Self-triggered carboxymethyl chitosan hydrogel for the convenient sustained release of ClO2 gas with environmental stability and long-term antimicrobial effect

Abstract

Challenges associated with the storage and uncontrolled release of ClO₂ gas present significant hurdles to its practical application. Herein, a clever strategy for self-triggering the sustained release of chlorine dioxide (ClO₂) gas is proposed by crosslinking carboxymethyl chitosan (CMCS) with Zn²⁺ to construct a novel CMCS-Zn@NaClO₂ gel with eco-friendly, environmental stability, and convenient, long term, and efficient antibacterial activity. The precursor (NaClO₂) in the CMCS solution was alkaline and triggered by the acidic Zn(NO₃)₂·6H₂O solution to achieve sustained self-triggering ClO₂ release. The ClO₂ gas self-release could be sustained on demand at different temperatures for at least 20 days due to the environmental structure stability of the gel. The hydrogels showed an increase in pore size after sustained release. Molecular dynamics simulations showed the spontaneous release of ClO₂ gas at room temperature and the contraction of the CMCS agglomeration, which were consistent with the macroscopic behaviour. The gel displayed a long-acting and high antibacterial efficacy, resulting in a bacteria-killing rate of over 99.9% (inhibitory concentrations of 2.5 mg mL⁻¹ against E. coli and 0.16 mg mL⁻¹ against S. aureus). The hydrogels could effectively extend the shelf life of fruits and demonstrated an excellent wide range of antibacterial properties. This work provides a new approach to solving the storage difficulty of ClO₂ gas and offers a fresh perspective on the design of materials with convenient self-triggering release by a precursor, as well as the relationship between the material microstructure and sustained-release behaviour.