Adsorption of paraquat from water by insoluble cyclodextrin polymer crosslinked with 1,2,3,4-butanetetracarboxylic acid

Abstract

An insoluble polymer was elaborated by crosslinking reaction between β-CD (β-cyclodextrin) and BTCA (1,2,3,4-butanetetracarboxylic acid) and it was firstly applied in adsorption of paraquat (PQ) from water. This insoluble polymer was synthesized at 180\xa0°C for 30\xa0min which displayed 74.1% of reaction yield, 3.80\xa0mmol\xa0g−\u20091 of ion exchange capacity (IEC) and 0.18\xa0mmol\xa0g−\u20091 of β-CD content. Physicochemical properties were evaluated by attenuated total reflection–Fourier transform infrared spectroscopy (ATR-FTIR), carbon-13 nuclear magnetic resonance (13C NMR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) method and stereoscopic microscopy. The optimal pH was 8 and the equilibrium time was 120\xa0min. At 30\xa0°C, the adsorption capacity was enhanced (10.8, 19.7, and 25.8\xa0mg\xa0g−\u20091) when the initial concentration of paraquat was increased (25, 50 and 200\xa0mg\xa0L−\u20091, respectively). Adsorption kinetics was described by the pseudo-second-order model and adsorption isotherm was appropriated to the Langmuir model. The negative standard enthalpy change (∆Hº) showed an exothermic process, the positive standard entropy change (∆Sº) displayed an increased disorder and the negative standard Gibbs free energy change (∆Gº) indicated a spontaneous adsorption method. Ultimately, the regeneration efficiency of polymer in methanol was 87.3% after four cycles. This polymer could be used as a potential adsorbent for removal of other cationic pesticides.