Recently, the research team led by Prof. Wu Hao and Prof. Deng Weiqiao from the Institute of Frontier and Interdisciplinary Science of Shandong University made a series of progress in the investigation of MXene-derived (hybrid) materials. The related works titled “MXene-Derived Metal-Organic Framework@MXene Heterostructures toward Electrochemical NO Sensing” and “Nb₂CT_xMXene Derived Polymorphic Nb₂O₅” were published successively in Small (JCR Q1, IF: 15.153). These works were mainly contributed by two PhD candidates, who are Tan Yi and Sun Lanju (the first authors) from Shandong University under the guidance of Prof. Wu Hao (the corresponding author).

MXene is a kind of thin layered metal carbides/nitrides/carbonitrides, which exhibits high electrical conductivity. The most common MXene was composed of 3-, 5- or 7-layer atoms, which normally were synthesized from their corresponding MAX phases by chemical etching treatments. Terminal atoms or functional groups, such as -O, -OH, and -F, would be introduced inevitably on the surfaces of MXene during the etching process, which render the surface attractive physicochemical property.

Previously, the team proposed a new strategy that could turn completely MXene precursors into metal-organic frameworks (MOFs). This strategy has realized tunable nanoscale MOFs, which are not attainable with the use of conventional metal salt precursors. Very recently, the authors put up the design of incomplete MXene-to-MOF conversion, leading to MOF@MXene heterostructures. The MOF@MXene heterostructure shows a high sensitivity, stability, and good anti-interference ability as a catalyst in electrochemical NO sensing. Moreover, plane-averaged charge density difference shows substantial charge redistribution occurred at the heterointerfaces, producing a built-in field, which facilitates charge transfer. Besides, molecular mechanics-based simulated annealing calculation reveals greatly enhanced adsorption energies of NO molecules on the heterointerfaces than that on separate MOF and MXene. Hence, the facilitated charge transfer and preferential NO adsorption are responsible for the dramatically promoted performance towards NO sensing. The prudent design of MOF@MXene heterostructure may spur advanced electrocatalysts for electrochemical sensing and the application of MXene materials.

With the use of Nb₂CT_xMXene precursors and H₂SO₄ regulating agents, the first case of phase tuning of Nb₂O₅ in low-temperature hydrothermal synthesis was realized. This research breaks away from the conventional high-temperature (>400℃) treatment for crystal phase tuning. The Nb₂CT_xMXene precursor was irreplaceable in comparison to other metal precursors. By varying the amount of the H₂SO₄ agent, 4 pure-phase Nb₂O₅ crystals and 3 mixed phases in-between are obtained. The required amount is found to be related to the H-covered surface energy calculated based on density functional theory. Moreover, crystallographic shear is observed in the MXene-derived B-phase Nb₂O₅, which induces oxygen vacancies. As a result, it exhibits high capacities as the lithium-ion battery anodes, which are 3 times higher than the routine synthesized one. This work inspires prudent synthesis of difficult-to-obtain crystal phases.

These works were supported by the National Key R&D Program of China, the Natural Science Foundation and the Science Foundation for Outstanding Young Scholars of Shandong Province, and the Qilu Young Scholars Program of Shandong University.

Link to the paper：https://doi.org/10.1002/smll.202204942;https://doi.org/10.1002/smll.202300914