The process of graphene defect generation was studied through the ball milling process. The effects of defect content and temperature on the graphene repair process were studied separately. The study found that the graphene defect repair process, the decomposition process of oxygen-containing functional groups, and the deposition process of active C atoms existed simultaneously in the CVD process. When the repair temperature was low, the C atom deposition process and the oxygen-containing functional group decomposition process dominated. In addition, when the repair temperature is high, the graphene defect repair process dominated. 3 wt% graphene/Cu composites were prepared by pressure infiltration, and it was found that the bending strength was increased by 48%, the plasticity was also slightly increased, and the thermal conductivity was increased by 10–40%. This research will help reduce graphene defects, improve the intrinsic properties of graphene, and provide theoretical guidance for the regulation of C defects in composites.Graphene has extremely high theoretical strength and electrothermal properties, and its application to Cu-based composites is expected to achieve a breakthrough in the performance of existing composites. As a nano-reinforced body, graphene often needs a long time of ball milling to make it uniformly dispersed, but the ball milling process inevitably brings damage to the graphene, causing the performance of the composite to deviate from expectations. Therefore, this paper uses CH Howeviscovery ,9,10. Griscovery ,12.4C3 is formed, which reduces the strength of the composites [The high performance of graphene is directly related to its intrinsic structure. The unique two-dimensional structure of graphene has delocalized electrons when intact, making it possess extremely high in-plane electrical conductivity, thermal conductivity, and mechanical properties . Howevermposites ,21.In order to solve the problem of graphene damage, researchers have conducted research from two perspectives: avoiding the introduction of defects during material processing and repairing graphene defects. Short-time high-energy ball milling can greatly reduce the damage to graphene caused by the dispersion process. Yue et al.  prepared5 S/m. It is much higher than RGO (7.96 × 103 S/m) which has only undergone chemical reduction. High-temperature graphitization has the best effect, but it is difficult to apply to metal matrix composite systems. Liquid repair and doping repair work by in-situ self-generation or diffusion into the graphene lattice under liquid conditions to prepare carbon atom-filled or heteroatom-doped graphene structures. It is suitable for liquid phase dispersion of graphene while realizing defect control. However, the repair effect is not obvious enough, and the improvement of material performance is small.By reducing the speed of the ball mill and shortening the time of the ball milling, serious damage to the graphene caused by the ball milling process can be avoided. However, short-term ball milling still inevitably introduces a small amount of defects to the graphene. In order to further reduce the defect content of graphene, other methods are used to repair the defects of low-damage ball-milled dispersed graphene. At present, the graphene repair methods reported mainly include high temperature graphitization repair ,24, Chem4 plasma to repair defects in graphene. The study found that the Hall mobility of graphene increases significantly with the increase in the degree of repair, from 1 cm/(V·S) to 52 cm/(V·S), while the resistivity decreases significantly. Grimm et al. [4 S/m, and the agglomeration between graphene layers is avoided, which effectively increases the specific surface area. However, in current research, CVD is mainly used for defect repair of graphene powder. After the graphene and metal powder is dispersed by ball milling, the method and extent of CVD repairing graphene have not been studied.CVD repair mainly uses free radicals generated by the decomposition of carbon-containing gas as a C source at high temperatures to fill and repair graphene defects spontaneously. Zhu et al.  used CH4m et al.  used isom et al.  used CVDIn this work, pure copper was selected as the matrix and GNPs as the reinforcement. GNPs/Cu composite powder was prepared by high-energy ball milling, and the defects of GNPs during the ball milling process were repaired by the CVD method. The graphene defects were characterized by Raman Spectrum (Raman) and X-ray Photoelectron Spectroscopy (XPS), the repair effect of CVD on graphene defects was studied, and the best defect repair process was explored. The powder is sintered into a composite by Spark Plasma Sintering (SPS). By comparing the mechanical properties, thermal conductivity, and microstructure of the composites with or without repair, the effect of defect repair on the performance is studied, which provides theoretical guidance for the preparation of low-damage GNPs/Cu composites.The pure Cu powder used in this study was purchased from Beijing Xingrongyuan Co., Ltd., Beijing, China, with a purity of 99.9% and an initial particle size of about 3 μm. The characterization results are shown in DI/GI = 0.19, and the value of DI/GI indicates the defect content of graphene. The graphene used in this experiment has fewer defects. The original graphene was subsequently characterized by XPS. The XPS results show that the GNPs C atoms are mainly sp3 C, with a small amount of sp2 C defects and some oxygen-containing functional group defects. The ratio of the peak area of sp3 C atoms to the total area can reflect the content of graphene lattice defects. From the figure, it can be seen that the defect content of the original graphene is about 30%, and the content of functional group defects is about 8%. The TEM characterization of graphene is shown in The graphene  used in this experiment was prepared by the exfoliation method, and its Raman spectrum test results and XPS test results are shown in 2 grinding balls were added to each ball milling jar . In addition, 500 g ethanol was added as a grinding aid. The ball mill selected a speed of 250 r/min, and the ball mill stopped for 25 min every 5 min to prevent the danger of overheating. The graphene and Cu were ball milled for 120 min to make them uniformly dispersed. After ball milling, the graphene-Cu mixed slurry was separated through a screen and dried at 70 °C for 24 h to obtain graphene-Cu mixed powder. The chemical state of graphene after ball milling was characterized by Raman and XPS.High-energy ball milling is a commonly used method to introduce graphene into Cu powders. This method is easy to operate and has a good mixing effect. However, the impact and shear of the graphene during the ball milling process will also destroy the integrity of the graphene structure. In this study, a planetary ball mill  was used to disperse the graphene, and the ball-milling speed of 250 r/min was used to ensure the uniform dispersion. 1.5 g of graphene, 48.5 g of Cu powder and 500 g of ZrO4) was chosen as the carbon source and argon (Ar) was chosen as the shielding gas. The ratio of Ar to CH4 is 10:1. In the experiment, 800 °C, 900 °C and 1000 °C were selected to treat the powder to characterize the evolution behavior of graphene defects at different temperatures. The gas flow rate is 20 sccm (stand mL/min), the pressure is 280 Pa, and the reaction continues for 30 min. After cooling in the furnace, the product was taken out for subsequent characterization and experiments.In order to reduce the damage of graphene, CVD is used to repair graphene defects. The CVD process is carried out in a pipe furnace . Methane  during sintering was 2:1. After the sintering is completed, the sample is cooled to room temperature in the mold with the furnace. Subsequent structural characterization and performance testing of composites.Morphologies of the GNPs/Cu powders and the composites were observed by FEI Quanta 200FEG . Raman analysis was performed on a JY-HR800 laser Raman spectrometer  using a 532 nm solid-state laser as an excitation source. X-ray Photoelectron Spectroscopy was performed on ESCALAB 250Xi  spectrometer with a monochromatic Al Ka radiation source at 15 kV and 150 W. Tensile samples with dimensions represented in our previous work have been tested on Instron 5569 universal electrical tensile testing machine  with a cross-head speed of 0.5 mm/min. All the tensile tests have been performed on at least four samples to improve the statistical significance of the results. The LFA467 laser thermal analyzer  was used to characterize the thermal diffusivity of the GNPs/Cu composites, and the test temperature was 25 °C.To study the ability to which CVD can repair GNPs defects, it is necessary to prepare GNPs with different defect contents. In order to obtain graphene with different defect content, four different ball milling times were designed, namely BM1h, BM2h, BM5h, and BM10h. DI) and the G peak (GI) is generally considered to be an apparent manifestation of the defect content of graphene. This is because when the defect content does not exceed a certain ratio, DI/GI is proportional to the average distance between the two defects on the graphene [DI and GI are the intensity of peak D and peak G in the Raman spectrum, respectively; λC is a constant related to the wavelength of the test laser; dL is the average distance between two defects on the graphene.The degree of damage of GNPs was characterized by Raman. The intensity of the D peak  and ball milled powder repaired by CVD at 1000 °C (1000 °C CVD-BM10h), which have the most defects and the most obvious graphene repair effect. The density and elastic modulus of the composite material were characterized, and the results were shown in Afterward, the composite material was tested for bending performance, and the results are shown in The fracture of the composite is observed as shown in The thermal conductivity of the two composites was characterized, the temperature used in the test was normal, and the results are as shown in In this paper, the evolution and control of defects in graphene processing are studied. Through mechanical ball milling, the damage behavior of graphene during ball milling was studied, and the relationship between ball milling time and graphene defect content was established. The graphene defects were repaired by CVD, and the effects of temperature and initial defect content on the graphene repair process were studied.Studies have found that CVD has a repairing effect on graphene defects, which can be significantly observed before and after the repair of graphene samples after ball milling for 5–10 h. The more the defect content, the more obvious the CVD repair effect. The defects of graphene ball milled for 10 h decreased significantly with the increase of CVD temperature, reflecting the promotion of temperature on the graphene repair process. Combined with Raman and XPS, the evolution mechanism of defects is analyzed. Since CVD repair is a process of carbon source gas cracking to generate active C atoms, which are deposited on the surface of graphene. Simultaneously existing in the CVD process: graphene repair, decomposition of oxygen-containing functional groups, and at the same time, with excess C atoms, new graphene with more defect content is generated in situ on the Cu matrix. When the CVD temperature is low, the deposition of C atoms dominates, and a large amount of new graphene with defects is deposited on the surface of the original GNPs-Cu, which leads to an abnormal increase in the content of defects. Increasing the CVD temperature will greatly increase the diffusion rate of C atoms, and the hole defects will be repaired by C atoms. The evolution of defects in graphene during CVD is the result of the coordination of three functions.On this basis, the mechanical properties and thermal conductivity of composite materials prepared by CVD repaired graphene were studied, and it was found that the bending strength was increased by 48%, and the plasticity was also slightly improved. After the repair, the thermal conductivity also has a significant increase in the in-plane and inter-layer thermal conductivity, which is mainly attributed to the repair of defects by CVD.


Flexible polymer-based actuators, often also called artificial muscles, are an essential part of biomimetic systems that mimic the movement principles of animal world creatures. The most used electrode material to force the actuator move is an ensemble of noble metal nanoparticles in the electroactive polymer surface. Noble metal electrodes have enough electrical conductivity and elasticity and are not subjected to oxidation. However, high cost of such electrodes and their tendency to cracking dictate the need for searching other materials, primarily carbon ones. The review considers several options for this search. For example, carbon nanotubes and graphene have excellent properties at the level of a single individually taken nanotube or graphene sheet. However, conservation of these properties in structurally imperfect film electrodes requires a separate study. In addition, there are problems of compatibility of such electrodes with the polymers that requires cumbersome technologies, e.g., hot pressing, which complicates the production of the actuator as a whole. The review concerns the technology options of manufacturing actuators and the results obtained on their basis, both including hot pressing and avoiding this procedure. In particular, the required level of the graphene oxide reduction in hydrazine provides sufficient adhesion at rather high electrical conductivity of the graphene film. The ability to simultaneous achieving these properties is a nontrivial result, providing the same level of actuation as with expensive noble metal electrodes. Actuators that additionally require greater lifetime resource should be obtained in other ways. Among them are using the graphdiyne electrodes and laser processing of the graphene electrodes. The use of carbon materials for the both electrodes and the electroactive membrane materials in actuators and other biomimetic devices is an intensively developing area in the progress of these devices. However, there are not many original works and reviews on this subject.This is due to a number of serious problems in using carbon materials. In their original form, these materials are essentially hydrophobic and therefore are poorly combined with the water base of electrolytes, which is the most effective environment for the actuators, and with water-filled membranes. On the other hand, in the process of functionalization, the conductive properties of carbon materials deteriorate notably. The existing methods of connecting electrically conductive membranes with ionic electroactive polymers (EAPs) are still either insufficiently effective or too expensive, and no effective solution has yet been found.This review partially overlaps the existing and well-known reviews on carbon materials as applied to the actuators ,2,3 and In the classical and the most advanced version, the electrode composite for the electrochemical actuator is formed on the basis of noble metal particles, impregnated into an ionic EAP; this polymer is filled with electrolyte. The entire composite structure of the actuator is called an ionic polymer-metal composite (IPMC) ,2.The IPMC actuator principle of operation is based on transport processes occurring inside a polymer membrane. During saturation with a liquid, a dry polymer is structured in such a way that the polymer chain hydrophilic ends are oriented towards the membrane pores filled with an ionizing solvent. The action of the electric field induced by the voltage applied to the electrodes leads to the charged liquid movement in the membrane along the system of through pores due to the processes of diffusion and electroosmosis. The arising electroosmotic fluid flow causes an increase in pressure at one electrode and a decrease near the other electrode. The pressure drop leads to the actuator deformation .The development of IPMC transducers is strongly restrained by the noble metal price  and electrode brittleness, resulting from conflicting requirements to the electrodes: flexibility, high conductivity, and a significant service lifetime at the same time. Besides that, the procedure of chemical coating of the Nafion membrane with electrode layers (the most common technology) requires a great deal of effort and time.For these reasons, an intensive search is under way for cheap electrode materials that possess the above combination of properties. This combination can be typical of carbon materials, primarily graphene and carbon nanotubes (CNTs), provided that they are produced in a fairly cheap way. For example, we can hardly talk about the prospects of mechanically exfoliated graphene, a standard material that demonstrates the unique electronic properties of graphene .The use of carbon materials in ionic EAP is not limited to replacing the noble metals of the electrodes with these materials. Another direction may be the ability to provide a high ionic conductivity of the membrane, which limits the operation of the actuator at high frequencies. Further, the attention will be focused on the latest results of the nanocarbon materials research: nanotubes, graphene, and graphdiyne as electrode materials for actuators.Although many different actuators  have been developed on the basis of carbon nanomaterials, we will restrict ourselves to ionic EAP actuators, whose standard components are the polymer and the electrolyte that fills it. Such actuators can be used in robotic systems as artificial muscles  as well The properties of graphene are the basis for understanding the reasons for interest in the entire family of carbon nanomaterials intensively studied at present, such as the graphene itself, CNTs, nanoribbons, fullerenes (to some extent), and some others.5 cm2/(V∙s) for a free mechanically exfoliated graphene monolayer.The key properties that determine the prospects for using the graphene in actuators are high-charge carrier mobility and exceptional elastic properties. Measurements carried out in 2005 through the 2010s ,9 indica12 cm−2, but the mobility decreases noticeable due to the influence of the substrate.Indeed, this huge value is only realized as high conductivity in the case of sufficiently high carrier concentration. Due to the specificity of graphene as a gapless semiconductor, this concentration is formally equal to zero for free graphene. By applying a gate voltage to graphene, it is easy to achieve the concentration as high as 10When creating such a potentially mass product as actuators, the graphene is usually represented as chemically exfoliated graphene, which is a product of a complex graphite exfoliation technology with strong acids. Such graphene always contains a significant number of grafted functional groups, some of which do not leave after material recovery of any kind.Thus, in the electrodes of actuators, graphene is always unintentionally doped, but the carrier mobility in it is quite low due to a significant number of reduction defects and residual functional groups. In addition, in a polycrystal electrode composed of a large number of graphene flakes, the actual conductivity is determined by the contacts between the flakes. Therefore, the feasibility of high mobility and, consequently, conductivity in practical graphene is relatively low.The same applies to elastic properties. So far, we cannot talk about a continuous graphene monolayer, which would cover the actuator surface and which could be rolled up into a tube without damage. The ability of a real polycrystalline graphene film to return to its original position at the level of individual graphene flakes should be evaluated in each case experimentally.Another property of the graphene , important for actuators, is the quantum capacity and the associated quantum elongation . This ef2/g) in supercapacitors by almost an order of magnitude [This quantum capacity, which “swallows” a huge part of the real capacity of carbon nanomaterial, is, in particular, the reason for the unattainability of the potentially high capacity of graphene .The peak of interest in the properties of the first of the listed materials (CNTs) was in the late 1990s–2000s. The primary motivation for using CNTs in actuator electrodes was the same reason as the apparent prospects of CNTs in the hydrogen accumulation problem—a huge specific surface area and electronic conductivity at one time. The other advantages were flexibility and electrochemical stability. However, it quickly became apparent clear that the hydrogen sorption capacity of all real nanotube materials is insufficient.On the other hand, the technique of obtaining thin nanotube paper , suitable for studying nanotubes in applied problems, was developed. As applied to actuators, such paper turned out to be a good substitute for traditional metal-film noble metal electrodes. Another option was composite thin films of gel-type nanotubes with a polymer or with an ionic liquid (IL) or with the both of these components (bucky-gel).L, the displacement amplitude D, the curvature radius R, and the outer side stretching (or the inner side compression) ΔL with the membrane thickness d and at small D/L ratio are determined by the almost obvious formulas:The diagram of how a bucky-gel electrode actuator responses to a meander voltage applied across the electrodes is shown in max), the principal parameter of the actuator is the maximum mechanical stress σ generated during actuation and recalculated from εmax and the Young’s modulus Y by the Hooke’s law: σ = εmaxY.Except the stress and the actuator displacement amplitude  generated by CVD technique or in arc with a metallized graphite anode. SWCNTs separated by subsequent chemical processing play the role of the CNT property demonstrator in the CNT research. This role is similar to that of mechanically exfoliated graphene in the graphene science. Various types of actuators have been developed on the basis of SWCNTs. In particular, the first electrochemical SWCNT-based actuator was created in 1999 by the authors of .The strips of the nanotube paper, cut by the shape, were adhesively attached to the opposite sides of a double-sided adhesive tape and a high voltage was applied to them. The principal mechanism of the structure actuation, according to the authors, was the electronic mechanism based on the electron injection into one electrode and the hole injection into the other one. As shown in quantum-chemical calculations, the electron injection is accompanied by significant tube stretching . On the This mechanism obviously works in the absence of ion movement as well. In fact, such electrostatic effect is very small regardless of the sign of the charge: the strip expands to a much greater extent than stretches.In the case of a SWCNT electrode in an electronic type actuator described in , the effAnother mechanism of actuation, different from electronic but similar to it, is ionic mechanism that is associated with the movement of the cations and anions. First of all, more mobile cations entrain water in a water-filled polymer. Owing to that, the stretching and the compression of the electrode occurs as a mechanic-hydrodynamic effect.In the case of IL, the stretching of one electrode and the compression of the other one occur due to significantly different sizes of the cation and anion. In addition, in the case of IL, near-electrode layers with different charge signs should be formed near the electrodes; thus, a capacitor arises. When it is charged/discharged by the electrolyte ions, both quantum elongation and electrostatic actuation as a sequence of the charge injection  should oIndeed, the electron-ion system of an individual nanotube at each of the electrodes, together with the adjacent electrolyte ions, forms an open quantum-mechanical system a. Theref+ ions in it—the cations”, it is the cations that face the electrolyte and form a capacitor with the anions at the opposite electrode.In addition, in the quasineutral ensemble “the nanotube electrons—the CIn what follows, we will consider only ionic actuators, whose displacement is caused by the ion migration in the electrolyte layer that fills the framework polymer (not necessarily electroactive) and then inside the electrode layers. In this case, a significant bending of the membrane occurs already at a low voltage of 1–5 V applied to the electrodes.When studying the ionic polymer composites with nanotube electrodes, the initial material of such electrodes was a SWCNT gel film with IL (SWCNT/IL-gel) .60, and CNTs). This is due to the interaction between IL cations and π-electrons of nanotubes. This is the reason why graphene, which have recently been produced in large quantities and by cheaper methods than nanotubes, have in no way ousted them from the actuator topic.It was found this way that only SWCNTs could form a good physical gel with an IL among all carbon materials ;The polymer effect study: it is known that the polymer able to give the mechanical integrity to the ribbon reduces the conductivity and capacity of the electrode layer; from this viewpoint, the optimal electrode film should not contain a polymer at all.Further optimization of the ionic EAP actuators with the SWCNT gel-based electrodes was carried out in the following directions:The optimization in the first two directions enabled high stretching amplitudes  togetherThe way of the SWCNT synthesis turned out to be the most important from the first two factors. The effective SWCNT film with an IL containing no polymer at all was successfully created but by using an extreme type of nanotubes—extra-long tubes obtained in the CVD process with water .Herewith, the Young’s modulus and tensile strength were ~160 and 15 MPa, respectively; the conductivity was 170 S/cm. After the hot pressing of the composite electrode with the IL/PVDF electrolyte layer, the actuator strip could bend almost perpendicularly to its initial position under DC voltage of 3 V. It is also significant that with the frequency increase from 1 to 10 Hz, the displacement amplitude decreased from 5 to 4 mm, i.e., very slightly. In air, the actuator strip could operate in a continuous mode  up to 10,000 cycles.To explain the fast response and significant displacement of the SWCNT/IL actuator electrodes at high frequency and low voltage, the authors of  used theThe mechanism consists in the redox reactions on the surface of an electrochemically active electrode, as a result of which a significant additional charge is transferred through the “electrode/electrolyte” interface. Similarly, in narrow spaces between nanotubes, the actuation barrier of reactions is significantly reduced, additional electrochemical currents are formed, and an electrochemical contribution to actuation appears.The electrochemical component influence can be sharply increased if capacitive materials, such as conductive polymers and metal oxides, are introduced into the electrodes. Thus, in , polyani2; the tension at an amplitude of 2 V and a frequency of 0.1 Hz was 0.88%, and the mechanical stress was 390 MPa. However, the electrodes could only perform effectively at low frequency. The authors saw the reason for this in slower proceeding of the redox reactions, during which the mechanical tension increases, in the presence of polymer.When compared in terms of the tension and the mechanical stress produced, the electrode structures “CNT/PANI” (50/10) turned out to be about five times better than the pure CNTs structures. The conductivity was 8.6 S/cm, and the capacity was 0.0852 F/cmAs already mentioned, SWCNTs, especially ultra-long ones, are very expensive and cannot be considered as a suitable modifier for such widespread use as actuators. Therefore, the possibility of much cheaper multi-walled carbon nanotubes (MWCNTs), which also have their own advantages and disadvantages, was also investigated in parallel.Whereas in SWCNTs, any chemical modification, which includes carboxylation and aminization, sharply reduces the electrical conductivity, such manipulation in MWCNTs affects the outer wall only, and the high conductivity set by the core of the tube remains. At the same time, it is easier to fix on the tube surface a group that enhances certain properties. Therefore, MWCNTs were under attention in the development of the other applications of nanotubes—double-layer capacitors and sensors.In addition to the properties enlisted above, the levels of “entanglement” and interaction between individual tubes are completely different in the SWCNT and MWCNT as in actually obtained materials. Thus, SWCNT films have a higher Young’s modulus (695 MPa) than MWCNT films (470 MPa) and, at the same time, relatively higher van der Waals interactions between individual tubes. The denser packing causes the nanotubes to “stick” together and to be packed more tightly in SWCNT nanotube paper than in MWCNT paper. This factor blocks ion transport to the periphery of the actuator and reduces the tension. This is especially true for films containing aligned nanotubes .2/g). Thus, the solution can be either surface modification or stimulation of the electrochemical component of the actuation.On the other hand, the disadvantages of MWCNTs in the problem of actuation are as significant as that of SWCNTs. Therefore, in the absence of real ion transfer through the nanotube channels, the effective surface area of the nanotube is small  is of the same order of magnitude as that in SWCNTs and much more than in MWCNTs . Mor+ ions) between the graphene layers followed by the electrolyte penetration [This occurs due to the intercalation of solvated ions  was the paper , where t3)2 solution. The positive Ag(NH3)2+ ions are readily absorbed on the negatively charged GO surfaces and are reduced with hydrazine. This leads to nucleation of the Ag nanoparticles (AgNPs) and their deposition on the GO surfaces. Then, the GO/Ag mixture is left overnight at 95 °C so that the mixture is reduced up to RGO/Ag .The hybrid electrode was obtained by evaporation of the RGO/Ag suspension onto a glass substrate. The film formed had a conductivity of 900 S/cm, much higher than the value of 50 S/cm, typical of the RGO electrodes. When producing the actuator with the RGO/Ag electrodes, two hybrid electrodes are connected by hot pressing with the electrolytic membrane of PVDF-HFP filled with the traditional IL—1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBFAs it is seen from The authors of  suppose +) appears in the electrolyte and adds to the IL components (BMIM+ и BF4−), the rapid displacement is determined by the Ag+ and BF4− ions that form the primary excessive concentrations of the Ag+ cations at the cathode and the BF4− anions at the anode.The second important effect is that the actuator with combined electrodes successfully “holds” the meander shelf at maximum amplitude a, in con+), which are larger in size and capable of holding the cathode stretching, almost cannot reach the cathode. However, in the case of the RGO/AgNP composite electrode, the wrapping of the RGO flakes around the AgNPs suppresses partially the Ag ⇄ Ag+ redox process.At the background of this distribution, the inertial component of the cations . In contrast to , we did The mechanism of how the graphene film conductivity is improved upon the introduction of silver is likely to consist in condensation of the silver particles at the junctions between the graphene flakes and providing conductive bridges between them. In addition, the introduction of silver can provide an additional mechanism for increasing flexibility, which will be discussed below.Assessment of the optimal concentration of silver in graphene should take into account that the silver bridges between the graphene flakes are formed in a series of parallel processes.3)2 and subsequent saturation of the solution with silver, the silver cluster condensation occurs primarily at the joints of the graphene flakes and then in the space between the flakes.At the first, during the reduction of silver from aqueous solution of Ag, the conductivity is only several times less than the possible maximum. We can take for this value mAg/mG ≈ 20–25, obtained in [ained in . In our ained in  can be aOne of hypothetical mechanisms (in addition to the silver ions non-outcome into the electrolyte), which determines an increase in the system resource when using graphene, is the membrane flexibility increase. We made no attempt to specifically improve the adhesion of the electrode material to the membrane body. Nevertheless, it is known that in the course of GO reduction, the functional groups that remain on graphene are not uniformly distributed over its surface but are localized at certain places, creating a superstructure ,36.The areas where the functional groups are aggregated, have better flexibility than more rigid graphene flakes, and can provide better flexibility to the structure as a whole. It is natural to think that such reasoning should apply primarily to the GO with silver deposited on the glass surface in an ordered manner, e.g., with using the Langmuir–Blodgett technique. The same technique should optimally suit the structure considered in the model under study. Greater tightness of the electrodes should provide a longer lifetime of the system.Another option for increasing both the graphene actuator efficiency and its lifetime is to ensure a stable adhesion between the graphene electrode and the electrolyte framework. In the actuator based on the ionic polymer-graphene composite (IPGC)  and charOn the contrary, ions easily pass through microcracks in platinum, which arise in the electrodes of classical metal-film actuator, so that these electrodes are sufficiently permeable to water .The production of the IPGC actuator includes vacuum filtration and laser scribing procedures. The GO paper is obtained by vacuum filtration of the GO suspension, and then, the paper is reduced with hydrogen iodide (HI) . Due to Since the inner surface of the laser-cleaned GO is responsible for interaction with the electrolyte, it must be very rough. The properties of this surface were researched in isolated glovebox. The key property under study is wettability, characterized by the contact angle. It can be seen that, in LrGO paper, wetting changes to almost complete non-wetting. X-ray spectroscopy data  indicateNon-permeability of the membrane explains the fact that the water loss rate in the RGO paper is 0.0046 g/h, which is 10 times less than in the GO paper . At the The connection of the graphene electrode with the surface of the ion-conducting membrane, including the polymer framework and the electrolyte, providing a long-term adhesion and discussed above, is achieved thermomechanically. Such a connection is reached by partial diffusion of IL into the lower layers of the graphene electrode under hot pressure conditions. The graphene film, which forms the electrode, is synthesized separately.The optimum conditions of this synthesis include a large number of parameters. Ideally, the film should include well-oriented graphene layers able to move freely parallel to each other. At the same time, this film, synthesized on a solid surface, should be sufficiently free to detach from it. As far as the authors know, the conditions for such synthesis were not researched since .In , an enseTherefore, with a large size dispersion, when acts of collision of a small flake with a large one are frequent, the film tends to irreversible coagulation of flakes.Anyway, manufacturing of the graphene film on a solid-state basis and its transfer to a polymer membrane is a complex technological procedure, which greatly increases the cost of the actuator as a whole. With additional laser treatment to improve the adhesion of the electrode and polymer membrane, an extra difficult procedure is added.Unexpected enough, the effect similar to that induced by rather difficult laser processing was achieved when we used in the membrane the polymer, somewhat different from commonly used Nafion. This is the Russian analogue MF-4SK, which was actually proposed earlier than Nafion. The initial motive for choosing MF-4SK was laboriousness of the hot pressing method for combining the Nafion polymer membrane with the graphene. The study of the MF-4SK material in combination with traditional metal electrodes was described by us in .In the paper  which foTo reduce the graphene from the GO, two methods of chemical reduction were used: in a water bath and in an oil bath. The details of the technology are presented in .As the MF-4SK material had not been previously studied for the actuation problems, we started with pouring GO from dispersion as the simplest technique for covering a surface with the graphene. Previously, by a similar method, we failed to deposit the RGO on Nafion: the adhesion of the resulting film was too low. At the same time, the study of the combination of MF-4SK and metal electrodes revealed that in a number of parameters MF-4SK differs from Nafion significantly.The MF-4SK membrane with a dry thickness of 120 ± 15 μm was pre-soaked in IL for several days. Then, a section on the membrane that seemed optimal was selected, and the partially reduced GO was drop-casted onto the membrane. It is essential that the entire area of the membrane was treated before cutting it into sections of individual actuators of a smaller area. After drying, a repeated coating was performed to ensure the required uniformity of the electrode film. Then the drop-casting procedure was repeated on the second side of the membrane.It is seen that the actuation curve that corresponds the graphene electrode retains its amplitude almost constant in a very wide frequency range from 2–3 to about 12 Hz, in contrast to the IPMC dependencies, which drop drastically to zero with increasing frequency and appear again only at relatively high frequencies of the mechanical resonance. The curve for the Pt/MF-4SK sample with a thickness of 290 μm, not shown in The dependence of the displacement amplitude on the applied voltage at low frequency of 1 Hz  also difExcept actuation characteristics, this simple method enables better uniformity and adhesion of the graphene layer to the polymer surface than to Nafion. The origin of this result is clearly seen from the analysis of the AFM profilograms of the MF-4SK polymer surface in . The maiThis result correlates well with the effect of improving the adhesion when the GO paper electrode is processed with a laser . One canIn order to understand the features of how the MF-4SK/RGO structure operates, we turned to the known experimental trends of this material, which distinguish it from the Nafion. They can be summarized as follows .lch (9.3 nm versus 9.8 nm in the MF-4SK) and size dispersion (2.15 nm versus 2.9 nm in the MF-4SK), if the Gaussian distribution dispersion is understood as the size under which the proportion of chains decreases by the factor e2 ~ 10 times (5.0–13.6 nm in the Nafion and 4.0–15.6 in the MF-4SK) [The Nafion polymer chains have a slightly shorter length  MF-4SK) .The mean size and the size dispersion of the Nafion’s water-filled pores in the water saturated polymer are ~5 nm and ~1.0 nm (5.0 ± 2.0 nm), respectively, and these values depend on the model accepted for the membrane structure. Anyway, the pores are connected by channels that ensure the permeability of the membrane for aqueous solutions, most of the pores being open. The water-filled pores in the MF-4SK have a larger scatter of sizes (5.0 ± 4.0 nm); herewith, the fraction of isolated pores in MF-4SK is much higher.The model developed in  successfExcept the polymer surface roughness, the reduction level of the GO in hydrazine plays a key role in the operation of the actuator, providing the required level of the negative functional groups substitution with amino groups is reached. In , the watIt should be noted that attempts to precipitate the aqueous dispersion of GO, which has already amino-modified (1 mg/mL), was unsuccessful. After the water bath, the aqueous dispersion of the reduced amino-modified GO was destroyed, and the graphene derivatives precipitated.4 ions with significant ionic strength, were analyzed in detail.Considering the operation of actuators with graphene electrodes, it is necessary to mention an alternative class of flexible electrode materials that is competitive with the graphene in terms of price. One of these options is the PEDOT:PSS conductive polymer. In , we analThe results of this research can be summarized as follows. Actuators with the PEDOT:PSS electrode have slight performance advantage at low electrode voltages compared to the noble metal actuators, especially in deionized environments. A similar detailed comparison with the graphene electrodes in the entire set of operation environments and modes has not been performed. However, no significant difference in the efficiency was observed. From the viewpoint of the cost of both the synthesis and the technology of combining electrodes with polymer membranes, the difference was also insignificant. Therefore, one can think that the choice of one or another electrode should be determined then by the characteristics of the environment and additional requirements .sp2-carbon is very low energy transduction efficiency (no more than 1%). This result is a sequence of the fact that the both actuation mechanisms involved in the carbon nanostructure (quantum and electrostatic stretching associated with the diffusion and the adsorption of ions) do not use the material’s own elastic properties.To summarize all the above, a number of nanocarbon materials and conductive polymers ensure steady, long-term operation of the actuator both in air and in liquid medium as the electrode material. They also have sufficiently high amplitude of the actuator displacement and good frequency characteristics. At the same time, in all the works described, the disadvantage of the electrodes based on These properties are realized in graphdiyne, which is a specific carbon form proposed by the authors of ,45,46, asp- and sp2-hybridized carbon atoms. The planar lattice of chains forms a system of triangular pores and possesses by tunable electronic properties. The interaction between the layers is much weaker than the covalent interaction and is similar to interactions between the graphene layers.Graphdiyne layers include hexagonal cells stabilized by binding carbyne-type chains ; i.e., each such layer includes Similar to individual graphene layers, the graphdiyne layers can form graphdiyne nanotubes by twisting from the edge of the “zigzag” or “armchair”-type nanoribbons . ExampleUnlike “classical“ CNTs, graphdiyne tubes have porous surface and can be used for hydrogen energetics as fuel accumulators. The carbon bond lengths in the graphdiyne nanotubes are not the same due to different types of hybridization in the carbon rings and diacetylene bridges.Eg down to 1 eV. Thus, it is natural that they are easier to work than the classical CNTs. With an increase in the graphdiyne tube diameter, ΔEg decreases.From the viewpoint of electronic properties, all the graphdiyne nanotubes are semiconductors with a band gap ΔComing back to the porous 3D structure of the flat graphdiyne layers, it should be noted that the structure suggests the possibility of the ion diffusion either along the layers or between the layers with small barriers.The bridges between the graphdiyne layer rings  can easily form molecular scale alkene-alkyne complexes. This complexation is important for electronics, photovoltaics, the energy storage, and catalysis ,49.Since the graphdiyne is a less known material than the nanotubes and the graphene, we will make some comments on its synthesis technique. Graphdiyne is synthesized on the surface of copper through cross-coupling reactions with hexaethynylbenzene, as shown in In the SEM image, graphdiyne is composed of nanoparticles that aggregate to form a porous hierarchical structure . In contWhen using in the actuators, the graphdiyne is interesting from the viewpoint of the tensions caused by molecular structural changes. This problem is put in , whose lThe assembly diagram and the structure of actuators with graphdiyne electrodes are shown in Herewith, the SEM shows that the adhesion to the electrolyte is very good.Comparative cyclic voltammograms (CV curves) for electrodes with the CNT, graphene, and graphdiyne, which formed the actuators of the same structure, are shown in 4 polyelectrolyte with an electrochemical window of 2.5 V and a scanning rate of 10–100 mV/s have a regular rectangular shape, i.e., exhibit good capacitive behavior. The specific capacity of the actuator with graphdiyne electrodes was 237 F/g at a current density of 1 A/g and a scanning rate of 10 mV/s, which is a value almost five times higher than that of the actuator with CNT electrodes.One can see that the actuator CV curves measured on the PVDF/EMIMBF2/g).It is important that the specific capacity of the actuator remains at a level of 200 F/g, which is inaccessible for the graphene and the CNTs as electrode material, even at a scan rate of 100 mV/s d. The abThe triangular pores and the porosity of the structure allow the ion migration during the charge/discharge process, whereas high specific surface makes the electrode act as an ion reservoir. The combination of these factors guarantees good energy storage.The schematic of the ion movement and bimorph actuator bending is shown in Initially, the cations and anions migrate to the cathode and anode, respectively. Then the cations interact with the graphdiyne structure and transform the alkyne complexes into the alkene ones to change the lengths in the covalent bond network in the cathode. There is no such transformation at the anode, where the anions enter. Unbalanced stretching of the opposite electrodes leads to stretching the cantilever bimorph structure as a whole.With the frequency increase, the actuator displacement amplitude decreases, just as it should be . The Young’s modulus, determined from the tension-load curves in The other fundamental technical results are as follows. The energy density  and the graphene electrodes (1.92 mN) several times.The most significant progress has been made in the energy transduction efficiency. It reached 6%, which is a factor several times higher than that of any actuator material such as piezoceramics, shape memory melts, and magnetostrictive materials.The actuator operated successfully within the range of 0.1–30 Hz for up to 100,000 cycles.The mechanism of how the alkyne complex transforms into the alkene one is described in  on the eActuated by electric voltage, the ions surrounding the graphdiyne site (EMIM cations) are adsorbed onto this site and then coordinated with the alkyne bonds. Due to the presence of an unbound orbital, alkyne bonds are converted into alkene bonds, and the bond length changes. This bond length transformation leads to a change in the size of the covalent bond network. The transition process is reversible and controlled by an external field.The theoretical value of the graphdiyne stretch during the complexation can be estimated from the change in the bond length, which is quite successfully simulated by various applied packages of quantum chemistry. It turned out that the elongation reaches 17%.The energy storage mechanism in the graphdiyne-based electrodes is that numerous alkyne sites of high ionic complexation activity enhance the graphdiyne binding with cations and increase the charge density of the electrodes during both the charge and discharge processes.The technology of the actuator electrodes based on nanocarbon is a promising area in the development of actuators. It allows avoiding the use of expensive noble metals and at the same time partially overcomes the problems of their use. For the electrodes made of graphene, which is the most promising and at the same time the most available nanocarbon material, both the materials of flexible polymer and the media that fills it, giving high response to external signal, have been found.2+ cations. Filling the polymer framework with an ionic liquid instead of the aqueous electrolyte provides weaker response than the aqueous electrolyte, which creates an extensive hydrated shell around the cations.To our opinion, such material, principally corresponding to the Nafion, is its Russian analogue MF-4SK with water filling and substitution of water cations by CuOn the other hand, the MF-4SK material provides good graphene adhesion to the flexible polymer and quite high conductivity of the electrode film even if it is applied from the partially reduced graphene oxide by the simplest method (drop-casting). The functionalization of the graphene with amino groups provides its electrostatic attraction to the negative groups on the Nafion surface. As a high level of this functionalization inevitably decreases the film electrical conductivity, the experiment with an acceptable degree of reduction can be considered a non-trivial result. Further progress in this case could be reached on the way of varying this functionalization. To a lesser extent, this applies to the traditional interelectrode membrane material, Nafion.A number of other methods are known to meet the conflicting properties demanded of actuators. These are based on hot clamping technology and are complemented by various methods  to avoid electrode cracking and drying and to guarantee a long service life. The technology of hot clamping is based on the partial penetration of the polymer deep into the graphene film, which is synthesized on a separate solid surface, then separation from this surface, and transferring to the polymer. Our experience shows that this method, when applied to a water-filled polymer like Nafion, is very challenging.In the case of polymers filled with ionic liquids, it is more successful, but the response of the actuator thus obtained is significantly weaker. Therefore, progress in such systems can be achieved by improving the quality of the film, which provides the maximum possible conductivity.By improving the quality, it seems to increase the size of the flakes and reduce their dispersion in size.In connection with the above, the problem of a clear classification of the graphene material and its properties is urgent. This requirement has been put forward as one of the main ones at graphene conferences of recent years.If we consider that the issue of obtaining sufficiently cheap graphene and its classification has been resolved, graphene can be used to obtain actuators that are cheap to manufacture.In this case, it seems that methods of obtaining actuators for operation in air and in a liquid medium should be separated.The use of graphdiyne-based actuators represents a qualitatively higher level of operational efficiency. At the same time, the method of obtaining the material itself is currently expensive. It can be assumed that the ratio between the use of these two materials can be similar to the use of monocrystalline silicon for obtaining high-efficiency solar cells and polycrystalline silicon for cheap cells with significantly lower efficiency. A further perspective may be the use of hypothetical carbon forms, similar to graphdiyne, but with an even stronger mechanical response to a change in the state of the connecting acetylene chains in them. Such forms can be graphiyne, super diamond, and some others.


Herein, we present a simple, low-cost, and scalable wet etching method for graphene patterning. The technique uses hypochlorite solution combined with ultraviolet light irradiation to rapidly remove unwanted graphene areas from the substrate. Raman spectroscopy, atomic force microscopy, scanning electron microscopy, and optical microscopy results showed that well-patterned graphene with micrometer scale regions was successfully prepared. Furthermore, graphene field effect transistor arrays were fabricated, and the obtained devices exhibited good current–voltage characteristics, with maximum mobility of ~ 1600 cm Graphene has attracted widespread attention for its potential use in the next generation of electronic devices and other fields ranging from biosensors to energy storage systems8. For these applications to be realized, well-defined architectures at micrometer and nanometer scales will need to be determined.Graphene, a one-atom-thick sheet of carbon atoms arranged in a honeycomb-like structure, is the thinnest, strongest, and most conductive material of both electricity and heat9. Bottom-up fabrication includes the spatially selective synthesis of graphene arrays by patterning of catalysts11, or selective decomposition of silicon carbide (SiC) to form graphene arrays12. Selective synthesis methods suffer from a variety of limitations, including the use of harsh synthesis conditions, complicated steps, demanding large-scale preparation, and structural limitations9. By contrast, top-down patterning by etching of designed areas is expected to be an effective strategy. The techniques of photolithography and electron beam lithography combined with dry etching by oxygen or plasma16, reactive ion etching17, helium ion ablation18, and laser ablation20 have been used for patterning graphene on substrates. Results indicate high pattern resolution down to 10 nm, and high alignment accuracy18. However, these dry etching processes suffer from a variety of limitations including high cost due to expensive equipment, and complex or inconvenient processing steps that are time-consuming and difficult to scale up. Additionally, the high power of plasma or ion beams may induce defects in patterned graphene as well as the substrate, which may damage the electronic properties.Various patterning approaches have been proposed, including bottom-up fabrication methods and top-down etching processes involving lithography21. Wet etching also has the advantage of being less damaging to the etched object, which expands the range of its practical applications. However, wet etching methodology has not yet been developed for graphene patterning. It is believed that the stable graphitic structure of graphene makes it difficult to remove or dissolve by chemical agents in solutions.By contrast, wet etching processes are generally simpler, use low-cost equipment, and are easier to scale up for industry production25 and graphene oxide26 could be degraded by hypochlorite, and the degradation rates could be enhanced significantly by combining with ultraviolet (UV) light irradiation. In the present work, we found that sodium hypochlorite (NaClO) could completely degrade monolayer graphene films, which can be used as a wet etchant for graphene patterning. Compared with the dry etching, the wet process is simpler, more affordable, scalable, and easier to control due to the ambient reaction conditions. The patterning process consists of three steps: protection with a gold (Au) cover through convenient electronic beam (EB) evaporation, wet treatment with hypochlorite, and stripping of the Au cover. Using this process, different graphene pattern designs were successfully prepared without damaging the structures, as evidenced by Raman spectra mapping, optical microscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM). Moreover, as a demonstration, graphene field effect transistor (FET) arrays were fabricated, and the obtained devices exhibited good current–voltage characteristics, confirming the feasibility of the developed technique. The results expand our knowledge about the degradation of graphene in solution, and provide a simple and practical method for electronic processing of graphene, which could expand the application potential of this material for use in micro- and nano-electronic devices.Recently, we found that carbon nanotubes (CNTs)2/Si substrate (labeled graphene/substrate hereafter) via a sacrificial copper film. The graphene film had a smooth surface with some lines and dark spot-like areas  was ~ 37 cm-1, and the peak intensity ratio (2D/G) was > 5, which indicated monolayer graphene  solution  was evaluated for patterned graphene arrays by Raman mapping of the D-band peak at 1350 cmTo explore device applications, FET arrays were fabricated as a demonstration. To contact the electronic probes on the patterned graphene arrays obtained using the above process, Au and Cr were deposited on the graphene arrays as electrodes at widths of 60 ± 10 µm; the space between the two electrodes was about 200 ± 10 µm Fig. a and b; ID-VGS) characteristics of the obtained FET was investigated by measurements made using 4-point probes in a vacuum chamber (2 × 10–2 Pa) at room temperature  in addition to NaClO. To explore the effects of the surfactant, we treated graphene films with NaClO solution (~ 6 wt%) with or without addition of AO  instead of bleach solution. The results showed that etching of graphene for patterning was possible through treatment with light/NaClO solution with or without surfactant, but addition of surfactant made the removal faster and more thorough Figure . We beli25.In addition, we found that NaClO at a concentration of 6 wt%  and inexpensive equipment. Moreover, the wet process was easily controllable and scalable because the reaction was performed by simply immersing the graphene/substrate in bleach solution at room temperature followed by UV light irradiation. For successful patterning, it is important to prepare a suitable protective cover, which can be prepared from a noble metal such as Au Fig.  or by us2/Si. The FET devices fabricated herein from the commercially available graphene samples exhibited ambipolar current–voltage characteristics. Although it is necessary to take electrode configuration into account when estimating hole mobility (µh), the highest value obtained herein was ~ 1600 cm2/Vs, confirming the feasibility of our wet etching technique. Notably, the gate voltage at Dirac points (VDirac) and the mobilities for different devices varied from 29 to 31 V and from 400 to 1600 cm2/Vs, respectively. This might be due to the different properties of local original graphene structures and/or interactions with substrates. Although the value of the charge mobility in the graphene FET obtained in this study was not outstanding compared with previous reports36, the results indicate that our wet etching process is applicable to the patterning of graphene for fabrication of electronic devices.In addition, the characteristics of the patterned graphene as well as the electrical properties of the FET are also affected by the quality of the original graphene film, especially regarding defects, layers, and the adherence state of graphene to substrates such as SiO240. It is probable that the degree of graphene coupling to the SiO2 substrate might induce hole doping37. We believe that p-type conduction was not due to the etching process using aqueous NaClO solution. The obtained hole mobilities of monolayer CVD graphene were in the range of reported data, which were calculated from channels of almost the same size40. To ensure good reproducibility, a high-quality and homogeneous graphene structure as well as appropriate adherence to the substrate are extremely important, alongside the patterning process.The p-type properties of these FET devices were consistent with previous reports for monolayer chemical vapor deposition (CVD) graphene on SiOIn conclusion, we found that monolayer graphene could be rapidly and completely eliminated by etching with a household bleach assisted by UV light irradiation. The etching process was simple, cost-efficient, and scalable, which enabled the successful patterning of graphene with various fine-tuned patterns. The FET arrays fabricated as a demonstration exhibited good performance in terms of ambipolar current–voltage characteristics and high hole mobility, indicating the feasibility of the developed wet etching technique. Further improvement in the graphene patterning process may be possible by preparing a high-precision protective cover at sub-micrometer scale, and by developing more appropriate conditions for etching graphene on different substrates. We believe that the wet etching technique proposed herein could be useful for various processes using graphene in electronic applications.2/Si by direct CVD via a sacrificial copper film. Graphene on the SiO2/Si substrate was 1 × 1 cm in size, with a coverage > 95%. The thickness of substrate was ~ 525 µm with a coating of thermal oxide (SiO2) of ~ 300 nm on both wafer sides. NaClO solution used in this study was a household bleach solution  with a NaClO concentration of ~ 6 wt% and AO surfactant (1–5 wt%). This bleach solution was used directly without dilution within 3 months after purchase. Besides the standard bleach solution, NaClO solutions with 1.1 wt%, 2.26 wt%, or 6 wt% were also tested, and were prepared by dissolving NaClO·5H2O powder  in deionized water.Monolayer graphene films with a thickness of ~ 0.345 nm were used as purchased . Films were deposited on SiO2, and the wavelength had a range of 240–550 nm.To investigate the degradation of graphene, the graphene/substrate was immersed in bleach or NaClO solution (~ 5 mL) at room temperature, and then irradiated by a UV light spot (1 cm diameter) using a Lightningcure LC5 light source unit  composed of a Hg-Xe lamp (200 W) and fiber cables. The UV light intensity at 365 nm was ~ 3.5 W/cmThe protective cover was made by decomposition of Au (thickness = 100 nm) on graphene film through a patterned mask using an EW-100S vacuum EB evaporation instrument . Two types of patterned mask were tested: one was a photoresistor polymer assisted by lithography  and 0.4 g I2 (Wako) in 50 mL water. When the yellow pieces of Au cover were floating on the surface, the graphene/substrate was taken out, rinsed three times with deionized water, and dried naturally at room temperature or blown gently using N2 gas.After wet etching, the graphene/substrate samples were immersed in KI/I-1, G-bands at ~ 1590, and D-bands at 1350 cm-1. SEM using an SU8220 instrument  combined with EDS using a 5060FlatQUAD instrument  were employed to assess the structure of patterned graphene, and to investigate the elemental distributions by mapping of carbon and oxygen in the graphene arrays. SEM and EDS measurements were performed at an acceleration voltage of 5 kV and an emission current of 10 µA. AFM images were obtained by a Nanosearch scanning probe microscope combined with an optical/laser microscope .After treatment or patterning, graphene was first evaluated by optical microscopy using a DSX 510 instrument  with 10× and 50× lenses. Images were captured using bright field (BF) mode, and samples were checked by micro Raman spectroscopy . Raman measurements were taken at an excitation wavelength of 532 nm. Raman mapping of patterned graphene was performed by measuring the peak intensities for 2D-bands at ~ 2683 cmPatterned graphene ribbon arrays were selected for preparation of FETs. The drain and source electronic probes were prepared using Cr/Au EB evaporation by an EW-100S vacuum EB evaporation instrument (Eiko Corporation) and a custom-made metal (Ni) mask. Cr and Au were successively deposed at a thickness of ~ 20 and ~ 100 nm, respectively.2 atmosphere (40 Pa) for 2 h to remove residues on the graphene surfaces that may otherwise cause resistance. Samples were then transferred to another vacuum system  for electrical measurements. The devices were heated to 473 K in the chamber before measuring electrical properties to remove any water molecules adhered to the graphene. ID as a function of VGS was measured at room temperature below 2.0 × 10–2 Pa using a standard four-probe technique with a 4200A-SCS semiconductor parameter analyzer . Under a constant drain-source voltage (VDS) of 0.1 V, VGS was swept from -40 to 40 V. The hole mobility was calculated using the following equation:Rs is the sheet resistance of the patterned graphene, e is the elementary charge (1.6 × 1019 C), Cox is the gate insulator capacitance (tSiO2 = 300 nm), and VDirac is the gate voltage at the Dirac point. The mobility at a hole concentration (p) of 2.0 × 1012 cm-2 is discussed in this study.To assess the performance of fabricated graphene FETs, the patterned graphene ribbons with Au/Cr electrodes were thermally treated at 623 K under an HSupplementary Information.


Protozoan predators form an essential component of activated sludge communities that is tightly linked to wastewater treatment efficiency. Nonetheless, very little is known how protozoan predation is channelled via bacterial communities to affect ecosystem functioning. Therefore, we experimentally manipulated protozoan predation pressure in activated-sludge communities to determine its impacts on microbial diversity, composition and putative functionality. Different components of bacterial diversity such as taxa richness, evenness, genetic diversity and beta diversity all responded strongly and positively to high protozoan predation pressure. These responses were non-linear and levelled off at higher levels of predation pressure, supporting predictions of hump-shaped relationships between predation pressure and prey diversity. In contrast to predation intensity, the impact of predator diversity had both positive (taxa richness) and negative (evenness and phylogenetic distinctiveness) effects on bacterial diversity. Furthermore, predation shaped the structure of bacterial communities. Reduction in top-down control negatively affected the majority of taxa that are generally associated with increased treatment efficiency, compromising particularly the potential for nitrogen removal. Consequently, our findings highlight responses of bacterial diversity and community composition as two distinct mechanisms linking protozoan predation with ecosystem functioning in activated sludge communities. The treatment of wastewater using activated sludge communities represents arguably the largest single biotechnological process world-wide . This crThe positive impacts of protozoan predation on ecosystem functioning have been traditionally explained by stimulating effects on bacterial physiology , 10. ForOne link with potentially considerable consequences for ecosystem functioning is the relationship between protozoan predation and bacterial diversity. Diversity is well-known to increase the rate of ecosystem functioning –23 and pK- and opportunistic r-strategists may equally persist at intermediate levels of top-down control  appear to have predominantly negative impacts . SampleIn all experiments, we assessed prey and predator community composition applying a meta-barcoding approach. Additionally, we used flow cytometry to evaluate HNA–LNA ratios of bacteria, which are interpreted as a potential indicator of bacterial cell activity . EnumeraHNF densities and HNA–LNA bacteria ratios were analysed on a BD Accuri C6 automatic flow cytometer  following largely the protocol by Gasol and Morán ; for fur, 515F  in QIIME2 . DNA-polThe effect of dilution on alpha diversity was assessed by comparing ASV richness, ASV evenness (Pielou’s evenness) and genetic diversity measured by the Faith index , after rA community similarity matrix was established based on Bray–Curtis similarity and visualised using non-metric multidimensional scaling . We then applied ANOVA with subsequent Tukey post-hoc tests to evaluate whether (i) communities in the predation or reduced-predation treatments at the end of the experiments were more similar in composition to the starting (inocula) communities and (ii) beta diversity (i.e. dissimilarity among communities) was different among the communities in the start inocula, predation or reduced predation treatments. Non-parametric tests were used when variance-homogeneity could not be achieved through transformation. Finally, we used ordinary least squares regressions to test the effect of HNF densities on prey alpha diversity within treatments  to assess whether this relationship is consistent at low and high predation pressure. Because we were able to measure HNF densities in undiluted samples only, we used the starting HNF densities for these within treatment assessments. We examined whether regression model residuals met the assumptions of normality, equal variances, and were not autocorrelated. All implemented regression models met these requirements. Nonlinearity between dependent and explanatory variables was assessed visually and by comparing models with log-transformed, exponentially-transformed and untransformed independent variables based on the smallest Akaike’s Information Criterion .Finally, we applied two complementary approaches to examine how shifts in bacterial community composition affected their putative functionality. First, we used an automated, taxonomy inferred approach to predict potential functional differences between treatments [METAGENassist ; resultsW > 326, p < 0.001). Yet, overall protozoan taxonomy was not well resolved as 31.1% of ASVs could only be assigned to class level.Experimental predator communities had a mean ASV-richness of 72 ± 28 (SD) and were dominated in richness and relative abundance by ciliates (mainly Peritrichia and Suctoria) and amoeba , evenness  and phylogenetic distinctiveness . Notably, communities with high richness were less sensitive to negative effects of dilution highlighted by their lower loss rates in phylogenetic distinctiveness in diluted microcosms , and only prey evenness was positively associated with HNF densities .We further tested whether predator densities were related to prey diversities within individual dilution treatments Fig. . The denF = 103, p < 0.001), leading to a homogenisation of communities illustrated as drop in beta diversity (Bray-Curtis dissimilarity) from 0.80 to 0.68  = 15.83, p < 0.001). Protozoan beta diversity, however, significantly increased from 0.76 to 0.86 in diluted microcosms .Bacterial beta diversity was strongly influenced by dilution and associated reduction in predation pressure. Bacterial community composition was predominantly driven by differences in inocula, but the composition of bacterial communities also changed over time Fig. . These tt test, t value = 3.8, p = 0.002; Figs. SCanditatus Accumulibacter), Comamonadaceae and Nitrospiraceae families (Table Bacterial communities in all treatments were dominated by Proteobacteria, but experimental dilution shifted dominance from Betaproteobacteriales to Pseudo- and Alteromonadales Fig. . Experimes Table . An excees Table .Fig. 6PhDespite the importance of protozoan predation for maintaining treatment efficiency in activated sludge communities , 4, the Dilution experiments to regulate predator-prey encounter rates are common tools in plankton ecology , 59, butK- and r-strategists, but also emerges from density-dependent predation and from the co-existence of multiple K-strategists with alternative predator-defence mechanisms.Predators themselves have adapted to antipredator defences of their prey  causing However, an increase in predation pressure does not necessarily result in a linear, positive impact on prey diversity , 28. We Positive impacts of diversity on functioning are well supported across ecosystem types and taxonomic groups , 70 and Beta diversity represents another biodiversity component that can improve ecosystem functioning, particularly at larger spatial and temporal scales , 76. We Dilution of microcosms resulted in strong changes in the identity of dominant bacterial ASVs in our experiments. These changes can in principle emerge from reductions in predator-prey encounter rates and predation pressure or from an increased resource supply in diluted communities. Dilution experiments are designed to maintain an equal initial resource availability across treatments , which tNitrospira and Candidatus Accumulibacter [At higher taxonomic levels, ASVs belonging to the same taxon exhibited partly contrasting responses to reduction in predation pressure Fig. . Diverselibacter , 7 increThe overarching goal of many recent studies and research applications is to maximise the positive impacts of bacterial communities on wastewater treatment efficiency , 5, 7. OSupplementary informationAnnex - associated R code


The monolayer character of two-dimensional materials predestines them for application as active layers of sensors. However, their inherent high sensitivity is always accompanied by a low selectivity. Chemical functionalization of two-dimensional materials has emerged as a promising way to overcome the selectivity issues. Here, we demonstrate efficient graphene functionalization with carbohydrate ligands—chitooligomers, which bind proteins of the lectin family with high selectivity. Successful grafting of a chitooligomer library was thoroughly characterized, and glycan binding to wheat germ agglutinin was studied by a series of methods. The results demonstrate that the protein quaternary structure remains intact after binding to the functionalized graphene, and that the lectin can be liberated from the surface by the addition of a binding competitor. The chemoenzymatic assay with a horseradish peroxidase conjugate also confirmed the intact catalytic properties of the enzyme. The present approach thus paves the way towards graphene-based sensors for carbohydrate–lectin binding. Two-dimensional 2D) materials hold a great potential for application as the active layers of sensors due to their strict monolayer character. Graphene, the epitomical example of a 2D family of materials, can achieve sensitivity down to single atoms under particular conditions . HoweverD materiaLectins are a broad family of proteins ,5, featuMonolayer graphene functionalized with specific carbohydrate ligands can serve as a suitable active sensing layer for detecting lectin activity . When plN-acetylglucosamine (GlcNAc) chitooligomers of varying lengths. WGA is a 34 kDa homodimeric lectin with a total of eight carbohydrate binding sites [In this work, we demonstrate the specific binding of wheat germ agglutinin (WGA) to monolayer graphene covalently functionalized with ng sites , which fng sites  to charang sites  and, theGlcNAc units , prepared chemically [d-glucopyranosyl-(1→4)-2-acetamido-2-deoxy-β-d-glucopyranoside (di-GlcNAc), 2-azidoethyl 2-acetamido-2-deoxy-β-d-glucopyranosyl-(1→4)-2-acetamido-2-deoxy-β-d-glucopyranosyl-(1→4)-2-acetamido-2-deoxy-β-d-glucopyranoside (tri-GlcNAc), 2-azidoethyl 2-acetamido-2-deoxy-β-d-glucopyranosyl-(1→4)-2-acetamido-2-deoxy-β-d-glucopyranosyl-(1→4)-2-acetamido-2-deoxy-β-d-glucopyranosyl-(1→4)-2-acetamido-2-deoxy-β-d-glucopyranoside (tetra-GlcNAc), and 2-azidoethyl 2-acetamido-2-deoxy-β-d-glucopyranosyl-(1→4)-2-acetamido-2-deoxy-β-d-glucopyranosyl-(1→4)-2-acetamido-2-deoxy-β-d-glucopyranosyl-(1→4)-2-acetamido-2-deoxy-β-d-glucopyranosyl-(1→4)-2-acetamido-2-deoxy-β-d-glucopyranoside (penta-GlcNAc) were then prepared by transglycosylation reaction based on a previously reported procedure [mono- to penta-GlcNAc are fully in accordance with the literature [For the preparation of 2-azidoethyl-functionalized chitooligosaccharides composed of β(1→4)-bound Ac units , we usedeviously . In thisemically , was userocedure . The strterature .2 layer by the copper etching/polymer-assisted method, and fluorinated as described earlier [N,N-dimethylformamide at room temperature for two hours and then washed with a large excess of methanol.Graphene was synthesized by the chemical vapor deposition method on a copper foil, transferred onto silicon chips with a 300 nm-thick SiO earlier ,27. The GlcNAc-O-EtN3 ligand (2 mg) was dissolved in CuSO4 solution  and mixed with sodium ascorbate solution , and tris(3-hydroxypropyltriazolylmethyl)amine solution —all aqueous. This mixture was dropped onto the propargylated graphene chip  and reacted at room temperature. After 30 min, an additional 50 µL of 20 mM sodium ascorbate solution was dropped onto each chip and reacted for an additional 90 min. All samples were then thoroughly washed with deionized water and air dried.Triticum vulgaris, Sigma-Aldrich, St. Louis, MI, USA) was dissolved in phosphate-buffered saline (PBS) at an approximate concentration of 1 mg/mL, and 100 µL of this solution was dropped onto each chip (ca 1 × 1 cm2). Incubation was performed at room temperature for 2 h, and the samples were then washed with PBS buffer. Competitive unbinding of WGA was performed using GlcNAc solutions of defined concentrations in PBS at room temperature for 2 h followed by washing with PBS and deionized water.Wheat germ agglutinin  after incubation with WGA in PBS showed a uniform layer thickness of 5–6 nm, which is the estimated size of the 34 kDa globular WGA protein. These results thus support the hypothesis that chitooligomer ligands on graphene bind to WGA binding sites and also rule out the possibility of multiple-layer non-specific aggregation. The summary of CA and AFM data is provided in The process of graphene functionalization was monitored after each step by several methods in order to unambiguously prove the successful grafting of the desired species according to the designed scheme. Graphene on the Si/SiOrophilic ,33, with−1, CH2 deformation at 1473 cm−1, C–H and C–OH deformation at 1128 cm−1, and anomeric C–H deformation at 866 cm−1  using sinapinic acid as the matrix. Functionalized graphene samples after incubation with either WGA and the reference WGA stock solution, deposited on silicon chips, both provided three dominant peaks at 8.5, 17.1, and 34.3 kDa a. The hiThe MALDI results were further corroborated by fluorescence imaging. FITC-labeled WGA was incubated with functionalized graphene samples deposited on glass coverslips, excited using the 488 nm laser, and detected on a sensitive EM-CCD camera. Specific binding of FITC-WGA to GlcNAc-functionalized graphene was clearly detectable at the graphene edge as an intense contrast line b. Finall−8 M, the layer thickness suddenly dropped to values corresponding to the functionalized graphene without WGA. The physical nature of AFM measurement did not allow us to obtain experimental points in the descending slope of the sigmoidal curve. The experimental data were fitted with the Hill function with a fixed Hill coefficient of 1.75 (positive cooperative binding) based on previous studies37 and provided dissociation constants of 7.3 × 10−9 and 3.4 × 10−8 M for mono- and di-GlcNAc-functionalized graphene, respectively. For tri-GlcNAc and longer chitooligomers grafted on graphene, the competition with mono-GlcNAc did not proceed even at high competitor concentrations (10−3 M GlcNAc), indicating that mono-GlcNAc is not an efficient competitor for tri- and longer chitooligomers immobilized on the graphene surface.An important feature of carbohydrate binding to lectins is the previously shown affinity increase  by approN-acetylglucosamine chitooligomers of varying lengths. Chitooligomers feature a high affinity for wheat germ agglutinin, a homodimeric lectin with eight carbohydrate binding sites. The successful functionalization of the graphene surface was confirmed by a set of complementary techniques including Raman, AFM, CA, SERS, fluorescence microscopy, and mass spectrometry. The critical issue of the binding specificity between lectin and chitooligomer ligands exposed on the graphene surface was investigated in a competitive binding assay using AFM as the monitoring technique. The extensive characterization consistently proved the mechanism of graphene functionalization and the specific binding of WGA to the carbohydrates grafted on the functionalized graphene. This study thus paves the way towards specific sensors for the quantitative determination of lectins, in diverse solutes, produced by industry or the natural environment.Monolayer graphene was functionalized with β(1-4)-linked


The aging in air inevitably results in the accumulation of airborne hydrocarbon contaminations on a graphene surface, which causes considerable difficulties in the subsequent application of graphene. Herein, we report an electron-beam-activated fluorination/defluorination cycle for achieving a long-term preservation of CVD graphene. After experiencing such cycle, the accumulation of airborne hydrocarbon on the graphene surfaces is strongly reduced, and the initial chemical status of graphene can be restored, which is confirmed by employing atomic force microscopy and X-ray photoelectron microscopy. Our reported approach provides an efficient method for the cleaning and long-term preservation of graphene, and it is particularly useful for graphene microscopy characterizations. To acer input .The typier input . The anner input . Moreoveer input  has prop2/Si substrate with a SiO2 thickness of 300 nm using a polymer-assisted wet chemistry method. The as-transferred graphene is then cleaned by applying a solvent (isopropanol/H2O for 2 min at room temperature) mixture treatment to effectively remove the polymer residues on the surface. The back-gated graphene devices are fabricated through standard electron beam lithography (EBL) in a Nanobeam nB5 EBL system, oxygen plasma etching in an Advanced Vacuum Vision 320 Reactive Ion Etching (RIE) system, and metal deposition in a Lesker PVD 75 system .The chemical vapor deposition of graphene on synthesized Cu foil is transferred onto a SiO−6 mbar under an electron acceleration voltage of 5 kV. The fluorination is carried out by the irradiation of graphene with an electron beam for 300 s with a size of 100 µm × 100 µm, while simultaneously injecting the XeF2 via GIS system in FIB . For the defluorination process, electron beam irradiation is carried out without gas injection for 100 min.Graphene samples are kept under ambient condition with a temperature of 20 ± 1 °C and a relative humidity of 45 ± 3% for aging. The electron-beam-activated fluorination of graphene is conducted in a FEI Strata DB235 FIB/SEM  at a vacuum condition of 10Raman and X-ray photoelectron spectra are acquired in Renishaw inVia Raman spectrometer , with a 532 nm excitation laser, and Physical Electronics Quantera II  Scanning XPS Microprobe monochrome Al Kα radiation (1486.7 eV), with a 45° angle of electron emission, respectively. The electrical measurements of the graphene back-gated devices are carried out using an Agilent B1500 semiconductor parameter analyzer  inside a Faraday cage with metal probes.2/Si substrate following a solvent mixture cleaning  to minimize the contamination from the polymer residues during transferring. 3 C peak located at 284.8 eV and the sp2 C peak located at 284.0 eV. The initial larger intensity of the sp2 peak can be mainly attributed to the intrinsic sp2 hybridization of graphene, whereas the sp3 bonds are contributed by the defects, polymer residues, and hydrocarbon. As the aging process is underway, the concentration of sp2 drops from 69.3% to 28.7%, while the sp3 bonds continuously increase, and this is mainly attributed to the accumulation of airborne contaminations on the graphene surface. Moreover, we have observed a considerable C–O peak located at 286.1 eV after 10 days of aging which can also be ascribed to the oxygen-containing contaminations coming from the air. The graphene samples are synthesized by chemical vapor deposition (CVD) at a large scale and subsequently transferred onto a SiO2 gas. After the aging experiment of the as-fluorinated sample in the air, the fluorinated graphene is again exposed to the electron beam without precursor gas to perform the defluorination process . The C1s XPS spectra of graphene at different steps of the fluorination/aging/defluorination cycle are shown in 2 signal located at 284.4 eV, and after fluorination there are 4 main components in the spectrum: the sp3 peak (284.8 eV), C–F peak (287.4 eV and 289.2 eV), C–F2 peak (290.0 eV) and C–F3 peak (292.0 eV). The absence of sp2 suggests the saturated fluorination of graphene. 2 signal, and the sp3 intensity is relatively low, similarly to that of the initial graphene sample. In order to confirm the reproducibility of this result, more C1s XPS spectra with corresponding AFM images of defluorinated graphene under the same process have been shown in To further investigate the evolution of the surface status of graphene during the fluorination/defluorination cycle, we have carried out an AFM analysis on the graphene surface at different processing steps, shown by 3 bonds Csp3 and C–F bonds CF with different aging time are shown in sp3 slightly and linearly increases from 60.2 ± 5.1% to 72.6 ± 3.5%, whereas CF drops accordingly with time increases. This result indicates the stability of fluorographene during aging, and it provides further proof of the hydrocarbon accumulation even on the fluorinated surface during aging.As the accumulation of hydrocarbon will inevitably happen on the fluorinated graphene, the concentrations of sp−1) besides the intrinsic G peak (located at 1580 cm−1) and 2D peak (located at 2690 cm−1), indicating the introduction of disordering after defluorination. Moreover, the broadening of the 2D peak also suggests the structural changes in graphene. This disordering can be mainly attributed to the damage from electron beam irradiation [2 V−1 S−1 to 233 cm2 V−1 S−1. The substantial drop in conductivity and mobility has further provided the evidence of the disordering after electron beam irradiation during defluorination. As the transport behavior of graphene can be mainly affected by the grain boundaries [In order to investigate the effect of the fluorination/defluorination cycle on graphene properties, the Raman spectroscopy and gated measurements have been carried out. adiation ,22. Figu2 signal dropping from 66.1% to 26.2%. We have demonstrated that by implementing the electron-beam-activated fluorination/defluorination cycle, the hydrocarbon accumulation can be eliminated, which restores the initial chemical status of graphene before fluorination. Moreover, we show that after the defluorination cycle the disordering is introduced due to the electron beam irradiation with an emerging D peak in Raman spectra and the degradation of mobility in gated measurements.In conclusion, we have reported a novel technique for achieving a long-term preservation of supported graphene by using an electron-beam-activated fluorination/defluorination cycle. In this research, the accumulation of hydrocarbon on CVD graphene due to the aging in the air has been observed and characterized by an XPS analysis, with the concentration of the sp