EFFECTS OF SURFACE FUNCTIONAL GROUPS AND NATURAL ORGANIC MATTER ON CLOFIBRIC ACID ADSORPTION BY MESOPOROUS SILICATE SBA-15

Abstract

The objectives of this study are to study the effect of surface functional groups on CFA adsorption mechanism by SBA-15 and to evaluate the effect of hydrophilic (HPI) and/or hydrophobic (HPO) natural organic matter (NOM) on clofibric acid (CFA) adsorption, including to calculate mass transfer parameters for design of the fixed bed adsorption. SBA-15 was synthesized via surfactant template method. 3N-SBA-15 and M-SBA-15 were synthesized via post-grafting method with 3-(trimethoxysilylpropyl)diethylenetriamine and 3-mercaptopropyl- triethoxysilane, respectively. The adsorption of CFA onto all adsorbents at high concentration was increased rapidly in the first 1 hr. and reach equilibrium within 6 hr. The adsorption kinetic and isotherm were compatible with pseudo-second-order and Freundlich isotherm, respectively. 3N-SBA-15 had highest CFA adsorption capacity. Highest removal capacities of CFA were achieved in acidic condition (pH 5), but decreased with increase in pH. Furthermore, the main role adsorption mechanisms were supposed to be a hydrophilic interaction through hydrogen bonding and electrostatic interaction. Moreover, adsorption isotherm of CFA at low concentration (50-250 microgram/liter) of 3N-SBA-15 was investigated and was compatible with Linear isotherm. The presence of HPO and HPI NOM can decrease the CFA adsorption capacity, which might be caused by direct adsorption competition and pore blocking onto 3N-SBA-15. The reported mass transfer parameters consist of liquid film mass transfer coefficient (kf), solid film mass transfer coefficient (ks), overall solid-phase mass transfer coefficient (Ks), overall liquid-phase mass transfer coefficient (Kf), and constant diffusivity (Ds), which was calculated from the adsorption kinetic data.