Catalytic ozonation for effective degradation of aniline by sulfur-doped copper–nickel bimetallic oxide in aqueous solution

Abstract

Sulfur-doped copper–nickel bimetallic oxide (S-CuNiO) was employed as the ozonation catalyst for aniline degradation. The results demonstrated that the removal efficiencies of aniline (0.1 mmol/L) significantly increased with the S-CuNiO dosage from 0 to 1.0 g/L and the ozone dose from 0 to 96.5 mg/(min L-liquid). More than 92% of aniline was decomposed within 20 min in the initial pH range of 2–11, and the removal of total organic carbon reached 71% at initial pH 6. S-CuNiO exhibited more excellent catalytic performance than CuNiO, S-CuO and S-NiO. Radical quenching experiments and electron paramagnetic resonance technique confirmed that •OH rather than O2•− played a dominant role in aniline degradation. Combined with characterization of the catalyst, the possible mechanism of catalytic ozonation was deduced. The ‒OH groups on the catalyst surface stimulated ozone to produce •OH, meanwhile ≡Cu+ and ≡Ni2+ on the surface of S-CuNiO promoted the decomposition of ozone via electron transfer to form •OH, accompanied by the production of ≡Cu2+ and ≡Ni3+. Subsequently, ≡Cu+ converted ≡Ni3+ into ≡Ni2+ and released ≡Cu2+, which was reduced to ≡Cu+ by S2− on the surface of the catalyst. Consequently, catalytic cycles were established to facilitate aniline degradation and improve its mineralization. Based on the analyses of intermediates by HPLC-TOF-MS, the possible pathways of aniline degradation were further proposed.