posted on 2020-03-19, 20:47authored byXiaohong Zhang, Aditya Savara, Rachel B. Getman
Adsorption is an
important step in heterogeneous catalysis as it
predetermines how many reactant molecules can participate in a surface
reaction per unit time. While the rate of adsorption processes is
well studied in gas–solid adsorption in both theory and experiment,
such rates are still not well studied for liquid–solid adsorption.
This is partly because the ever-changing configurations of liquid-phase
solvent molecules impede the ability to study a molecule approaching
a surface from a liquid phase by either experiment or theory. In this
work, we develop a method using molecular dynamics (MD) simulations
to study the rate of adsorption in liquid–solid adsorption
processes. Specifically, we use MD to model the diffusion of a methanol
molecule in aqueous solvent and its adsorption to a Pt(111) surface.
We find that by approximating the solute motion as following the same
displacement rates as a random walk model, the adsorbed and non-adsorbed
states of the methanol molecule near the Pt(111) surface can be discerned
and quantified. In particular, this methodology enables extracting
a sticking coefficient and a macroscopically relatable adsorption
rate. This method can be applied to arbitrary types of reactants and
surfaces, as well as different liquid environments, thus providing
a general tool for predicting quantitative adsorption rates of liquid–solid
adsorption systems.