Influence of the Surface Modification of Mesoporous Activated Carbon on the Removal of Humic Acid From Aqueous Solution

Abstract

Humic acids (HA) constitute the major fraction of natural organic matter in water supplies. HA are very problematic with regard to drinking water treatment and supply since, not being completely removed by conventional treatment processes, they react with chlorine resulting in formation of carcinogenic and regulated disinfection-by products. Adsorption of brown (BHA) and gray (GHA) fractions of humic acid on starting and modified mesoporous activated carbons was investigated. BHA and GHA are fractions of humic acid extracted from young brown coal (Czech Republic) which differ essentially in their characteristics in terms of structure and physicochemical properties. Mesoporous activated carbon was modified by two ways: ammonization (AC/N) and high-temperature hydrogen treatment (AC/H). All activated carbons studied, showed higher adsorption capacity towards BHA comparing to GHA, what is attributed to the smaller molecular weight of BHA molecules, as determined by ultrafiltration method. Comparing to starting AC, nearly 2- and 2.5-fold higher removal degree of both BHA and GHA was observed for AC/N and AC/H, respectively. This observation was found to be a consequence of the increase in aromacity degree of both adsorbents, as shown by increase in the C/H atomic ratio. In the case of AC/H the electrostatic interaction between positively charged surface of AC/H and HA molecules, enhances the extent of adsorption. Adsorption results were discussed in terms of Freundlich adsorption model. The shape of isotherm indicates a strong competition for adsorption centers on AC surface between water and HA molecules, which decreased in the direction AC>AC/N>AC/H. At increased ionic strength of the solution (0.01 M NaCl), no difference in the extent of adsorption between AC/N and AC/H was observed.