| At present, scientists all over the world have been engaging in the study of photocatalytic materials because of mineralizing multitudinous organic substances, especially in nano-materials powder of metal-oxides, which presents a brilliant application prospect in environmental protection and other domains. On the whole, investigators pay more attention to nano-TiO2 than others, because of its excellent photocatalysis. In this paper, structural characteristic, preparation method and modified ions of chromium oxide were systemically investigated, which Serves as photocatalyzer feasibility was discussed. In the following article, two parts are mainly focused on: the theoretic prospect and experimental verification.In the first part, by using ab initio method and DFT method, regularities of band-gaps of chromium oxide with cluster models increasing was investigated, effects on band-gaps and photocatalytic degradation properties were discussed concretely when Cr8O12 was modified by Ti4+,Al3+,Ni2+,Co2+,Fe3+,Zn2+ ,and the Photocatalytic decomposed mechanism of phenol was also analysed . When calculating band-gaps for all models, I selected UHF (6-31g basis set) method and DFT method. The results indicated that non-neutral models didn't exhibit an obvious quantum effect, because charges of models themselves are different to actual material`s. For the neutral models, such as Cr4O6, Cr8O12, Cr12O18, Cr16O24 and Cr24O36, quantum effect is distinct with development of cluster model, the band-gaps are gradually near the body phase material's, and the largest space dimension is the most vital factor. I also get such a conclusion by quantum chemistry calculation that right ion modification is the most effective way to change the band-gaps, for example, the band-gaps of chromium oxide doped with Ni2+, Co2+ and Fe3+ is diminished, but chromium oxide doped with Ti4+ and Al3+ has an adverse result, and for the same compound doped with Zn2+, the band-gaps has an ill-defined variety. In another case, if we drive at the utilization factor of sunlight, chromium oxide doped with Ni2+, Co2+ and Fe3+ has a higher utilization factor, which can be propitious to improve photocatalytic efficiency. For the decomposed mechanism phenol of phenol, I can suppose that the most crucial step is the phenyl ring's opening ring reaction, and it is the controlling step. The reaction of ·OH and phenyl ring belong to a kind of electrophilic reaction, that is the higher the electron cloud is, the lower energy barriers, and methylene blue has a higher electron cloud density compared with phenol for its several activated groups, so ·OH is easier to oxidate methylene blue. In experiment, I finished the following work: preparation of nano-chromium oxide, electroless composite coating and the study for photocatalysis. In the preparation course of nano-chromium oxide, I used a solid-phase reaction, stearic acid as complex agents, dispersant agents and solvents, and the experiment course and the products were investigated by TG –DSC, FTIR, XRD and AFM. According to those, the optimal ratio of stearic to chromic nitrate is 4:1, and the stearic acid and chromium ion is bonded in evidence in gel. At 560℃,organic substances were removed thoroughly, and average grain sizes of the product is about 17nm. During the course of syntheses, both temperature and ratio of raw material are very important to particle dimension of the product. In order to improve economically photochemical catalysis of nanometer particles, chromium oxide was fixed on steel bodies, during the process of electroless composite coating, I singled out the following formula, NiSO4·6H2O 25g/L, Cr2O3(17.40nm) 10g/L, NaH2PO2·H2O 28g/L, NaAc(crystal) 5g/L, C3H6O3 20ml/L, pH 4.5, temperature 85oC, time 30 min. According to this formula, layers of electroless composite coating are the highest content of chromium oxide, a better corrosion resistance, and high photocatalysis. In the study of photocatalysis, I found that nano-chromium oxide prepared at different temperature has different ca... |
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