Fabrication of UiO-66-(OH)2/MnO2-TiO2 composites for use in combined adsorption and efficient visible-light-driven photocatalytic degradation of gaseous formaldehyde

Photocatalysts UiO-66-(OH) 2 /MnO 2 -TiO 2 with intimate contact interfaces were successfully synthesized by impregnation methods and all of the composites were characterized by a variety of analytical techniques. The results indicated that MnO 2 and TiO 2 form a heterojunction and tightly attached to the surface of UiO-66-(OH) 2 , the generation of MnO 2 -TiO 2 heterojunction improved the catalyst electron-hole separation efficiency, and there was a strong electronic interaction between MnO 2 -TiO 2 and UiO-66-(OH) 2 in the composite. The synergistic combination of high adsorption capacity of UiO-66-(OH) 2 , and efficient interfacial charge transfer between UiO-66-(OH) 2 and MnO 2 -TiO 2 have a significant impact on the enhanced photocatalytic performance for formaldehyde removal. Meanwhile, the hydroxyl radicals (·OH) and superoxide radicals (·O 2 - ) also play a major role in removal of formaldehyde. The formaldehyde removal rate of 70UO/MnO 2 -TiO 2 (1 g 0.15 m 3 ) in self-made closed system under high pressure mercury lamp irradiation is 88.19 % within 5.5 h, if the removal time is extended to 24 h, the formaldehyde removal rate can reach 95.19 %, and the continuous photocatalytic reaction showed that the composite is a highly stable catalyst.