Water-insoluble cyclodextrin polymer crosslinked with citric acid for paraquat removal from water

The anionic water-insoluble cyclodextrin polymer (polyCTR-beta-CD) was crosslinked between beta-cyclodextrin (beta-CD) and citric acid (CTR) at 180 degrees C during 30 minutes to eliminate paraquat (PQ) from water. The reaction yield was equal to 70.2%, the ionic exchange capacity corresponded to 3.29 mmol center dot g(-1) and the beta-CD content was 0.29 mmol center dot g(-1). Then, samples were characterized by SEM, ATR-FTIR, TGA, BET and stereoscopic microscope. Adsorption experiments were investigated with different factors such as pH of the solution, contact time, initial concentration of paraquat and adsorption temperature. The relevant pH was equal to 6.5 and the optimal contact time was 120 minutes to attain adsorption equilibrium. At 30 degrees C, the adsorption capacity was increased (9.4, 17.4 and 20.8 mg center dot g(-1)) when the initial concentration of paraquat was raised (25, 50 and 200 mg center dot L-1 respectively). Adsorption kinetics was appropriated to the pseudo-second-order model and adsorption isotherm was fitted to the Langmuir model. For thermochemistry parameters at different temperatures, the negative Delta G degrees showed a spontaneous adsorption process, the negative Delta H degrees indicated an exothermic process and the positive Delta S degrees exhibited an increase disorder. Finally, the reusability of the insoluble polymer was reached 78.3% after four regeneration cycles in methanol.