An assessment of the fate of metal oxide nanomaterials in porous media

Developing procedures for assessing the potential environmental fate and transport of nanomaterials is an active endeavor of the environmental technical research community. Insufficient information exists for estimating the likelihood of nanomaterial deposition on natural surfaces in aquatic environments. This work develops a framework for estimating potential metal oxide nanomaterial self-aggregation through the combined application of recent developments in diffuse layer model surface complexation theory with historical Derjaguin-Landau-Verwey-Overbeek (DLVO) procedures. Findings from the work include: 1) the surface, diffuse layer, and/or zeta potentials of nanomaterials in environmental aqueous systems are likely to have an absolute value less than 25 mV, 2) only nanomaterials with a Hamaker constant as large as 1E-19 J (and an absolute surface potential < 25 mV) will likely aggregate in most environmental aquatic media, 3) natural organic matter coatings may render metal oxide nanomaterials less likely to aggregate in aquatic systems, 4) nanomaterials in aqueous suspension will likely have an absolute surface potential less than their micron-sized counterparts of the same composition, and 5) robust diffuse layer model databases of intrinsic surface site reactivity constants with multivalent aqueous environmental ions will need to be developed in order to provide accurate mechanistic estimates of the surface potential of nanoparticles suspended in aqueous environmental systems.