Regulation of SiO Nanoparticles on the Adsorptive Fractionation of Dissolved Organic Matter by Goethite.

SiO nanoparticles (SiONPs) are most widely available and coexisting with DOM at the mineral-water interface; however, the role of SiONPs in DOM fractionation and the underlying mechanisms have not been fully understood. Using Fourier transform ion cyclotron resonance mass spectrometry, combined with Fourier transform infrared spectroscopy and X-ray adsorption fine structure spectroscopy, was employed to investigate the adsorptive fractionation of litter layer-derived DOM on goethite coexisting with SiONPs under different pH conditions. Results indicated that the inhibitory effect of the coexisting SiONPs on OM sorbed by goethite was waning as environmental pH increased due to the reduced steric interactions and the concurrent elevated hydrogen bonding/hydrophobic partitioning interactions on the goethite surface. We observed the coexisting SiONPs inhibited the adsorption of high carboxylic-containing condensed aromatic/aromatics compounds on goethite under different pH conditions while improving the adsorption of highly unsaturated aliphatic/phenolic and carbohydrate-like compounds in an alkaline and/or circumneutral environment. More nitrogen-containing structures may favor the adsorption of phenolic and nonaromatic compounds to goethite by counteracting the negative effect of SiONPs. These findings suggest that DOM sequestration may be significantly regulated by the coexisting SiONPs at the mineral-water interface, which may further influence the carbon-nitrogen cycling and contaminant fate in natural environments.