Rhamnolipid Biosurfactant and Soy Protein Act as Effective Stabilizers in the Aggregation and Transport of Palladium-Doped Zerovalent Iron Nanoparticles in Saturated Porous Media

Abstract

Palladium-doped nanosized zerovalent iron (Pd-NZVI) particles can contribute to the transformation of chlorinated solvents and various other contaminants into innocuous products. To make Pd-NZVI an effective in situ subsurface remediation agent, these particles need to migrate through a targeted contaminated area. However, previous studies have reported very limited mobility of these particles in the groundwater environment and attributed it to rapid aggregation and subsequent pore plugging. In this study, we systematically investigated the influence of selected natural and nontoxic organic macromolecules (carboxymethyl cellulose, rhamnolipid biosurfactants, and soy protein) on the aggregation and transport behavior of bare and coated Pd-NZVI. Aggregation behavior was investigated using dynamic light scattering by monitoring the evolution of hydrodynamic diameter as a function of time, whereas transport behavior was investigated by conducting water-saturated sand-packed column experiments. While bare Pd-NZVI is prone to rapid aggregation, we observed good colloidal stability and concurrent enhanced transport of Pd-NZVI coated with carboxymethyl cellulose, rhamnolipid biosurfactants, and soy protein. Each surface modifier performed well at lower ionic strength (IS) (10 mM NaHCO3), and one of the rhamnolipid surface modifiers (JBR215) significantly enhanced transport of 150 mg/L Pd-NZVI at concentrations as low as 10 mg/L total organic carbon. However, an increase in the solution IS induced significant Pd-NZVI aggregation with a simultaneous decrease in the transport potential in accordance with the DLVO (Derjaguin, Landau, Verwey, and Overbeek) theory of colloidal stability. Nonetheless, at the highest IS (300 mM NaHCO3) investigated, the mobility of rhamnolipid-coated Pd-NZVI is significantly higher than that of Pd-NZVI coated with the other surface modifiers, suggesting that biosurfactants may be the most suitable surface modifiers in field application. Overall, this study emphasizes how stabilization of Pd-NZVI with natural macromolecules such as rhamnolipids can improve the transport potential of these reactive nanoparticles in subsurface remediation applications at concentrations significantly lower than those of other commonly used polymers.

Recent advances on iron oxide magnetic nanoparticles as sorbents of organic pollutants in water and wastewater treatment

“…(28, 29) Surfactants can be non-ionic, amphoteric, cationic or anionic depending on the end application. Recently, magnetic permanently confined micelle arrays (Mag-PCMAs) have been synthesized and have proven to be effective in removing organic contaminants from aqueous solutions.…”

Agglomeration behaviour of titanium dioxide nanoparticles in river waters: A multi-method approach combining light scattering and field-flow fractionation techniques

“…R 2.8 ). In fact, the PDI of this sample was quite low (Table 3); suggesting a relatively narrow monomodal particle size distribution (Basnet et al, 2013). The sizes reported by both DLS (Table 3) and FlFFF (Fig.…”

The effects of viscosity of carboxymethyl cellulose on aggregation and transport of nanoscale zerovalent iron

“…Several studies have demonstrated that IS can substantially affect the stability and transport of NZVI particles (Basnet et al, 2013. The transport of 250K CMCand 700K CMC-NZVI particles in 3 mM and 10 mM solutions as well as washed 250K CMCand 700K CMC-NZVI particles were investigated and compared in this study and shown in Figures 3c and 3d.…”