Nickel in-situ doped cobalt-carbon composite loading on nickel foam to promote high-valent cobalt-oxo generation in peroxymonosulfate activation for ultra-fast organic oxidation and mechanism

Abstract

The cobalt-carbon composite (C@Co) stands out as an ideal catalyst for generating high-valent cobalt-oxo (Co(IV)=O) species during peroxymonosulfate (PMS) activation, however, its application is badly constrained by the disadvantages of the inefficiency and unstable of Co(IV)=O generation, along with the challenge of recycling. To solve this limitation, in this work, Ni in-situ doped C@Co grown on nickel foam (C@CoNi/NF) was fabricated. The C@CoNi/NF-700 prepared at 700℃ had the highest PMS activation efficiency toward bisphenol A (BPA). Almost 100 % of BPA can be removed in 100 s with the first-order reaction constant (k_obs) of 3.98 × 10^-2 s⁻¹. It was revealed that the Co(IV)=O played the pivotal role in BPA degradation with the contribution being 97.60 %. This led to the system exhibited high selective oxidation for organics, excellent anti-interference capabilities for co-existing ions in real water, wide pH adaptability and high stability. Theoretical calculation results showed that Co(IV)=O was generated with the cleavage of S-O and O-O bonds of PMS, which was totally different from the previous studies via the O-O and O–H bond cleavage. Additionally, the doped Ni⁰ can lower the reaction energy barrier of Co(IV)=O generation of C@Co. Finally, the continuous-flow experiment revealed the C@CoNi/NF-700 + PMS system exhibited a long-term stability and has a promising potential in practical purifying wastewater. This work not only developed one stable and easily recovery catalyst for rapidly selectively removing organics in wastewater, but also provided new insights into the Co(IV)=O generation pathway in PMS based AOPs.