Long-Term Interfacial Fouling of g-C3N4 in Complex Aquatic Environments: Evolution, Photocatalytic Deactivation, and Activity Recovery

Abstract Long-term fouling of photocatalysts in complex aquatic environments remains poorly understood, despite its importance for wastewater treatment. This study systematically investigated the temporal variation of photocatalytic activity of g-C3N4 after long-term exposure to real wastewater systems and single background components without external light sources. The maximum fouling efficiencies reached 63.5%, 28.8%, and 56.3% in real wastewater, humic acid (HA), and algal suspension systems, respectively. Beyond interfacial adsorption fouling, background components coexisting in a free state were also found to influence the photocatalytic activity of g-C3N4. Sequential cleaning showed that NaCl washing achieved the highest activity recovery, followed by NaOH and urea washing, indicating that electrostatic adsorption, biofouling, and organic-layer coverage may jointly govern fouling formation. During early stage fouling, biologically derived organic components may preferentially accumulate and thereby facilitate the subsequent codeposition of HA and other organic constituents, ultimately contributing to the formation of a stable composite fouling layer. The novelty of this study lies in decoupling persistent interfacial fouling from the transient effects of coexisting constituents and in further elucidating the dynamic evolution of photocatalyst fouling in complex aquatic environments. The study can provide theoretical guidance for the development of photocatalyst with high activity and long-term antifouling performance.