Synthesis of dipolar grafted hydroxyethyl cellulose and its application for the removal of phosphate ion from aqueous medium by adsorption.

A novel amphoteric graft copolymer was prepared by first grafting of a cationic monomer, (3-Acrylamidopropyl) trimethyl-ammonium chloride (APTAC) using potassium peroxydisulfate (K2S2O8) as radical initiator, followed by sulfation with chlorosulfonic acid as sulfating agent onto hydroxyethyl cellulosic (HEC) backbone. Several techniques like FTIR, 1H NMR, FESEM, XRD and TGA/DTGA studies were used to characterize the graft copolymer. The dipolar graft copolymer, sulfated hydroxyethyl cellulose-g-polyAPTAC (SHEC-g-PAPTAC) so obtained was used for phosphate ion adsorption from water medium. Various operating variables affecting the phosphate adsorption were studied which showed that the maximum phosphate adsorption was obtained at pH 5, time 45 min, temperature 50 °C, adsorbent dose 0.02 g and initial phosphate ion concentration 120 mg/L. Adsorption mechanism was theoretically interpreted by Density Functional Theory (DFT), using Gaussian 09 software which supports the experimentally obtained data. The adsorption follows pseudo-second-order kinetic and Langmuir isotherm model with Qmax value 46.94 mg/g. Calculation of thermodynamic parameters (negative value of Gibbs free energy change (ΔG°)) indicates the spontaneous nature of the adsorption. Adsorption capacities of both hydroxyethyl cellulose-g-polyAPTAC (HEC-g-PAPTAC) and SHEC-g-PAPTAC copolymer were also compared under optimum conditions. Desorption study showed that the sulfated polymer was retained almost 86% regeneration efficiency after four adsorption-desorption cycles.