The diameter of the synthesized nanomaterial can be limited due to the existence of these pores, but the additional template matrix material needs to be further removed to obtain the desired nanorod nanomaterial. Recent molecule-based templates can overcome these shortcomings. Professor Lin Zhiqun's research team at the Georgia Institute of Technology in the United States reported a synthesis method that can precisely control the diameter, composition, morphology and structure of the synthesized nanomaterials. The polymer brush used by the researchers to synthesize nanowires is different from that reported in previous articles. Professor Lin Zhiqun of Georgia Institute of Technology used a bottle-scrubbing block copolymer (BBCP), which has a cellulose skeleton with dense grafting functional block copolymers as side chains, including multiple cavities. In addition, the tri-substituted hydroxycellulose functional groups on the cellulose backbone allow dense polymer side chains to be grafted onto the cellulose backbone. The researchers used this advantage to synthesize the required straight BBCP. A series of BBCPs were synthesized by atom transfer radical polymerization. Then the BBCP was dispersed in DMF polar solvent. Due to the difference of polarity between BBCP and the solution, the molecular chains in BBCP were pulled together to form a large reaction chamber. The inorganic precursors dispersed in the solvent are preferentially distributed in the reaction chamber formed by the molecular chains in the BBCP due to the polar effect of the solvent, so the high concentration of aggregation drives the nucleation of inorganic materials and the growth of inorganic nanorods. (Science, 2016, DOI: 10.1126/science.aad8279) Figure 14. Amphoteric molecule use straight cylinder type Illustration of the synthesis mechanism of BBCP as a nanoreactor for the synthesis of one-dimensional nanocrystals A) nanorods synthesized with the assistance of a cellulose template; (B) a nanorod with a core-shell structure which is synthesized by adopting a template-assisted method; (C) nanotubes synthesized by a cellulose template-assisted method; Figure 15. Transmission electron micrographs of different kinds of nanorods synthesized with the assistance of cellulose templates A year later, Andr Andrés Guerrero-Mart Martínez, Luis M. Liz Marz Marzán, and OvidioPe OvidioPeña-Rodr Rodríguez reported a femtosecond laser pulse annealing process that reshaped gold nanorod sols so that their SPR spectra were as sharp as single gold nanorods. Figure 16. Characterization of gold nanorods after laser treatment Lei's team reported a simple batch preparation technology for oxide nanowires, which directly converts bulk alloy materials into oxide nanowires without catalysts or external conditions. (Science 2017, 355, 267-271.) Figure 17. Morphology of nanowire during synthesis 3. Two-dimensional material Two-dimensional materials refer to materials in which electrons can only move freely (planar motion) in two dimensions of non-nanometer scale (1-100 nm), such as nano-thin films, superlattices and quantum wells. Two-dimensional materials were proposed with the successful isolation of graphene, a single atomic layer of graphite material, by Geim's group at the University of Manchester in 2004. Transition metal disulfides (TMDs) such as MoS2, MoSe2, WS2, etc., their 2D atomic crystals have attracted much attention in recent years due to their excellent electronic properties. In order to exploit their more application potential, we need to find a reliable synthesis method that can precisely control their chemical composition and electronic structure. Professor Duan Xiangfeng of Hunan University (the first unit) and the University of California, Los Angeles, and Duan Xidong of Hunan University reported a universal synthesis method that can control the growth of 2D atomic crystals of multiple heterojunctions, multiple heterojunctions and superlattices. By modified vapor deposition, titanium filler rod ,titanium tubing price, with a reverse gas flow during a continuous vapor deposition process with temperature fluctuations, existing 2D crystals can be cooled to prevent unwanted thermal degradation and uncontrolled homogeneous nucleation, thus enabling highly robust block-by-block epitaxial growth.
While not being limited to a single heterojunction, More different 2D heterojunctions (e.g., WS2-WSe2 and WS2-MoSe2), multi-heterojunctions (e.g., WS2-WSe2-MoS2 and WS2-MoSe2-WSe2), and superlattices (e.g. WS2 − WSe − WS2 − WSe − WS2) were successfully fabricated by precise spatial modulation. The prepared WSe2-WS2 exhibits excellent diode characteristics with a high rectification ratio of 105. (Science，2017，DOI: 10.1126/science.aan6814) Figure 18. By modification CVD, Robust Epitaxial Growth of 2D Single-Layer Heterojunctions, Multi-Heterojunctions, and Superlattices Figure 19. Different Growth of 2D lateral heterojunction Accurate design of high performance semiconductor films with vertical structure at the atomic scale can be used in modern integrated circuits and new materials. One way to obtain such films is to achieve continuous layer-by-layer self-assembly, that is, to use two-dimensional building materials stacked in the vertical direction and connected by van der Waals forces. Two-dimensional materials have been developed vigorously in recent years, but at present, graphene and transition metal disulfides, which are only 1 or 3 atoms thick, are used to realize some heterojunctions which are difficult to prepare earlier, and show excellent physical properties. Moreover, there is no large-scale self-assembly method that can not only maintain the intrinsic characteristics of two-dimensional material construction, but also produce interlayer interface, which limits the transformation of layer-by-layer self-assembly method to a small-scale large-scale preparation. Jiwoong Park et al., Cornell University, reported methods to achieve high levels of spatial uniformity and intrinsic sandwich interfaces to produce semiconductor thin films on a wafer-scale scale. The vertical component of the film is realized by the self-assembly of two-dimensional material modules on the atomic scale in vacuum. At the same time, some large-scale and high-quality heterojunction films and devices have been prepared, including superlattice films, resistance-adjustable tunnel junction arrays produced in batches, band-controlled heterojunction tunnel diodes and millimeter-scale ultra-thin films. The stack of films is removable, interruptible, and compatible with interfaces such as water and plastic, enabling integration with other optical and mechanical systems. （Nature，2017，Doi:10.1038/nature23905） Figure 20. High-quality semiconductor film obtained by layer-by-layer self-assembly Figure 21. Programmed vacuum stack (PVS) process In view of the strong in-plane (intra-layer) stability and the relatively weak out-of-plane (inter-layer) interaction of two-dimensional materials, such materials can be stacked with each other to form a variety of device types with a wide range of functions. To some extent, building two-dimensional material heterostructures is like building Lego bricks. In order to better control the function of two-dimensional heterostructures, it is necessary to prepare two-dimensional material modules at the level of single-layer thin films and control their single-level stacking. However, the current lift-off method for preparing the single-layer sheet has the disadvantages of high cost and difficulty in stably lift-off the two-dimensional crystal structure, so it is urgent to introduce a new preparation method to improve the existing lift-off process. A team led by Jeehwan Kim of the Massachusetts Institute of Technology in the United States has developed a general technology of layer resolution separation (LRS) to produce two-dimensional material monolayers on a wafer scale (5 cm in diameter). This technology first requires the rapid growth of thicker two-dimensional materials on the wafer, then the collection of single stacked layers of these materials, and finally the preparation of single layers through multiple splitting processes. The method can be used for preparing a plurality of single-layer materials including molybdenum disulfide and tungsten sulfide, and the van der Waals heterostructure designed and prepared on the basis has atomic-scale thickness and good performance.
(Science, 2018, DOI: 10.1126/science.aat8126） Figure 22. Process for preparing monolayer two-dimensional material by LRS technology Figure 23. Fabrication of Wafer Level Monolayer 2D Materials by LRS Artificial superlattices based on van der Waals heterostructures of two-dimensional atomic crystals (such as graphene or molybdenum disulfide) have solved the problems that existing materials have not yet broken through. Typical strategies for making such artificial superlattices rely on arduous layer-by-layer peeling and re-stacking, with limited yield and reproducibility. Bottom-up methods using chemical vapor deposition can produce high-quality heterostructures, but become increasingly difficult for higher-order superlattices. While the intercalation of two-dimensional atomic crystals with alkali ions provides an alternative to superlattice structures, these generally have poor stability and severely modify the electronic properties. In the same year, Professor Duan Xiangfeng, Professor Huang Yu and Professor Liao Lei of the University of California, Los Angeles, reported an electrochemical molecular intercalation method for a new class of stable superlattices in which single molecular atomic crystals alternate with molecular layers. Using black phosphorus as a model system, the insertion of cetyltrimethylammonium bromide produces a monomolecular phosphorus molecular superlattice in which the interlayer distance is more than twice that in black phosphorus, effectively separating the phosphorus heterocyclic monolayer. A study of transistors fabricated from a single layer of phosphorus molecular superlattices shows on/off current ratios in excess of 107, as well as excellent mobility and superior stability. It has further been shown that several different two-dimensional atomic crystals, such as molybdenum disulfide and tungsten diselenide, can be intercalated with quaternary ammonium molecules of different sizes and symmetries to produce crystals with specific molecular structures, interlayer distances, phase compositions, etc. These studies define a versatile materials platform for fundamental research and potential technology applications. Figure 24. In the process of dynamic intercalation , Evolution of structure and properties from BP to MPMS Figure 25. From TEM characterization of the structural evolution of BP to MPMS Graphene is a two-dimensional carbon nanomaterial with hexagonal honeycomb lattice composed of carbon atoms with sp ² hybrid orbitals. Graphene is considered to be a revolutionary material in the future because of its excellent optical, electrical and mechanical properties, and its important application prospects in materials science, micro-nano processing, energy, biomedicine and drug delivery. Andre Geim and Konstantin Novoselov, physicists at the University of Manchester, UK, won the 2010 Nobel Prize in Physics for successfully separating graphene from graphite by micromechanical exfoliation. The common production methods of graphene powder are mechanical exfoliation, oxidation-reduction and SiC epitaxial growth, and the film production method is chemical vapor deposition (CVD). However, due to the low yield, sub-micron thickness and poor electrical properties of single-layer graphene, the preparation process of solution exfoliated graphene sheets still faces great challenges. The monolayer graphene oxide with larger lateral size can be obtained by adopting the graphene oxide for exfoliation, and the yield is less than 100%; although a large amount of work is completed in the research, the complete removal of oxygen-containing functional groups still cannot be realized, so the obtained reduced graphene oxide has high disorder, Resulting in inferior physicochemical properties to materials prepared using chemical vapor deposition (CVD). Reduced graphene oxide (Rgo) has been considered to have potential applications in the fields of catalysis and energy, and even the disordered Rgo still has great value. How to reduce graphene oxide efficiently is an urgent problem to be solved. Professor Manish Chhowalla of Rutgers University in the United States reported a microwave method to prepare high-quality graphene in only 1-2 seconds. When the graphene material prepared by the method is used as a channel material in a field effect transistor, the electron mobility can be more than 1000m2/V/s, and the graphene material used as a catalyst carrier material shows excellent oxygen evolution catalytic performance.
(Science, 2016, DOI: 10.1126/science.aah3398) The researchers used an improved hummers method to remove graphene oxide and dissolve it into multilayer graphene oxide sheets in aqueous solution. The stable graphene oxide array dispersion solution can be recombined into different forms (e.g., film-like, paper-like, fibrous) in an aqueous solution. The synthesized oxidized graphene precursor is insulating due to the oxygen-containing functional groups which are covalently connected with carbon atoms inside the oxidized graphene precursor. Oxidized graphene with a side thickness of tens of microns was placed in a traditional microwave oven and heated at 1000 W for 1-2 s to achieve the reduction of oxidized graphene. Excitation of graphene oxide under microwave conditions has been previously reported, but the reduction efficiency is still very low. Researchers first put the material under microwave for pre-annealing, which can make the material conductive, so as to absorb the microwave, so as to achieve rapid heating of oxidized graphene, and finally the microwave heating process can achieve the desorption of oxidizing functional groups, and make the surface of the material ordered. Figure 26. With intact single graphene oxide , reduced graphene oxide, and CVD-grown graphene, characterization results of the physical properties of the microwave-assisted reduced graphene oxide Scanning electron micrograph of a monolayer graphene oxide sheet deposited on a silicon substrate. The nanoarray of graphene oxide has a lateral dimension of 50 um. The Raman spectrum is consistent with the Raman spectrum of the graphene grown by CVD, showing a symmetric 2D band and a minimum D band, and the sharp Raman peaks indicate that the microwave-assisted reduction oxidized graphene has high crystallinity and microwave-assisted reducibility. The crystal size and I2D/IG of microwave-assisted reduced graphene oxide are close to those of the samples prepared by other methods, but significantly higher than those of reduced graphene oxide and dispersed graphene materials. In addition to graphene, researchers have developed a new material, boron nitride, in recent years. Known as white graphene, hexagonal boron nitride (hBN) consists of atomically flat layers of alternating hexagonal B and N atoms held together by interlayer van der Waals interactions. Unlike the excellent conductivity of graphene, hNB has extremely excellent insulating properties, which makes it play an important role in various basic scientific and technological fields, such as charge fluctuation, contact resistance, gate dielectric, passivation layer and atomic tunneling layer. Although micron-sized polycrystalline hBN has been realized and used for fundamental research, wafer-scale single-crystal hBN (SC-hBN) thin films are not yet available for practical applications. One way to synthesize sc-hBN films is to start with randomly oriented triangular particles and eventually merge them to form polycrystalline hBN (pc-hBN) films. However, the grain boundaries between randomly oriented hBN grains inevitably produce PC-hBN films, and the large number of grain boundaries in PC-hBN leads to charge scattering and site trapping, which hinders the development of high-performance electronic devices. Therefore, researchers are expected to obtain an alternative to SC-hBN films. Young Hee Le of Sungkyunkwan University, Ki Kang Kim of Dongguk University, and Soo Min Kim of KIST-Research Institute, Korea, jointly reported a method for synthesizing a wafer-scale single-crystal hBN (SC-hBN) monolayer film by chemical vapor deposition. The limited solubility of boron (B) and nitrogen (N) atoms in liquid gold promotes a high degree of diffusion of atoms at the liquid surface at high temperatures, resulting in round hBN particles. These grains further evolve into closely packed grains through the self-alignment of B and N edges formed by the electrostatic interaction between grains, and finally form the SC-hBN film on the wafer scale. This SC-HBn film also enables the synthesis of wafer-scale graphene/hBN structures and single-crystal tungsten disulfide.
(Science, 2018, DOI: 10.1126/science.aau2132) Figure 27. Single crystal Synthesis of hBN film In addition to the above new methods of preparing two-dimensional materials, Kourosh Kalantar-zadeh and Torben Daeneke of RMIT University successfully prepared very thin sub-nanoscale HfO2, Al2O3 and Gd2O3 by using liquid metals. Liquid metal refers to an amorphous metal. Liquid metal can be regarded as a mixture of positive ion fluid and free electron gas. Liquid metal is also an amorphous, flowable liquid metal. Room-temperature liquid metals have many interesting surface and volume properties, which make them widely used in various engineering applications, including flexible electronic devices and microfluidics. Gallium-based eutectic alloys such as EGaIn (containing gallium and indium), gallium-indium-tin alloys are liquid at room temperature, non-toxic, and are held together by metallic bonds. Unlike molecular and ionic liquids, liquid metals are rarely used as reaction solvents. The team pointed out that although two-dimensional (2D) oxides have a wide range of applications in electronics and other technologies, many oxides are not easy to synthesize 2D materials by conventional methods. The team used a non-toxic eutectic gallium-based alloy as the reaction solvent and added the alloyed desired metal to the melt. Thermodynamically, the composition of self-limiting interfacial oxides is predicted. At the same time, the surface oxides are separated as 2D layers both on the substrate and in the suspension, and it is found that very thin sub-nanoscale HfO2, Al2O3 and Gd2O3 can be produced. The reaction route based on liquid metal can be used to produce 2D materials which can not be obtained by conventional methods before. Using liquid metal at room temperature as the reaction environment for the synthesis of low-dimensional oxide nanomaterials is another powerful tool for the method of obtaining 2D materials. (Science,2017,DOI:10.1126/science.aao4249) Figure 28. Basic principle and synthesis method Figure 29. Characterization of materials obtained by the gas injection method In addition to the above large-scale two-dimensional nanomaterials, there is another kind of two-dimensional nanosheet morphology with smaller size. In 2016, Professor Huang Xiaoqing's team prepared multi-level Pt-Co nanosheets by wet chemical reduction method, and combined with a series of advanced characterization methods and theoretical simulations, characterized in detail the ordered intermetallic structure, high-index crystal surface and platinum-rich nanostructure on the surface of multi-level Pt-Co nanosheets. The effect of this unique structure on the catalytic performance of MOR, EOR, and ORR was studied in depth. Among them, the ORR performance of Pt3Co nanosheets is the best among the reported ORR catalysts in the Pt-Co system, even comparable to that of many Pt-Ni-based catalysts. This study has important guiding value and significance for the fine control of the surface structure of one-dimensional platinum-based nanomaterials, the design of high-index crystal planes and ordered intermetallic nanostructures, and the control of the catalytic performance of nanomaterials. (Science, 2016, 354, 6318, 1410-1414) Figure 30. Structure and DFT Simulation of Pt-Co Nanosheet 4. Other Noble metal catalyst is a kind of efficient and popular catalyst at present, and the research on noble metal catalyst has been continuously carried out in recent years. Atomic-scale noble metal catalysts have the highest atom utilization efficiency, and their catalytic activity is many times higher than that of nanoparticles, clusters and bulk noble metals. Over time, catalysis by individual transition metal atoms (not just noble metals) has become increasingly popular. Figure 31. Development History of Material Morphology The process of preparing a single transition metal atom catalyst is generally to reduce the ratio of the amount of metal precursor to the amount of substrate, then to use a solvent or other means (usually using vacancies or defects in the substrate) to increase the interaction between the metal precursor and the substrate, and finally to reduce the metal precursor to a single metal atom.
Of course, in this process, there is no mention of how to disperse the monoatomic metal precursor uniformly on the substrate, which is a common challenge in the study of single transition metal atom catalysts. Following the evolution in fig. 29, some of the same rules and challenges can be obtained. 1) the amount of the transition metal precursor: generally, the amount of the transition metal precursor is reduced to ensure that individual transition metal atoms are not agglomerated into clusters, nanoparticles, etc. According to some work reported in the latest literature, the ratio of the amount of metal precursor to that of the substrate is generally less than 0.5%, however, If the amount of transition metal precursor can be increased while achieving uniform dispersion of individual metal atoms, it will be beneficial to the industrialization of atomic-scale catalysts. 2) The study of catalytic mechanism: It is generally discussed whether a single transition metal atom activates its surrounding atoms to form a new active site, or whether a single transition metal atom still plays a role in reducing the activation energy of the reaction. At the same time, whether the path of a single transition metal atom participating in the catalytic reaction is consistent with that of the traditional catalytic reaction. 3) Stability: whether a single noble metal atom can stably exist on the substrate. For example, a single noble metal atom is dispersed on graphene, but due to the weak bonding ability between carbon atoms and noble metal atoms, a single metal atom will agglomerate in the catalytic reaction, so whether Pd atoms in this paper can stably exist on the titanium dioxide substrate is worth further study. In response to these challenges, Professor Zheng Nanfeng of Xiamen University and his team reported a photochemical method for preparing atomically dispersed Pd1/TiO2 catalysts with relatively high content and high stability at room temperature in Science. The first author of this paper, Dr. Liu Pengxin et al., successfully realized the stable dispersion of single-atom Pd on TiO2 nanosheets protected by ethylene glycol by photodeposition technology, and the loading of Pd atoms reached 1.5%. The Pd1/TiO2 catalyst exhibited a very high catalytic activity for the hydrogenation of carbon-carbon double bonds, and its performance was still 9 times that of the commercial Pd catalyst after 20 cycles! More importantly, the Pd1/TiO2 catalyst-eg system can catalyze the hydrogenation of aldehydes by splitting hydrogen molecules, which is 55 times higher than that of commercial Pd catalyst! Figure 32. Pd/TiO2 catalyst preparation method A certain amount of H2PdCl4 acid was added to a beaker in which titanium dioxide was uniformly dispersed, and the chloropalladate acid was adsorbed by titanium dioxide, then irradiated by low-density UV light of a xenon lamp for 10 min, and then washed with deionized water. Finally, a light gray dispersed product is obtained. Similarly, noble metal catalysts have excellent catalytic performance and have good application prospects in many aspects, such as catalytic conversion, fuel cells and so on. However, due to the high price of precious metals, the production cost has been seriously increased, which greatly hinders the actual development of precious metal catalysis. This requires us to reduce the loading of noble metals as much as possible while maintaining the high activity and stability of noble metals, such as the preparation of atomic-scale catalysts, the synthesis of hollow or core-shell catalysts. However, these methods can not accurately control the composition and size of the core and shell, and in the catalytic process, the catalyst is easy to recombine, form alloys and lose its original activity. In view of the above problems, Sean T. Hunt et al. Of MIT used a template method to prepare a single-atomic-layer noble metal-supported core-shell catalyst with a transition metal carbide surface (Science, 2016, DOI: 10.1126/science.aad8471). The noble metal salt and that transition metal oxide are wrap in a SiO2 template at first, then the SiO2 template is carbonized step by step, and finally the SiO2 template is remove, so that the transition metal carbide surface loaded single-layer noble metal core-shell structure catalyst is prepared, and the catalyst shows ultrahigh electrocatalytic activity and stability. The following is a detailed explanation of the work.
Figure 33. The preparation method Figures A-E show the whole evolution process of material preparation. First, the silica-coated noble metal salt and oxide nanoparticles (A) are calcined in CH4/H2 mixed gas at 200 (B), 600 (C) and 900 (D), respectively. Finally, the SiO2 template is removed to prepare the single-layer Pt/WC core-shell structure catalyst. The lower part is the STEM diagram of each stage. The element distribution and linear scan of E diagram well illustrated the successful preparation of Pt/WC core-shell structure catalyst. In daily life, the endless flow of vehicles on the road will emit harmful gases such as CO, NO and various hydrocarbons, which will pollute the environment and reduce air quality. Therefore, in the automobile manufacturing industry, diesel oxidation catalyst materials (DOCs) are widely used in automobile exhaust emissions, in which Pt metal can play an efficient catalytic role in this oxidation reaction process (the application of noble metal catalysts based on single atoms has attracted wide attention due to their high catalytic activity and high catalytic selectivity for catalytic substrates). However, under high temperature oxidation conditions, Pt nanoparticles sintered on oxide supports tend to form larger particles (single-atom-based catalysts have strong mobility and aggregation properties, which make such materials prone to agglomeration during heating), thus reducing the catalytic effective area and thus reducing the catalytic reaction efficiency. How to keep the efficiency of the catalyst unchanged in the process of using the catalyst at high temperature for a long time has been a key research topic for the actual commercialization of the catalyst. The research team of Abhaya K. Datye (corresponding author) from the University of New Mexico in the United States used Ce oxide powder with the same surface area and different exposed crystal faces, and mixed CeO2 with Pt/Al oxide catalyst for heat treatment at 800 C in air. Researchers have ingeniously used the high-temperature mobility of metal atoms to prepare a high-temperature resistant single-atom Pt/CeO2 catalyst. The experimental results show that the Pt particles will move to the surface of CeO2 and be trapped during the high temperature heat treatment. The characterization results show that polyhedral and nanorod CeO2 are more efficient in immobilizing Pt atoms than cubic CeO2. Meanwhile, the high-temperature synthesis condition ensures that the binding sites of Pt atoms and CeO2 are in the most stable binding state, so the catalyst material with atomic-level dispersion and high temperature resistance can be prepared. (Science 353.6295 (2016): 150-154. DOI: 10.1126/science.aaf8800) Figure 34. Synthesis mechanism and properties In the field of catalysis, in addition to the current hot monatomic systems, porous materials have also attracted considerable attention due to their wide range of industrial applications, from gas separation to catalysis. The topological characteristics (in particular the size of the pores in the individual pores and the uniformity of these pores) are key factors in determining their excellent performance in a particular application. The construction of hierarchical porous structures that maintain their overall crystalline sequence is theoretically desirable because highly ordered structures can, in turn, significantly improve performance. At present, there are some studies related to the above theory, such as mesoporous TiO2 single crystals with significantly improved conductivity and electron mobility compared with nanocrystalline TiO2, and mesoporous crystalline zeolite molecular sieves have stronger framework acidity and stability compared with amorphous molecular sieves. Professor Li Yingwei of South China University of Technology and Professor Chen Banglin of the University of Texas at San Antonio have constructed highly oriented and ordered micropores in metal-organic framework (MOF) single crystals, opening up a new era of three-dimensional ordered macro-microporous materials (I. E. Materials containing both macro-and micro-pores) in the form of single crystals. This strategy benefits from the powerful modeling effect of the polystyrene nanosphere template and the dual solvent-induced heterogeneous nucleation method.
This process synergistically enables the in situ growth of MOFs within the ordered voids, resulting in single crystals with oriented and ordered macroscopic microporous structures. Compared with conventional polycrystalline hollow and disordered pore ZIF-8, the improved diffusion properties of this layered framework and its stable single-crystal properties enable it to have excellent catalytic activity and recyclability for macromolecular reactions. (Science,2017,DOI:10.1126/science.aao3403) Figure 35. In-situ Synthesis of SOM-ZIF-8 Nanoparticles and Its Structural Confirmation In addition, DNA is widely used in the assembly of nanoparticles to construct highly ordered materials. Through the interaction between specific DNA sequences, nanoparticles can be controlled to form a variety of structures, including more than 30 different lattice symmetrical structures, and the distance between nanoparticles can be controlled from 3 nm to 130 nm. Compared with a variety of assembly structures of nanoparticles in solution, DNA-mediated surface assembly of nanoparticles has only a very limited number of structures. Moreover, at present, the performance of nanoparticle assembly technology, including DNA regulation, on nanoparticle surface assembly is also unsatisfactory. The size, shape, and composition of the nanoparticles involved in the formation of independent nanostructures cannot be clearly explained in the formation of two-dimensional and three-dimensional extended lattices. At present, there is still a lack of nanoparticle assembly technology that can quickly, accurately and controllably control the assembly of nanoparticles on a large surface to form the expected two-dimensional or three-dimensional structure, and can clearly explain its size, shape and composition. Three professors, Vinayak P. Dravid, Koray Aydin and Chad A. Mirkin, from Northwestern University in the United States, worked together to glue 300 nm thick PMMA on the surface of a gold-plated silicon wafer, and then use electron beam lithography (EBL) to form an orderly hole array on the PMMA. The exposed gold surface at the bottom of the well is densely decorated with DNA sequences with sticky ends. The surface of gold nanoparticles was also modified with DNA sequences with sticky ends. These DNA-modified gold nanoparticles are assembled layer by layer on the gold surface at the bottom of the PMMA pore through complementary base pairing at the sticky end. The nano-particle assembly technology which uses PMMA as a template and is regulated by DNA can control the arrangement, the interval and the sequence of the nano-particles in each assembly structure so as to realize controllable broadband absorption. In addition, this assembly technology can form responsive plasmonic nanostructures that cannot be formed by other assembly technologies. (Science，2018，DOI：10.1126/science.aaq0591) Figure 36. With Schematic Diagram of Reconfigurable Nanoparticle Assembly Regulated by DNA with PMMA as Template Figure 37. With DNA-mediated monolayer assembly of nanoparticles using PMMA as templates Figure 38. Two floors Three-layer nano particle assembly structures 5. Sum up In a word, through the unremitting efforts of researchers worldwide, the synthesis and application of nanomaterials have made gratifying progress in the past 20 years, providing a series of high-quality nanostructures with precisely controllable structures and properties at the molecular or atomic level for subsequent basic and applied research. As a functional structural unit, high-quality nano-morphology structure can also be widely used in self-assembly research. Although gratifying progress has been made in the synthesis and application of nanomaterials, its development still has a long way to go, which requires the efforts of interdisciplinary and interdisciplinary researchers to carry forward the past and forge ahead into the future. Due to the limited ability of Xiaobian, if there is any omission, please add it! This article is contributed by Z, Chen,titanium tubing price, the academic group of the editorial department of Material Man, and edited by Material Niu. Cailiaorenvip Back to Sohu, see more Responsible Editor:. yunchtitanium.com
- Список форумов
- Часовой пояс: UTC+02:00 Европа/Калининград
- Удалить cookies форума
- Наша команда
- Связаться с администрацией
Advertisements by Advertisement Management
Создано на основе phpBB® Forum Software © phpBB Limited
Русская поддержка phpBB