra, DFT calculations of the graphene layer, functionalized by either a single epoxide or hydroxyl group, were further performed. AOs of the oxygen and carbon atoms of either the epoxide or hydroxyl groups can be derived, and the energy distribution of the overall electron density localized at the examined atoms can be visualized. Given these results, one can identify whether the spectral feature in the examined range of BEs is related to a molecular-related state in the epoxide or hydroxyl group and, if yes, determine the type of the corresponding MO—nonbonding, which refers to lone pair electrons on the oxygen atom, or π or σ C-O bonding.To assess the nature of the AOs of oxygen, carbon, and hydrogen atoms in the vicinity of the epoxide or hydroxyl. To accurately derive the corresponding EDs, the whole energy range was divided into nine regions denoted as . Regions B0 and B7 were not related to the experimentally indicated spectral features, but were discerned since they were presented by a particular ED configuration. At the same time, the other regions corresponded to a particular experimental spectral feature , being established in such a way that the corresponding spectral feature  laid approximately in the center of the corresponding region, and the regions had close widths, while the overlap of the regions, corresponding to different ED configurations, would be absent.Thus, the derived pDOS spectra for the C, O, and H atoms along with their sum  are displayed in the bottom sections of MOs occupied by oxygen 2p nonbonding lone pair electrons n’O2p (HOMO). Moving to higher BEs, the dominant maximum in the OpDOS component was indicated for both the E-xy and H-xy graphenes. Based on the analysis of the ED spatial distribution, the states in this energy range were attributed to 2p-type oxygen AO, oriented parallel to the basal plane of the graphene layer.As seen, the B0 region did not contain any pronounced maximum except intensive onset, which completely came from the OpDOS component. According to the respective images of the ED distributed within the B0 region in both the E-xy and H-xy graphenes, the corresponding electronic states apparently arose from Despite the similarity in the band structure of E-xy and H-xy graphene in the B0 and B1 regions, the following B2-B4 regions for these graphene derivatives had a distinct structure. The nature of the maximum in the B3 region was asserted to be related to a system of covalent σ bonds between atoms of the graphene layer and oxygen, constituting the C-O-C heterocycle of the epoxide group. This was seen from the respective ED pattern, demonstrating a high electron density surrounding the O and C atoms and filling the space between them. This was furthermore supported by the fact that corresponding electron density was not concentrated on one certain energy level, as in the case of molecular-like bonding, but distributed over a sufficiently wide band of energy levels of a similar nature as in the case of solid-state-like bonding. Particularly, the electron density, which participates in the formation of σ bonding between all three atoms of the E-xy group, continued to retain its spatial configuration at least in two neighboring regions to B3, that is, in the B2 and B4 ones.MOs of the σ(O-H) bonding in the hydroxyl groups, whereas the ED in the B3 region mainly stemmed from the σ(C-O) bonding between the group and the graphene layer. This assertion is well supported by the respective ED spatial configurations, for which a high electron density around the hydrogen atom was indicated in the case of the B2 and B4 regions, with its absence in the case of the B3 energy range.Unlike the case of the E-xy graphene, the TpDOS of the H-xy graphene exhibited three rather pronounced maxima located in each of the B2-B4 regions. The comparative analysis of the displayed pDOS showed that the maxima in the TpDOS of the B2 and B4 regions coincided with the maxima in the HpDOS, while in the case of the B3 region, no contribution came from HpDOS. Accordingly, the states localized in the B2 and B4 regions were considered to be related to the AOs, namely C2z AOp for the latter ones, were visualized quite easily. For this reason, the relatively weak maxima located for the TpDOS of both groups in the B5 and B6 regions practically did not manifest themselves visually. Moreover, the ED images corresponding to these regions showed a significant weakening of the covalent bonds between all atoms of the group, simply due to a noticeable decrease in the amount of the ED participating in the formation of these bonds.Moving to the B5-B7 regions, the apparent diminishment of the OpDOS was indicated, with a minor impact of the ED localized on the O atoms, verifying that the DOS in this energy region was mainly constituted by the states of the graphene network. It is worth noting that the ED corresponding to the graphene domains was distributed uniformly in a layer, covering all the carbon atoms that comprised the supercell. As a result, it was extremely difficult to visualize its density maxima coinciding with the critical points of the graphene band structure. On contrary, the maxima of the ED lying outside this layer, i.e., the ED corresponding to the oxygen and carbon s and C 2s AOs.Finally, a drastic and narrow rise in the TpDOS, driven mainly by the OpDOS, was observed in the B8 region, which laid outside the range of the graphene VB electron states. Owing to this fact and based on both the comparison of the pDOS and the respective ED visualization, the corresponding electronic states were assigned to the shallow core levels corresponding to the σ(C-O) bond formed mostly by the overlapping of the O 2A, B, C, and G(G’) upon functionalization by epoxides and hydroxyls in terms of the introduction of the molecular states related to the introduced functional groups. Particularly, the A spectral feature was related to the states of the 2p-type oxygen AO of the modifying groups, whereas the B and C spectral features contributed to the states assigned to the C-O σ bonding, both in the E-xy and H-xy graphene, and additionally to the O-H σ bonding in the latter case. Furthermore, the fact that the G spectral feature is related to the O 2s shallow core level, which participates in the C-O σ-bonding, has been additionally verified by the performed calculations. The absence of any signs of the molecular-related states of the 2p nonbonding lone pair electrons in the range of 0–1 eV in the experimental VB spectra was attributed to the adsorption of the water molecules. Owing to the lone pair electrons of the hydroxyls and epoxides participating in the hydrogen bonding, the corresponding states diminished, as was demonstrated earlier [Thus, the performed theoretical calculations fully verified the relevance of the interpretation of the VB spectra modification and the appearance of the  earlier ,68. TablK-edge XAS spectra were refined, whereas the deconvolution of the graphene derivative C 1s spectra with the discerned spectral components related to the epoxide and hydroxyl groups was proposed and justified by comparing to the FTIR and NMR spectroscopic data. Given this approach, the relative and absolute concentrations of exclusively an epoxide or hydroxyl group, not just their sum, can be derived from the acquired C 1s spectra. This is crucial for a set of strategies for the synthesis of graphene-based bio- and nanocomposites, in which either an epoxide ring or hydroxyl group is required for the reaction to proceed. Furthermore, such processing of the C 1s spectra of the GO and rGO layer grants an accurate estimation of the functionalization degree independently by epoxides or hydroxyls, which is of high interest for both fundamental studies and the practical application of these materials in the field of electrochemistry.To summarize, advanced features of examining graphene functionalized by epoxide and hydroxyl groups via the core-level methods were signified. The fingerprints of these oxygen groups in the C MOs of the modifying functionalities was shown and identified by applying DFT calculations by means of using a projection of the total density of states. The applied approach allowed the decomposition of the impact of the localized states corresponding to non-bonding lone pair electrons of npO2, σ, and π bonds. The presented results highlight graphene functionalization by an epoxide or hydroxyl group to be an advanced tool for engineering its deep electronic states, complementing the common studies on the basal-plane functionalization for the alteration of its bandgap. Moreover, the performed examination of the VB spectra can be regarded as a powerful tool to additionally elucidate the chemistry of graphene materials.Besides chemistry analysis, the peculiarities of the graphene VB alteration upon introduction of the epoxide and hydroxyl groups were specified. The appearance of localized states related to the Taken together, these findings guide and extend the frames of studying graphene derivatives and engineering their band structure for practical applications.


Optoelectronic devices are key building blocks for sustainable energy, imaging applications, and optical communications in modern society. Two-dimensional materials and perovskites have been considered promising candidates in this research area due to their fascinating material properties. Despite the significant progress achieved in the past decades, challenges still remain to further improve the performance of devices based on 2D materials or perovskites and to solve stability issues for their reliability. Recently, a novel concept of 2D material/perovskite heterostructure has demonstrated remarkable achievements by taking advantage of both materials. The diverse fabrication techniques and large families of 2D materials and perovskites open up great opportunities for structure modification, interface engineering, and composition tuning in state-of-the-art optoelectronics. In this review, we present comprehensive information on the synthesis methods, material properties of 2D materials and perovskites, and the research progress of optoelectronic devices, particularly solar cells and photodetectors which are based on 2D materials, perovskites, and 2D material/perovskite heterostructures with future perspectives. As modern technology improves by leaps and bounds, optoelectronic devices, such as solar cells and photodetectors, have become indispensable parts of society. These semiconductor devices that convert optical signals into electrical ones have wide applications in the areas of renewable energy, imaging systems, biomedical devices, and optical communications ,2,3,4. O2D materials, including graphene and its derivatives, transition metal dichalcogenides (TMDCs), and black phosphorous (BP), have attracted intense interest in optoelectronic applications due to their distinctive optical, electrical, and mechanical characteristics ,18,19,2014 Jones and fast response speed at the nanosecond level . T. T39]. T ammonia ,42,43. CThe CVD of graphene is typically performed on copper or nickel through a thermal method. Methane is a commonly used carbon source. As it is exposed to the heated metal surface, the metal catalyzes the loss of hydrogen and dissolves the remaining carbon, leading to a layer of metal carbide . As the 2, MoSe2, and WS2, have gained great attention because they show properties different from their bulk counterparts . A. A49]. A3, WO3, Se powder, and H2S . I. I63]. Iter size . Howeverter size . To solvI3 films .3 via laser irradiation 4− octahedrons. The difference between these phases lies in the stacking displacement of adjacent layers. The RP phase is characterized by the interdigitated organic bilayer which causes the inorganic layers staggered by half a unit cell . The DJ phase features a perfect stacking  and bivalent organic cation spacers. In the ACI phase, A-site cations not only appear in the cuboctahedral cages but also alternate with the spacers in the organic layer. Many linear monoammonium cations, such as butylammonium, pentylammonium, and hexylammonium, can adopt RP structures . . 2-based12 Jones) and photoresponsivity (0.4–1.0 A/W) from ultraviolet to near-infrared region. However, due to the emergence of TMDCs, graphene was substituted with TMDCs for photodetector applications.Ever since the successful exfoliation, graphene has been widely applied to photodetector applications. Here, we summarize significant works based on graphene. First, a graphene photodetector was integrated into a silicon bus waveguide, demonstrating a chip-integrated photodetector technology based on graphene . The couIn recent years, waveguide-integrated graphene photodetectors have been proposed for datacom applications. Schuler et al. used a silicon photonic waveguide to guide the light in a confined graphene area to facilitate light-matter interaction . The dev2, MoTe2, and MoS2 . . 3−xClx-2 layer by a facile microwave-assisted method as an ETL in MAPbI3 perovskite solar cells for the first time . . 3 PQDs 3 nanosheet as the light-absorbing material and MXene as electrodes, which was fabricated by all-sprayed-processable methods [3 and a fast response speed of 18 ms, which was attributed to the highly conductive MXene electrodes, and excellent crystallinity of CsPbBr3 nanosheet, and well-matched energy level at the CsPbBr3/MXene interface. In addition, the device retained 85% of its original photocurrent after applying 1500 times of cyclic bending, demonstrating its excellent physical stability. The device performance of photodetectors reviewed in For flexible photodetectors, a large-area photodetector was realized by utilizing a 2D CsPbBr methods . The obtTo date, the 2D material/perovskite heterostructure has demonstrated great potential for advanced optoelectronics and numerous efforts have been made to improve the performance of devices. However, several challenges still remain which hinder the further improvement of commercial applications.3 nanocrystals into dense SiO2 solid and the PL intensity of perovskite maintained 100% of its initial value for 1000 h under illumination [An open challenge is that the heterostructure generally suffers from poor stability in the ambient air because perovskite is very sensitive to humidity, heat, and light. In recent years, novel perovskites have been developed and demonstrated to be more stable than 3D perovskites. 2D RP perovskites have attracted much attention because their hydrophobic organic ligands could protect perovskites from water invasion . In addimination .Apart from the stability issue, the large-scale production of 2D material/perovskite heterostructures has been limited by fabrication methods. On the one hand, the majority of high-quality heterostructures are constructed using solid-state methods, such as wet/dry transfer, mechanical exfoliation, CVD, and physical vapor deposition (PVD), which require complicated procedures and high cost. On the other hand, although facile solution-processed methods provide access to large yield, the heterostructures suffer from low quality and reduced charge transport due to the poor contact at the interface . In thisLastly, the most widely researched perovskites in the heterostructures involve toxic and hazardous heavy metals, particularly Pb, which is harmful to the environment as well as human beings. Considerable efforts have been made toward replacing Pb with environmentally friendly or less hazardous elements, such as Sn, Mn, and Zn, where Sn is the most promising candidate among those substitutes ,201,202.The review covered the synthesis methods of 2D materials and perovskites, as well as their applications in solar cells and photodetectors. First, the basic properties and common synthesis routes of 2D materials and perovskites were addressed to provide a fundamental picture of these materials. Then, we summarized the recent research progress of optoelectronic devices based on 2D materials or perovskites. Despite their great potential in state-of-the-art optoelectronics, some issues regarding weak light absorption and poor stability restricted their commercial applications, which led to the introduction of 2D material/perovskite heterostructure. We analyzed the underlying benefits of this novel concept and reviewed the recent development of optoelectronic devices applying this heterostructure. Finally, we introduced the existing challenges and possible solutions for developing stable and high-quality 2D material/perovskite heterostructures, and also the need for environmentally friendly perovskites for green optoelectronics.


To prepare a new kind of electromagnetic wave absorber, and improve the processing technology and accessional value of natural microcrystalline graphite minerals (NMGMs), reduced microcrystalline graphene oxide (rGO-M), a novel absorber with high absorption, low reflection and a wide absorption band, was prepared from NMGMs using a solvent-assisted thermal reduction method. Moreover, the as-produced rGO-M with adjustable electrical resistivity can be easily transferred into well distributed bulk materials by freeze-drying technology. These unique structures and compositions make a great contribution to the impedance match, and cause strong conductive loss and various dipole polarization effects which greatly enhance the absorption. Meanwhile, the effective bandwidths below −5 dB and −10 dB are 11.7 GHz and 3.32 GHz respectively, and the reflection loss can reach −42.68 dB. The study will be beneficial to the development of carbon resources and carbon materials research. Besides, it can provide a scientific basis for the further improvement of the comprehensive utilization and the level of deep processing technology of NMGM resources. Reduced microcrystalline graphene oxide (rGO-M), a novel absorber with high absorption, low reflection and a wide absorption band, was prepared from NMGMs using a solvent-assisted thermal reduction method. Although these absorbers operate via dielectric and magnetic mechanisms of energy absorption as well as having advantages of low cost and mass production, their disadvantages of density and thermal stability make them lose their development potential when compared to the competition. Conventionally, magnetic materials have better electromagnetic wave absorption properties, but it is unavoidable that the absorption performance is governed by Snoek’s limiting high weight penalty, particularly for applications.10 At the same time, carbon-based dielectric absorbers have the disadvantage of narrow bandwidth, but their performance can be improved by constructing different space structures of carbon atoms. In addition, the matching ability between the material and the incident electromagnetic wave  is also an important index to measure the performance of absorbing materials, which is related to whether the electromagnetic wave can penetrate the material and be absorbed.Advanced absorbent composites with various potential applications, such as in aircraft, communication devices, and cutting-edge electronics, are attracting growing attention based on their unique nature.11–13 carbon nanofibers,14–16 carbon spheres,17–19 carbon foams,13,20 graphite,21–23etc., have been utilized as the main component of novel electromagnetic absorbers. Since it was successfully prepared, graphene has received great attention due to its excellent electrical and thermal conductivity, as well as its superior mechanical properties.24–26 As a kind of two-dimensional material, in addition to fullerenes , carbon nanotubes  and graphite , graphene has supplemented its use and perfected the field of carbon materials. After monolayer graphene was successfully prepared by the micro-mechanical peeling method,27 a variety of preparation methods have been reported, such as the oxidation–reduction method,28–30 chemical vapor deposition,31–33 and chemical synthesis.34–36 In particular, the oxidation–reduction method can efficiently prepare graphene under relatively mild conditions, and the defects and residual oxygen functional groups on the reduction products can improve the activity of the reduced graphene oxide (rGO), which is beneficial for expanding its application range. Therefore, as a new kind of nano-filler, graphene has been widely applied to prepare composites.Carbon-based materials have been considered as the best choice for electromagnetic shielding and attenuation since World War II. Up until now, a range of carbon materials with different forms, both traditional carbon materials and new nano-carbon materials such as carbon nanotubes,37 Therefore, finding out how to adjust the conductivity of graphene to control the impedance matching characteristics of materials is an important problem in current research.With the development of graphene and graphene-like materials, the exploration of graphene as an electromagnetic wave absorber has undergone great breakthroughs. However, there are still some problems to be solved, like the inability to realize batch production, agglomeration of graphene and so on. The core problem is that graphene is a non-magnetic material with excellent conductivity, and so the impedance matching characteristics of the material are very poor and the incident electromagnetic wave cannot smoothly penetrate the material, but will be reflected back.The core of our work is to adjust the conductivity of graphene absorbers from many aspects, so as to improve the impedance matching performance of the materials. Herein, NMGMs were chosen as the raw material, and the conductivity of rGO-M was adjusted by the solvent-assisted thermal reduction method. The purpose is to prepare a kind of high quality absorbent.2.2.138 The microcrystalline graphene in this paper refers to the graphene prepared from NMGM. The following outlines the preparation of reduced graphene oxides from natural microcrystalline graphite (rGO-M): firstly, GO-M was prepared through the modified Hummers method from natural microcrystalline graphite . Subsequently, a 120 mg amount of GO-M was dispersed in 40 ml of aqueous solvent by sonication for 0.5 h. Thereafter, the GO-M suspension was treated using the solvothermal method in a Teflon-lined autoclave at 180 °C for 12 hours to form rGO-M intermediate products. Finally, the rGO-M intermediate products were frozen at −50 °C for 6 hours, followed by 24 hours of sublimation under a vacuum of −50 μbar to obtain the rGO-M.All of the chemicals in our experiments were analytical grade reagents and were used directly without further treatment. Graphene oxide from natural microcrystalline graphite (GO-M) was prepared by the oxidation of NMGM powder.2.2λ = 1.54 Å) with 40 kV scanning voltage, 40 mA scanning current and scanning range from 3° to 70°. In addition, the Raman spectrum of the samples was investigated on a LabRAM HR800 spectrometer  using laser excitation at 514.5 nm. Moreover, Fourier transform infrared spectroscopy-attenuated total reflectance spectra were recorded on a WQF-510A spectrometer . The scanning electron microscope is equipped with an Oxford X-Max20 Energy spectrum system for energy dispersive X-ray spectroscopy analysis (EDS). X-ray photoelectron spectra were measured on an X-ray photoelectron spectrometer  using Al Kα (hν 1486.6 eV) X-rays as the excitation source. The electrical resistivity of the samples was measured by a four-probe resistivity meter . The most important permittivity (ε′ and ε′′) and permeability (μ′ and μ′′) values of the samples with dimensions of concentric rings  were measured by a vector network analyzer  with the waveguide method at 2–18 GHz.The morphology of the samples was identified by field emission scanning electron microscopy , transmission electron microscopy  and atomic force microscopy . The crystal structure of the samples was identified using an X-ray diffractometer , using Cu target Kα radiation  were characterized by SEM, TEM and AFM . It was θ = 20–30°, and a relatively obvious graphite diffraction peak (100) appears at 2θ = 42.5°. This indicates that through the above experimental treatment, the graphene sheet was damaged and piled irregularly, and retained a portion of the graphite structure. The Raman spectrum  scale" fill="currentColor" stroke="none"><path d="M0 440 l0 -40 320 0 320 0 0 40 0 40 -320 0 -320 0 0 -40z M0 280 l0 -40 320 0 320 0 0 40 0 40 -320 0 -320 0 0 -40z"/></g></svg>C, CO, C–O–C, C–OH and O–H functionalities, while the peak at 1380 cm−1 represents the bending vibration of C–H.42–44 After reduction, the characteristic peaks of all oxygen-containing groups are weakened or even tend to disappear, which indicates that a number of oxygen-containing groups have been removed.spectrum  of the r2p, Si2p and S2p gradually decreases and finally disappears during the preparation process of rGO-M from NMGN, indicating that impurities are greatly removed during liquid phase processing. Compared with the GO and rGO-M spectra, a significant change in the ratio of the C peak to the O peak shows that the reduction of the sample is successful. The effects of oxidation and reduction can be quantitatively characterized by the atomic ratio of carbon to oxygen , C–O (286.8 eV), and CO (288.3 eV). The results above suggest that GO contains various oxygen-containing functional groups. Through the previous characterization, the reduction process can obviously remove these functional groups. A significant decrease in heterocarbon components is observed in the C1s spectra in 45–49In order to quantitatively analyze the change of functional groups and components in the preparation process, peak fitting of NMGM, GO, and rGO-M by Cg states . For NMGl groups . The dat3.2ε′) and imaginary (ε′′) parts of the relative complex permittivity from 2 to 18 GHz. As a whole, both the real part and the imaginary part present a downward trend across the whole band. Except for the samples with 50% ethanol concentration, the range of which is more than 10, the trend of the remaining samples varies very slowly, and the range of variation remains within 7 (ε′ from 3.03 to 5.56 and ε′′ from 2.30 to 6.49). It can be seen in μ′) or imaginary (μ′′) parts of the relative complex permeability show a certain trend but the change range is very small (<0.25), and this value is consistent with the paraffin matrix material, so there is almost no value for analysis. The result of the relative complex permeability indicates that the material is almost non-magnetic. The change of the dielectric loss tangent (tan δε) with frequency in different ethanol concentrations is shown in δε in different ethanol concentrations is to decrease at first, then increase, and finally return to decreasing, but the change is not significant, and the variation is between 0.3 and 1. In δμ) shows the opposite trend with tan δε, that is, increasing in the range of −0.02 to 0.12. Subsequently, referring to the data in front of μ′ and μ′′, it can be concluded that the rGO-M is not an absorber for magnetic loss.In order to research the effects of rGO-M as an absorbent, ethanol concentration was used as a variable to explore the microwave absorbing performance. −1. As the concentration of ethanol increases, the conductivity can reach hundreds of S m−1, which shows a difference in orders of magnitude. Under high temperature and high pressure conditions, with the removal of oxygen-containing functional groups, the self-assembly process of graphene sheets will occur in the presence of noncovalent interactions, which affects the conductivity of the graphene prepared. The increase in the ethanol concentration makes the degree of self-assembly increase, resulting in the reduction of isolated graphene sheets. The conductivity increases with the increase in free electrons in the structure.According to the discussion above, it can be confirmed that rGO-M is a kind of electromagnetic wave absorber with electric loss. In order to subsequently study its electrical properties, the electrical conductivity changes with the concentration of ethanol were tested . With thZin of a metal-backed electromagnetic absorbing layer, reflection losses of the rGO-M/paraffin composites can be calculated from the measured dielectric characteristics according to the following equations (d = 4 mm).21Based on the generalized transmission line theory and the normalized input impedance d = 4 mm. When the ethanol concentration is 50%, the change in the effective absorption bandwidth is very obvious, but the difference in the absorption peak intensity is not big, and no special point appears.According to the theory of linear transmission, the thickness of the material has an influence on its electromagnetic absorption performance. The reflection loss of rGO-M/paraffin under different thickness conditions is show in 21 In rGO-M/paraffin, rGO-M and impurities can be regarded as isolated islands in the paraffin matrix, and form a large number of interfaces between the islands and the matrix. Reflection and refraction occur when the electromagnetic wave meets the interface between the islands and the matrix in the transmission process. The reflected electromagnetic wave continues to propagate in the substrate until other interfaces are encountered, by which point the wave may have reflected many times inside the material. Therefore, the existence of these isolated islands greatly increases the transmission path of electromagnetic waves in the material and such propagation would cause electromagnetic waves to lose some of their energy. The reflection loss of energy not only occurs among large numbers of isolated islands, but also within the isolated islands. rGO-M has a two-dimensional lamellar structure, causing multiple reflection losses. As for rGO-M, there are residual defects and groups on graphene sheets, corresponding to the formation of many micro-interfaces, which mean the electromagnetic wave needs to consume more energy to continue to spread. The two structural characteristics further strengthen the reflection loss. In conclusion, the electrical properties of graphene’s isolated islands are indeed conducive to absorbing electromagnetic waves. The dielectric property results suggest that the rGO-M has a strong dielectric loss capability, which can effectively dissipate electrical energy. In the composite, the rGO-M forms many conductive micro-networks, and if an external electric field is applied to the material, the energy will be induced into many microcurrents, generating a strong conductive loss, and resulting in the increase in the electromagnetic wave absorption capability. As mentioned above, according to dielectric spectroscopy, there are many interfaces in the materials, where polarization loss may occur. When the materials were exposed to an electromagnetic field, a small amount of unneutralized positive and negative free charges accumulated on various interfaces and abundant boundaries, and then plenty of dipoles were formed once these charges were trapped by defects. From the discussion above, it can be concluded that the enhanced microwave absorption performance of rGO-M/paraffin is ascribed to the better impedance match, the special hierarchically porous system and its polycrystalline structure.50–53The oxidation process can fully disperse the graphite ore, and release the impurities wrapped in the ore into the solution. Solvent-assisted thermal reduction can promote the self-assembly of graphene sheets, and the impure particles are prevented from being wrapped again. What is more, the electronic structure of graphene is restored, giving the material a moderate conductivity, and the residual oxygen-containing functional groups can help to reduce the conductivity of the material, thus improving the impedance matching performance. 4.In summary, microcrystalline graphene oxide was successfully fabricated by a solvent-assisted thermal reduction. The recovery of conductive properties can achieve the desired effect with lower mass fraction conditions. The as-received microcrystalline graphene oxide has a unique conjugated graphene network and amorphous nanostructure which is usually required for applications in microwave absorption. With adjustable electrical resistivity, it is rather easy for the as-produced microcrystalline graphene oxide to be transferred into well distributed bulk materials. Based on the conjugated graphene network and amorphous nanostructure, microcrystalline graphene oxide demonstrates an extremely superior microwave absorption performance in the GHz band. The graphene/paraffin composites with different thicknesses show different trends and can be regulated according to requirements. Meanwhile, the effective bandwidths below −5 dB and −10 dB are 11.7 GHz and 3.32 GHz respectively, and the maximum reflection loss can reach up to −42.68 dB. rGO-M/paraffin composites made by solvent-assisted thermal reduction as electromagnetic wave absorbers can significantly improve absorption performance in the low frequency band.There are no conflicts to declare.