Sustainable degradation of bisphenol A using a pH-responsive TiO₂/g-C₃N₄/rGO photocatalyst with easy recovery

Bisphenol A, a widespread and potent endocrine disruptor in aquatic environments, poses significant health risks, emphasizing the need for advanced photocatalysts to effectively remove this contaminant from water while enabling easy and cost-effective recovery for repeated use. Accordingly, this study presents the development of such a material by combining titanium dioxide (TiO₂) nanoparticles, graphitic carbon nitride nanoflakes (g-C₃N₄), and reduced graphene oxide (rGO) nanosheets. Subsequent dip-coating of the ternary composite with a rationally designed diblock polymer enables its surface wettability to switch from hydrophilic to hydrophobic depending on the pH of the reaction medium. Due to the synergistic effects of TiO₂ (strong oxidative potential), g-C₃N₄ (moderate bandgap for visible light absorption), and rGO (high electron mobility), the TiO₂/g-C₃N₄/rGO composite exhibits superior textural, optical, and electrochemical properties, thereby promoting efficient photocatalytic activity. Additionally, the pH-responsive wettability improves interaction with bisphenol A in acidic conditions and facilitates composite recovery by inducing aggregation under alkaline conditions. Notably, under optimal conditions, the ternary composite with the appropriate TiO₂ content achieved 95.6 % degradation of bisphenol A within 180 min under visible light. Mechanistic studies indicated that superoxide anions and hydroxyl radicals were primarily responsible for the dissociation of bisphenol A. The composite also demonstrated excellent reusability, maintaining its remarkable photocatalytic capabilities over multiple cycles. Furthermore, TiO₂/g-C₃N₄/rGO showed promising performance in degrading bisphenol A across various real water matrices, with degradation efficiency ranked as follows: tap water > river water > municipal wastewater. This work highlights the importance of developing photocatalysts with switchable surface characteristics to realize their practical applications in wastewater treatment and related fields.