Mechanism of temperature-induced in-situ phase transition of BiOCOOH for regulating built-in electric field intensity in heterojunctions

The simultaneous removal of organic dyes and heavy metal ions from complex wastewater remains a formidable challenge due to the competitive redox requirements of different pollutants. In this work, we report a robust in-situ phase transformation strategy to construct a temperature-mediated S-scheme Bi 2 WO 6 /Bi 2 O 2 CO 3 heterojunction. By precisely modulating the hydrothermal temperature, the BiOCOOH phase was strategically transformed into Bi 2 O 2 CO 3 on the Bi 2 WO 6 surface, establishing an intimate interfacial contact. The resulting heterojunction induces a potent internal electric field (IEF), which dictates a high-efficiency S-scheme charge transfer pathway. This mechanism not only maximizes the spatial separation of photogenerated carriers but also preserves the powerful redox potentials of the individual components. Under visible light irradiation, the optimized BCW-2 catalyst exhibited exceptional performance, achieving near-complete removal of Rhodamine B (RhB) and Cr(VI) within 90 min, with reaction rate constants of 0.08911 min −1 and 0.06157 min −1 , respectively. Detailed experimental characterizations and density functional theory (DFT) calculations provided deep mechanistic insights into the band alignment and interfacial electronic behavior, confirming the S-scheme pathway. This study offers a transformative paradigm for the rational design of S-scheme heterojunctions with tailored redox capabilities for advanced environmental remediation.