To predict the fate and transport of aqueous pollutants, we need a better understanding of homogeneous and heterogeneous Fe(III) (hydr)oxide nucleation and growth on mineral surfaces. In this study, we used small angle X-ray scattering (SAXS) and grazing incidence small angle X-ray scattering (GISAXS) to investigate the simultaneous homogeneous and heterogeneous precipitation of Fe(III) (hydr)oxides on quartz and 10-4 M Fe(III) solution (at pH = 3.7 ± 0.2). Then, to further elucidate effects of substrate properties on precipitation, we examined nanoparticle formation on other environmentally abundant mineral surfaces, such as muscovite, corundum (α-Al2O3), and organic-coated substrates. Along with SAXS/GISAXS, we employed atomic force microscopy (AFM), dynamic light scattering (DLS), contact angle analysis and conducted zeta potential and aqueous concentration measurements. Among inorganic substrates, interestingly, both the fastest heterogeneous nucleation and slowest growth occurred on corundum compared to quartz and muscovite. The slow growth was found to result from local saturation changes by electrostatic forces between the charged Fe(III) (hydr)oxide polymeric cluster and substrate surfaces and the substrate–water interfacial energy; while, structural mismatches between the substrates and precipitates were main contributing factors for the fast nucleation on corundum. For organic-coated substrates, polyaspartate- and alginate-coated substrates were used. After 2 h of reaction, polyaspartate (the most negatively charged substrate) had 10 times less precipitation of positively-charged iron hydroxide nanoparticles than quartz (least negatively charged substrate) implying that electrostatics do not govern nucleation. Quantification of surface functional groups suggested that polyaspartate fewer surface functional groups than alginate; yet, more than two times as many surface functional groups than quartz. Contact angle measurements indicated that hydrophilicity can be the dominant mechanism as quartz is highly hydrophilic. This study provides unique qualitative and quantitative information about the size, volume, and number evolution of Fe(III) (hydr)oxide particles newly formed in the presence of diverse environmental substrates. These results can provide a better understanding of the fate and transport of pollutants in the environment as well as in water treatment facilities, and help design environmentally-sound nanoparticle synthesis process.

Fe(III) (hydr)oxide nucleation, and growth: Influences of local saturation changes, structural matches, and hydrophilicity

249th National Meeting (2015)

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