Preparation Of BiOX(X=I, Br, Cl) Nanocrystals And Their Performance For Photocatalytic Reduction Of Cr(?)

Hexavalent chromium Cr(?) is one of the forms of chromium that poses a health risk to humans because of its high acute toxicity and carcinogenic activity. This species is generally released in effluent in various industrial activities, including electroplating, leather tanning, metal finishing, dyeing, textile production, and steel fabrication. Other applications that involve paint and pigments, fertilizer use, and photography also have potential to release Cr(?) into the environment. Trivalent chromium Cr(III) is another form of chromium that is much less toxic and less mobile than Cr(?). It can be easily removed from wastewater as a solid by alkalinification and precipitation. Thus, development of effective technologies to reduce Cr(?) to Cr(III) is of great importance in the treatment of wastewater and water for consumption.The present work stars with the preparation of a series of Bi OX, then characterizing Bi OX nanocrystals with XRD, SEM, BET and DRS, and evaluating their performance for photoreduction of Cr(?) ions under visible light irradiation. The main points are as follows:1. Bi OBr nanocrystals with {001}, {110} dominant facets were controllable synthesized by facile hydrothermal methods and hydrolysed methods, and used for the photocatalytic reduction of Cr(?) under visible light. Results reveal that the specific activity of Bi OBr with different crystal planes follows {110} > {001}, which may be attributed to the surface energy and the surface atomic structure of different facets.2. Bi OX heterostructure photocatalysts were successfully synthesized by a facile hydrolysis method. The as prepared samples were characterized by SEM, XRD, BET and UV-vis DRS spectra. The photocatalytic activities of the Bi OX composites were evaluated by photocatalytic reduction of Cr(?) under visible light irradiation. Compared with pure Bi OX(X = Cl, Br, I), the composities of Bi OI/Bi OBr, Bi OI/Bi OCl, Bi OI/Bi OBr/Bi OCl show higher photocatalytic activities. Especially, Bi OI/Bi OCl and Bi OI/Bi OBr/Bi OCl exhibit better photocatalytic activities, the reduction efficiency could reach over 95% within 90 min. The enhanced photocatalytic activity performance was attributed to appropriate band gap, strong visible light assimilation and preferably high-efficiency transfer rate of the photogenerated electron-hole pairs in semiconductors.3.Bi OI plates, hollow micro-spheres, microspheres and random nanoplates were prepared and evaluated in the reduction of hexavalent chromium under visible light irradiation. Results reveal that Bi OI with high exposure of {110} facets exhibit higher photocatalytic performance for reduction of Cr(?) and the activity order of Bi OI with different morphologies follows: microspheres > hollow micro-spheres > plates > random plates.