Photo‐Manipulating the Interlayer Spacing of MXene Toward Switchable Electrochemical and Gas Sensing Functionality

Abstract Manipulating the interlayer spacing of 2D MXene materials through rapid and noninvasive light methodology represents a promising approach to tuning their physical and chemical properties, which will promote their practical applications in photo‐sensing and photo‐switchable devices. In this study, a new pillared Ti 3 C 2 T x MXene compound is presented, which exhibits tunable interlayer spacing behavior through the introduction of photoisomeric cationic azobenzene derivatives. UV–vis absorption spectra confirm that the increase in inter‐flake distance originated from the tran s‐to‐ cis isomerization of the p ‐[2‐(2‐hydroxyethyldimethylammonio)ethoxy]azobenzene (AZ + Br – ), while the reverse process is driven by visible light induced cis ‐to‐ trans relaxation. As a consequence, the interlayer spacing of Ti 3 C 2 T x MXene can be effectively adjusted by the conformational changes of the AZ + layer, achieving a reversible expansion and contraction of ≈0.5 Å under alternating UV/visible light irradiations. Electrochemical analysis reveals that the conductivity and capacitance can be reversibly photo‐switched with high durability and repeatability. In addition, the adjustable interlayer spacing enables the photo‐controlled gas capture and release feature, showing that AZ + ‐Ti 3 C 2 T x with larger interlayer spacing can accommodate more ethanol molecules and exhibit higher sensitivity to ethanol vapor changes. This work provides a feasible strategy for the design of novel 2D MXene‐based materials and devices with tunable and photo‐responsive functionality.