Biochars-inlaided nano zero-valent iron reactors: A tool for visualized analysis of soil-nanomaterials...

It is a great challenge to depict the evolution process of soil-nanomaterials micro-interfaces during soil remediation. A novel biochar loaded nano zero-valent iron (BC-nZVI) reactor with low density, high reactivity and suitable magnetism was prepared using the method we established. Fe⁰ nanoparticles (NPs) with the size <10 nm uniformly embedded in a layer of porous carbon networks, which attached firmly in the pores and outer surface of biochars. The BC-nZVI reactors efficiently degraded and mineralized pentachlorophenol (PCP) in soil in a wide pH range within 72 h at room temperature. BC-nZVI were easily collected from soil using sieving method or floating technology followed with magnetic separation. The evolution of interfacial properties of BC-nZVI was measured using XPS, Raman spectroscopy, XRD and SEM-EDS. Even supported by BCs, aggregation and oxidation of Fe NPs inevitably took place on the outer surface of BC-nZVI in PCP remediation process. For BC-nZVI_FeSO4 prepared via traditional impregnation and carbothermal method, severe agglomeration and various aging products of Fe NPs were seen in the pores as well. Due to the protection of porous carbon networks, Fe NPs aggregation was greatly mitigated in the pores of BC-nZVI and the Fe²⁺/Fe³⁺ ratio on BC-nZVI surface was still as high as the fresh one. Meanwhile, about 10-20 % of carbon matrix was oxidized and turned into amorphous carbon. The Fe NPs corrosion products, broken carbon phase, and K⁺ of BC-nZVI reactors were released into soil and had little effect or even enhanced the soil bacterial community diversity and biomass. However, the BC-nZVI itself showed certain adverse effect to soil microbes.