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-Fe 1-x S was modified by stable iron oxide (Fe 3 O 4 ) and biochar (BC AA /Fe 1-x S/Fe 3 O 4 ), which showing a core (Fe 1-x S) shell (Fe 3 O 4 )-like structure with homogeneous dispersion on the surface of BC AA . The composite overcame the disadvantages of nano-Fe 1-x S and achieved high removal efficiency of 100% and 99.98% for QNC and Cr(VI), respectively. Based on XPS analysis, Fe(II) content has been reduced from 53.3% to 34.2% and S(II) content from 13.0% to 6.5%. Fe(II) species in the composite are the main active substance for QNC degradation and Cr(VI) reduction, and S(II) species also indirectly provide electrons to promote Fe 2+ /Fe 3+ cycling. Then, we identified the intermediates of QNC and active radicals • OH or SO 4 •− in the system to suggest possible degradation pathways. We further found 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.
Biochar currently served as the support for dispersed metal nanoparticles and cooperated with pyrite to generate more reactive radicals in organic pollution degradation system. But the mechanism of interaction between biochar and pyrite has not been elucidated. In this paper, biochar with oxygen-containing functional groups (OFGs) served as a stable dispersant to prepare nano-FexSy loaded biochar materials (BCOFGs@FexSy). BCOFGs coordinated with nano-FexSy to overcome its drawbacks, boosting QNC removal efficiency from 28.64% to 100%. The XPS and the linear sweep voltammetry (LSV) results revealed higher Fe(II) content and higher electron transfer rate on used BCOFGs@FexSy, further validating that hydroxyl functional groups on biochar surface provided electrons to Fe(III) to achieve efficient Fe(II)/Fe(III) cycling. Based on comparative experiments and studies on the roles of iron, S(II) species and OFGs, we clearly revealed that OFGs on biochar materials surface coordinated with nano-FexSy to catalyze the degradation of QNC. The degradation efficiency of BCOFGs@FexSy for QNC was still as high as 91.39% after five cycles, providing full demonstrations that OFGs and S(II) as the abundant electron donor coordinated with Fe species for QNC catalytic degradation and further enhanced the catalytic performance and stability of nano-FexSy.
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