Sulfur-doped copper-yttrium bimetallic oxides: A novel and efficient ozonation catalyst for the degradation of aniline

Sulfur-doped copper-yttrium bimetallic oxides (S-CuYO) were synthesized by a co-precipitation method and for the first time utilized for the catalytic ozonation of aniline. For comparison purposes, sulfur-doped monometallic oxides (S-CuO and S-YO) and non-doped copper-yttrium bimetallic oxide (CuYO) were also prepared via the same processes. The S-CuYO exhibited a highest catalytic activity among these catalysts. In the catalytic ozonation with S-CuYO, the degradation efficiency and total organic carbon (TOC) removal of aniline (10 mg/L) were 96% and 57%, respectively, within 15 min under optimum conditions. The high performance of the S-CuYO was ascribed to the synergy between the Cu(I) and Y(III) species via providing the catalyst with more abundant surface hydroxyl groups, a larger surface area, and a larger pore size. The surface hydroxyl groups provided active sites for ozone adsorption and the Cu(I) on the surface catalyzed the ozone decomposition to produce free radicals via electron transfer. Besides, the low-valent S species (S2-/SO32-) in the catalyst led to the reduction of Cu(II) to Cu(I), which maintained the high catalytic activity of the S-CuYO. A free radical investigation indicated that (OH)-O-center dot radicals were the main reactive oxygen species responsible for the removal of aniline. Six main intermediates of the aniline degradation were identified by high-performance liquid chromatography-mass spectrometry (HPLC-MS). The possible degradation pathways of the aniline by catalytic ozonation with the S-CuYO were further proposed. Based on the results obtained in this study, it is concluded that the catalytic ozonation with S-CuYO is a promising approach for wastewater treatment containing aniline.