The Raman spectra and photoluminescence properties of the GF and ZGCF were characterized before and after the sliding friction. A remarkable phenomenon was observed that after friction the GF generated a more pronounced luminescence response than it had prior, apparently due to graphene quantum dots which were found in the wear debris of the GF. Furthermore, the introduction of graphene into YSZ:Er nanoparticles (NPs) resulted in an unmistakable red-shift on the main luminescence bands of ZGCF after the applied friction. This is explained by the formation of considerable graphene scrolls in the wear debris of ZGCF due to the interaction of the graphene and the YSZ:Er NPs. It can be concluded that changes to the configuration of graphene greatly influence the tribo-induced photoluminescence response. Our findings justify further investigation into the composition and morphology of worn surfaces in order to better understand how photoluminescence relates to frictional effects. In addition, this work proposes the in situ fabrication of graphene quantum dots and nanoscale scrolls as a new potential application of the tribo-induced photoluminescence study.In the present work, a novel method was developed to study the evolving surface state of graphene film as it is subject to friction, characterized by photoluminescence properties. We prepared the graphene film (GF) and YSZ:Er (Er In the present work, a novel method was developed to study the evolving surface state of graphene film as it is subject to friction, characterized by photoluminescence properties. In the past decade, several tribological mechanisms have been proposed to explain the friction processing of freshly worn surfaces along with the associated formation and transfer of debris.5,6 However, due to limitations of the experimental tools, it remains challenging to thoroughly analyze the role of shearing reactions during the friction process. Of particular interest is the shearing phenomena within the sliding contact area in situ at the molecular-level.7 Certain weak physical and chemical effects observed on the surface or the interface of sliding partners were typically neglected in the past, but presently these phenomena become increasingly significant in regard to changing friction service conditions.8 For example, harsh friction conditions can lead to a cascade of excitation and de-excitation processes of tribological interface or fractured surfaces, producing luminescence and emitting charged particles. Consequently, several investigations on tribo-induced magnetization,9 luminescence10 and surface charges11 have been reported. Nakayama et al.12,13 studied the phenomena of triboplasma and triboemission, as well as the occurrence of shearing reactions during the friction process. They found that various solids, especially insulating solids, emit UV photons during the sliding process; they also found that the triboemission depends greatly on the electric resistivity of the sliding partners. Nevshupa14 found that energy dissipation at a tribo-contact can depend on a variety of elementary physical processes and chemical reactions; they studied several factors, such as the surrounding gas, the surface coating and the types of rubbed materials, that can influence triboluminescent behavior.Extreme external loading conditions can significantly impact the worn surfaces of many materials that are widely used in industrial and marine fields.15–17 Recently, due to its compact size and extremely thin laminated structure, the tribological properties of graphene have been intensively examined for potential applications in micro- and nano-mechanical devices.18,19 The size effect of graphene in conjunction with a surface coating of functional groups or metallic ions was proved to contribute to extraordinary optical properties.20,21 It is also known that friction may induce considerable changes in the size, defect structure, and surface adsorption of counterface materials.22 Mishina et al.23 reported an in situ observation of such effects on surface crystal grains during a sliding friction process and witnessed a wear debris generated from the solid surface. However, up to now, research has been rarely focused on how the morphologies of graphene wear-debris could affect the physical phenomena and chemical reactions on the tribological surfaces or the graphene interface, in particular regarding the tribo-induced photoluminescence during the process of sliding friction.Graphene, as a 2D-honeycomb structural carbon sheet, possesses exceptional optical, electrical and mechanical properties.In the present work, we prepared graphene film (GF) and YSZ:Er/graphene composite film (ZGCF) see  and founvia a standard metallographic procedure and then were cleaned with acetone. Subsequently, the treated stainless steels were implemented using the laser drilling technique with pulsed laser . The diameter of each hole was 150 μm and each two of the adjacent rows was evenly spaced with 350 μm.The surfaces of stainless steels (20 mm × 20 mm × 3 mm) were mechanically polished 4 as an oxidizing agent. For this purpose, 50 mL of H2SO4 (AR) was introduced into a three mouth flask with constant stirring. 1 g flake graphite  and 1.2 g KNO3 (AR) were added into the three mouth flask. After stirring for five minutes, 6 g KMnO4 (AR) was slowly added to the mixture. The reaction mixture was maintained at 40 °C for 3 h. Then, 80 mL deionized water was slowly added into the three mouth flask and the mixture was maintained at 70 °C for 30 min. After the oxidation step, the resulting mixture was added to a beaker containing 400 mL of deionized water and 20 mL of H2O2  in order to quench the reaction. 2 mol L−1 NaOH (AR) solution was slowly added into the above-mentioned solution in order to adjust the PH value to 6. After static precipitation and removing the supernatant, the precipitate was centrifuged and washed with distilled water and ethanol for three times. The product obtained was reduced by hydrazine hydrate . The obtained reduced graphene oxide (rGO) obtained via Hummers' method was dispersed in ethanol at a pre-determined ratio using the ultrasonic treatment. A spin-coating on the stainless steel was applied and dried in an oven at 80 °C. The preparation process of the GF is shown in Graphene oxide was synthesized by the Hummers method. The first step consists of the oxidation of graphite using KMnO2·8H2O (AR), ErCl3 (99.9%), Y(NO3)3·6H2O (≥99.99%), NaOH (AR), lactic acid (AR) and deionized water were used as raw materials. A procedure for the sample with 1 at% Er3+, 10 at% Y3+:ZrO2 synthesis is typically described as follows: 2.578 g ZrOCl2·8H2O, 0.3064 g Y(NO3)3·6H2O (acted as stable agent), 0.0219 g ErCl3 were first dissolved in 24 mL deionized water. Then 5 mL lactic acid was added to the above solution then mixed well with a magnetic stirrer. 10 mol L−1 NaOH solution was slowly added into the above solution to adjust the PH value to 6. After mixing evenly, the mixed solution was transferred to Teflon liner. Hydrothermal treatments were conducted at 160 °C for 24 h. After the synthesis reaction, the product obtained was centrifuged and washed with distilled water and ethanol, and dried at 80 °C during 12 h. In the last step, the dried YSZ:Er samples were annealed at 700 °C for 2 h in air. YSZ:Er NPs, rGO obtained via Hummers' method, and salicylic acid were dispersed in ethanol at a pre-determined ratio using the ultrasonic treatment. A spin-coating on the stainless steel was applied and dried in an oven at 80 °C. The preparation process of the ZGCF is also illustrated in YSZ:Er (Er-doped yttria stabilized zirconia (YSZ)) nanoparticles (NPs) were prepared by the hydrothermal synthesis method. YSZ:Er was prepared by a hydrothermal method. ZrOCl3N4) with diameter of 3 mm, and announced mean roughness of 0.02 μm were used as the stationary upper counterparts. The friction-coefficient-versus-time curves were generated automatically. All experiments were performed under ambient conditions of 25 °C and 26% relative humidity.The dry friction test at room temperature in air was conducted with a WTM-2E tribometer  in a ball-on-disc contact configuration at a load of 1 N and a speed of 200 rpm for 20 minutes. Commercially available silicon nitride balls .Raman and photoluminescence spectroscopy were performed in the wear and non-wear track by using the laser spectrometer  with 514 nm and 325 nm excitation wavelengths to assess the quality of graphene and the luminescent behavior before and after friction. The light source with excitation wavelength was used to test each sample at three random points.λex = 633 nm) of graphene and YSZ:Er/graphene nanocomposite. On the Raman spectrum of graphene, the exhibited G band (∼1605 cm−1) is corresponding to sp2-hybridized carbon while a D band (∼1350 cm−1) is corresponding to disordered carbon. The spectra of YSZ:Er/graphene shows a combination of the characteristic peaks from both the graphene sheets  and the ZrO2 (m-phase at Ag 634 cm−1 and t-phase at Eg 269 cm−1 and B1g 312 cm−1). The measured signal intensity of D and G peaks of the ZGCF sample is higher than that of GF under the same testing condition. The difference in the Raman spectra of GF and ZGCF is due to the surface enhanced Raman spectroscopy (SERS) effect caused by chemical enhancement. It is generally known that there are many functional groups on the surface of GO, which can interact with YSZ:Er NPs. The obtained ZGCF is something like charge transfer complex, which can absorb the light at the excitation frequency, consequently resulting in chemical SERS.242 in YSZ:Er NPs and ZGCF, respectively, which indicate that the characteristic peaks of both ZrO2 in YSZ:Er NPs and ZGCF are similar. The difference in the peak intensity of is attributed to the presence of graphene wrapping NPs in ZGCF, which is caused by the interaction between the graphene and YSZ:Er NPs.3N4 counterface. Owing to the fact that the graphene sheets exhibit a relatively low shear strength, the interlayer interaction is weakened and thus deceases the COF. In contrast, 3N4 counterface. The wrapping around the YSZ:Er NPs by graphene starts at the initial friction stage,25 which coincides with substantial dropping of the COF value. As the friction proceeds, graphene sheets are divided into a considerable number of patches and then the YSZ:Er NPs are exposed on the wear surface. Hence, the YSZ:Er NPs act as a nano-ball bearing and can roll between the Si3N4 counterface and substrate, which reduces the friction and provides extra mechanical strength. Therefore, the COF of ZGCF has a higher COF than that of GF, while both of them have the lower COF than the substrate.−1 of iron oxide debris besides in Raman spectrum of GF after the friction. As for the new band peak located at 667 cm−1 of GF, many researches have reported26–28 that the peaks at about 660 cm−1 exhibited existence of the magnetite (Fe3O4). The hole structure produced by laser drilling can not be filled by the graphene sheets, which affects the release of the graphene lubricant and the wear life of GF. The Raman spectra show that the intensity ratio of D band over G band (ID/IG) after the friction is higher (1.03) than that before friction (0.95), as indicated in 29 where the increase of ID/IG ratio is due to the increased number and size of sp2 clusters. The surface structure and composition of graphene sheets were greatly shown to be influenced by plastic deformation and heat transfer during the friction; these two factors play an important role in the evolution of graphene configurations.30,31 The insets of 2 shifts from 634 cm−1 (before friction sliding) into 642 cm−1 (after friction sliding). Interestingly, unlike the case of GF, the ID/IG before friction (0.97) is surprisingly higher than that after friction (0.83), indicating that the embedded YSZ:Er NPs do affect the defect structure in the graphene. Specifically, when these YSZ:Er NPs are removed from the graphene, we observed the formation of many graphene scrolls that are very similar to CNT-like structures32  from the encapsulated YSZ:Er NPs that essentially drive the motion of the rolling graphene to form into a scroll shape.35,36 During the friction, the shear stress arises and weakens the interaction between the graphene and NPs. When the wear debris is dispersed into an alcohol solution for microstructure characterization, many YSZ:Er NPs become detached from the curled graphene and the hollow graphene scrolls finally can be formed.i.e., the tribo-induced photoluminescence. 37,38 it was found that optical responses are due to the quantum confinement effect of graphene as well as the presence of defects. Consistently, in the present work this obvious photoluminescence behavior of GF is observed at the wavelengths of 430 nm and 505 nm within the spectrum, as plotted in 39 that graphene-oxide NPs can exhibit a red-shift of the band-edge and a significant reduction of the band gap. These phenomena can be explained by the photoluminescent mechanisms illustrated in 40 Meanwhile, the friction environment enables the adsorption of a little amount of oxygen on the graphene surface accompanied by the composition of the debris, which gives rise to the presence of sp3 carbon atoms covalently bonded to the oxygen-bearing functional groups in addition to the sp2 hybridization in the pristine graphene. Therefore, a finite electronic bandgap generated by the disruption of π-networks, to a certain extent, can facilitate in opening up the bandgap of graphene and thus enhance its photoluminescence quantum yield. In contrast, the changing photoluminescent behavior of ZGCF can be explained with a mechanism (see the illustration in 41 Our current study demonstrates that the tribo-induced interaction between YSZ:Er NPs and graphene nanoscrolls has a unneglectable effect on the electronic structure and bandgap, which in turn influences the luminescent emission and results in the red-shifts on the spectra.The above-mentioned wear debris of unique microstructures culminated in an unexpected physical response, In summary, we proposed and implemented a novel strategy for studying the surface state and interface phenomena of sliding contact materials during the friction process. More importantly, we report the phenomenon that GF exhibits pronounced friction-induced photoluminescent properties due to the formation of graphene quantum dots as well as the defect structures formed in the graphene sheets. Furthermore, ZGCF displayed a noticeable red-shift of luminescent bands due to the combined effects of YSZ:Er NPs and graphene scrolls during the friction process. The discovery of the presence of graphene quantum dots and graphene scrolls that are induced by friction provides a potential new approach for multi-morphology fabrication of graphene. Lastly, the tribo-induced luminescent behavior reported in current research can be served as an incentive for further inquiry into tribo-physical phenomena and tribo-chemical reactions in the near future.There are no conflicts to declare.


The interfaces in 2D hybrids of graphene and h-BN provide interesting possibilities of adsorbing and manipulating atomic and molecular entities. In this paper, with the aid of density functional theory, we demonstrate the adsorption characteristics of DNA nucleobases at different interfaces of 2D hybrid nanoflakes of graphene and h-BN. The interfaces provide stronger binding to the nucleobases in comparison to pure graphene and h-BN nanoflakes. It is also revealed that the individual dipole moments of the nucleobases and nanoflakes dictate the orientation of the nucleobases at the interfaces of the hybrid structures. The results of our study point towards a possible route to selectively control the orientation of individual molecules in biosensors. The interfaces in 2D hybrids of graphene and h-BN provide interesting possibilities of adsorbing and manipulating atomic and molecular entities. These studies indicate that the noncovalent interactions such as π–π stacking and X–π  interactions stabilize the nucleobases adsorbed on graphene and h-BN.19–25 This shows the potential of using graphene and h-BN in biosensing applications. Moreover, graphene nanoribbons have been proposed to rapidly sequence DNA by measuring the time-dependent conductance as the nucleotides of single-stranded DNA are brought sequentially in contact with the nanoribbon.26 Recently Lee et al. have studied the interaction of nucleobases with h-BN and graphene using an approach that incorporates van der Waals interactions into the density functional scheme. They found that the binding energies of the different nucleobases with two sheets (h-BN and graphene) are similar and an interfacial dipole is induced between the sheet and base molecule during adsorption.27Graphene,28 Gao et al. have explained the formation of CBN with different edges using Rh (111) substrate and they have shown that formation of zigzag edges is more favorable than that of armchair edges.29 The CBN monolayer can be used as an ultrathin solar cell with PCBM fullerene as an acceptor.30 Although, the physical properties of these CBN materials have been studied, the interaction of nucleobases with CBN surfaces has not yet been reported. It should be noted that the interaction between the dipoles in the nucleobases and hybrid nanoflakes can give rise to non-trivial properties based on the mutual orientations at the interface of dissimilar flakes. In the present study, we have carried out density functional calculations to investigate different orientations of nucleobases, namely adenine (A), guanine (G), thymine (T) and cytosine (C) adsorbed on CBN nanoflakes with different edges, namely armchair, as well as zigzag with either N- or B-termination. Specifically, we have studied the equilibrium geometries, binding characteristics, and role of dipoles in dictating the mutual orientations.Very recently, 2D hybrids (CBN) of graphene and h-BN have been prepared through chemical vapor deposition method. These hybrids are found to have unusual electronic, magnetic and transport properties including half-metallicity.31 Throughout this article, we refer to interfaces with armchair edges as Arm, to those with zigzag edges where N bonds with C as Zig-N, and to those with zigzag edges where B bonds with C as Zig-B. We have employed ab initio calculations based on Density Functional Theory32,33 (DFT) and the Linear Combination of Atomic Orbitals (LCAO) as implemented in Gaussian09 34 and SIESTA35 codes. We used two levels of calculations to validate our results and give greater confidence in the accuracy of the study: one of them was hybrid meta exchange–correlation functional M06-2X36 with 6-31+G basis set, while for the second one, we used Generalized Gradient Approximation (GGA-PBE)37 with van der Waals corrections38,39 to take into account dispersive interactions. For the SIESTA calculations, we considered a box of 30 Å3 to avoid the interactions between periodic images. Double-ζ polarized basis sets (DZP) and norm-conserving pseudopotentials40 were used. To obtain equilibrium structures, forces in three directions on each atom were minimized below 0.01 eV Å−1. From here on, meta-GGA is meant to refer to Gaussian09 calculations while GGA + vdW refers to SIESTA calculations.Structural models of CBN flakes with armchair (Arm) and zigzag (Zig) interfaces were considered from previous studies.The stability of the flakes was evaluated using the formation energy as per the following equation:ET, ni, μi, N refer to: total energy of the flake, number of each species in the flake, corresponding chemical potential, and total number of atoms in the flake, respectively. In the second equation, Eflake is the total energy of the hybrid flake . EGR flake is the total energy for the graphene reference system, μi  is the chemical potential of each species and Ni  is the number of extra or missing atoms for a particular species in comparison to the reference graphene flake. Ntot is the total number of atoms comprising of C, N and B involved in the equation.In the first equation, −1 considering GGA + vdW and 3.38 (7.34) kJ mol−1 for meta-GGA respectively. The results follow the same trend using both functionals; the cohesive energy difference between the most stable flake (Zig-N) with the least stable (Zig-B) is about two times bigger than that for the second-most stable (Arm) flake. Next, we have calculated the formation energies for the hybrid flakes with GR flake as a reference using the equation given above and the values are 384.32, 473.24, and 479.37 kJ mol−1 for the Zig-N, Arm, and Zig-B flake respectively. This result follows the same trend as that of cohesive energies. It should be noted that the positive formation energies indicate that the flakes can be metastable but still possible to form as seen in experiments. The corresponding values are calculated as −457.68, −368.77, −362.63 kJ mol−1 when a BN flake is considered as the reference. These values indicate that the hybrid flakes can be spontaneously formed. The difference in these two cases is related to the growth conditions with different reservoirs. As the flake with the B-terminated zigzag edge (Zig-B) is found to be the least stable in all the cases, we will consider only adsorption complexes involving Zig-N and Arm from now on.The cohesive energies for the three flakes are given in 41 For the flakes, we note that Zig-N possesses a total dipole moment about 1.5 to 1.7 times bigger than the Arm flake.As nucleobases and flakes possess distinct dipole moment values and orientations, an interesting question can be addressed regarding the mutual interaction and the resulting stability of the complexes formed between the nucleobases and the nanoflakes. Specifically the relative orientation between a nucleobase and a nanoflake is of primary interest to us in the present study. To explore this question, we have investigated two fundamentally different geometries for each complex, in which the dipole moments of the constituting subsystems are either parallel or antiparallel to each other.E = EP − EAP) can provide insights into the relative stabilities and are listed for all explored combinations of Zig-N and Arm flakes with the four nucleobases in vs. 1.33 kJ mol−1), whereas in meta-GGA, the reverse is true (0.54 vs. 2.50 kJ mol−1). This difference may occur due to distinct considerations of dispersion corrections in GGA + vdW and meta-GGA.Indeed it is found that for all nucleobases on either of the two studied nanoflakes, the antiparallel configuration is always more stable than the parallel one in the Arm and Zig-N flakes, as confirmed by both functionals. However, the nucleobases A and T on Arm are almost degenerate in energy for parallel and antiparallel configurations, indicating no strong preference for either orientation. However, a closer inspection reveals that for GGA + vdW, the antiparallel configuration for A is more stabilized than that for T  arrangement: G > C > T > A. It is interesting to note that these results follow the same hierarchy as that of the isolated nucleobases. For the anti-parallel (AP) orientation, the trend is reversed,  moments . The sitIflake+DNA is the total charge density for the full system and Iflake(IDNA) is for the flake (DNA), respectively. The charge density difference plots shown in i.e., the accumulation of positive charge in the graphene side and a negative one in the h-BN side.To understand in detail the interaction due to adsorption, we calculated charge density differences between the flake-DNA nucleobase complexes and the sum of the charge densities of flakes and DNA nucleobases as described in the following expression:Finally, we discuss the binding energies of the nucleobases on different interfaces of CBN flakes. For comparison, we have also calculated the binding energies on pure graphene and h-BN flakes of the same size as the hybrid systems. These calculations have been carried out using the meta-GGA approach. From the binding energies presented in e.g., for the purpose of DNA sequencing, by improving the signal-to-noise ratio due to the reduction of spatial fluctuations of the nucleobases.In the present work, we have performed first-principles calculations to study the interaction of nucleobases with 2D hybrid nanoflakes formed of graphene and h-BN, considering three different types of interfaces. Our results reveal that the dipole moment orientation of the nucleobases relative to the dipole moment of the hybrid nanoflake interface plays the decisive role in stabilizing these complexes. The antiparallel orientation of dipole moments of the nucleobases with respect to those of the nanoflake interfaces is found to be more stable than the parallel orientation in the armchair and N-terminated zigzag interfaces. Furthermore, the binding energies of the nucleobases on the hybrid flakes are found to be higher than those on both pure graphene and pure boron nitride flakes of the same size. Our study hints at the possibilities of using hybrid flakes to achieve better sensitivity in detecting and identifying specific nucleobases, There are no conflicts to declare.


How to prepare graphene@MXene hybrid through a simple, safe and eco-friendly synthetic route is highly desired. Compared with traditional synthesis technology, ultrasound synthesis strategy displays the merits of simplicity, low cost and environment protection. Herein, MXene (Ti3C2Tx) nanoflakes coupled with graphene nanosheets (graphene@MXene) were prepared in N-methylpyrrolidone (NMP) by simple ultrasound-assisted liquid-phase exfoliation method for the first time. Besides, the effect of types of solvent with different viscocity, sonication temperature and sonication duration time on the property of graphene@MXene hybrids were systematacially investigated. It is found the liquid-phase exfoliated graphene owned excellent electron transfer ability and the MXene (Ti3C2Tx) nanoflakes possessed outstanding adsorption property, the as-synthesized graphene@MXene hybrid exhibited significant signal synergistic enhancement effect toward the oxidation of hazardous veterinary drug residue compound (chlorpromazine) and food additives (rhodamine B). Based on this, a novel and sensitive electrochemical sensor was fabricated, the linear detection ranges were 5 nM to 0.5 μM for chlorpromazine with sensitivity of 1090 µA μM−1 cm−2, and 10 nM to 2.5 μM for rhodamine B with sensitivity of 440 and 102.14 µA μM−1 cm−2. Besides, the detection limits were evaluated to be as low as 1.25 nM and 2.45 nM for chlorpromazine and rhodamine B, respectively.To date, multiple graphene@MXene hybrids have been reported  For instance, the Yang group developed a highly sensitive electrochemical sensing platform for the detection of organic dye Sudan I basing on the chemically reduced graphene oxide In recent years, ultrasound-assisted synthesis method has been considered to be a kind of simple, green, low-cost and promising technology for preparing various functional nanomaterials. During the sonication process, plenty of cavitation bubbles were generated and then collapsed in the liquid environment, the collapsed cavitation bubbles can result in instantaneous high temperature and high pressure, which make it possible to actuate certain physical/chemical reaction and obtain the nanomaterials with different morphology and composition 3C2Tx) nanosheets, the as-synthesized graphene@MXene hybrid exhibited impressive signal enhancement effect toward the oxidation of chlorpromazine and rhodamine B. Chlorpromazine is a kind of common central nervous system drugs, which may be illegally added to the animal feed to reduce the animal activity and promote animal weight. Excessive intake of chlorpromazine may increase the liver damage risk of humans In this work, novel graphene@MXene hybrid was prepared through simple, green and eco-friendly ultrasound-assisted liquid-phase exfoliation approach for the first time . It is f22.13AlC2 powder was added and kept stirring for 24 h at 40 °C. Subsequently, the suspension was treated by centrifugation and the obtained solid residue was repeatedly washed by deionized water until the pH of the supernatant reached to approximately 7. The final solid product was then dried in vacuum drying oven at 60 °C for 12 h, and the obtained powder was denoted as etched Ti3AlC2 powder. After that, 0.5 g etched Ti3AlC2 powder and 0.5 g graphite powder were respectively added into 25 mL NMP with initial concentration of 20 mg mL−1, and sonicated for 5 h in an ultrasonicator  under the persistent nitrogen gas protection, and the sonication temperature was controlled at about 30 °C. At last, the obtained graphene and MXene suspensions were centrifuged at 3000 rpm for 60 min to remove the large particles, and the resulted colloidal suspensions consisted of MXene (Ti3C2Tx) nanosheets or graphene nanosheets were then separately collected. The concentrations of the MXene and graphene suspensions were then evaluated to be about 0.78 mg mL−1 and 0.18 mg mL−1 by weighing method, respectively. Besides, MXene and graphene powders were also obtained by filtrating the resulted MXene or graphene suspension. When studying the effect of types of solvents with different viscosity, sonication time and sonication temperature on the structure of graphene and MXene, similar experiment procedures were conducted.First, 1.6 g LiF powder was mixed with 20 mL HCl (9 mol/L) until the LiF powder was fully dissolved. After then, 1 g pristine Ti2.2−1) was mixed with 900 μL of graphene suspension (0.18 mg mL−1) and then sonicated for 10 min to obtain the homogeneously dispersed graphene@MXene hybrid suspension. In order to prevent the oxidation of MXene nanoflakes, the sonication mixing process of MXene and graphene nanosheets was also conducted under the persistent nitrogen protection. Basing on this, the volume ratio of MXene in the graphene@MXene suspension was 10 vol% and the total weight concentration of the as-synthesized graphene@MXene hybrid was calculated to be about 0.24 mg mL−1. Besides, the weight fractions of MXene and graphene in the hybrid were then calculated to be 32.5 % and 67.5 %, respectively. Other graphene@MXene hybrids with various composition were also prepared via changing the volume ratio of MXene suspension to 2.5 vol%, 5.0 vol%, 20 vol% and 30 vol%, the weight fractions of MXene in these hybrids were then assessed to be about 10.0 %, 18.6 %, 52.0 % and 65.0 %, respectively.Graphene@MXene hybrid was easily prepared by mixing the liquid-phase exfoliated MXene and graphene suspensions with certain volume ratio. For a typical procedure, 100 μL of MXene suspension  for further electrochemical detection. For the detection of rhodamine B in red chilli powder, 1 g red chilli powder was first dispersed into 10 mL acetonitrile and sonicated for 20 min. The mixture was then centrifuged at 5000 rpm for 10 min. The supernatant liquid was collected and another 10 mL acetonitrile was further used to extract rhodamine B from the residual solid again. When the extract solution was mixed together, 1 g NaCl and 2 mL water was added in succession, and the mixed solution was placed in a refrigerator with −20 °C for 5 h to remove the natural pigments and lipids. After that, the resulted solution was centrifuged at 5000 rpm for 10 min, and the upper acetonitrile solution was collected for the following electrochemical analysis. Spiked samples were obtained by adding a certain amount of chlorpromazine or rhodamine B standard before the pretreatment.The real pork and red chilli powder samples were purchased from the local food market. Before the detection of chlorpromazine in pork and rhodamine B in red chilli powder, the samples were treated by the following procedures 33.13AlC2, HF-etched Ti3AlC2, ultrasound-assisted synthesis of graphene, MXene (Ti3C2Tx) and graphene@MXene powders were first obtained to study their crystal structure  crystal face of the layer-like Ti3C2Tx material. This result suggested that only partial Al element was removed from the pristine MAX phase, and the HF-etched Ti3AlC2 powders were composed of bulk Ti3AlC2 and Ti3C2Tx. Compared with the pristine bulk Ti3AlC2 and HF-etched Ti3AlC2, their characteristic peaks that located at about 2θ = 39° disappeared in MXene, demonstrating the Al element was successfully removed and only the bulk Ti3C2Tx powders in the HF-etched Ti3AlC2 can be exfoliated into thin-layer of Ti3C2Tx nanosheets. Besides, the (0 0 2) diffraction peak of MXene shifted to a lower 2θ angle value relative to that of bulk Ti3AlC2, demonstrating the enlarged interlayer spacing, which could be also attributed to the effective etching of the Al layer XRD patterns of the pristine Titructure a. It is 3C2 precursors can be exfoliated into the flake-like nanostructure. High-resolution XPS spectra of the C 1 s was divided into five well-defined peaks that located at 281.8, 282.3, 284.8, 286.2 and 288.8 eV, which could be ascribed to C-Ti, C-Ti-O, C—C, C—O and O PBM data was replaced with SVG by xgml2pxml:<glyph-data id="pc-E00C" format="PBM" resolution="300" x-size="12" y-size="9">000000000000000000000000000000000000111111111111000000000000111111111111000000000000000000000000000000000000</glyph-data><svg xmlns="http://www.w3.org/2000/svg" version="1.0" width="20.666667pt" height="16.000000pt" viewBox="0 0 20.666667 16.000000" preserveAspectRatio="xMidYMid meet"><metadata>Created by potrace 1.16, written by Peter Selinger 2001-2019</metadata><g transform="translate scale" fill="currentColor" stroke="none"><path d="M0 440 l0 -40 480 0 480 0 0 40 0 40 -480 0 -480 0 0 -40z M0 280 l0 -40 480 0 480 0 0 40 0 40 -480 0 -480 0 0 -40z"/></g></svg>C-O bonds, respectively (3/2/Ti 2p1/2), which could be assigned to the Ti-C (455.2 eV/461.1 eV), Ti2+ (456.2 eV/462.9 eV), and Ti3+ (458.9 eV/464.7 eV) bonds (X-ray photoelectron spectroscopy (XPS) analysis was further conducted to study the surface chemical states and composition of the as-synthesized graphene nanosheets, MXene nanosheets, and graphene@MXene hybrid b. The XPectively c. In addV) bonds d [22], [3AlC2 powders, both graphite and Ti3AlC2 displayed irregular shape with size ranging from 5 to 30 μm. After etching by HF, only partial particles exhibited the accordion-like morphology , numerous nanoflakes were observed for the MXene  scanning in the absence and presence of 1 μM chlorpromazine a and 1 μ2O, ethanol (EtOH), NMP, DMSO, and their viscosity coefficient were 0.553, 0.802, 0.894, 1.07, 1.65, 1.99 mPa.s, respectively. It is seen that bulk graphite powder can be exfoliated into graphene nanosheets in DMF and NMP while bulk etched Ti3AlC2 can be exfoliated into MXene nanoflakes in H2O and NMP. Considering only NMP can be used for the synchronous exfoliation of graphene and MXene, thus NMP was selected as the optimum solvent to prepare graphene, MXene (Ti3C2Tx) and graphene@MXene nanoflakes suspensions. More importantly, both the resulted graphene and MXene nanosheets exhibited good stability in NMP. Studies showed that only when the surface energy of solvent was closed to that of the target material, bulk two-dimensional precursors can be easily transformed into the sheet-like nanomaterial through sonication-assisted liquid-phase exfoliation 2 flow. It is seen that when the sonication temperature varied from 10 °C to 40 °C, the exfoliation efficiency and morphology of graphene and MXene changed little  and volume (20 mL) were first treated by vacuum filtration on the organic porous films, we could see that compact and flat flexible films were easily obtained (R) values of MXene, graphene, and graphene@MXene hybrid were determined as 5.54 MΩ, 3.0 kΩ and 7.6 kΩ, respectively  of chlorpromazine and rhodamine B linearly raised with their continuously increased concentrations , and the corresponded linear relationships can be depicted as: i = 0.0763C − 0.0023 for chlorpromazine in the range of 5 nM to 500 nM, and i1 = 0.0308C − 0.0066 in the range of 10 nM to 250 nM and i2 = 0.00715C + 6.2647 in the range of 250 nM to 2500 nM for rhodamine B. Based on the 3σ/m criterion, where σ is the standard deviation of ten DPV tests for the blank electrolyte and m is the slope of the linear plots, the detection limits of chlorpromazine and rhodamine B were then evaluated to be as low as 1.25 nM and 2.45 nM, respectively.In order to achieve the highly sensitive detection of chlorpromazine and rhodamine B, the effect of pH of electrolytes, accumulation potential, accumulation time and amount of suspension on the current responses of chlorpromazine and rhodamine B at the surface of graphene@MXene hybrid were investigated . It is sThe reproducibility of graphene@MXene hybrid modified electrodes was then evaluated by recording the repetitive DPV curves and current responses of 0.25 μM chlorpromazine and 1 μM Rhodamine B at ten different electrodes. The relative standard deviation (RSD) was then measured to be about 3.8 % for chlorpromazine and 4.8 % for rhodamine B, confirming its good reproducibility.Stability evaluation was conducted by recording the oxidation peak currents of 0.25 μM chlorpromazine and 1 μM rhodamine B at the same sensor for every day. The fabricated sensor was used for only once for each test. After each electrochemical test, the GCE was polished with 0.05 μm alumina powder, sonicated in deionized water and ethanol, modified with 5 μL graphene@MXene suspension, and drying under an infrared lamp in the air. After that, the graphene@MXene modified GCE was stored in air at room temperature for different time for the next test. It is found that the current responses of chlorpromazine and rhodamine B at graphene@MXene hybrid modified electrode still can reached to 93.1 % and 91.2 % of their initial values after two weeks, respectively, demonstrating the long-term stability of graphene@MXene hybrid modified electrodes. For further judging the stability of graphene@MXene hybrid modified electrode in the electrolyte solution, graphene@MXene modified GCE was immersed in the blank electrolyte solution for different time and the oxidation peak signals of 0.25 μM chlorpromazine and 1 μM rhodamine B at graphene@MXene modified GCE was then recorded by DPV test . It is f+, K+, Mg2+, Ca2+, Fe3+, Cu2+, SO42−,Cl−, NO3−, 200 folds of moxifloxacin metronidazole, ofloxacin, fleroxacin, erythrocin, gatifloxacin, dinotefuran has no obvious effect on the electrochemical response of 0.25 μM chlorpromazine. 500 folds of Na+, K+, Mg2+, Ca2+, Fe3+, Cu2+, SO42−,Cl−, NO3−, 100 folds of ascorbic acid, congo red, quinoline yellow, lemon yellow, alizarin red, carmine has no obvious effect on the electrochemical response of 1 μM rhodamine B. These results manifested the as-synthesized graphene@MXene hybrid owned strong anti-interference ability for the detection of chlorpromazine and rhodamine B.Anti-interference ability of graphene@MXene hybrid modified electrodes was also investigated. The potential interference substances were severally adding into 0.25 μM chlorpromazine or 1 μM rhodamine B and the oxidation peak currents of chlorpromazine and rhodamine B were then recorded. It was found that 500 folds of NaIn order to further verify the feasibility of the electrochemical sensor, the content of chlorpromazine in pork sample and rhodamine B in red chilli powder sample were evaluated under the optimal test conditions by DPV. Each sample was parallelly detected for three times, and the content of the target analyte was measured by standard addition method. The analysis results were summarized in 4Ultrasound-assisted liquid-phase exfoliation method has been confirmed to be a simple and effective method for the preparation of novel graphene@MXene hybrid. Due to the synergistic effect, the as-synthesized two-dimensional graphene@MXene hybrid was endowed with superior electron transfer ability and physical adsorption property. Basing on this, excellent electrochemical activity toward the oxidation of chlorpromazine and rhodamine B was achieved, and a facile and sensitive electrochemical sensor was established for the simultaneous voltammetric detection of chlorpromazine and rhodamine B. Besides, the fabricated sensor displayed satisfied reproducibility, stability and practicability. Considering the diversity of MAX phase materials, the proposed liquid-phase exfoliation strategy is believed to be instructive for preparing other graphene@MXene hybrids for various applications.Shenchao Shi: Methodology, Conceptualization, Software, Visualization, Validation, Writing – original draft, Writing – review & editing. Ruizheng Zhong: Methodology, Conceptualization, Formal analysis, Writing – original draft. Lele Li: Methodology, Conceptualization. Chidan Wan: Supervision, Formal analysis, Writing – review & editing, Funding acquisition, Project administration. Can Wu: Supervision, Formal analysis, Writing – review & editing, Funding acquisition, Project administration.The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.


Iodine-doped graphene oxide is attracting great attention as fuel cell (FC) electrocatalysts with a high activity for the oxygen reduction reaction (ORR). However, most of the reported preparation techniques for iodine-doped graphene (I/rGO) could be transposed into practice as multiple step procedures, a significant disadvantage for scale-up applications. Herein, we describe an effective, eco-friendly, and fast technique for synthesis by a microwave-tuned one-stage technique. Structural and morphological characterizations evidenced the obtaining of nanocomposite sheets, with iodine bonded in the graphene matrix. The ORR performance of I/rGO was electrochemically investigated and the enhancement of the cathodic peak was noted. Based on the noteworthy electrochemical properties for ORR activity, the prepared I/rGO can be considered an encouraging alternative for a more economical electrode for fuel cell fabrication and commercialization. In this perspective, the iodine-based catalysts synthesis can be considered a step forward for the metal-free electrocatalysts development for the oxygen reduction reaction in fuel cells. Iodine-doped graphene oxide is considered to have an increased technological capability as a catalyst for the reduction reaction of oxygen (ORR) in fuel cells. Nowadays, fuel cells (FCs) are thought to be one of the most highly performant electrochemical-based systems that are using fuel (hydrogen) electrochemical reduction to obtain electrical energy, for both mobile and stationary applications. The increased importance of fuel cell utilization for energy production applied in a large number of systems confirms the idea that electricity produced by fuel cells could be considered a rapidly emerging progress in the age of energy, ready for commercialization. One such solution is the proton exchange membrane fuel cell (PEMFC) technology, which definitely has the capability of becoming a sustainable and clean electricity source. PEMFC shows the most promise due to the demonstrated high efficiency and low pollution ,2. Low-tOn the other hand, since graphene’s discovery as another allotrope form of carbon, it has been proven that it has remarkable physical–chemical properties for many electrochemical systems, such as fuel cells, electrolyzers, solar cells, etc. Graphene is known as a single-layered graphite composed of a one-atom-thick carbon sheet constituting a hexagonal lattice structure. Graphene oxide represents the oxidized form of graphene. Graphene oxide (GO) has attracted interest as a suitable route to produce graphene. The presence of different functional groups leads to a hydrophilic behaviour that is strongly influenced by the oxidation level. The GO sheets indicate a good dispersion capacity resulting from a strong electrostatic charge and hydrophilicity. The reduction of GO is a common route to obtain a graphene-like structure. Different chemical, thermal, or photo-thermal reduction methods can be used to prepare rGO structures. Depending on the methods used, the rGO produced can be more or less close to the pure structure of graphene. Reducing agents are either inorganic (sodium borohydride) or organic (phenyl hydrazine hydrate or hydroxylamine) chemical agents. Typically, thermal reduction occurs in an inert atmosphere at high temperatures 300–2000 °C. The photochemical reduction of GO involves a direct laser beam at wavelengths below 390 nm . The proIn order to make graphene active from an electrochemical point of view, it is necessary to change the carbon structure by its functionalization with different types of heteroatoms such as halogens. Currently, the halogen-doped graphene presents high catalytic activity for the ORR reaction ,11,12,13Between halogens, the iodine forms diatomic molecules, where two iodine atoms share a pair of electrons to obtain a stable octet; at high temperatures, these diatomic molecules reversibly dissociate a pair of iodine atoms. Similarly, the iodinated anion, I-, is the strongest reducing agent among the stable halogens, being the lightest oxidized back to the diatomic I2. Iodine is the halogen with the largest atomic radius in the group, it can form partially ionized bonds that can promote charge transfer. The ORR activity can be improved through electrocatalytic efficiency due to iodine doping, facilitated by the formation of load transfer complexes (I3- and I5-) that increase the doping capacity and functionality of the graphene support.To dope the graphene-based materials with iodine atoms is a difficult target that brings a high level of difficulty from a synthesis point of view, since the iodine atomic radius is bigger compared with the carbons’ making it more difficult to transfer the charge from one surface to another. However, the negative ion I3- is formed during the iodine graphene doping process. This will enhance the number of positives in the graphene structure and improve ORR’s functionalized graphene catalytic activity. In this context, it should be noted that during iodine doping bonds are formed between iodine and the graphene matrix that can transport the charge between the halogenated iodine groups.2, the O–O bonds of the adsorbed oxygen are reduced, hence enabling effective transformation to water after reduction and protonation.Furthermore, due to the high potential of the halogen-doped graphene to link OMost of the reported synthesis methods of iodine-doped graphene are multiple step procedures, a significant disadvantage for scale-up applications. Having this target, several works have been developed. Iodine-functionalized graphene nanoplatelets for ORR could be prepared by using sequential steps of ball milling for 24 h. The co-doping of iodine with ammonia on the GO surface was accomplished at a high temperature of over 950 °C. Iodine-doped rGO could be obtained by mixing graphite oxide with PI3 followed by refluxing for 24 h. High-quality I/rGO was reported by using a ball milling time of 48 h and further freeze-drying for 48 h. Iodine-doped graphene was prepared by thermal annealing at temperatures between 500 and 1100 °C. Another method involved a high-efficient heat-pressing technique to obtain I/rGO nanosheets . Our recThe microwave (MW) process has been widely applied in many chemical syntheses; however, this research is the first of its type where it is applied for the iodine doping process together with the reduction of graphene oxide, by using a simpler, more effective, faster, and more economical protocol at atmospheric pressure. Through this paper, a canvas-like structure I/rGO was synthesized starting from the graphene oxide (GO) by involving the MW route under mild conditions. This work emphasizes the capability of I/rGO to work as an ORR electrocatalyst used for fuel cells electrodes development, as a low-cost alternative to the commercial platinum-based catalysts.4, Scharlau, 98%), and the reaction mixture was ultrasonicated (80 Hz) for 10 min. The obtained solution was spilled in the microwave reactor  cylindrical vessels. The single-stage microwave (MW) iodine-doping process parameters, in terms of temperature and reaction time, were optimized for mild conditions: atmospheric pressure, temperature 40–60 °C, power 800 W, and reaction time 15 min. The product was chilled moderately to room temperature. The obtained black solid was separated by ultracentrifugation, and then, alternately, washed using DW and ethanol . Finally, the product was dried by lyophilization.The volatiles from the commercial graphene oxide (GO) powder  were removed by degassing at 110 °C. GO was then was added into demineralized water (DW) and stirred for 15 min. The hydroiodic acid (HI)  was completed and the solution was mixed by 10 min sonication. This compound was further reduced with sodium borohydride  involving the nitrogen adsorption measurements at 77 K. The adsorption–desorption isotherms were obtained in low-pressure nitrogen atmosphere. Prior to the BET analysis, the I/rGO powder humidity was eliminated under vacuum outgassing at 388 K, for 240 min. The pore size distribution and total pore volume were calculated by Barrett–Joyner–Halenda (BJH) method and was applied to evaluate the porous surface of iodine-doped graphene as well as of starting graphene oxide. The mass changes with temperature of the reduced graphene oxide (rGO) and iodine-doped samples (I/rGO), respectively, were studied by thermogravimetric analysis (TGA) using TGA-DSC e NETZCH STA 449 F5 Jupiter system. The TGA measurements were done in air flow, in the temperature domain of 27–1000 °C, heating the sample with a rate of 2 K min−1. In order to prove the iodine doping of the reduced graphene oxide support, ATR-FTIR method was used. The Frontier FT-NIR spectrometer was used for the attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR) characterization. The infrared spectra were recorded in transmittance, in domain of 650–4000 cm−1.X-ray photoelectron spectroscopy (XPS) characterization was done using the X-ray photoelectron spectrometer . XPS spectra were measured using monochromatic Al Kα radiation (1486.7 eV). The qualitative elemental analysis was undertaken by recording the broad spectra, and the identification of the different types of chemical bonds that are formed on the surface was obtained from the high-resolution spectra deconvolution. The PHI-MultiPak software was used for the XPS spectra interpretation. The quantitative elemental analysis in terms of chemical elements atomic concentration was performed by calculating the peak areas by considering the sensitivity factors of the analyzed elements. The yield of iodine was 95 ± 2% based on XPS analysis data of three separately prepared samples. Microstructural investigation and elemental analysis were performed using a Carl Zeiss FEG SEM equipped with an EDX system. The I/rGO powder was transferred for SEM investigation on a double-sticky carbon tape and the surplus was blown with compressed air. The specific surface area of the I/rGO samples was measured by Brunauer–Emmett–Teller (BET) method, using AutosorbIQ (Quantachrome). BET technique is generally consecrated method to estimate the specific surface area (S2 glassy carbon (GC) disk was used as working electrode (WE). A 3 M Ag/AgCl (Metrohm) was used as reference electrode (RE) and a platinum wire as counter electrode (CE). All the measurements were done alkaline electrolyte (0.1 M KOH) that was flushed with oxygen for one hour before each experiment. The pH of our 0.1 M KOH aqueous electrolyte in which KOH salt is dissolved is 13, that means a strong base solution. This electrolyte concentration (pH) is commonly used for the catalysts’ electrochemical properties characterization , and it was chosen according to the most published papers in the domain. The potential presented in this work are versus Ag/AgCl RE. The catalyst aliquot was prepared by stirring overnight 5 mg rGO-based powder together with 240 µL isopropyl alcohol, 10 µL DW, and 20 µL 5 wt.% Nafion® solution. For measurements, 7 µL of catalyst solution was deposited onto GC surface, that was previously polished with alumina and diamond paste, cleaned with demineralized water and dried in air.Oxygen reduction reaction (ORR) of the iridium-doped samples (I/rGO) was measured in comparison with non-doped reduced graphene (rGO). The measurements were carried out in commercial glass cell with three electrodes using a 2273 potentiostat (Princeton Applied Research). A controlled speed OrigaTrod rotating disk electrode (RDE) with 0.196 cmn) transferred during the ORR process, linear sweep voltammograms were recorded with 5 mV/s, between 0.4 V and −0.7 V and at various rotation speeds (ω) (among 250–1000 rpm). Linear sweep voltammetry (LSV) curves for I/rGO were plotted as j, which is the measured current density (mA−1 cm2geo) vs. ω−1/2 (rad s−1)−1/2 and studied following Koutecky–Levich (KL) Equations (1)–(3) [Lj—maximum (limiting) current density required to achieve ORR reaction (A cm−2); kj—kinetics current density (A cm−2); F—Faraday constant (96.485 kCmol−1); A—area of the RDE electrode (0.196 cm2); C0—concentration of oxygen (1.2 × 10−6 mol cm−3) in 0.1 M KOH electrolyte; D0—diffusion coefficient of oxygen in the electrolyte (1.9 × 10−5 cm2 s−1); ν—kinematic viscosity (0.01 cm2 s−1) in 0.1 M KOH; and k—the rate constant (cm s−1) for the electron transfer [In order to calculate the number of electrons ( (1)–(3) ,16,17.. XPS spectroscopy was used to determine the chemical state of iodine forms corresponding to the I/rGO sample.5/2 and I3d3/2) in the 616–635 eV interval. 2 hybridized C–C bonds certifies the efficaciousness of the graphene oxide matrix reduction. The C–C bonds are dominant since the HI acid reduction occurred, because most of the hydroxyl and epoxy groups were removed. However, some oxygen-containing functional groups still remain in the rGO sheets, which are typical for chemically reduced GO. The elemental composition and iodine bonding types were investigated. As presented in 5/2 (~618.8 eV) and I3d3/2 (~631.3 eV), respectively, suggests the enhancement of the iodine interaction with the graphene oxide matrix. The deconvoluted I3d5/2 peak shows two peaks: first is the 617.96 eV peak of triodide (I3−), and the second is 620.21 eV corresponding to pentaiodide (I5−). These results are the same with the one reported in literature [3− and I5− remained on its surface after the microwave process. According to chemical composition calculated through this method, the iodine concentration of 1.3 wt.% was obtained.As iodine was used as a dopant, its content was very small, 0.13% in the synthesized doped rGO, and the data were collected with noise, but two Gaussian curves were clearly adjusted to the data with FWHM. The noisy XPS deconvoluted spectrum may be due to the high surface sensitivity of XPS, since it has been reported that iodine is a strong p-type dopant for graphene. The XPS signal-to-noise ratio (C-I) is the height of a signal (peak) above a background relative to the noise in the scan/spectrum measured at some point off the peak.The mechanism for the adsorption of iodine molecules on the GO has been studied both theoretically and experimentally to adjust the electronic structure of the GO surface. Theoretically, the adsorption of halogen atoms on GO/rGO was investigated by using a semi local function. It was accepted that an iodine atom can accept 0.5 electrons from the carbon substrate. The doping of the rGO by the physical adsorption is interesting since it can increase the concentration of the carriers without affecting carrier mobility as in the case of chemical adsorbed dopants, where the covalent function can produce crystalline defects and irreversibly alter the electron structure .0 domain in the 0.1 and 0.3 (multipoint model). According to this, the linear high-pressure part is suitable for evaluation of the primary mesopore volume and the external surface area. The secondary mesopore volume (which does not form ordered structures) is calculated as a distinction between the total pore volume and the primary mesoporous volume. The model calculates the maximum amount adsorbed at pressures close to the saturation vapour pressure by converting it to the volume of liquid adsorbed, similar to the evaluation of the micropore volume [With the view to understand the iodine doping impact towards the structure and porosity of graphene oxide support, further investigations are carried out. One of these is gas adsorption that gives an extensive description of the porous materials in comparison with the specific porosity, surface area, and pore size distribution. From the shape of sorption/desorption isotherms obtained during the BET analysis, it is possible to understand the elementary reactions linked to the sorption and desorption of nitrogen and its comportment in spongy-like solid structures. The BET model is based on the multilayer adsorption of gas on the surface of the adsorbent. The BET method determined the specific surface area through the P/Pe volume .2 adsorption/desorption isotherms for both samples correspond to the type IV isotherm according to the specifications from IUPAC. The micropore volume was calculated in the low-pressure region, as the intercept with the adsorbed amount axis represents the volume adsorbed in micropores. It is important to note the excellent linearity starting from the lowest adsorbed amount and also the correlation coefficient R2 very close to one, both indicating a well-defined monolayer and constituting the indicative for the BET data validity.The results calculated using the isotherms for adsorption/desorption are presented in Both adsorption–desorption isotherms present a typical behavior for a mesoporous structure with a uniform pore size distribution, suggesting that the prepared materials have good transport properties among micropores, mesoporous, and macro-porous channels. The calculated specific surfaces and the estimated textural properties for the pore volumes are presented in 0 = 0.02, and a hysteresis loop from P/P0 = 0.45 to P/P0 = 1.0, which is due to the co-existence of both micropores and mesopores. Moreover, it can be noticed that there are little ultra-micropores in the doped graphene material, thus the porous material could provide more active sites and thus improve the redox reactions. The pore size is a critical parameter that affects the basic physicochemical properties and applications of porous doped−graphene, but the preparation of I/rGO with a controllable pore size is still a big challenge. In this paper, the model BJH was applied for the estimation of the pore volume distribution (both for rGO and I/rGO) ) and the pore size and half pore width (nm). The results clearly indicated that a textural change occurred. According to the BJH, most of the pores from the iodine-doped graphene oxide have a size below 5 nm. The doping of iodine into the graphene network provides the modifications of surface area and also for the pore size of the doped material, according to 3 hysteresis loop is correlated with slit-shaped pores, possibly between parallel layers.Herein, iodine−doped graphene presents a vertical uptake under P/P2/g) that is significantly more reduced than that corresponding to rGO (922 m2/g). We can presume that after the iodine inclusion into the graphene framework, the surface area will decrease as an effect of the doping process that favors the tendency and probability of restacking.Iodine-doped graphene has a BET surface area . The calculated pore volumes indicated an open stacking order. The iodination process maintains the sheet-like morphology also observed by SEM microscopy. Perhaps the layers become graphitized and this is reflected in the strongly reduced BET surface area. The pore volumes correspond to open 3D staking of reduced graphene oxide-based powders.A linear relationship between the pore volume and the relative pressure The thermal decomposition curves of the reduced graphene and iodine-doped reduced graphene are presented in −1, respectively. Iodine presence in the I/rGO structure can be noticed from the band at C–I assigned to the C−I stretching vibration.2) in comparison with 1.52 mA/cm2 from 0.383 V of rGO, respectively. Moreover, the I/rGO ORR peak position is shifted with 50 mV to a more positive potential. These findings strongly indicate that the iodine-doped reduced graphene oxide have ORR catalytic activity. The influence of the sweeping towards the I/rGO CV shape and ORR current density is presented in 2 corresponding to 10 mV/s, to 24 mA/cm2 associated with 100 mV/s. This comportment is assigned to the I/rGO surface extensive oxidation with the sweeping rate. The catalytic performance of rGO and I/rGO for the oxygen evolution reaction (ORR) was characterized in alkaline electrolyte (0.1 M KOH) using the cycling voltammetry method (CV) at 50 mV/s . In FiguThe electrochemical activity can be assigned to the ORR mechanism by taking into account the higher electronegativity of iodine (2.66) than carbon (2.55), polarizing carbon atoms and favoring oxygen adsorption as well as the charge transfer.−1 cm2geo) vs. ω−1/2 (rad s−1)−1/2, for various rotation speeds (among 250–1000 rpm) and different potentials (0.4–0.7 V). From the fitted K–L plots, a fair linear relationship at all potentials is noticed, which confirms the electroreduction of iodine. The number of transferred electrons is between 3.41 and 4.09, indicating the preponderance of the four-electron transfer mechanism in the ORR corresponding to the direct reduction of O2 to H2O [n) was calculated to be in the range of 3.41–4.09, suggesting a predominant four-electron O2 reduction in combined two-electron and four-electron pathways of the ORR process [n value is around 3.4, indicating that a hydroperoxide anion HO2− is formed as an intermediate reduction product of the two-electron reduction of O2. The HO2− is reduced into OH− at the electrode at more negative potentials, thus restoring the overall four-electron ORR process. The value of n slightly over 4 towards −0.70 V vs Ag/AgCl suggests a possible another reduction reaction than ORR occurring in the studied catalytic system [In 2 to H2O . The num process ,22. At lc system . In our c system . Accordi3− and I5−) that increase the functionalization capacity of the graphene support. Developing a green chemistry method to prepare I/rGO using MW could be a step forward in obtaining affordable electrodes with ORR activity.This work indicates that starting from a commercially accessible material—graphene oxide—through a specially designed process for chemical synthesis in the microwave field, iodine-doped graphene with specific morphological and structural properties could be obtained. The single-stage microwave (MW) iodine-doping process parameters in terms of temperature and reaction time, were optimized for mild conditions: atmospheric pressure, a temperature of 40–60 °C, a power of 800 W, a reaction time of 15 min, and a doping concentration of 1.3 wt.% was obtained. Cycling voltammetry and rotation disk electrode polarization methods were employed to study the I/rGO electrocatalytic activity with regard to the ORR. The good ORR activity of the I/rGO probe can be explained by the iodine doping of the rGO matrix, promoted by the formation of load transfer complexes (I


Two different modes of improving the strength of the hybrid composite have been followed; one is by the inclusion of graphene at three levels of 0.1, 0.2 and 0.3%, and another by the processing route, squeeze casting technique by compression of the molten hybrid composite slurry before casting. The microstructure and characterisation of the composite material are examined and analysed with the help of XRD, SEM, EDAX and chemical spectroscopy. A microstructure evaluation is employed to justify the homogenous dispersal and the existence of reinforced particles. A tensile test is conducted at room temperature and high temperature environments to assess the tensile strength. The research outcome affirms that a significant improvement in tensile and hardness has been noted in comparison with base alloy. The fracture-morphology results affirm the change in fracture mode from brittle to ductile when the tensile testing environment changes from room temperature to high temperature. Finally, the dispersion strengthening mechanism is validated with an empirical approach.The development of aluminium composite with the inclusion of advanced materials is a continuous research process due to the increasing industrial demand for advanced hybrid materials. To cater for this need, this research work focuses on the development of Al 7075 alloy reinforced with TiB Han Wang et al. [2 reinforced Al 7075 matrix composite, and the authors concluded that the grain size of the composite is smaller than the Al 7075 base alloy. The inhibit property of TiB2 to promote nucleation is the reason for the grain growth. B.P. Sahoo et al. [2 particles infused Al 7075 matrix through experimental and theoretical approach. The research outcome states that nearly 58% of grain size reduction is achieved with the higher content of TiB2 and in turn the noticeable improvement of mechanical properties. Vineet Chak et al. [2O3 through liquid melt deposition followed by hot extrusion and conducted characterization, high temperature tensile and fracture study. They reported that the maintained yield strength up to 150 °C and the fracture analysis revealed the transition failure from brittle to ductile.There are extensive research outcomes and initiations in developing novel metal matrix composites. The recent challenges in the product development to meet the requirement of higher specific strength with minimal weight pave the opportunities for the consistent research in the development of metal matrix composite. In particular, the automobile and aircraft industries mainly focus on and encourage the development of novel metal matrix composite ,2,3,4. T4C) ,6,7,8, o ZrSiO4) , borides2, AlB2)  and nitr2, AlB2)  have rep[3 W/mK) ,12,13, YK) [2/g) ,15,16 reK) [2/g) ,18 statiK) [2/g) . GeneralK) [2/g) . Bi JianK) [2/g)  developeg et al.  investigo et al.  validatek et al.  synthesik et al.  studied k et al.  concludek et al.  carried k et al.  develope2 and graphene. The objective of the present work is to advocate for a dual way of enhancing the mechanical and tribological properties of Al 7075 composite, one way being through the encapsulation of graphene with hard boride particles and another is by achieving porous-free composites through the processing route. Three different levels of graphene content are being followed to compare the effect of graphene inclusion. Additionally, very specific attention has been paid to expose the tensile response of the composite materials at room and high temperature environments. Subsequently, the fracture analysis is also being discussed with the help of micrographs.Numerous research reports that address the improvement of properties of aluminium alloy with the reinforcement of various hard particles are available. However, very scarce research was conducted with the inclusion of graphene on Al 7075 and through the squeeze casting route. In particular, none of the work has been reported with inclusion of TiB2 purchased from Metal mart Coimbatore and the graphene flakes purchased from Shilpa enterprises are used as reinforcements. The mechanical properties of TiB2 and graphene are tabulated in Aluminium 7075 alloy is used as a matrix material and its mechanical properties are depicted in 2 particles and graphene powders with premeasured quantity were preheated to 200 °C to eliminate chemical impurities and moisture. Then, the aluminium alloy was melted to 800 °C in an electric furnace in an open atmosphere. The present work followed constant weight percentage of TiB2 as 10% [2 and graphene in each sample is presented in Initially, the TiB2 as 10% ,28,29 anm, ρrρ and cρ represent the density of matrix, reinforcement and composite, respectively. m, VrV indicate the weight percentage of matrix and reinforcement. Furthermore, the particle size analysis is carried out using CILAS 1064 Liquid setup.The characterization of the developed hybrid composite was carried out in four different ways. Scanning electron microscopy (SEM), chemical spectroscopy (ChemS), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) techniques were employed to study the phase and microstructure. The specimen was cut into the size of 10 mm × 10 mm × 10 mm and subsequently rinsed in acetone followed by polishing through silicon carbide emery sheet. An SEM study was conducted using De-Wintor inverted trinocular metallurgical microscope . The chemical composition and elemental analysis were executed with the help of X-ray Diffraction and chemical spectrometer from Malvern Panalytical . The experimental density of the composite was determined with the help of a densimeter  working under the Archimedes’s principle of displacement. The theoretical density was evaluated with the following relation of the rule of mixture Equation (1), and the percentage of porosity was calculated using the below equation Equation (2).d is the size of the crystallite, k is the shape factor, λ is the wavelength, θ is Bragg angle, and β is the diffraction peak at half-width maximum intensity.The results of XRD were employed to determine the crystallite size and lattice strain. The Sherrer equation, as shown below, was utilized to calculate the crystallite size .(3)d=kλλ is the wavelength, A is constant, θ is Bragg angle, β is the diffraction peak at half-width maximum intensity, and ε is lattice strain.The lattice strain was manipulated by using the following equation, (4)β cosNow the dislocation density can be determined for every specimen by using the following relation ,(5)ρ=3ερ represents dislocation density, ε, bv and d indicate lattice strain, Burgers vector and crystallite size, respectively.In this equation, The tensile test was conducted in two different modes: room temperature and elevated temperature tensile testing. The size of the test specimen was trimmed as per ASTM 638-03 (165 mm length × 19 mm width × 3 mm thickness). The tensile test was carried out at Associated Scientific Engineering works with a range of maximum 5-ton load. Specimens were heated up to 250 °C through an electric furnace to conduct the elevated temperature test.2 was evaluated with the following relation,M is the bending moment in N mm, Y is the distance between the neutral axis to the extreme fibre measured in mm, and I is the moment of inertia of the section calculated in mm4. M is the bending moment, Y is the distance between the neutral axis to the extreme fibre, and I is the moment of inertia of the section.The hardness test was conducted by following ASTM E-10 standard (25 mm × 25 mm × 10 mm) with the help of a micro-Vickers hardness tester , with testing load range of 10 g to 1 kg. As per ASTM D-790 standard, flexural test was carried out in the three-point bending mode. The maximum bending stress in N/mm2 and graphene reinforcement is presented in The deviations between the experimental and theoretical density of the composite with the TiB2 particles and graphene nanoflakes. The inclusion of TiB2 particles is an additional factor for the enhancement of the microstructure by controlling the precipitation mechanism (2 particles. 2. Characterisation and phase identification were conducted with four different methods, namely SEM, EDS, XRD and ChemS. From SEM micrographs, it has been inferred that the homogeneity in the distribution of the two reinforcements exists. The absence of voids and porous microstructure is observed through the micrographs. The compression pressure to the extent of 100 MPa helped to relieve the voids and porosity. The EDS and chemical spectroscopy results confirm the existence of TiBechanism a. Excell2 are in the position to be noticed, whereas the graphene peaks are non-noticeable due to its meagre level of inclusion. The same observation was reported by the researcher [searcher . However2 particles where the weighted mean particle size is observed to be 3.9 µm. The peak for TiB2 particles is narrow and depicts an average value of 3.75 µm.2 and graphene flakes, and the other is by the way of the porous-free squeeze casting processing technique. The phenomenal increment in strength is attributed to the fine-grain structure of the hybrid composite. The noticeable enhancement in grain structure is achieved by the two modes. First, with the addition of TiB2 particles, the composite attains a more refined grain structure with the help of the heterogeneous nucleation capacity of TiB2 to form a dendrite structure [tructure . Second,The empirical prediction reveals that the increased content of graphene increases the dislocation density by resisting the impending dislocation movement. The dislocation density calculated for different proportions of graphene with an empirical approach is given in 2 particles and piling up of dislocation movement into dense dislocation owing to the barrier of graphene particles. The heating of the specimens at high temperatures might cause an increment in the thickness of the oxide layer over the surface of Al particles [The composite specimens were fed into tensile test under an elevated temperature of 250 °C to assess the deformation behaviour in a high-temperature environment. articles . The broIt is evident from the results that the percentage of elongation of all the specimens including the higher content of graphene also records a higher percentage of elongation than the specimens at room temperature. This reflects the thermal softening effect of the hybrid composite due to the high temperature. Moreover, the quick peak in strength followed by the consistent plastic deformation is attributed to the chance of diffusing dislocation density at one point in high temperature and allowing the dislocation to move freely . This phThe investigation of fracture surface at both room temperature and high-temperature composite specimens reveals the change of failure mode with respect to the physical and thermal loading. At room temperature, the mode of failure is in a brittle manner. The plane of failure is at an angle of 90° to the axis of loading with negligible neck formation. This sudden failure is attributed to the stress concentration at the grain boundaries. When the stress value increases, the dislocations are piled up to form dislocation density due to the graphene particle inclusion. Furthermore, the stress value increases, and the stress concentration develops over the grains due to the impediment of dislocations, which initiate a micro void formation. The coalescence of micro void forms the crack, as shown in The dimples in more numbers with shallow depths, as shown in micrograph 2 and graphene justifies the hardness value. The increment in hardness for every fold of increasing graphene content is attributed to the higher number of graphene flakes that resist the indentation due to its high aspect ratio and unique strength. The squeeze casting processing route accelerates the formation of fine-grain structure due to the consistent compaction during solidification. The hardness value is inversely proportional to the grain size advocated by Hall-Petch [ll-Petch ; hence, 2 and graphene on the improvement in flexural strength is represented in The effect of the inclusion of TiB2 and graphene reinforced Al 7075 hybrid composite in the room and at high-temperate environments arrives at the following conclusions.The investigation of the tensile response of squeeze casted TiBThe theoretical and experimental evaluation of the density of the developed composite affirms the negligence void content of 0.2%. The excellent agreement between the theoretical and experimental results of density acknowledges the porous-free nature of the hybrid composite.The characterisation results earned through XRD, SEM and chemical spectroscopy confess the existence of constituent material in the homogenously dispersed state. Moreover, the improved grain structure has also been detected.The room temperature tensile test conducted for the specimens with varying graphene content, including base alloy, reveals the increment in tensile strength for every fold of graphene increment. The higher graphene content of 0.3% records a drastic improvement of 112%, in comparison with the base alloy.Due to the high temperature, the thermal softening effect makes the hybrid material more plastic with a noticeable increment in the percentage of elongation. The reduction in tensile strength and increment in elongation percentage are 18.5% and 28%, respectively.The fracture morphology confirms the change in fracture mode from brittle to ductile, while the tensile examination changes from room temperature to high temperature. The plasticized dimples in SEM micrographs with noticeable length confirms the increment in elongation percentage, and hence the ductile failure is understood.The hardness results proclaim the evident increase in hardness of higher graphene content to the extent of 67.8%, when compared to the base alloy.An improvement of nearly 80% in the flexural strength of the hybrid composite has been reported, in comparison with the Al 7075 alloy, from the flexural strength results.


The design benefits from the collective excitation of localized surface plasmon resonances of graphene-coated hole array, providing simpler fabrication fellow and more compact structure with respect to graphene-coated spherical nanoparticle array with similar plasmonic behavior. Geometrical parametric study of the reflecting mode shows that the device has lots of degrees of freedom for spectrum tuning and can highly tolerate fabrication imperfections. Moreover, the reflection rate is slightly affected by the dielectric substrate height, which can be tuned to achieve strong absorption by backing it with a metallic mirror. The designed absorber efficiently captures a wide range of obliquely incident transverse electric (TE) and transverse magnetic (TM) waves. Also, the operating frequency of both reflecting and absorbing modes can be tuned after fabrication, thanks to the two-dimensional nature of graphene material. Finally, using vanadium dioxide (VO For instance, the near field enhancement provided by the spherical graphene shells is discussed in the framework of modified Mie Lorenz theory and by extracting equivalent RLC ladder circuit for the resonance behavior of the plasmonic nanoparticles2. Furthermore, graphene oxide wrapped gold nanoparticles are utilized for intracellular Raman imaging and drug delivery3. In other applications, the localized surface plasmon resonances of the graphene wrapped nanoparticles are used to design electromagnetic cloaks and superscatterers5. Moreover, reconfigurable sub-wavelength strong absorbers are proposed by square/hexagonal lattice of graphene shells with spherical morphology8. Graphene hollow spheres have also found applications in supercapacitors, being superior to their planar counterparts9. Also, graphene-coated spherical shells are proposed as a cover for cylindrical wires to reach dual-polarized extinction cross-section enhancement10. Although fabrication of graphene-based spherical geometries is feasible considering current nanofabrication technology11, still, they suffer from complex fabrication fellow. Thus, proposing a geometry with similar optical performance, yet a simpler fabrication process, is helpful for practical usage.Graphene-coated dielectric or metallic spherical nanoparticles has been used in the design of different optical devices respectively due to the localized surface plasmon excitation arising from the charge carriers in the graphene shell and the interplay between plasmons supported by the bulk core and the graphene shell12. Generally, graphene-based structures provide enhanced optical performance with respect to their metallic and high index dielectric counterparts because of being low-loss and supporting highly confined waves13. Thus, the present research aims to investigate the graphene-coated hole arrays as an alternative plasmonic device to metallic hole arrays, benefiting from the exotic properties of graphene material to reach a switchable reflector/absorber performance. Metallic hole arrays support pronounced Fano resonances as interference between light directly transmitted through the holes and light indirectly scattered because of the excitation of localized surface plasmon polaritons, propagating surface plasmon polaritons, or/and waves due to Wood’s anomaly14. A potential application of the metallic nano-hole array is the refractive index sensing for label-free detection15 and can be fabricated by low-cost colloidal sphere lithography16.Previous studies show that extraordinary transmission through arrays of sub-wavelength holes in thin metal films is due to the excitation of surface plasmons17. Also, absorption enhancement in the graphene sheet is obtained by a square lattice of air holes in the high index dielectric18. Moreover, graphene/hBN/graphene multilayer hole array leads to a photonic plasmonic absorption of the electromagnetic wave19. The present paper benefits from the combined use of graphene-based hole arrays and phase change materials to design a reconfigurable switchable reflector/absorber device. Gate tunable feature of graphene material and thermal tunable property of the VO2 material provide two degrees of freedom for the dynamic response achievement20. A switchable absorber/reflector device provides a wide range of applications such as active camouflaging, modulating, electro-optic switching, antenna beam steering, hyper-spectral imaging, and compressive imaging22. The paper is organized as follows. The reflecting mode of the square array of graphene-coated dielectric hole array is investigated by exhibiting the excited localized surface plasmon resonances on graphene shells. Later, by using an optical mirror, the reflecting mode is converted to the absorbing mode and its robust performance in terms of the incident angle of the incoming wave is discussed. Finally, a phase change material is used to switch between these modes.By the use of hole arrays in conjunction with other plasmonic elements or material combinations, the optical performance can be further manipulated. For instance, strong coupling between a nanoparticle dark mode with a high-order metallic hemispherical nano-cavity, bright mode has been exploited for optical field enhancement through Fano resonance excitationIn this section, the design of optical reflector, absorber, and switchable reflector/absorber devices using graphene-coated hole arrays are considered. The performance of all devices relies on the excitation of localized surface plasmon resonances on the spherical shell-shaped graphene holes, where the functionality can be controlled by the substrate.R, embedded in a dielectric medium with the relative permittivity of ε1, as in Fig. p and are drilled on a substrate with the height of h1. Two-dimensional graphene material is wrapped around the sidewalls of the hole as hemispherical shells and it is characterized by its optical parameters, namely, relaxation time τ and chemical potential µc. These parameters essentially manipulate the graphene surface conductivity σ. Note that there are two approaches to simulate the graphene material for optical applications, either to model it with a zero-thickness shell with the surface conductivity calculated by the Kubo formulas or consider it as a very thin dielectric layer with the thickness δ with the equivalent bulk permittivity of ε = 1 + jσ/ωε0δ, where the real part of the permittivity is negative. To avoid three-dimensional fine volumetric meshing due to the contrast between the graphene layer thickness and other dimensions, the former approach is applied in the simulations25. The initial parameters are as follows: R = 100 nm, ε1 = 2, p = 240 nm, h1 = 100 nm, τ = 2 ps, and µc = 1.5 eV. The device is excited from its top side , and chemical methods have been used for wrapping graphene sheets around curved objects36.To understand the origin of high reflection, in Fig. 32. When extracting these results, the distance between the adjacent elements is considered 2R+40 nm in all cases. Moreover, Fig. Once the advantage of the graphene-coated hole array with respect to graphene-coated spherical nano-particle array is discussed, it is illustrative to investigate the optical performance manipulation regarding different parameters. In Fig. 37.In Fig. S parameters38. To this end, the hole array has resided on top of a metal-backed dielectric substrate for transmission blockage and its height is modulated such that a perfect absorption is achieved39. The metal termination is formed by h3 = 20 nm silver layer with the surface conductivity of σs = 6.3 × 107 S/m and it will be replaced by a VO2 layer in the metallic phase in the next section40. For simplicity, the dielectric material is the same as the one used to reside the hole array previously (ε1 = ε2). The final structure is shown in Fig. h2 = 120 nm, perfect absorption is achieved and it is illustrated in Fig. c = 1.2 eV.In this section, the excited localized surface plasmon resonances in the graphene-based hole array are used to design an optical absorber. The absorption rate is calculated from the The sensitivity of the optical absorption to the incident angle of the incoming wave is investigated in Fig. 2 layer with the thickness of 10 nm. Due to the phase transition in VO2, it behaves as a metal with the surface conductivity of 2 × 105 S/m at the temperature of T = 350 K in the metallic phase while behaves as a dielectric with the permittivity of 9 and surface conductivity of 200 S/m in its dielectric phase44. The choice of thickness is to ensure the transmission blockage in the absorbing mode and the substrate height h2 ranges from 260–320 nm. Figure 2 around the same frequency. Importantly, the device has a robust performance against the substrate height.In other to enable switching between the reflecting and absorbing modes, the metallic mirror beneath the proposed absorber is replaced by a VOGraphene-coated hole arrays are a promising candidate for the future optical device design since they support localized surface plasmon resonances similar to the graphene-coated spherical nanoparticle arrays, yet provide simple fabrication fellow. This geometry can be used either in the reflecting or absorbing mode, originating from the fact the reflection rate is not sensitive to the substrate height, thus can be tuned to achieve a high absorption rate. Interestingly, switching between these two modes is also feasible using a phase change material. The proposed geometry has lots of degrees of freedom for spectrum engineering. Importantly, the performance is reconfigurable due to the use of two-dimensional graphene material.45. The absorption rate (A) of the structure is calculated as46:S11 and S12 are the scattering parameters.To investigate the optical performance, numerical simulations are conducted in CST commercial software under unit cell boundary conditions and Floquet port excitation. Graphene material has been opted from the software library