From: https://chem.jlu.edu.cn/info/1007/13707.htm

Recently, Professor Chen Feijian from the School of Chemistry of Jilin University and the State Key Laboratory of Inorganic Synthesis and Preparative Chemistry and Academician Yu Jihong, together with researchers from Stockholm University in Sweden, Peking University, and Madrid Institute of Materials in Spain, reported a case of a new three-dimensional stable superporous silicate molecular sieve material synthesized by one-dimensional to three-dimensional topological condensation.ZEO-3, the relevant research results were published online in the journal Science on January 20 under the title of "A 3D Extra-Large Pore Zeolite Enabled by 1D-to-3D Topotactic Condensation of a Chain Silicate. The material was developed by Professor Chen Feijian and Academician Yu Jihong's research group. They first synthesized a novel 1D chain silicate material ZEO-2, and ZEO-2 directly underwent topological condensation after high-temperature calcination to generate a 3D stable fully connected superporous molecular sieve ZEO-3. Dr. Li Jian of Stockholm University/Peking University in Sweden finally determined the precise structure of these two materials by using advanced continuous tilt three-dimensional electron diffraction (cRED) technology combined with X-ray powder diffraction fitting refinement method. ZEO-3 has a 3D sixteen-membered ring (16MR) and fourteen-membered ring (14MR) interspersed with super-large pore structure (Figure 1). It is the first pure silicon molecular sieve with a fully connected three-dimensional super-large pore stable structure. It is the smallest known silicon dioxide polymorph so far. Its successful creation is an important breakthrough in the synthesis of super-large pore pure silicon molecular sieves. The ZEO-3 has ultra-high stability, and is still stable after calcination at 1200°C. Its specific surface area exceeds 1000 m2/g. Compared with other zeolites and metal organic frameworks, it exhibits excellent volatile organic compounds (VOCs) adsorption treatment performance. The discovery of the new mechanism of 1D to 3D topological condensation in this work provides new enlightenment for understanding the crystallization mechanism of traditional molecular sieves, and has important guiding significance for the design and synthesis of new molecular sieves and the further clarification of the crystallization mechanism of molecular sieves. At the same time, Science published a commentary on the work entitled "Clicking zeolites together: A new mechanism to synthesize catalytic zeolites gives a previously unknown Russell" by professor E. Morris, a famous expert in the field of molecular sieves. he compared the topological condensation of 1D to 3D to "click chemistry" in molecular sieves and pointed out that the discovery of this mechanism will definitely lead to new topological structures, it is very attractive for the laboratory synthesis of a large number of new molecular sieve structures predicted by theory, thus opening up new application fields.

Zeolite molecular sieves (zeolite) is a kind of crystalline microporous aluminosilicate, which has the characteristics of uniform pore size distribution, regular pore structure, adjustable active center, large specific surface area, good stability and so on. As catalyst, adsorbent and ion exchanger, it has important applications in traditional chemical industry, environmental field and emerging energy storage, photoelectric device, biological medicine, fuel cell, biomass conversion and other fields, especially as a catalyst in petroleum refining, petrochemical, coal chemical, daily chemical and other aspects have an extremely important application. For example, the ultra-stable Y macroporous molecular sieve successfully developed in the 1990 s, due to its large pore structure, its application in the crude oil cracking process triggered a "technological revolution in the refining industry". At present, the industry urgently needs to develop a three-dimensional stable macroporous molecular sieve material with a larger pore system. Because the crystallization mechanism of molecular sieve is not clear, hydrothermal synthesis is difficult to achieve directional control, in the artificial synthesis of zeolite molecular sieve more than 80 years of research history, the synthesis of three-dimensional stable super-large pore silicate molecular sieve has been the goal of the field of molecular sieve, but few breakthroughs in decades, the creation of new stable three-dimensional super-large pore molecular sieve is the original source of innovation, which is also a great challenge in the field of molecular sieve synthesis.

The synthesis of molecular sieves with new topological structures is an important part of molecular sieve research, and most molecular sieves are directly synthesized by hydrothermal or solvothermal synthesis. A few molecular sieves can be obtained by calcining their two-dimensional layered precursors. This calcination is a topological condensation process that does not change the layer structure. Layered precursors can be synthesized directly orThe ADOR(assembly-disassembly-organization-reassembly, assembly-decomposition-reforming-reassembly) process decomposes some germanium-containing molecular sieve structures. Although layered precursors have brought new possibilities for the synthesis of molecular sieves, the synthesized molecular sieves are mainly small pore molecular sieve structure types. It is worth noting that decades of extensive and systematic molecular sieve synthesis studies have not found a topological transformation from one-dimensional (1D) chain silicate molecular sieve precursors to three-dimensional (3D) molecular sieves.

Figure1. ZEO-3 super-large channel system (source: Science)

1D silicate precursor ZEO-2 is a needle-like crystal synthesized with tricyclohexylmethylphosphonium (tricyclohexylmethylphosphonium,tCyMP) as an organic template, and its complex chain-like structure is determined by cRED technology. ZEO-2 hasC2/cspace group, the structure of the silicate chains along[001] direction, each chain inabThe face is surrounded by four identical chains (Fig.2A and C), while at the edge of the chain there are four silicon hydroxyl (Si-OH) or silicon oxygen anions (Si-O-) groups form a single four-membered ring (S4R), the S4R between the chains is slightly staggered but forms a large number of hydrogen bonds in pairs along the [110] and [1-10] directions to stabilize the ZEO-2 structure (Figure 2B). ZEO-2 high-resolution 29Si solid-state nuclear magnetic resonance spectroscopy reveals four Q3and seven kindsQ4ofSi site (Figure 2D), which is consistent with its crystal structure data.

Figure2. ZEO-2 structure: (a) chain along [001] direction;(B) hydrogen bond between two S4R between chains; (c)abChain arrangement on the surface; (D)29Si solid-state NMR spectrum (source: Science)

high temperature calcinationZEO-2, the hydrogen bonding between the two S4Rs will also dehydrate and condense to form a Si-O-Si bridge and D4R (fig. 3A), which is also the first time in the absence of F-ions obtained in pure silica molecular sieve systemD4R. Thus, the ZEO-2 precursor of 1D is topologically transformed into a 3D pure silicon molecular sieve ZEO-3. The ZEO-3 structure retains the ZEO-2 symmetry and chain topology, but compared to ZEO-2, its unit cellaandbThe shaft has contracted17%、cThe shaft expanded only0.4 percent. ZEO-3 is a fully connected superporous molecular sieve with the first 3D 16 × 14 × 14 MR channel system (fig. 3B and c), which is the most stable superporous fully connected pure silicon molecular sieve. its 29Si solid nuclear magnetic spectrum further proves the topological structure transformation from 1D to 3D, I .e. only Q4ofSi sites (Figure 3D).

Figure3. ZEO-3 structure:(A)D4R unit;(B) 14MR channels along [110] and [1-10] directions; (c) 16MR channels along [001] direction; (d) 29Si solid nuclear magnetic resonance spectrum (source: Science)

Spherical aberration electron microscopy once again confirmedZEO-2 and ZEO-3 structures (Figure 4). A weak signal corresponding to the template agent also appeared between the ZEO-2 chains, and this position will become a ZEO-3 14MR channel after the topology transformation, while the ZEO-3 16MR and 14MR channels are clearly visible, and the smaller 4, 5 and 6MR structures in the two materials are also observed.

Figure4. Spherical aberration electron micrographs of ZEO-2 and ZEO-3:(A) ZEO-2 along [110] belt axis;(B) ZEO-3 along [110] belt axis;(C) ZEO-3 along [001] belt axis (Source: Science)

The ZEO-3 has ultra-high stability and remains stable when calcined at 1200°C; it has a very open skeleton structure with a skeleton density (FD) of only 12.76 tetrahedral atoms (T)/1000 Å3, itsThe BET specific surface area also reaches 1000 m2/g; its theoretical density is close to that of water, only 1.27g/cm3., less than quartz (2.65 g/cm3) half of the density. All these excellent features makeZEO-3 exhibited excellent VOCs adsorption treatment performance (FIG. 5).

Figure5. Performance of ZEO-3 treatment VOCs:(A) static adsorption;(B) dynamic adsorption;(C) desorption curve (source: Science)

Further doping with skeleton heteroatoms or metal loading as a catalyst carrier will make it have important industrial catalytic application potential in many fields such as macromolecular catalysis, petrochemical and so on.

The communications contact for this work is Stockholm University, Sweden/Dr. Li Jian of Peking University, Professor Miguel A. Camblor of the Institute of Materials of Madrid, Spain, Professor Chen Feijian of Jilin University and Academician Yu Jihong; Dr. Li Jian, Dr. Gao Zihao of the Institute of Materials of Madrid, Spain and Dr. Lin Qingfang of Jilin University are co-first authors. This work has been supported by the National Natural Science Foundation of China Basic Science Center project, key research and development plan and 111 plan.

Full text link:https://www.science.org/doi/10.1126/science.ade1771