基于酸式固态杂多酸可见光催化协同消减重金属离子/有机污染物的复合体系设计与调控

High efficiency of Cr (VI) reduction by TiO2 photocatalysis was limited by low pH, and the reduced product Cr(III) which easily deposited on the catalyst surface led to decreased life time of catalyst. On the basis of our preliminary studies, the present project will choose acidic and solid-state polyoxometalates (POMs) instead of TiO2, using dye as visible light absorbing material, combined with metal ions Mn+ with variable valence state (M: Fe, Cu, Ag, and etc.) as surface modifiers, a multiple composite system containing dye/POMs/Mn+/Cr(VI) will be established. The electron tranferring pathway will be regulated by Mn+/M(n-1)+ cycling. When Cr(VI) coexisting with different organic pollutants, the fate of dye (degradation or stable) can be controlled by regulating reactive atmosphere (aerobic or anaerobic). Finally, the synergistic reduction of Cr(VI) and degradation of coexisting organic pollutants will be achieved in weakly acidic/neutral conditions using visible light as driving force. We will focus on investigating the methods to keep micro-region acidity of polyoxometalates. The regulatory law of Mn+ on the photocatalytic activity as well as inhibited adsorption of Cr(III) will be explored. Finally, the problem of catalyst deactivation will be solved. Development and optimization of the present photocatalytic system will provide a new, viable design principles and technical support for the remediation of actual Cr (VI)/organic mixed pollution.

TiO2光催化还原Cr(VI)时，高反应活性受限于低pH、催化剂表面易沉积产物Cr(III)致寿命缩短。本课题在前期研究基础上，提出以酸式固态杂多酸替代TiO2，以染料为吸光物质，辅以Mn+（Fe3+、Cu2+、Ag+等）为修饰剂，构建染料/杂多酸/Mn+/Cr(VI)多元复合体系。利用Mn+/M(n-1)+变价循环，调控电子传输路径；针对共存有机污染物的不同，调节反应气氛（有氧/厌氧），控制染料的归宿（降解/稳定），实现可见光驱动、弱酸性/中性条件下高效还原Cr(VI)协同降解有机污染物。将重点研究杂多酸微区域酸性的保持方法；探索Mn+、染料对光催化活性的调控规律，及对产物Cr(III)吸附的抑制作用，解决催化剂易失活的难题。该体系开发和完善为实际Cr(VI)/有机物复合污染水体的修复提供了新的、可行的设计原理和技术支撑。

针对重金属离子与有机污染物共存的难题，本研究重点发展可见光下能高效运作的固态杂多酸（POM）基催化剂，实现Cr(VI)还原和有机污染物协同降解。（1）以磷钨杂多酸盐为基础，构建能在可见光照射下高效、稳定处理含Cr(VI)印染废水的复合体系。研究发现：以K+为对离子的POM表面修饰适量的Fe3+不仅能抑制产物Cr(III)吸附、提升催化剂循环使用寿命，还能通过Fe3+/Fe2+循环调控电子转移途径，促进染料和Cr(VI)的协同消减。此外，氧气/活性氧是单电子转移条件下染料开环的必要条件。催化剂的比表面积相对于催化剂的结晶度在本体系中占主导作用；染料、催化剂、Cr(VI)三者之间的良好接触是高效电子转移的前提；电子从POM到Cr(VI)的转移是限速步骤。进一步，对固态杂多酸铯盐改性，制备的Au/CsxH3-xPW12O40、Cs3P12Mo40/Bi2O3均能在可见光照射下实现Cr(VI)和有机污染物（染料、苯酚、EDTA等）的协同消减。（2）以磷钼杂多酸银盐AgPMo为基础，结合Ag3VO4、Ag3PO4制备了多元复合可见光催化剂。AgPMo的导带电子被复合物传递，避免Ag+原位还原，解决银系催化剂的稳定性难题。进一步原位紫外还原得到Ag plasma，显著提升可见光吸收、增加热电子浓度。以含Cr(VI)废水为污染物，考察复合光催化剂的可见光催化活性。结果表明：Ag@Ag3VO4/AgPMo对Cr(VI)的还原速率约是AgPMo的16倍，具有良好的循环使用稳定性。以Ag3PO4取代Ag3VO4，复合催化剂的可见光催化性能进一步提升，是AgPMo体系的29倍。导致这一差别的原因是恰当的导带、价带位置有利于HO•和O2•–的生成，光生电子-空穴对更易于生成和分离、电子转移阻力降低。（2）以Fe3+为对离子，实现磷钨酸、硅钨酸、磷钼酸的非均相化，制备了不同铁基杂多酸盐光催化剂（FePMo、FePW、FeSiW）。近中性条件下FePMo具有最优的、稳定的光催化还原Cr(VI)活性。进一步将FePMo负载在金属有机框架Fe-MOF表面，通过增大比表面积来提升光催化性能。其中，FeSiW/Fe-MOF异质结具有最佳的光催化活性。此外，发展了多种新型可见光催化剂/电极（3D Bi2O3-BiOI、Fe2O3-GQDs/NF-TiO2、AgI/TiO2-NTs、AgI/Bi2O3-B