Synergistic enhancement of bisphenol A photodegradation by BiOCl via nitrite-induced charge separation and reactive oxygen species generation: A dual role for nitrite in pollutant degradation and transformation

Bisphenol A (BPA), a significant endocrine disruptor, can be efficiently degraded via photocatalysis. However, when applying photocatalytic technology for BPA degradation in wastewater or contaminated water remediation, photosensitive ions present in the aqueous matrix may interfere with the process. Nitrite (NO 2 − ), a common photosensitive ion in aquatic environments, was investigated for its effect on BPA degradation using bismuth oxychloride (BiOCl) photocatalysts. We elucidated the nonlinear regulatory role of this ubiquitous ion within the BiOCl photocatalytic process. The BiOCl/NO 2 − synergistic system revealed that trace NO 2 − regulates the dynamics of photogenerated carriers through two distinct pathways. First, NO 2 ⁻ acts as an efficient electron donor, which suppresses the recombination of photogenerated holes (h⁺) and thereby enhances the generation of superoxide radicals (O 2 •- ) and singlet oxygen ( 1 O 2 ). Second, NO 2 ⁻ serves as a reaction substrate that is oxidized by h⁺ to form highly reactive nitryl radicals (•NO 2 ). The attack of •NO 2 radicals on BPA diverted the conventional degradation pathway, forming nitrated byproducts. Furthermore, the introduction of NO 2 − enhanced the spatial separation of photogenerated charges and synergistically boosted redox activity, while simultaneously converting the highly toxic NO 2 ⁻ into harmless NO 3 − . These findings provide valuable insights for applying BiOCl photocatalysts in real water remediation scenarios where NO 2 − is present.