Effect of the molecular structure and surface charge of a bismuth catalyst on the adsorption and photocatalytic degradation of dye mixtures

Abstract

[Bi₆O₆(OH)₃](NO₃)₃·1.5H₂O plates were prepared by a facile hydrothermal method. The effect of the pH value, hydrothermal temperature, reaction time, and concentration of Bi(III) ion and additives on the morphology and properties of the samples were investigated. The as-synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Brunauer–Emmett–Teller (BET) surface area and UV-vis diffuse reflectance spectroscopy (UV-DRS). It was found that under ultraviolet light irradiation (≤420 nm), the sample prepared at pH = 0.72 displays a higher photocatalytic activity than those prepared at higher pH values, which has been mainly ascribed to the promoted oxygen adsorption at low pH values. Moreover, we investigated the effects of the molecular structure and surface charge on the adsorption and photocatalytic degradation of dye mixtures (methyl orange (MO)–methylene blue (MB) and MO–rhodamine B (RhB)). The results show that in the MB–MO mixture, the adsorption and degradation of both MO and MB are promoted greatly by electrostatic forces; while in the RhB–MO mixture, the degradation of RhB is greatly reduced by MO due to competitive adsorption. These findings help us to understand degradation processes for real wastewater samples containing more than one pollutant.