Different strategies for the synthesis of graphene/ZnO composite and its photocatalytic properties

Owing to its unique physical and chemical properties, graphene has attracted tremendous attention in the preparation of graphene-based composites for various applications. In this study, two different strategies have been developed to load zinc oxide (ZnO) nanorods onto reduced graphene oxide (RGO) sheets, i.e., in situ growth and a self-assembly approach. The microstructure and morphology of the synthesized RGO/ZnO nanocomposites was investigated by X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM) and Brunauer–Emmett–Teller (BET) measurements. Fluorescence emission spectra (PL) of RGO/ZnO composites were performed to attribute quality of combination between RGO and ZnO. Significantly enhanced photocatalytic activity of RGO/ZnO nanocomposites in comparison to bare ZnO nanoparticles was revealed by the degradation of methylene blue under irradiation, which can be attributed to the inhibition of electron–hole pair recombination and enhanced adsorption due to the presence of RGO sheets.     

Preparation and characterization of graphene/CdS nanocomposites

Graphene-based nanocomposites are emerging as a new class of materials that hold promise for many applications. In this paper, we present a facile approach for the preparation of graphene/CdS nanocomposites through simple reflux processes, in which thiourea (CS(NH₂)₂) and thioacetamide (C₂H₅NS) act as a sulphide source, respectively. The samples were characterized by the X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectrum (FT-IR), ultraviolet-visible (UV-vis) spectroscopy and thermogravimetry analysis. It was shown that in the nanocomposites, the CdS nanoparticles were densely and uniformly deposited on the graphene sheets, and the sulphide source used has a great influence on the morphology, structure and property of the graphene/CdS nanocomposites. The good distribution of CdS nanoparticles on graphene sheets guarantees the efficient optoelectronic properties of graphene/CdS and would be promising for practical applications in future nanotechnology.     

Synthesis and characterisation: Zinc oxide–sulfide nanocomposites

A novel synthesis method is presented for the preparation of nanosized-semiconductor zinc oxide–sulphide (ZnO/ZnS) core–shell nanocomposites, both formed sequentially from a single-source solid precursor. ZnO nanocrystals were synthesized by a simple co-precipitation method and ZnO/ZnS core–shell nanocomposites were successfully fabricated by sulfidation of ZnO nanocrystals via a facile chemical synthesis at room temperature. The as-obtained samples were characterized by X-ray diffraction and transmission electron microscopy. The results showed that the pure ZnO nanocrystals were hexagonal wurtzite crystal structures and the ZnS nanoparticles were sphalerite structure with the size of about 10 nm grown on the surface of the ZnO nanocrystals. Optical properties measured reveal that ZnO/ZnS core–shell nanocomposites have integrated the photoluminescent effect of ZnO and ZnS. Based on the results of the experiments, a possible formation mechanism of ZnO/ZnS core–shell nanocomposites was also suggested. This treatment is suggested to improve various properties of optoelectronically valuable ZnO/ZnS nanocomposites. These nanosized semiconductor nanocomposites can form a new class of luminescent materials for various applications.     

Fabrication and characterization of graphene oxide/zinc oxide nanorods hybrid

This work presented a hybrid architecture of graphene oxide (GO)/ZnO nanorods (ZNs) with ZNs attached parallel onto GO sheets. ZNs were synthesized by refluxing zinc acetate dehydrate in methanol solution under basic conditions followed by surface modification of 3-aminopropyl triethoxysilane (ATS), and then the preformed ZNs were attached onto GO sheets by reaction of the amino groups on the outer wall of ZNs with the carboxyl groups on the GO surface. Transmission electron microscopy (TEM) image of the as-prepared hybrid reveals the morphology of the architecture of GO/ZNs hybrid. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA) ultraviolet-visible (UV-vis) and fluorescence spectroscopy were also performed to characterize the structure and properties of the GO/ZNs hybrid. It was shown that ZNs maintained their initial morphology and crystallinity in the hybrid and the luminescence quenching of yellow-green emission of ZNs confirmed the electron transfer from excited ZnO to GO sheets.     

ZnO nanoparticles anchored on nitrogen and sulfur co-doped graphene sheets for lithium-ion batteries applications

Herein, we demonstrate a facile one-step hydrothermal synthesis route to anchor ZnO nanoparticles on nitrogen and sulfur co-doped graphene sheets. The detailed material and electrochemical characterization have been carried out to demonstrate the potential of novel ZnO/NSG nanocomposite in Li-ion battery (LIBs) applications. The structure and morphology of nanocomposite were assessed by X-ray diffraction (XRD), Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The as-synthesized ZnO/NSG nanocomposite has been studied as anode material in LIBs and delivered a high initial discharge capacity of 1723 mAh g^?1, at the current density of 200 mA g^?1. After 100 cycles, the ZnO/NSG nanocomposites demonstrated a high reversible capacity of 720 mAh g^?1 and coulombic efficiency of 99.8%, which can be attributed to the porous three-dimensional network, constructed by ZnO nanoparticles and nitrogen and sulfur co-doped graphene. Moreover, the designed nanocomposite has shown excellent rate capability and lower charge transfer resistance. These results are promising and encourage further research in the area of ZnO-based anodes for next-generation LIBs.     

Vacancy filling effect of graphene on photoluminescence behavior of ZnO/graphene nanocomposite

We report on the aerosol synthesis and optical characterization of ZnO/unoxidized graphene (UG) platelets nanocomposite films with high optical transparency (>85% at visible wavelengths). The ZnO/UG composite films, in which UG nanoplatelets are embedded in nano‐grained ZnO, were fabricated from colloidal suspensions of UG platelets with an aqueous zinc precursor. From photoluminescence (PL) spectra of the UG composite films, it was found that PL intensity decreases with the addition of UG platelets. The features of PL intensity in the UG composites are in contrast to that of ZnO/graphene oxide (G‐O) platelets composites, and can be explained by the absence of an oxygen vacancy filling effect, due to the unoxidized nature of UG and an increase in defect sites in its composites. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

High UV-shielding Performance of Zinc Oxide/High-Density Polyethylene Nanocomposites

Zinc oxide/high-density polyethylene nanocomposites with high-UV-shielding efficiency were reported. Zinc oxide nanoparticles were synthesized by the homogeneous precipitation method and calcination of the precursor at different temperatures. Zinc oxide/high-density polyethylene nanocomposites were subsequently prepared from high-density polyethylene and as-prepared zinc oxide nanoparticles via melt mixing process. The structural properties of the as-prepared zinc oxide nanoparticles and nanocomposites were studied in detail using X-ray diffractometer, Fourier transform infrared spectrometer, thermogravimetry, differential scanning calorimeter, ultrasonic pulse echo technique, scanning electron microscopy, and transmission electron microscope. The optical properties of the obtained nanocomposites were shown to depend on zinc oxide particle size and content. The nanocomposite containing zinc oxide nanoparticles with an average particle size of 25.22 nm after calcination at 350°C was found to have the most optimal optical properties, namely high-visible light transparency and high-UV light shielding efficiency, which are desirable for many important applications.     

氧化石墨烯/硒化锌纳米光电材料的制备及其蓝光发射特性

采用一种简单有效的原位水热合成方法,使用石墨烯氧化物（GO）作为反应物和晶体生长基底成功制备出了还原氧化石墨烯/硒化锌（r-GO/ZnSe）纳米复合材料。采用X射线粉末衍射（XRD）、透射电子显微镜（TEM）、高分辨透射电镜（HRTEM）以及红外-可见光谱（FT-IR）等方法对r-GO/ZnSe纳米复合材料进行了检测。结果表明,平均粒径在30 nm的立方闪锌矿晶体结构的ZnSe粒子均匀分散在氧化石墨烯片层上,构成纳米复合结构。 UV-Vis光谱显示,纳米复合材料的光学吸收的起始波长在445 nm附近。PL光谱显示,纳米复合材料在470 nm附近存在一个很强的发射峰。这种石墨烯基纳米复合材料在白光二极管领域中有重要的应用价值。     

Preparation of poly(3-hexylthiophene)/graphene nanocomposite via in situ reduction of modified graphite oxide sheets

Poly(3-hexylthiophene) (P3HT)/graphene nanocomposites were facilely prepared via an in situ reduction of modified graphite oxide (mGO) in the presence of P3HT. The chemical and aggregated structures of the P3HT/mGO nanocomposites were successfully characterized by means of atomic force microscope (AFM), transmission electron microscope (TEM), photoluminescence (PL), Raman spectra, X-ray photoelectron spectroscopy (XPS) and UV-vis measurements. Coated by P3HT, reduced modified graphite oxide (re-mGO) could significantly improve their processing problem in common organic solvent. It was shown that P3HT chains were attached to re-mGO sheets closely and there existed the pi-pi interaction between P3HT and re-mGO. The P3HT/mGO nanocomposites exhibited good dispersion in chloroform and show high storage stability (>20 days). This finding provides an efficient method for fabricating a light energy conversion materials with new optical and electrical properties, combining excellent mechanics, heat-stabilization properties of graphene and excellent optical, electrical, processing and film forming properties of soluble polythiophene materials.     

In Situ Synthesis and Characterization of Polypyrrole/Graphene Conductive Nanocomposites via Electrochemical Polymerization and Chemical Reduction

Polypyrrole/graphene sheets (PPy/GNs) nanocomposite electrodes were in- situ synthesized via electrochemical polymerization and chemical reduction from pyrrole (Py) and graphene oxide (GO). The surface morphologies of the nanocomposites were observed by scanning electron microscopy (SEM). The SEM results showed graphene sheets (GNs) scattered on the surface of the polypyrrole (PPy), and the morphologies of PPy/GNs nanocomposites manufactured by pulse current (PC-PPy/GNs) or direct current (DC-PPy/GNs) were smoother than that of PC-PPy. The electrochemical capacitance properties of the nanocomposite films were measured by cyclic voltammetry (CV), galvanostatic charge and discharge (GC), and electrochemical impedance spectroscopy (EIS) techniques in 3 mol·L^?1 KCl aqueous solutions. The results indicated that the specific capacitance of the DC-PPy/GNs nanocomposite was 13.5% higher than that of a PC-PPy electrode. Comparison of the electrochemical performance of the nanocomposites indicated that the PC-PPy/GNs nanocomposite had higher specific capacitance and better charging/discharging capability than that of the DC-PPy/GNs nanocomposite. The specific capacitance of the PC-PPy/GNs nanocomposite could reach to 280 F·g^?1 at a scanning rate of 100 mV·s^?1.     

Flexible and transparent resistive switching devices using Au nanoparticles decorated reduced graphene oxide in polyvinyl alcohol matrix

We have investigated the resistive switching mechanism in solution processed Au-reduced graphene oxide-polyvinyl alcohol (PVA) nanocomposites on flexible substrates. Monodispersed gold nanoparticles (Au NPs) attached to reduced graphene oxide (RGO) in aqueous PVA solution have been synthesized using a novel one pot technique. The fabricated hybrid device showed high On/Off switching ratio more than 10³ with low operating voltages. The performance of hybrid device can be effectively enhanced over control RGO device. The switching mechanism occurs from the electrochemical reduction/oxidation process of partially reduced graphene oxide. The proposed devices reveal superior asymmetric bipolar resistive switching characteristics attractive for solution processable flexible and transparent non-volatile memory applications.     

Defect-controlled growth of ZnO nanostructures using its different zinc precursors and their application for effective photodegradation

Various zinc precursors, such as zinc acetate, zinc nitrate, zinc sulfate, and zinc chloride, have been used to control the formation of zinc oxide (ZnO) nanostructures onto aluminum substrate by chemical means. FESEM images of the ZnO nanostructures showed the formation of different morphologies, such as flakes, nanowalls, nanopetals, and nanodisks, when the nanostructures were synthesized using zinc acetate, zinc nitrate, zinc sulfate, and zinc chloride precursors, respectively. The TEM image of disk-like ZnO nanostructures formed using zinc chloride as a precursor revealed hexagonally shaped particles with an average diameter of 0.5 μm. Room-temperature photoluminescence (PL) spectra revealed a large quantity of surface oxygen defects in ZnO nanodisks grown from zinc chloride compared with those using other precursors. Furthermore, the ZnO nanostructures were evaluated for photocatalytic activity under ultraviolet (UV) light illumination. Nanostructures having a disk-like shape exhibited the highest photocatalytic performance (k = 0.027 min⁻¹) for all the ZnO nanostructures studied. Improved photocatalytic activity of ZnO nanodisks was attributed to their large specific surface area (4.83 m² g⁻¹), surface oxygen defects, and super-hydrophilic nature of their surface, which is particularly suitable for dye adsorption.     

The Effect of Zinc Oxide and Calcium Carbonate Nanoparticles on the Thermal Conductivity of Polypropylene

The thermal conductivity (TC) of compression-moulded polypropylene (PP) and PP filled with 5–15% zinc oxide (ZnO) or calcium carbonate (CaCO₃) nanoparticles, prepared by extrusion, was studied using a thermal conductivity analyzer (TCA). The effect of nanoparticle content and crystallinity on the thermal conductivity was investigated using conventional methods, including SEM, XRD, and DSC. The incorporation of nanoparticles improved the crystallinity and thermal conductivity simultaneously. The experimental TC values of the PP nanocomposites with different level of nanoparticles concentration showed a linear increase with an increase in crystallinity. The TC improvement in PP/ZnO nanocomposite was greater than that of PP/calcium carbonate nanocomposites. This fact can be attributed to the intrinsic, better thermal conductivity of the ZnO nanoparticles. Several models were used for prediction of the TC in the nanocomposites. In the PP/ZnO nanocomposites the TC values correlated well with the values predicted by the Series, Maxwell, Lewis and Nielson, Bruggeman, and De Loor models up to 10 wt%.     

In situ deposition of flower-like ZnO on silk fibroin fibers

In this paper, a convenient biomineralization technique has been developed to form and assemble flower-like zinc oxide (ZnO) on silk fibroin fiber (SFF). Therein, SFF functions as supporting substrate and reactive sites for the in situ generation of ZnO particles. The photoluminescence (PL) of the resulting nanocomposite ZnO/SFF is investigated extensively. The PL peaks are mainly in the visible region (red), which is different from the usual ZnO region (green and violet). As-prepared ZnO/SFF nanocomposites could be useful in the medical field, photoelectron transfer devices, biomolecular detection, and antibacterial agents.     

Synthesis and properties of CdSe Quantum Dot sensitized ZnO nanocomposites

In this work, zinc oxide nanocrystals with an average particle size of 13–22 nm are readily synthesized in aqueous medium by the wet synthesis method. Different sized nanocrystals obtained with change in calcination temperature are characterized by PL photoluminescence (PL) and UV–vis absorption spectroscopies, X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The average crystal size of the as prepared ZnO nanopowder is determined by XRD and was found to be in good agreement with the UV–vis absorption analysis. The quality of different ZnO nanopowders is confirmed by XRD spectra. On the basis of different characterizations, ZnO calcined for 1 h (due to its large size and less agglomeration) is chosen for synthesis of ZnO–CdSe nanocomposites with variable sized CdSe QD's (Quantum Dots). Nano-composites are synthesized using bifunctional linker molecule Mercaptopropionic Acid (MPA), and by directly adsorbing CdSe QD's over the surface of ZnO nanocrystals. The difference in charge transfer mechanism in ZnO–CdSe nanocomposites due to different crystallite size of CdSe QD's is studied. Higher crystallinity of ZnO–CdSe nanocomposites can be determined from XRD characterization. Size and mode of attachment in various ZnO–CdSe nanocomposites are determined by SEM studies.     

Electrostatic spray deposited zinc oxide films for gas sensor applications

In this work, thin films of zinc oxide (ZnO) for gas-sensor applications were deposited on platinum coated alumina substrate, using electrostatic spray deposition (ESD) technique. As precursor solution zinc acetate in ethanol was used. Scanning electron microscopy (SEM) evaluation showed a porous and homogeneous film morphology and the energy dispersive X-ray analysis (EDX) confirmed the composition of the films with no presence of other impurities. The microstructure studied with X-ray diffraction (XRD) and Raman spectroscopy indicated that the ZnO oxide films are crystallized in a hexagonal wurtzite phase. The films showed good sensitivity to 1 ppm nitrogen dioxide (NO₂) at 300 °C while a much lower sensitivity to 12 ppm hydrogen sulphide (H₂S).     

石墨烯/银纳米复合材料的制备及其影响因素研究

以硝酸银、鳞片石墨为原料, 在强碱环境下, 制备得到石墨烯/银纳米复合材料, 采用X射线衍射、红外吸收光谱、透射电子显微镜、紫外可见分光光度计对所制备的石墨 烯/银纳米复合材料进行了表征.结果表明: 氧化石墨烯和银离子在强碱NaOH的作用下, 氧化石墨烯失去部分含氧官能团, 被部分还原为石墨烯(rGO), 银离子被还原为纳米银颗粒, 均匀分布在氧化石墨烯片层表面, 颗粒大小和分布受硝酸银用量、反应温度、NaOH的加入顺序及前驱物混合方式等因素影响, 在GO与Ag粒子质量比为 1:1.08时, 负载在石墨烯片层上的银纳米颗粒集中在12 nm左右. 关键词： 石墨烯/银纳米复合材料 强碱溶液     

In situ preparation and fluorescence quenching properties of polythiophene/ZnO nanocrystals hybrids through atom-transfer radical polymerization and hydrolysis

In this paper, a new approach for in situ preparing nanocomposites of conjugated polymers (CPs) and semiconductor nanocrystals was developed. Polythiophene grafted poly(zinc methacrylate) (PTh-g-PZMA) copolymer was synthesized by atom-transfer radical polymerization (ATRP) of zinc methacrylate (ZMA) initiated from the macroinitiator poly(2,5-(3-(bromoisopropyl-carbonyl-oxymethylene) thiophene)) (PTh-Br) with pendant initiator groups. Subsequently, the polythiophene grafted poly(methacrylate)/ZnO (PTh-g-PMA/ZnO) hybrid heterojunction nanocomposites were successfully prepared by in situ hydrolysis of PTh-g-PZMA casting films in alkaline aqueous solution. The structures of PTh-Br, PTh-g-PZMA and PTh-g-PMA/ZnO were confirmed by the proton nuclear magnetic resonance (¹H NMR) spectra, Fourier transform infrared (FTIR) spectra and X-ray photoelectron spectroscopy (XPS). The morphologies of PTh-g-PMA/ZnO films prepared for different hydrolysis time were observed in the cross-sections by scanning electron microscope (SEM). The SEM images revealed that ZnO nanocrystals were uniformly dispersed in polymers without any aggregation and the appearances of ZnO nanocrystals changed from nanoparticles to nanorods with the hydrolysis treatment time increasing. The optical properties of these nanocomposites were studied by ultraviolet-visible (UV-vis) absorption and fluorescence spectroscopy. UV-vis absorption spectroscopy showed that the adsorption band of PTh-g-PMA/ZnO hybrids was broader than that of PTh-Br, implying that the existence of ZnO nanocrystals increased the optical absorption region of hybrids. The photoluminescence (PL) spectra of the hybrids showed that fluorescence quenching occurred in PTh-g-PMA/ZnO blends and a maximum of 85% of the fluorescence intensity quenched in the PTh-g-PMA/ZnO obtained from treatment in NaOH aqueous solution for 2 h, which revealed the existence of photo-induced charge transfer between the polythiophene chains and ZnO. These results indicated that the hybrid heterojunction nanocomposites could be promising candidates for photovoltaic applications.     

The role of pH variation on the growth of zinc oxide nanostructures

In this paper we present a systematic study on the morphological variation of ZnO nanostructure by varying the pH of precursor solution via solution method. Zinc acetate dihydrate and sodium hydroxide were used as a precursor, which was refluxed at 90 °C for an hour. The pH of the precursor solution (zinc acetate di hydrate) was increased from 6 to 12 by the controlled addition of sodium hydroxide (NaOH). Morphology of ZnO nanorods markedly varies from sheet-like (at pH 6) to rod-like structure of zinc oxide (pH 10-12). Diffraction patterns match well with standard ZnO at all pH values. Crystallinity and nanostructures were confirmed by high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) pattern, which indicates structure grew along [0 0 0 1] direction with an ideal lattice fringes distance 0.52 nm. FTIR spectroscopic measurement showed a standard peak of zinc oxide at 464 cm⁻¹. Amount of H⁺ and OH⁻ ions are found key to the structure control of studied material, as discussed in the growth mechanism.     

Decorating reduced graphene oxide with Co3O4 hollow spheres and their application in supercapacitor materials

In this paper, a composite of reduced graphene oxide decorated by Co₃O₄ hollow spheres (Co₃O₄/RGO composite) has been synthesized by a one-pot solvothermal method. The samples are characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FT-IR), Raman spectra and so on. The results demonstrate that the Co₃O₄ hollow spheres with good purity and homogenous size are absorbed onto the reduced graphene oxide sheets as spacers to prevent the aggregation of the graphene oxide sheets. Furthermore, the well electrochemical properties demonstrate that the Co₃O₄/RGO composite might have potential applications as electrode materials for supercapacitors.