Recent progress in surface and heterointerface engineering of 2D MXenes for gas sensing applications

MXenes, a new category of 2D nanomaterials, have garnered interdisciplinary attention since groundbreaking work on Ti3C2Tx in 2011. The distinctive properties of MXene, including its high electrical conductivity, excellent anisotropic carrier mobility, and rich surface functionalities with tunable electronic structure, make it suitable for sensing applications. This review provides an overview of the recent advancements in the use of MXenes in chemiresistive gas sensors. The discussion begins with exploring the diverse range of MXene structures and compositions, along with contemporary developments in their synthesis methodologies. Following this, it elucidates the gas sensing parameters, principles, and techniques for fabricating sensing films using MXene-based materials. Subsequently, this review explores multiple strategies to comprehensively understand and systematically advance MXene through surface and heterointerface engineering. It highlights several surface engineering strategies for MXene, encompassing the tailoring of surface terminations, introduction of active sites, surface functionalization, intercalation of MXene with metal ions or organic molecules, surface oxidation, and heteroatom doping. Furthermore, it delves into heterointerface engineering strategies involving composites of noble metals, metal oxides (MOs), graphene, transition metal dichalcogenides (TMDs), layered double hydroxides (LDHs), and polymers to enhance the gas-sensing capabilities of MXene. The engineering of MXene-based materials facilitates synergistic effects and complementary advantages, introduces catalytic sites, constructs heterojunctions, promotes charge transfer, improves carrier transport, and/or introduces protective/sieving/enrichment layers. These collective improvements effectively enhance the gas sensors' sensitivity, selectivity, and stability. Finally, this review underscores ongoing challenges and prospects for the future advancement of MXene-based gas sensors.