Performance and mechanism of the biochar-supported Ni0/Co0/MnO composite catalyst for peroxymonosulfate activation to degrade iopamidol

A biochar-supported Ni0/Co0/MnO composite catalyst was prepared from the cathode material (CM) of spent ternary 523 lithium-ion batteries (LIBs) and buckwheat hulls. The effect of pyrolysis temperature (x) and different loading ratios (y) of xBCyCM on the activation of peroxymonosulfate (PMS) was investigated. The results showed that the loading of Ni0/Co0/MnO on the biochar (BC) enhanced the IPM degradation and effectively reduced metal ions’ leaching. The 850BC10CM/PMS system degraded iopamidol (IPM) within the wide pH range of 5.0–10.0. The pseudo-first reaction rate constant kobs was 0.0944 min−1 during 25 min under optimal conditions (catalyst dose of 0.1 g·L−1, 0.5 mM of PMS, and an initial pH value of 10.0), while the leaching concentrations of Ni, Co, and Mn were 0.089, 0.035, and 0.067 mg·L−1, respectively. Furthermore, the 850BC10CM degraded IPM by radicals (·OH, SO4•−, and ·O2-) and non-radical pathways (1O2 and an electron transfer). As the pH value increased from 7.0 to 10.0, the fluorescence analysis and quenching experiments revealed a decrease in the effects of SO4•− and ·OH, while the effect of 1O2 was enhanced. The 850BC10CM could still achieve a removal rate of 86.6 % for IPM after four cycles. Based on the liquid chromatography-mass spectrometry (LC-MS) results of degradation intermediates, five possible degradation pathways were proposed. The 850BC10CM inhibited the formation of the iodoform CHI3. In short, the 850BC10CM, which was prepared by using a green, sustainable development of waste utilization, exhibited a safe and effective performance for the removal of emerging IPM pollutants. [Display omitted] •The composite catalyst was fabricated from spent LIBs and buckwheat hulls.•BC acted as a carrier of Ni0/Co0/MnO, while reducing the leaching of metal ions.•850BC10CM effectively inhibited the formation of CHI3.•The effect of 1O2 increased as the initial pH changed from 7.0 to 10.0.