Regulating Singlet Oxygen Generation via a Z-Scheme IEF-11/TiO2 Heterojunction for Degradation of Phenolic Pollutants

Abstract Photocatalytic technology has emerged as a promising strategy for the treatment of phenolic contaminants in wastewater. Upon light irradiation, it produces highly reactive oxidative species, which can promote the significant mineralization of pollutants. Herein, Ti-MOF (IEF-11) nanoparticles were uniformly anchored to layered TiO2 nanosheets via a hydrothermal strategy, forming an IEF-11/TiO2 heterojunction with enhanced photocatalytic activity. The optimized composite with 3.0 wt % IEF-11 exhibits excellent visible-light-driven degradation efficiencies of 92.8%, 80.4%, and 83.5% toward phenol, 4-chlorophenol, and 2,4-dichlorophenol, respectively. The corresponding apparent reaction rate constants were 5.91, 6.46, and 4.54 times those of pristine TiO2. Reactive species trapping experiments identify singlet oxygen (1O2) and photogenerated holes (h+) as the dominant active species. Mechanistic investigations indicate that a Z-scheme heterojunction forms between IEF-11 and TiO2, which not only accelerates the efficient separation and migration of photogenerated charge carriers but also retains strong redox capacities. This favorable structure promotes the generation of 1O2 and enhances photocatalytic performance. Recycling experiments confirm the composite’s high cycling stability. Moreover, the degradation pathways of the three phenolic contaminants were systematically elucidated using high-performance liquid chromatography–mass spectrometry (HPLC-MS), and a plausible photocatalytic degradation mechanism was proposed.