Pyrazine substituted chitosan: an adsorbent material for the efficient removal of anionic dyes from aqueous solutions

In the present work, a novel pyrazine based chitosan material was synthesized by functionalizing chitosan with chloroacetyl chloride and further modification with ethylene 1,2 diamine, thus a polymer matrix is obtained. Further the adsorbent material was characterized and verified using analytical techniques such as XRD, SEM, FTIR and TGA. The adsorbent material was analyzed for the adsorptive take-up process with a initial dye concentration varying from 20–100 mgL⁻¹ and the adsorptive process occurred due to the electrostatic interaction between the nitrogen atom of chitosan and the methyl orange dye molecule. The equilibrium adsorptive capacity obtained for the synthesized adsorbent material was 45.45 mg g⁻¹. The adsorptive mechanism predicted the electrostatic interaction between the two atoms and the increased in the adsorption efficiency is contributed by the increased number of hetero atoms in the chitosan structure and the adsorption kinetics was found to be pseudo-second-order kinetics and with a monolayer coverage process indicating the Langmuir adsorption isothermal fit. Further, the evaluated thermodynamic parameters showed the adsorption process to be non-spontaneous and endothermic in nature. A regeneration and reusability study was achieved for the composite material using convenient stripping solutions and the adsorbent was successfully regenerated.