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.