Hydroxypropyl chitosan-based dual self-healing hydrogel for adsorption of chromium ions

A facile, environmentally benign approach had been developed for the preparation of dual self-healing and adsorption hydrogel through hydroxypropyl chitosan (HPCS), polyacrylamide (PAM) and polyvinyl alcohol (PVA). The self-healing capability of the hydrogels without any external stimulus was ascribed to dynamic Schiff-base bonds, borate bonds and hydrogen bonds, while the adsorption capacity of hydrogels came from the protonated amino group effect at a specific pH. It was demonstrated that the HPP DN hydrogel had a maximum equilibrium swelling ratio of 643% and a maximum compressive strength of 267 kPa. The weight loss of HPP DN hydrogel was 14.26% lower than that of HPCS/PAM single network hydrogel, furthermore, HPP DN hydrogel could achieve self-healing within 10 h. Due to the large number of active groups, the adsorption capacity of Cr6+ reached 95.31 mg/g. It could adsorb in a wide pH range of 1 to 6, and could describe by pseudo-first-order kinetic model and Langmuir adsorption isotherm model, which would provide a new idea for the adsorption and removal of heavy metal ions. In short, the prepared HPP hydrogel had dual self-healing ability, adsorption capacity and mechanical strength, which would make it a promising candidate for long-life adsorbent.