Adsorption of Glycols, Sugars, and Related Multiple −OH Compounds onto Activated Carbons. 1. Adsorption Mechanisms

Several different experimental methods were used to understand better the mechanisms of adsorption of glycerol, glycols, and sugars from dilute aqueous solution onto activated carbons. From batch equilibrium experiments, the affinity and capacity (25 °C) of carbons for single and multiple −OH compounds were greatest for solutes having larger positive deviations from solution ideality. Carbons with progressively oxidized surfaces exhibited reduced uptakes for all multiple −OH solutes. Larger isosteric heats of adsorption on carbons were measured for compounds with fewer −OH groups or higher molecular weight. Thermogravimetric analysis showed that the volatility of the adsorbed multiple −OH solute was reduced by higher molecular weight and solute hydrophobicity. Collectively, these findings show that the adsorption mechanism is characterized by: (a) attractive dispersion interactions between surface and solute, (b) solution-phase nonidealities, and (c) secondary, competitive interactions of the solute −OH groups(s) or surface oxygen groups with water.