Efficient elimination of tetracycline hydrochloride by polydopamine-decorated CoFeS2 activated peroxymonosulfate

Abstract

In this study, polydopamine-decorated CoFeS₂ (PDA@CoFeS₂) was successfully synthesized for activating peroxymonosulfate (PMS) to remove tetracycline hydrochloride (TCH). SEM, EDS, XRD, FT-IR, XPS and EPR were employed to characterize the PDA@CoFeS₂ composite. The PDA@CoFeS₂ composite displayed XRD diffraction peaks similar to CoFeS₂, but with reduced peak intensity. SEM results indicated that CoFeS₂ particles were adhered and wrapped by PDA. The XPS analysis suggested that Co²⁺ and Fe²⁺ on the catalyst surface reacted with PMS to generate reactive oxygen species, and itself was oxidized to Co³⁺ and Fe³⁺. Meanwhile, the low-valence sulfur (S²⁻, S₂²⁻ and S_n²⁻) could achieve the redox cycles of Co³⁺/Co²⁺ and Fe³⁺/Fe²⁺. The influence factors including catalyst dose, PMS concentration, initial pH, initial TCH concentration and reaction temperature on the elimination of TCH in the PDA@CoFeS₂/PMS system were systematically investigated. The results showed that PDA@CoFeS₂ had better catalytic performance compared with CoFeS₂, and the degradation effectiveness of TCH (15 mg/l) was 96.0% and the elimination efficiency of total organic carbon (TOC) was 49.6% in 90 min under the optimal conditions ([PDA@CoFeS₂]₀ = 45 mg/L, [PMS]₀ = 1.0 mM and pH = 5.3). Electron paramagnetic resonance (EPR) analyses and reactive oxygen species (ROSs) capture experiments confirmed that ROSs such as SO₄^·−, ^·OH, ¹O₂, and O₂^·− participated in the degradation of TCH. The high catalytic performance of PDA@CoFeS₂ is closely related to two aspects: one is the collaborative effect of Co³⁺/Co²⁺ and Fe³⁺/Fe²⁺ cycles in the activation of PMS, and the other is that sulfur species and PDA promote the cycling of Co³⁺/Co²⁺ and Fe³⁺/Fe²⁺. In summary, PDA@CoFeS₂ composite is a promising heterogeneous catalyst for water pollution treatment.