Adsorption of nitrate and phosphate ions from aqueous solutions using organically-functionalized silica materials: Kinetic modeling

A variety of propylammonium functionalized mesoporous silica materials (MS-NH3+) were synthesized via post-synthesis grafting and co-condensation and their efficiency to remove nitrate and phosphate anions in aqueous solution was investigated. Under the experimental conditions explored, the maximum removal for nitrate (36%) was obtained using MCM-48 functionalized via grafting. In the case of phosphate anions, SBA-15 functionalized via grafting exhibited the best removal of 56%. The corresponding adsorption capacities reached 45 and 57 mg/g-adsorbent for nitrate and phosphate, respectively. Using the MCM-48 functionalized via grafting, a kinetic investigation was conducted at temperatures ranging from 5 to 45 degrees C. For both anions, the adsorption was shown to be very fast reaching the equilibrium within the first 5 min of contact time between the adsorbent and the anions solutions. The pseudo-first order, pseudo-second order and intra-particle diffusion kinetic models were used to describe the obtained data. The pseudo-second-order model was found to describe adequately the experimental kinetic data. The activation energies of adsorption evaluated using the pseudo-second-order rate constants were 6.91 and 8.59 kJ/mol for nitrate and phosphate anions, respectively. (C) 2012 Elsevier Ltd. All rights reserved.