Enhanced adsorption of molecules on surfaces of nanocrystalline particles

Quantitative measurements of adsorption from solution show up to a 70-fold increase in the adsorption coefficient when a variety of organic acids are adsorbed onto 6 nm compared to 16 nm nanocrystalline titania particles. A Langmuir adsorption model modified to include the dependence of interfacial tension (interfacial free energy) on particle size predicts an increase in the adsorption constant (K_ads) as the crystallite size decreases, in agreement with the experimental results. The increase in K_ads arises predominantly from the increased molar surface free energy of the nanocrystalline particles. The rapid increase in adsorption as particle size decreases has important implications for understanding and modeling natural and experimental systems.