Visible-light-activated photocatalytic degradation of rhodamine B using WO3 nanoparticles

Semiconductor photocatalysis is touted to be one of the most efficient and cost-effective methods of degrading organic pollutants in various water matrices. Herein, highly agglomerated WO3 nanoparticles were synthesized via a facile acid precipitation method and tested on rhodamine B dye as the model pollutant. The physicochemical properties of the particles were investigated using various characterization techniques which include X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) and zeta potential measurements. The effects of calcination temperature, initial pH, catalyst loading and initial pollutant concentration were investigated. The results showed that under optimum conditions of 300 degrees C calcination temperature, 5 g L-1 catalyst loading, 5 ppm initial pollutant concentration and a pH of 9.5, the catalyst achieved an excellent degradation efficiency of 96.1% after 4 h of visible light irradiation. The degradation tests revealed a strong dependence on initial pH with acidic pHs favouring adsorption and alkaline pHs favouring photocatalysis. The degradation kinetics followed the Langmuir-Hinshelwood model for catalyst loadings of less than 10 g L-1, which typically describes heterogenous photocatalytic surface reactions. Scavenging experiments revealed that reactive superoxide and hydroxyl free radicals were the primary drivers for rhodamine B dye degradation.