Visible light-driven photocatalytic permanganate activation for efficient water purification

Permanganate (PM)-based advanced oxidation process (AOP) is a promising methodology for the efficient degradation of organic pollutants and water purification. Photocatalytic PM activation is an attractive strategy by using clean sustainable solar irradiation, but still faces great challenges in terms of energy source (i.e., ultraviolet light) and catalyst recovery. Here we report a visible light (VL)-driven photocatalytic PM activation strategy as a new platform technology that enables highly efficient degradation of organic pollutants by coupling PM oxidation with photocatalysis. This platform technology is compatible with a wide range of photocatalysts, refractory organic pollutants, pH conditions, and real-water systems. Using micron‑bismuth vanadate (BiVO₄) and ciprofloxacin (CIP) as the model catalyst and pollutant, a rapid and complete degradation of CIP was achieved within 7 min with an apparent rate constant of 0.52 min^-1, which was 40 and 9 times higher than those of the PM oxidation and VL-assisted PM oxidation processes, respectively. Physical, theoretical, and in situ spectroscopy investigations showed that the thermodynamically favorable adsorption of PM on BiVO₄ significantly enhanced the separation and utilization of photogenerated electrons, resulting in the concurrent formations of reactive manganese and oxygen species with the former as the primary oxidizing species, and hence contributed to the superior oxidation performance. This strategy achieves a synergy between PM oxidation and photocatalysis that can address their respective critical challenges. Importantly, a horizontal-flow photocatalytic reactor was designed that enabled a continuous degradation of CIP with water treatment capacity of 20 L h^-1 under outdoor solar irradiation. This study provides new insight into photocatalytic PM activation and offers a robust AOPs for water purification.