| Abstract | As the nature and quantity of new/novel nanomaterials continue to expand to meet industrial, medical, and domestic demands, their accidental or intentional release becomes inevitable. To this end, an evolving understanding of the interaction dynamics between nanomaterials and naturally occurring geomaterials is central to supporting continued sustainable development and use of nanomaterials. The current study explores the chemodynamics of the organic nanomaterial, polyamidoamine (PAMAM) dendrimers, binding to (and debinding from) ferrihydrite. Specific focus is placed on how PAMAM size and pH affects the reaction between three carboxyl-terminated PAMAMs (Gx.5-COOH) sorbing/desorbing to/from the variably- charged ferrihydrite (FFH). Since both ferrihydrite and PAMAM exhibit pH-dependent variation of speciation, it is expected that binding/debinding dynamics of differing sizes of PAMAM will vary. Investigating the quantity, rate, and dynamics of these reactions provided insight into the type of bonding occurring, location of bonding, and differences in behavior at pH 7. At pH 5, bonding is approximately 80% physisorption, 10% electrostatic bonding, and 10% hydrogen bonding, with the proportion of physisorption increasing and electrostatic bonding decreasing at pH 3 and pH 7. Irrespective of pH, the proportion of hydrogen bonded PAMAMs stays consistent, with 4-13% remaining strongly bound to the ferrihydrite after the desorption cycle. Bonding occurs both in a first surface reaction that is 2.2X to 3X faster than the secondary diffusion reaction into pore spaces. At pH 7, higher proportions of surface sorption and slower rates of sorption for PAMAM G1.5 and G5.5 are potentially attributable to pH dependent aggregation. The information gained from this study will help to develop a more holistic picture of the environmental fate of synthetic nanomaterials. |
