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

Abstract

The anionic water-insoluble cyclodextrin polymer (polyCTR-β-CD) was crosslinked between β-cyclodextrin (β-CD) and citric acid (CTR) at 180 °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·g−1 and the β-CD content was 0.29 mmol·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 °C, the adsorption capacity was increased (9.4, 17.4 and 20.8 mg·g−1) when the initial concentration of paraquat was raised (25, 50 and 200 mg·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 ΔG° showed a spontaneous adsorption process, the negative ΔH° indicated an exothermic process and the positive ΔS° exhibited an increase disorder. Finally, the reusability of the insoluble polymer was reached 78.3% after four regeneration cycles in methanol.