Enhanced Generation of Reactive Oxygen Species under Visible Light Irradiation by Adjusting the Exposed Facet of FeWO Nanosheets To Activate Oxalic Acid for Organic Pollutant Removal and Cr(VI) Reduction.

In this work, taking FeWO nanosheets as an example, the activation of oxalic acid (OA) based on facet engineering for the enhanced generation of active radical species was reported, revealing unprecedented surface Fenton activity for pollutant degradation. Density functional theory calculations confirmed the more efficient generation of reactive oxygen species over FeWO nanosheets with the {001} facet exposed (FWO-001) under visible light irradiation compared to the efficiency of FeWO nanosheets with the {010} facet exposed (FWO-010), which could be attributed to a higher density of iron and the efficient activation of OA on the {001} facet. The HO-derived OH tended to diffuse away from the active sites of FWO-001 into solution to favor the continuous activation of OA into the active radicals for pollutant redox reactions, but preferred to remain on FWO-010 to hinder the further activation of OA on the {010} facet. Additionally, the generation of CO endowed FeWO with a strong reduction ability. Compared with FWO-010, FWO-001 exhibited enhanced redox activity for the catalytic degradation of organic pollutants and Cr(VI) in the optimized conditions. These findings can help in understanding the facet dependent surface Fenton chemistry of catalytic redox reactions and in designing efficient catalysts for environmental decontamination.