Visible-light activation of persulfate ions by Z-scheme perylene diimide/MIL-101(Cr) heterojunction photocatalyst towards efficient degradation of iohexol

Persulfate (PS) is widely used as an oxidant in sulfate radical-based advanced oxidation process for contaminants degradation. A novel Z-scheme perylene diimide (PDI)/MIL-101(Cr) (PM) heterojunction was fabricated via a one-pot process and employed for PS activation assisted with visible light. PDI self-assembly, surface Cr reduction, and heterojunction formation were achieved simultaneously. Under visible light irradiation, rapid degradation of iohexol (IOH) was realized by PS/PM-7 (PDI:MIL-101(Cr) = 9:7, w/w, 0.5 g/L) with reaction rate 8.8 times that of PDI/PS/Vis system. The radical quenching tests showed that h+ and •OH were perceived as the dominant contributors. According to experimental results and density functional theory calculation, IOH experienced oxidation, hydrolysis, deiodination, and hydrogen extraction reactions in the PM-7/PS/Vis system. The PM-7/PS/Vis system also demonstrated promising efficiency for IOH elimination either in treatment of real water body or irradiated by natural sunlight. The Z-scheme PM heterojunction possessed high charge-transportation efficiency with induced-electrons injected from the conduction band of MIL-101(Cr) to the valence band of SA-PDI. PS can be employed as a photogenerated electron acceptor to boost the migration of charge carriers and promote the production of more reactive oxygen species, thereby accelerating IOH oxidation. This work provides new perspectives into the synergistic effects between photocatalysis and PS activation, constructing an eco-friendly system for removal of organic pollutants.