Preparation Of Cu₂O Thin Films And Study Of Their Photocatalytic Properties

With the development of economy and society, People’s living standard hasincreased day after day, but serious environmental deterioration and energy crisis areshown behind the rapid development. Some noxious and nonbiodegradation organicpollutions have more harmful influence on people’s survival and development ofhuman beings, so much newspaper about the harm of organic pollution on human andanimals is very common. Some living and industrial sewage are mostly containingorganic pollution, and the pollutions are hard to degradation by traditional technologies.Recently, many countries and people pay more and more concern on environmentalpollution, following by some new methods and technologies update. Solar energy is aunlimited clean energy, many specialists and scholars are beginning to research how tomake use of solar energy to degrade organic pollutions. Photocatalytic technology, awarm oxidation technology, has high oxidation efficiency and degradation rate, couldutilization solar energy efficiently, above all, it is able to reuse the photocatalyst, andavoid the second pollution. TiO2has been investigated with many advantages such ashigh oxidation efficiency, good stability and high photocatalytic activity, however,TiO2only use small irradiation of solar energy due to the wide band gap (3.2eV), andtherefore it has the high cost in the real application. It will be more significant todevelop a photocatalyst which can utilize solar energy efficiently.Cu2O is an important p-type direct band gap semiconductor, with a band gap of2.17eV. Because Cu2O has a good performance of photocatalysis in manysemiconductor photocatalysts, therefore, it becoming the research highlight inphotocatalytic field. Recently, most investigation was limited to Cu2O nanosizedparticles, and exhibited effective photocatalytic activity. However, the nanoparticlesare easy to aggregate, and difficulty in separation and recovery, which greatly limits itscommercial applications. In order to overcome this limitation, Cu2O thin films wereprepared as photocatalyst to investigate their photocatalytic performance. In addition,some prepared parameters were also discussed in detail. The research work and resultswere presented as follows:1. Cu2O thin films were prepared by one-step chemical bath deposition approach,the morphology, crystallite size and optical properties of Cu2O thin film were tuned bychanging chelating agent addition, Cu2+concentration, deposited temperature and pHvalue. Furthermore, based on the effect of chelating agent on the morphology and orientation evolution, the mechanism responsible for the morphological transformationwas proposed. The samples were characterized via X-ray diffractometry, scanningelectron microscopy and UV-vis spectrophotometry. The results illustrated that themorphology, crystallite size and optical property of Cu2O thin films could be tuned byadjusting the deposited parameters. The chelating agent has the influence on theconfiguration of crystal nuclei, which resulting in a transition in the orientation andmorphology.2. The photocatalytic performance of Cu2O thin films under visible lightirradiation were evaluated by the degradation of MO. Some parameters such as theinfluence of pH value, initial dye concentration and the addition of H2O2onphotocatalytic activity of Cu2O thin films were investigated. In addition, the synergisticeffect of Cu2O thin films and H2O2, recyclability tests and photocatalytic mechanism ofCu2O thin films were investigated highlightly, meanwhile, the reasonable morphologyevolution mechanism after photocatalytic reaction was also purposed. The resultshowed that the addition of a small volume (<113.75μl) of H2O2had a synergistic effectand considerably increased the photodegradation efficiency, otherwise, H2O2inhibitedthe photocatalytic activity. The photodegradation of MO as a function of the pHrevealed that the photodegradation efficiency of MO in acidic media was much higherthan that in alkaline media. The high initial concentration of MO was bad for theincreasing photodegradation efficiency, and first order kinetics was observed for thephotodegradation of MO. The Cu2O thin films were recycled ten times in thephotodegradation of MO and exhibited a stable and high photocatalytic activity in thepresence of H2O2, and the degradation efficiency was more than85%after the tenthrecycle. In addition, the increasing specific surface area of Cu2O was observed as thenumber of cycles increased. The morphological transformation of Cu2O thin films wasdue to dissolution and recrystallization growth mechanisms by the characterization ofsamples after photocatalytic reaction.