Sorption kinetics and isotherm studies of a Reactive Black 5 dye on chitosan hydrogel beads modified with various ionic and covalent cross-linking agents

Abstract

The research reported aimed to determine the influence of the type of a crosslinking agent on Reactive Black 5 sorption kinetics and sorption capacity of chitosan sorbents. The novelty of this work is the comparison of sorption properties of chitosan sorbents crosslinked with 6 different crosslinking agents (3 ionic: sodium citrate, sodium tripolyphosphate, sulfosuccinic acid and 3 covalent ones: glutaraldehyde, epichlorohydrin, trimethylopropane triglycidyl ether). The scope of the research included determinations of: the effect of solution pH on the efficiency of dye sorption (pH 2–12), pHPZC of sorbents, sorption kinetics (pseudo-first and -second order model, intramolecular diffusion model), and sorption capacity (Langmuir 1 and 2, Freundlich isotherm). The sorbents tested were also subjected to the FTIR analysis. Ionic crosslinking significantly affected sorption capacity of the chitosan hydrogel in the first days of the sorption process. After 24 h of the process, the sorption capacity for chitosan crosslinked with sodium citrate and sulfosuccinic acid was higher compared to the non-crosslinked chitosan by 46.7 % and 37.2 %. An opposite effect was observed for chitosan crosslinked with glutaraldehyde and trimethylopropane triglycidyl ether, when sorption capacity after 24 h of sorption was lower by 35.3 % and 26.6 % than that of the unmodified chitosan. Once the sorption equilibrium had been reached, the highest sorption capacity was displayed by the unmodified chitosan (Qmax = 2307 mg/g), whereas sorption capacities of the ionically crosslinked hydrogels were in the range of Qmax = 2005−2164 mg/g and these of the covalently crosslinked hydrogels were in the range of Qmax = 2083−2183 mg/g.