Preparation, characterization, adsorption kinetics and thermodynamics of chitosan adsorbent grafted with a hyperbranched polymer designed for Cr(VI) removal

Tetracarboxylic acid ester was synthesized with diethyl malonate and methyl acrylate, and an amino terminated hyperbranched polymer (HBP-NH2) was prepared by reaction of a tetracarboxylic acid ester with diethylenetriamine (DETA). Hyperbranched polymer grafted chitosan (HBP-g-chitosan), a novel adsorbent material for Cr(VI) removal, was prepared from HBP-NH2 and chitosan with epichlorohydrin as crosslinking agent. The adsorbent was characterized by thermogravimetric analysis, Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray photoelectron spectrophotometry, and X-ray diffraction. The influence of the initial concentration of Cr(VI), the dosage of adsorbent, pH value and the coexisting anions on the adsorption performance were studied. An isotherm of the adsorption process was generated and studied by Langmuir and Freundlich models. The results showed that the Freundlich model proved to be more suitable than the Langmuir model. The adsorption kinetics were determined by pseudo-first order and pseudo-second order kinetics. In doing so, it was found that the pseudo-second order kinetic model was more reliable than the pseudo-first order kinetic model.