Enhanced peroxymonosulfate activation for organic decontamination by Ni-doped δ-FeOOH under visible-light assistance

There is an urgent need for efficient and cost-effective methods without secondary pollution to decompose pollutants from contaminated water in the face of severe water pollution caused by the extensive use of synthetic dye in industry. In this work, Ni-doped δ-FeOOH was synthesized using co-precipitation method at room temperature and was applied as the catalyst in a visible-light-assisted peroxymonosulfate system for assessing its catalytic performance in RhB removal. An optimum RhB degradation of 99.5% was achieved after 30 min with the addition of 20 mg of PMS and 60 mg of isomorphic substituted δ-FeOOH at an initial pH value of 7. Through various characterization, degradation experiments and DFT calculation, the enhanced photocatalytic PMS performance of Ni-20 wt% doped δ-FeOOH compared to pure δ-FeOOH can be attributed to higher specific surface area and faster electron transfer, which resulted in the generation of more reactive oxygen species (ROSs), including SO₄^•-, ^•OH, O₂^•- and ¹O₂, all involved in the abatement of RhB. The possible RhB degradation pathways were inferred based on intermediates detected by liquid chromatograph-mass spectrometer (LC-MS), combined with Fukui indices and the analysis of bond lengths. The toxicity of the intermediates was evaluated using T.E.S.T. software, which proved that the system could effectively reduce the biotoxicity of the parent pollutant RhB.