Photovoltaic properties of graphene oxide sheets beaded with ZnO nanoparticles

A hybrid material of graphene oxide (GO) sheets beaded with ZnO nanoparticles was prepared. The material extends over a few hundred square nanometers, in which the ZnO nanoparticles (average diameter (∼5 nm)) are dispersed evenly on the GO sheet. Both the surface photovoltage or surface photocurrent intensity for the material are much stronger than for pure ZnO nanoparticles, meaning that the free charge carriers can effectively be transferred from ZnO nanoparticles to GO sheets, which can serve as a probe to monitor the electron transfer from excited ZnO to GO. Anchoring ZnO nanoparticles on two dimensional carbon nanostructures such as GO can pave a way towards the design of ordered nanostructure assemblies that can harvest light energy efficiently.     

Hydrothermal synthesis of reduced graphene sheets/Fe2O3 nanorods composites and their enhanced electrochemical performance for supercapacitors

Reduced graphene nanosheets/Fe₂O₃ nanorods (GNS/Fe₂O₃) composite has been fabricated by a hydrothermal route for supercapacitor electrode materials. The obtained GNS/Fe₂O₃ composite formed a uniform structure with the Fe₂O₃ nanorods grew on the graphene surface and/or filled between the graphene sheets. The electrochemical performances of the GNS/Fe₂O₃ hybrid supercapacitor were tested by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge–discharge tests in 6 M KOH electrolyte. Comparing with the pure Fe₂O₃ electrode, GNS/Fe₂O₃ composite electrode exhibits an enhanced specific capacitance of 320 F g⁻¹ at 10 mA cm⁻² and an excellent cycle-ability with capacity retention of about 97% after 500 cycles. The simple and cost-effective preparation technique of this composite with good capacitive behavior encourages its potential commercial application.     

The fabrication of flower-like graphene/octadecylamine composites

Three-dimensional flower-like nanomaterials have wide application due to the large specific surface area. In this letter, the morphology of octadecylamine (ODA) from several common solvents is studied and it is found that from the chloroform and acetone solution, ODA assembles into petal-like structure, which further forms the spherical or flower-like architecture. Furthermore, the composite materials incorporated reduced graphene oxide (rGO) and ODA could well keep the flower-shaped structure of ODA. XRD results show that the introduction of graphene has little influence on the structure of ODA and contact angle test indicates good hydrophobic performance of the rGO/ODA material.     

Synthesis of ruthenium/reduced graphene oxide composites and application for the selective hydrogenation of halonitroaromatics

Reduced graphene oxide （RGO） supported ruthenium （Ru） catalyst was prepared by an impregnation method using RuCI3 as a precursor and RGO as a support. The catalyst Ru/RGO was used for the selective hydrogenation ofp-chloronitrobenzene （p-CNB） to p-chloroaniline （p-CAN）, showing a selectivity of 96% at complete conversion of p-CNB at 60 ℃ and 3.0 MPa H2. The Ru/RGO catalyst was extremely active for the hydrogenation of a series of nitroarenes, which can be attributed to the small sized and the fine dispersity of the Ru nanoparticles on the RGO sheets characterized by TEM. Moreover, the catalyst also can be recycled five times without the loss of activity.     

Comparison of various methods of grafting of modified-PEG onto maghemite nanoparticles in aqueous medium including synthesis by microwave refluxing

Three methods in the synthesis of functionalized maghemite nanoparticles in aqueous medium by grafting triethoxysilane monomethylene-PEG (Si-mPEG) onto maghemite nanoparticles were compared including synthesis by microwave refluxing which is an original device designed by our research team. The maghemite nanoparticles were characterized by zeta potential measurement, X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). The spinel structure of maghemite nanoparticles was determined and successful grafting of m-PEG was evidenced. Thermogravimetric analysis (TGA) reveals that microwave heating tends to improve the grafting rate compared to conventional heating.     

Synthesis of maghemite sub-microspheres by simple solvothermal reduction method

Maghemite sub-micrometer-sized spheres were successfully prepared by a simple solvothermal reduction route at relatively low temperature. The as-obtained sample was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), electron diffraction (ED), X-ray photoelectron spectroscopy (XPS) and superconducting quantum interference device (SQUID) measurements. XRD and XPS analyses indicate the formation of γ-Fe₂O₃ phase. TEM results reveal that the γ-Fe₂O₃ particles are spherical with the diameter of 200-400 nm. Magnetic measurements show that the Curie temperature of γ-Fe₂O₃ sub-microspheres is over 400 K and the sample exhibits ferromagnetic behavior at room temperature. It is found that the sub-microspheres possess high saturation magnetization of 81 emu/g at 300 K.     

Green synthesis of graphene nanosheets/ZnO composites and electrochemical properties

A green and facile approach was demonstrated to prepare graphene nanosheets/ZnO (GNS/ZnO) composites for supercapacitor materials. Glucose, as a reducing agent, and exfoliated graphite oxide (GO), as precursor, were used to synthesize GNS, then ZnO directly grew onto conducting graphene nanosheets as electrode materials. The small ZnO particles successfully anchored onto graphene sheets as spacers to keep the neighboring sheets separate. The electrochemical performances of these electrodes were analyzed by cyclic voltammetry, electrochemical impedance spectrometry and chronopotentiometry. Results showed that the GNS/ZnO composites displayed superior capacitive performance with large capacitance (62.2 F/g), excellent cyclic performance, and maximum power density (8.1 kW/kg) as compared with pure graphene electrodes. Our investigation highlight the importance of anchoring of small ZnO particles on graphene sheets for maximum utilization of electrochemically active ZnO and graphene for energy storage application in supercapacitors.     

Synthesis of N-aryl imidazoles catalyzed by copper nanoparticles on nanosized silica-coated maghemite

A magnetically recoverable catalyst consisting of copper nanoparticles (CuNPs) on nanosized silica-coated maghemite is presented. The catalyst has been prepared under mild conditions by mixing the magnetic support with a freshly prepared suspension of CuNPs obtained by fast reduction of anhydrous CuCl₂ with lithium sand and a catalytic amount of DTBB (4,4′-di-tert-butylbiphenyl) as electron carrier. This copper-based catalyst has shown to be very efficient in the N-(hetero)arylation of imidazole using (hetero)aryl bromides and iodides as arylating agents under ligand-free conditions. The catalyst is easily recovered by means of an external magnet and can be reutilized in three N-arylation cycles without apparent loss of catalytic activity.     

A dense graphene monolith with poloxamer prefunctionalization enabling aqueous redispersion to obtain solubilized graphene sheets

The realization of good aqueous dispersibility of commercial graphene products composed of exfoliated graphene sheets is of significance for downstream applications. However, the tap density of commercial graphene powder is quite low (0.03–0.1 kg/m³), meaning that 1 kg graphene powder occupies about 10–30 m³ in volume during transportation. And, the available content of commercial graphene dispersion/slurry in aqueous medium cannot exceed 5 wt%, although the density is high (≈ 1050 kg/m³). In this work, a graphene monolith was prepared by oven-drying of graphene sheets prefunctionalized with poloxamer surfactants. Our graphene monoliths not only have a high density (1500 kg/m³) and high graphene content (≈ 10 wt%), but also a full capability to be completely redispersed (≈ 100%) in water by bath sonication to obtain solubilized graphene sheets, whose lateral size and thickness are unchanged compared to as-exfoliated ones. Moreover, a simple empirical method was proposed to predict the redispersion capability of graphene monoliths using different poloxamers by contact angle measurements. Our results provide a universal approach to make exfoliated graphene-based products with better downstream availability and lower transportation cost.     

石墨烯/电气石/二氧化钛复合材料的制备及其光催化降解异丙醇性能

光催化是一种理想的应对全球能源短缺和环境污染问题的绿色化学技术,可以实现有机物降解、水分解和二氧化碳光还原等.光催化反应效率受诸多因素影响,其中光生载流子(电子和空穴)的分离和传输具有至关重要的作用.以往研究表明,构筑多元复合光催化材料体系有利于光生电子和空穴有效分离和传递,促进催化剂表面的还原和氧化反应,从而提高其光催化效率.基于以上考虑,我们提出了一种新型的石墨烯/电气石/TiO2三元复合光催化材料体系,其中TiO2因其价格低廉、无毒和抗光腐蚀等优点而被广泛用作光催化材料;石墨烯(G)拥有独特的二维结构、高的电子迁移率、大的比表面积,是一种优异的催化剂载体;电气石(T)的一个重要性质是表面存在自发极化的静电场,该静电场将会影响光激发载流子的分离、传递和光催化反应过程.利用水热法合成了不同成分的石墨烯/电气石/TiO2三元复合材料体系.为了对比研究石墨烯表面电荷性质的影响,其中一组的石墨烯(氧化石墨)为直接采用改良的Hummers法所制备,其表面带负电;另一组的石墨烯经聚二烯丙基二甲基氯化铵(PDDA)修饰,使其表面带正电.X射线衍射结果显示,三元复合材料中TiO2为锐钛矿相,其结晶性没有因为与石墨烯和电气石的复合而受到影响.扫描和透射电子显微分析表明,TiO2的平均颗粒大小为15 nm左右,并且与石墨烯和电气石均匀复合.傅里叶变换红外光谱和zeta电位表征分析证实,PDDA可以有效地对石墨烯进行功能化改性,使其表面带正电.紫外-可见分光光谱显示,石墨烯/电气石/TiO2三元复合材料与TiO2的吸收带边一致,复合材料中石墨烯和电气石并没有改变TiO2的光吸收特征.光催化降解异丙醇实验表明,石墨烯/电气石/TiO2三元复合材料优于单纯的TiO2、石墨烯/TiO2以及电气石/TiO2二元复合材料,当石墨烯和电气石的质量百分比分别为0.5%和5%时,三元复合材料降解异丙醇产生丙酮的速率达到最高(223μmol/h).特别值得指出的是,由表面带负电的石墨烯组成的复合材料比由带正电荷的PDDA-石墨烯组成的复合材料具有更高的光催化性能,原因如下:在水溶液中显示正zeta电位值的TiO2与带负电的石墨烯/电气石复合物静电吸引而均匀紧密复合,有利于TiO2中光生电子和空穴的快速分离和传递,从而使得石墨烯/电气石/TiO2三元复合材料具有较高的光催化性能;而带正电的PDDA-石墨烯/电气石复合物和TiO2颗粒相互排斥而不宜复合,导致PDDA-石墨烯基复合材料的光催化活性降低.机理研究揭示,在三元复合材料光催化降解异丙醇的反应中起主要作用的是光生电子和空穴.基于以上研究结果,我们提出了三元复合材料光催化降解异丙醇的反应机理.     

石墨烯基复合材料对污水净化的研究进展*

石墨烯基复合材料具有较大的比表面积、较高的表面能,对污染物具有较强的吸附能力,可用于去除水中的污染物,从而达到净化污水的目的。本文综述了几种石墨烯基复合材料的制备和其对水中化学类物质,如重金属离子、有机染料和其他污染物的吸附特性,并简述了溶液的酸度、接触时间和金属离子初始浓度等对石墨烯基复合材料吸附污染物的影响。     

Azo dyes degradation using TiO2-Pt/graphene oxide and TiO2-Pt/reduced graphene oxide photocatalysts under UV and natural sunlight irradiation

The photocatalytic degradation of azo dyes with different structures (amaranth, sunset yellow and tartrazine) using TiO₂-Pt nanoparticles (TPt), TiO₂-Pt/graphene oxide (TPt-GO) and TiO₂-Pt/reduced graphene oxide (TPt-rGO) composites were investigated in the presence of UV and natural sunlight irradiation. The composites were prepared by a combined chemical-thermal method and characterized by Transmission Electron Microscopy (TEM), X-ray powder diffraction (XRD), Infrared (FTIR) and UV–Vis spectroscopy. The modification of TiO₂-Pt with graphene oxide shifted its optical absorption edge towards the visible region and increased its photocatalytic activity under UV and natural sunlight irradiation. The efficiency of catalysts on azo dyes degradation (in similar conditions) reached high values (above 99%) under sunlight conditions, proving the remarkable photocatalytic activities of obtained composites. TPt-GO nanocomposite exhibited higher photoactivity than TPt or TPt-rGO, demonstrating degradation efficiencies of 99.56% for amaranth, 99.15% for sunset yellow and 96.23% for tartrazine. The dye photodegradation process follows a pseudo-first-order kinetic with respect to the Langmuir-Hinshelwood reaction mechanism. A direct dependence between azo dyes degradation rate and chemical structure of dyes has been observed.     

Facile synthesis of cobalt oxide/reduced graphene oxide composites for electrochemical capacitor and sensor applications

Reduced graphene oxide sheets decorated with cobalt oxide nanoparticles (Co₃O₄/rGO) were produced using a hydrothermal method without surfactants. Both the reduction of GO and the formation of Co₃O₄ nanoparticles occurred simultaneously under this condition. At the same current density of 0.5 A g⁻¹, the Co₃O₄/rGO nanocomposites exhibited much a higher specific capacitance (545 F g⁻¹) than that of bare Co₃O₄ (100 F g⁻¹). On the other hand, for the detection of H₂O₂, the peak current of Co₃O₄/rGO was 4 times higher than that of Co₃O₄. Moreover, the resulting composite displayed a low detection limit of 0.62 μM and a high sensitivity of 28,500 μA mM⁻¹cm⁻² for the H₂O₂ sensor. These results suggest that the Co₃O₄/rGO nanocomposite is a promising material for both supercapacitor and non-enzymatic H₂O₂ sensor applications.     

Functionalized reduced graphene oxide/epoxy composites with enhanced mechanical properties and thermal stability

One-pot hydrothermal reduction of graphene oxide (GO) in N-methyl-2-pyrrolidone (NMP) suspension was performed, wherein GO surface were functionalized by free radicals generated from NMP molecules. The NMP functionalized reduced GO (NMPG) nanosheets were then incorporated into epoxy matrix to prepare epoxy composites. The significant improvement of 100 and 240% in fracture toughness (critical intensity factor, K_IC) and fracture energy (critical strain energy release rate, G_IC) achieved from single edge notched bending (SENB) test revealed the excellent toughening ability of NMPG. The improved compatibility and interfacial interaction between the epoxy matrix and NMPG yielded∼28, 19 and 51% improvement in tensile strength, Young's and storage modulus, respectively. Thermal stability of pure epoxy and its composites was determined at 5, 10 and 50% weight loss, which showed 30, 27.5 and 29 °C improvement with 0.2 wt% NMPG loading. The work provides a simple method to prepare graphene-based epoxy composites with improved performance.     

Removal, preconcentration and determination of Mo(VI) from water and wastewater samples using maghemite nanoparticles

Removal and recovery of Mo(VI) from aqueous solutions were investigated using maghemite (γ-Fe₂O₃) nanoparticles. Combination of nanoparticle adsorption and magnetic separation was used to the removal and recovery of Mo(VI) from water and wastewater solutions. The nanoscale maghemite with mean diameter of 50 nm was synthesized by reduction coprecipitation method followed by aeration oxidation. Various factors influencing the adsorption of Mo(VI), e.g. pH, temperature, initial concentration, and coexisting common ions were studied. Adsorption reached equilibrium within <10 min and was independent of initial concentration of Mo(VI). Studies were performed at different pH values to find out the pH at which maximum adsorption occurred. The maximum adsorption occurred at pHs between 4.0 and 6.0. The Langmuir adsorption capacity (q_max) was found to be 33.4 mg Mo(VI)/g of the adsorbent. The results showed that nanoparticle (γ-Fe₂O₃) is suitable for the removal of Mo(VI), as molybdate, from water and wastewater samples. The adsorbed Mo(VI) was then desorbed and determined spectrophotometrically using bromopyrogallol red as a complexation reagent. This allows the determination of Mo(VI) in the range 1.0–86.0 ng mL⁻¹.     

High thermal conductivity of graphene and structure defects:Prospects for thermal applications in graphene sheets

The utilization of thermal energy from different sources is an important development direction for conserving energy.With the development of technology,refined and rapid utilization of thermal energy is required.Traditional thermal conductive materials cannot meet the growing needs of human beings.Therefore,people pay attention to two-dimensional graphene film materials for their thermal conductivity.This review collects current modeling group of thermal transport on graphene,including non-equilibrium Green function(NEGF) theory,molecular dynamics(MD) simulations modeling and Boltzmann transport equation method.These models can well explain several phenomena of phonon transport in graphene.Furthe r,structural de fects were discussed and expounded the effect for graphene thermal conductivity,including doping,grain bounda ry and defects.Deeply understanding of defects on graphene,we can better grasp the thermal conductivity of graphene from the microscopic point of view.     

Bio-electrocatalysis of NADH and ethanol based on graphene sheets modified electrodes

Characterization and application of graphene sheets modified glassy carbon electrodes (graphene/GC) have been presented for the electrochemical bio-sensing. A probe molecule, potassium ferricyanide is employed to study the electrochemical response at the graphene/GC electrode, which shows better electron transfer than graphite modified (graphite/GC) and bare glassy carbon (GC) electrodes. Based on the highly enhanced electrochemical activity of NADH, alcohol dehydrogenase (ADH) is immobilized on the graphene modified electrode and displays a more desirable analytical performance in the detection of ethanol, compared with graphite/GC or GC based bio-electrodes. It also exhibits good performance of ethanol detection in the real samples. From the results of electrochemical investigation, graphene sheets with a favorable electrochemical activity could be an advanced carbon electrode materials for the design of electrochemical sensors and biosensors.     

Fabrication of the electrochemically reduced graphene oxide-bismuth nanoparticles composite and its analytical application for an anticancer drug gemcitabine

The present study explores an electroreduced graphene oxide-bismuth nanoparticles composite(ErGOBi) as an electrochemical sensor for the determination of an anticancer drug, gemcitabine hydrochloride(GMB). The Er-GOBi interface was prepared by drop casting of bismuth nitrate-graphene oxide suspension on a glassy carbon electrode(GCE) followed by electro-reduction in the potential range of 0.6 V to 1.7 V. SEM, FTIR, EDAX and AFM techniques were employed for the characterization of prepared materials. Cyclic voltammetric and electrochemical impedance spectroscopic methods were used to understand the charge transfer properties of stepwise modification of Er-GOBi/GCE. GMB exhibited an irreversible oxidation peak at 1.144 V on Er-GOBi/GCE in phosphate buffer of p H 3. A 100-fold enhanced oxidation peak current was observed at Er-GOBi/GCE when compared to that at bare GCE.Sensing performance of Er GO-Bi/GCE was optimized by varying peak current dependent parameters.Linear relationship between the peak current and concentration of GMB was observed in the range of 0.1–51.1 mmol/L in differential pulse voltammetric method and 2.1–61.1 mmol/L in linear sweep voltammetric method. The practical utility of the proposed sensor, Er-GOBi/GCE was demonstrated by determining GMB in pharmaceutical formulations and spiked urine samples.     

Synthesis and electromagnetic properties of polyaniline-coated silica/maghemite nanoparticles

Polyaniline coated silica/maghemite nanoparticles (PANI/SiO₂/γ-Fe₂O₃ composites) were synthesized by the combination of a sol-gel process and an in-situ polymerization method, in which ferrous and ferric salts as well as tetraethyl orthosilica (TEOS) acted as the precursor for γ-Fe₂O₃ and silica, respectively. As a result, the SiO₂/γ-Fe₂O₃ particle showed a core-shell structure, with γ-Fe₂O₃ as the magnetic core and silica as the shell of the particle. The shell thickness can be controlled by changing the TEOS concentration. The PANI/SiO₂/γ-Fe₂O₃ composites revealed a multilayer core-shell structure, where PANI is the outer shell of the composite. The doping level and the conductivity of PANI/SiO₂/γ-Fe₂O₃ composites decreased with increasing the TEOS content due to the presence of the less coated PANI on the SiO₂/γ-Fe₂O₃ core at higher TEOS content. For a SQUID analysis at room temperature, all γ-Fe₂O₃ containing composites showed a typical superparamagnetic behavior. The saturation magnetization of SiO₂/γ-Fe₂O₃ nanoparticles decreased with increasing the TEOS content due to the increase in silica shell thickness, while the saturation magnetization of PANI/SiO₂/γ-Fe₂O₃ composites also decreased with increasing the TEOS content, which is attributed to the lower conductivity of PANI in the composites at higher TEOS content.     

Introduction of CdO nanoparticles into graphene and graphene oxide nanosheets for increasing adsorption capacity of Cr from wastewater collected from petroleum refinery

Graphene and graphene oxide nanocomposites are promising and fascinating types of nanocomposites because of their fast kinetics, unique affinity for heavy metals, and greater specific area. Initially, in this study, a green, cost-effective and facile method was utilized to prepare G, GO, CdO, G-CdO, and CdO-GO nanocomposites by Azadirachta indica and then analyzed using UV–vis spectroscopy, Fourier-transform spectroscopy, Raman, X-ray diffraction and scanning electron microscope. The synthesized nanocomposites were explored for chromium elimination from wastewater collected from a petroleum refinery. CdO-GO, G-CdO nanocomposites showed remarkable adsorption capability of 699 and 430 mg g^?1 which was higher than G (80 mg g^?1), GO (65 mg g^?1), and CdO (400 mg g^?1). Based on the R² (correlation coefficient) values, the kinetic statistics of Cr (VI) onto the G, GO, CdO, G-CdO, and CdO-GO were effectively obeyed by pseudo-second-order than by all other models. The R² values for the five nano-bioadsorbents were extraordinarily high (R² greater than 0.990) which ensured the chemisorption. This study ensured that the adsorptive removal rate of Cr (VI) is still greater than 85 % after repeated five cycles, suggesting that the produced nanomaterials are adsorbents with strong recyclability.