title: Characterisation of Fe-oxide nanoparticles coated with humic acid and Suwannee River natural organic matter.
abstract: Iron oxide nanoparticles are becoming increasingly popular for various applications including the treatment of contaminated soil and groundwater; however, their mobility and reactivity in the subsurface environment are significantly affected by their tendency to aggregate. One solution to overcome this issue is to coat the nanoparticles with dissolved organic matter (DOM). The advantages of DOM over conventional surface modifiers are that DOM is naturally abundant in the environment, inexpensive, non-toxic and readily adsorbed onto the surface of metal oxide nanoparticles. In this study, humic acid (HA) and Suwannee River natural organic matter (SRNOM) were tested and compared as surface modifiers for Fe2O3 nanoparticles (NPs). The DOM-coated Fe2O3 NPs were characterised by various analytical methods including: flow field-flow fractionation (FlFFF), high performance size exclusion chromatography (HPSEC) and Fourier transform infrared spectroscopy (FTIR). The stability of the coated NPs was then evaluated by assessing their aggregation and disaggregation behaviour over time. Results showed that both HA and SRNOM were rapidly and readily adsorbed on the surface of Fe2O3 NPs, providing electrosteric stabilisation over a wide range of pH. HPSEC results showed that the higher molecular weight components of DOM were preferentially adsorbed onto the surface of Fe2O3. As SRNOM consists of macromolecules with a higher molecular weight than HA, the measured size of the SRNOM-coated Fe2O3 NPs was 30% larger than the HA-coated Fe2O3 NPs. FTIR results indicated the occurrence of hydrogen bonding arising from electrostatic interaction between the DOM and Fe2O3 NPs. Finally, a stability study showed that after 14 days, small agglomerates and aggregates were formed. The HA-coated Fe2O3 NPs formed agglomerates which were easily disaggregated using a vortex mixer, with the coated NPs returning to their initial size. However, SRNOM-coated Fe2O3 NPs were only partially disaggregated using the same method, which indicates that these aggregates have a more compact structure.
authors.affiliation: School of Civil and Environmental Engineering, University of Technology, Sydney, Post Box 129, Broadway, NSW 2007, Australia.
authors.forename: Laura
authors.initials: L
authors.lastname: Chekli
authors.forename: Sherub
authors.initials: S
authors.lastname: Phuntsho
authors.forename: Maitreyee
authors.initials: M
authors.lastname: Roy
authors.forename: Ho Kyong
authors.initials: HK
authors.lastname: Shon
mesh_terms: D000327:Adsorption; D002850:Chromatography, Gel; D005290:Ferric Compounds / Q000737:chemistry*; D031521:Fractionation, Field Flow; D006812:Humic Substances / Q000032:analysis*; D057446:Hydrodynamics; D006860:Hydrogen Bonding; D053758:Nanoparticles / Q000737:chemistry*; D010316:Particle Size; D017550:Spectroscopy, Fourier Transform Infrared; D055672:Static Electricity; D013499:Surface Properties
chemical_list: D005290:Ferric Compounds; D006812:Humic Substances; C000499:ferric oxide
keywords: Aggregation; Disaggregation; Dissolved organic matter; FlFFF; Iron oxide nanoparticles