Heterogeneous activation of peroxymonosulfate by supported cobalt catalysts for the degradation of 2,4-dichlorophenol in water: The effect of support, cobalt precursor, and UV radiation

In order to generate sulfate radicals (SRs) as oxidizing species for the degradation of 2,4-dichlorophenol (2,4-DCP) in water, we explored heterogeneous activation of peroxymonosulfate (PMS) by supported cobalt catalysts. More attention was given to the effect of support materials (Al₂O₃, SiO₂, TiO₂) and cobalt precursors (Co(NO₃)₂, CoCl₂, CoSO₄) on cobalt–support interaction, cobalt leaching, and reactivity of the catalysts. Especially, the feasibility of simultaneous generation of SRs and hydroxyl radicals (HRs) in PMS-Co/TiO₂ systems was first studied under ultraviolet (UV) radiation. Much lower cobalt leaching was observed in Co/Al₂O₃ and Co/TiO₂ systems than that of Co/SiO₂ most probably due to their relatively strong cobalt-support interaction. Co/TiO₂ catalyst prepared with Co(NO₃)₂, compared to CoCl₂ or CoSO₄ (where Cl⁻ and SO₄²⁻, respectively, were not completely removed upon heat treatment at 500 °C), showed strong cobalt–support interaction, and thereby exhibited negligible cobalt leaching. Under UV radiation, Co/TiO₂ at Co/Ti molar ratio of 0.001 showed significant improvement in the degradation of 2,4-DCP due to HRs. The effective generation of HRs in the system can be explained with Co(III)-mediated charge transfer from the photoinduced electrons to PMS, inducing facilitation of photoinduced electron-hole separation. However, high cobalt loading (i.e., Co/Ti molar ratio of 0.1) on TiO₂ surface exhibited negligible enhancement of 2,4-DCP transformation under UV radiation since the penetration of UV light to TiO₂ was prohibited by the cobalt.