Ni–Ca metastable–nonmetastable bimetallic sites induced ·OH directed generation and efficient water purification

Abstract

Strongly oxidizing ·OH can non-selectively degrade various organic pollutants, but how to selectively generate ·OH is a great challenge. In this study, the directed generation of ·OH was achieved based on Ni–Ca metastable–nonmetastable bimetallic sites, Ni²⁺/Ni³⁺ valence cycling provided electrons for ·OH generation induced by the non-variable Ca-based sites, which constructed a nearly 100% selective generation pathway of ·OH (O₃ → HO₃/HO₂ → OH). The antibiotic pefloxacin could be completely removed in 15 min, and the COD removal efficiency for other hard-to-degrade pollutants such as oxalic acid and chlorobenzoic acid could reach more than 90%. Ni doping significantly increased the oxygen vacancy and Lewis acid content, and DFT calculations showed that Ni–Ca dual-site had a lower reaction energy barrier and the complexed hydroxyl radical intermediate *OO had a higher spin density (−0.6), which was more favorable for the generation of ·OH. Therefore, this study provides new ideas for efficient treatment of actual wastewater.