Kinetic stability of Fe-based nanoparticles with rheological modification by xanthan gum: A critical stabilization concentration and the underlying mechanism

Enhanced kinetic stability of Fe-NPs in groundwater is a focus in application of Fe-NPs for groundwater remediation. The effect of surfactants (Triton X-100 and SDBS) and polymers (XG, SA, CCS, PSS and PVP) on the kinetic stability of Fe-NPs were studied with sedimentation experiments. Polymers improved stability of nFe3O4 and XG had the best effect, while surfactants had minimal effect. There was a critical concentration (CSC) for XG to stabilize nFe3O4, which was 2.0 g/L. At such a concentration nFe3O4, nFe2O3, and nCuO did not settled in 10 h, while the settlement occurred below the concentration and increased with decreasing XG concentration. At CSC XG could stabilize 20 g/L of nFe3O4 for >30 days and 8.0 g/L of nZVI for 13 days. Rheology studies indicated that the enhanced stability was due to the entanglement of XG molecules in the concentration range of 0.5–2.8 g/L and the formation of a uniform entangled network at CSC concentration was responsible for non-sedimentation of Fe-NPs. At hyper-CSC concentrations under the regime of concentrated network (>2.8 g/L), the stability of nFe3O4 and nFe2O3 decreased due to depletion interaction. The rules for XG to stabilize particles and information about the critical concentration will improve XG application in groundwater remediation using Fe-NPs.