Preparation And Activities Modulation Of Bismuth Oxyhalides Photocatalytic Materials

Since the 21 st century, the environmental problems have become seriously in our country, various environmental pollution events have emerged endlessly, and the extent of damage has become larger and larger. Photocatalytic oxidation technology, as a new type of environmentally friendly technology with obvious energy saving, high efficiency, stability, no secondary pollution and other advantages, has attracted more and more attentions. Although for a long time in the past, a large number of studies had focused on the development and optimization of new photocatalytic materials, there still existed some disadvantages limiting its widely use, such as small active crystal surface exposed area, narrow light absorption, low separation efficiency of electron-hole and so on.Because of its adjustable layered structures, bismuth oxyhalides photocatalytic materials exhibited excellent absorption capability from ultraviolet to visible light, and had high research value. In this paper, three methods were used to create efficient bismuth oxyhalides nanomaterials, including the increasing of the unit volume of the active crystal face exposed surface area, the building of few-layer solid solutions nanostructures and in situ reduction of Bi to form Bi/BiOI composite photocatalyst. Specific contents were as follows:1. Series of BiOBr nanosheet samples with different sizes were synthesized by solvothermal reaction. Rhodamine B, methyl orange and phenol were selected as degradation objects to study the influence of {001} crystal face exposure ratio and size of BiOBr photocatalyst on the performance. The results showed that Bier nanosheets with similar {001} crystal face exposure ratio but different sizes exhibited different photocatalytic performance, and small size of BiOBr exhibited more efficient photocatalytic activity. Moreover, the size of the length and thickness direction had different effects on photocatalytic performance, and the influence of thickness was obviously superior to that of length. In addition, by analyzing the relationships between the thickness and the unit volume of the {001} facets exposed surface area, the unit volume of {001} facets exposed surface area and {001} facets exposed ratio, the intrinsic reasons for thickness affecting photocatalytic activity was that the unit volume of {001} facets exposed surface area involving in the photocatalytic reaction can be controlled by the thickness of BiOBr nanosheet. In the range of 0.022 nm-1 to 0.111 nm-1, the unit volume of {001} facets exposed surface area and the photodegradation rate constant k showed a good linear relationship. Thus, photocatalytic activity of BiOBr nanosheets was controlled by the unit volume of {001} facets exposed surface area rather than {001} facets exposed ratio.2. Using the synergistic effect of the unit volume of the active face exposed surface area and the special structure of solid solutions on photocatalytic performance, few-layer BiOClxBr1-x solid solutions nanostructures were synthesized through solvothermal reaction. The phase and morphology of BiOClxBr1-x were studied. The results showed that few-layer BiOClxBr1-x solid solutions nanostructures instead of BiOCl and BiOBr composite were successfully synthesized, and the thickness of the prepared solid solutions nanosheets was controlled below 6 nm with highly exposed {001} planes. The bandgap and valence band maximum position of the as-obtained BiOClxBr1-x solid solutions with different proportions were analyzed. The results showed that with the increasing of x value, the bandgap value and the valence band maximum position of solid solutions were gradually increased, indicating that the bandgap and the valence band top position of BiOClxBr1-x solid solutions were adjustable. Under visible light irradiation, rhodamine B, methyl orange and phenol were selected as degradation agents, when x = 0.4, BiOCl0.4Br0.6 showed the highest photocatalytic activity. In addition, by comparing the photocatalytic activities of BiOCl0.4Br0.6 solid solutions with different thickness on degradation of rhodamine B and methyl orange, the result showed that the photocatalytic performance of ultrathin BiOCl0.4Br0.6 solid solutions was significantly better than that of the thicker one.3. Using Bi（NO₃）₃·5H₂O, NaI, glucose and distilled water as Bi source, source of iodine, a reducing agent and solvent, respectively, Bi/BiOI composite photocatalysts were successfully synthesized by in-situ reduction of bismuth ions through a simple hydrothermal method. The phase, morphology and optical properties of the synthesized composites were analyzed. The results indicated that the obtained composite photocatalysts were plate-like, and Bi loaded on BiOI nanosheets in the form of nanoparticles, and the best condition for preparing Bi/BiOI composite photocatalyst was 160 oC, 6 h, 0.8 g glucose. Rhodamine B was selected as the degradation object to evaluate the photocatalytic activity of the as-prepared samples under visible light irridation, and the effect of hydrothermal reaction temperature, reaction time and the amount of glucose on photocatalytic activity of the prepared Bi/BiOI were also discussed. The results showed that Bi/Bi OI composite photocatalyst obtained at 160 oC, 6 h, 0.8 g glucose exhibited the best photocatalytic activity.