Annealing Of Graphene Oxide Research Articles

Role of oxygen functional groups and attachment of Au nanoparticles on graphene oxide sheets for improved photodetection performance.

Integrating low-dimensional graphene oxide (GO) with conventional Si technology offers innovative strategies for developing ultrafast wideband photodetectors. In this study, we synthesized GO and explored its potential application in broadband photodetection alongside silicon heterostructures. The as-synthesized GO contains various oxygen functional groups, as evidenced by X-ray photoelectron and Fourier transform infrared spectroscopy. These functional groups contribute to increased photo absorption, enhancing photodetection performance. The systematic reduction of these functional groups from the GO surface via thermal annealing decreases photo absorption and consequently lowers the photocurrent. This reduction diminishes photo absorption and amplifies the dark current by approximately 25 times, from 20 nA to 496 nA. This dark current increase is attributed to the electron mobility following the reduction of functional groups. However, attaching plasmonic gold nanoparticles (Au NPs) to the GO surface enhances UV-Vis absorption in the visible region, enabling broadband detection. The even distribution of attached Au NPs on the GO surface is confirmed through field emission transmission electron microscopy. While thermal annealing of GO diminishes the responsivity from 4.6 A W-1 to 3.0 A W-1, the attachment of Au NPs augments the responsivity by more than two-fold, reaching 10.0 A W-1. Thus, it highlights the importance of rich oxygen functional groups in GO and the attachment of Au NPs to achieve more efficient photo-sensing properties.

Electron paramagnetic resonance

We have studied literature from investigation of the impact of Mechanothermal effects in the creation of defect structures in dispersed systems after prolonged mechanical treatment of ZnO powders. This work illustrates some potential applications of electron paramagnetic resonance. EPR application beginning of a variety of paramagnetic processes is based on the knowledge that this centre happens when some materials are mechanically treated. These facilities can act as EPR sondes of various thermal processes that appear when systems are being mechanically treated consisting of ZnO.Zn was evaporated in air, dry and humid argon flow, and dry and humid nitrogen flow to create Zno tetrapod nanostructures. SEM, X-ray diffraction, photoluminescence, photoluminescence excitation (PLE) spectroscopy (at various temperatures), and electron paramagnetic resonance (EPR) spectroscopy at −160 ℃ and room temperature have all been used to explore the characteristics. It is discovered that the fabrication conditions have a considerable impact on the acquired EPR and PL spectra. while some of the samples exhibit a g = 1.96 EPR signal. We used microwave processing to create and mix ZnO nanoparticles (ZnO-NPs) with various amounts of graphene oxide (GO) (10 %, 20 %, and 30 %).The process delivered evenly distributed ZnO-NPs onto and between the rGO layers.(GZCs). The UV–vis absorption, PL emission, defect states of the ZnO, EPR signals, photo-electrochemical reaction, and charge transfer properties were all influenced by the annealing temperature and graphene oxide content. The GZCs' HRTEM microscopy pictures revealed interpenetrating structures and vacancy flaws that were easily seen. The findings showed that following hybridization with GO, the defect sites (Zn interstitials, oxygen vacancy, ionised oxygen vacancy, and oxygen interstitials) greatly decreased. The GZC-10photo-conversion 10 %'s efficiency(ŋ= 13.1 × 10-3%) We have studied literature from Ref.[1]which show that.

Assessing the evolution of oxygenated functional groups on the graphene oxide surface upon mild thermal annealing in water.

Graphene oxide (GO) is known to be a 2D metastable nanomaterial that can be reconstructed under thermal annealing into distinct oxidized and graphitic phases. Up to now, such phase transformation, mainly related to epoxide and hydroxyl functional groups, has been usually achieved by thermally treating layers of GO in the solid state. Here, we present the mild annealing of GO dispersed in an aqueous medium, performed at two temperatures, 50 °C and 80 °C, for different intervals of time. We show experimental evidences of the epoxide instability in the presence of water by means of XPS, cyclic voltammetry and Raman spectroscopy, demonstrating the reorganization of epoxide and hydroxyl moieties initiated by water molecules. In fact, at 50 °C an increase in oxygen content is detected in all annealed samples compared to untreated GO, with a transformation of epoxide groups into vicinal diols. On the other hand, at 80 °C the oxygen content decreases towards the initial value since the vicinal diols, previously formed, transform into single hydroxyls and C[double bond, length as m-dash]C bonds. Moreover, the higher temperature annealing likely favours oxygenated functional groups rearrangements and clustering, in accordance with the literature, leading to a higher electron affinity and conductivity of the graphenic network.

Multifunctional sites on reduced graphene oxide synergistically improving the degradation of diclofenac in peroxydisulfate systems

Carbonaceous catalysts are highly efficient in activation of persulfate thus attracting much attention in pollutant control. A reduced graphene oxide (rGO600) was carefully prepared via thermal annealing graphene oxide to activate peroxydisulfate (PDS) for generating nonradical and radical degradation pathways of diclofenac (DCF) in this study. The rGO600 had multifunctional groups, high defective degree (vacancies, CO and C−O−C; abundant reactive sites to activate PDS) and specific surface area. In the rGO600/PDS/DCF system, DCF was fast adsorbed on the surface and degraded via 1O2, electron transfer complex and O2•−. The rGO600/PDS/DCF system was resistant to the presence of Cl−and NO3−. Reductive NO2− and humic acid significantly retarded the absorption and activation of PDS by rGO600. Ten intermediate products from DCF were tentatively identified and proposed by using high-resolution mass spectrometry. The major adsorption sites for DCF and major catalytic sites for PDS were not exactly the same sites. The coexist of abundant reactive oxygen species (ROS)-generation sites and adsorbed DCF on the adsorption sites should favor the quick utilization of the generated ROS. The multifunctional sites on rGO600 improved the activation of PDS with pseudo first-order kinetics and the degradation of DCF.

Graphene-Based Aqueous Magnesium Ion Hybrid Supercapacitors with an Appealing Energy Density Advanced by a KI Additive

The electric double-layer capacitance (EDLC)-based capacitor is hindered with low capacitance and low energy density. Here, in this report, we focused on the fabrication of a symmetric device having graphene as an EDLC electrode material and redox additive KI-integrated aqueous MgSO4 as an electrolyte. The high surface area of graphene was produced by annealing of graphene oxide in an inert atmosphere and confirmed through X-ray photoelectron spectroscopy and Raman spectroscopy. The strategic 6% KI into MgSO4 delivered the highest specific capacitance with a wide working window of 0.7 V. Electrochemical measurements showed that graphene delivered a significantly greater specific capacitance (727.6 F/g) in a KI-integrated electrolyte (MgSO4 + KI) compared to 89.2 F/g in a MgSO4 electrolyte, owing to species such as IO3− and I3−(oxidation states of I). The symmetric device showed the maximum energy density (ED) of 69.3 Wh/kg, which can be achieved at the power density of 2.5 kW/kg, better than reported values in monovalent-based electrolyte devices. In this report, the charge storage mechanism, interactive association between Mg2+ ion insertion/extraction, and integration of redox KI had been comprehensively studied. The strategy shows a new path in the design of excellent ED capacitors without compromising the supercapacitor properties.

High‐capacity anode derived from graphene oxide with lithium‐active functional groups

Applications utilizing Li-ion batteries (LIBs) have recently been broadened from portable electronic devices to electric vehicles. Graphite has been applied as an anode material for commercialized LIBs; however, there is a growing demand for application-oriented LIBs with higher energy and power densities, and faster charging, compared with its limited electrochemical properties. Heteroatom-doped graphene has been considered as a potential alternative to graphite, although its synthesis is complex and costly. In this study, we introduced a facile strategy to realize advanced anode materials through fine control of the sheet size and oxygen-containing functional groups on the surface of graphene oxide (GO) as a raw material for heteroatom-doped graphene. The sheet size of GO is inversely proportional to the amount of oxidizing agent, which affects the formation of various types of oxygen-containing functional groups at the edges of GO. Mild annealing of GO selectively removes the functional groups with weak binding strength, leading to the formation of GO maximized with carbonyl groups, which can interact with Li ions quickly and reversibly. The GO with the average sheet size of 500 nm developed in this study exhibits capacities of up to 779 and 220 mAh g−1 at 0.1 and 2 A g−1, respectively. Therefore, decreasing the sheet size of GO with mild-temperature annealing increases the number of carbonyl groups formed on the additional exposed edge of the sheets, resulting in facile Li-ion interaction and a higher capacity as an anode material.

An electrochemical DNA biosensor fabricated from graphene decorated with graphitic nanospheres

Graphene decorated with graphitic nanospheres functionalized with pyrene butyric acid (PBA) is used for the first time to fabricate a DNA biosensor. The electrode was formed by attaching a DNA probe onto PBA, which had been stacked onto a graphene material decorated with graphene nanospheres (GNSs). The nanomaterial was drop-coated onto a carbon screen-printed electrode (SPE) to create the GNS-PBA modified electrode (GNS-PBA/SPE). A simple method was used to produce GNS by annealing graphene oxide (GO) solution at high temperature. Field emission scanning electron micrographs confirmed the presence of a spherical shape of GNS with a diameter range of 40–80 nm. A stable and uniform PBA-modified GNS (GNS-PBA) was obtained with a facile ultrasonication step. Thus allowing aminated DNA probes of genetically modified (GM) soybean to be attached to the nanomaterials to form the DNA biosensor. The GNS-PBA/SPE exhibited excellent electrical conductivity via cyclic voltammetry (CV) and differential pulse voltammetry (DPV) tests using potassium ferricyanide (K3[Fe(CN)6]) as the electroactive probe. By employing an anthraquinone monosulfonic acid (AQMS) redox intercalator as the DNA hybridization indicator, the biosensor response was evaluated using the DPV electrochemical method. A good linear relationship between AQMS oxidation peak current and target DNA concentrations from 1.0 × 10−16 to 1.0 × 10−8 M with a limit of detection (LOD) of less than 1.0 × 10−16 M was obtained. Selectivity experiments revealed that the voltammetric GM DNA biosensor could discriminate complementary sequences of GM soybean from non-complementary sequences and hence good recoveries were obtained for real GM soybean sample analysis. The main advantage of using GNS is an improvement of the DNA biosensor analytical performance.

Hollow “graphene” microtubes using polyacrylonitrile nanofiber template and potential applications of field emission

We report a simple process to connect graphene sheets forming graphene hollow microtubes (GHMs), where the tube diameter can be adjusted in the 100–500 nm range by changing reaction conditions. We discovered that graphene sheets can be seamlessly linked to each other if C atoms are substituted for N atoms at the edges of the sheets during annealing of graphene oxide(G-O)-coated electrospun PAN carbon fibers in ammonia atmosphere. The G-O/carbon hybrid nanofibers framework served as a confining template around which graphene sheets curved to form tubular structures. The GHMs formed by this process are similar to (very) large diameter carbon nanotubes (CNTs) with relatively low curvature whose electron field-emission properties include a low turn-on voltage of 0.18 V/μm (at J = 10 μA/cm2), low threshold field of 0.35 V/μm (at J = 10 mA/cm2), and high field-emission stability. This process to produce GHMs can be scaled up to fabricate GHMs of variable diameter in bulk quantities.

Effective reduction of graphene oxide via a hybrid microwave heating method by using mildly reduced graphene oxide as a susceptor

Due to the poor microwave absorption ability of graphene oxide (GO), direct reduction of GO by solid-state microwave irradiation is inefficient. In this study, GO was reduced effectively by a hybrid microwave heating (HWH) method by using mildly reduced graphene oxide (MG) membrane as a external susceptor, in which MG was obtained by annealing of GO at 300 °C for 1 h under nitrogen by a conventional heating method. When the mass ratio of MG to GO is 0.045, the C/O atomic ratio of GO increases from 1.8 to 17.84 by microwave irradiation under argon at 2000 W for 30 s. However, when GO was irradiated solely under the same conditions, the ratio of C/O was unchanged (1.88). For comparison, the MG was further irradiated by microwave at 2000 W for 30 s, its C/O ratio is enhanced from 4.17 to 8.46, demonstrating the higher reduction efficiency due to a mixed heating mode in the HWH process. The conventional heating of GO occurs during the initial stage and a two-way heating mode during the later stage, in which MG heats the GO from the surface and the microwave heating from the GO itself. Therefore, more amount of carboxyls and epoxides can be removed in the HWH process to achieve higher C/O ratio compared with that of the product obtained by direct microwave irradiation of MG.

Fabrication and investigation on the Fe3O4/thermally annealed graphene aerogel/epoxy electromagnetic interference shielding nanocomposites

Ethylenediamine functionalized Fe3O4 (NH2-Fe3O4) nanoparticles and graphene oxide (GO) were compounded firstly, followed by the addition of l-ascorbic acid, to obtain the Fe3O4/thermally annealed graphene aerogel (Fe3O4/TAGA) by thermal annealing method. And the Fe3O4/TAGA/epoxy nanocomposites were then fabricated via template-casting method. When the mass ratio of GO to NH2-Fe3O4 was 2:1 and the total mass fraction of Fe3O4/TAGA was 2.7 wt% (1.5/1.2 wt% Fe3O4/TAGA), the obtained Fe3O4/TAGA/epoxy nanocomposites presented the highest electromagnetic interference shielding effectiveness (EMI SE of 35 dB in the X-band), much higher than that of epoxy nanocomposites (10 dB) filled with the same Fe3O4/thermal annealing graphene oxide (Fe3O4/TAGO) loading. Meantime, the corresponding Fe3O4/TAGA/epoxy nanocomposites also presented the outstanding electrical conductivity of 27.5 S/m.

Lattice defects of ZnO and hybrids with GO: Characterization, EPR and optoelectronic properties

We have prepared and combined ZnO nanoparticles (ZnO-NPs) with different graphene oxide (GO) contents (10%, 20% and 30%) via microwave processing. The procedure provided well-dispersed ZnO-NPs between and onto the rGO layers (GZCs). The annealing temperature and graphene oxide contents affected the UV-Vis absorption, PL emission, defect-states of the ZnO, EPR signals, photo-electrochemical response and charge transfer properties. The HRTEM microscopy images of the GZCs showed interpenetrating structures and clearly visible vacancy defects. The results indicated that the defect sites (Zn interstitials, oxygen vacancy, ionized zinc vacancy and oxygen interstitials) significantly decreased after hybridization with GO. The photo-conversion efficiency of the GZC-10% (η = 13.1 x 10-3%), is 13 times higher than the ZnO-NPs (η = 1.02 x 10-3%) illustrating higher exciton production and separation efficiency of the GZCs under photo-excitation. The GZC-10% has lower (8-15 Ω) charge transfer resistance (Rct) compared to all the GZCs under same experimental conditions, therefore an important reason of better performance of the GZC 10%. The EPR spectra showed presence of radicals in all the samples with GZC 10% most intense signal among the different GZCs.

Electrodeposition of flower-like platinum on electrophoretically grown nitrogen-doped graphene as a highly sensitive electrochemical non-enzymatic biosensor for hydrogen peroxide detection

An efficient non-enzymatic biosensor electrode consisting of nitrogen-doped graphene (N-graphene) and platinum nanoflower (Pt NF) with different N-graphene loadings were fabricated on indium tin oxide (ITO) glass using a simple layer-by-layer electrophoretic and electrochemical sequential deposition approach. N-graphene was synthesized by annealing graphene oxide with urea at 900°C. The structure and morphology of the as-fabricated non-enzymatic biosensor electrodes were determined using X-ray diffraction, field emission electron microscopy, transmission electron microscopy, Raman and X-ray photoelectron spectra. The as-fabricated Pt NF-N-graphene-modified ITO electrodes with different N-graphene loadings were utilized as a non-enzymatic biosensor electrode for the detection of hydrogen peroxide (H2O2). The behaviors of the hybrid electrodes towards H2O2 reduction were assessed using chronoamperometry, cyclic voltammetry and electrochemical impedance spectroscopy analysis. The Pt NF-N-graphene-modified ITO electrode with a 0.05mgml−1 N-graphene loading exhibited the lowest detection limit, fastest amperometric sensing, a wide linear response range, excellent stability and reproducibility for the non-enzymatic H2O2 detection, due to the synergistic effect between the electrocatalytic activity of the Pt NF and the high conductivity and large surface area of N-graphene.

High-Quality Graphene Ribbons Prepared from Graphene Oxide Hydrogels and Their Application for Strain Sensors.

Reduced graphene oxide (rGO) ribbons with arbitrary lengths were prepared by dry spinning of the hydrogels of graphene oxide (GO) formed via thermal annealing GO dispersions, and followed by chemical reduction. These rGO ribbons are flexible, having ultrahigh tensile strengths of 582 ± 17 MPa, ultrahigh fracture energies of 18.29 ± 2.47 MJ m(-3), high conductivities of 662 ± 41 S cm(-1), and an extremely large breakdown current density of about 11,500 A cm(-2). Strain sensors based on the meshes of these ribbons showed sensitive recoverable responses to different tensile strains with excellent cycling stability, promising for the applications in wearable devices.

Facile synthesis of iron oxides/reduced graphene oxide composites: application for electromagnetic wave absorption at high temperature.

Iron oxides/reduced graphene oxide composites were synthesized by facile thermochemical reactions of graphite oxide and FeSO4·7H2O. By adjusting reaction temperature, α-Fe2O3/reduced graphene oxide and Fe3O4/reduced graphene oxide composites can be obtained conveniently. Graphene oxide and reduced graphene oxide sheets were demonstrated to regulate the phase transition from α-Fe2O3 to Fe3O4 via γ-Fe2O3, which was reported for the first time. The hydroxyl groups attached on the graphene oxide sheets and H2 gas generated during the annealing of graphene oxide are believed to play an important role during these phase transformations. These samples showed good electromagnetic wave absorption performance due to their electromagnetic complementary effect. These samples possess much better electromagnetic wave absorption properties than the mixture of separately prepared Fe3O4 with rGO, suggesting the crucial role of synthetic method in determining the product properties. Also, these samples perform much better than commercial absorbers. Most importantly, the great stability of these composites is highly advantageous for applications as electromagnetic wave absorption materials at high temperatures.

Nitrogen-doped graphene for generation and evolution of reactive radicals by metal-free catalysis.

N-Doped graphene (NG) nanomaterials were synthesized by directly annealing graphene oxide (GO) with a novel nitrogen precursor of melamine. A high N-doping level, 8-11 at. %, was achieved at a moderate temperature. The sample of NG-700, obtained at a calcination temperature of 700 °C, showed the highest efficiency in degradation of phenol solutions by metal-free catalytic activation of peroxymonosulfate (PMS). The catalytic activity of the N-doped rGO (NG-700) was about 80 times higher than that of undoped rGO in phenol degradation. Moreover, the activity of NG-700 was 18.5 times higher than that of the most popular metal-based catalyst of nanocrystalline Co3O4 in PMS activation. Theoretical calculations using spin-unrestricted density functional theory (DFT) were carried out to probe the active sites for PMS activation on N-doped graphene. In addition, experimental detection of generated radicals using electron paramagnetic resonance (EPR) and competitive radical reactions was performed to reveal the PMS activation processes and pathways of phenol degradation on nanocarbons. It was observed that both (•)OH and SO4(•-) existed in the oxidation processes and played critical roles for phenol oxidation.

Enhanced thermal oxidation stability of reduced graphene oxide by nitrogen doping.

Nitrogen-doped reduced graphene oxide (N-doped RGO) samples with a high level of doping, up to 13 wt. %, have been prepared by annealing graphene oxide under a flow of pure ammonia. The presence of nitrogen within the structure of RGO induces a remarkable increase in the thermal stability against oxidation by air. The thermal stability is closely related with the temperature of synthesis and the nitrogen content. The combustion reaction of nitrogen in different coordination environments (pyridinic, pyrrolic, and graphitic) is analyzed against a graphene fragment (undoped) from a thermodynamic point of view. In agreement with the experimental observations, the combustion of undoped graphene turns out to be more spontaneous than when nitrogen atoms are present.

Sulfur-doped porous reduced graphene oxide hollow nanosphere frameworks as metal-free electrocatalysts for oxygen reduction reaction and as supercapacitor electrode materials.

Chemical doping with foreign atoms is an effective approach to significantly enhance the electrochemical performance of the carbon materials. Herein, sulfur-doped three-dimensional (3D) porous reduced graphene oxide (RGO) hollow nanosphere frameworks (S-PGHS) are fabricated by directly annealing graphene oxide (GO)-encapsulated amino-modified SiO2 nanoparticles with dibenzyl disulfide (DBDS), followed by hydrofluoric acid etching. The XPS and Raman spectra confirmed that sulfur atoms were successfully introduced into the PGHS framework via covalent bonds. The as-prepared S-PGHS has been demonstrated to be an efficient metal-free electrocatalyst for oxygen reduction reaction (ORR) with the activity comparable to that of commercial Pt/C (40%) and much better methanol tolerance and durability, and to be a supercapacitor electrode material with a high specific capacitance of 343 F g(-1), good rate capability and excellent cycling stability in aqueous electrolytes. The impressive performance for ORR and supercapacitors is believed to be due to the synergistic effect caused by sulfur-doping enhancing the electrochemical activity and 3D porous hollow nanosphere framework structures facilitating ion diffusion and electronic transfer.

Catalyst-free synthesis of reduced graphene oxide–carbon nanotube hybrid materials by acetylene-assisted annealing graphene oxide

A facile catalyst-free approach for synthesis of reduced graphene oxide-carbon nanotube (RGO-CNT) hybrid materials was presented by acetylene-assisted annealing graphene oxide. The weight ratio of CNTs to RGO can be adjusted by regulating the annealing temperature, and it can be tuned in a relatively wide range of 0.33 to 7.039. The catalyst-free method opens up the possibility for the synthesis of RGO-CNTs for various applications.

Exploration of the active center structure of nitrogen-doped graphene-based catalysts for oxygen reduction reaction

We present two different ways to fabricate nitrogen-doped graphene (N-graphene) and demonstrate its use as a metal-free catalyst to study the catalytic active center for the oxygen reduction reaction (ORR). N-graphene was produced by annealing of graphene oxide (G-O) under ammonia or by annealing of a N-containing polymer/reduced graphene oxide (RG-O) composite (polyaniline/RG-O or polypyrrole/RG-O). The effects of the N precursors and annealing temperature on the performance of the catalyst were investigated. The bonding state of the N atom was found to have a significant effect on the selectivity and catalytic activity for ORR. Annealing of G-O with ammonia preferentially formed graphitic N and pyridinic N centers, while annealing of polyaniline/RG-O and polypyrrole/RG-O tended to generate pyridinic and pyrrolic N moieties, respectively. Most importantly, the electrocatalytic activity of the catalyst was found to be dependent on the graphitic N content which determined the limiting current density, while the pyridinic N content improved the onset potential for ORR. However, the total N content in the graphene-based non-precious metal catalyst does not play an important role in the ORR process.

Production of graphene nanospheres by annealing of graphene oxide in solution

We report a simple method to produce graphene nanospheres (GNSs) by annealing graphene oxide (GO) solution at high-temperature with the assistance of sparks induced by the microwave absorption of graphite flakes dispersed in the solution. The GNSs were formed by rolling up of the annealed GO, and the diameters were mostly in the range 300–700 nm. The GNS exhibited a hollow sphere structure surrounded by graphene walls with a basal spacing of 0.34 nm. Raman spectroscopy and X-ray photoelectron spectroscopy of the GNSs confirmed that the GO was efficiently reduced during the fabrication process. The resulting GNSs may open up new opportunities both for fundamental research and applications, and this method may be extended to the synthesis of other nanomaterials and the fabrication of related nanostructures. Open image in new window