Gallic acid modified hyper-cross-linked resin and its adsorption equilibria and kinetics toward salicylic acid from aqueous solution

We synthesized a series of gallic acid modified hyper-cross-linked resins named HJ-D11, HJ-D22, D44, HJ-D55 and HJ-D66 from macroporous chloromethylated styrene-divinylbenzene copolymer (PS) by adjusting the Friedel-Crafts reaction time from 1 h to G h and a further chemical modification by sodium gallate. These resins held different chemical structure (different uploading amounts of gallic acid on the surface) and different pore structure (different Brunauer-Emmett-Teller (BET) surface area and pore volume), which determined their different adsorption selectivity toward salicylic acid. HJ-D55 had the largest adsorption capacity toward salicylic acid and hence was employed as a specific adsorbent for adsorption equilibria and kinetics from aqueous solution. The isotherms were correlated by four linear Langmuir and a Freundlich equations and the Langmuir-II equation was shown to be the most suitable. The enthalpy Delta H, Gibb's free energy Delta G and entropy Delta S were calculated to be negative. The kinetics was fitted by the pseudo-first-order and four linear pseudo-second-order rate equations and it was found that the pseudo-second-order rate equation-I was the best one for characterizing the kinetics. (C) 2012 Elsevier B.V. All rights reserved.