The relative differentiation of attenuations (RDA) in presence of relative humidity (RH) is measured by Optical Loss Test Set at two standard-wavelengths-telecommunication (1310 nm and 1550 nm). Results show that the etched single-mode fiber (ESMF) coated with G/GO has relatively high and one by one function for RDA versus RH (more than 30%). Also, its sensitivity and variance are reasonable. The MoSe2 based sensor is applicable at humidity below 30% because of higher RDA. However, it is not useful at humidity more than 30% due to the absence of one by one function for RDA versus RH. Besides, ESMF coated with MoS2 has indistinctive behavior and is not useful as a humidity sensor.In this investigation, etched-fibers are coated by 2D layers such as Molybdenum disulfide (MoS However, optical fiber sensors can be used to measuring different physical properties, such as measurements of RI, strain3, temperature5, and humidity10. The mechanism of these sensors is very dependent on changes in the refractive index4. Usually, these sensors are made by modifying the geometry of optical fiber such as side-polished fiber, a long period fiber grating (LPG), and hollow-core fiber sensors that are very complicated13. Recently, in order to improve the sensing properties, coating of optical fibers by nanomaterials has been used.Sensors based on optical fibers have a key role in industrial, biomedical, and home security purposes. The great advantages of optical sensors such as high speed, insensitive to electromagnetic interference, anti-explosion, small size, low weight, durable and chemically inert, and low transmission make them practical and affordable16. In addition, the ability to absorb water molecules depends on the surface’s functional groups of 2D materials. Electrical gap and consequently refractive index changes with bonding between the water molecule and surface of coated optical fiber.The humidity sensor is one of the most widely used sensors. So far, extensive researches have been done on the optical humidity sensors due to their advantages. However, the very low permeability of the protective layer and clad of fiber to the vapor leads to slight changes in the refractive index and so very poor sensitivity and non-linearity response. Researchers used physical and chemical changes on the external surface of optical fiber to improve humidity sensing. Especially, coating of two dimensional (2D) materials have attracted great attention in high-sensitive sensors due to their high surface to volume ratio and other intrinsic properties23. Among other applications, the exceptional surface to volume ratio and high electron mobility in room temperature entitles G as a promising candidate for sensing applications24. Usually, in the synthesis process, different functional groups create on the surface of G and change its properties. Oxygen functional groups such as hydroxyl, carboxyl, epoxide, and carbonyl are the main functional groups that convert graphene to graphene oxide (GO). Presence of these groups increases surface and interlayer adsorption of water molecules through the polar bonding25.Graphene (G), as the first experimental 2D materials, has attracted a wide range of interest due to its fascinating electronic, mechanical, and thermal properties such as extremely high carrier mobility, mechanical flexibility, optical transparency, and chemical stability27, others have preferred graphene oxide because of its hydrophilic property and changes in its refractive index by adsorption of water molecules between its layers30. It seems that by use of G and GO simultaneously, make it possible to use the benefit of both them in humidity sensing based on optical fiber which has not been studied until now.Different humidity sensors based on optical fiber with different geometrical shape coated with G or GO have been investigated. Although some groups have used humidity sensors based on fiber optic with reduced graphene coating due to changes in carrier density by variations of relative humidity32. The monolayer of Molybdenum Disulfide (MoS2) and Molybdenum Diselenide (MoSe2) is an outstanding example, in which molybdenum atoms are sandwiched between two layers of Sulfur and Selenium atoms respectively. The humidity sensor based on the side-polished optical fiber coated with these nanosheets have been investigated at 1550 nm wavelength35. The use of mechanical polishing method results in insertion loss of the side-polished fiber and smoothness of edges is difficult.Also, the layered transition metal dichalcogenides (TMD) materials—a new family of 2D materials have attracted huge attention due to tunable direct band gap, high mobility, low-level toxicity, and large surface areaHowever, chemical polishing methods have preserved the cylindrical shape of the optical fiber and is much simpler and more practical than other methods. As far as we have researched, so far the optical fibers that have been chemically thinned and layered with 2D materials have not been applied as humidity sensor.2 and MoSe2 on the etched-SMF (ESMF) are used to investigate the humidity sensing properties of optical fiber. So, at first G/GO, MoS2 and MoSe2 are synthesized and qualified by Scanning Electron microscopy (SEM), Transmission Electron Microscopy (TEM), Energy-Dispersive X-ray spectroscopy (EDX), Raman, FTIR (Fourier-transform infrared spectroscopy) and XRD (X-ray Diffraction) analysis. Then, etched-SMFs are coated by synthesized 2D materials. In the end, the relative differentiation of attenuation (RDA), repeatability, sensitivity, and variance versus relative humidity (RH) at two standard- wavelengths- telecommunication (1310 nm and 1550 nm) are measured.In this study, for the first time, chemical etching the surface of single-mode optical fiber (SMF) by hydrofluoric acid (HF) as a simple polish method and coating 2D materials such as the composition of G and GO (G/GO) to use the advantage of both them, MoSAlso, the behavior of the introduced humidity sensor has been analyzed based on the surface functional groups and the semiconductor type (n-type or p-type) of the coated 2D materials on the ESMF. We have not found this type of analysis in the field of humidity sensing by fiber optic as far as we have studied.2, and MoS2) to achieve desirable evanescence field. The Optical Loss Test Set (OLTS) as an analyzer  and Optical power meter (OPM)) was used to measure RDA versus RH.In this research, SMF is used as the main part of the optical-humidity sensor. To modify the sensing, the diameter of SMF reduced by corroding it in HF acid and layered with 2D materials . The G and D bands correspond to the presence of sp2 carbon-type structures within the sample, and defects in the hexagonal structure of graphite respectively  groups41.The presence of C–O, C=O and C–H bands at 1020, 1624 and 2,923 cm42.The XRD of G/GO sheets Fig. f illustr2 was down by Solvothermal method24 in normal ambient environmental conditions. In this method Se powder, Na2MoO4, distilled water, and Hydrazine Hydrate are mixed in a container. The materials are stirred constantly and heated with rate The synthesis of MoSeAfter water evaporation by kept the solution in oven at 60 ℃ for 45 min, the residual powder was washed with water and ethanol 3 times and again was kept in oven at 60 ℃ for 10 h until all the water was evaporated and the dark powder was left.2 powder in water, the obtained powder is stirred in alcohol for 12 h, dried in the environmental conditions and finally, 5mgr of it dispersed in 10 cc distilled water and sonicates to separate individual layers.To easy distribution of MoSe2 is achieved after centrifugation at 6000 rpm for 3 h. The quality of MoSe2 layers is investigated by TEM, SEM, EDX, Raman, FTIR and XRD analysis.The transparent liquid above sediments that contain few/mono-layer of MoSe2 by SEM and TEM images. The few-layer structure of MoSe2 is seen in these pictures. Figure 2 by EDX.Figure −1) and 290 (cm−1) approximately that correspond to off-plane links (A1g) and intramolecular links (E2g) respectively34.The Raman spectrum in Fig. −1), 992 (cm−1) and 1137 (cm−1) valleys are related to Mo–O, Mo=O and Se–O bonding respectively43.Figure 2, respectively45.Figure 2 sheets synthesis by chemical exfoliation method. In this method, MoS2 was dispersed in a mixture of ethanol and water with 45% and 55% volume ratio. After stirring the composition for 10 min, it was sonicated for 12 h in 40 Hz frequency to separate MoS2 sheets from each other. The quality of MoS2 layers is investigated by TEM, SEM, EDX, Raman, FTIR, and XRD analysis , and the out-of-plane A1g (~ 405 cm-1). E2g mode corresponds to the Mo and S atoms vibrating in one direction, while A1g mode is due to the Sulfur atoms vibrating25. The difference between these two modes (~ 24 cm-1) can be used as a reliable identification for few-layers MoS246.The SEM and TEM images show the microstructure of synthesized MoS2 Fig. b and indrum Fig. c. The Rayer Fig. d exhibit−1 respectively. The appearance of a spread peak in the region of 3287 is related to the tensile vibration of OH groups47.The FTIR spectrum Fig. e shows t2 sheets in Fig. 2 single layer by d-spacing of 6.3 nm. Other peaks are characteristic of crystalline nature of MoS2 materials48.The XRD of MoSIn this research, SMF is used as the main part of the optical-humidity sensor. To modify the sensing, the diameter of SMF reduces from 34.45 µm by corrosion. For this purpose, 3 cm of the protective layer of SMF was stripped and wiped up with alcohol, then put it in HF acid for 60 min. The process etched some of the clad-layer on the core of SMF to achieve the desirable evanescence field. Figure 2 and MoSe2. These solutions are prepared by adding 5 mg of synthesized powders to 10 cc Distilled water separately, sonicating for 2 h, and centrifuging. The SEM images of ESMF coated with G/GO, MoSe2 and MoS2 illustrate in Fig. In order to make more changes in the refractive index by water absorption, 2D materials have deposited on the surface of ESMF by dip coating in transparent solution contain one or few layers of G/GO, MoSThe OPS and OPM are used as OLTS to analyze RDA, repeatability, sensitivity, and variance versus RH. To create the RH in the range of 20–90% in 25 ∘C, we used a cloud chamber consist of humidifier, humidity control box, temperature controller, and standard humidity sensor as shown in Fig. 2 has zero RDA at RH below 30% and at higher RH has lower RDA relative to ESMFs coated with MoSe2 and G/GO. So it cannot use as an efficient humidity sensor. Unlike it, the ESMF coated with MoSe2 has very good humidity sensing at low RH up to 30%. However, the humidity sensor based on MoSe2 is not applicable at medium and high RH due to the lake of the one-to-one function of RH. The ESMF coated with G/GO has high RDA, especially at RH higher than 40%, and also its RDA has the one-to-one function of RH.RDAs as a function of RH for ESMF with different coatings are illustrated in Fig. g). According to the Penn model, Eg are inversely correlated to refractive index49.The optical humidity sensing mechanism of coated ESMF is related to variation of refractive index by bonding between water molecules and the surface of 2D materials. This physical interaction changes the density of carriers in 2D materials coated on the ESMF and results in the variation of electronic gap energy  coted ESMF at RH more than 30% (60%) increases and has more magnitude in 1550 nm wavelength relative to 1330 nm wavelength. While, MoSe2 coated ESMF has very low sensitivity at both wavelengths.Sensitivity has defined as a ratio between the differential of the output signal and measured properties (humidity), variance for the investigated sensor is small in the RHs less than 40%. In addition, variance is so little in 1310 nm wavelength than 1550 nm. So, results obtained from the humidity sensor based on etched-fiber coated with G/GO have better accuracy at low humidity and 1310 nm wavelength.Variances of any test from the average value are plotted in Fig. 2, and MoS2 to application as humidity sensing are prepared. The RDA, repeatability, sensitivity, and variance analyzes are investigated versus RH at both standards wavelengths of telecommunication (1310 nm and 1550 nm). Results show that the sample coated with MoSe2 has higher RDA at low humidity (less than 30%). So it can be used as a low humidity sensor. However, the sensor based on MoSe2 is not practical at humidity more than 30% due to low and lake of the one-to-one function of RDA versus RH. The ESMF coated by MoS2 has indistinctive behavior by variation of RH because of n-type and p-type impurities on the surface of MoS2. The best humidity sensor, in this research, is the ESMF that coated by G/GO. It has partially high and one by one function RDA versus RH. The sensitivity for it is reasonable and the low variance shows its accuracy. Also, repeatability can modify by thermal treatment.In this research, ESMF that coated by G/GO, MoSe


Light is one of the most important environmental filters for forest understory grass communities. It is predicted that light can select species with the same light requirements, resulting in a decrease in species compositional dissimilarity among grass communities experiencing the same light intensity, and an increase in community dissimilarity under variable light intensities. However, these predictions have been questioned recently in light of modern coexistence theories, and evidence for them in natural communities is often indistinguishable from patterns created by dispersal limitation and biotic interactions. To help fill this gap, we sampled 48 understory grass communities that had regenerated from the same soil seed bank in Southern China. Plots were established under a light intensity gradient. Changes in species composition and neighborhood densities were monitored over a growing season. Our experimental setup controls for bias from dispersal limitation and is useful for detecting the effects of biotic interactions at different intensities of light. As expected, (1) compositional dissimilarity of grass communities increased between communities with different light intensities. The extent to which communities became more dissimilar was positively correlated with the difference in the light intensity. (2) No significant change in compositional dissimilarity was observed among communities experiencing the same light intensity. (3) Finally, relative neighborhood density significantly decreased in communities with moderate to high shading treatments. Our results clearly show that light can drive compositional divergence among communities under different light densities. However, the light may not lead to convergence among communities experiencing the same low light intensity, because intense competition induced by low light might enlarge species compositional differences, as shown with the neighborhood density analysis. Therefore, our study provides more convincing evidence for the importance of light on understory grass communities in subtropical forests and highlights the need to jointly consider biotic interactions when testing for evidence for environmental filtering. One of the most pervasive concepts in community ecology is the metaphor of environmental filter, which refers to abiotic factors that prevent the establishment or persistence of species in a particular location . This fiTwo distinct methods were proposed for rigorously testing the effects of light on plant communities. The first advocates for the use of experimental manipulations that control for the different confounding processes influencing community assembly . For insvia death and establishment of individuals, but it does not modify the relative magnitudes of neighborhood densities at different neighborhood scales. Therefore, scale-independent changes in neighborhood density will be observed under pure environmental filtering  community compositional dissimilarity will increase among communities with distinct shading treatments, and the extent of the increase will be positively correlated with the magnitude of the difference in light intensity; ii) community compositional dissimilarity will decrease among communities experiencing the same shading treatment; and iii) changes in community compositional dissimilarities may be reduced or enhanced depending on the strength of the biotic interactions revealed by the changes of relative neighborhood densities.The study was conducted within the Heishiding Nature Reserve in Guangdong Province, Southern China . The reserve consists primarily of typical subtropical evergreen broadleaved forest, with a total area of 4,200 ha. The mean annual temperature of the reserve is 19.6°C, and the mean monthly temperature ranges from 10.6°C in January to 28.4°C in July. Annual precipitation is 1,740 mm, and precipitation mainly occurs between April and September. Elevation ranges from 150 to 927 m above sea level .Ageratum conyzoides, a common grass species. In March 2012, all of the grass was cut and removed; then we tilled the soil to 30 cm depth and removed large root balls from the soil. During the next 7 days, the topsoil  of the field was removed and replaced by surface soil randomly collected from the nearby forest . The transplanted soil thus functioned as a large seed bank of mostly native understory grass species in the region. The surface soil replacement also enabled us to maximally isolate the potential bias of dispersal limitation from the light. Before transplanting, the collected soil was first homogenized by thoroughly mixing all samples. The whole field was then divided into 48 plots , a typical illumination intensity in the understory of the subtropical forest communities in the region  among plots and subplots were used to test our first two expectations. For any two grass communities j and k we define j and k at time t1 and t2. The advantage of this index is its low sensitivity to extreme values in the data , which is defined as the expected number of individuals within a ring with radius r centered at a specific individual. The density is then standardized by dividing by the square of the mean point density in the plot (t1(r)] and end [pcft2(r)] of the grass communities for each plot. The effect of biotic interactions during the experiment can thus be quantified as Δpcf(r)=pcft2(r)-pcft1(r). A 95% confidence interval of Δpcf(r) was calculated from the 12 replicates for each shading treatment. If the whole interval of Δpcf(r) is below or above zero, negative  and positive  species interactions were assumed to be responsible for such changes in relative neighborhood density.The scale dependence of relative changes in neighborhood density was used to approximately detect the effect of biotic interactions on our grass communities. Here, the relative neighborhood densities of each plot were quantified using the pair correlation function, pcf . Thus, tOur results highlight the importance of considering biotic interactions in studies of abiotic filtering, particularly at local scales. Biotic interactions may intensify the effects of abiotic filtering among different abiotic conditions, and they can also weaken the abiotic filter under similar abiotic environments. Therefore, abiotic filtering and biotic interactions are not independent ecological processes but are internally related to each other at local scales . Any effIn summary, our experiment shows that the species composition of understory grass communities will diverge under different intensities of light, but that they will not always converge in communities experiencing the same light intensities. This inconsistency may be attributed to the expectation that shading intensifies competition among grass species. Therefore, jointly considering both abiotic filtering and biotic interactions is necessary to fully understand and precisely project understory gass communities at local scales and under future climate change scenarios.The datasets generated for this study are available on request to the corresponding author.GS, ST, and BL designed and performed the experiment. XS, YC, and GS analyzed the data. All authors contributed to the article and approved the submitted version.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.


Achieving structural superlubricity in graphitic samples of macroscale size is particularly challenging due to difficulties in sliding large contact areas of commensurate stacking domains. Here, we show the presence of macroscale structural superlubricity between two randomly stacked graphene layers produced by both mechanical exfoliation and chemical vapour deposition. By measuring the shifts of Raman peaks under strain we estimate the values of frictional interlayer shear stress (ILSS) in the superlubricity regime  under ambient conditions. The random incommensurate stacking, the presence of wrinkles and the mismatch in the lattice constant between two graphene layers induced by the tensile strain differential are considered responsible for the facile shearing at the macroscale. Furthermore, molecular dynamic simulations show that the stick-slip behaviour does not hold for incommensurate chiral shearing directions for which the ILSS decreases substantially, supporting the experimental observations. Our results pave the way for overcoming several limitations in achieving macroscale superlubricity using graphene. Superlubricity in macro-scale graphitic samples is hampered by commensurate stacking domains that prevent facile sliding between adjacent graphene layers. Here, the authors show the presence of macroscale structural superlubricity between two randomly stacked graphene layers produced by both mechanical exfoliation and CVD upon the imposition of a tensile stress. This weak interlayer coupling significantly affects the properties of multi-layers. From the mechanics point of view, the in-plane tensile fracture strength tends to decrease with the increase in thickness2, and recent experiments have also shown a decrease in the in-plane compressive strength as a result of premature cohesive shear failure3. Experiments performed using friction force microscopy (FFM) by shearing an atomic force microscopy (AFM) tip over the surface of 2D crystals (graphene and hBN) with various numbers of layers in thickness, have indicated that 2D materials possess thickness-dependent friction properties; for graphene, the friction has been found to increase with the decrease in thickness4. Due to its significance for the use of graphitic materials as lubricants in a number of applications, the friction behaviour of graphene11 and graphite15 has been the subject of extensive research.Two-dimensional (2D) layered solids such as graphite comprise single layers held together via van der Waals forces and possess extraordinary mechanical properties16. Structural superlubricity can occur between two solid surfaces of crystalline nature when they are stacked in an incommensurate configuration. This is also manifested by the mismatch of their lattice constants, as for example in the case of graphene and hexagonal boron nitride17. In fact, there are a number of factors that affect the shear behaviour of graphite and consequently the friction, such as the dimensions of the test specimen and the shearing direction of the graphene layers in respect to each other16. For graphite flakes with large dimensions (>10 μm), the interlayer shear strength tends to increase, and the lubricant behaviour does not hold because of the presence of many commensurately stacked domains in the large contact areas that cause mechanical interlocking between the individual layers16. Recently, it was reported that superlubricity can be achieved at the micron scale when hexagonal boron nitride is sheared over graphite; these 2D crystals have an intrinsic lattice constant mismatch that favours sliding for all directions18. Lubricant behaviour has also been observed for single-layer graphene, even at the macroscale, when sliding a surface coated with graphene against another surface with diamond like carbon and nanodiamond particles, which makes graphene a very versatile, thin and transparent coating material for use in a variety of applications19. To date, the experimental approach for studying interlayer shear behaviour involves sliding an AFM tip over the sample. To our knowledge, measurements with large contact areas and macroscale observation of superlubric behaviour in graphene has not been done as yet, and has been accomplished only for carbon nanotubes (CNTs)20. Another issue that plays a crucial role in the lubricant properties of graphene and graphite is the presence of water. Recent studies show that high relative humidity enhances the lubricant behaviour of graphene on SiO221, and also water can be intercalated between two graphene layers and affects the interlayer interactions22.Graphite is a well-known solid lubricant, a property that originates from the low interlayer shear strength between individual graphene layers23 stacking in contrast to the composition of four subpeaks of a Bernal-stacked (AB) bilayer24. The specimens are subjected to tensile strain on flexed beams under a Raman microscope as explained previously26. The top single layer is selected to be smaller than the bottom layer in such a way that it is not in contact with the polymer, and therefore is stretched only by the strain transferred solely by the bottom layer. In fact, the different levels of strain in the two layers lead to 2D peak splitting that allows the monitoring of strain applied on each layer and the estimation of interlayer shear stress using continuum theory. On the contrary, the 2D peak of an AB-stacked bilayer shifts as one unit under strain27. As argued herein, the measured range of shear stresses (which are relaxed/reduced during sliding) indicates a superlubric behaviour. This behaviour persists macroscopically since the CVD information is collected from an extensive contact area in the range of mm2, which is much larger than in any previously reported works. Molecular dynamic (MD) simulations are also performed to further elucidate the experimental findings. Specifically, we examine the effect of wrinkles and shearing direction on the ISS of bilayer graphene. The wrinkles tend to decrease the ISS between the graphene layers, while shearing in incommensurate chiral directions breaks the stick-slip behaviour accompanied with a dramatic decrease in ISS.Herein, we report direct measurements of the interlayer shear stress in incommensurately stacked bilayer graphenes produced both by mechanical exfoliation of graphite and chemical vapour deposition (CVD) synthesis, simply supported on a polymer substrate. As each specimen consists of two randomly overlapping monolayers, its 2D Raman peak is a single peak indicating AA29 is approximately four times higher than that expected from a single layer due to the changes induced to the double-resonance process compared with a single layer. Additional differences are also recorded/identified, such as the decrease in the full width at half maximum (FWHM) and the shift to a higher-frequency value for the sample at rest . The two-layer graphene was formed by mechanically folding a single layer during deposition. In Fig. est Fig. . The und−1 %−1 that compares well with the value of ~−48.7 cm−1 %−1 obtained from the single-layer area as expected30. The small difference noted in the shift rate for the bottom graphene is because the average shift obtained from the folded area is somewhat reduced by the build-up from the edges  and between graphene/graphene as interlayer shear stress (ILSS). We observe that the strain profile of the top graphene layer follows a similar pattern, as the predominant mechanism here is also shearing, but in this case between the two individual graphene layers. The edge on the right  than the bottom graphene layer that is in contact with the polymer −1 %−1 that agrees well with the results obtained from other studies36, and the average shift of the top layer is ~−5.9 cm−1 %−1. It is remarkable that the ratio of shift rates between the top and bottom layer is similar for both exfoliated and CVD graphene, with values of 0.52 and 0.37–0.45 for the exfoliated and CVD, respectively. This finding indicates that in both cases, the axial strain transferred to the top layer from the bottom graphene layer for the case of non-Bernal stacking is about half of the corresponding strain induced to the bottom layer from the polymer substrate. In Fig. 36. In Fig. The shift rate of the bottom CVD single layer is ~−14.4 cm37. The maximum ILSS obtained for the CVD/CVD from the edge of the bilayer is in the range of ~0.04–0.16 MPa, in very good agreement with the results obtained from the exfoliated bilayer  distance. Due to the amount of time required to perform such Raman maps, we selected a tensile strain of 0.50% to perform extended maps in order to examine if a similar behaviour is reproduced at the macroscale. In Fig. 12, or shearing an AFM tip of a few nanometers in diameter over graphene4. Controllable uniform straining without size limitations can be applied, limited only by the time taken for collecting the Raman data. Moreover, the Raman maps collect information from large contact areas. The different level of strain in each single layer induces a mismatch between the lattice constant , and thus, gradual incommensurable stacking occurs, leading to interfacial sliding as interlayer shear strength is overcome. The effect of lattice mismatch induced by strain has been examined by simulations that show robust superlubric behaviour when sliding a graphene on strained graphene40. As is experimentally evident, our approach provides an alternative for achieving macroscale superlubricity using two CVD graphene layers.The present experimental approach is vastly different than the usually adopted method of dragging a layer of graphite43. Despite the stress concentration that might be present in such cases, the mismatch in the lattice constant between the two layers eliminates such effects. For example, as explained in the case of hBN/graphene interface with inherent lattice constant mismatch18, the possible presence of small friction anisotropy does not alter the overall system behaviour. Moreover, MD simulations on shearing a graphene layer on a strained graphene show that the friction dramatically decreases with the increase in graphene size. This is because the large contact areas result in a much larger length than that of Moiré patterns, and the friction force tends to the value of the incommensurate state39. Thus, such effects can hardly affect the interlayer shear stress measured at the micron/mm scale of our experiments.We note here that two lattices in incommensurate state form Moiré patterns that affect the spatial distribution of strain, and consequently the interlayer shearing depends on the Moiré characteristics16. In Fig. 45. This might lead one to expect that the presence of wrinkles in the graphene–graphene interface could increase the interlayer friction and consequently the ILSS; however, this is not in accordance with the present findings. The case of stress transfer of wrinkled graphene on polymer is different, and we refer the reader to previous work47. Moreover, under tension, the wrinkles are flattened out, and new wrinkles are formed laterally to the applied tension49. The second factor is the strong dependence of the shear strength to the relative direction of shearing of the graphene sheets12. It is thus of great importance to examine these two effects by simulations on shearing of a graphene layer over another one. We performed molecular dynamic (MD) simulations to examine the influence of the presence of wrinkles on the stress-transfer efficiency in bilayer graphene, as well as to access any dependence of the interlayer shear stresses on chirality of shear directions.Besides the lattice constant mismatch that was discussed above, the presence of wrinkles that exist at grain boundaries of CVD graphene and the relative shearing direction are critical factors for the manifestation of superlubricity that need to be examined to understand their effect on shearing of the two graphene layersTo illustrate the effect of wrinkles on the interlayer shearing between two graphene layers, molecular dynamics simulations were performed on supported bilayer graphene that had been previously subjected to compressive strain of –0.6% in order to induce the formation of wrinkles. The results show that the presence of wrinkles, either in the parallel or perpendicular direction, does not contribute to any increase in the ILSS. On the contrary, wrinkles or out-of-plane deformations due to the roughness of the substrate contribute to the lowering of the ILSS by a factor of ~2, if other phenomena do not come into play. The overall analysis is presented in Supplementary Note 51. This range has been recently significantly narrowed down, and the crucial role of the shearing direction was identified16. By adopting a technique that was originally proposed for self-cleaning of graphitic surfaces52, Liu et al. performed shearing experiments on graphitic mesas that were capped with SiO216. In doing so, they managed to estimate narrow shear strength value ranges for two cases: when the sheared flake was in the lock-in state, and when it was in the superlubric-incommensurate state. From their analysis on the self-retraction force, they reported an upper-bound estimate for the superlubric shear strength of τupperf = 0.02–0.04 MPa for flakes of ~10 microns in length, and from their analysis on the deformation of a tungsten tip, they reported a value for the lock-in shear strength of τlock-in = 0.1 ± 0.04 GPa. The superlubric shear strength upper bound corresponds to relatively small graphite flakes, and has a strong size and direction dependence16. Here, we examined the effect on the ILSS of the relative orientation of the two graphene layers. The top layer was moved along the bottom layer armchair direction . To account for the effect of stacking orientation, distinct simulations were performed with the top layer having been constructed with five different chiral angles, namely, zigzag (0°), 7.5°, 15°, 22.5° and armchair (30°). The ILSS plots that emerge are given in Fig. τlock-in = 0.1 ± 0.04 GPa. The effect is also captured by repeating the simulations employing the AIREBO potential53, as discussed in Supplementary Note 57.We now move on to the investigation of the effect of the shearing direction on the interlayer shearing that is the most crucial factor. There is a large range regarding the reported values of interlayer shear strength of graphitearmchair 0°. The I16. A reduction is also possible to occur from the presence of wrinkles as discussed here and in Supplementary Note 22. In the work by Liu et al.16, the results were obtained from graphite mesas with thickness of hundreds of nm. It was recently shown that the interlayer shear strength of few-layer graphene is thickness dependent, and tends to decrease with the increase in the thickness3.For all of the intermediate (to the main) chiral directions, a significant drop in ILSS is immediately apparent. This ILSS reduction is also encountered when the simulations are repeated at a temperature of 1 K, so this effect does not emerge from thermal rippling. The computed ISS values for the turbostratic stacking reach as low as ~1 MPa that is higher than the reported upper bound of superlubric shear strength mentioned above, but in very good agreement with the results from the same work obtained with a tip that exhibits plastic deformation16 where the self-retraction phenomenon begins to break down. Moreover, the ILSS obtained from bilayer graphene blister has a maximum value of 0.06 MPa and an average of 0.04 MPa58, which is in good agreement with the lower values of the present work obtained for exfoliated graphene and somewhat lower from the average values. A small reduction in the value of ILSS is to be expected when the graphene size is smaller than the transfer length, which is a plausible explanation for this small difference and in agreement with the results by Liu et al.16. At any rate, the CVD bilayer manifests macroscale superlubricity.Another crucial factor is the size of the examined samples. The strain transfer shearing mechanism is remarkably similar in qualitative terms to that of graphene–polymer, and thus, a certain length is required in order to have efficient strain transfer as evident by the experiments. From the results of both exfoliated and CVD experiments, this length is estimated to be maximum ~4–12 microns  was mechanically cleaved using a scotch tape and the graphitic materials deposited on a PMMA-SU-8 substrate. The SU-8 photoresist was spin-coated on the top of a PMMA bar of thickness ~3 mm with rotational speed of ~4000 rpm. The single-layer graphene and its folded part were identified by the lineshape of the 2D Raman peak. A four-point-bending jig under the Raman microscope was used for simultaneously recording Raman spectra and mechanically loading the sample. Laser lines of 785 nm and 514 nm were used for the execution of the experiments. The strain was applied incrementally with a step of ~0.1–0.15% for all cases.59. The graphenes were rinsed with distilled water four to five times59 in order to clean their surfaces. Extra caution was taken in order that the top layer is supported only by the bottom graphene. This was succeeded by depositing a relatively large CVD to the bottom , and for the top layer about half the dimensions of the bottom layer. As mentioned below, the initial CVD sample has a dimension of 7 cm2 × 7 cm2; thus, no size limitations were encountered during this procedure. Finally, the sample was left to dry under nitrogen flow, and zero relative humidity over 24 h for the removal of any water molecules. We note that we did not subject the sample to heat to avoid the potential compressive strain induced by heating. A schematic of the procedure is given in the Supplementary Information  under 25 mbar. The foil was heated at 1000 °C and was kept there for 5 min for annealing. Afterwards, the sample was cooled down to 925 °C, while methane was introduced into the chamber (10 sccm) as carbon feedstock to initiate the graphene growth on copper foil surface. After 5 min, the H2 flow was terminated, the chamber was cooled down to 650 °C, CH4 flow was terminated and finally the chamber was cooled down to room temperature under Ar atmosphere.Graphene was synthesized on copper foils by chemical vapour deposition (CVD) in an AIXTRON® BM Pro CVD chamber. Copper was supplied by Viohalco® and used as the catalyst substrate. For the production, the foil was cut into 7 cm60 that offers Morse-type long-range interactions that exclude the nearest neighbours, and offers a suitably parameterized short-range term that does not lead to unrealistic structural defects60. The simulations were fully dynamic for the dynamic particles of the system . Periodic boundary conditions were used in all cases, throughout. The bottom layer is periodic in both directions, was corrugated though compression as detailed in the Supporting Information and remained rigid during the sliding stage. The top layer was periodic in the direction normal to its displacement over the corrugated rigid bottom layer. The components of the forces along the displacement direction acting on all of the top-layer atoms were summed and averaged every 2000 time steps. A small time step of 0.5 fs was used. We denote here the simulations as “chiral” to assess the effect of chiral shear direction on ILSS, see main text. For the “chiral” set of simulations, computational cells of different sizes were used (provided in Supplementary Note y axis) in analogy to nanoribbons that take their name (by convention) from the chirality of the long edge (length). With an AC bottom layer, top layers with chiral angles of 7.589°, 15.295°, 23.413°, AC and ZZ were examined . The bilayer sheets lay over an interacting (Lennard–Jones) mathematical surface  with parameter values ε = 6.8 meV and σ = 3.133 Å. All simulations were performed using the LAMMPS package61. Computational cells in the Supporting Information were visualized using OVITO62.Molecular dynamics simulations were performed by employing the LCBOP potentialSupplementary InformationPeer Review File


Graphene-based nanocomposites possess excellent mechanical, electrical, thermal, optical, and chemical properties. These materials have potential applications in high-performance transistors, biomedical systems, sensors, and solar cells. This paper presents a critical review of the recent developments in graphene-based nanocomposite research, exploring synthesis methods, characterizations, mechanical properties, and thermal properties. Emphasis is placed on characterization techniques and mechanical properties with detailed examples from recent literature. The importance of characterization techniques including Raman spectroscopy, X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM) for the characterization of graphene flakes and their composites were thoroughly discussed. Finally, the effect of graphene even at very low loadings on the mechanical properties of the composite matrix was extensively reviewed. This paper provides a critical review of the synthesis, properties and characterizations perspectives of recent advances in graphene-based nanocomposites. A critical review of the characterization of graphene and graphene nanocomposites was presented in 2, sp3): zero-dimensional sp2 fullerenes, the two-dimensional sp2 honeycomb lattice of graphene, or three-dimensional sp3 crystals—diamond [2 ~graphitelike to sp3 ~diamondlike bonds [2-bonded carbons with various degrees of graphitic ordering, ranging from microcrystalline graphite to glassy carbon. Accordingly, these materials have been greatly investigated because of the exceptional mechanical and electronic properties.Carbon has several allotropes, which can be classified according to the type of chemical bond related with hybridization  have been successfully used in many applications including in smart phones, ultra-thin flexible displays [Since its discovery in 2004, graphene has become the center of many research activities ,28,29,30displays , hydrogedisplays , transpadisplays , chemicadisplays ,35, biosdisplays ,37,38, adisplays . It has Graphene reveals remarkable optical properties, which makes it very promising for photonic and optoelectronic applications ,40,41. IGraphene has great prospects for industrial applications, such as polymer composites, conductive coatings, fuel cells batteries, and ultracapacitors due to its distinctive properties of high strength and exemplary electrical and thermal conductivity ,3. TheseThere are several approaches available to produce graphene . These tMost of the graphene produced for research over the past decade was fabricated by mechanical exfoliation (scotch tape method) ,52,53. ILiquid-phase exfoliation (LPE) b is one The CVD method is widely used for the synthesis of carbon nanostructures (CNTs) for composite materials with outstanding mechanical properties ,57,58. FResearch on polymer nanocomposites (PNC) has been growing over the past decade due to their remarkable material properties, yield strength, toughness, electrical conductivity, thermal conductivity, and optical properties, and their applications are growing substantially ,78,79,80Graphene possesses many desirable properties such as high strength and elastic modulus, high electrical and thermal conductivity, high aspect ratio, high thermal stability, high gas impermeability, and good dimensional stability ,10,11,12Graphene can be produced in large quantities from graphite precursor by oxidation. Hence, graphene-based polymer nanocomposites have attracted considerable research interest around the globe. Various polymers, such as epoxy ,86,87,88Graphene-based nanocomposites are increasingly being used for the development of new materials for alternative energy sources, for example, (a) in lithium-ion batteries, graphene-based nanocomposites show better performance as they have high power density and energy density and a fast charging speed in hydrogen fuel cells; (b) graphene is used as an electrode material to enhance electrocatalytic activity; (c) in solar cells, graphene-based composites are used in photovoltaic devices because of their unique characteristics of high carrier mobility and low resistivity; and (d) in thermoelectric materials. Characterization of nanocomposites is crucial to understand the basic physical and chemical properties of the nanocomposites. Graphene materials available in the market are made by different companies through different techniques. It is expected that these graphenes are quite different from each other in flake width, thickness, and defect concentration. All the different techniques to modify the filler surface as well as to synthesize the polymer nanocomposites need to be supplemented with robust characterization of these processes as well as resulting composite properties to gain insight into the various factors affecting the nanocomposite microstructure. Several techniques have been used in the characterization of nanocomposites, dispersion, distribution, and orientation within polymer matrix. These techniques include optical microscopy, scanning electron microscopy, high transmission electron microscopy, Raman spectroscopy, atomic force microscopy and X-ray diffraction; these have been shown to be very useful for quantification of nanocomposites. It is also, in many instances, necessary to employ more than one characterization technique in order to accurately characterize the nanocomposite material.Nanocomposites contain matrices of diverse materials such as polymer, metal or ceramic, and also include different nanoparticle fillers . These fillers enhance the mechanical, thermal and electrical properties of the material ,111,112.Depending upon the degree of dispersion of the nano-sized layer structure, polymer composites can be divided into three main categories: microcomposites, intercalated nanocomposites, and exfoliated nanocomposites ,113,114.The properties of graphene nanocomposites are dependent on chemical compatibility between the filler and the matrix, the volume fraction of the filler and the processing conditions such as dispersion and exfoliation of filler. To achieve optimal results, appropriate fabrication methods must be employed ,60. MoreIn situ polymerization is an effective technique for the formulation of highly dispersed graphene in a polymer matrix. This process involves the polymerization of monomer in the presence of the layered materials a. DuringMelt blending is the preferred method for the synthesis of various polymer hybrids with inorganic nanoparticles . It is fThe most common method of synthesizing polymer nanocomposites is melt intercalation or melt blending ,117,119.A more effective way to achieve interfacial adhesion between the filler and matrix is exfoliation adsorption c 114,12,123,124.2/g, high mobility (15000 cm2/V·s) [Graphene is a material with outstanding properties, such as high specific surface area 2600 mcm2/V·s) ,15, supecm2/V·s) , and extcm2/V·s) ,129,130,cm2/V·s) ,133,134.Raman spectroscopy is a standard nondestructive tool for the characterization of crystalline, nanocrystalline, and amorphous carbons ,150,151.−1), G band (~1580 cm−1), and 2D band (~2700 cm−1), were observed for these two graphitic materials. The intensity ratio of D/G (ID/IG) for the prepared graphene was 0.10, lower than that of ultrasonication exfoliated graphene (0.29) [Zhiliang et al.  demonstre (0.29) .60/rGO samples were characterized by Raman spectra. 60, and C60 graphene. The two intense peaks in rGO are designated to the D and G band. The G band and D band are a result of the presence of defects that have been introduced throughout the oxidization and reduction technique. The G band has moved to 1582 cm−1 in the C60/graphene hybrid, indicating the effect of graphene on C60.Zhang et al.  carried −1) emerged as the most important feature of the Raman spectra. In addition, the double 2D band considerably weakened, while the G band around was broadened due to the presence of a defect.Chemical functionalization of graphene (CFG) enables graphene to be processed by solvent assisted techniques, such as layer-by-layer assembly, spin-coating, and filtration. It also prevents the agglomeration of single-layer graphene during reduction and maintains the inherent properties of graphene ,157,158.Atomic force microscopy (AFM) is one of the most powerful microscopy techniques for studying samples at nanoscale. AFM is a type of scanning probe microscopy (SPM), with a resolution on the order of fractions of a nanometer . For exaReduced graphene oxides (rGO) are single-layered sheets derived from the chemical reduction of graphene oxide (GO). The rGO possess electrical and mechanical properties similar to those of graphene; thus, this makes them versatile for a number of applications. Various synthetic routes have been reported for the synthesis of reduced graphene oxide ,167,168.Gurunathan et al., demonstrated the synthesis of water-soluble graphene through reduction of GO using bacterial biomass . The proGraphene fabricated by different techniques contains many defects depends on the process. Defects in graphene have negative impacts on the high mobility and other physical and mechanical properties of graphene. Accordingly, it is essential to characterize these defects using SEM or other advanced microscopy techniques. SEM is an advanced microscopy instrument in characterization of micro- and nanostructured materials. Along with its high power to offer a 2D analysis of substantial aspects of the sample, SEM can also provide information and varied qualitative data on several physical properties such as roughness, morphology, surface consistency, size, and chemical structure of materials. Nano scale features of graphene including wrinkles, grain shapes, and folding lines can be specifically characterized utilizing the SEM ,162.Many studies demonstrated that the state of dispersion of graphene sheets in the matrix has a strong effect on the mechanical properties of the composite ,168,169.2 detection [Graphene is quite a robust material in hydrogen sensors due to a possible improvement of its surface area and susceptibility of its electronic properties to the changes caused by adsorbing atoms and molecules including hydrogen. However, the pristine graphene sensitiveness to hydrogen is limited . Sharma etection . Figure HRTEM is a very powerful structure characterization technique for graphene. It is a unique tool for characterizing the atomic structures and interfaces of graphene ,171. It 2 carbon atoms of the π network into a sp3 configuration, resulting in adjustments of the innate physical and chemical properties of graphene [Due to strong interactions and van der Waals forces, exfoliated graphene sheets have a strong tendency to irreversibly aggregate or even restack, reverting to multilayer structures such as graphite . Therefographene .2O3–graphene structure, namely sheet-on-sheet nanostructure by a solvothermal method. Fe2O3 nanoparticles were also prepared on graphene nanosheets. The Fe2O3–graphene sheet-on-sheet nanostructure was fabricated as an anode for Li-ion batteries. It was confirmed that Fe2O3 nanosheets were uniformly dispersed among graphene nanosheets, forming a unique sheet-on-sheet nanostructure. HRTEM of the morphological analysis of Fe2O3–graphene nanocomposites is shown in 2O3 nanoparticles are shown in this figure. Their particle sizes are 30–50 nm size. The particle-on-sheet and sheet-on-sheet nanostructures can be easily confirmed by the HRTEM images of The lithium-ion battery is considered to be one of the best power sources to maximize the efficiency of energy use. Graphite has been widely used as an anode material for commercial Li-ion batteries because of its good electrochemical properties. Kan et al.  prepared2 carbon materials [XRD is an important analytical tool for the characterization of the intercalated and exfoliated nanocomposites ,175,176.aterials ,150.The application of X-ray diffraction (XRD) for phase determination and confirming the reduction of GO to graphene is a very useful tool. Of course, it is not as powerful as the other approaches  due to the limited information collected. Therefore, its application is always accompanied by other methods such as Raman, XPS, and FTIR to provide more information about the catalyst structure.60) had been effectively integrated into the surface of graphene.Polymer-based thermoelectric materials have been the focus of many studies for the past 10 years ,180,181.Chieng et al.  preparedGraphene-based nanocomposite materials exhibit significant improvement in mechanical properties compared to the standard composites ,186,187.Most of the properties of the nanocomposites were superior compared to the polymer matrix ,210,211.Pinto et al.  investigKing et al.  fabricatLi et al.  prepared1/2 with a graphene loading of 0.5 wt.%, suggesting major improvements due to graphene. The microhardness indentations and radial cracks on the polished surface of 58S-0.5 were characterized by SEM to identify the mechanism responsible for the enhanced mechanical properties  can be produced via the rapid heating of GO under inert gas and high temperature (1000 °C) . TRG is Nanoindentation is a widely used technique for measuring the nano and microscale mechanical properties in nanomaterials and nanocomposites. This technique has been commonly used in determining the mechanical properties of polymers ,207,208.−1. The fracture strength that signifies the intrinsic strength (σint) of the sheet was ~42 N m−1. The corresponding values for the bulk graphite were E = 1.0 TPa and σint = 130 GPa.Shen et al.  used nanAll electronic units produce excessive heat and thus demand thermal management to prevent premature failure ,219,220.−1K−1) compared to copper (400 Wm−1K−1). The thermal properties of graphene have become an important research topic and are attracting tremendous interest in the area of thermoelectric waste heat recovery. Thermal properties of graphene are related to its low mass and the strong bond of carbon atoms. Thermal properties of graphene and its use in electronics and thermal management applications have been the subject of many scientific studies [Graphene has drawn tremendous attention for heat dissipation due to its extraordinarily high in-plane thermal conductivity  was a very effective nanofiller for epoxy composites. They reported a remarkable increase in thermal conductivity (3000%) at 25 vol% loading. They attributed the remarkable increase in thermal properties of this composite to the optimum combination of the high aspect ratio, stiffness, and low thermal interface resistance of the GNPs.Yu et al. prepared graphite nanoplatelets (GNPs) by thermally exfoliating graphite . ResultsZhang et al.  fabricat3O4 nanoparticles allowed them to align the fillers in an external magnetic field during dispersion of the thermal paste to the connecting surfaces [The variation in thermal conductivity with different forms of graphene and graphite nanocomposites is reviewed in surfaces . The filThis article reviewed the recent progress in graphene-based polymer nanocomposites, focusing on two areas: properties and characterization. Emphasis was placed on the unique roles and advantages of advanced graphene characterization techniques, such as Raman spectroscopy, XRD, AFM, and HRTEM. Characterization of 2D graphene involves different types of microscopic and spectroscopic techniques to obtain the structural, morphological, and chemical information of as-synthesized graphene. Raman spectroscopy is a remarkable analytical tool that can detect small changes in the structural morphology of carbon nanomaterials. It is used to determine the number of layers, defects, strain, and chemical modifications. HRTEM is one of the most powerful characterization techniques for graphene’s structural characterizations. Several examples of graphene polymer composite characterizations using Raman, SEN, TEM, AFM, XRD, and HRTEM were discussed.Most common graphene synthesis techniques have been discussed. The mechanical exfoliation of graphene is a simple technique for graphene fabrication. The process has the ability to fabricate a single crystal of graphene with various numbers of layers. However, control over the wafer scale synthesis and reproducibility is very difficult. Liquid-phase exfoliation is one of the most practical methods for commercial manufacturing of graphene because of its low cost and potential scalability. Graphene prepared by this technique exhibited a low percentage of defects and oxygen functional groups.Chemical synthesis techniques are suitable for low volume production of graphene at low temperature. Furthermore, the process can yield graphene film or graphene coatings on several substrate materials. Graphene synthesized using chemical processes exhibits a high surface area and easy functionalization. CVD is widely used for the synthesis of carbon nanostructures. This method has been effectively used for producing carbon filaments which are the basis for composite materials with outstanding mechanical properties.Graphene–polymer nanocomposites display remarkable mechanical properties compared to the pure polymer. −1K−1). Graphene and MLG, produced by the liquid-phase exfoliation technique, were successfully used to fabricate novel nanocomposites to be used as TIM in electronic applications. Remarkable enhancement of thermal conductivity of the epoxy matrix (increase by 23×) was achieved at the 10% volume of graphene loading. Graphene and xGnP are potential key materials for the next generations of ICs and 3D electronics. Graphene chemical functionalization caused outstanding improvement in the thermal conductivity of the polymer composites. Thermal conductivity is affected by several factors, such as the graphene loading, dispersion, and the thermal resistance of the interface.Graphene and xGnP have attracted tremendous attention for heat removal due to their extraordinarily high in-plane thermal conductivity (2000~4000 Wm


Graphene oxide is an important member of the graphene family which has a wide range of applications. The chemical method, especially the liquid phase method, is one of the most common and important methods for its preparation. However, the complex solution environment not only gives them rich structure, but also brings great challenges for its large-scale industrial synthesis. In order to better realize its industrial application, it is important to understand its structure, such as the source of oxygen-containing functional groups. Here we studied the contribution of four oxygenated acids to oxygen-containing functional groups in Hummers’ method using first principles. We found that the permanganic acid molecules that exist instantaneously due to energy fluctuations can be the source of oxygen-containing functional group. In addition, Stone-Wales defect have a certain effect on the formation of oxygen-containing functional groups, but this effect is not as good as that of solvation effect. This work provides a guide for exploring the source of oxygen-containing functional groups on graphene oxide. Graphene oxide (GO), a very important member of the graphene family, has a wide range of applications in many fields, such as field effect transistors , sensorsNumerous methods have been developed to synthesize GO, which can be categorized into eight : 1) chem3) with nitric acid (HNO3) (Brodie and Staudenmaier methods), combination of potassium permanganate (KMnO4) and sulfuric acid (H2SO4) (Hummers’ method), etc., so that there are a large number of different functional groups on the surface and on the edge of the graphene to get the GO. Different methods result in different structures . The source of oxygen-containing functional group, especially that of oxygen, is one of the most important question because these groups can greatly affect the structure and properties of GO . Oxygen 2O2  and KClO2O2 , nitric acid (HNO3), permanganic acid (HMnO4), chloric acid (HClO3) and their mixture acid) present in Hummers’ method and non-defect and Stone-Wales defect graphene using first principles. We looked at the role of not only individual components but mixtures of components in order to explore the contribution of each component. We also consider the perturbation of these components by water molecules. Density of states (DOS), adsorption energy, bond length, charge transfer and overlapping population were mainly used to study the relationship between molecules and non-defect and Stone-Wales defect graphene. This work provides a guide for exploring the source of oxygen-containing functional groups on graphene oxide.Solving these problems requires a deep understanding of the relationship between graphene and these oxygenated solvents. Here, we investigated the relationship between some oxygenated acid  , which i–6 eV/atom is applied in SCF. In this work, two sizes of substrate model were used for the calculation. For non-defect graphene, the model has 32 atoms, and it has 50 atoms when it contains Stone-Wales defect. K-point grid of 5 × 5 × 1 is applied to compute these models. It was raised to 7 × 7 × 1 when DOS is calculated. All models are optimized so that these forces are less than 0.02 eV/Å.In this study, the cut-off energy is set to 600 eV. Vacuum space of 15 Å is applied to avoid the effect of periodicity on the Z axis. Convergence threshold of 1 × 102SO4, HNO3, HMnO4 and HClO3 with non-defect and Stone-Wales defect graphene, respectively. The latter, on the other hand, includes four types: mixture of H2SO4 and HNO3, that of H2SO4 and HMnO4, that of HNO3 and HMnO4, and that of all three.In this study, we set up two types of comparison groups. One consisted of a single component, and the other one consisted of multiple components. For the former, it involves the reaction of Hads), bond length, charge transfer (△Q) and overlapping population) are shown in We first studied the case of single-component without water. DOS of single-component acid molecules reacting with the non-defective and Stone-Wales defect graphene are shown in 2SO4. As shown in 2SO4 molecule contains two OH•, one of which is close to the graphene and the other is far away from it. Therefore, the one close to the graphene will experience energy dispersion due to electron injection, while the other will remain relatively local.There is only weak physical adsorption between these molecules and non-defect or Stone-Wales defect graphene, as is shown in 4, the results are different when it reacts with non-defect and Stone-Wales defect graphene. The molecule will dissociate to form MnO3• and OH• when it reacts with non-defective graphene. In this case, MnO3• and OH• are combined together to form a group through strong Coulomb interaction that takes place between two oxygen atoms . While this dissociation did not occur between HMnO4 and Stone-Wales defects. The manganese atom and the oxygen atom in OH• are still bound together by a relatively strong ionic bond (population of Mn-O bond: 0.15). In the case of HMnO4 reacting with non-defective graphene, therefore, there are many energy levels with strong localization in the DOS of MnO3• and OH• around the Fermi level, especially in the range of −10∼−5 eV, which are mainly contributed by the 2p orbital of oxygen atom, seeing in 3• and OH•. Besides, the level to the right of Fermi level of OH• formed by dissociation still has a high localization, indicating that this part has fallen off from the molecule. In the other case, levels near the Fermi level are non-local because it does not dissociate. In other words, there not have levels with strong localization near the Fermi level. The 1s orbital of hydrogen atom at the right of Fermi level becomes diffused due to the charge received from graphene because the bond between HMnO4 and Stone-Wales defect graphene is strong chemisorption, seeing in 4. This phenomenon indicates that the Stone-Wales defect does have selectivity for functional groups, as previous study have shown that it is conducive to the introduction of epoxy groups  although the HMnO4 does not dissociate, indicating that OH• tends to detach from the molecule. Therefore, as shown in 3• and OH• in the range of −10∼−5 eV. The energy values corresponding to these energy levels are consistent, indicating that there is still a strong bond between MnO3• and OH•. By contrast, HMnO4 dissociates on Stone-Wales defect graphene to form MnO3• and OH•. But MnO3• and OH• did not combine together to form a neutral group by strong coulomb interaction like the case of HMnO4 disassociate on the defection-free graphene. These two parts are relatively independent. Therefore, there are very few energy levels with similar energy values near the Fermi level between MnO3• and OH•, seeing in The dissociation of HMnOReaction of Single Component With Graphene, this section further studied the reaction between the mixed acid molecules and graphene. In this section, the reactions between H2SO4, HMnO4 and HClO3 and graphene are mainly calculated, considering the types of reagents needed for the preparation of GO. In the calculation, two contrast groups were set up for the reaction with non-defective graphene and Stone-Wales defect graphene. Each of the above categories included the following three groups: H2SO4 and HMnO4, HNO3 and HMnO4, H2SO4 and HNO3 and HMnO4.In the preparation of GO, a mixture of solvents is usually used rather than a single-component reagent. Therefore, on the basis of DOS of these are shown in 2SO4 and HNO3 molecules will not dissociate form OH•, but their presence will lead to the occurrence of solvation effect. It can promote the dissociation of HMnO4 to form MnO3• and OH•, as shown in 4 is not dissociated. These phenomena further prove that the effect of solvation is stronger than that of topological defects although the latter has selectivity for functional groups.Similar to the case of single components, there is only weak physical adsorption between sulfuric and nitric acid molecules and graphene in the mixed condition, whether graphene is perfect or with Stone-Wales defects. HIn order to be closer to the experimental content of the preparation of GO, water molecules were added to the above model to further confirm the above conclusions. DOS of these are shown in 2SO4 and HNO3 molecules and graphene under the condition of mixed acid, no matter for perfect or Stone-Wales defect graphene. The amount of charge transfer between these molecules and graphene is very small, seeing in 2SO4, and HNO3 molecules leads to solvation effect that dissociates HMnO4 to form OH•. Meanwhile, this effect is enhanced due to the presence of multiple components. In all the models, HMnO4 disassociates to produce OH•. These OH• can attach to the surface of graphene and become the source of hydroxyl groups in GO. They can also react with the oxygen present in the solution or air to form carboxyl groups. They are able to react with other components to generate further dissociation and become the source of the epoxy functional groups, too. These phenomena strongly prove that the effect of solvation is stronger than that of topological defects although Stone-Wales defects have selectivity for functional groups. Therefore, based on the above situation, it can be considered that the HMnO4 molecules generated instantaneously due to energy fluctuations in the solution environment can become the source of oxygen-containing functional groups on GO.Consistently with the previous results, there is only weak physical adsorption due to van der Waals forces between H4 molecules that exist instantaneously due to energy fluctuations can disassociate to form OH•, and OH• can be a source of hydroxyl groups in GO. They can also react with the oxygen present in the solution or air to form carboxyl groups. They are able to react with other components to generate further dissociation and become the source of the epoxy functional groups, too. In this process, the Stone-Wales defect plays a certain role in the formation of functional groups, but this role is far less than that of the solvation effect. In complex solution environment, many particles will interact and influence each other. Among them, non-permanganate related components from graphene and solution can constantly transfer charge to permanganate. The mixed components can make the reaction proceed in the direction of dissociation, so as to promote the dissociation of permanganate to form OH•. This work provides a guide for exploring the source of oxygen-containing functional groups on GO.In summary, in the solution environment where GO is prepared, the HMnO


In this work, few-layer graphene materials were produced from Fe-lignin nanocomposites through a molecular cracking and welding (MCW) method. MCW process is a low-cost, scalable technique to fabricate few-layer graphene materials. It involves preparing metal (M)-lignin nanocomposites from kraft lignin and a transition metal catalyst, pretreating the M-lignin composites, and forming of the graphene-encapsulated metal structures by catalytic graphitization the M-lignin composites. Then, these graphene-encapsulated metal structures are opened by the molecule cracking reagents. The graphene shells are peeled off the metal core and simultaneously welded and reconstructed to graphene materials under a selected welding reagent. The critical parameters, including heating temperature, heating time, and particle sizes of the Fe-lignin composites, have been explored to understand the graphene formation mechanism and to obtain the optimized process parameters to improve the yield and selectivity of graphene materials. The challenges of sustainable development have driven people to find facile, environmentally friendly ways to produce carbon-based materials. Biomass presents an abundant and low-cost source of carbon. However, there have been limited studies on the use of wood or agricultural biomass as the carbon source to produce graphene-based materials. Lignin is the second major component of lignocellulosic biomass and the most abundant aromatic biopolymer resource on Earth . More th2, H2O, CO2, and CH4. The graphene shells are peeled off the metal core and simultaneously welded and reconstructed to graphene materials under a selected welding reagent. The graphene shells will be joined through the unsaturated bonds of the carbon atoms on the edges, linked by carbon atoms from decomposed welding molecules, or agglomerate through van der Waals forces [A batch type manufacturing process for converting kraft lignin to graphene materials has been developed by FPL and Domtar . The mets forces  under his forces . Applicas forces , sensorss forces , electros forces , fuel ces forces , solar cs forces , capacits forces , batteris forces , thermals forces , electros forces , inks ans forces , barriers forces , etc.4, H2, CO2, and their mixtures to examine processing gas effects on graphene formation and product component distributions [It has been reported that the graphitization of solid carbon-based species is mainly affected by the heat treatment temperature , while oibutions . In addi3)3·9H2O) and tetrahydrofuran were purchased from Sigma-Aldrich . Kraft lignin (BioChoice) was supplied by Domtar Inc. .Iron (III) nitrate nonahydrate  were identified as the main gaseous products H2, CH4, CO, and CO2, respectively.Fifty grams (50 g) of the decomposed Fe-lignin composites were each packed in the middle of a 2-inch OD ceramic tubular reactor. The carrier gas argon (99.99% purity) was first introduced into the reactor at a flow rate of 100 mL/min for 30 min. The reactor was heated at a temperature-programmed rate of 10 °C/min to a carbonization temperature  and kept at the carbonization temperature for 1 h. The furnace was cooled down by 10 °C/min to room temperature under an argon flow. An online Hiden QGA quantitative gas analysis system  was used to measure gaseous products during the graphitization process. The signals from the mass spectra of 2, 16, 28, and 44 (Effect of reaction temperature: Fifty grams (50 g) of the GEIN sample were packed in the middle of a 2-inch OD ceramic tubular reactor. Argon (99.9% purity) was first introduced into the reactor at a flow rate of 50 mL/min for 30 min. Then, 80 mL/min methane was co-fed into the reactor and the reactor was heated to MCW temperature  with a heating rate of 10 °C/min and kept at the heating temperature for 1 h. The vent gas from the reactor was monitored using the online QGA system.Effects of GEIN grain particle sizes: The GEIN grains were separated into different sizes: ≤50, 50–150, 150–250, and 500–700 μm. Fifty grams (50 g) of each sample were packed in the middle of a 2-inch OD ceramic tubular reactor in each run. The welding gas was introduced into the reactor. The reactor was temperature-programmed with a heating rate of 10 °C/min to 1000 °C and kept at 1000 °C for 1 h. The furnace was cooled down by 10 °C/min to room temperature.Effects of reaction time: Fifty grams (50 g) of GEINs (150–250 μm) were packed in the middle of a 2-inch OD ceramic tubular reactor in each run. The welding gas was introduced into the reactor. The reactor was temperature-programmed with a heating rate of 10 °C/min to 1000 °C and kept at 1000 °C for 0.5, 1, 3, or 5 h. The furnace was cooled down by 10 °C/min to room temperature.1 was the carbon in the MCW sample, and M0 was the weight of GEIN sample before MCW. The solid carbon in the MCW sample was measured by TGA: Twenty milligrams of the MCW sample (20 mg) was put on a ceramic sample pan for TPO analysis in a Shimadzu TGA-50H instrument . The sample was heated in high flow of air (100 mL/min) from room temperature to 800 °C at a heating rate of 10 °C/min, and the weight change was recorded as related to carbon burning.The yield of graphene product was calculated by−1. The Jade powder diffraction analysis software from Materials Data, Inc.  was used for both qualitative and quantitative analyses of polycrystalline powder materials. The mean particle size, L, was calculated for the most intense diffraction peaks of α-Fe, γ-Fe, and Fe3C using the Scherrer formula. The morphology of a thermally treated iron-promoted lignin mixture was investigated with a scanning electron microscope . All SEM samples were precoated with 10-nm Pt before being introduced into the vacuum chamber. The system was operated with accelerating voltage of 10 kV. The particle sizes of thermally treated iron-promoted lignin mixtures were examined with a JEOL JEM-100CX II transmission electron microscope  operated at accelerating voltage of 200 kV. All TEM samples were sonicated in ethanol solution for 1 min before being transferred to copper grids. Raman spectra of thermally treated iron-promoted lignin mixtures were obtained on a Jobin-Yvon microspectrometer  equipped with an excitation laser source emitting at 514 nm and an incident power around 1 mW on a thin surface. Twenty spectra were collected for each sample. Deconvolution of the spectra was performed with the assumption of mixed Gaussian/Lorentzian peaks describing both the main D- and G-bands and the two minor ones. The D, G, and 2D peaks were fitted with Lorentz functions. The AD/AG ratio was calculated using the integrated area of D to G peaks, which is related to the graphitic degree of graphene materials.The surface area of the thermally decomposed Fe-lignin composites was carried out using an automatic adsorption unit . The samples were degassed at 300 °C for 5 h prior to analysis to remove any adsorbed moisture or other impurities bonded to the surface of the sample. X-ray powder diffraction (XRD) patterns of thermally treated iron-promoted lignin mixtures were obtained using a Rigaku Ultima III X-ray Diffraction System  operated at 40 kV and 44 mA using Cu-Kα radiation with a wavelength of 1.5406 Å from 15° to 80° at a scan rate of 0.02 °sGEINs are the main product in the solid residues of catalytically graphitized biomass when iron is used as the transition metal . Two pos3C) with different carbon contents  and side aliphatic chains [2 formation is contributed by elimination of hydrogen from C−H bonds in aliphatic CHx (x = 1–3) and aromatic rings via catalytic dissociation [Quantitative analysis of gaseous products from temperature-programmed catalytic graphitization (TPCG) of Fe-lignin composite was performed by an online RGA (Hiden QGA with a mass range of 300 AMU). 0–524 °C a, implyir groups . Signifir groups . Methanec chains , which aociation .−1 are related to OH stretching vibrations of alcoholic and phenolic hydroxyl groups (involved in the hydrogen bonds) in lignin and hydroxyl groups in Fe(OH)3, respectively. The band intensity of the OH groups reduced significantly when the Fe-lignin composite was heated to 300 °C and 400 °C, indicating a decrease of the free hydroxyl groups on the kraft lignin and decomposition of Fe(OH)3 by dehydration reactions. With a further increase of the temperature to 600 °C and above, the hydroxyl groups are completely lost from the sample. The band at 2933 is assigned to aromatic methoxyl groups and methyl and methylene groups of the side chains; the band at 2841 cm−1 is assigned to symmetric C–H stretching in the -CH2- and tertiary C–H groups. The intensity of these two bands reduces drastically after heating the sample to 300 °C and 400 °C, likely due to the decomposition of the methyl and methylene groups in the side chains. The bands at 1710, 1665, 1456, 1362, 1210, and 1078 cm−1 are related to the C=O and C–O groups in lignin, and they disappear after the sample is heated at 300 °C and above. Bands of nitrate groups at 1535 and 1330 cm−1 are observed to disappear completely when the sample is heated at 300 °C and above. The bands at 1594, 1511, 1426, 1265, 1124, and 1031 cm−1 are assigned to vibrations of aromatic rings, and the intensities of these bands decrease with the increase of the heating temperature up to 600 °C and completely disappear at 800 °C and above. The FTIR results in 3C) phase formation was observed for the sample produced at 700 °C and above. Fe3C is related to carbon deposition from the carbonaceous gases [us gases  through 3C and γ-Fe diffraction peaks became more intense. As the temperature increased to 900 °C and 1000 °C, the material mainly showed the strong Fe3C diffraction peaks, which may be due to more carbon atoms diffused and dissolved into iron particles.The samples produced at 700 °C and above were stable in the air, possibly due to the iron particles being encapsulated in inert iron carbide and carbon shells. With further increase of the temperature to 800 °C, the FeAD/AG values of Fe-lignin composites heated at various reaction temperatures. The calculated AD/AG values were found to be 2.62, 2.38, 2.03, 1.59, and 1.15 at 600°C, 700 °C, 800 °C, 900 °C, and 1000 °C, respectively. Smaller AD/AG values correlate with a higher graphitization degree. The decreased AD/AG value with increasing reaction temperature indicates more of the well-ordered graphitic carbon is formed at a high temperature. Thus, in the present case, a higher graphitization degree was observed for the Fe-lignin composites carbonized at 1000 °C.The crystallinity and graphitization degree can be further explained using 3C and γ-Fe through the carbon atoms diffusion into α-Fe at 700 °C; these iron nanoparticles were encapsulated by carbon shells and embedded in the amorphous carbon matrix. No clear graphitic–carbon structure was observed in these carbon shells in samples heated up to 700 °C. One to two layers of graphitic carbon were observed to form around iron nanoparticles in the Fe-lignin composite carbonized at 800 °C, indicating the minimum temperature for the formation of GEINs was 800 °C; these GEINs were surrounded by amorphous carbon. The image of the Fe-lignin-900 sample showed similar GEIN structures formed with the Fe-lignin composite, where the graphitic carbon around iron nanoparticles increased to two to four layers, and the amorphous carbon was observed to convert to the turbostratic stacking structure [The microstructure and morphology of the Fe-lignin composites graphitized at temperatures between 500 and 1000 °C were investigated by HRTEM, and the images are illustrated in tructure . When thTwo forms of GEINs were observed in the graphitized Fe-lignin composites. The major GEINs (>90%) are nanoparticles with a uniform particle size of 3–10 nm a,b, have4) through a catalytic vapor decomposition (CVD) process [In addition to the majority smaller size GEINs, larger nanoparticles distributed over the surface of the GEIN grains having diameters ranging from 10 to 100 nm  interface layer of GEINs using active reagents at a high temperature. Therefore, to break the GEINs, cracking molecules are used during the MCW process. Cracking molecules refer to reactive gaseous molecules that have the capability to react with the metal core . H2O, CO2, O2, H2, and CH4 can react with the metal core [2O, CO2, O2, and CH4 to diffuse and penetrate through the few-layer graphene shell if there are no defective cracks. Fortunately, as the smallest molecule, H2 can easily diffuse and transport in solid materials like metals [2 is well-known to play the key role in the damage to steel and other metal alloys by the high temperature hydrogen attack (HTHA) [2 at 900 °C; these images demonstrate the formation of fissures in the GEINs and the cracked GEINs. Compared to other active reagents, hydrogen is the best choice for the cracking molecule. Based on the structures of GEINs, it is reasonable to disintegrate the graphene shell and cementite  . To crac3C was reported to be much higher than in the iron phases, since hydrogen reacts more rapidly with carbon in Fe3C than the carbon dissolved in γ-Fe [3C in the interface of the core–shell particles is first and quickly decarburized by hydrogen to iron phase and carbon is released as methane (CH4). While carbon in γ-iron is relatively stable compared to that of Fe3C, it is slowly decarburized to form methane. The pressure of the methane, which cannot diffuse from the iron layer formed from the decarburization of Fe3C, may exceed the cohesive strength of the iron core and cause interlayer fissuring between the original Fe3C and γ-iron layers. Within the fissures, part of the methane generated during decarburization is decomposed over surface iron atoms to graphene and hydrogen, explaining why there are two to three layers of graphene inside the iron cores:The activity of carbon in Fe in γ-Fe . Therefo3C, γ-Fe and even α-Fe. (II) The diffused hydrogen molecule may dissociate into atomic hydrogen, then combine with local carbon atoms to form methane molecules. (III) Due to its larger size compared to atomic hydrogen, methane molecules from the decarburization process cannot diffuse through iron or graphitic structures and are trapped close to the reaction sites, leading to the build-up of methane pressure inside the GEIN structure. Increasing gas pressure inside solid particles promotes the extension of defects and appearance of fissures. Part of the methane generated during decarburization may be decomposed over surface iron atoms to form graphene and hydrogen. (IV) With time, methane pressure continues to increase at these fissures and causes cracks in the GEIN structure. The cracked graphene shell can then be peeled off the iron core.The cracking process of GEINs by hydrogen molecules may undergo the following steps: (I) hydrogen diffuses and penetrates through the graphene shell into the iron core and reacts with carbon inside Fe2 from methane decomposition will help to crack the GEINs and gasify the amorphous carbons in the grains of GEINs to form gaseous carbon-containing molecules, followed by re-deposition to form ordered graphene-based materials. The carbon atoms from methane decomposition will serve as an atomic glue to join the cracked graphene shells and can also deposit to vacancy or defect sites in the cracked graphene shells to improve the quality of the graphene product.Hydrogen also has strong etching effects on graphene structures by a gasification reaction at high temperatures. Methane is therefore selected as both the cracking and the welding reagent in this work, since methane can decompose to hydrogen gas and a carbon atom in the MCW process. H4 mixture (50-mL/min Ar80-mL/min CH4) through a fixed-bed reactor loaded with a 50-g GEIN sample. The reactor was heated to 1000 °C, with a heating ramp rate of 10 °C /min. The flow rates  and the particle size of the carbon matrix embedded with GEINs. The process conditions and the yields of the graphene materials are listed in The effects of heating temperature on the yield of graphene-based materials from GEINs were evaluated in the range of 700–1000 °C and the results are plotted in 3C peaks decreased, possibly due to cementite (Fe3C) in the outer layer of the iron core being decarburized and partially transformed to α-Fe and γ-Fe. Further increasing the temperature to 900 °C, α-Fe and γ-Fe peaks grow even sharper, while the Fe3C peaks continue to turn wider and weaker, indicating that the decarburization of Fe3C is ongoing in the metal cores of the GEINs. In addition to the α-Fe, γ-Fe, and Fe3C peaks, a diffraction peak at around 26.5° appears in the product materials, indicating the formation of graphene due to the MCW reaction process, where the graphene shells are cracked, peeled off from the iron cores, and welded into the graphene nanoplatelets. The stronger graphene diffraction peak when the temperature is increased to 1000 °C implies the graphene nanoplatelets are growing larger and thicker. The α-Fe, γ-Fe, and Fe3C peaks are also stronger and sharper for the 1000 °C sample, because after the GEINs are cracked and the graphene shells peeled off, the iron cores are now naked with high mobility and will migrate and sinter to large-sized iron particles. Methane can react with the naked iron particles to form iron carbide.XRD patterns of the graphene materials produced from GEINs under different heating temperatures are shown in 3C by hydrogen from the decomposed methane. When the temperature increases to 900 °C, the core–shell structures of the GEINs are cracked, and the graphene shells are skinned off the iron cores to form graphene nanoplatelets. The sizes of the iron particles significantly increased to 30–100 nm due to coalescence of the naked iron cores. HRTEM image of the cracked GEIN sample at 1000 °C demonstrates the continuation of the MCW process; more graphene materials are formed, and the iron particles are separated from the graphene structures.HRTEM images of the GEIN samples cracked by methane molecules for 1 h at different reaction temperatures  are shown in The impact of the GEIN grain particle size on the MCW process was studied in the current work. Four initial GEIN grain particle size fractions: <50, 50−150, 150−250, and 500−700 µm were screened for studying the effect of particle size on the yield of graphene materials, which is illustrated in 3C peaks also grow strong and narrow for smaller GEIN grains, possibly due to high mobility of the cracked graphene shells and the iron cores from the smaller particles. The peeled graphene shells and the naked iron particles from the smaller GEIN grains are the most mobile during the MCW process. Welding of the graphene nanoplatelets and sintering of the iron cores will be accelerated by the free movement. The graphene nanoplatelets can be jointed into larger and thicker pieces through all possible directions, while the iron cores will migrate and coalesce to large-sized iron particles. These large iron particles can react with methane to form iron carbide. Due to particle agglomeration in the large GEIN grains, the cracked graphene shells and the iron cores have relatively low mobility; therefore, the welding reactions of graphene shells and sintering of iron particles are limited during the MCW process and result in smaller and fewer layers of graphene materials.The XRD patterns of graphene materials prepared from GEIN precursors with different grain sizes are shown in −1 represents either defect or amorphous carbon, whereas the G-band at 1573 cm−1 represents the ordered graphene structures. The graphitization degree of the graphene materials is measured through the intensity ratio of AD/AG. AD/AG had an increasing trend as the GEIN grain size increased from below 50 µm to 500−700 µm, confirming the lower graphitization degree of the larger GEIN particle samples.The quality of the graphene materials was investigated using Raman spectroscopic measurements. As presented in Overall, the experimental results in 4.The reaction time is also an important parameter for the production of graphene from GEINs through the MCW process. To study the effect of the reaction time, it was varied 0.5, 1, 2, and 3 h while keeping the reaction temperature constant at 1000 °C; the reactant gas was 50-mL/min argon and 80-mL/min CH2 from methane decomposition can react with amorphous carbon in the GEIN grains to form gaseous carbon-containing molecules , followed by re-deposition to form graphene materials. Atomic carbon from methane can deposit in the voids or defects on the graphene materials to improve their quality. The extra methane in the flow can serve directly as a reactant to form graphene over the surface of the metal particles.The effects of reaction time on the yield of graphene materials are plotted in 3C peaks also grow sharp and tight with the longer reaction time, possibly due to sintering of the iron cores with the extended reaction.AD/AG)  c. The ADFew-layer graphene materials were synthesized from lignin resources using the MCW method over a fixed-bed reaction system. This is a single-step process with two stages. In the first stage, few-layer graphene-encapsulated iron nanoparticles (GEINs) were formed through the catalytic graphitization of Fe-lignin nanocomposites. Then, in the second stage, these GEINs were cracked and opened into few-layer graphene shell-like structures, which were welded and reconstructed under high temperatures with selected welding reagent gases to form few-layer graphene materials . The influences of heating temperature, heating time, and Fe-lignin composite particle size on the yield of few-layer nano-shell graphene materials produced from lignin resources were investigated. The ideal welding temperatures were found to be at least 1000 °C, with the heating time ranging from 0.5 to 1 h. The optimized Fe-lignin composite particle size was found to be between 150 and 250 μm.


This paper investigates the use of a Magnetite Polydimethylsiloxane (PDMS) Graphene array sensor in ultra-wide band (UWB) spectrum for microwave imaging applications operated within 4.0–8.0 GHz. The proposed array microwave sensor comprises a Graphene array radiating patch, as well as ground and transmission lines with a substrate of Magnetite PDMS-Ferrite, which is fed by 50 Ω coaxial ports. The Magnetite PDMS substrate associated with low permittivity and low loss tangent realized bandwidth enhancement and the high conductivity of graphene, contributing to a high gain of the UWB array antenna. The combination of 30% (ferrite) and 70% (PDMS) as the sensor’s substrate resulted in low permittivity as well as a low loss tangent of 2.6 and 0.01, respectively. The sensor radiated within the UWB band frequency of 2.2–11.2 (GHz) with great energy emitted in the range of 3.5–15.7 dB. Maximum energy of 15.7 dB with 90 × 45 (mm) in small size realized the integration of the sensor for a microwave detection system. The material components of sensor could be implemented for solar panel.  Nowadays, the application of antennas as sensors is stressed most in terms of bandwidth and efficiency improvement despite miniaturization . SubstraRecently, a sensor made of a polymer composite substrate with preferable mechanical and electrical characteristics has attracted the interest of researchers. Various kinds of elements are composed with a variety of additions, possibly nickel ferrite, ceramic, and titanium . One of Physically, sensors for microwave imaging must be compact, light, and planar . Anothert) effect of a magneto-dielectric towards bandwidth enhancement [PDMS is one the kind associated with flexibility, less permittivity, resistance to water, as well as the ability of mixing other elements to enable a variety of fabricated substrates for the antenna ,18,19. Iancement , as demo−1 nm (nano size), 108 s/m (high conductivity), 7.7 × 10−1 mg/1 m (light element), and 150 × 106 psi (strong element) of the single layer carbon atoms in 2-D honeycomb lattice constructed the Graphene. On the other hand, Graphene has gained much interest among researchers to replace copper as a radiating material of the patch antenna sensor. A comprehensive Graphene study revealed graphene to be totally advanced compared to copper, single and multi-wall carbon nanotubes ,21. The As for detection purposes, using a microwave frequency range called microwave imaging, bandwidth and gain of the sensor are among the most important elements to be considered compared with others element . The antIn this paper, a Graphene sensor array, which is fully embedded in a composite substrate of magnetic-based PDMS dielectric (PDMS-Ferrite), is presented as well as the study of the combination efficiency of the substrate and the graphene. This is done by comparing the proposed antenna sensor with a similarly dimensioned antenna fabricated on a dielectric (Taconic) substrate. Although the concept of PDMS-magneto materials has been reported in literature recently, the validation study towards the scientific relation between polymer dielectric with magnetic-based substrates and a Graphene sensor in terms of the bandwidth and gain described in this paper is among the earliest.2 make the UWB sensor suitable for microwave detection purposes [An overview of such antennas published in the literature is presented in purposes .8 s/m for the conductivity value and PDMS-Ferrite is set to 2.6 and 0.01 for permittivity and loss tangent respectively. The array circular patch has been measured through specific calculation prior to being simulated using computer simulation software. Once being improved, the optimized patch size was determined at 15 mm in diameter. A 50 Ω microstrip line acts as feed source placed at the center right back of the patch for direct connection between the feed source and patch. In order to realize high gain sensor, a single circular patch is multiplied to produce a 4 × 1 array. A corporate feeding structure is applied by adding feedlines for the connectivity of each patch. Identical power delivery of all patches could be realized by applying a quarter-wave transformer impedance matching method. Hence, 100 Ω and 50 Ω feedlines are coordinated using quarter wave transformers of 70.71 Ω [The magnetite PDMS Graphene array sensor is generally constructed of Graphene to form an array circular patch, incorporate a feeding line, parasitic element, and partial ground, as well as PDMS-Ferrite to form magnetite dielectric substrate. For simulation, Graphene has been set to 3.8 × 10 70.71 Ω .8 s/m, respectively [ectively . On the Magnetic Ferrite in three different ratios  and PDMS  is well blended respectively to realize three different mixed solutions of novel PDMS-Ferrite dielectric substrate with magnetic characteristics and a diversity of unique features. It is proven that the ratio of 30% iron oxide nanoparticles leads to improving dielectric properties which directly enhance the sensor performance. However, the sensor performance started to degrade once the ratio achieved 50% of Ferrite because of the excessive magnetic element existence leads to high magnetic losses. The PDMS-Ferrite substrate has been measured in terms of permittivity as well as loss tangent using a dielectric probe and VNA. The PDMS-Ferrite substrate measurement results for permittivity as well as loss tangent with 30% of Ferrite concentration in the form of liquid and solid are shown in On the other hand, the waveguide approach is another method to determine PDMS-Ferrite permeability. A study has been performed to investigate the optimum thickness of PDMS-Ferrite by varying the thickness of simulated PDMS-Ferrite in the range of 0.4–2.0 mm, as shown in The FESEM image of graphene in 8 s/m, resistivity of 2.01 × 10−3 Ω.m, voltage of 0.2 V, and current of 9.48 × 10−1 A. The measured high conductivity and low resistivity values are good in agreement with early reported work on the conductivity and resistivity of graphene by several researchers [A four point probe device was used to measure graphene conductivity, as shown in earchers . The obsearchers .Fabricated sensors of the Magnetite PDMS Graphene array and Copper-Taconic are illustrated in On the other hand, the Magnetite PDMS Graphene array sensor E-plane radiation pattern at frequency of 3, 4, 5, and 6 GHz is shown in 8) higher than copper (3.7 × 107).In a nutshell, the addition of a magnetic element, Ferrite, to a PDMS solution enables to reduce the permittivity value and loss tangent of the sensor substrate. Ferrite and PDMS with in the proportion of 30% and 70% each were selected and integrated to realize low permittivity as well as low loss tangent of 2.6 and 0.01 correspondingly for the Magnetite PDMS Graphene array sensor substrate. The proposed sensor recorded UWB operated frequency within the range of 2.2−11.2 (GHz) and great energy was emitted in the range of 3.5–15.7 dB due to ferrite relative permeability as well as permittivity exceeding the unity (εr and μr > 1) and low permittivity of PDMS. The sensor with PDMS-Ferrite substrate managed to have bandwidth enlargement as much as 28%, which is equal to 2 GHz for this paper as compared with the conventional Taconic substrate. In terms of the gain, the proposed Magnetite PDMS Graphene Array sensor recorded the maximum gain of 15.7 dB compared with Copper-Taconic antenna which recorded 13.5 dB for maximum gain due to the presence of graphene as the radiating element that has a conductivity value (3.7 × 10