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Scientists Reveal the Uniqueness of Ullmann Reaction Path

a research team reported that the Ullmann reaction path is unique regardless of predesigned assembled structures, dominated by the fact that weak intermolecular interaction in assembled nanostructures is suppressed by strong covalent bonding during reactions.

　　On-surface Ullmann coupling has been intensely utilized for the tailor-made fabrication of conjugated frameworks towards molecular electronics, however, reaction mechanisms are still limitedly understood. While manipulating the noncovalent intramolecular interaction and cage effect on surface have been proven to be effective in steering Ullmann coupling reactions, reaction mechanisms are still under intensive investigation nowadays.
　　Motivated by such a challenge, a research team led by Prof. Fei Song at Shanghai Advanced Research Institute (SARI), along with collaborators from Shanghai Institute of Applied Physics, Soochow University, Central South University and Harbin Institute of Technology, reported that the Ullmann reaction path is unique regardless of predesigned assembled structures, dominated by the fact that weak intermolecular interaction in assembled nanostructures is suppressed by strong covalent bonding during reactions. The research results were published in Nano Research entitled "Identifying the convergent reaction path from predesigned assembled structures: Dissymmetrical dehalogenation of Br2Py on Ag(111)”.
　　Surface Ullmann coupling of 2,7-dibromopyrene (Br2Py) on Ag (111) has been elucidated by scanning tunnelling microscopy (STM), X-ray photoelectron, spectroscopy (XPS) and density function theory (DFT). By manipulating deposition conditions, diverse assembled architectures have been constructed for Br2Py on Ag (111). Stepwise annealing leads to an identical reaction diagram for the surface Ullmann coupling from individual assembled structures convergent into the brick-wall-pattern OM dimers first, and then into elongated OM chains in order and eventually long-range polymers with direct C–C coupling. While the reaction mechanism is demonstrated to be dominated by the metal coordinated and halogen bonding motifs, interestingly, it has also been revealed that surface adatoms and dissociated Br atoms play a crucial role in coupling reactions.
　　Although previous reports have claimed that pre-self-assembly strategy can be utilized to steer Ullmann reaction paths and intermediate species, however, for Br2Py on Ag (111) herein, distinct phenomenon is observed while no apparent relationship is found between predesigned nanostructures and reaction path (reactants). Thus, this report proposes essential insights on fundamental understanding of surface Ullmann coupling towards high-yield surface synthesis of functional nanostructures for nono-electronics.
　　Convergent reaction path from diverse assembled structures. (Image by Prof. SONG’s group)

2021-05-25 more+

Researchers Develop a Novel Approach to Heterogeneous Photosynthesis of Azo- Compounds in Continuous Flow

a research team reported a novel approach of gas-liquid-solid segmented flow, which enabled utilizing the solid photocatalysis in continuous flow without clogging. Owning to the inner recirculation in liquid segments and the formed thin film, this method ensures the effective suspension of solid catalysts in flow, resulting in enhanced mass transfer and irradiation.

　　Photocatalytic reactions, which allow unlocking some chemical transformations under mild conditions that are unavailable to conventional ground-state pathways, can save energy consumption and improve intrinsic safety of the processes. As a sustainable and low-carbon technology, it has high potential to contribute to the national commitment of carbon peak and carbon neutrality. Continuous flow chemistry can, to a large extent, migrate the “light limitation” problem in traditional batch protocols, and the use of heterogeneous photocatalysis can overcome the disadvantages of difficult catalyst recovery in homogeneous systems. However, effective handling of the solid photocatalysis in continuous flow still remains very challenging.
　　Motivated by such a challenge, a research team led by Prof. TANG Zhiyong and Associate Prof. Zhang Jie at Shanghai Advanced Research Institute (SARI), Chinese Academy of Sciences, reported a novel approach of gas-liquid-solid segmented flow, which enabled utilizing the solid photocatalysis in continuous flow without clogging. Owning to the inner recirculation in liquid segments and the formed thin film, this method ensures the effective suspension of solid catalysts in flow, resulting in enhanced mass transfer and irradiation. The research results were published in Chemical Engineering Journal entitled “Tuning the Gas-Liquid-Solid Segmented Flow for Enhanced Heterogeneous Photosynthesis of Azo- Compounds” .
　　Azobenzene and azoxybenzene are important precursors in pigment industry, electronic industry and pharmaceutical industry. In this work, the selective synthesis of azo- compounds from nitrobenzene by graphitic carbon nitride (g-C3N4) photocatalysis was selected as model photocatalytic reaction. By combing the visual flow experiments, the model reaction under gas-liquid-solid segmented flow was investigated thoroughly. Meanwhile, the effects of flow behavior on the photoreaction performance were quantified.
　　Scientists found that the continuous flow could greatly shorten the reaction time. The photocatalytic reaction performance was very sensitive to the gas-liquid-solid segmented flow conditions, which needed to be carefully tuned. It was identified that the increasing inert gas fraction resulted in more stable segmented flow with shorter liquid segments and thinker liquid film. The maximum productivity per volume of the continuous photo-microreactor reached 26.1 mmol/h*L. Benefiting from the advantage of “numbering-up”, this value was more than 500 times that of the batch reactor (80 L) reported in the open literature. These results demonstrated great potential of gas-liquid-solid segmented flow in the field of heterogeneous photocatalysis.
　　This work provides a new route to utilize the heterogenous catalysis in continuous flow, which can be applied as a universal method to intensify the synthesis of functional materials, fine chemicals and active pharmaceutical ingredients (APIs), thereby promoting the transformation from conventional batch processes to green, safe and efficient continuous flow processes.
　　This work was supported by the Youth Innovation Promotion Association of Chinese Academy of Sciences, the STS Program of Chinese Academy of Sciences, and Frontier Scientific Research Project funded by Shell.
　　Figure 1. Heterogeneous photosynthesis of azo- compounds in gas-liquid-solid segmented flow (Image by SARI)
　　Figure 2. Comparison of the photocatalytic performance between (a) the batch reactor and (b) the continuous flow microreactor (Image by SARI)
　　Figure 3. Effects of total flow rate on the nitrobenzene conversion and the liquid segment length in the gas-liquid-solid segmented flow (Image by SARI)
　　Contact: TANG Zhiyong
　　Shanghai Advanced Research Institute, Chinese Academy of Sciences
　　Email: tangzy@sari.ac.cn
　　

2021-05-17 more+

Researchers Propose a Novel Approach to Precisely Control the Gas-liquid Taylor Flow Pattern for Continuous Flow Chemistry

A research team reported a novel approach of adding pulsation field to precisely regulate the gas-liquid Taylor Flow.

　　Microreactor exhibits great potential for intensified synthesis of advanced materials and chemicals in continuous flow mode, for its various advantages such as excellent heat and mass transfer efficiency, high controllability, easy scale-up, etc. Among numerous flow patterns, gas-liquid Taylor flow represents the characteristics of wide operation window, low axial back mixing and good radial mixing, thus, has been proven as an ideal flow regime to enhance chemical reactions. However, the method to precisely control the Taylor flow pattern is still lacking.
　　Motivated by such a challenge, a research team led by Prof. TANG Zhiyong and Associate Prof. Zhang Jie at Shanghai Advanced Research Institute (SARI), Chinese Academy of Sciences, reported a novel approach of adding pulsation field to precisely regulate the gas-liquid Taylor Flow. The research results were published in Chemical Engineering Journal entitled “Regulation of Gas-Liquid Taylor Flow by Pulsating Gas Intake in Micro-channel” .
　　In this work, the research team used a simple valve arrangement to introduce the pulsation filed, thus producing periodic acceleration and deceleration motion of liquid slugs. By combing visual flow experiments with computational fluid dynamics (CFD) simulation, the temporal-spatial migration of the Taylor flow pattern under pulsating gas intake conditions was investigated. A high-speed camera is used to track the trajectory of gas-liquid interface by the Lagrangian method, while the numerical simulation is used to acquire the flow field distribution at different moments using the Euler method. Meanwhile, the involved forces during bubble formation and the characteristics of bubble length and velocity under pulsation were analyzed in detail.
　　By studying the temporal-spatial migration of the pattern, scientists found that the pulsation can increase the power of inertial force on the Taylor flow pattern. Moreover, the pattern can be destroyed when the pulsation energy exceeds a certain value.
　　This work provides a new route to regulate precisely the gas-liquid Taylor flow, and will contribute to future applications of this technique to intensify various gas-liquid reactions in continuous flow.
　　This work was supported by the Youth Innovation Promotion Association of Chinese Academy of Sciences, the STS Program of Chinese Academy of Sciences and Frontier Scientific Research Project funded by Shell.
　　Figure 1. Regulation of Gas-Liquid Taylor Flow by Pulsating Gas Intake in Micro-channel (Image by SARI)
　　Figure 2 Space-time distribution of gas fraction in bubble formation process (Image by SARI)
　　Figure 3 (a) Forces versus pulse frequency f at the T-junction, (b) Bubble velocities at downstream(Image by SARI)
　　

2021-04-09 more+

Scientists Propose a Novel Self-modulation Scheme in Seeded Free-Electron Lasers

The FEL teams at Shanghai Advanced Research Institute and Shanghai Institute of Applied Physics of the Chinese Academy of Sciences collaborated and reported a novel self-modulation method for enhancing laser-induced energy modulation, thereby significantly reducing the requirement of an external laser system.

　　Seeded free-electron lasers (FELs), which use frequency up-conversion of an external seed laser to improve temporal coherence, are regarded ideal for supplying stable, fully coherent, soft X-ray pulses. However, the requirement for an external seed laser with sufficient peak power to modulate the electron beam can hardly be met by the present state-of-the-art laser systems, it remains challenging for seeded FELs to operate at high repetition rate, e.g., MHz repetition rate.
　　Motivated by such a challenge, the FEL teams at Shanghai Advanced Research Institute and Shanghai Institute of Applied Physics of the Chinese Academy of Sciences collaborated and reported a novel self-modulation method for enhancing laser-induced energy modulation, thereby significantly reducing the requirement of an external laser system. The research results were published in Physical Review Letters entitled "Self-Amplification of Coherent Energy Modulation in Seeded Free-Electron Lasers."
　　Based on the Shanghai soft x-ray FEL test facility, the self-amplification of coherent energy modulation in a seeded FEL is experimentally verified. The peak power requirement of an external seed laser is demonstrated to be relaxed by a factor of 10 to 25 when utilizing the proposed scheme.
　　Moreover, the high harmonic generation in a seeded FEL is realized by using an unprecedentedly small energy modulation. A 795 MeV electron beam with a laser-induced energy modulation amplitude as small as 1.8 times the slice energy spread is used for lasing at the 7th harmonic of a 266-nm seed laser in a single-stage high-gain harmonic generation (HGHG) and the 30th harmonic of the seed laser in a two-stage HGHG.The results pave the way for a high-repetition-rate seeded FEL, which is expected to show great promise for multidimensional coherent spectroscopies, far beyond what has been demonstrated to date. Furthermore, the self-modulation scheme proposed in this work is also promising for solving other critical problems of seeded FELs such as reaching shorter wavelengths and improving stability.
　　Figure 1. The self-modulation scheme together with the electron-beam longitudinal phase spaces at various positions (Image by SARI)
　　Contact: DENG Haixiao
　　Shanghai Advanced Research Institute, Chinese Academy of Sciences
　　Email: denghaixiao@zjlab.org.cn

2021-03-10 more+

New Framework Proposed for Analyzing the Fouling/Scaling behavior of MD Membrane

A research team led by Prof. HE Tao proposed a hydrodynamic theory of slippery surface for fouling/scaling resistance of superhydrophobic membranes.The latest result on the hydrodynamic behavior and scaling/fouling resistance of MD membranes was published in Desalination.

　　Membrane distillation (MD) is a thermal driven desalination technology using hydrophobic membranes for separation. In MD, heat is utilized to compensate the latent heat of evaporation, and ultrapure water desired by the industry is produced in the process. MD can treat streams containing high total dissolved solids with nearly complete rejection to non-volatile matters. Since there is abundant low-grade heat available in various industries, MD is a potential technology to reuse wastewater, dewater products before crystallization, so as to manage the energy balance and reduce carbon footprint in many chemical, petrochemical, steel industries.
　　However, the targeted fluids are mostly highly saline and contain complicated organic and inorganic chemicals, which incur fouling and scaling to the hydrophobic membranes. Thus, understanding the fouling/scaling phenomenon of hydrophobic membranes has long been the research focal of MD.
　　Recently, researchers have been attempting to adopt superhydrophobic membranes for improving the scaling and fouling resistance of MD. But discrepancy in results when using different models has been reported. To unravel this puzzle, a research team led by Prof. HE Tao at Shanghai Advanced Research Institute (SARI) of the Chinese Academy of Sciences, collaborating with Prof. YIN Huabing at University of Glasgow in the UK and Professor VOLKOV Alexey from A.V. Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, proposed a hydrodynamic theory of slippery surface for fouling/scaling resistance of superhydrophobic membranes.
　　To prove the theory, scientists created and implemented a delicate design of a porous membrane with micro-pillar arrays. A superhydrophobic membrane (MP-PVDF) was successfully prepared using a micromolding phase separation (mPS) method. The team further utilized a rheolometry measurement to quantify the slip length of the membrane surface. Simulation of the surface wetting indicated that there is a strong correlation of surface wetting, slip and scaling/fouling resistance. The latest result on the hydrodynamic behavior and scaling/fouling resistance of MD membranes was published in Desalination entitled “Understanding the fouling/scaling resistance of superhydrophobic/omniphobic membranes in membrane distillation.”
　　The new framework for analyzing the fouling/scaling behavior of MD can identify the wetting and hydrodynamic character of the membrane, which is important for hydrophobic membrane design and further development of membrane distillation.
　　Fig.1 Scaling mitigation in membrane distillation (Image by Prof. HE’s group)
　　Contact: HE Tao
　　Shanghai Advanced Research Institute, Chinese Academy of Sciences
　　Email: het@sari.ac.cn
　　

2021-02-22 more+

Researchers Reveal In-situ Manipulation of Active Au-TiO2 Interface

An international joint research team reported an in-situ strategy to manipulate interfacial structure with atomic precision during catalytic reactions. Results were published in the latest issue of Science.

　　An international joint research team from Zhejiang University, Shanghai Advanced Research Institute of the Chinese Academy of Sciences, and Technical University of Denmark, reported an in-situ strategy to manipulate interfacial structure with atomic precision during catalytic reactions. Results were published in the latest issue of Science.
　　The interface between nanoparticles and substrates plays a critical role in heterogeneous catalysis because most active sites are located at the perimeter of the interface. It is generally believed that this interface is immobile and unchangeable, thus can hardly be adjusted in reactive environments. As a result, it has been challenging to promote catalytic activity through precise control of the interfacial structure.
　　In this study, the scientists first used environmental transmission electron microscopy to directly visualize the epitaxial rotation of gold nanoparticles on titanium dioxide (TiO2) surfaces during CO oxidation at the atomic level. A perfect epitaxial relationship was observed between Au nanoparticles and TiO2 (001) surfaces under an O2 environment in real time.
　　Theoretical calculations including density functional theory calculations and thermodynamics analysis were then carried out, indicating that the epitaxial orientation could be induced by changing O2 adsorption coverage at the perimeter interface. The Au nanoparticle was more stable with adsorption of more O2 molecules at the Au-TiO2 interface, but became less stable with the consumption of O2 with CO.
　　To exploit the promoted activity of Au-TiO2 interface, researchers conducted additional top-view observations and found that this configuration remained unchanged when cooling from 500 °C to 20 °C in CO and O2 reactive environments, showing the rotation of the Au nanoparticle was also temperature dependent in reaction conditions.
　　Taking advantage of the reversible and controllable rotation of the Au nanoparticle, the scientists achieved in-situ manipulation of the active Au-TiO2 interface at the atomic level by changing gas and temperature.
　　This study sheds light on real-time manipulation of catalytic interface structure in reaction conditions at the atomic scale, which may inspire future approaches to real-time design of the catalytic interface under operating conditions.
　　Figure 1. Geometric and electronic structure of Au-TiO2 interface under CO/O2 (A, C, E) and O2 environment (B, D, F) (Image adapted from Science)
　　Figure 2. Manipulation of the Au-TiO2 interface using temperature and gas control (Image adapted from Science)
　　Figure 3. Schematic illustration of In-situ manipulation of active Au-TiO2 interface (Credited by Yong Wang, Zhejiang University)
　　Contact: GAO Yi
　　Shanghai Advanced Research Institute, Chinese Academy of Sciences
　　Email: gaoyi@zjlab.org.cn
　　

2021-01-29 more+

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