Progress in the precise regulation of the single-atomic layer elements of the MAX phase in Ningbo
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[ Instrument Network Instrument Development ] MAX phase, a kind of nano-layered transition metal compound with hexagonal lattice structure, the molecular formula is Mn+1AXn, (where M is the former transition metal, A is mainly IIIA and IVA elements, X is Carbon or / and nitrogen, n = 1-3). The crystal of the MAX phase material has hexagonal symmetry, and the space group is P63/mmc. It is formed by alternating stacking of Mn+1Xn unit and A atomic layer. There are about 150 kinds of MAX phases reported so far. MAX phase materials combine metal and ceramic properties such as good electrical and thermal conductivity, excellent thermal shock resistance and damage tolerance, good oxidation and corrosion resistance, and easy processing. At high temperature electrodes, friction and wear Such fields have broad application prospects as high security structural materials. Therefore, the creation of new MAX phase materials for the integration of structure and function has become a frontier problem in this field in the world. Recently, the Advanced Energy Materials Engineering Laboratory of the Institute of Materials Technology and Engineering, Ningbo Institute of Chinese Academy of Sciences, synthesized a series of MAX phases with A-site Zn by A-site element replacement strategy (J. Am. Chem. Soc. 2019, 141, 4730- 4737), revealing the feasibility of the presence of a late transition metal in the single-phase A layer of the MAX phase. Like the post-transition metal element such as Zn, the Cu element is not filled with the outermost d-orbital electrons. It can be predicted that the introduction of Cu can make the traditional MAX phase structure material have more d-electron-related functions, such as catalysis, biomarker, and transmission. Feeling and so on. However, there is no effective synthesis method to achieve precise control of Cu atoms between the A-sites of the MAX phase material.
The Advanced Energy Materials Engineering Laboratory of Ningbo Materials Research Institute used the "A-Site-Replacement Reaction" strategy to find that Cu atoms show a certain degree of orderly arrangement in the two-dimensional plane of the A-site of the Ti3AlC2 MAX phase, and pass Cu-Al. The binary phase diagram discusses its formation mechanism. Theoretical analysis shows that Cu atoms are weakly bonded to the Ti3C2 sublayer between the A sites, but are effectively isolated by the high conductance Ti3C2 sublayer, so it is expected to play a role in single atom catalysis. Experiments show that the MAX phase occupied by this Cu atom can oxidize 3,3',5,5'-tetramethylbenzidine (TMB) to form a blue solution by catalytic hydrogen peroxide decomposition, which shows excellent catalytic activity. And still maintain catalytic activity and catalytic stability at high temperatures. The laboratory and the University of Ningbo collaborated to assemble the new MAX phase materials of this type of enzyme catalytic properties into electrochemical biosensors. Compared with traditional nano-particles such as Cu, Au, Pt, Ag, etc., the MAX phase sensor has the advantages of wide linear range, low detection limit (0.06 μM) and high sensitivity in detecting H2O2. It is in the fields of food safety and tumor treatment. Very good application prospects.
Compared with the partial replacement of Cu in the Ti3 (AlxCu1-x)C2 MAX phase A above, how to prepare a new MAX phase material with A-site pure Cu is a more serious challenge, and has not been synthesized in the world so far. This type of MAX phase material. It is predicted from the Cu-Al equilibrium phase diagram that the Al atoms in the MAX phase should not be completely replaced by Cu atoms. However, considering that the A-site single atom is actually affected by the two-dimensional space limitation of the MX layer, the element replacement reaction is also Rich in tunability. The Advanced Energy Materials Engineering Laboratory realized the new MAX phase Ti2(Al0.1Cu0.9)N with high ratio of Cu substitution by selecting Ti2AlN as the precursor of MAX phase. After that, Nb2AlC was used as the precursor material of MAX phase, and finally A was successfully prepared. The MAX phase Nb2CuC is completely Cu-substituted. The above work not only shows the effectiveness of the A-bit element replacement strategy in the creation of new materials for MAX phase, but also reflects the rich structural possibilities and functional expansion of MAX phase.
The above work was published in the International Materials Journal ACS Nano (2019, 13, 9198-9205) and Materials Research Letters (DOI: 10.1080/21663831.2019.1672822), applying for a Chinese invention patent (CN201810751944.0). The study was funded by the National Natural Science Foundation of China (21671195, 21805295, 21875271).

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