Demystifying constructive strategies on designing functionalized lamellar Nb2CTx nanosheet membrane architectures under confined space

Abstract

Lamellar membranes of Nb₂CT_x nanosheets have received significant research interest as cost-effective and efficient materials for desalination, water purification, energy conversion and storage, and ion separation. However, constructive strategies for designing lamellar architectures formed by surface-modified Nb₂CT_x nanosheets have not been explored. In order to tackle this problem, exploring the ion transport mechanism (apart from size exclusion) within the nanochannels is of primary significance. Here, we report new approaches on demystifying one possible mechanism of pre-designed membranes with high water permeation and ion rejection or selective separation of ions at multiple concentrations within the confined lamellar layers of the membranes. These membranes are functionalized with carboxyl, hydroxyl, or carboxyl/hydroxyl mixed functional groups. The carboxyl-functionalized membrane enables fast water permeation, while the hydroxyl-functionalized membrane could have higher rejection capability. Surprisingly, the introduction of mixed carboxyl and hydroxyl functional groups plays a significant role in achieving fast and selective ion transport within a surface-modified membrane, which might be due to the interactions between ions and water within the confined space. This work demonstrates a synergistic effect between ion–water cluster and dynamic ion–water exchange process that enables selective permeation, which provides a constructive strategy on designing functionalized Nb₂CT_x nanosheet lamellar membranes.