Synergistic Enhancement of Carrier Migration by SnO2/ZnO@GO Heterojunction for Rapid Degradation of RhB.

Organic dyes in natural waters jeopardize human health. Whether semiconductor materials can effectively degrade dyes has become a challenge for scientific research. Based on this, this study rationally prepared different nanocomposites to remove organic dyes effectively. Pure SnO2 quantum dots, ZnO nanosheets, and SnO2/ZnO (ZS) binary nanocomposites are prepared using the hydrothermal method. Subsequently, SnO2/ZnO@GO (ZSG) ternary composites containing different amounts of GO, i.e., ZSG-5, ZSG-15, and ZSG-25, are synthesized by an ultrasonic water bath method, in which ZS was coupled with GO to form Z-type heterojunctions. The ZSG-15 ternary composites exhibited excellent photocatalytic activity for the degradation of rhodamine B by simulating sunlight. The test results show that the degradation rate of ZSG-15 is about 7.6 times higher than ZnO. The increase in photocatalytic activity is attributed to the synergistic effect of SnO2 and GO to improve the separation efficiency of photogenerated carriers in ZnO. Notably, the large specific surface area of GO increases the reactive sites. Compared with binary nanocomposites, ZSG-15 broadens the response range to light while further accelerating the electron transport rate and improving the photoelectric stability.

Green synthesis of flower shape ZnO-GO nanocomposite through optimized discharge parameter and its efficiency in energy storage device.

Numerous solution-based methods are used to prepare zinc oxide (ZnO) and graphene oxide (GO) nanocomposite (ZnO-GO NCs) such as sol-gel, hydrothermal, and precipitation. These methods require lots of reagents and involve many stages. In this study, a novel one-step solution-based discharge method is used to prepare ZnO-GO NCs through an electrochemical discharge process (ECDP) without the use of any catalyst or toxic chemical reagent. This study focused on analyzing the effects of input parameters on the production rate of ZnO-GO NCs. The experiment was performed by using Taguchi L9 orthogonal array. Materials removal rate (MRR) is considered as output response. The results reveal that voltage is the most significant factor, followed by temperature and duty cycle for obtaining higher MRR. The optimum parameters obtained from the Minitab software for higher MRR are 40 V, 30%, and 45 °C. Further, the morphology of the nanoparticles (NCs) produced at optimum parameters is analyzed which shows flower shape NCs with multilayer graphene oxide, confirmed by the FESEM and TEM images. The XRD peak at 11.27° and Raman spectroscopy peak of G and D bands reveal GO formation. The prepared ZnO-GO NCs tested as supercapacitor activity in the KOH solution. At the optimum parameter, the specific capacitance is observed to be 523.4 F/g at 2A/g current density. The NCs electrode shows good cyclic stability, with 86% retention of specific capacitance after 5000 cycles. This study shows a promising future of converting the e-waste product into valuable nanomaterials such as GO and ZnO from used dry cell batteries.

Sustainable removal of Cr(VI) using graphene oxide-zinc oxide nanohybrid: Adsorption kinetics, isotherms and thermodynamics.

Metal-based adsorbents are limited for hexavalent chromium [Cr(VI)] adsorption from aqueous solutions because of their low adsorption capacities and slow adsorption kinetics. In the present study, decorated zinc oxide (ZnO) nanoparticles (NPs) on graphene oxide (GO) nanoparticles were synthesized via the solvothermal process. The deposition of ZnO NPs on graphene oxide for the nanohybrid (ZnO-GO) improves Cr(VI) mobility in the nanocomposite or nanohybrid, thereby improving the Cr(VI) adsorption kinetics and removal capacity. Surface deposition of ZnO on graphene oxide was characterized through Fourie Transform Infra-red (FTIR), UV-Visible, X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive Spectroscopy (EDS), and Brunauer-Emmett-Teller (BET) techniques. These characterizations suggest the formation of ZnO-GO nanocomposite with a specific area of 32.95 m2/g and pore volume of 0.058 cm2/g. Batch adsorption analysis was carried to evaluate the influence of operational parameters, equilibrium isotherm, adsorption kinetics and thermodynamics. The removal efficiency of Cr(VI) increases with increasing time and adsorbent dosage. FTIR, FESEM and BET analysis before and after the adsorption studies suggest the obvious changes in the surface functionalization and morphology of the ZnO-GO nanocomposites. The removal efficiency increases from high-acidic to neutral pH and continues to decrease under alkaline conditions as well. Mathematical modeling validates that the adsorption follows Langmuir isotherm and fits well with the pseudo 2nd order kinetics (Type 5) model, indicating a homogeneous adsorption process. The thermodynamics study reveals that Cr(VI) adsorption on ZnO-GO is spontaneous, endothermic, and entropy-driven. A negative value of Gibb's Free Energy represents the thermodynamic spontaneity and feasibility of the sorption process. To the best of our knowledge, this is the first study of Cr(VI) removal from aqueous solution using this hybrid nanocomposite at near-neutral pH. The synthesized nanocomposites prove to be excellent candidates for Cr(VI) removal from water bodies and natural wastewater systems.

Preparation of Electrospun Gelatin Mat with Incorporated Zinc Oxide/Graphene Oxide and Its Antibacterial Activity.

Current wound dressings have poor antimicrobial activities and are difficult to degrade. Therefore, biodegradable and antibacterial dressings are urgently needed. In this article, we used the hydrothermal method and side-by-side electrospinning technology to prepare a gelatin mat with incorporated zinc oxide/graphene oxide (ZnO/GO) nanocomposites. The resultant fibers were characterized by field emission environment scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffractometry (XRD) and Fourier transform infrared spectroscopy (FTIR). Results indicated that the gelatin fibers had good morphology, and ZnO/GO nanocomposites were uniformly dispersed on the fibers. The loss of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) viability were observed to more than 90% with the incorporation of ZnO/GO. The degradation process showed that the composite fibers completely degraded within 7 days and had good controllable degradation characteristics. This study demonstrated the potential applicability of ZnO/GO-gelatin mats with excellent antibacterial properties as wound dressing material.

Graphene-Like Porous ZnO/Graphene Oxide Nanosheets for High-Performance Acetone Vapor Detection.

In order to obtain acetone sensor with excellent sensitivity, selectivity, and rapid response/recovery speed, graphene-like ZnO/graphene oxide (GO) nanosheets were synthesized using the wet-chemical method with an additional calcining treatment. The GO was utilized as both the template to form the two-dimensional (2-D) nanosheets and the sensitizer to enhance the sensing properties. Sensing performances of ZnO/GO nanocomposites were studied with acetone as a target gas. The response value could reach 94 to 100 ppm acetone vapor and the recovery time could reach 4 s. The excellent sensing properties were ascribed to the synergistic effects between ZnO nanosheets and GO, which included a unique 2-D structure, large specific surface area, suitable particle size, and abundant in-plane mesopores, which contributed to the advance of novel acetone vapor sensors and could provide some references to the synthesis of 2-D graphene-like metals oxide nanosheets.

Zinc oxide/graphene oxide nanocomposites specifically remediated Cd-contaminated soil via reduction of bioavailability and ecotoxicity of Cd.

From both environment and health perspectives, sustainable management of ever-growing soil contamination by heavy metal is posing a serious global concern. The potential ecotoxicity of cadmium (Cd) to soil and ecosystem seriously threatens human health. Developing efficient, specific, and long-term remediation technology for Cd-contaminated soil is impending to synchronously minimize the bioavailability and ecotoxicity of Cd. In the present study, zinc oxide/graphene oxide nanocomposite (ZnO/GO) was developed as a novel amendment for remediating Cd-contaminated soil. Our results showed that ZnO/GO effectively decreased the available soil Cd content, and increased pH and cation exchange capacity (CEC) in both Cd-spiked standard soil and Cd-contaminated mine field soil through the interaction between ZnO/GO and soil organic acids. Using Caenorhabditis elegans (C. elegans) as a model organism for soil safety evaluation, ZnO/GO was further proved to decrease the ecotoxicity of Cd-contaminated soil. Specifically, ZnO/GO promoted Cd excretion and declined Cd storage in C. elegans by increasing the expression of gene ttm-1 and decreasing the level of gene cdf-2, which were responsible for Cd transportation and Cd accumulation, respectively. Moreover, the efficacy of ZnO/GO in remediating the properties and ecotoxicity of Cd-contaminated soil increased gradually with the time gradient, and could maintain a long-term effect after reaching the optimal remediation efficiency. Our findings established a specific and long-term strategy to simultaneously improve soil properties and reduce ecotoxicity of Cd-contaminated soil, which might provide new insights into the potential application of ZnO/GO in soil remediation for both ecosystem and human health.

Multifunctional nanohybrid for simultaneous detection and removal of Arsenic(III) from aqueous solutions.

Herein, for the adsorption and detection of As (III), multifunctional nanohybrid have been synthesized using a solvothermal approach. Structural and functional characterizations confirmed the impregnation of the ZnO over graphene oxide. Nanohybrid exhibits a remarkable qmax (maximum adsorption capacity) of 8.17 mg/g, at an adsorbent dose of 3 g/L and pH of 8.23. Higher adsorption with nanohybrid was attributed to a large BET surface area of 32.950 m2/g. The chemical nature and adsorption behaviour of As(III) on ZnO-GO were studied by fitting the data with various adsorption isotherms (Langmuir & Freundlich) and kinetics models (six models). It is observed from the findings that removal of As(III) with ZnO-GO nanocomposite appears to be technically feasible with high removal efficiency. The feasibility of the nanocomposite to function as a sensor for the detection of As(III) was also evaluated. The fabricated sensor could detect As(III) with a lower limit of detection of 0.24 µM and linear range up to 80 µM. Overall, this study is significant in nanohybrid as a multifunctional composite for the adsorption and detection of As (III) from wastewater.

Sonoprecipitation dispersion of ZnO nanoparticles over graphene oxide used in photocatalytic degradation of methylene blue in aqueous solution: Influence of irradiation time and power.

In this paper, ZnO/Graphene Oxide (ZnO/GO) is synthesized via ultrasound assisted precipitation method and the effect of power and ultrasound time irradiation is studied on photocatalyst properties. The synthesized samples are used for methylene blue (MB) degradation as an organic water pollutant. Physicochemical properties of the samples are investigated by XRD, FESEM, EDX, BET-BJH, FTIR and DRS techniques. Moreover, pHpzc of the sample with the best performance is calculated to study the effect of acidity on the photocatalyst efficiency in photocatalytic process. Ultrasound has a positive effect on photocatalyst performance that is because of its effect on distribution of particles and semiconductor band gap, but it has no effect on photostability of the nanocomposite. Sonication has modified distribution of particles by enhancing the active sites for oxidation process. Making structural gaps by ultrasound irradiation increases available surface area which has a similar effect on photocatalyst performance. Graphene oxide as electron collector and transporter prevents electron-hole recombination and it can be an acceptable reason for enhancement at photocatalyst performance. Finally, some of operational parameters such as pH, photocatalyst loading and dye concentration are investigated.