Synthesis of novel cross-linked cyclopolymer bearing polyzwitterion-dianionic moieties and its sorption efficiency for Ni(II) removal from waters

The study reports the synthesis of a unique cross-linked polymer containing zwitterionic (±) and dianionic (=) moieties in each repeating unit via tert -butyl hydroperoxide-initiated cyclopolymerization of N,N -diallyl- N -sulfopropyl ammonio-propyl phosphonic acid in the presence of a cross-linker to give a cross-linked polyzwitterion (CPZ). The cross-linked polyzwitterion/dianion (CPZDA) was accessed by the treatment of CPZ with NaOH. The structure and morphology of the polymer were characterized by using FTIR, TGA, EDX and SEM. The adsorption performance of the resin was evaluated using Ni(II) as a model under the influence of various parameters such as pH, initial metal ion concentration, contact time and temperature to arrive at the optimum conditions. The mechanism of the adsorption was investigated using kinetic, diffusion, isotherm and thermodynamic models. The maximum adsorption capacity at 296 K was found to be 45.5 mg/g at pH 5.5. The adsorption process fitted well pseudo-second order kinetic model and its mechanism was studied by intraparticle diffusion model. The thermodynamic parameters revealed the adsorption process as endothermic in nature with activation energy of 15.8 kJ/mol. In the context of metal ion removal, resin CPZDA has demonstrated its advantage of good stability, fast uptake, high capacity, and the ease of reusability. The resin's excellent ability to remove nickel(II) ions even from wastewater samples makes it a potential candidate for real sorption applications.