Boosting the photocatalytic degradation of ethyl acetate by a Z-scheme Au–TiO2@NH2-UiO-66 heterojunction with ultrafine Au as an electron mediator

Abstract

TiO₂ based photocatalytic oxidation has been regarded as a promising technology for VOC removal, although it remains challenging in view of the limited visible light response and low photogenerated charge separation efficiency. Herein, a charge space separated Z-scheme Au–TiO₂@NH₂-UiO-66 photocatalyst was synthesized for highly efficient degradation of VOCs by encapsulation of Au and TiO₂ into visible light responsive NH₂-UiO-66 with Au nanoclusters as electron mediators. The obtained Au–TiO₂@NH₂-UiO-66 nanocomposite could broaden the light absorption of TiO₂ from the UV to visible region due to the excellent localized surface plasmon resonance of Au nanoclusters confirmed by UV-vis diffuse reflectance. Furthermore, electron paramagnetic resonance, photoelectrochemical measurements, steady-state PL spectra and time-resolved PL spectra unveil that the Au–TiO₂@NH₂-UiO-66 ternary photocatalyst followed the Z-scheme mechanism and the ultrafine Au on this heterojunction as an electron mediator can significantly accelerate photogenerated electron transfer. Due to the enhanced interfacial electron transfer by the Au electron mediator and high redox abilities of photogenerated carriers in the Z-scheme heterojunction, the Au–TiO₂@NH₂-UiO-66 nanocomposite greatly boosted the separation efficiency of photogenerated electron–hole pairs, thus producing abundant strong oxidative species, including photogenerated holes, ˙O²⁻ and ˙OH radicals, to mineralize VOCs. Impressively, the mineralization efficiency reached 85% at 94.6% ethyl acetate degradation over the 1 wt% Au–TiO₂@NH₂-UiO-66 photocatalyst within 360 min of xenon lamp irradiation, which was 12.1, 10.6 and 2.83 times higher than that of TiO₂, NH₂-UiO-66 and TiO₂@NH₂-UiO-66, respectively. This work would provide a valuable guideline in the synthesis of highly efficient visible light responsive photocatalysts for VOC degradation.