Photocatalytic degradation of rhodamine B by Bi2WO6 with electron accepting agent under microwave irradiation: Mechanism and pathway

Bi2WO6 was successfully synthesized by a facile hydrothermal method, and characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and BET. As a result, Bi2WO6 crystals displayed mainly square-plate-like morphologies with a short edge and the average crystalline size was in the range of 50-150 nm. Then microwave-assisted photocatalytic degradation of rhodamine B (RhB) using Bi2WO6 was investigated. The results illustrated that RhB (10 mg/L) was bleached effectively and the removal efficiency was about 94% in 60 min. Effect of electron accepting agent (air, H2O2) on the degradation efficiency of RhB was also examined. Degradation intermediates of RhB in the presence of H2O2 were identified by LC/MS/MS and GC/MS. All five N-de-ethylated intermediates were monitored by LC/MS/MS easily, and seven organic acids such as succinic acid, benzoic acid, adipic acid, 3-hydroxybenzoic acid, phthalic acid, etc., were also detected by GC/MS. The possible degradation mechanism of RhB in the presence of H2O2 included four processes: N-de-ethylation, chromophore cleavage, opening-ring and mineralization, which coexisted in microwave-assisted photocatalytic system. (C) 2008 Elsevier BY. All rights reserved.