Microwave induced poly(acrylic acid) modification of Cassia javanica seed gum for efficient Hg(II) removal from solution

Microwave induced poly(acrylic acid) modification of Cassia javanica (CJ) seed gum furnished an efficient Hg(II) sorbent. Copolymer samples of different performances in terms of Hg(II) binding were synthesized by changing acrylic acid concentration at fixed microwave power and exposure time. The optimum sample has been characterized using FTIR spectroscopy, X-Ray diffraction, BET and SEM analysis and using this sample adsorption of mercury (II) was studied as a function of pH, sorbent dose, initial Hg(II) concentration, % grafting, temperature and ionic strength. Equilibrium isotherm data were analyzed using the Langmuir and Freundlich isotherms. The Langmuir model yielded a much better fit than the Freundlich model indicating unilayer sorption. Isotherms have also been used to obtain the thermodynamic parameters such as free energy, enthalpy, and entropy of sorption. The maximum sorption capacity was 135 mg g−1at 30 °C. In order to investigate the mechanism of sorption, kinetic data were modeled using the first order Lagergren, pseudo-second-order and intra-particle diffusion model where intra-particle diffusion and chemical reaction both seem relatively significant in the rate controlling step. The regeneration experiments revealed that the CJ-graft-poly(acylic acid) can be successfully reused for six cycles without any significant loss in the sorption capacity.