Enhanced Adsorption of Sulfate Radicals through CaO-Induced D-Band Electron Modulation on Transition Metals

The sulfate radical (SO₄^•-) generated in the heterogeneous persulfate catalyzed oxidation system can be released into the bulk solution or adsorbed on the catalyst surface. The oxidation capacity of the surface adsorbed SO₄^•- is relatively mild, but this also gives it a longer life cycle and a stronger ability to resist the environmental interference, giving it more potential for practical sewage treatment. However, to date, there is still a lack of effective strategies to regulate its existence state. Herein, a series of MO-CaO (M = Cu, Co, Ni, etc.) catalysts were prepared by combining CaO with typical transition metal oxides for the purpose of activating peroxymonosulfate. Mechanistic investigations revealed that the strong electron coupling effect between CaO and Cu/Co significantly altered the electronic structure of the composite catalysts, causing a shift in the d-band center relative to the Fermi level. Specifically, compared to Co₃O₄-CaO (-2.401 eV), the d-band center of CuO-CaO (-1.870 eV) showed a more pronounced downward shift, significantly enhancing the chemisorption capacity for SO₄^•-. Additionally, the SO₄^•-adsorbed on the catalyst surface effectively avoids its accumulation in the reaction system and thus improves its utilization efficiency. This study affirms the viability of manipulating the adsorption characteristics of SO₄^•-onto the catalyst surface. Furthermore, it offers a pivotal strategy for modulating the adsorption dynamics of pertinent reactive oxygen species on the catalyst surface within heterogeneous persulfate reaction systems.