Fabrication of Polyvinylpyrrolidone-Stabilized Nano Zero-Valent Iron Supported by Hydrophilic Biochar for Efficient Cr (VI) Removal from Groundwater

Today, eco-friendly and cost-effective nanomaterials are vital to ultimately removing contaminants from groundwater as an essential part of freshwater. In this study, polyvinylpyrrolidone (PVP)-stabilized nano zero-valent iron (nZVI) supported by hydrophilic wheat straw biochar (HWS) (PVP-nZVI@HWS) was prepared and compared with the nZVI-HWS sample for Cr (VI) removal from aqueous media. The morphology and functional group structure of PVP-nZVI@HWS composites demonstrated that nZVI could be dispersed homogeneously on the hydrophilic biochar substrate by adding PVP (owing to a large number of -OH functional groups). Based on BET analysis, despite a minimal reduction in the surface area of the PVP-nZVI@HWS hybrid material compared to the nZVI-HWS sample (7.19 m(2) g(-1)), the pore volume and adsorption average pore diameter increased. Superior reduction efficiency (99.63 % elimination in only 5 min) of 20 ppm Cr (VI) was achieved using the proposed hybrid material. Pseudo- second-order kinetics (R-2=1) and Langmuir isotherm models (R-2=0.9407) were attained via the PVP-nZVI@HWS (0.2 g L-1) under groundwater condition (sodium chloride solution at pH=3.2). In addition, on a large scale, the proposed hybrid material could reduce 97.22 % of Cr (VI) in 180 minutes from the water. The mechanism of catalytic and absorption behaviour for two catalysts was compared, and the investigations showed that absorption action for the nZVI-HWS sample, and catalytic behaviour for the PVP-nZVI@HWS hybrid material were predominant.