Enhanced Photocatalytic Drug Degradation via Nanoscale Control of Bismuth Molybdate

As a visible light-responsive photocatalyst with a unique structure, the development of bismuth molybdate (BMO) materials for the efficient degradation of pollutants has attracted considerable attention. In this work, BMO materials with molar Bi/Mo precursor ratios between 1.1:1 and 3.0:1 were synthesized by a solvothermal process using ethylene glycol as a solvent and subsequently calcined. To investigate the influence of this ratio on the structural, textural, and optical properties of the BMO materials, they were comprehensively characterized using complementary methods. The characterization results showed that the Bi/Mo ratio had no influence on the size of the spherical microstructure formed; however, it significantly affected the shape of the Bi2MoO6 nanostructure that builds the microstructure. In addition, at Bi/Mo ratios of 2.3:1 or higher, a heterojunction is formed, consisting of irregularly shaped Bi2MoO6 nanoplates and a Bi-rich phase with low Mo content. To assess the performance of the BMO materials, the model substances diclofenac sodium (DCF) and ciprofloxacin (CIP) were photocatalytically degraded by irradiation with blue LED light (λmax = 467 nm). For BMO synthesized with a Bi/Mo ratio of 2.3:1 or higher, improved degradation and mineralization performance were observed. Within 180 min, 98% of the DCF was degraded, and the TOC content decreased by 80%. CIP was completely degraded during this period, and mineralization reached 44%. The boosted photocatalytic performance is attributed to the close contact between Bi2MoO6 and the Bi-rich BixMoyOz phase, which creates an internal electric field, leading to improved charge transfer efficiency and suppressed photoelectron–hole recombination. Finally, experiments in recirculation mode were carried out to evaluate the photocatalytic stability of the synthesized BMO catalyst.