ENGINEERING TECHNOLOGY

The cube “turns” new materials


Born in the School of Engineering and Fine Arts, not only mathematicians have a soft spot for it, but now materials scientists have also found research ideas because of the Rubik’s Cube.

Huang Qing’s team from Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences (hereinafter referred to as Ningbo Institute of Materials), provides a new path for precise regulation of the atomic structure of MAX phase and MXene materials through the chemical intercalation strategy assisted by “chemical scissors”, and enriches the elemental composition and microstructure of the target material.

On March 17, the related research was published in Science with the title “Structural Editing Strategy of Layered Transition Metal Carbides Assisted by “Chemical Scissors””, with Ningbo Materials Institute as the first unit and communication unit. And this result comes from a group of experiments that were originally considered “failed”.

People who play with the “Rubik’s Cube”

Rubik’s Cube is a popular educational toy in recent years. Then, if each square is identified as an element, then the MAX ternary material can just be composed of 3 blocks juxtaposed, just like a 3rd order Rubik’s cube.

MAX phase (Mn+1AXn) refers to a class of non-van der Waals layered materials with a hexagonal crystal structure, where M is mainly a pretransition group metal, A is mainly a main group III.A and IV.A main group elements, and X is carbon, nitrogen or boron.

Due to the characteristics of both metal materials and ceramic materials, MAX phase materials as an excellent structural material have shown broad application prospects in the application fields of high-speed iron pantographs, high-temperature heating elements, turbine blades, high-temperature heat shields, wear-resistant coatings and so on.

After extracting the atomic layer at position A, the MAX phase material derives into a new, two-dimensional carbonitride material MXene (Mn+1XnTx, T is the surface end group), with a similar atomic arrangement to graphene. It shows great application potential in the fields of optoelectronic devices, electrochemical energy storage, electromagnetic shielding, surface catalysis, and separation membranes.

MAX Phase Cube Courtesy of Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences

When organizing a professional forum, Huang Qing once gave a special small gift “MAX Cube” to participants from all over the world, allowing everyone to exert their creativity, “maybe who will open their minds and make new breakthroughs”.

Huang Qing is a “who” who opens his mind. He likes to play with the Rubik’s Cube, find inspiration from the structure of the Rubik’s Cube, and put forward the concept and research method of “MAX Phase Rubik’s Cube”: by reversing the “Rubik’s Cube”, more new MAX phases and MXene materials that cannot be achieved by conventional synthesis paths can be created.

Two-dimensional? Three-dimensional? “Chemical scissors” to reverse each other

The constant transformation and combination of elements on the “Rubik’s Cube” gives endless imagination to material research.

To make these visions a reality, Huang’s team proposed a structure editing strategy for the MAX phase and MXene (layered transition metal carbon/nitrogen compound) assisted by “chemical scissors”.

This strategy first turns the middle block of the “Rubik’s Cube” – using Lewis acid molten salts and reducing metals as “chemical scissors” to open the layers of the MAX phase or MXene, and then puts specific “blocks” into the middle of the “Rubik’s Cube” – introducing metal atoms, anions and other different guest intercalation substances to carry out intercalation.

“We can imagine that during the torsion process of the ‘Rubik’s Cube’, the elements or color blocks continue to leave their original position, which represents the etching process; the new elements and new color blocks are recombined into a third-order ‘Rubik’s Cube’, which represents the homocrystalline displacement reaction process.” Huang Qing told China Science News.

Through the method of structure editing, on the one hand, a series of A-position elements containing traditional elements such as aluminum and gallium, or MAX phase materials such as bismuth, antimony, iron, platinum and other non-traditional elements can be obtained.

The introduction of non-traditional A-position elements, such as magnetic elements and precious metals, is expected to expand the research of MAX materials from the field of high-temperature structures to functional applications, such as magnetism, optoelectronics, catalysis, superconductivity and so on.

On the other hand, by making MXene materials with end groups of halogens, sulfur and nitrogen groups, it is expected to promote the application of MXene in catalysis, energy storage, electromagnetic shielding and other fields.

For this work, Science reviewers believe that the “chemical scissors” method achieves “the mutual transformation between different MAX stages and MXene” and “is a breakthrough for MXenes.”

Huang Qing explained: “Previous research has only been converted from three-dimensional MAX phase to two-dimensional MXene, but this time the two-dimensional to three-dimensional conversion route has been realized, which provides new ideas for the atomic construction of non-van der Waals and van der Waals layered materials. ”

Perseverance in “thinking the experiment was not successful”

“It seems that if the ‘Rubik’s Cube’ is played well, the MAX phase can be done well.” Talking about the MAX phase research that has been paying attention to, Chai Zhifang, an academician of the Chinese Academy of Sciences, said with a smile, “However, researchers can open up a unique way to open up a path for the conversion of two-dimensional MXene to three-dimensional MAX phase, in the final analysis, it is still years of scientific research accumulated into instinct.” ”

Not long after Huang Qing returned to China in 2010, Chai Zhifang began to invite this “newcomer” to give a conference report, and it was not until 2019 that Huang Qing gradually published the original results of MAX, Huang Qing never thought of giving up, and Chai Zhifang always gave academic support and help.

Whether research can produce some results sometimes depends on luck, but it must not work without persistence.

“When doing the displacement test, since the phase structure of MAX has not changed, its diffraction peak will not change much, it is difficult to observe the characterization change, and we thought that the experiment was not successful.” Huang Qing is still very lucky, “In the follow-up work, we carried out elemental analysis by chance, only to find that the element of position A had been replaced. ”

“During the two sessions of the National People’s Congress this year, NPC deputies and members hotly discussed strengthening basic research.” Chai Zhifang also called for a larger and more relaxed environment and support for basic research, as well as a more diversified evaluation mechanism, to help researchers immerse themselves in long-term research and achieve major original innovations.

“This ‘scissors’ is quite magical, but it is still a phased achievement.” Chai Zhifang put forward more expectations, “Can the ‘scissors’ be sharpened a little brighter?” Can the materiality of ‘cutting’ be more stable and richer, and is it even possible to make ‘scissors’ have its own cognitive function through material genetic engineering technology and make it ‘live’? “There will be more exciting material discoveries. (Source: Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences)

Related paper information:https://doi.org/10.1126/science.add5901

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