Neutral microenvironment-driven catalytic polymerization for closed-loop wastewater treatment and resource recovery

Persulfate-based polymerization-oriented advanced oxidation processes (PS-P-AOPs) represent a promising strategy for simultaneous pollutant removal and resource recovery. However, their practical applications have been limited by efficient polymer product recovery and catalyst regeneration. Here we design a Ni–Zn layered double hydroxide (NiZn-LDH) catalyst that creates a self-buffered neutral microenvironment via amphiphilic ≡Zn(OH)₂ groups. This microenvironment enriches Ni at the slipping plane, affording favourable electronic structures for selective peroxymonosulfate activation into high-valent Ni(IV)=O species which triggers phenol polymerization through a proton-coupled electron transfer mechanism. A high polymerization efficiency (85.7%) is achieved and the resulting polymers are recovered via facile acid washing and applied as coating materials with outstanding anticorrosion capacity. Meanwhile, the NiZn-LDH catalyst is regenerated through alkaline ageing of the residual solution for further cyclic use. The efficiency of 1.5NiZn-LDH/peroxymonosulfate was assessed for the treatment of industrial coking wastewater (15 litres, 277.17 mg l⁻¹ chemical oxygen demand), achieving 82.8% chemical oxygen demand and 81.6% total organic carbon removal, 0.91 g polymer recovery and 97.6% catalyst regeneration. This closed-loop approach provides substantial advantages over homogeneous Fenton systems, delivering improved sustainability, reduced operational costs, and enhanced efficiency. We demonstrate a closed-loop PS-P-AOPs strategy that integrates selective pollutant removal, polymeric product valorization and catalyst reuse, offering a low-emission strategy for sustainable wastewater treatment.