Coating CoFe2O4 shell on Fe particles to increase the utilization efficiencies of Fe and peroxymonosulfate for low-cost Fenton-like reactions

Abstract

Bimetallic composites (Fe@CoFe₂O₄) with zero-valent Fe as the core encapsulated by CoFe₂O₄ layers are synthesized by a coprecipitation-calcination method, which are applied to activate PMS for the degradation of bisphenol A (BPA). Enhanced activity of Fe@CoFe₂O₄ is achieved with very fast degradation rate (k_obs = 0.5737 min^-1). In the fixed-bed reactor, the catalyst lifetime (t_ul) of Fe@CoFe₂O₄ is determined to be 22 h compared to 11 h of Fe, and the deactivation rate constant (k_d) for Fe@CoFe₂O₄ is 0.0083 mg·L^-1·h^-1, only ∼1/10 of Fe (0.0731). The XPS results indicate that the core-shell structure of Fe@CoFe₂O₄ could promote the redox cycles of Co³⁺/Co²⁺ and Fe³⁺/Fe²⁺. It is proved that the coating of CoFe₂O₄ shell on Fe⁰ can protect the Fe⁰ core from being oxidized by PMS to form passivation layer. The electrons of Fe⁰ can therefore be used effectively for activating PMS to produce ROSs via the CoFe₂O₄ shell. This modification method of Fe⁰ would decrease the cost of PMS based wastewater remediation greatly, thus should have great potential on an industrial scale.

Keywords: CoFe(2)O(4); Core–shell structure; Fix-bed reactor; Utilization efficiency; Zero-valent iron.