The Preparation Of BiOCl Thin Film At Low Temperature And Its Photocatalytic Activity

BiOX (X=Cl, Br, I), a series of indirect band gap semiconductor, is composed of a tetragonal PbFCl structure containing [Bi2O2] layer and X layer. It is a kind of novel photocatalyst. BiOX has many advantages, such as, high photocatalytic activity, stable chemical property, large specific surface area, low consumption in photocatalytic process, low toxicity, good compatibility to organic substance, excellent absorption to the sun light and so on. Therefore BiOX attracted more and more attentions in recent years. The powder catalyst expresses poor dispersion in solution and difficulties in separation and reuse, especially tiny particles with micro-nano structure. In order to solve the problems about the powder catalyst, we prepared BiOCl thin film photocatalyst in a simple, practical and low energy consumption method, tested the effects of the parameters in preparation process on the catalytic activity of BiOCl thin film, and expected to provide basic data to the practical application of photocatalytic degradation organic pollutants.BiOCl thin film was prepared by the alcoholysis-coating method and electrochemical method at low temperature. The obtained thin film was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), electronic energy spectrum (EDS) and ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS). The photocatalytic activities of BiOCl thin films prepared in different conditions were also evaluated by the degradation of methyl orange (MO) in water under UV light irradiation. All the obtained results are listed as follows:Part I The preparation of flower-like BiOCl thin film via alcoholysis-coating method and its photocatalytic activity1. Flower-like BiOCl thin film was prepared in the alcoholysis-coating method, which is simple and does not need calcination. And the results showed that the obtained BiOCl film without calcination was composed of flower-like sphere structure with tetragonal phase and had a good absorption to ultraviolet. The sample was composed by Bi, O and Cl three elements, and had a ratio close to the stoichiometric ratio of BiOCl.2. The photocatalytic activity and stability of BiOCl thin film was evaluated by the degradation of MO in water under UV light irradiation. The degradation experimental results confirmed that the thin film prepared at low temperature expresses a high photocatalytic activity and can achieve a97%degradation to10mg/L MO solution after150min UV light irradiation. The photocatalytic activity still remained an above94%removal of MO after used four cycles, and the XRD spectra of the sample before and after use were not changed, which showed that the obtained BiOCl thin film expressed a good stability. 3. A possible formation mechanism of BiOCl thin film was also inferred and the results suggested that the ethylene glycol solvent may contribute to the formation of flower-like sphere structure. Through investigate the influence of capture agent on the photocatalytic activity of BiOCl thin film, we get that hole (h+) may play the key role in photocatalytic degradation process of MO. Part II The preparation of BiOCl thin film at room temperature via electrochemical method and its photocatalytic activity1. BiOCl thin film was prepared on the Ti substrate through the cathodic deposition and anodic oxidation method at room temperature. The BiOCl thin film obtained at the best preparation condition was composed by nanoplates with tetragonal phase and had a good absorption to UV irradiation. The sample was composed by Bi, O and Cl three elements, and had a ratio close to the stoichiometric ratio of BiOCl.2. The oxidation voltage and oxidation time had the effect on the lattice orientation, morphology, photocatalytic activity and stability of BiOCl thin film. The results showed that when the Film1was oxided at2.0V for60min the obtained BiOCl thin film had an obvious110orientation, was composed by interlaced nanoplates, and performed the best photocatalytic activity (about98%in150min) and stability.3. In the degradation process, the UV-vis whole wave scanning curves of MO solution were determined. We also compared the roles of photolysis, adsorption and photocatalysis in the photocatalytic process. The results indicated that the MO in the solution was decomposed gradually in the photocatalytic process. The photocatalysis played the predominant role. The photocatalytic activity of the prepared BiOCl thin film still remained an about90%removal of MO after used five cycles, which showed the good stability of the BiOCl thin film. In addition, the MO could be decomposed slightly in presence of BiOCl thin film under the similated sunlight.