Review on Zinc Oxide-Graphene Oxide Nanocomposites: Synthesis Techniques, Properties and Applications

: Graphene-oxide nanocomposites have promising applications like chemical sensor, photocatalysts, fuel cells, super capacitors etc. and are useful for monitoring the toxicity, in ﬂammability, and explosive nature of chemicals. Metal oxides like ZnO, TiO 2 , SnO 2 , when combined with graphene oxide in the form of nanocomposites have excellent potential for detecting trace amounts of hazardous gases and chemicals. ZnO-GO nanocomposites have various applications like gas sensors, humidity sensors, UV sensors, water purification, capacitors and optoelectronic applications. Various techniques have been used by researchers for the synthesis of ZnO, GO and ZnO-GO nanocomposites. This paper presents a comprehensive review of the available synthesis techniques, properties and applications of ZnO-GO nanocomposites. nm are uniformly deposited on the graphene sheets. The electrochemical properties of the nanocomposites were examined by measuring the speci ﬁc capacitance in 6M KOH solution using CV and electrochemical impedance spectroscopy. XRD evolution demonstrates wurtzite structure of ZnO and a particle size of 150 nm as determined from SEM. G-ZnO nanocomposites showed a good capacitive behavior with a maximum speci ﬁc capacitance of 122.4 F/g as compared to GO (2.13 F/g) and rGO (102.5 F/g) at 5 mV/s scan rate. The G -ZnO electrode is a promising material for high-performance supercapacitor applications. Graphene/ZnO nanocomposites as electrode material for electrochemical capacitors successfully synthesized by Ejikeme Raphael Ezeigwe et.al.[11] from highly pyrolytic graphite via a green, facile, effective and scalable solvothermal technique. The XRD analysis shows of during solvothermal The surface characteristics and elemental of The electrochemical properties of the nanocomposites were examined by galvanostatic charge–discharge, electrochemical impedance spectroscopy (EIS) and CV. The Graphene/ZnO nanocomposites weight ratio of 1:8 (G:ZnO) displayed an improved capacitive of 236F/g at a scan rate of 10mV/s, excellent cyclic performance, and an average energy and power density of 11.80Wh/kg and 42.48kW/kg respectively. The improved electrochemical performance of the nanocomposites can be ascribed to the good electroactive property of ZnO and the high electrical conductivity of the synthesized pristine graphene. showed that ZnO nanocrystals (NCs) are well formed on the GO surface and average size of ZnO NCs was found to be about 21.7 ± 2.3nm from the XRD patterns. The effect of ZnO/GO nanocomposite concentrations incorporated into the electrode was investigated and found highest electrochemical signal. The results shows that the developed nanocomposite with the high surface area and electrocatalytic activity offer great promise for a non-enzymatic biosensor. samples were characterized by XRD, UV–Visible absorption spectroscopy, AFM and Raman spectroscopic technique. The photo-sensitivity of the films towards UV was studied by current–voltage measurements UV irradiation and under visible. The electric field produced by the UV radiation can pull the holes to the surface whereas at the surface the adsorbed oxygen ions will trap the photo-generated holes by the recombination of surface electrons and holes, which results in the increase of photocurrent gain. A better response was observed for the ZnO/rGO polymer composite film because of large surface roughness and localized electrons within the GO sheet. using on of quality hybrid nanocomposites The hybrid nanocomposite structure has been developed by an optimized hydrothermal process at low temperature. In hybrid nanosensor, the ZnO nanoparticles act as UV absorbing and charge carrier generating material, while its superior electrical conductivity. The EDX spectra confirmed the exact chemical composition of the structure. UV-VIS measurement shows an enhanced optical absorption of UV-light at an absorption band centered on 375 nm. The optical and electrical properties were observed at an optimum relative concentration of 1:10. These results can be promising for future enhanced UV- sensing applications. Tao Chung et.al. [17] reported that Zinc oxide nanoparticles were well-known for the enhanced antifouling and antibacterial properties. The functionalization of ZnO onto GO nanoplates was targeted for better distribution and both ZnO and ZnO-GO NPs were synthesized using sol-gel method. The nanoparticles characterized by XRD, TEM, and FESEM. The Polysulfone-nanohybrid membranes were successfully fabricated with various percentage of ZnO (1, 2, 3 wt%) nanoparticles and ZnO-GO (0.1, 0.3, 0.6 wt%) nanoparticles. The optimum membrane performance was shown in membrane with 2 wt% of ZnO and 0.6 wt% of ZnO-GO. The unique characteristics of ZnO and ZnO-GO NPs were establish with several analyses i.e. XRD, TEM and FESEM and the enhancement of membranes was explored by varying the concentrations of the NPs. Both membranes presented significantly improved performance such as enhanced hydrophilicity, high permeability and porosity, improved humic acid rejection, pore size, rejection tendency rate as well as good antifouling and antibacterial control. Hence, ZnO and ZnO-GO NPs were superb nanomaterials in the fabrication of PSF-nanohybrid membranes with significant hydrophilicity and fouling control enhancement which was suitable in various separation and purification applications. the ZnO NPs were decorated and spread on the rGO. HRTEM images of the NPs show that the ZnO NPs were single crystals without any defects. The FTIR results showed that the post-annealing method removed the gelatin medium and formed the ZnO structure and it shows GO was transformed into RGO by the post-annealing process. The photocatalyst activity revealed the high MB removal ef ﬁciency of the ZnO -NPs/rGO as compared to the ZnO NPs. This technique may be used for the large-scale removal of pollutants from wastewater.