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.