Exploring a broadened operating pH range for norfloxacin removal via simulated solar-light-mediated Bi₂WO₆ process

Semiconductor photocatalysis can be operated over a narrow pH range for wastewater treatment. In this study, a simulated solar-light-mediated bismuth tungstate (SSL/Bi₂WO₆) process is found to be effective for norfloxacin degradation over a narrow pH range. To broaden the operating pH range of the SSL/Bi₂WO₆ process, an NH₄ ⁺ buffer system and an Fe³⁺ salt were introduced under extremely basic and acidic pH conditions, respectively. The NH₄ ⁺ buffer system continuously supplied hydroxyl ions to generate •OH radicals and prevented acidification of the solution, resulting in improved norfloxacin removal and mineralization removal under alkaline conditions. In contrast, the Fe³⁺ salt offered an additional homogeneous photo-sensitization pathway. The former treatment assisted in norfloxacin decay and the latter increased the collision frequency between the photo-generated hole and hydroxyl ions. Moreover, the effect of parameters such as pH and Fe³⁺ dosage was optimized.