Catalytic activity of bimetallic Zn/TiO2 catalyst for degradation of herbicide paraquat: synthesis and characterization
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The preparation and characterization of Zn/TiO2 catalysts were performed and the photocatalytic properties of the resulting catalysts were tested using the paraquat degradation reaction under UV and solar light irradiation. The effect of the preparation method, amount of Zn loading, the calcination temperature and the thermal annealing during the autoclave aging were studied as well as the light irradiation during the testing reaction. The initial concentration of paraquat was 400 ppm, the pH during the catalytic testing was seven and the reaction temperature was 30 °C. The characterization information were obtained from XRD, XPS, UV–vis diffuse reflectance, FTIR, TEM and BET techniques. They were used to explain the expressed catalytic activity of Zn/TiO2. The results showed that the Zn/TiO2 catalyst from the hydrothermal method could remove about 80% of the paraquat from the solution (using 4 g l−1 of catalyst). The characterization data showed that the surface area, porous structure and dispersion of Zn species could affect the ability of the paraquat removal rather than the crystallnity of the TiO2 in the catalyst. The XPS spectra suggested that the preparation method, between the sol gel and hydrothermal, could not affect the state of the Zn and Ti, which presented in the Zn2+ and Ti4+ forms. This primary result will lead us to further study to elucidate the main active site by the XPS technique. Moreover, it clearly showed that the lowering of the band gap energy in the Zn/TiO2 was achieved (compared to bare TiO2), and this phenomena was one of the factors that gave the higher photocatalytic activity of the Zn/TiO2 catalyst.Keywords:
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The effects of calcination temperature on the microstructures and photocatalytic activity of sol-gel synthesized TiO 2 , WO 3 , SnO 2 and ZnO metal oxides were investigated. The synergistic effect of the phase structure, surface area, and crystallinity of the photocatalysts after calcination and on the photocatalytic activity was investigated. 1,2-dichlorobenzene (DCB) was used as a model contaminant in this study. The highest photocatalytic activity was obtained using TiO 2 calcined at 900oC with large particle size, could be ascribed to the enhancement by the presence of defect site. Similarly, WO 3 calcined at 900oC exhibited the best photocatalytic activity in the series of calcination temperature ranging from 400-1000oC. SnO 2 calcined at 800oC showed the best photocatalytic activity while ZnO was found to give the lowest percent of DCB degradation. In this study, sudden increase in the surface area at higher temperature was correlated with the enhancement in the photocatalytic activity of each catalyst.
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To get CaTiO3catalyst with high photocatalytic properties,the effect of calcination conditions,on the photocatalytic activity of CaTiO3 was investigated.The calcination conditions included heating rate of calcination precursors,calcination temperature,calcination time and cooling rate of calcination products,The catalyst was synthesized by solid-state reaction method with Ca(NO3)2and TiO(OH)2as raw materials and NaOH as mineralizer.The physical properties of the catalyst were characterized using XRD and SEM.The experimental results showed that the activity increased until reached a maximum,and then decreased with the increasing heating rate of calcination precursors;the photocatalytic activity decreased drastically with the fast cooling rate of calcination products.Moreover,the optimal values of calcination temperature and calcination time were obtained.As a result,the CaTiO3catalysts with high photocatalytic activity can be obtained under an optimized calcination conditions after loading CoO(0.2 wt%)co-catalyst.
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Heterogeneous bimetallic catalysts have broad applications in industrial processes, but achieving a fundamental understanding on the nature of the active sites in bimetallic catalysts at the atomic and molecular level is very challenging due to the structural complexity of the bimetallic catalysts. Comparing the structural features and the catalytic performances of different bimetallic entities will favor the formation of a unified understanding of the structure-reactivity relationships in heterogeneous bimetallic catalysts and thereby facilitate the upgrading of the current bimetallic catalysts. In this review, we will discuss the geometric and electronic structures of three representative types of bimetallic catalysts (bimetallic binuclear sites, bimetallic nanoclusters, and nanoparticles) and then summarize the synthesis methodologies and characterization techniques for different bimetallic entities, with emphasis on the recent progress made in the past decade. The catalytic applications of supported bimetallic binuclear sites, bimetallic nanoclusters, and nanoparticles for a series of important reactions are discussed. Finally, we will discuss the future research directions of catalysis based on supported bimetallic catalysts and, more generally, the prospective developments of heterogeneous catalysis in both fundamental research and practical applications.
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Abstract The effects of calcination temperature of titanium dioxide photocatalyst have been investigated on the photocatalytic degradation of an azo dye, acid red 1. The photocatalytic activity of the developed catalyst was greatly influenced by the mode of calcination. Photocatalysts subjected to high calcination temperatures (500°C) were not as effective as those calcined at lower temperature and those heat treated in a cyclic mode outperformed those which were calcined in a straight run. The photocatalysts developed were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, surface scanning electron microscopy, and N2 physisorption. Thus, it was found that the properties of the photocatalysts were significantly responsible for their photocatalytic activities.
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In this paper, the p-n junction photocatalyst Co3O4/In2O3 was prepared by coprecipitation method and it was characterized by X-ray powder diffraction (XRD). The photocatalytic activity of the photocatalyst Co3O4/In2O3 was evaluated by photocatalytic reduction of Cr2O7(superscript 2-) and photocatalytic oxidation of Methyl Orange. The effect of the doped amount of Co3O4, different calcination temperatures and different calcination time on the photocatalytic activity of Co3O4/In2O3 was investigated, respectively. The results showed that the optimum amount of doped Co3O4 was 5 wt. %. The optimum calcination temperature and the optimum calcination time were 300℃ and 2h, respectively. The photocatalytic reduction activity and photocatalytic oxidation activity of the p-n junction photocatalyst Co3O4/In2O3 were much higher than that of the pure In2O3 under visible and UV light irradiation. The possible mechanisms of influence on the photocatalytic activity of the p-n junction photocatalyst Co3O4/In2O3 were also discussed.
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In this paper,the p-n junction photocatalyst Co3O4/In2O3 was prepared by coprecipitation method and it was characterized by X-ray powder diffraction(XRD).The photocatalytic activity of the photocatalyst Co3O4/In2O3 was evaluated by photocatalytic reduction of Cr2O72-and photocatalytic oxidation of Methyl Orange.The effect of the doped amount of Co3O4,different calcination temperatures and different calcination time on the photocatalytic activity of Co3O4/In2O3 was investigated,respectively.The results showed that the optimum amount of doped Co3O4 was 5 wt.%.The optimum calcination temperature and the optimum calcination time were 300°C and 2h,respectively.The photocatalytic reduction activity and photocatalytic oxidation activity of the p-n junction photocatalyst Co3O4/In2O3 were much higher than that of the pure In2O3 under visible and UV light irradiation.The possible mechanisms of influence on the photocatalytic activity of the p-n junction photocatalyst Co3O4/In2O3 were also discussed.
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Abstract The existence of bimetallic particles (and their reducibility and location on/or in the support) in Ru–Co/NaY and Pt–Co/NaY samples has been studied by in situ X‐ray adsorption spectroscopy (XAS). It is established that in Ru–Co/NaY the monometallic clusters maintain their identity, whereas in Pt–Co/NaY the existence of small bimetallic particles can be established. In both cases the results are supported by other techniques, such as XPS and temperature‐programmed reduction. Copyright © 2002 John Wiley & Sons, Ltd.
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