Gum karaya (Sterculia urens) stabilized zero-valent iron nanoparticles: characterization and applications for the removal of chromium and volatile organic pollutants from water

This paper illustrates a method for the stabilization of nanoscale zerovalent iron (NZVI) suspensions with a “green” biopolymer, Gum Karaya (GK). The stability, sedimentation, aggregation behavior and reactivity towards Cr( vi ) and volatile organic compounds using NZVI–GK (GK stabilized NZVI) and bare NZVI, were assessed. The stabilization mechanism of NZVI–GK was demonstrated using ATR-FTIR, XRD, XPS, TEM, SEM, TGA and particle size analysis. The NZVI–GK nanoparticle suspension was found to be stable for at least three months, suggesting a superior stability rendering property of GK which forms a scaffold to prevent NZVI from aggregating. Batch experiments, centred on Cr( vi ) reduction and degradation of volatile organic compounds, confirmed that NZVI–GK was more reactive than bare NZVI. Furthermore, XPS and ICP-MS results revealed that Cr( vi ) was reduced to Cr( iii ) by NZVI–GK and the remaining Cr( iii ) in solution was adsorbed onto GK, thereby completely removing chromium from the contaminated water. Our study suggests that an important role is played due to the attributes of GK (which include non-toxicity, biodegradability and cost-effectiveness) in conjunction with the ability of NZVI to remove all chromium viz. [Cr( vi ) and Cr( iii )] coupled with the total degradation and removal of VOCs ( cis -1,2-dichloroethene, perchloroethene and trichloroethene) from water.