Structure Of Graphene Oxide Research Articles

Effect of a Ag-rGO structure on the SERS activity of PEDOT:PSS films

π-Conjugated organic semiconductors with tunable electronic structures are new prospective active substrate materials for surface-enhanced Raman scattering (SERS). However, observing higher SERS activity when using organic semiconductors as substrates could be difficult because there is no plasmonic effect of hot electrons. Here, we designed a Ag-reduced graphene oxide (rGO) structure, introduced it into a poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS) solution, and spin-coated the solution to obtain a Ag-rGO/PEDOT:PSS (ARPP) film. Our analyses demonstrate that the introduction of this Ag-rGO structure can not only enhance the electromagnetic field effect based on plasmon resonance but also improve the interaction between the target molecule and the substrate in the ARPP film. This innovative approach not only improves the SERS activity of π-conjugated organic polymers but also provides novel ideas for the preparation of other organic semiconductor-based SERS substrates.

THE EFFECT OF SPIN COATING’S SPEED ON GRAPHENE-OXIDE’S LAYER TOPOGRAPHY AND QCM VISCOELASTICITY

Spin coating speed controls the deposition process, affecting the formation of the layer’s topography of graphene oxide and the viscoelastic properties of quartz crystal microbalance (QCM). In this work, the graphene oxide was deposited on the QCM surface by spin coating method with speeds ranging from 500 to 800 rpm. The layer’s surface topography was subsequently measured and analyzed using a roughness multiparameter, which included the area average (Sa), area roughness deviation (Sq), localized surface roughness (Sz), surface skewness (Ssk), and surface kurtosis (Sku). The Sa, Sq, and Sz, which were decreased as the spinning speed increased. The measurements indicated that the graphene oxide layer deposited at 500 rpm had a rough and clumpy texture, while at a high speed of 800 rpm, the layer had a much smoother texture. A detailed analysis using the Sku and Ssk parameters revealed that the clumpy texture in the 500 rpm sample contains tapered sharp graphene oxide structures and a small amount of porosity. On the other hand, the sharp structures were significantly reduced, and porosity was dominant in the sample deposited at high speeds of 700 rpm and 800 rpm. The effect of the spinning speed and the topography on the viscoelasticity was studied using an impedance analyzer. The impedance of the layer deposited at 500 rpm was relatively higher than that at 800 rpm. The frequency shift was also relatively significant for the sample deposited at low speed and was reduced at higher speed. The impedance analysis demonstrated that the layer’s viscosity is affected by its mass, roughness, texture, and porosity.

Quantifying defects in graphene oxide structures

Oxidation of graphite and subsequent exfoliation leads to single layer graphene oxide (GO). One of the key structural features of GO is the presence of different kinds of defects that dictates their various physical and chemical properties. Molecular dynamics simulations with ReaxFF force fields have been widely used to generate realistic models of GO. In these simulations, the extent and distribution of the defects are varied by changing the initial oxygen (O)/carbon (C) ratio while the defect density is often measured by the total number of non-graphitic carbon (non-gC) atoms. Our calculations suggest that this parameter overestimates the defect densities at low O/C ratio. Herein, we employ the relative area of the defects as an alternative metric to gauge the defect density. Being exclusive to the defects and sensitive to the structural irregularities, this metric works well at both low and high defect densities. In another example, we consider the reduction of GO to reduced graphene oxide (rGO) for different O/C ratios, where the decrease in the number of non-gC atoms is associated with the formation of comparatively larger defects. Hence, it is unclear whether the extent of reduction in the defect density (if at all) should vary monotonically with the O/C ratio. The defect area, unlike the count of the non-gC atoms, mirrors this ambiguity and the change with respect to O/C ratio is not strictly monotonic. Additionally, we also investigate the dependence of the defect distribution and defect area on the size of the simulation cell.

High Long‐Term Performance of 325‐Mesh Silicon Microparticle Anodes in Li‐Ion Batteries Enabled by Hierarchical Structure of Graphene Oxide and DNA Binder

AbstractThe promise of silicon anodes for lithium‐ion batteries (LIBs), owing to the high theoretical capacity, is significantly affected by the huge volume changes (over 300%) during the lithiation/delithiation process. This leads to particle cracking during cycling impacting the electrode at multiple levels, from continued solid‐electrolyte interphase formation, particle contact losses, to delamination of the coating from the current collector. As a results, there is increased electrolyte consumption, and significantly shortened cycle life, hindering its commercial application. The problem is severe for commercially viable larger silicon microparticles (SiMPs > 1 µm). Herein, the cycling of 325 mesh (≤45 µm) SiMPs is successfully demonstrated using a composite binder consisting of inner graphene oxide coating and outside DNA polymer. The resultant hierarchical structure, with cycling‐induced 3D interconnection, maintains the electrodes integrity, as well as helps to stabilize the SEI. Thus, an excellent cycle life is observed, retaining a capacity of 808 mAh·g−1 after 450 cycles at a current density of 840 mA·g−1. This double protection strategy with a robust particle coating and a chemically bonded soft polymer offers an effective strategy for cyclability of SiMPs in practical LIBs.

Comparative Study Among Graphene Oxide Structures and Their Influence on Electrical Conductivity

Comparative Study Among Graphene Oxide Structures and Their Influence on Electrical Conductivity

Study of the structure of graphene oxide obtained by oxidation of intercalated graphite compound by Raman light scattering method

This work shows the strategy of GO synthesis from intercalated graphite compound, rotation of the synthesis conditions was carried out, and the starting material and synthesis products were characterized in detail by a complex of physical and chemical methods: scanning electron microscopy, transmission electron microscopy, atomic force microscopy, Raman spectroscopy, and high-temperature catalytic oxidation. It was found by Raman spectroscopy that the initial IGC sample is a graphite structure with a low content of defects in graphene layers. Oxidation of this sample leads to a gradual increase in the measure of disordered carbon framework. One of the reasons for this is a decrease in the size of graphite-like crystallites with subsequent reorientation in the space of graphene layers. It has been established by a complex of physicochemical methods of research that the oxidation of IGC graphite with increasing oxidation time leads to an increase in the defectivity of the initial carbon framework due to a decrease in the linear size of carbon crystallites. When a certain reaction time is reached, the initial structure of the sample changes, and there is a partial reorientation of the crushed graphite-like fragments with a simultaneous increase in the number of defects.

Scalable preparation of flexible heterogeneous graphene oxide structures for high-performance wet power generation

A heterostructured GO-rGO wet power generation device with volt-level potential difference generated by the interaction of water molecules with oxygen groups on graphene oxide and ion-induced diffusion.

Supercapacitor electrode based on graphene covalently functionalized with cross-linking inorganic-organic molecule

This work presents the fabrication of a supercapacitor electrode based on covalently cross‐linked graphene structure. It introduces a simple method to fabricate modified graphene oxides with an inorganic and organic cross-linked agent. The supercapacitive performance of this cross-linked graphene oxide structure (C-GO) is approved by conventional electrochemical procedures, such as cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy. The calculated specific capacitance amounts of 231 F/g and 240 F/g was achieved via CV and GCD curves at ѵ= 10 mVs−1 and I = 0.8 A g−1, respectively. This C-GO based-supercapacitor indicates a 9 % reduction in specific capacitance value after measurement of 3000 continuous cycles in the CV.

Pretreatment impact on electrochemically synthesized graphene oxide

The production of graphene oxide by the electrochemical method is more environmentally friendly, faster and suitable for mass production than the chemical method. Although this technique is very practical, the correct parameters must be selected to produce graphene oxide. Therefore, it is very important to investigate the factors affecting graphene oxide synthesis in the electrochemical process. In this study, the effect of pretreatment on graphene oxide produced by the electrochemical method was investigated. Structural characterization of the produced graphene oxide was carried out using X-ray diffraction, Raman spectroscopy and energy-dispersive X-ray spectroscopy, while morphological research was performed using scanning electron microscopy. Due to the increase in the electrochemical oxidation performance of dilute nitric acid with the effect of the pretreatment process, an effective increase in the oxygen content in the structure of graphene oxide was detected.

Trace level sensitivity and selectivity of room temperature NH3 gas sensors based on RGO/ZnO@SiNWs heterostructure

Ammonia (NH3) is one of the most common gaseous pollutants in various environmental and industrial processes which is accountable for various health issues, even for life-threatening situations. Due to this, high-precision detection of NH3 has become a top priority for various sectors so that healthy and safe environment could be ensured. Therefore, this work aims to develop a simple, reliable, and effective sensor with spatially distributed monitoring of NH3 gas wherein reduced graphene oxide (RGO) and Zinc oxide (ZnO) nanocomposite structure prepared using refluxing method were chosen to interact with NH3 gas. The vertically aligned silicon nanowires (SiNWs) were developed by using metal-assisted chemical etching (MACE) method. The RGO/ZnO nanostructure was then deposited on SiNWs to develop a selective and stable sensor for the trace level detection of NH3 gas with varying concentration from 0.01 ppm to 5 ppm at Room temperature (∼30 °C). The prepared materials were characterized using scanning electron microscope (SEM), transmission electron microscope (TEM), energy dispersive spectroscopy (EDS), X-ray diffractometer (XRD), Raman spectrometer, X-Ray Photoelectron Spectrometer (XPS) and Ultraviolet–visible spectrophotometer which provide a thorough explanation about the developed nanostructures. The sensitivity of the sensor was observed to lie between 21 % at 0.01 ppm and 176 % at 5 ppm concentration of NH3 wherein the response/recovery time was measured to be 3 s/6 s and 5 s/12 s respectively. The fast response of the sensor for NH3 gas at low limit of detection (LOD) could be attributed due to the precise interaction of the analyte at the interface of RGO/ZnO@SiNWs Schottky heterostructure. Hence, the reported sensor can continuously be utilized to monitor the target analyte that is NH3 gas at low concentrations and reduces the chance of an unfortunate incident.

Economical-effective purification of brackish water through an integrated capacitive desalination & boron adsorption system

The escalating scarcity of high-quality water for potable, industrial, and agricultural use necessitates innovative methods to augment freshwater supply from unconventional sources. This study primarily aims to lower boron (B) and chloride (Cl−) levels in brackish water to meet water quality standards of B < 0.5 mg/L and Cl− < 250 mg/L. To meet this goal, an innovative adsorbent, OQAS-AC@NGO, was used for boron removal. It combines organosilicon quaternary ammonium chloride (OQAS) modified activated carbon (AC) within a self-assembled nitrogen-doped graphene oxide (NGO) structure. Before boron removal, a capacitive deionization (CDI) system was used, employing OQAS-AC as the anode and COOH-modified AC as the cathode for chloride ion electrosorption. Through this cooperation procedure, the treated water meets the required quality standards while significantly reducing chemical costs by approximately 13.5 times when compared to conventional ion exchange resin methods for adsorbent regeneration. Moreover, the OQAS-AC@NGO adsorbent sustains its efficiency through multiple cycles, outperforming non-assembled N-GO in terms of yield, performance, and water flux. This underscores the cost-effective adsorbent preparation and enhanced water productivity. Economic analysis endorses the integrated CDI & B adsorption approach, advancing both sustainable water treatment processes and practical industrial applications.

The impact of functionalization modes on the third-order nonlinear optical properties of reduced graphene oxide

Covalent and noncovalent interaction mechanisms were implemented for the modification of reduced graphene oxide nanosheets through functionalization with zinc oxide nanoparticles employing chemical reduction and ultrasonication methods. The zinc oxide nanoparticles appear as hexagonal wurtzite structures in bare and composite. The partial removal of oxygen groups in rGO is further confirmed by the decline in d spacing in the XRD pattern. In Raman spectra, a reduction in defect ratio points to the restoration of the π conjugated system with the formation of the composite. The observed electronic spectra further confirmed the formation of composite and effective interaction between the components. The morphological analysis revealed that the zinc oxide nanoparticles dispersed over the layered reduced graphene oxide structure. The open aperture z-scan studies suggested increased absorption at the focus (Reverse saturable absorption), which was further exploited for analyzing the optical limiting behavior. The closed aperture z-scan curve implied the self-defocusing feature of the samples. The composite rGO/ZnO C has a β value of 20.31 cmGW at an input intensity of 4.59 GWcm2 and an optical limiting threshold value of 21.54 Jcm2. These superior results are due to the effective interaction and charge conveyance among rGO and ZnO. The work focuses on analyzing the effect of interaction between components in the composite, input laser intensity, and sample concentration on the nonlinear optical properties. The obtained value of nonlinear optical parameters showed the importance of the functionalization mode in enhancing the optical limiting property of the composite. The results have implications for developing novel materials with improved nonlinear optical behavior.

GOQDs and GOQDs-NS-doped Carbocatalysts: A Concise Study on Production and Use in One-pot Green MCRs.

Nowadays, the catalysts' usage in chemical reactions is unavoidable, and this has led scientists to look for producing and using catalysts which not only cause pollution and toxicity in the reactions and products, but also generate economical benefits. Our goal in this paper is to produce a fully biocompatible, non-toxic and inexpensive carbocatalyst with a graphene oxide structure for use in multi-component reactions as a heterogeneous catalyst. The research has been carried out to simplify the method of preparing carbocatalysts. In this article, we heated citric acid and thiourea in the simple bottom-up method in which nitrogen and sulfur were atomically inserted into a carbon-carbon bond of graphene oxide. The results have been obtained by comparing graphene oxide quantum dots (GOQDs) and functional graphene oxide quantum dots (GOQDs) and functional nitrogen and sulfur-doped graphene oxide quantum dots (NS-doped-GOQDS) using the produced carbocatalyst in the synthesis of spiro indoline pyrano pyrazoles and highly substituted pyridine derivatives with chemical and pharmacological properties. A simple and affordable bottom-up method has been developed to synthesize fluorescent NS-doped-GOQDS by the condensation of CA in the presence of thiourea with water elimination at 185 ℃. After the production of NS-doped-GOQDS, the carbocatalyst is used in the synthesis of spiro[indoline-3,4'-pyrano [2, 3-c]pyrazole] derivatives in four-component reactions and pyridine derivatives in five-component reactions.

Activated carbon derived from Satureja seed biomass for improving the capacitive performance of composite based on Aprepitant functionalized graphene oxide and ionic liquid

In this work, three chemicals, including Aprepitant functionalized graphene oxide (APR-FGO), PhenmimCl ionic liquid (IL), and activated carbon derived from Satureja seed (AC-SS), were synthesized and used in a supercapacitor system as electrode materials. After the structural description of the synthesized materials, the electrochemical performance of APR-FGO, APR-FGO/AC-SS, and APR-FGO/AC-SS/IL electrodes was investigated in a three-electrode system. Based on the comparison of electrochemical results, the APR-FGO/AC-SS/IL electrode was able to provide the best performance compared to the other two electrodes. It was observed that the APR-FGO/AC-SS/IL electrode presented the specific capacitance (Cs) of 493.24 F g−1 at 1 A g−1. Also, the Cs retention value of the APR-FGO/AC-SS/IL electrode was 95.2 % at 8 A g−1 over 10,000 charge-discharge cycles. Furthermore, in a two-electrode system, the APR-FGO/AC-SS/IL electrode obtained a Cs of 214 F g−1, an energy density of 32.22 Wh kg−1, and a power density of 850 W kg−1 at 1 A g−1. These findings prove the ideal electrochemical performance of this composite as a supercapacitor electrode. The superior performance of the APR-FGO/AC-SS/IL electrode can be attributed to the presence of groups containing nitrogen and fluorine in the Aprepitant functionalized graphene oxide structure, the essential role of AC-SS as a substrate for performing electrochemical reactions, and the high conductivity of the PhenmimCl ionic liquid. Therefore, the proper synergy of these three materials shows that the APR-FGO/AC-SS/IL electrode has a high potential for energy storage systems.

Effect of electric potential on the structure and yield of graphene oxide using electrochemical exfoliation method

Optimization of the electrochemical exfoliation of graphene oxide synthesis was investigated in this report using varying potentials. Graphite from waste lithium-ion batteries was used as the electrodes for the DC (direct current) electrochemical set-up. Electric potentials of 7.5 V, 12 V, and 15 V were applied for 225 minutes using 0.2M H2SO4 as the electrolyte. The characterization of the produced graphene oxide was done using Raman spectroscopy, high-resolution scanning electron microscopy (HRSEM), and energy dispersive x-ray spectroscopy (EDS) attached to the scanning electron microscope (SEM). The results obtained showed that both the rate of graphene oxide yield and the C/O ratio increased correspondingly with the increase in electric potential. However, the structure of graphene oxide produced at 7.5 V was of superior quality compared to others produced at higher potentials with regards to the crystallite lattice characteristics such as defects, lateral dimensions, thickness, and the number of graphene layers. Consequently, tailor-made graphene oxide properties (and yield) for target applications may be achieved using the electrochemical exfoliation method via the choice of the electric potential.

Effects of different electrolytes on the structure and yield ofgraphene oxide produced via electrochemical exfoliation

The most suitable electrolyte for graphene oxide synthesis, in terms of both production efficiency and quality, using the electrochemical exfoliation technique has been investigated and reported in this study. Simultaneous anodic and cathodic graphene oxide production using ten (10) different electrolytes, including acids (H2SO4, HCl, HNO3), bases (KOH, Ca(OH)2, Mg(OH)2, NaOH), and salts (NaCl, (NH4)2SO4, K2SO4), was studied under the same experimental conditions of bias voltage, graphite nature, exfoliation time, electrolyte molarity, and post-exfoliation treatments. Assessment of the graphene oxide structures and production rates was supported using Raman spectroscopy, high-resolution scanning electron microscopy (HRSEM), and EDS (energy dispersive x-ray spectroscopy), attached to the scanning electron microscope. Analysis of the results obtained reveals that H2SO4 showed the highest graphene oxide yield (86%) but with comparably low graphene oxide quality in terms of defect concentration, presence of oxygen functional group contamination, and crystallite properties. The aqueous NaCl, Ca(OH)2 and Mg(OH)2 electrolytes did not show any graphene oxide exfoliation effect. However, from the series of electrolytes examined, aqueous (NH4)2SO4 exhibited an excellent combination of efficient graphene oxide yield and high-quality characteristics due to its relatively high yield of 74% and superior quality of the produced graphene oxide with the comparatively lowest defect density, ?D, and highest C/O (carbon-to-oxygen) ratio. The tortuous, agglomerated, and planar layers of the distinct 2D graphene oxide sheets were also clearly revealed by the SEM images. In essence, the roles played by dissociated sulfate (SO42?), nitrate (NO32?), chlorides (Cl?), and hydroxides (OH?) ions in the series of complex electrochemical reactions toward the intercalation, exfoliation, yield, and properties of graphene oxide produced are discussed. From the series of electrolytes tested, aqueous (NH4)2SO4 emerged as the most relatively suitable electrolyte for the synthesis of graphene oxide because it combines both high yield and fine quality.

Performance evaluation of microbial fuel cell fabricated using green nano-graphene oxide as coating anode material

AbstractA dual-chamber microbial fuel cell (MFC) was fabricated and optimized for electricity generation. Titanium wire, graphite rod, and carbon cloth supported on stainless steel mesh were the best current collector, anode, and cathode electrode materials, respectively. To enhance the efficacy of the system, carbon-based materials in nano-scale (nanocarbonized materials) were prepared from pomegranate peel waste at different hydrothermal temperatures (300, 500, and 700 oC), and were used as anode coating material. The synthesized coating materials were characterized using EDX, FT-IR, Raman spectroscopy, XRD, TEM, fluorescence, UV, and XPS analyses. Data showed that nanocarbonized material prepared at 500 oC exhibited high surface area (682 m2/g), high pore size (122 nm), and indicated the presence of graphene oxide (GO) structure. The electrochemical behavior of MFC was monitored by cyclic voltammetry and impedance measurements. Results revealed that the anode coated with GO provided high MFC performance with a maximum voltage of around 1000 mV, and a maximum current of 0.1 mA, corresponding to a maximum power density of 12.46 W/m2, which is 2.85-fold higher than that of a cell with a free graphite plate as an anode. Furthermore, the large charge transfer resistance and the low diffusive resistance observed upon coating the anode demonstrated the anode is functioning as a capacitor. The reported results proposed graphene oxide prepared from pomegranate peels as a novel coating anode material prepared from waste sustaining the idea of green curricular economy

Surface-enhanced Raman scattering of graphene oxide chemically modified by perylene diimide

A soluble perylene diimide derivative are bonded to graphene oxide via esterification, which is applied as the flexible surface-enhanced Raman scattering active substrate for detecting rhodamine 6G. The esterification destroys the crystalline structure of graphene oxide and causes graphitization to some extent. The efficient charge transfer processes from rhodamine 6G and perylene diimide to graphene oxide result in the weak emissions and reduce the background signals. The enhanced Raman signals of rhodamine 6 G on graphene oxide-perylene diimide is increased nearly four times that on graphene oxide without modification. The analysis of the optical spectra and energy levels of the compounds indicates that the multiple charge transfer processes contribute to the enhanced Raman signals of rhodamine 6G on graphene oxide-perylene diimide.

Study of the structure and electrical properties of graphene oxide (GO) and graphene oxide+nanocellulose (GO+NC)

Proton exchange membranes (PEMs) that function at elevated temperatures surpassing 100°C and exhibit exceptional mechanical, chemical, and thermochemical stability have garnered significant interest. This is primarily due to their practical utility in proton exchange membrane fuel cells (PEMFCs). In the present era, an extensive array of polymers and polymer-blended membranes have been scrutinized for their applicability in this domain. Each of these materials presents a set of advantages and disadvantages. However, the realm of PEMFCs is still in search of the perfect membrane endowed with distinct properties. Graphene oxide, a two-dimensional substance arising from the oxidation of graphite, has manifested itself as a promising candidate. Oxygen (O) functional groups are incorporated within the sp2 carbon (C) plane of the oxidized graphite, forming graphene oxide. This material can be synthesized by exfoliating graphite oxide, a three-dimensional carbon-based compound, into layered sheets using ultrasonic or mechanical agitation. The presence of multiple reactive oxygen functional groups renders graphene oxide suitable for a diverse array of applications, such as composite polymers, energy conversion materials, environmental safeguards, sensors, transistors, and optical components. This versatility is attributable to its outstanding electrical, mechanical, and thermal properties. Among the various methodologies for graphene oxide synthesis, the modified Hammer method stands out for its simplicity, cost-effectiveness, and high yield. This research delves into the structural analysis of graphene oxide obtained through the Hammer method, utilizing commercially available graphite. The study involves the creation of membranes based on carboxymethylcellulose (NC) that integrate dispersed graphene oxide (GO) sheets. These novel membranes, as well as pristine graphene oxide, were subjected to a comprehensive array of analytical techniques including XRD, XPS, Raman, FTIR, and SEM microscopy. Additionally, electrophysical characterizations were undertaken employing electrochemical impedance spectroscopy (EIS) measurements. The investigation uncovered that the introduction of NC into the graphene oxide matrix significantly enhances the electron conductivity of the composite membrane. Simultaneously, the presence of graphene oxide contributes to the mechanical robustness and thermomechanical stability of the membrane structure. The principal impetus behind this article lies in furnishing vital insights into the physical and structural attributes of graphene oxide membranes relevant to their deployment in hydrogen energy applications.

Derivatives of Sri Lankan Vein Graphite: Atomic Scale Study of Graphene Oxide and Reduced Graphene Oxide

Aims: The present study examines the atomic-scale structures of Graphene Oxide (GO) and Reduced Graphene Oxide (RGO). Background: Electron microscopic studies on Sri Lankan vein graphite are considerably less; hence, this study focuses on the atomic-scale study of Sri Lankan vein graphite, using advanced electron microscopic techniques. Objective: The purpose of this research is to utilize the data obtained to explore the multidisciplinary characteristics of graphene to the maximum prospectively. Method: We report an atomic-scale study on Sri Lankan vein graphite (purest) derivatives using advanced electron microscopic techniques, including High-Resolution Transmission Electron Microscope (HRTEM), Scanning Transmission Electron Microscope (STEM), and Electron Energy Loss Spectroscopy (EELS). The present study examines the atomic-scale structures of Graphene Oxide (GO) and Reduced Graphene Oxide (RGO). Result: The results obtained exhibited an inter-atomic layer distance of 3.54 Å for RGO. The EELS study performed with the electron dose optimization for GO and RGO distinguished the differences in the C K edge with the oxygen functionalities. The XPS study confirmed the changes in oxygen functionalities obtained with EELS. Conclusion: The advanced electron microscopic techniques and other molecular spectroscopic analysis techniques allowed us to obtain a comprehensive study on Sri Lankan vein graphene-based structural and chemical features on an atomic scale.