From waste to resource: A plasma-flocculation synergistic strategy for flonicamid removal and upcycling of residues into electrocatalysts.

Abstract

Treating fluorinated pesticide wastewater poses dual challenges: efficient decontamination and sustainable management of the generated solid waste. Here, we propose a plasma-assisted flocculation system that simultaneously removes flonicamid (FLO) and upcycles the Cu-containing flocculation residue into a high-performance electrocatalyst for the nitrate reduction reaction (NO₃RR). By leveraging polyacrylamide (PAM) to promote pollutant-associated aggregation and create localized reaction domains, this strategy enhances interactions between FLO and plasma-generated reactive species, achieving > 95% FLO removal. Mechanistic analyses support a synergistic coupling between PAM-mediated aggregation and plasma oxidation. The recovered solid residue is directly converted into a CuO_x-C catalyst rich in mixed-valence Cu⁰/Cu⁺/Cu²⁺ sites and oxygen vacancies. This catalyst delivers an exceptional NH₃ yield of 44.53 mg·h^-1·mg_cat^-1 and a Faradaic efficiency of 92.19% at -0.6 V vs. RHE. Residual liquid intermediates are deeply mineralized via anodic oxidation. In-situ spectroscopies further reveal a sequential deoxygenation-hydrogenation pathway for NO₃RR, and a 2500 mL continuous-flow system further demonstrates the feasibility of operation at an increased treatment volume. This work integrates pollutant degradation with resource recovery, providing a sustainable "waste-to-catalyst" paradigm for pesticide wastewater valorization.