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Customizable Ligand Exchange for Tailored Surface Property of Noble Metal Nanocrystals

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研究（英文） 2020年第3期 192-203页

作者： Qikui Fan Hao Yang Juan Ge Shumeng Zhang Zhaojun Liu Bo Lei Tao Cheng Youyong Li Yadong Yin Chuanbo Gao Frontier Institute of Science and Technology State Key Laboratory of Multiphase Flow in Power EngineeringXi'an Jiaotong University Xi'an Shaanxi 710054 China Institute of Functional Nano & Soft Materials (FUNSOM) Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices Joint International Research Laboratory of Carbon-Based Functional Materials and Devices Soochow UniversitySuzhou Jiangsu 215123 China Department of Chemistry University of California Riverside California 92521 USA

It is highly desirable,while still challenging,to obtain noble metal nanocrystals with custom capping ligands,because their colloidal synthesis relies on specific capping ligands for the shape control while conventional ligand exchange processes suffer from 'the strong replaces the weak' limitation,which greatly hinders their ***,we report a general and effective ligand exchange approach that can replace the native capping ligands of noble metal nanocrystals with virtually any type of ligands,producing flexibly tailored surface *** key is to use diethylamine with conveniently switchable binding affinity to the metal surface as an intermediate *** a strong ligand,it in its original form can effectively remove the native ligands;while protonated,it loses its binding affinity and facilitates the adsorption of new ligands,especially weak ones,onto the metal *** this means,the irreversible order in the conventional ligand exchange processes could be *** efficacy of the strategy is demonstrated by mutual exchange of the capping ligands among cetyltrimethylammonium,citrate,polyvinylpyrrolidone,and *** novel strategy significantly expands our ability to manipulate the surface property of noble metal nanocrystals and extends their applicability to a wide range of fields,particularly biomedical applications.

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Thermal Modulation of Radiation Fields Enhancing the Adaptability of Cpv-Hydrogen Systems to Hot Outdoor Conditions

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SSRN 2023年

作者： Zhu, Yizhou Zhang, Ting’an Geng, Jiafeng Jing, Dengwei Xi'an University of Science and Technology China Department of Chemical Engineering School of Water and Environment Chang'an University Shaanxi Xi’an710064 China International Research Center for Renewable Energy State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Shaanxi Xi’an710049 China

The efficiency of photovoltaic (PV) modules operating outdoors often subject to significant decrease due to high PV surface temperature under hot outdoor conditions despite of the high irradiation in this period. Meanwhile, the commercial electrolytic water splitting unit requires additional heat sources to preheat the electrolyte, which is neither economical nor energy efficient. This study introduces a proton exchange membrane (PEM) water electrolyzer system coupled with concentrated photovoltaic (CPV) and a pipe-based liquid spectral beam splitting filter acting also as an electrolyte preheater. The results of continuous experiments during local summer daytime show that the average PV surface temperature of the proposed system can be reduced by 23.5 K compared to that without spectral beam splitting filter. Moreover, the average efficiencies of photovoltaic, electrolysis and solar-to-hydrogen can be increased by 7.5%, 8.1% and 5.2%, respectively. Both simulation and experimental results confirm that our design can reduce the sensitivity of system efficiency toward weather factors, especially high-intensity summer irradiation. This work provides a promising option for application of large-scale solar hydrogen production in regions with sufficient sunlight while high outdoor temperature. © 2023, The Authors. All rights reserved.

关键词： Hydrogen production

Development, Validation and Application of Sub-Channel Thermal-Hydraulic Analysis Code for Liquid Metal Cooled Reactor

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SSRN 2024年

作者： Wang, Jinshun Chen, Ronghua Liang, Yu Gui, Minyang Zhu, Xinyang Tian, Wenxi Qiu, Suizheng Su, Guanghui School of Nuclear Science and Technology Shaanxi Key Laboratory of Advanced Nuclear Energy and Technology State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China Nuclear Power Institute of China 328 Changshun Avenue Chengdu610213 China Science and Technology on Reactor System Design Technology Laboratory Nuclear Power Institute of China Chengdu610213 China College of Nuclear Science and Technology Harbin Engineering University Harbin150001 China

The liquid metal reactor, specifically the lead-based fast reactor and the sodium-cooled fast reactor, are generally recognized as the most significant representatives of the Gen IV reactors due to their sustainability, economy, security and reliability. In order to conduct thermal-hydraulic safety analysis for liquid metal cooled fast reactors, adaptive improvements are made to the model and solution algorithms based on the sub-channel analysis method, and a Sub-channel Analysis Code Of Safety for Liquid Metal cooled Reactor (SACOS-LMR) is developed. The validation of SACOS-LMR is conducted using classic experimental data of liquid metal. The results show that the dimensionless temperature deviations of ORNL 19-pin test and Toshiba 37-pin test are within 10%, and the relative temperature deviations of KIT-KALLA 19-pin test are within 25%. These findings confirm the accuracy and reliability of SACOS-LMR in predicting the temperature distribution of liquid metal reactors. Ultimately, calculations conducted on the ALFRED lead-cooled fast reactor demonstrated the practical utility of the code and have certain guiding significance for its subsequent design and development. © 2024, The Authors. All rights reserved.

关键词： Liquid metals

Comparison of Lifetime Performance of Pemfc Stacks with Two Cooling Strategies Under Different Humidity

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SSRN 2024年

作者： Yang, Yunjie Bai, Minli Zhou, Zhifu Wu, Wei-Tao Lv, Jizu Hu, Chengzhi Li, Yang Li, Yubai Song, Yongchen Key Laboratory of Ocean Energy Utilization and Energy Conservation of Ministry of Education Dalian University of Technology Dalian116024 China State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi’an710049 China School of Mechanical Engineering Nanjing University of Science and Technology Nanjing210094 China School of Mechanical Engineering Guangdong Ocean University Zhanjiang524088 China

While reducing the size and Pt loading can achieve a lower proton exchange membrane fuel cell (PEMFC) stack cost, it is also very important to focus on the performance changes of the PEMFC stack during the long-term operation. A 3D PtCo catalysts long-term performance model is established in this study, and PEMFC stacks with one cooling unit per cell (1-cell stack) and three cells (3-cell stack) are employed as the computational domains, respectively. The effective area of each cell is 50 cm2, and the changes in current density as well as effective catalytic area of PEMFC stacks with two cooling strategies before and after long-term operation under different humidity conditions are investigated at low Pt loadings. The results show that there are large differences in the output voltage and current density distributions between the three cells due to the poor membrane hydration affected by the non-uniform temperature distribution, although the 3-cell stack can significantly reduce the size. Localized catalyst degradation in both 3-cell and 1-cell stacks is closely related to the geometry of the cathodic flow field, and non-uniform catalyst degradation is found to increase the activation and mass transfer losses and change the distribution of current density within the membrane. In addition, the 3-cell stack is found to perform even better in terms of durability, especially under high humidity conditions, which provides a potential solution to improve the durability of PEMFC stacks operating in harsh conditions. © 2024, The Authors. All rights reserved.

关键词： Durability

Thermal Simulation for a Mechanical Spindle With External Cooler Across Grease Coated Interface

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Research Square

Research Square 2021年

作者： Zhao, Liang Lei, Mohan Ren, Hongdi Wang, Jinshi Wang, Shuai Li, Ben Q. Yang, Jun Mei, Xuesong Xi'an Jiaotong University China State Key Laboratory for Manufacturing Systems Engineering Xi'an Jiaotong University Xi'An710049 China Shaanxi Key Laboratory of Intelligent Robots Xi'an Jiaotong University Xi'An710049 China School of Mechanical and Precision Instrument Engineering Xi'an University of Technology 710048 China State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China Department of Mechanical Engineering College of Engineering and Computer Science University of Michigan MI48128 United States

Spindles in precision boring machine often work in low speed and heavy load without internal cooling, and the thermal error is nonnegligible. So an external cooling system was designed, and the effectiveness of the designed scheme needs to be preliminarily verified by simulation before building the cooling system. Thermal simulations of the spindle with an external cooler require calculating the thermal resistance of the thermal grease-coated interface between the cooler and spindle. Models describing the contact thermal resistance and total thermal resistance for metal contact filled with silicone grease based on solid-liquid interface force equivalence were described in this paper, and experiments were also conducted to verify the accuracy of these models. The contact thermal resistances between the cast iron/copper and silicone grease on flat or arc surfaces were calculated, and the bulk thermal resistance of the silicone grease layer was calculated. The total heat transferred between the cooler and the silicone grease-coated interface of the spindle were calculated. Heat transfer and heat generation in the spindle were calculated, and a finite element model was established to verify the effectiveness of the designed external cooling scheme. Finally, results from experiments for the spindle in different conditions show that the external cooling system decreases the time to reach thermal equilibrium by more than 60%. The RMSE of the simulated thermal elongation is less than 5.7044 μm when the rotating speed of 3000 rpm, and is less than 3.9714 μm when the rotating speed is 1500 rpm. © 2021, CC BY.

关键词： Cooling

Effects of Combustor Wall Temperature on the Outer Recirculation Zone Combustion Modes Transition in Lean Premixed Dme/Air Swirl Flames

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SSRN 2024年

作者： Lin, Wenjun Zhang, Weijie An, Zhenhua Wang, Jinhua Huang, Zuohua Zhang, Huangwei State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China Department of Mechanical Engineering National University of Singapore 9 Engineering Drive 1 Singapore117576 Singapore Department of Mechanical Engineering and Science Kyoto University Kyoto daigakuKatsura Nishikyo-ku Kyoto615-8540 Japan

In this study, the effects of wall thermal conditions on the ORZ combustion modes transition in the DME/air swirl flames are investigated using the Large Eddy Simulation (LES) and Flamelet Generated Manifold (FGM) method. The results show that the ORZ chemistry and temperature are highly sensitive to the wall thermal condition. Based on the correlation between the temperature and species observed in the time-averaged numerical results, the relation between the combustion mode and temperature in the ORZ is discovered. Through temporal analysis of species and heat release rate in the ORZ, the stable Mode II and Mode IV as well as the unstable Mode III are identified. The chemical reaction pathway analysis for typical probe in the ORZ reveals that different combustion modes undergo distinct (lowtemperature or high-temperature) chemical reaction pathways. Afterwards, the definition of combustion modes used in experiments is refined by utilizing the chemical reaction data from the simulations. And it is applied to identify the combustion mode across the entire computational domain. The results confirm the consistency between the combustion modes determined in experiments based on OH and CH2O and those determined in simulations using chemical reaction rates. Finally, this explains the mechanism of the flickering flame in Mode III is the competition between the low-temperature and high-temperature reaction in the ORZ. Whereas the unstable Mode III can be stabilized by changing the wall temperature to reach the Mode II or Mode IV. © 2024, The Authors. All rights reserved.

关键词： Temperature

Deterministic Synthesis of Pd Nanocrystals Enclosed by High-Index Facets and Their Enhanced Activity toward Formic Acid Oxidation

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Precision Chemistry 2023年第6期1卷 372-381页

作者： Maochang Liu Siyu Zhou Sang-Il Choi Younan Xia The Wallace H.Coulter Department of Biomedical Engineering Georgia Institute of Technology and Emory UniversityAtlantaGeorgia 30332United States International Research Center for Renewable Energy State Key Laboratory of Multiphase FlowXi’an Jiaotong UniversityXi’anShanxi 710049P.R.China School of Chemical and Biomolecular Engineering Georgia Institute of TechnologyAtlantaGeorgia 30332United States School of Chemistry and Biochemistry and School of Chemical and Biomolecular Engineering Georgia Institute of TechnologyAtlantaGeorgia 30332United States

Noble-metal nanocrystals enclosed by high-index facets are of growing interest due to their enhanced catalytic performance in a variety of ***,we report the deterministic synthesis of Pd nanocrystals encased by high-index facets by controlling the rate of deposition(V_(deposition))relative to that of surface diffusion(V_(diffusion)).For octahedral seeds with truncated corners,a reduction rate(and thus deposition rate)faster than that of surface diffusion(i.e.,V_(deposition)/V_(diffusion)>1)led to the formation of concave trisoctahedra(TOH)with high-index *** the reduction was slowed down,in contrast,surface diffusion dominated the growth *** the case of V_(deposition)/V_(diffusion)≈1,truncated octahedra with enlarged sizes were *** the reduction rate was between these two extremes,we obtained concave tetrahexahedra(THH)without or with *** growth patterns were also observed for the cuboctahedral *** the Pd octahedra,concave TOH,and concave THH were tested for electrocatalyzing the formic acid oxidation(FAO)reaction,those with high-index facets were advantageous over the conventional Pd octahedra enclosed by{111}*** work not only contributes to the understanding of surface diffusion and its role in nanocrystal growth but also offers a general protocol for the synthesis of nanocrystals enclosed by high-index facets.

关键词： palladium surface diffusion high-index facet unconventional morphology kinetic control

Insight into the key Role of Imine Groups in Polyaniline for Adsorbing Heavy Metal Ions: Experimental and Density Functional Theory Study

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SSRN 2023年

作者： Shi, Bofang Li, Hang Fu, Xiaojie Zhao, Chengcheng Rao, Yongfang Li, Mingtao Komarneni, Sridhar Yang, Honghui Xi’an Key Laboratory of Sustainable Energy Materials Chemistry Department of Applied Chemistry School of Chemistry Xi’an Jiaotong University Xi’an710049 China State Key Laboratory of Multiphase Flow in Power Engineering Department of Environmental Science and Engineering School of Energy and Power Engineering Xi’an Jiaotong University Xi’an710049 China Department of Ecosystem Science and Management Materials Research Institute 204EEL The Pennsylvania State University University ParkPA16802 United States

In polyaniline (PANI) or polyaniline-based adsorbents, the views on nitrogen group that has the highest chemical affinity to heavy metal ions and dominates the adsorption process remain in debate. Herein, we focus on deciphering the main adsorption sites and adsorption mechanism of PANI using both experiments and density functional theory (DFT) calculations. The characterization results of adsorption product demonstrate that the metal ions were adsorbed via coordination bond between nitrogen atom and metal ion. The theoretical calculations by DFT reveal that −N= group is the key adsorption site rather than other groups in PANI, and the key step of PANI adsorption process is a ligand exchange reaction. The H+ ions with a higher affinity to −N= group can inhibit the adsorption of metal ions due to the consumption of adsorption sites and ion exchange reaction. This work provides a molecular-level understanding of adsorption sites, adsorption mechanism, and H+ competition for metal ion adsorption by PANI, which is beneficial for the development of PANI-based adsorbents. © 2023, The Authors. All rights reserved.

关键词： Density functional theory

Turbulent heat transfer in a horizontal helically coiled tube

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Heat Transfer 2000年第5期28卷

作者： Bofeng Bai Liejin Guo Ziping Feng Xuejun Chen State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University China

An experiment has been conducted in detail to study the turbulent heat transfer in horizontal helically coiled tubes over a wide range of experimental parameters. We found that the enhancement of heat transfer in the coils results from the effects of turbulent and secondary flows. With Reynolds number increasing to a high level, the contribution of the secondary flow becomes less to enhance heat transfer, and the average heat transfer coefficient of the coil is closer to that in straight tubes under the same conditions. The local heat transfer coefficients are not evenly distributed along both the tube axis and the periphery on the cross section. The local heat transfer coefficients on the outside are three or four times those on the inside, which is half of the average heat transfer. A correlation is proposed to describe the distribution of the heat transfer coefficients at a cross section. The average cross-section heat transfer coefficients are distributed along the tube axis. The average value at the outlet section should not be taken as the average heat transfer coefficient. © 1999 Scripta Technica, Heat Trans Asian Res, 28(5): 395–403, 1999

关键词： turbulent heat transfer horizontal helically coiled tube secondary flow local heat transfer