Electron-storing floating Z-scheme WS2-TiO2 nanotube heterostructures for round-the-clock photocatalytic degradation of bisphenol A

Conventional photocatalytic wastewater treatment is inherently constrained by its dependence on continuous irradiation, limiting its effectiveness under realistic day-night cycles. Herein, we present a multifunctional floating Z-scheme heterostructure that integrates interfacial charge engineering with electron storage capacity to achieve round-the-clock photocatalytic degradation of bisphenol A (BPA). A heterostructure composed of TiO2 nanotubes (TNT) and WS2 nanospheres was engineered to promote directional charge transfer via a Z-scheme pathway, while WS2 chalcogenide acts as an electron reservoir that enables reversible redox reactions in the dark. Immobilization onto a porous polyurethane scaffold (PUF) creates a floating triphase interface, enhancing photon capture and oxygen diffusion at the air-water boundary. The optimized WS2-TNT-1@PUF (1:1 wt ratio of photocatalysts) exhibited a high surface area (192 m2/g) and improved visible-light response (narrowed bandgap to 2.8 eV), achieving > 97% BPA degradation (initial concentration of 10 mg/L) within 60 min under simulated sunlight, following first-order kinetics (apparent rate constant of 0.069 min−1). Importantly, the system demonstrated electron storage capacity (1–1.8 μmol/h), sustaining around 89% degradation in the absence of light via delayed electron release. Photoelectrochemical analysis, EPR spectroscopy, and scavenger experiments confirmed a Z-scheme-mediated mechanism dominated by •O2- radicals, arising from electron accumulation in WS2 and subsequent discharge. The floating configuration further enabled photocatalyst recovery and stable activity over five cycles. This work represents the next generation of photocatalyst design that integrates Z-scheme heterostructures, electron storage, and floating triphase systems, providing a viable strategy to overcome solar intermittency and enabling energy-autonomous photocatalytic wastewater treatment.