Single-step solvothermal process for synthesizing SnO2/Bi2WO6 composites with high photocatalytic activity in the photodegradation of C.I. Reactive Red 2 under solar light

Abstract

Bi2WO6 (BW) and SnO2/Bi2WO6 composites (SnBWs) were synthesized by a single-step solvothermal process. Four SnO2/BW molar ratios, 0.1, 0.25, 0.5 and 1 were used to generate 0.1SnBW, 0.25SnBW, 0.5SnBW and 1SnBW. The surface characteristics of BW, SnO2 and SnBWs were elucidated by X-ray diffractometry (XRD), transmission electron microscopy, specific surface area analysis, UV–vis spectrophotometry, photoluminescence spectrophotometry and X-ray photoelectron spectroscopy. C.I. Reactive Red 2 (RR2) was used as a target pollutant to compare the photocatalytic activities of the prepared SnBWs. The effects of RR2 concentration and photocatalyst dosage on RR2 photodegradation were elucidated. The XRD results revealed that all of the peaks of SnBWs in XRD patterns could be assigned to SnO2 or BW, and no other peak was found, indicating that SnO2 and BW were successfully composited. The band gaps of SnO2, BW, 0.1SnBW, 0.25SnBW, 0.5SnBW and 1SnBW were estimated to be 3.75, 2.85, 2.95, 2.94, 2.93 and 2.97 eV, which correspond to RR2 photodegradation rates under simulated solar light irradiation of 0.0025, 0.0255, 0.0333, 0.0279, 0.0408 and 0.0174 min−1. 0.5SnBW had the highest photocatalytic activity in RR2 photodegradation. The RR2 photodegradation rate increased as the 0.5SnBW dose increased, but decreased as the RR2 concentration increased. The results of adding scavengers suggested that the photogenerated holes were the main oxidative species in RR2 photodegradation in the 0.5SnBW system. The findings of this study suggest that the effective suppression of the recombination of electron–hole pairs in 0.5SnBW may improve the photocatalytic activity of 0.5SnBW over those of pure BW and SnO2.