Adsorption of Substituted Benzene Derivatives on Silica: Effects of Electron Withdrawing and Donating Groups

A fundamental understanding of the forces that drive uptake and binding of aromatic molecules on well-characterized surfaces such as silica is important for predicting the fate of toxic industrial compounds in the environment. Therefore, the adsorption of simple substituted benzene derivatives has been investigated on a hydroxyl-functionalized surface to probe the effects of electron withdrawing and donating functional groups on gas-surface binding. Specifically, this work probes how methyl and halide functional groups affect the properties of the OH---pi hydrogen bond and other surface-adsorbate interactions that play an important role in the uptake of aromatic molecules. Our approach utilizes infrared spectroscopy to study hydrogen-bond formation and temperature programmed desorption to measure activation energies of desorption. Results from this work indicate that substituted benzene derivatives adsorb to silica via a cooperative effect involving the SiOH---pi hydrogen bond and additional substituent-surface interactions that result in unusually high desorption energies.