Dimensional and Crystalline-Domain Engineering of 2D Chitin Nanomaterials for Selective Ion Transport.

Efficient and selective ion transport under nanoscale confinement underlies many emerging technologies, yet current nanofluidic membranes remain predominantly optimized for cation transport. The development of high-performance anion management systems is still in its early stages. Chitin-a sustainable polysaccharide featuring a Bouligand‑type hierarchical structure and readily modifiable functional groups-offers a uniquely advantageous platform for creating positively charged nanofluidic materials that address this gap. In this perspective, we highlight how directional disassembly can unlock a family of two-dimensional chitin nanomaterials, ranging from dense and porous nanosheets to sub-nanosheets and single-molecular-layer nanoribbons. These size‑defined units establish distinct ion transport behaviors, revealing that dimensional engineering and crystalline-domain engineering act as dual core strategies for tuning ion pathways and selectivity. We further argue that crystalline-domain regulation presents a complementary strategy: by expanding polymer chain spacing through precise coordination chemistry, additional intra-layer ion channels can be introduced without compromising structural stability. Taken together, these insights suggest a broader design paradigm in which size-effect modulation and crystalline-domain engineering can be jointly harnessed to construct next-generation chitin-based nanofluidic membranes. Such integrated strategies may pave the way for high-efficiency anion transport control, helping to overcome the long-standing challenges in developing sustainable biomass-based ion-selective systems.