Breaking the permeability–selectivity trade-off in separation membranes with vertically aligned MXene nanosheets

Two-dimensional MXenes (transition metal carbides and nitrides), defined by their atomically layered architecture, precisely tunable sub-nanometer interlayer channels, and abundant surface functional groups, combine exceptional hydrophilicity with metallic conductivity. These characteristics render them an ideal platform for constructing high-performance separation membranes capable of overcoming the intrinsic permeability–selectivity trade-off that constrains conventional membrane materials. This review systematically surveys the landscape of MXene research and introduces the concept of vertically aligned MXene nanosheets. It provides a comprehensive synthesis of green preparation strategies, fundamental physicochemical properties, and methodologies for membrane fabrication, while elucidating the synergistic optimization mechanisms arising from the interplay between vertical architecture and the intrinsic attributes of MXenes. The results demonstrate that such membranes exhibit separation performance, flux, and stability superior to those of conventional materials in applications including gas separation, water treatment, and organic solvent purification. The review further explores emerging frontiers such as biomimetic intelligent responsive membranes and integrated membrane–catalysis systems, while identifying critical challenges for industrialization: scalable fabrication, long-term oxidative stability, and membrane fouling control. Collectively, this work aims to establish a systematic knowledge framework to support both the in-depth investigation and practical deployment of MXene-based separation membranes. • Vertical alignment and MXene chemistry boost both flux and selectivity simultaneously. • MXene membranes outperform conventional materials in various separations. • Aligned MXene sheets reduce tortuosity and mass-transfer resistance sharply. • Key bottlenecks and solutions for scalable MXene membranes are identified.