“Frozen” π-π stacking on perylene diimide molecules induces oxygen vacancies synergistic activation of persulfate towards degradation of tetracycline

Oxygen vacancy-rich self-assembled perylene diimide (OV-SA-PDI) supramolecules were prepared via freeze-drying, which froze the molecular backbone by retaining π-π stacking to induce additional OVs. The OVs content on OV-SA-PDI (1.956 × 1013 spins·mm−3) was 1.9 times that of SA-PDI (1.029 × 1013 spins·mm−3) with vacuum drying. The photocatalytic performance of OV-SA-PDI was demonstrated to be excellent in activating persulfate (PS) to degrade tetracycline (TC), achieving a remarkable degradation efficiency of 94.6 % in 60 min under visible light (Vis). Mechanistic studies revealed a synergistic interaction among OV-SA-PDI, PS, and Vis to produce an abundance of active species. Vis activated a small portion of PS to produce •OH and SO4•−, whereas the photogenerated electrons generated by OV-SA-PDI directly cleaved the O-O bond to produce abundant SO4•−. Furthermore, the OVs acted as an electron trap to promote carrier separation and produced 10.0 μM 1O2 within 12 min. The active species were determined to decompose TC into low-toxicity products with lower molecular weights (m/z = 352, 340, and 227). This study presented a novel approach to the introduction of OVs into organic semiconductors and offered a mechanistic analysis of the synergistic relationship between defective organic semiconductors and sulfate radical-based advanced oxidation processes for wastewater treatment.