In situ DRIFT and kinetic studies of photocatalytic degradation on benzene vapor with visible-light-driven silver vanadates

The visible-light active silver vanadates with different types of crystallines (Ag4V2O7 and Ag3VO4 phases) were synthesized by an environmentally friendly aqueous process. The parameters of hydrothermal temperature and hydrothermal time were tuned to maximize the photocatalytic efficiency for the decomposition of benzene vapor under visible-light irradiation. The quantum efficiencies of the photocatalysts are compared on the basis of the crystalline phases, surface area, intensity of surface hydroxyl groups, and Bronsted acid sites. From the results of DRIFTS studies, the photocatalytic activities strongly depend on the intensities of the Bronsted acidity and hydroxyl groups presented on the silver vanadates. The sample synthesized at 140 degrees C and 4 h (HM140) exhibits the best photocatalytic activity: it has a reaction rate constant (k(app)) of 1.42 min(-1), much higher than that of P25 (k(app) = 0.13 min(-1)). For an irradiation time of 720 min, the mineralization yields of benzene were 48% and 11% for HM140 and P25, respectively. Based on the short-term decrease of benzene concentration and the long-term increase of CO2 concentration, the photocatalytic ability of the HM 140 sample is significantly superior to that of P25. The highest activity can be attributed to the synergetic effects of the richest Bronsted acid sites, and a favorable crystalline phase combined with abundant surface hydroxyl groups. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.