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 reme-diation. 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 nFe(3)O(4) and XG had the best effect, while surfactants had minimal effect. There was a critical concentration (CSC) for XG to stabilize nFe(3)O(4), which was 2.0 g/L. At such a concentration nFe(3)O(4), nFe(3)O(4), 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 Fe3O4 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 nFe(3)O(4) and nFe(3)O(4) 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.