Photodegradation of sulfamethazine in an aqueous solution by a bismuth molybdate photocatalyst

Abstract

The objective of this study was to synthesize bismuth molybdate (Bi₂MoO₆) nanostructures with different morphologies for potential application in the removal of sulfamethazine (SMZ) from wastewater. Bismuth molybdate nanostructures were synthesized via a simple hydrothermal route followed by calcination. The nanosheet and microsphere morphologies of the Bi₂MoO₆ obtained were controlled by adjusting the pH value of the reactants. The solids were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), Raman spectroscopy, N₂-Brunauer–Emmett–Teller and UV–vis DRS methods. The optimal catalyst with the best photocatalytic performance was determined by batch experiments. The Langmuir–Hinshelwood kinetic model was employed to examine the heterogeneous photocatalysis reaction. The results indicated that the photocatalyst was very effective for SMZ photodegradation under solar light irradiation and that the photolysis followed pseudo-first order kinetics. The catalyst with the optimal photocatalytic performance could be obtained by controlling the precursor pH value, and the nanocrystalline morphology of the Bi₂MoO₆ played an important role in determining its catalytic activity. The main reactive species involved in the photocatalytic degradation of SMZ were identified, showing that superoxide radicals and holes were mainly responsible for the SMZ photodegradation by Bi₂MoO₆. Five reaction intermediates/products were observed and identified by gas chromatography–mass spectrometry (GC–MS) analysis, and a tentative reaction pathway was proposed. Toxicity tests further confirmed that the toxicity of the initial SMZ solution was efficiently eliminated during this photocatalytic process.