(630f) Probing Surface-Adsorbate Interactions and Energetics through Active Particle Dynamics

Despite deep relevance to catalytic reactions, experimental measurement of the attraction of organic molecules to metal surfaces as well as the resulting steady-state adsorbate coverage in the liquid phase remains challenging. Here, we show the utility of active particles for in-situ quantification of the affinity and saturation coverage of adsorbates (thioglycerol, furfural, and ethanol) onto a platinum surface under steady-state reaction conditions.

Active particles with Janus Pt catalyst architecture were synthesized. The particles were incubated with varying adsorbate concentrations and the MSD and drift velocity of the particles at each condition was used to construct adsorption isotherms.

Thioglycerol rapidly saturated the Pt surface and full coverage was achieved at 2 mM. Furfural, however, did not fully block H₂O₂ access to the surface and saturation instead resulted in a maximum coverage of ~60%. Ethanol (at much higher concentrations) similarly saturated at less than half coverage. Each adsorbate coverage plot was fitted to a Langmuir adsorption isotherm and the maximum coverage (θ_max) the surface affinity of each adsorbate (K_a) were extracted. The affinity of thioglycerol towards the surface was the highest, followed by furfural and then ethanol (K_a 16.6±4.3, 0.47±0.04, and 0.0011±1e-4, respectively). Interestingly, the extracted maximum coverage appeared to trend with the affinity of each adsorbate. Moreover, measured isotherms at different temperatures allowed for extraction of the adsorption enthalpy for furfural and ethanol (−ΔH: 81 and 20 kJ/mol, respectively) onto the Pt surface.

Adsorption of solute molecules onto metal surfaces has important implications in catalysis and this work shows that important parameters of this process can be captured using active particles. This approach is particularly attractive as it helps capture one of the most salient aspects of catalysis, i.e., the competitive in situ interactions of the adsorbate, peroxide, and metal surface under steady state reaction conditions in an aqueous phase.