Enhanced visible-light photocatalytic activity to volatile organic compounds degradation and deactivation resistance mechanism of titania confined inside a metal-organic framework.

Poor visible-light-driven activity and deactivation property as well as wide band gap of the most common TiO2 photocatalyst significantly limits its practical application in volatile organic compounds (VOCs) purification. In this study, tiny TiO2 nanoparticles incorporated into a typical metal-organic framework (MOF), NH2-UiO-66, with controllable TiO2 content and size, were synthesized based on the hard-soft acid-base (HSAB) principle and applied to VOCs purification. Compared to bare TiO2, the TiO2@NH2-UiO-66 composites could extend the optical absorption to the visible light range and accelerate the photogenerated electrons-holes separation, due to the excellent interface contact between TiO2 and NH2-UiO-66. Moreover, the abundant interconnected 3D cavities of the outer MOF allowed for VOCs to easily diffuse into the pores, producing a concentration microenvironment around the encapsulated TiO2. The TiO2@NH2-UiO-66 composites exhibited a markedly improved photocatalytic efficiency and a good resistance to deactivation during the photocatalytic degradation of gaseous styrene under visible light illumination, which were associated with the synergetic effects between the TiO2 and MOF. The TiO2@NH2-UiO-66 with 5 wt% TiO2 could efficiently mineralize styrene to CO2 to some extent companying with the removal ratio >99% within 600 min, whereas the removal efficiency over the bare TiO2 only 32.5%.