The reduction of ZnO in a ZnO-supported catalyst to metallic zinc, the alloying of metallic zinc with a second metal and the evaporation of zinc species in a reductive atmosphere of hydrogen was investigated in this study. The results show that the reduction temperature was the determining factor for the transformation of zinc species. The complete removal of ZnO in a ZnO-supported catalyst can be achieved at 700 °C. The effects of different metals supported on ZnO on the transformation of ZnO were also investigated. Cu, Co and Ni species can slow the ZnO loss due to the priority for the reduction of these metal oxides and the formation of metal–Zn intermetallics. Fe based catalysts noticeably accelerated the loss of ZnO, which can be ascribed to the high oxophilicity of Fe and the strong interactions between the metal and support.
To explore electrochemistry of the composites of ZnO and reduced graphene oxides (rGO), graphene oxide (GO) was in-situ reduced with Zn powders. The morphology and micro-structure of synthesized ZnO@rGO composites were characterized using scanning electron microscopy, transmission electron microscopy , and atomic force microscope . Energy dispersive spectroscopy, X-ray diffraction, Raman, and Fourier Transform infrared spectroscopy were employed to clarify the chemical composition of ZnO@rGO composites. Electrochemical properties of ZnO@rGO composites were studied using cyclic voltammetry and impedance, revealing a large surface area and many active sites. Accordingly, electrochemical sensing of a neutral organic dye Sudan I and a charged metal ion Pb 2+ was achieved on ZnO@rGO composites. The strategy of in-situ reduction of GO with Zn powders thus owns great application prospects in constructing a universal and sensitive electrochemical sensing platform.
Dan Wu,Xukai Li,Jingxian Zhang,Weirui Chen,Ping Lu,Yiming Tang,Laisheng Li
ZnO-reduced graphene oxide (ZnO-rGO) was synthesized successfully at 423 K by a hydrothermal method. The presence of reduced graphene oxide significantly improved the photocatalytic performance of ZnO and its optimal loading ratio was 0.6 wt%. The XRD, SEM, UV–vis and FT-IR were applied to characterize the prepared catalyst. Comparative experiments were conducted to evaluate perfluorooctanoic acid (PFOA) degradation efficiency and the results showed that 99.2% PFOA was degraded in persulfate-assisted photocatalytic ozonation with low dosage of ozone and persulfate at room temperature. The impact factors on PFOA degradation efficiency including loading ratios of GO on ZnO, reaction temperatures and persulfate concentration were inspected and analyzed. The sodium persulfate and ammonium persulfate were compared as common oxidants in photocatalytic ozonation for PFOA degradation and sodium persulfate showed the better PFOA removal. Chloride and humic acid (HA) were common substances in natural water, and they showed inhibition effects on PFOA degradation. Conversion of persulfate to sulfate ion was studied and persulfate concentration during PFOA oxidation was monitored. PFHpA, PFHeA, PFPeA and PFBA were main intermediates during PFOA degradation.
ZnO@the reduced graphene oxide (rGO) nanorod arrays were grown in-situ on the ceramic tube substrate by one-step hydrothermal without any template or surfactant. The reduced graphene oxide was evenly coated around the ZnO nanorods through the controllable assembly of the rGO and ZnO heterojunction interface. rGO contributed to the improvement of material conductivity and provided more active sites to adsorb NO 2 molecules. The combination of rGO and ZnO significantly enhanced the response of the composite to NO 2 at room temperature . It showed an excellent selectivity to NO 2 and a good linear relationship in the concentration range of 0.1∼10 ppm. In order to explore the response mechanism of ZnO@rGO composite to NO 2 , the change of element composition and status was performed by XPS technology before and after the exposure of the composite to NO 2 . The gaseous products after the reaction were also tested by GC–MS technology. DFT calculations were performed based on the test results, which demonstrated that the p-n heterostructure produced by the ZnO@rGO composite had a beneficial effect on improving the gas response capability.
Junxing Hao,Caoling Li,Kangbing Wu,Chengguo Hu,Nianjun Yang
The magnetic-bead-based electrochemical enzyme-linked immunoassay (MB-eElisa) represents an attractive approach to develop cost-effective systems that are suitable for sensing complex biological samples. Its sensitivity essentially depends on the transduction efficiency of enzyme catalytic reactions into electrochemical responses. Here, an ultrahigh signal-to-noise alkaline phosphatase (ALP)-based MB-eElisa system is developed with a renewable zinc oxide-reduced graphene oxide composite modified carbon paste electrode (ZnO@rGO/CPE). This biosensing system employs one antibody decorated MB (MB-Ab1) to capture a model tumor marker—carcinoembryonic antigen (CEA)—from samples, while other antibody coated gold nanoparticles-ALP bioconjugates (Ab2-AuNPs-ALP) convert 1-naphthyl phosphate (1-NPP) into electroactive 1-naphthol (1-NP). Benefitting from the unique electrochemical properties of a ZnO@rGO/CPE, including nearly zero background and significantly enhanced responses toward the hydrolyzed 1-NP in the presence of trace surfactants, the MB-eElisa system detects selectively CEA in a calibration range of 0.01–6.0 ng mL–1 and with a detection limit of 4.0 pg mL–1 (S/N = 3). Such a system was further applied to the detection of CEA in serum samples of cancer patients. The combination of MB-based ALP-linked immunoassay with a ZnO@rGO/CPE thus establishes a reusable and inexpensive electrochemical sensing platform for the rapid and sensitive detection of ultratrace biomarkers in complex biological samples.
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