Nano-Fe1−xS embedded BCAA/Fe3O4 as the stabilized catalyst for simultaneous quinclorac oxidation and Cr(VI) reduction

Quinclorac (QNC) and Cr(VI), are common contaminants in surface waters, posing serious hazard to human and ecological health. Nano FeS, an effective catalyst that has excellent redox properties, is susceptible to over-oxidation and agglomeration problems, which impede its practical application. Herein, nano-Fe1−xS was modified by stable iron oxide (Fe3O4) and biochar (BCAA/Fe1−xS/Fe3O4), which presented the core (Fe1−xS) shell (Fe3O4)-like structure uniformly dispersed on BCAA surface. The composite overcame the disadvantages of nano-Fe1−xS and achieved high removal efficiency of 100% and 99.98% for QNC and Cr(VI), respectively. Based on XPS analysis, Fe(II) content was reduced from 53.3% to 34.2% and S(II) content from 13.0% to 6.5%. Fe(II) species in the composite were the main active substance for QNC degradation and Cr(VI) reduction, and S(II) species also indirectly provided electrons to promote Fe2+/Fe3+ cycling. Then, we identified the intermediates of QNC and active radicals •OH or SO4•− in the system to suggest possible degradation pathways. We further discovered no mutual interference between QNC and Cr(VI) and proposed the possible mechanism for simultaneous removal that QNC degradation by radical attack and Cr(VI) reduction by electrons.