Knowledge of binding interaction of organic compounds with various surfaces is critical to the areas of nanotechnology, pollution remediation, environmental fate and transport, catalysis, and petroleum processing. Specifically, adsorption from solution phase to the liquid/solid and liquid/liquid interfaces of colloids plays a key role in various natural and industrial chemical processes. In this work, we demonstrate that the adsorption kinetic, both rate and mechanism, can greatly vary with respect to the size and surface composition of the colloid. Using second harmonic generation (SHG), an interface-specific technique, we have explored adsorption of an organic SHG dye onto various colloids of distinct compositions – polymer microplastics, nano-emulsions, and mineral oxides. Kinetic measurements have been made <i>in situ</i> and in real-time, with a time resolution of sub-milliseconds. Our results show that for these interfaces, the kinetic processes are not characteristic of a single step adsorption. The SHG profile as a function of time reveals multiple processes. In particular, a size dependent variation in SHG-based kinetics is observed for the polymeric particles. In addition, the effect of surfactant charge (positively charged CTAB vs. negatively charged SDS) oil/water nano-emulsions on the dye adsorption kinetics has been explored. Comparison of these kinetic data in the context of the effect of different surface interactions (electrostatic and hydrophobic) on the adsorption kinetics will be discussed.

<i>In situ </i>adsorption kinetics of organic dyes onto soft interfaces – effect of particle size and surface composition

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ACS Fall 2022

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In situ adsorption kinetics of organic dyes onto soft interfaces – effect of particle size and surface composition