Decolourization of rhodamine B and methylene blue dyes in the presence of bismuth tungstates: a detailed investigation on the effect of grain size

Abstract

Solid-state reaction method was opted for the preparation of bismuth tungstates (Bi2WO6) in the stoichiometric ratio. The structural characterization related that the material has got orthorhombic symmetry. The high-energy ball milling did not show any structural change, but a reduction in grain size was observed from 100 to 34 nm after 5 h. The higher activity for the decolourization of rhodamine B (RHB) and methylene blue (MB) in the presence of UV light has been studied by employing Bi2WO6 as a catalyst. The dye degradation was observed by a decrease in the absorption spectrum and decolourization in the presence of UV irradiation. The degradation efficiency was found to be dependent on the size of the catalyst added in the dye solution, which may be due to increased surface area that increased the number of active sites for the reaction. The degradation efficiency of the unmilled and 5-h ball milled (Bi2WO6) catalyst was observed to be 32 and 90% in RHB, respectively. While in MB, 24 and 49% degradation efficiency was achieved by unmilled and 5-h ball milled (Bi2WO6) catalyst. The degradation rate coefficient was found to be in the decreasing order of RHB > MB, which pursued the first-order kinetic mechanism. Therefore, Bi2WO6 can act as a catalyst for the treatment of noxious and imperishable organic pollutants in water.