Formation Mechanism Of Graphene Research Articles

Application of Graphene-Based Derived Rice Husk Waste for Membrane Gas Separation Technologies: A Comprehensive Review

This study intends to comprehensively evaluate the application of graphene-based nanofillers obtained from rice husk waste in the field of membrane gas separation technologies. Graphene, owing to its distinctive structural characteristics, has emerged as a highly promising filler material for membrane fabrication in gas separation applications. This comprehensive review provides an in-depth evaluation of the diverse synthesis methods employed and the resulting properties of graphene obtained from rice husk waste materials, with an inclusive chemical mechanism of graphene formation from rice husk waste. Furthermore, this study reveals the inherent capabilities of graphene in enhancing the performance of membranes while also examining the influence of nanofillers on solubility selectivity. In conclusion, it is imperative to underline the need for additional research and development activities aimed at expanding the efficiency and scalability of the membrane fabrication process through the utilization of graphene nanofillers derived from rice husk waste.

Catalytic effect of metal alloy sublayers on graphene formation in thermally annealed amorphous carbon ultrathin films

The exceptional properties of graphene, such as mechanical strength, flexibility, thermal conductivity, electron mobility, biocompatibility, and transparency, make it an ideal material for numerous applications. The objective of this study was to develop a one-step process of graphene formation that uses inert thermal annealing of amorphous carbon (a-C) ultrathin films deposited onto different metal catalyst sublayers to transform highly sp3 hybridized a-C nanostructures within the film to sp2 hybridized graphene nanostructures. To elucidate the mechanism of graphene formation and the catalytic effect of the sublayers on sp3-to-sp2 transformation, Si/FeNi/a-C and Si/FeCo/a-C stacks were fabricated by physical vapor deposition techniques. X-ray photoelectron and Raman spectroscopies were used to analyze the structure of as-deposited and thermally annealed a-C films. Moreover, molecular dynamics simulations provided insight into graphenization at the atomic level. The sp3 fraction of as-deposited a-C films was found to play a pivotal role in the formation of graphene during thermal annealing. The carbon concentration in the catalyst sublayers and the compressive stress in the a-C films strongly affected atomic carbon hybridization and, consequently, the graphene quality. Differences in the catalytic effectiveness of the sublayers in producing graphene are interpreted in terms of the sublayer carbon concentration, atomic packing, and electronic structure of the valence band of elements affecting the interaction between carbon and transition metals, ultimately influencing graphene nucleation.

A Study of the Key Factors on Production of Graphene Materials from Fe-Lignin Nanocomposites through a Molecular Cracking and Welding (MCW) Method.

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.

On the mechanism of electrochemical deposition of graphene on Al foils and AlSi10MgCu particles

The graphene synthesis via the electrochemical method and electrochemical deposition of graphene on Al foils and AlSi10MgCu particles were studied. The thickness of deposited graphene layers was varied from 3 to 20 layers and, thus, they were classified as multi-graphene. The chemically pure sucrose C12H22O11 was used as a raw material for graphene synthesis. It was shown that the deposition of graphene layers was affected mainly by the pH values of electrolyte mediums. In the electrochemical reaction at H2SO4 water solution at pH < 7, the graphene was deposited on Al foils and on AlSi10MgCu particles from the electrolyte. The microstructure and composition of graphene formed on Al foils and AlSi10MgCu particles' surface were studied by Raman spectroscopy, SEM, EDX, and TEM methods. The chemical mechanism of graphene formation was defined as follows: the sucrose was recovered via the reaction route C12H22O11 → C6H12O6 → Cgraphene in acidic aqueous media. An increase in the H2SO4 concentration from 0.05 M to 0.80 M has resulted in the formation of graphene layers with up to 6 μm thickness on AlSi10MgCu particles.

Structural characterization of graphene nanostructures produced via arc discharge method

Few-layered graphene (FLG) was produced via substrate-free direct current arc discharge between pure graphite electrodes in an originally designed reactor chamber. Previously, parameters influencing the synthesis condition and properties of graphene-like discharge density, precursor composition, electrode diameter/length, reactor design and type and pressure of buffer gases were optimized. In this study, it was observed that carbon structures with different properties deposited in the different regions of the DC arc reactor. The mechanism of graphene formation by the arc discharge method was investigated in terms of the collection side and distance to the arc region. Variations in the distance to arc region result in dissimilar temperature gradients in the reactor chamber, thereby the deposition mechanism of carbon clusters differs with regard to reactor zones. The products collected from the different regions of the reactor were characterized via Raman Spectroscopy and integrated intensity ratio (ID/IG and IG/I2D), full width half at maximum (FWHM), crystallite size (La), defect density (ηD) values were examined. The crystallite size (L002) and average number of graphene layers (N) were determined by X-Ray diffraction (XRD) analyses. In addition, their morphological properties were investigated with scanning electron microscopy (SEM) and transmission electron microscope (TEM). As a result, the carbon nanostructures with high purity and few-layered morphology collected on the anode region of the reactor. While, the purity of few-layered graphene decreased as moving away from the anode region of the chamber. Therefore, it was determined that the properties of graphene were influenced greatly by the temperature distribution and its gradient around the arc plasma.

Green Preparation of Few‐Layer Graphene Sheet Materials Using Naturally Occurring Calcium Carbonate and Plant Leaves

AbstractGraphene sheets were prepared by calcination of calcium carbonate with plant leaves under the protection of an argon gas atmosphere. This is an environmentally friendly approach to produce graphene. Calcium carbonate decomposes with the evolution of carbon dioxide at high temperature, which is reduced into graphene by the magnesium from plant leaves. The formation mechanism of graphene is discussed in detail. The synthesized graphene sheets were characterized by scanning electron microscopy (SEM), X‐ray diffraction (XRD), and Raman spectroscopy. Calcium carbonate and plant leaves are readily available and inexpensive natural resources, and this new methodology can be applied for large‐scale graphene production in industry.

In Situ Friction-Induced Graphene Originating from Methanol at the Sliding Interface between the WC Self-Mated Tribo-Pair and Its Tribological Performance.

Alcohols are reported to have superlubricity at low loads during sliding; however, their lubricity under high loads has rarely been reported. Meanwhile, the lubrication mechanism of alcohols under high loads is still not well understood. Here, we first report the lubricity of methanol under 98 N and 1450 rpm and demonstrate the formation of graphene and fullerene-like nanostructures induced by tribochemical reactions. Results show that the lubrication mechanism was mainly attributed to the friction-induced graphene under boundary lubrication condition. Besides that, the wear rate of a YG8 hard alloy ball mainly occurred at the run-in processes, and the friction-induced graphene effectively inhibited further wear after the run-in processes. The formation mechanism of graphene was well investigated, and the flash temperature rise and catalyst (WC, WO2, and WO3) were the major causes for the formation of graphene.

Extraordinary macroscale lubricity of sonication-assisted fabrication of MoS2 nano-ball and investigation of in situ formation mechanism of graphene induced by tribochemical reactions

We first fabricate MoS2 nano-ball in isopropanol using sonication-assisted method. We systematically probe the lubrication mechanism of MoS2 nano-ball in isopropanol. Hydroxylated MoS2 nano-ball could effectively reduce the contact area for GCr15 steel balls and possess superior load-capacity and make the tribosystem achieve ultra-low friction and wear under 98 or 196 N and 600 rpm. For comparison, the lubricity of tribosystem sliding in isopropanol is conducted. Interestingly, graphene layers are formed sliding under 196 N and 600 rpm, the graphene-based transfer film on GCr15 steel ball makes the lubrication condition fast transfer from mixed lubrication condition to full film lubrication condition, which results in high friction and wear. The formation mechanism of graphene is discussed and proposed in details.

Continuous preparation and formation mechanism of few-layer graphene by gliding arc plasma

Environmental-friendly, rapid, and continuous preparation process of few-layer graphene has been developed by alternative-current (AC) rotating gliding arc plasma, which contains the characteristics of equilibrium plasma and non-equilibrium plasma. In the process, methane was directly cracked in the plasma and then graphene sheets were generated. The effects of hydrogen and gas flow rate on the yield, size, morphology and structure of graphene have been investigated. In addition, the formation mechanism of graphene was also revealed by using the reactive molecular dynamic method. The simulation results showed that the growth process of graphene clusters by methane radicals includes three stages: elongation of the carbon chains, cyclization of the carbon chains, and condensation and sheeting of clusters. The carbon source concentration influences the graphene clusters. Increasing the carbon source concentration was found to enlarge the size of graphene clusters but are more prone to curling and closing. The formation of C–H bonds can reduce the peripheral dangling bonds of the clusters, thereby delaying the closure of the clusters. It laid a foundation for understanding the growth mechanism of graphene.

Graphene Formation Mechanism by the Electrochemical Promotion of a Ni Catalyst

In this work, we show that multilayer graphene forms by methanol decomposition at 280 °C on an electrochemically promoted nickel catalyst film supported on a K-βAl2O3 solid electrolyte. In operando...

Preparation of Three-Layer Graphene Sheets from Asphaltenes Using a Montmorillonite Template

We propose a novel approach to synthesize graphene sheets with fine quality by calcinating the composites intercalated with montmorillonite (MMT) and asphaltene. The graphene sample thus fabricated could reach 10.79 μm long, with smooth and continuous morphology and with little defects. By analyzing the XRD patterns of graphene/MMT composites at different conditions, the graphene formation mechanism is elucidated and the optimal calcination conditions are researched. This study may provide useful insights for low-cost and scalable fabrication of graphene from asphaltene extracted from heavy crude oil.

Mechanism of Graphene Formation via Detonation Synthesis: ADFTB Nanoreactor Approach.

With the development of theoretical and computational chemistry, as well as high-performance computing, molecular simulation can now be used not only as a tool to explain the experimental results but also as a means for discovery or prediction. Quantum chemical nanoreactor is such a method which can automatically explore the chemical process based only on the basic mechanics without prior knowledge of the reactions. Here, we present a new method which combines the semiempirical quantum mechanical density functional tight-binding (DFTB) method with the nanoreactor molecular dynamic (NMD) method, and we simulated the reaction process of graphene synthesis via detonation at different oxygen/acetylene mole ratios. The formation of graphene is initiated by the breaking of acetylene (C2H2) molecules by collision into pieces such as H atoms, ethynyl (HC≡C•), and vinylidene (H2C═C:) radicals. It is followed by the formation of long straight carbon chains coupled with a few branched carbon chains, which then turned intoa2-D framework made of carbon rings. Trace oxygen could modulate the size of the rings during graphene formation and promote the formation of regular graphene with fused six-membered rings as we see, but the addition of high oxygen content makes more C-containing species oxidized to small oxide molecules instead of polymerization. The calculation speed of the DFTB nanoreactor is greatly improved compared to the ab initio nanoreactor, which makes it a valuable option to simulate chemical processes of large sizes and long time scales and to help us uncover the "unknown unknowns".

Graphene layer formation in pinewood by nanosecond and picosecond laser irradiation

Potential applications of graphene-based materials in nanoscale electronic devices depends heavily on the versatility of synthesis and modification methods. The significant trend of graphene materials production is based on laser-induced synthesis. In this work, we investigate the laser-induced formation of graphene layers in pinewood by utilising near-infrared picosecond (10 ps) and nanosecond (10 ns) pulses. Effect of laser irradiation dose and pulse duration time on the quality of graphene materials was comparatively evaluated. Raman measurements showed the formation of high-quality few-layer graphene structures with I(2D)/I(G) and I(D)/I(G) ratios of 1.10 and 0.69, respectively, at the nanosecond-laser irradiation dose of 662 J cm−2. The average in-plane crystallite size estimated from the Raman data was found to be 31 nm. Sheet resistance measurements showed a correlation with Raman data and revealed a significant decrease in electric resistance for the ns-laser prepared sample with the highest I(2D)/I(G) ratio. To get insight into the graphene formation mechanism, we performed modelling of the pinewood surface temperature after the laser pulse irradiation. Higher surface temperatures reached and ablation process during picosecond laser irradiation disturb crystalline lattice structure forming lower-quality graphene platelets. We found that the nanosecond laser produces less defected graphene layers.

Low‐Temperature Synthesis of Graphene by ICP‐Assisted Amorphous Carbon Sputtering

AbstractEfficient and affordable synthesis of graphene at low temperatures remains a significant challenge that potentially limits the use of this material in real‐life applications. We describe here a simple, efficient, highly controllable technique to synthesize graphene by sputtering carbon from a solid source with the assistance of inductively coupled plasma (ICP), followed by controllable low‐temperature annealing at about 550 oC. Raman scattering and X‐ray diffraction characterizations have revealed the formation of a few layer graphene of high quality, confirmed by a low (∼0.48) ID/IG ratio. Raman analysis of samples formed at various annealing temperatures has revealed an upper limit for annealing temperature of 585 oC, beyond which the formed graphene reversibly dissolves in the metal. The ICP‐assisted process was innovatively employed to improve the quality of thus‐fabricated graphene at low temperatures. The mechanism of graphene formation was attributed to the metal induced graphitization in combination with the carbon precipitation onto the catalyst surface.

A prospect for applications of graphene fabricated from an organic solution

Graphene and graphite thin films were produced by using deposited benzene ring from dip-coat. This process provided a possibility to make graphene and graphite easily and quickly. In this work, we mainly focused on the formation mechanism of graphene on nickel thin film. The grain size dependence of the nickel on the graphene growth was discussed. Furthermore, it was suggested that the nitrogen is considered to be incorporated in to the graphene layer by the thermal decomposition of an azo group which would be useful for the doping of graphene.

Optimized growth of graphene on SiC: from the dynamic flip mechanism.

Thermal decomposition of single-crystal SiC is one of the popular methods for growing graphene. However, the mechanism of graphene formation on the SiC surface is poorly understood, and the application of this method is also hampered by its high growth temperature. In this study, based on the ab initio calculations, we propose a vacancy assisted Si-C bond flipping model for the dynamic process of graphene growth on SiC. The fact that the critical stages during growth take place at different energy costs allows us to propose an energetic-beam controlled growth method that not only significantly lowers the growth temperature but also makes it possible to grow high-quality graphene with the desired size and patterns directly on the SiC substrate.

Mechanism of graphene formation by graphite electro-exfoliation in ionic liquids-water mixtures

Graphene was produced from graphite electrode by exfoliation in ionic liquid. The influences of process parameters such as ionic liquid concentration, electrolysis potential and the type of anions in the ionic liquid on the production of graphene were studied, and a new mechanism is proposed. The results show that the increase of ionic liquid concentration is beneficial for the formation of graphene, and it is easier to produce graphene by increasing the applied voltage. Ionic liquids anions have great effect on the production of graphene. Both graphite anode and graphite cathode can be modified to graphene during electrolysis. Gases formed inside of the electrode play an important role for the production of graphene, while ionic liquids serve to accelerate the switching rate of graphite to graphene.

Stability and reactivity of steps in the initial stage of graphene growth on the SiC(0001) surface

The stability and reactivity of steps in the initial stage of the graphene growth by sublimating the SiC(0001) surface is theoretically studied by the first-principles calculation. The steps are not necessarily unstable and reactive during the formation of the zeroth graphene layer. Temperature, Si pressure, and C coverage affect the stability and reactivity of the step. The growth mode shows a phase transition. The step is unstable and reactive after the zeroth graphene layer is formed. These findings are tightly related to the graphene formation mechanism on this surface. They are discussed with experimental results and suggest a way to control the quality of graphene.

Evidence of atomically resolved 6×6 buffer layer with long-range order and short-range disorder during formation of graphene on 6H-SiC by thermal decomposition

Scanning tunneling microscopy (STM) is performed to study the formation mechanism of graphene on 6H-SiC by thermal decomposition in situ and the evolution of an atomically resolved 6×6 structure in the buffer layer is revealed. The long-range order of the 6×6 structure is maintained during growth, but the short-range arrangement changes with temperature. Based on STM images acquired at different voltages, a structure consisting of triangular silicon clusters with the 6×6 structure and filled by amorphous carbon atoms is proposed. The 6×6 silicon clusters serve as the template and amorphous carbon atoms provide the carbon source for graphene growth.

Solvothermal synthesis of boron-doped graphene and nitrogen-doped graphene and their electrical properties

In this work, pristine graphene, nitrogen-doped graphene and boron-doped graphene were synthesized by a facile solvothermal process using potassium or lithium nitride as catalyst. The formation mechanism of graphene and doped graphene was discussed, and the chlorine gas generated during the reaction performed a significant role. High yield of graphene and doped graphene can be produced via the solvothermal route with relatively mild conditions, and X-ray photoelectron energy spectroscopy analysis confirmed the doping status and concentration of nitrogen or boron within graphene sheets. Especially, electrical properties of graphene-based field effect transistors revealed that the introduction of nitrogen or boron atoms into graphene sheets can effectively tailor electrical property of graphene from conducting characteristics to semiconducting behaviors.