多级笼铃结构Bi2WO6-CeO2纳米异质结可控制备及可见光催化降解氰化物性能研究

Most recently, a great deal of highly toxic cyanide is present in effluent water of several industries especially in chemical synthesis, mineral processing, electroplating and metallurgy, which is becoming a serious environmental problem. Therefore, cyanide must be destroyed or removed from wastewater prior to discharge. Visible light photocatalytic detoxification of cyanide is a sustainable method as it is driven by naturally available sunlight. However, the reports on visible light photocatalytic mineralization of cyanide are quite rare. The difficulty can be attributed to such reasons. The pKa of HCN is 9.3, and to avoid its volatilization, photocatalysis is to be carried out in a highly alkaline medium. This requires the photocatalyst to be stable in a highly basic medium. The carbon in the cyanide ion is more strongly bound to nitrogen than with atoms in dye molecules. Furthermore, the adsorption of the CN-1 on the photocatalytic surface becomes more difficulty with the increase of negative charge. Herein, photocatalytic removal of cyanide under visible light is still a great challenge. To solve these problems, we chose coupled Bi2WO6-CeO2 to demonstrate our concept and propose a facile generic solvent-induced-assembly strategy to prepare cage-bell nanostructured Bi2WO6@CeO2 heterojunction with high quantum efficiency, high surface areas, high stability, easy recycling and enhanced photocatalytic activity on detoxification of cyanide. The intrinsic ring-shaped microstructure makes multiple reflections of light within the chamber, allowing more efficient use of the light source compared with solid structure. The heterojunction effect can lead to enhanced charge separation and interfacial charge transfer efficiency due to the existence of an internal electric field. Therefore, it exhibits a remarkable photocatalytic detoxification of cyanide and degradation of dye under visible light. The formation mechanism of cage-bell Bi2WO6-CeO2 heterojunction with controlled morphologies and photocatalytic detoxification mechanism of cyanide are also thoroughly researched. The study will provide theoretical guidance and technical support for photocatalytic detoxification of cyanide by CeO2-based heterojunction materials under visible-light.

近年来随着化工、矿业、电镀、冶金等工矿企业的快速发展，产生大量含氰废水，导致氰化物水体污染日益突出。利用太阳能常温常压下可见光催化降解氰化物具有广阔的应用前景。然而，由于HCN的酸度系数（pKa）为9.3，为了避免挥发，光催化剂需要在强碱性环境下保持较好的稳定性；CN-中的C原子与N的结合力远远强于有机染料中C与N的结合力，更难分解；较高的负电荷量导致CN-吸附在催化剂表面的难度增大等问题。因此，可见光催化降解氰化物仍面临巨大的挑战。为解决上述问题，本研究结合异质结和新颖纳微结构的优势，采用溶剂诱导自组装技术合成具有高量子效率、大比表面积、稳定、易回收的多级笼铃结构Bi2WO6@CeO2纳米异质结可见光催化剂。深入探讨其可控合成机制及可见光催化降解氰化物机理。为CeO2类纳米异质结材料可见光催化降解氰化物提供理论指导和技术支持。

利用太阳能可见光催化还原氰化物及高价态的重金属Cr具有广阔的应用前景。然而，由于HCN的酸度系数（pKa）为9.3，为了避免挥发，光催化剂需要在强碱性环境下保持较好的稳定性；CN-中的C原子与N原子的结合力远远强于有机染料中C与N的结合力，更难分解；较高的负电荷量导致CN-吸附在催化剂表面的难度增大等问题。因此，可见光催化降解氰化物仍面临巨大的挑战。为解决上述问题，本研究结合异质结和新颖纳微结构的优势，分别合成了纳微中空核壳结构Bi2WO6-CeO2、CeO2@TiO2、自掺杂SnS、CeO2@g-C3N4可见光催化剂，对合成产物的相组成、形貌、结构进行了分析表征。在光照60 min内, CeO2@Bi2WO6可将CN-1从原来的4.78mM迅速降解到0.08mM，去除率高达98.3%；TiO2@CeO2在90 min内使得氰离子的浓度由初始的4.70 mM降至0.18 mM，降解率达到96.17%，这两个样品都表现出良好的可见光催化性能。同时采用比表面光电压、ATR-原位红外光谱、非原位XRD和拉曼技术分析样品的光催化机理。其高效降解的原因是此材料独特的内部中空结构使得光线多次反射，提高光能利用率，同时由于该材料异质结的存在使得电荷分离率和界面电子转换效率提高。上述研究为CeO2类纳米异质结材料可见光催化降解氰化物及高价态重金属Cr的还原提供了理论指导和技术支持。同时，深入研究了材料的形成机制与纳微结构控制原理；系统研究材料的合成条件、组成、形貌及微观结构与光催化性能的关系，为该类材料的研究开发提供实验和理论基础。