Low-power visible LED driven persulfate-assisted degradation of phenolics using narrow-bandgap lanthanum perovskites

Abstract

Persulfate (PS, S₂O₈²⁻) based heterogeneous photocatalytic activation has sparked great scientific interest because of its effectiveness and environmental friendliness. Nevertheless, it remains a challenge to find low-energy consuming, environmentally acceptable light sources for PS activation that balance energy consumption and photocatalytic efficiency while providing more design flexibility for different kinds of photocatalytic reactors. Herein, a series of lanthanum perovskites (LaMO₃; M = Ni, Co, Cu, Fe) were synthesized, characterized, and evaluated for efficient degradation of phenolic compounds via PS activation using low power-consuming visible light-emitting diodes (LEDs) as a source of light. The effects of key influencing reaction parameters on degradation efficiency were thoroughly evaluated. In comparison to other perovskite catalysts, LaNiO₃ exhibited 98.4 % bisphenol A degradation efficiency with 69.3 % TOC removal within 50 min, owing to accelerated Ni²⁺/Ni³⁺ redox cycling, decreased rate of e⁻/h⁺ recombination, effective charge separation, and electron mobility. Additionally, over 91.0 % degradation efficiencies were maintained over a broad pH range (3.0–11.0), and for other phenolic compounds (phenol (95.8 %), 4-chlorophenol (85.7 %), and 4-nonylphenol (100 %)). Notably, the LaNiO₃/PS/Vis-LED system displayed excellent stability and reusability after five reuse cycles. Further, humic acid (HA) and inorganic ions have minimal negative effects on degradation efficiency. Radical quenching tests indicate that SO₄^•-, ^•OH, h⁺ and O₂^•- were dominant reactive species in the LaNiO₃/PS/Vis-LED system. These findings shed light on the treatment of phenolic polluted wastewater through persulfate activation and provide new approach for application of low-power consuming visible-LEDs in water treatment.