Preparation of highly stable and easily regenerated sulfuretted nZVI via one-pot fast pyrolysis method for the removal of diclofenac

Abstract

Sulfide-modified nanoscale zero-valent iron (S-nZVI) is a commonly used reductive agent in pollutant removal. However, the aggregation of S-nZVI can lower its reduction capacity in the water, and its regeneration remains challenging. To overcome these limitations, one-pot fast pyrolysis of FeSO4-loaded lignocellulosic biomass was proposed to obtain highly stable biochar-supported S-nZVI (S-nZVI/BC) nanoparticles. During this process, Fe2+ were reduced and sulfuretted in situ to form S-nZVI and subsequently covered by the freshly formed carbon film. A series of S-nZVI/BCs pyrolyzed at different temperatures (500–1000 °C) were prepared, among which S-nZVI/BC pyrolyzed at 800 °C (S-nZVI/BC-800) exhibited a fast and stable removal of diclofenac (DCF) via adsorption and reduction. The DCF removal efficiency of S-nZVI/BC-800 reached 80.1% within 4 h, with a particle dosage of 0.5 g/L and Fe dosage of 1 mmol/g. The adsorption and reduction efficiencies of DCF by S-nZVI/BC-800 were 43.2% and 36.9%, respectively. The improved reactivity of S-nZVI/BC-800 can be attributed to the formation of iron sulfides (i.e., FeS and Fe1−xS) in ZVI particles, which increased the electrical conductivity and improved the material selectivity for the reduction of DCF in the water. S-nZVI/BC-800 could be easily regenerated through pyrolysis, during which the carbon film could act as the electron donor. This study provides a facile and skillful method to prepare a highly stable and refreshable S-nZVI, which could be a promising permeable reactive bed material for the remediation of halogenated organic pollutants in contaminated water.