Heteroaggregation of graphene oxide nanoparticles and kaolinite colloids.

Graphene oxide (GO) is a material with rapid production growth, and consequently GO nanoparticles are expected to eventually penetrate subsurface formations, where fine mineral particles are in abundance. This study examines the heteroaggregation of GO nanoparticles with kaolinite (KGa-1b) colloids under various conditions. Dynamic batch experiments were conducted in solutions with different pH values (pH=4, 7, and 10), different ionic strengths (I=7, 12, and 27mM), and at three controlled temperatures (8, 14, and 25°C). The experimental results showed that a relatively small amount of GO nanoparticles (5-20% of the initial concentration) attached immediately onto KGa-1b colloids, and reached equilibrium in <20min. It was shown that neither temperature nor pH played a significant role in the attachment of GO nanoparticles onto KGa-1b colloids. In contrast, the attachment of GO nanoparticles onto KGa-1b colloids was shown to increase with increasing I. Additionally, time-resolved dynamic light scattering (DLS) was used to identify the influence of I on heteroaggregation between GO nanoparticles and KGa-1b colloids. The critical coagulation concentration (CCC) for the interaction between GO nanoparticles and KGa-1b colloids was 152mM (NaCl). The interaction energies were calculated, for all experimental conditions, by using measured zeta potentials and applying the classical DLVO theory. The equilibrium experimental data were fitted with a Freundlich isotherm, and the attachment kinetics were described very well with a pseudo-second-order model. Furthermore, thermodynamic analysis revealed that the attachment process was nonspontaneous and exothermic.