Influence of temperature and voltage on electrochemical reduction of graphene oxide

In this paper, the influence of temperature and voltage on direct electrochemical reduction were discussed in detail. Reduced graphene oxide is characterized with X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT–IR) and field emission scanning electron microscopy (FE–SEM). It is found that the reduction degree of graphene oxide (GO) decreases gradually with the increase of applied temperature. The optimal applied temperature found in our experiment is 20 °C; Meanwhile, as the applied voltage increases from 0·1 to 12·5 V, the reduction degree of graphene oxide increases gradually. However, above 2·5 V, increasing voltage has little effect on the reduction degree of graphene oxide.     

Influence of graphite oxide drying temperature on ultra-fast microwave synthesis of graphene

Ultra-fast synthesis of graphene has been reported by microwave assisted graphene oxide reduction. In this article, the graphene oxide was initially dried above room temperature. The initial heat treatment of graphene oxide demonstrates a distinct improvement of exfoliation rate of graphene sheets. This method provides an efficient way for mass production of high quality graphene sheets. Raman spectroscopy, scanning electron microscopy, and X-ray diffraction techniques has been used to characterize reduced graphene sheets. The quality of reduced graphene was found to be affected by the initial drying temperature of graphite oxide.     

低温一步制备氧化石墨烯及微波还原研究

以天然鳞片石墨为原料,通过低温一步氧化制备氧化石墨烯,经微波热还原得到低缺陷的还原氧化石墨烯。讨论了低温氧化过程中氧化剂用量、氧化时间对氧化石墨烯层间距、氧化程度的影响。结果表明:在高锰酸钾与天然鳞片石墨的质量比为1∶3,氧化温度为0℃,氧化时间为48h的条件下,制备出碳氧原子比为1.98、高C—O结构、低缺陷结构( I D∶ I G=0.63)的氧化石墨烯,避免了Hummers制备过程中由于CO 2的形成导致六元环断裂以及碳原子的缺失而使得氧化石墨烯的缺陷增加;经微波热还原后,得到的还原氧化石墨烯的两点平均缺陷距离 L D=12nm,缺陷密度 n D=2.21×10 11 cm -2 , I D∶ I G仅为0.85(Γ G=32.1cm -1 ),制备出低缺陷的还原氧化石墨烯。     

高压釜热还原制备稳定分散的石墨烯溶液

以天然鳞片石墨为原料,用改进的Hummers法制备氧化石墨。超声分散制备氧化石墨烯溶液,通过加入不同量的水合肼调节溶液的pH值,再通过水热法热还原,制备了在水中稳定分散的石墨烯溶液。利用扫描电子显微镜(SEM)、高分辨透射电镜(HR-TEM)、拉曼光谱(Raman)、原子力显微镜(AFM)、X射线衍射分析(XRD)、zeta电位及光学显微镜对制备的样品进行了表征,研究了不同温度、pH值对石墨烯溶液稳定性的影响。     

Microbial reduction of graphene oxide by Shewanella

Graphene oxide (GO) can be reduced to graphene in a normal aerobic setup under ambient conditions as mediated by microbial respiration of Shewanella cells. The microbially-reduced graphene (MRG) exhibited excellent electrochemical properties. Extracellular electron transfer pathways at the cell/GO interface were systematically investigated, suggesting both direct electron transfer and electron mediators are involved in the GO reduction.     

Effect of temperature and time on the exfoliation and de-oxygenation of graphite oxide by thermal reduction

The effect of thermal reduction temperature and time on the structure and composition change of reduced graphite oxide sheets was studied. The results show that the exfoliation degree increased with the elevation of temperature, as evidenced by the decreased layers in the defected nanocrystallites formed by the collapse of graphite oxide sheets. Although, the exfoliation degree shows reverse trend with the extension of time studied. As for the de-oxygenation, both the elevation of temperature and the extension of time favor the reduction process, evidenced by the increasing atomic ratio of carbon to oxygen, and a quite marked de-oxygenation effect was obtained with atomic ratio of 499 by heating at 1000 °C for 2 h. A structural schematic of thermally reduced graphite oxide sheets was proposed for the understanding of the reduction process.     

柠檬酸钠绿色还原制备石墨烯

采用环境友好型还原剂柠檬酸钠,成功实现了温和条件下氧化石墨(GO)的控制还原,制备得到了石墨烯材料.利用扫描电子显微镜(SEM)、X-射线衍射(XRD)、紫外可见吸收光谱(UV-vis)、傅立叶红外光谱(FT-IR)等对所得产物进行了分析表征,并研究比较了氧化石墨与氧化石墨烯还原产物(RGO)的电子输运性能.结果表明:柠檬酸钠可在温和条件F还原氰化石墨得到高质量的石墨烯.     

Effect of the exposure time of hydrazine vapor on the reduction of graphene oxide films

Preparation of highly uniform graphene with superior electrical properties is one of the key issues in graphene researches. The use of hydrazine vapor for reducing the graphene oxide (GO) has attracted considerable attention in recent year due to the simplicity, reproduciblilty and availibility of one-step procedure. Here, we investigated the effect of the exposure time of hydrazine vapor on the reduction of GO films. Raman spectroscopy, UV-vis spectroscopy, X-ray photoelectron spectrophotometer, and X-ray diffraction results showed that the reduction rate of the GO films by hydrazine vapor was very fast in the initial 10 min, and thereafter the reduction rate slowed down. Upon 12 hours of hydrazine vapor treatment, the reduction came to a level that further hydrazine vapor treatment did not bring about significant improvement of the reduction. We demonstrated that this might be attributed to the slow penetration of hydrazine vapor into the GO films in order to reduce the inner sheets of the GO films.     

Synthesis of high-performance graphene nanosheets by thermal reduction of graphene oxide

High-performance graphene nanosheets have been synthesized by thermal reduction of graphene oxide (GO) under ethanol atmosphere. The reduced GO nanosheets were characterized by X-ray photoelectron spectroscopy, Raman spectroscopy and electrical transport measurements, respectively. The results indicated that the thermal reduction of GO under ethanol atmosphere can effectively remove the oxygen-containing functional groups and restore its graphic structure compared to the ones obtained using hydrazine or hydrogen. The electrical measurements indicated that the electrical mobility of single-layer graphene sheet reduced under ethanol atmosphere at 900 °C can reach 29.08 cm² V⁻¹ S⁻¹.     

Fast and simple reduction of graphene oxide in various organic solvents using microwave irradiation

The fabrication of graphene has been widely studied and chemical reduction is considered the most suitable approach to achieve large-scale production and graphene functionalization due to its versatility of chemical routes. We report here a fast and simple reduction of graphene oxide in various organic solvents using microwave irradiation. The reduction can be completed in several minutes, and the oxygen content and conductivity (10,000 S/m) of the reduced graphene oxide were comparable to the previously reported results which reported between 1 hr and 24 hrs for the reduction. We also found that an amide group containing a solvent like NMP or DMF reduced graphene oxide (GO) more effectively than did other solvents. Further, free radicals generated from NMP significantly enhanced deoxygenation of graphene oxide. Moreover, this approach is a non-toxic and environmentally-friendly method to obtain highly conductive reduced GO for a wide range of applications including graphene-based composites, batteries, and electrodes for super-capacitors.     

化学还原氧化石墨烯制备高性能石墨烯自组装水凝胶

提出了一种以抗坏血酸钠为还原剂,通过化学还原氧化石墨烯制备高性能石墨烯自组装水凝胶的方法.用扫描电镜,流变及电导率测试,光电子能谱,X-射线晶体衍射和拉曼光谱等手段对该石墨烯水凝胶的结构与性能进行了表征.结果表明:化学还原氧化石墨烯对形成石墨烯水凝胶具有决定性作用.该石墨烯水凝胶具有优异的导电性(1 S·m-1),机械强度和电化学性能.在1 mol·L-1的硫酸电解质溶液中,通过1.2A·g-1恒电流允放电测试,石墨烯水凝胶电极的比电容高达240F·g-1.

Abstract：

Three-dimensional self-assembled graphene hydrogels (SGHs)have been fabricated by chemical reduction of graphene oxide (GO)with sodium ascorbate. The SGHs were characterized by scanning electron microscopy,rheological tests,electrical conductivity measurements,X-ray photoelectron spectroscopy,X-ray diffraction,and Raman spectroscopy. Results indicate that the reduction of GO promotes the assembly of graphene sheets. The SGHs are electrically conductive(1s·m-1)and mechanically strong and exhibit excellent electrochemical performance.In 1 mol·L-1 aqueous solution of H2SO4,the specific capacitance of SGHs was measured to be about 240F·g-1 at a discharge current density of 1.2·-1.     

Low temperature reduction of graphene oxide film by ammonia solution and its application for high-performance supercapacitors

Here we demonstrate that graphene oxide (GO) film on Ni foam can be doped with nitrogen atoms and reduced directly at a lower temperature of 90?°C using ammonia solution as reducing agent and nitrogen source. The reduction and nitrogen doping of GO occur simultaneously when GO film on Ni foam is immersed into ammonia solution. The nitrogen doping can be realised and the content of N in graphene film turns out to be rather good as high as 3.60%. When used as binder-free electrode, the resulting graphene film on Ni foam delivers a gravimetric capacitance of 230 F g^?1. It also exhibites relatively an outstanding rate capability of 164 F g^?1 at 83.3 A g^?1 and better cycle stability that capacitance retention maintains at 96.7% of its initial capacitance capacitance after 2000 cycles. The method also provides a universal route for preparing a binder-free graphene-based electrode.     

Effect of sintering temperature and time on microwave dielectric properties of lanthanum tin oxide

This study examines the microwave dielectric properties of La₂Sn₂O₇ ceramics with a view to the use of these ceramics in mobile communication. La₂Sn₂O₇ ceramics were prepared by the conventional solid-state method with various sintering temperatures and times. The highest density obtained, 6.61 g/cm³, was that of La₂Sn₂O₇ ceramic that was sintered at 1,580 °C for 34 h. Dielectric constants (ε _r ) of 13.2–14.4 and quality factors (Q × f) of 34,300–40,500 GHz were obtained by sintering at temperatures in the range 1,520–1,610 °C for 34 h. Dielectric constants (ε _r ) of 10.3–14.4 and quality factors (Q × f) of 15,300–40,500 GHz were obtained using sintering times of 30–38 h at a sintering temperature of 1,580 °C. When La₂Sn₂O₇ was sintered at 1,580 °C for 34 h, a dielectric constant (ε _r ) of 14.4, a quality factor (Q × f) of 40,500 GHz and a temperature coefficient of resonant frequency (τ _f ) of ?54 ppm/ °C were obtained.     

Influence of temperature and aging time on HA synthesized by the hydrothermal method

The influence of temperature and aging time on the morphology and mechanical properties of nano-sized hydroxyapatite (HA) synthesized by a hydrothermal method is reported here. The pre-mixed reactants were poured into a stirred autoclave and reacted at temperatures between 25–250°C for 2–10 h. HA powders thus obtained were examined using X-ray diffraction (XRD), high-resolution field emission scanning electron microscopy (FESEM) and a particle size analyzer. It was found that the aspect ratio of the particles increased with the reaction temperature. The length of the HA particles increased with the reaction temperature below 170°C, but it decreased when the temperature was raised above 170°C. The agglomerates of HA particles were formed during synthesis, and their sizes were strongly dependent on reaction temperatures. As the reaction temperature increased, the agglomerate size decreased (p = 0.008). The density of the discs pressed from these samples reached 85–90% of the theoretical density after sintering at 1200°C for 1 h. No decomposition to other calcium phosphates was detected at this sintering temperature. A correlation existed (p = 0.05) between the agglomerate sizes of HA particles synthesized at various conditions and their sintered densities. With the increase of the agglomerate size, the sintered density of the HA compact decreased. It was found that both the sintered density and flexural strength increased with increasing aging time and reaction temperature. A maximum flexural strength of 78 MPa was observed for the samples synthesized at 170°C for 5 h with the predicted average at these conditions being 65 MPa. These samples attained an average sintered density of 88%.     

水热合成温度对氧化钒纳米管的影响

采用溶胶-凝胶法和水热法,以国产V2O5粉末、H2O2、十六胺为原材料,制备氧化钒纳米管。借助扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线衍射(XRD)、傅立叶红外光谱(FT-IR)及循环伏安法(CV)等技术手段,重点研究了水热合成温度对氧化钒纳米管的形貌、结构及电化学性能的影响。结果表明:在150℃水热反应条件下制备的氧化钒纳米管产率高、形貌均一、管状结构完整;循环伏安测试表明该条件下的氧化钒纳米管具有较高的比容量和良好的锂离子嵌入/脱出可逆性。     

Exfoliation and reduction of graphene oxide at low temperature and its resulting electrocapacitive properties

Low-temperature reduced graphene oxide (LT-RGO) powder with full exfoliated morphology was achieved directly from freeze-dried graphite oxide (GO) aqueous solution in air atmosphere, which is simple and energy-saving. For explaining this phenomenon, the microstructure and thermal behavior of freeze-dried GO and vacuum filtered GO film was compared. Moreover, the thermal-induced reduction process of freeze-dried GO has been in situ monitored by temperature-dependent infrared spectroscopy. The results show that freeze-dried GO demonstrates the floc morphology with larger interlayer distance than that of vacuum filtered GO film, which should be the essential reason for its low-temperature reduction and exfoliation behavior. The dispersibility and capacitance property of as-prepared LT-RGO has also been investigated. At current density of 6 A g^?1, the specific capacitance of 460 F g^?1 was achieved, shows that the prepared LT-RGO holds great application potential in electric energy storage.     

Photoluminescence and Raman studies of graphene thin films prepared by reduction of graphene oxide

Photoluminescence (PL) and Raman studies have been performed to investigate the optical properties of graphene thin films prepared by chemical and thermal reductions of graphene oxide (GO). The G peak in Raman spectra red-shifted after reduction of GO. Thermal reduction resulted in a more red-shift of the G peak than chemical reduction. A strong intensity of the D peak indicated that the prepared graphene films have significant structural disorders. A blue-shifted emission in PL spectra suggested that sp² clusters are embedded in a sp³ matrix that acts as a tunnel barrier, causing a strong fluctuation in the local band gap.     

High-quality single-layer graphene via reparative reduction of graphene oxide

Reduction of graphene oxide (GO) is a promising low-cost synthetic approach to bulk graphene, which offers an accessible route to transparent conducting films and flexible electronics. Unfortunately, the release of oxygen-containing functional groups inevitably leaves behind vacancies and topological defects on the reduced GO sheet, and its low electrical conductivity hinders the development of practical applications. Here, we present a strategy for real-time repair of the newborn vacancies with carbon radicals produced by thermal decomposition of a suitable precursor. The sheet conductivity of thus-obtained single-layer graphene was raised more than six-fold to 350–410 S/cm (whilst retaining >96% transparency). X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy revealed that the conductivity enhancement can be attributed to the formation of additional sp²-C structures. This method provides a simple and efficient process for obtaining highly conductive transparent graphene films.     

Optoelectronic properties of graphene thin films prepared by thermal reduction of graphene oxide

Graphene thin films have been prepared by thermal reduction of graphene oxide. Raising the reduction temperature results in a red-shift of the G peak in Raman spectra. The reduction temperature turns out to strongly affect the morphology of the prepared graphene film. Photoluminescence (PL) results show that the band gap of graphene can be tuned by varying the reduction temperature. The thermal reduction process has been optimized in an effort to minimize the formation of wrinkles/folds on the graphene surface leading to enhanced PL and Raman peak intensities and reduced electrical sheet resistance.