Hierarchical B and Cu co-doped Co3O4 nanoarrays for nitrate reduction coupled with polyethylene terephthalate plastic upcycling

Abstract

The polyethylene terephthalate (PET) hydrolysate oxidation reaction (PETHOR) coupled nitrate reduction reaction (NO₃RR) electrolysis system represents an innovative, green and sustainable approach that enables the upcycling of PET plastic waste and the treatment of nitrate-containing wastewater. Herein, B and Cu co-doped Co₃O₄ ultrathin nanosheet arrays supported on nickel foam (B, Cu–Co₃O₄/NF) are synthesized by the cyanogel-NaBH₄ method and a post boronation approach. Owing to the optimized electronic structure configuration as well as the ultrathin hierarchical structure with abundant active sites, B, Cu–Co₃O₄/NF shows promising activity for both the NO₃RR and PETHOR. For NO₃RR performance, B, Cu–Co₃O₄/NF can deliver an ammonia (NH₃) yield of 1.78 mmol cm⁻² h⁻¹ with a faradaic efficiency (FE) of 98.4% at −0.3 V potential. Additionally, B, Cu–Co₃O₄/NF exhibits high selectivity in the electrooxidation of ethylene glycol (EG) derived from PET, which can achieve a formate yield of 1.23 mmol cm⁻² h⁻¹ and a FE of 98% at 1.5 V potential. Impressively, an integrated two-electrode system has been established by coupling the NO₃RR with the PETHOR, requiring merely an electrolysis voltage of 1.10 V to simultaneously obtain NH₃ and formate at 50 mA cm⁻².