New Insights into Black Carbon Nanoparticle-Induced Dispersibility of Goethite Colloids and Configuration-Dependent Sorption for Phenanthrene

Black carbon nanoparticles (nano-BC) are one of the most active components in pyrogenic carbonaceous matter and involved in many biogeochemical processes. This study investigated heteroaggregation of nano BC with goethite (a model of natural mineral colloids) and the configuration effect of heteroaggregates on phenanthrene (PHE) sorption. Nano-BC could significantly enhance the dispersion of goethite via heteroaggregation when its concentration was higher than the critical concentration (Cc). The Cc was dependent on the surface potential of nano-BC, which was directly measured for the first time in this study. Configuration and stability of the heteroaggregates were regulated by BC-goethite mass ratio and solution pH. At pH 5.3, oppositely charged goethite and nano-BC interacted with each other through electrostatic attraction and the configuration of heteroaggregates was dependent on BC-goethite mass ratio. At pH 7.4, where both goethite and nano-BC were negatively charged, they heteroaggregated with each other mainly through H-bonding and Lewis acid base mechanisms, and the configuration of heteroaggregates was independent of BC-goethite mass ratio. For PHE sorption, small-sized heteroaggregates were more favorable than large ones due to the higher content of active sorption sites. Interestingly, at a higher concentration of PHE, we found that the solute molecules could probably penetrate into and/or alter the configuration of heteroaggregates and enhance its sorption capacity for PHE. These findings are useful for understanding the effect of nano-BC on colloidal stability and organic compound sorption of minerals.