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, HJ-D44, HJ-D55 and HJ-D66 from macroporous chloromethylated styrene–divinylbenzene copolymer (PS) by adjusting the Friedel–Crafts reaction time from 1 h to 6 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 ΔH, Gibb's free energy ΔG and entropy ΔS 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.

► Five gallic acid modified hyper-cross-linked resins with different chemical structure and pore structure were synthesized.
► These resins possessed different adsorption selectivity toward salicylic acid.
► The uploaded gallic acid on HJ-D55 is important and its function is a solid-phase extraction.
► Four different linear Langmuir equations were employed to fit the adsorption isotherms.
► Four different linear pseudo-second-order rate equations were employed to fit the adsorption kinetics.