Narrow Results

The most difficult aspect in electrochemical synthesis of graphene oxide (GO) is preventing graphite from disintegrating on the surface of the anode, which affects microstructural characteristics and yield. In this study, the effect of applied potential, electrolytic temperature, and types of electrolytic solution on yield, anode surface disintegration and microstructural properties of electrochemically synthesized GO has been investigated. The GO has been synthesized in an aqueous solution of 1 M piranha solution and sulfuric acid (${\mathrm{\text{H}}}_2{\mathrm{\text{SO}}}_4$) via electrochemical method by applying 24 V DC power source. After that, the GO was thermally reduced at around 650${\circ }^{}$C in a muffle furnace, and cooled down inside the muffle furnace. The yield, pH of the electrolytic solution, and anode surface disintegration all looked to be affected by the applied voltage and electrolyte temperature. Between the temperatures of 50${\circ }^{}$C and 70${\circ }^{}$C, the maximum yield was observed. During UV–Vis and XRD investigation, the absorbance, crystal structure, and interplanar distance appear to be unaffected by the reduction temperature, high voltage, electrolyte temperature and hydrogen peroxide addition. As demonstrated by Raman spectra, TEM, FE-SEM, AFM, and TGA analysis, high voltage, electrolyte temperature, and hydrogen peroxide addition have an important effect on the degree of defect, microstructure, and oxygen percentage, surface roughness and thermal stability of thermally reduced graphene oxide (TRGO).

Surface modification by using citric acid (CA) in the graphene is a process to modify the physicochemical properties of graphene oxide. The strategy that has been proposed depends upon the electrochemical exfoliation of reduced graphene oxide (rGO), and simultaneously, the surface modification of rGO with CA carried out in accordance with the green technique. The synthesis of graphene oxide that has been doped with CA was accomplished via an electrochemical process in an aqueous medium containing fresh lime juice and sulphuric acid (electrolyte heating aided method at $60^{\circ }$C) as an electrolyte. The electrolyte has been prepared using CA & H₂SO₄ (sulphuric acid), and both were mixed in a proportion of 1:2. In order to dilute the H₂SO₄ and perform the sonication, the water that has been pasteurized (according to the USP standards for irrigation) was used. The crystallite size, structural disorder, structure and surface morphology of the CA-doped graphene oxide were identified through X-ray diffraction (XRD) analysis, Raman spectroscopy, Field emission scanning electron microscope (FE-SEM). The presence of oxygen-containing functional group and adsorption has been analyzed using Fourier transform infrared (FTIR), and UV–Vis spectroscopy. The thermal stability of the CA-doped, and without CA-doped thermally reduced graphene oxide (TRGO) has been analyzed via thermogravimetric analysis (TGA). A green, simple, and environmentally friendly method has been demonstrated for the synthesis of CA-doped TRGO by electrochemical synthesis method by using natural dopant.

The control over microstructural characteristics of graphene oxide (GO) is one of the most serious issues in the domain of graphene synthesis as this affects the graphene’s properties, and functionality. In this study, the primary objective is electrochemical synthesis graphene in the presence of magnetic field that is applied externally. During the synthesis process, the magnetic field was applied in a direction that was perpendicular to the applied potential. This causes the electrolyte to spin flow around the cell. Subsequently, the goal is to provide a comparative analysis between the microstructural characteristics of graphene that has been synthesized in situ and ex situ magnetic field. The cylindrical graphite was used as an anode, and a carbon electrode that had been recovered from a waste dry cell battery was used as a cathode. The pre-oxidized graphite was sonicated (synthesized under magnetic field, and without magnetic field) in sterilized water for 10min with a probe-type sonicator and thermally reduced at same temperature i.e., 850^∘C followed by furnace cooling. The findings of the Raman spectroscopy, atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) characterizations indicate that the magnetic flux that was applied has a significant influence on the surface height and roughness, microstructure, and surface state, a structural disorder in comparison to when there was no magnetic field applied to the thermally reduced graphene oxide (rGO). On the other side, from the data obtained by XRD and TGA analysis, the applied magnetic field seems to have very little effect on phase, lattice parameter and thermal stability.

Graphene is a two-dimensional monolayer planar sheet containing carbon atoms that are sp²-bonded to one other and tightly packed in a honeycomb crystal structure. Because of its extraordinary qualities, graphene and its derivatives, such as functionalized graphene, graphene oxide (GO), and reduced graphene oxide (rGO), have attracted substantial attention in a variety of applications. The synthesis of graphene and its derivatives of high quality can be accomplished by the employment of a several different methods. When subjected to various reduction methods, GO and rGO emerge with distinctive sets of properties. These features, in turn, have an impact on the graphene’s overall usefulness and performance. This paper provides an overview of the influence that thermal annealing has on the structural and physical properties of graphene. Following the thermal annealing, GO was converted into rGO, and this allowed for the coherent crystal structure of rGO to be restored. It has been found that the annealing temperature has a direct relationship with the crystallite size. The results of the recorded Raman spectra demonstrate that the degree of imperfection ($I_D∕I_G$ ratio) can sometimes be found to increase while at other times it can be found to decrease. There has not been any conclusive evidence to support either the hypothesis that annealing is employed to polish graphene or the hypothesis that this can lead to changes in doping, defect levels, and strain consequences. Additionally, the impact that thermal annealing has on the functionality and performance variations of rGO has been analyzed and explained. This study concluded with a concise review, a discussion of the challenges faced, and a discussion of the opportunities presented by the graphene.

A high-quality, bulk synthesis of graphene that is inexpensive, and environmentally safe is highly desired because of the broad range of applications. In comparison to the chemical vapor deposition (CVD) method, epitaxial growth on silicon carbide, etc., the electrochemical approach is thought to be the most straightforward and eco-friendly way for the cost-effective bulk production of graphene from graphite. Moreover, the thermal reduction method appears to be a particularly cost-effective way to eliminate oxygen-containing functional groups when compared to chemical reduction. The yield of graphene is also impacted by the choice of cathode low-cost, which is extremely important and played a critical role during the synthesis process. In this work, we demonstrate a green, eco-friendly, and cost-effective electrochemical method for the synthesis of reduced graphene oxide (RGO) followed by thermal reduction. To accomplish electrochemical exfoliation for the graphene synthesis, a constant DC power of 65W ($\mathrm{\text{voltage}}=\sim 20$V and $\mathrm{\text{current}}=\sim 3.25$amp) has been supplied within an electrolytic cell that contains 2M of sulphuric acid as an electrolytic solution. The aluminium has been utilized as a cathode in place of the platinum, carbon cathode, etc. Moreover, to prepare the electrolytic solution and for the sonication process, sterilized water has been used in place of DI (deionized water). Thereafter, previously oxidized graphite oxide has been thermally reduced at a temperature of $800^{\circ }$C. The phase, crystallinity, and interatomic distance were investigated using X-Ray diffraction (XRD) analysis. X-Ray data show that the RGO crystal structure has been recovered following high-temperature annealing. The diffraction peak seems to be at $26.4^{\circ }$ with an interplaner distance of 3.48Å. The intensity of the defect, as measured by the $I_{\mathrm{\text{D}}}∕I_{\mathrm{\text{G}}}$ ratio (intensity ratio), was analyzed using Raman spectra, and the result of that investigation was found to be 0.196. The findings of the Raman study unambiguously reveal that the severity of the defects is judged to be on the lower end of the spectrum. The surface texture, microstructure, and elemental analysis were performed using atomic force microscopy (AFM), Field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), and EDX analysis. Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) were used to determine the number of oxygen-containing functional groups that existed in the RGO sample and their thermostability. The results of FTIR and TGA analysis clearly demonstrate that the reduction temperature has a major role in determining the proportion of oxygen that is present in the graphene. This study presents a large-scale, cost-effective, and eco-friendly graphene synthesis method for industrial applications.

Annealing at high temperatures holds the possibility of concentrating defects in the graphene. Moreover, a significant increase in annealing temperature destroys the surface properties. In this work, the reduced graphene oxide (RGO) was prepared by an electrochemical technique with a high voltage ($V=\sim 24$V, $I=\sim 3.25$A). Then, the potential effects of impact on thermal treatment in a temperature range of 800–1000^∘C in nitrogen-rich environment on the microstructure and surface morphology, thermal stability, phase and crystallinity, structural disorder, absorption properties, and optical properties of RGO for optoelectronic applications were investigated. In addition, a link was established between the estimated crystallite sizes determined by X-ray diffraction (XRD) and Raman data. The microstructural data indicate that the annealing temperature has a significant effect on the microstructure and carbon–oxygen (C/O) ratio. The C/O ratio increases as a function of annealing temperature. Atomic force microscope (AFM) analysis revealed that the root mean square (RMS) roughness of annealed RGO increases with increasing annealing temperature indicating an increase in crystallite size during annealing. Since most organic compounds were removed from the surface of the annealed RGO, oxygen functionalities appear to have minimal effect on the thermal stability of RGO. The size of graphene crystallites increases with annealing temperature, as shown by XRD observations. The crystalline structure was restored by annealing. The Raman results show that in the “low” defect density zone, the $I_D∕I_G$ values increase because a larger defect density causes a stronger elastic scattering. UV–Vis spectroscopy shows that the absorption of RGO is not affected by annealing temperatures between 800^∘C and 900^∘C. The optical bandgap of annealed RGOs decreases from 4.08 to 3.72eV upon annealing in the temperature range of 800–1000^∘C.

The requirement for restoring graphene’s electrical and thermal properties necessitates the implementation of reduction processes that remove oxygen atoms from the surface of graphene oxide sheets. Nevertheless, has been reported that the synthesis of graphene with a minimal oxygen content remains an obstacle in the field of graphene synthesis. The partial restoration of the initial graphene characteristics brought on by the recombination of carbon–carbon double bonds is primarily constrained by the existence of leftover oxygen atoms and lattice flaws. However, the absence of polar dioxide-based groups of function makes it difficult for the substance to disperse. Oxygen-containing functional groups also serve as reaction sites to bond active molecules to reduce graphene sheets. The literature describes many chemical methods to reduce graphene oxide for these reasons. It’s crucial to choose a chemical method that allows a thin modulation of residual oxygen content to tune the end product’s properties. This research demonstrates a synthesis mechanism for the low oxygen-containing thermally reduced graphene oxide (T-R-GO) by employing an electrochemical technique, which is then followed by thermal reduction. An environment-friendly, eco-friendly, simpler, and scalable electrochemical approach was initially used to synthesize graphite oxide. A steady power source of 24V DC (direct current) has been applied while the exfoliation process is being carried out. It has been noticed that there is a potential difference of 1V during the process of exfoliation. This difference is because the electrochemical cell creates a resistance, which results in a potential difference. Within the muffle furnace, the preoxidized graphite was subjected to a thermal reduction process at a temperature of 900${}^{\circ }$C. The microstructure, elemental composition, as well as C/O ratio (ratio of carbon and oxygen), was analyzed using field emission scanning electron microscopy (FESEM), transmission electron microscopy as well as energy dispersive X-ray (EDX). According to the results of EDX, reduction temperature serves a crucial role in the elimination of oxygen functionalities or their derived compounds. The surface topography and thermal stability analysis were analyzed using atomic force microscopy (AFM) and thermogravimetric analysis (TGA). The crystallinity and disorder in microstructure were investigated using X-ray powder diffraction (XRD) and Raman spectroscopy analysis. X-Ray data show that high-temperature annealing restored the RGO structure of the crystal. The interplanar distance is 3.824Å and the diffraction peak is 26.42${}^{\circ }$. Raman bands measured the defect’s I${}_D$/I${}_G$ ratio (intensity ratio) as 0.423. The Raman study shows that the flaws are minimal. This research offers a massive, economical, and environmentally friendly method for synthesizing graphene for use in industry.

The transition of graphene from the lab to consumer goods is still a challenging job that necessitates efficient and cost-effective large-scale graphene production. This study combines electrochemical exfoliation in an aqueous solution of sulfuric acid (1M H₂SO${}_4)$ and hydrogen peroxide (3% H₂O${}_2)$ followed by thermal deoxygenation at a temperature of 800${}^{\circ }$C within the ambient environment. This method allows the inexpensive synthesis of pristine graphene for various industrial applications. X-Ray diffraction (XRD) results for pristine graphene showed a distinct peak at 2$𝜃=26.39^{\circ }$ with a corresponding interplanar distance ($d_{\mathrm{\text{hkl}}})$ of 3.3754 Å and a crystallite size of 18 nm. XRD statistics indicated that the crystal structure of the original graphene was preserved. The crystalline structure was recovered and the interplaner distance was decreased following the high temperature thermal reduction. According to Raman spectroscopy, the impurity degree (I${}_D$/I${}_G)$ region fraction of pristine graphene was 0.211. This indicates that the original graph produced by the current method has little distortion. Raman analysis shows that there is a linear red shift in peaks D-band (D), G-band (G), and second order of the D-band (2D) due to the increase in phonon–phonon nonlinear interactions with increasing temperature, so that peaks (D), (G) and (2D) shifts are shown. The majority of the functional groups were discovered to be eliminated after high temperature thermal treatment. The three-dimensional graphene sheet is highly defined and intricately coupled in the microstructure analysis, resulting in a laxer and porous structure. When treated at a temperature below 800${}^{\circ }$C, there was only minor damage to the reduced graphene oxide (RGO) microstructure. The results of the Atom Force Microscope (AFM) demonstrated that the flaws spread over time from the layer boundaries and pores to the edges and eventually resulted in a separate RGO archipelago. According to TGA analysis, at temperatures up to 800${}^{\circ }$C, the RGO sheet loses up to 45% of its weight.

In this study, we provide electrochemical techniques for synthesizing thermally reduced graphene nanomaterial that have high potential, low defects, cost-effectiveness, and ecological sustainability. The electrochemical exfoliation is carried out by employing a 195 W DC (voltage = 60V and current = 3.25 A) power source at a maximum electrolyte temperature of about 92.5^∘C within the aqueous suspension of 2M of sulfuric acid (H₂${\text{SO}}_4)$. Thereafter, the synthesized nanomaterial was treated in the weak piranha [combination of sulfuric acid and hydrogen peroxide (H₂${\text{O}}_2)$] solution using an electrochemical technique inside the water bath sonicator at 80^∘C. X-ray diffraction (XRD) analysis shows the peak of diffraction to the (002) plane of the reduced graphene oxide (RGO) samples emerges at around 2$\theta =26.40^{\circ }$ and 26.56^∘ with an interplanar distance of 3.40 Å and 3.54 Å. According to the XRD data, after the high-temperature thermal reduction phase, the structure of the crystals and interplanar separation were recovered. The size of the crystallite of RGO produced under H₂SO₄ conditions was discovered to be greater than the crystallite size of graphene oxide produced under piranha solution conditions. The Raman analysis results show that the degree of disorder of the graphene synthesized within the H₂O₂ was higher than in comparison to the graphene synthesized in H₂SO₄. Field emission scanning electron microscopy (FE-SEM) results show that graphene synthesized in the presence of H₂O₂ has a thin and porous microstructure in comparison to H₂SO₄ with no significant effect on the presence of the availability of the C/O ratio. The atomic force microscopy (AFM) analysis indicates that the surface roughness of the graphene synthesized in the H₂O₂ was higher than that of the H₂SO₄. The Fourier transform infrared spectroscopy (FT-IR spectroscopy) analytical results show that the majority of the functional groups have been eliminated within the samples.