Enhanced degradation of organic water pollutants by photocatalytic in-situ activation of sulfate based on Z-scheme g-C₃N₄/BiPO₄

In recent years, the excellent performance of sulfate radical (SO₄·⁻) in advanced oxidation process has attracted more and more attention. However, it requires the consumption of expensive persulphate (PMS/PDS), and the resulting sulfate ion (SO₄²⁻) requires subsequent processing procedures, which limits its practical application value. In this work, a Z-scheme heterojunction g-C₃N₄/BiPO₄ (CNBx) photocatalyst was constructed to in-situ activate the residual SO₄²⁻, H₂O and dissolved O₂ in organic wastewater simultaneously and produce SO₄·⁻, ·OH and O₂·⁻ efficiently, so as to realize enhanced organic pollutant treatment by using clean and renewable solar energy resources. Under the condition of 10 mM SO₄²⁻ addition and 100 mW·cm⁻¹ illumination, the degradation rate of BPA (C₀ = 20 mg·L⁻¹) by optimized CNB₁₅₀ catalyst was 0.30 min⁻¹, which was 50% higher than that without SO₄²⁻ (0.20 min⁻¹). Detailed characterizations shown that a direct Z-scheme heterojunction was formed between g-C₃N₄ and BiPO₄, which could be simultaneously stimulated by light, and then effective charge separation and migration could be achieved through the internal electric field caused by the Fermi-level difference between the g-C₃N₄ (-0.12 eV) and BiPO₄ (0.01 eV). In general, this study makes full use of renewable solar energy and provides a feasible path for promoting the simultaneous in-situ utilization of small molecules (SO₄²⁻, H₂O and O₂) that originally exist in water, which makes organic wastewater treatment more economic, eco-friendly and sustainable.