Kinetic study on visible-light photocatalytic removal of formaldehyde from air over plasmonic Au/TiO2

Abstract

Previously, the kinetic of UV photocatalytic oxidation (PCO) of formaldehyde in air over anatase TiO2 films was reported [Chem. Eng. J. 279 (2015) 897–903]. In the present work, the kinetic of visible-light (VL, λ>420nm) PCO of HCHO over plasmonic Au/TiO2 in a single-pass continuous-flow reactor is studied. The Au/TiO2 activated by oxygen plasma (OP) sample is selected for the kinetic study by comparing with the sample activated by calcination. The effects of light intensity, humidity and HCHO initial concentration on induction period and HCHO conversion are investigated. Subsequently, the VL light intensity- and humidity-dependent rate constant of the first-order reaction, k(I, H)VL, is expressed quantitatively as a function of I and H and accordingly the inherent rate constant kVL and humidity impact factor fH are deduced. In low light-intensity (I) regime, the exponent n of I equals 1 and kVL=0.05cm2s−1mW−1. In medium and high I regimes, n equals 0.36 and 0, kVL equals 1cm2s−1mW−1 and 7s−1, respectively. The humidity impact factors equal 11.0, −15.4 and −0.1 and quantitatively express the strongly positive, strongly negative and slightly negative net effects on the VL PCO rate in the low, medium and high humidity regimes, respectively.