Synthesis of inulin hydrogels by electron beam irradiation: physical, vibrational spectroscopic and thermal characterization and arsenic removal as a possible application

Abstract

Inulin is a natural polysaccharide from the fructan carbohydrate subgroup. It is a great candidate to be used as a precursor of new materials for environmental and medical applications. In this work, two novel inulin hydrogels were synthesized by electron-beam irradiation: inulin-acrylamide (Inu-AAm) and inulin-polyvinyl alcohol (Inu-PVA). The use of mixed factorial experimental designs, with the swelling percentage as the response variable, allowed to find the best conditions for the preparation of the hydrogels. The best hydrogels of each type were characterized by the determination of their gel fraction, thermogravimetry (TGA) and differential scanning calorimetry (DSC) measurements. The infrared and Raman spectra confirmed the formation of new materials (xerogels). The best conditions for the preparation of the Inu-Aam hydrogel were AAm concentration of 22% (w/w), Inu-AAm ratio of 20:80 (w/w) and radiation dose of 30 kGy. For the Inu-PVA hydrogel, the best conditions were PVA concentration of 7.5% (w/w), Inu-PVA ratio of 20.78:79.22 (w/w) and a radiation dose of 20 kGy. The best Inu-AAm and Inu-PVA hydrogels showed swelling percentages of 3013 and 2408%, respectively, and values of gel fraction higher than 70%. The Inu-AAm xerogel had higher thermal stability than its precursors, while the Inu-PVA xerogel had less thermal stability than polyvinyl alcohol but more than inulin. The Inu-AAm hydrogel was selected for the sorption tests of arsenic. The sorption of arsenic followed pseudo second-order kinetics and the equilibrium sorption of arsenic on the hydrogel had a good fit to the Freundlich model.