Nanofluidic membrane for confined ion transport: From uniform to composite strategy

Nanoconfined ion transport behaviors, mimicking natural transmembrane processes in ion channel proteins of living organisms, have attracted increasing attention. It provides effective paradigms in many physical, chemical, material fields to encourage fundamentally breaking science discoveries and develop cutting-edge technologies with advanced materials in energy conversion, energy storage, environmental technologies. Based on our previous research of uniform nanochannel, herein, we present a systematic review and current fundamental understanding of the mechanisms, bottom-up design strategies, and fabrication methods for state-of-art composite nanofluidic membrane systems, including heterogeneous and hybrid structures. The structure of the heterogeneous nanofluidic membrane is asymmetric and has the ion rectification feature, while that of hybrid nanofluidic membrane with enhanced performance is symmetric. Generic strategies for constructing composite nanofluidic systems are proposed from basic views of diverse materials dimensions and preparing methods. Meanwhile, the latest progress, major achievements, and breakthrough discoveries in the composite nanofluidic system are summarized. Promising and future applications of nanofluidic composite membranes are illustrated in fields of ions/molecules sieving, nanofluidic energy conversion, and sensor, which are important for the development of nanofluidics-based science and technology.