Preparation and Property Investigation of Chitosan-Based Anion-Exchange Membranes with Different Cross-Linking Structures

In this paper, two novel different cross-linked structures and uncross-linked anion-exchange membranes (AEMs) based on chitosan (CS) were prepared and characterized. Cross-linked N-(1-methyl-1-chloropropyltriethoxysilane)piperidyl chitosan (CNSiPCS) and cross-linked N-(1-methyl-1-dibromohexane)piperidyl chitosan (CNHePCS) were synthesized by the reaction of 1-methyl-1-chloropropyltriethoxysilane-4-piperidon and 1,6-(1-methyl-4-piperidone)yl hexane with CS, and quaternized N-4-methylpiperidinechitosan (QNMPCS) was prepared as uncross-linked AEMs. The alkaline stability and mechanical properties of CNSiPCS and CNHePCS were improved as opposed to QNMPCS due to the effective cross-linking structure. In addition, experiments showed that the cross-linked structure may hinder the transport of OH– and formation of ion channels, resulting in CNSiPCS and CNHePCS with lower ionic conductivity relative to QNMPCS. The Si–O–Si network structure can effectively promote microphase separation, making CNSiPCS possess relatively higher ionic conductivity compared to CNHePCS. Meanwhile, the ionic conductivity retention of all AEMs reached more than 90% after 120 h of immersion in 8 M KOH solution. This study provides a resource for potential future work on CS-based AEMs.