Novel CS/MIL-53(Fe)/CdS type-II heterojunction with improved charge transfer: Mechanistic insights, photocatalytic activity, and toxicological evaluation

Semiconductor heterostructures play a vital role in accelerating the transfer and separation of interfacial charges, resulting in enhanced photocatalytic ability. In this study, we designed a MIL-53(Fe)/CdS type-II heterojunction on charcoal sponge (CS) with large macroscopic area, excellent mechanical properties, and high photocatalytic activity. CS/MIL-53(Fe)/CdS demonstrated a broad light absorption range (200-800 nm) and enhanced transfer efficiency of carriers. Notably, CS/MIL-53(Fe)/CdS displayed exceptional removal efficiency of Cr(VI) (92.7 %) compared to CS/MIL-53(Fe) (76.9 % Cr(VI)) or CS/CdS (60.1 % Cr(VI)) through the photocatalytic reaction. CS/ MIL-53(Fe)/CdS achieved its maximum degradation efficiency of 92.5 % for tetracycline (TC) at pH= 11 with 5 mM H2O2. Moreover, CS/MIL-53(Fe)/CdS still achieved good removal efficiency for wastewater containing both Cr(VI) and TC (TC with Cr(VI) (83.8 %), Cr(VI) with TC (83.1 %)). Toxicity tests proved that CS/MIL-53 (Fe)/CdS has no inhibitory effect on the growth and egg-laying quantity of the snails implying environmental safety. Combining density functional theory (DFT) and radical capture tests, the possible mechanism of MIL-53 (Fe)/CdS type-II heterojunction was proposed. The above results show that CS/MIL-53(Fe)/CdS is expected to be applied to actual wastewater treatment.