Controllable Preparation And Photocatalytic Properties Of MO/MA₂O₄（M=Zn, Cu, Ni） Composite Oxides

Environmental pollution and energy crisis have become two serious challenges. Semiconductor photocatalyst such as ZnO, TiO2has attracted much attention because of its potential use in clean environment and solar energy conversion. However, their both rapid recombination rate of the photogenerated electron-hole pair and the narrow light response range limited their applications. The study on the composite metal oxide becomes a research focus in the field. Based on the new photocatalyst of spinel MAl2O4, the dissertation investigated the preparation methods and conditions. Various special structures, such as "sphere in sphere", hierarchical and porous composite photocatalyst MO/MA12O4with heterojunction, have been prepared via a spontaneous self-formation process. The relationship between the structure, composition, morphology, textural properties and photocatalytic performance of the MO/MAl2O4were further investigated in detail. The results involved are presented as follows.1) ZnO/ZnAl2O4nanocomposites with heteronanostructures were successfully prepared by using the coprecipitation method. The photocatalytic activities of the as-prepared samples were evaluated by the photocatalytic degradation of methyl orange and inactivation of Escherichia coli in suspension under the irradiation of the simulated sunlight. The results show that when the concentration of ZnO/ZnAl2O4photocatalyst with the Zn/Al molar ratio of1:1.5and calcined at600℃is1.0g·L-1, the results show the maximum photocatalytic decoloration rate of (98.5%) can be obtained in50min. A99.8%inactivation of E.coli was achieved in60min under the same conditions.2) ZnO/ZnAl2O4composite hollow microspheres were fabricated using glucose as template via polyethylene glycol (PEG-4000)-assisted one-pot hydrothermal method. After the starting materials with the molar ratio of Zn to Al ion of1:1.5, the molar ratio of glucose to metal ion of1:1,10wt.%mass ratio of PEG to ZnO/ZnAl2O4were mixed in pH value of9, the specific surface area of ZnO/ZnAl2O4sample calcined at500℃for4h are158.3m2·g-1. Within60min irradiation of simulated sunlight, the maximum photocatalytic decoloration rate of25mg·L-1methyl orange was98.7%when the concentration of ZnO/ZnAl2O4was0.5g·L-1.3) Using glucose as template and polyethylene glycol (PEG-4000) as dispersion agent, CuO/CuAl2O4(Al2O3) with porous sturcture were prepared via one-pot hydrothermal process. The effects of the preparation methods and conditions on crystallite phase and photocatalytic degradation activity was studied. After the starting materials with10wt.%mass ratio of PEG to CuO/Al2O3were mixed, the obtained mixture was calcined at500℃for4h, the specific surface area of the CuO/CuAl2O4(Al2O3) was167.1m2·g-1When the concentration of CuO/CuAl2O4(Al2O3) was0.5g·L-1, the maximum photocatalytic decoloration rate of25mg·L-1methyl orange was96.7%under60min irradiation of simulated sunlight, which increased by6.5%compared to the sample without PEG under the same conditions. The effect of co-catalysts of Pt and CuS on photocatalytic activity for H2evolution was further investigated under the simulated sunlight irradiation. After loading1.0wt.%CuS and1.0wt.%Pt on CuO/Al2O3, the maximum H2evolution rate (4.51mmol·g-1·h-1) was obtained by using oxalic acid as sacrificial reagent, which increased up to1.44times,1.24times and1.17times than that of CuO/Al2O3, Pt-CuO/Al2O3and CuS-CuO/Al2O3, respectively.4) NiO/NiAl2O4nanocomposites were prepared via coprecipitation method. The effects of the ratio of Ni to Al, calcination temperature and the concentration of NiO/NiAl2O4on the photocatalytic degradation activity were studied. When the concentration of NiO/NiAl2O4was0.5g·L-1, the maximum photocatalytic decoloration rate of25mg·L-1methyl orange was88%under60min irradiation of UV-light. The role of the loaded metal oxide (or sulfides) was further investigated. When the molar loading of CuO is1%, the photocatalytic activity increases by9.1%in comparison with that of the unloaded sample under the same conditions.5) By varing the molar ratios of metal ions and calcination temperature, ZnCu (Ni) Al-LDHs and the corresponding composite oxide with controllable composition and particle size were prepared via a hydrothermal method. ZnO/CuO/ZnAl2O4nanocomposite derived from [Zn2+]/[Cu2+]/[Al3+] initial molar ratio of1:2:1and calcination at500℃exihibit excellent photochatlytic properties. The maximum photocatalytic decoloration rate of25mg-L-1methyl orange was93.1%within60min irradiation of simulated sunlight. ZnO/NiO/ZnAl2O4nanocomposite derived from [Zn2+]/[Ni2+]/[Al3+] initial molar ratio of2:1:1and calcination at500℃show much excellent photochatlytic properties. The maximum photocatalytic decoloration rate of100mg·L-1methyl orange was95.3%within60min irradiation of simulated sunlight. This paper has91figures,8tables and188references.