Catalytic ozonation with carbon-coated copper-based core-shell catalysts (C/Cu-Al2O3) for the treatment of high-salt petrochemical wastewater

Abstract

High-salt petrochemical wastewater requires advanced treatment for water reuse due to its high salinity and the presence of refractory organic compounds. Heterogeneous catalytic ozonation is an effective advanced treatment method, with the key to its success lying in the preparation of catalysts. A novel carbon-coated copper-based core-shell catalyst (C/Cu-Al2O3) was successfully prepared. In this work, Al2O3 was used as a carrier and copper as an active component to construct a catalyst with levodopa (L-DOPA) shell and embedded copper sites through the self-polymerization of L-DOPA. The active groups in L-DOPA molecules such as amine and carboxyl groups can be introduced into catalyst and L-DOPA also served as carbon source to reduce Cu(II) to more reactive Cu(I) and Cu(0). Under optimal conditions, its chemical oxygen demand (COD) removal rate for high-salt petrochemical wastewater reached 62.5%. After 20 cycles, its COD removal rate was maintained at above 53%. Electron paramagnetic resonance (EPR) investigations, quenching tests, and degradation experiments of oxalic acid revealed that the generation of embedded copper sites (Cu-O, Cu-N) and the construction of the carbon shell provided the catalyst with rich surface hydroxyl groups and Lewis acid sites, which promoted the decomposition of ozone into hydroxyl radicals (•OH), superoxide radicals (•O2-), and singlet oxygen (1O2) and achieved efficient degradation of organic compounds.