Rare earth “flashes” at the nanometer scale

Although China is a large country with rare earths, basic research in application is lagging behind. "Industrial monosodium glutamate" can only be as cheap as potatoes and cabbage. Since 1995, the Yan Chunhua team of Peking University has, after 15 years of continuous research and development, established a method for the controlled preparation of rare earth nano-functional materials, which has opened up new ways for the efficient and high-value utilization of rare earth resources in China; "Controllable Synthesis, Assembly and Structure-Activity Study of Materials" won the 2011 National Natural Science Award.

Prof. Yan Chunhua, Professor of Cheung Kong Scholarship, Academician of the Chinese Academy of Sciences, and Director of the State Key Laboratory of Rare Earth Material Chemistry and Application of Peking University, have conducted systematic and in-depth innovative research on rare earth separation, application of rare earth functional materials, etc. Extraction and separation technologies have made outstanding contributions to the world's leading level.

At Peking University's Department of Chemistry, he used a popular language to carry out science popularization for journalists: The so-called nanometer is a billionth of a meter, and its length is equivalent to one-thousandth of the diameter of human hair. When a material becomes smaller in size and as small as only nanometers in length, it exhibits many strange features. This is the subtlety of nanoscience.

“On the nanometer scale, the nature of the material is greatly affected by the surface state.” He made an analogy: A complete brick, whose properties are related to the internal structure but not to the surface; when the brick is ground to ten One-hundred-millionth of a metre of debris, when the number of atoms on the surface is comparable to the number of internal atoms, the nature of the surface becomes active. "Therefore, controlling the surface and morphology at the nanometer scale can often bring about dramatic changes in properties."

Yan Chunhua’s research on rare earth nano-functional materials is based on this principle. From 1995, he led the team to establish a series of synthetic methods to controllably prepare rare earth materials with nanostructures and effectively control their size, morphology and surface. "We can make rare earth materials spherical, cubic, triangular, etc."

It is not difficult to make nano-materials small, but it is difficult to do small and uniform. The key to the synthesis method created by Yan Chunhua et al. is to synthesize rare earth compounds into "monodisperse" nanostructured materials with specific morphology, size and structure. The so-called "monodisperse" is uniform. The chemical community has a mantra: the structure determines the nature. At a new scale, rare-earth materials are made into uniform-sized materials, stabilizing past unstable structures, and new properties can be produced or discovered.

“Experiments have found that different compounds will always exhibit new properties for different systems, which will greatly broaden the role and scope of use of rare earth compounds.” Yan Chunhua said that the current study can be applied to bioimaging, energy conversion and environmental protection. And other fields.

Water flows downwards, and energy conversion follows the same principle. "Energy always runs from high to low, so in rare earth luminescent materials, it is usually absorbed by high-energy ultraviolet light, which emits low-energy visible light." Yan Chunhua and others fully utilized the superior upconversion luminescence properties of rare earth fluorides, which are controllable. Monodisperse nanomaterials have been prepared to efficiently convert energy from low to high - absorb two or more low energy infrared photons and efficiently emit relatively high energy visible light. "Infrared imaging technology has special advantages in biological monitoring. It is more penetrating and safer for organisms." Up-conversion rare earth nano-fluorescent materials can emit blue, green and red under the excitation of near-infrared light. Light can be widely used in laser devices, cancer diagnosis and treatment, and other fields.

In terms of enhanced material conversion and environmental protection, rare earth compounds with nanostructured yttria have a large surface area, which effectively improves the catalytic efficiency. At the same time, this material can also produce uniform size pores, making it possible to achieve more superior selective catalysis. The orderly mesoporous fluorene-based composite catalyst prepared by the Yan Chunhua team can achieve complete conversion of toxic carbon monoxide gas to non-toxic carbon dioxide gas at lower temperatures, and thus may provide new materials for low cost and clean discharge of automobile exhaust gas.

If it is from 1982, Yan Chunhua has been working in the field of rare earth research for 30 years. He said that basic research is magical. The 17 elements of the rare earth family, each of which is endowed with unique nature, are fundamental. The basic research is also arduous and it is bound to face various difficulties. "In the field of rare earths, we learned a little but we don't know more about it." Yan Chunhua said, "Only by maintaining a learning heart can we go forward."

At the end of the interview, Yan Chunhua said sincerely: “This 15-year study is entirely the result of a collective effort. Every teacher and student in the team has worked hard.”