Metallic Active Sites on MoO₂(110) Surface to Catalyze Advanced Oxidation Processes for Efficient Pollutant Removal

Advanced oxidation processes (AOPs) based on sulfate radicals (SO₄^⋅-) suffer from low conversion rate of Fe(III) to Fe(II) and produce a large amount of iron sludge as waste. Herein, we show that by using MoO₂ as a cocatalyst, the rate of Fe(III)/Fe(II) cycling in PMS system accelerated significantly, with a reaction rate constant 50 times that of PMS/Fe(II) system. Our results showed outstanding removal efficiency (96%) of L-RhB in 10 min with extremely low concentration of Fe(II) (0.036 mM), outperforming most reported SO₄^⋅--based AOPs systems. Surface chemical analysis combined with density functional theory (DFT) calculation demonstrated that both Fe(III)/Fe(II) cycling and PMS activation occurred on the (110) crystal plane of MoO₂, whereas the exposed active sites of Mo(IV) on MoO₂ surface were responsible for accelerating PMS activation. Considering its performance, and non-toxicity, using MoO₂ as a cocatalyst is a promising technique for large-scale practical environmental remediation.