Regulation of Lewis acid sites on ZnO/SiW₁₁Co for tunable photocatalytic activity toward water remediation

The function of surface acidity in catalytic reactions has been well studied in the field of conventional catalysis, nevertheless, regulating surface acidic sites and unveiling its roles during heterogeneous photocatalysis has been less frequently reported. To address this issue, we constructed a novel heterojunction photocatalyst of ZnO/SiW₁₁Co with abundant Lewis acid sites for wastewater treatment. Under visible light irradiation, the optimal ZnO/SiW₁₁Co was found to have the highest photocatalytic activity, achieving a degradation efficiency of 97.7% for Rhodamine B (RhB), 96.1% for tetracycline (TC), and 91.4% for methyl orange (MO). The RhB removal rate remained at 91.3% even after five cycles, indicating excellent stability and practicality of ZnO/SiW₁₁Co. By compositing with SiW₁₁Co, a typical polyoxometalates with unique super acid properties, ZnO/SiW₁₁Co formed plentiful surface Lewis acid sites, as confirmed by the pyridine adsorption FT-IR and NH₃-TPD. The as-formed Lewis acid sites could provide more active sites, making it easier for reactants to coordinate to the photocatalyst surface, which reduced the activation energy of photocatalytic reactions and accelerate RhB removal. Density functional theory (DFT) calculations unveiled the redistribution of electron-hole pairs, optimizing the light absorption and charge separation efficiency, which obeyed a Z-scheme mechanism. Combined active species capture experiments and electron spin resonance, •O₂⁻, h⁺, and •OH were the main active substances for the photocatalytic degradation of RhB. Besides, the possible degradation pathways for RhB were analyzed using liquid chromatography-mass spectrometry (LC-MS). The work provided useful strategy for the design of high-performance photocatalysts via regulating surface Lewis acid sites toward water remediation.