The Study Off The Effects Of BiOl Morphologies On Their Ability And Mechanism To The Photocatalytic Oxidation Of Arsenic In Waste Water

As human’s activities become more frequent, the arsenic pollution in aquatic system is more serious. How to deal with the arsenic waste water is a problem we must deal with. In aqueous solution, the oxidation states of inorganic arsenic are trivalence and pentavalence, the former is more harmful to human health and more hard to remove by adsorption method. Therefore, it is important to preoxidate the As(Ⅲ) to As(V) before the succedent processing steps. Among various treatment methods which have been reported to transform As(Ⅲ) to As(Ⅴ), the photocatalytic oxidation of As(Ⅲ) has been considered as one of promising methods because of the low energy consumption, high efficiency, and low secondary pollution. Up to now, the photocatalysts used for oxidating of As(Ⅲ) reported in many literatures are TiO2-based materials. As we all know, the TiO2 has a fatal weakness that it can not absorb visible light which accounts for about half of the solar light energy because of its wide band gap. So, it is significant to develop stable and efficient photocatalysts which can absorb visible light in broad range, and use them in the process of photocatalytic oxidation of As(Ⅲ).As alternative photocatalyst, BiOI has recently been found to be a promising photocatalyst under visible light illumination due to its unique layered structure and high activity. The absorption band edge of BiOI can reach about 650 nm because of its low band-gap(1.77-1.92 eV), resulting in its large absorption range in visible light. Here in, we use four kinds of solvents with increasing viscosity, including water, ethanol, ethylene glycol and glycerol, to synthesize BiOI with tunable morpholorgies. All of the nanosheets are exposed (001) facets, and their thickness become more and more thinner as the viscosity of the used solvents is larger, which is beneficial for the seperation of photogenerated carriers. It is found that BiOI synthesized using glycerol has the best ability of removing arsenic from water, and the concentration of total arsenic(As(Ⅲ) and As(Ⅴ)) even can be decreased below 10 μg/L(national standard). On the other hand, we successfully synthesized BiOI hierarchitectures which is assembled by nanosheets with exposed (010) facets after adding NaOH to neutralize H+ generated during the rection. It is proved that the nanosheets which are exposed (001) and (010) facets show opposite charge. The nanosheets with exposed (001) facets exhibit better photocatalytic ability than (010) facets.The main innovation points about this paper show below:(1) The BiOI hierarchitectures with tunable morphologies have been synthesized by hydrothermal/solvothermal methods. (2) The thickness of the nanosheets with exposed (001) facets can be adjusted by changing the viscosity of the used solvents. (3) It is the first time to remove arsenic from water by using BiOI hierarchitectures, and the results are satisfactory. (4) The BiOI hierarchitectures which are assembled by nanosheets with exposed (010) facets have been successfully synthesized. It is proved that the nanosheets with exposed (001) and (010) facets have opposite charge and the former has better photocatalytic abilities.