An in-situ Fourier transform infrared spectroscopy investigation of the adsorption of organic and inorganic adsorbates at the mineral oxide surface

This work documents the adsorption characteristics of organic and inorganic adsorbates at mineral oxide surfaces. The first study focuses on the adsorption of oxalate dianion at γ-aluminum oxide. Attenuated total reflection Fourier transform infrared spectroscopy (ATR FTIR) was used to investigate the In-Situ surface binding geometry and surface equilibrium. The binding geometry was determined to be bidentate mononuclear. Using electric double layer theory as a model, the intrinsic binding constant of oxalate dianion at γ-aluminum oxide obtained through fitting the experimental data to the model was 2.29 × 103 M−1. This value was compared to published data on iron oxide dissolution rates, and the close correlation of values suggest that surface coverage is a term in the dissolution rates law.; The second study focused on the adsorption of humic acid and phosphate at ferrihydrite at pH 7. The same ATR FTIR instrumental design was used to investigate the competitive adsorption of the two compounds. The data suggested that humic acid at 0.5 to 0.9% and phosphate at 1mM do not displace each other when adsorbed in a sequential manner. The exact binding structure for phosphate was not resolved by the study, although bidentate binding appears to dominate.