The Experts below are selected from a list of 13227 Experts worldwide ranked by ideXlab platform
Younan Xia - One of the best experts on this subject based on the ideXlab platform.
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Using Reduction Kinetics to Control and Predict the Outcome of a Colloidal Synthesis of Noble-Metal Nanocrystals.
Inorganic chemistry, 2021Co-Authors: Quynh N Nguyen, Zhiheng Lyu, Ruhui Chen, Younan XiaAbstract:Improving the performance of noble-Metal Nanocrystals in various applications critically depends on our ability to manipulate their synthesis in a rational, robust, and controllable fashion. Different from a conventional trial-and-error approach, the reduction kinetics of a colloidal synthesis has recently been demonstrated as a reliable knob for controlling the synthesis of noble-Metal Nanocrystals in a deterministic and predictable manner. Here we present a brief Viewpoint on the recent progress in leveraging reduction kinetics for controlling and predicting the outcome of a synthesis of noble-Metal Nanocrystals. With a focus on Pd Nanocrystals, we first offer a discussion on the correlation between the initial reduction rate and the internal structure of the resultant seeds. The kinetic approaches for controlling both nucleation and growth in a one-pot setting are then introduced with an emphasis on manipulation of the reduction pathways taken by the precursor. We then illustrate how to extend the strategy into a biMetallic system for the preparation of Nanocrystals with different shapes and elemental distributions. Finally, the influence of speciation of the precursor on reduction kinetics is highlighted, followed by our perspectives on the challenges and future endeavors in achieving a controllable and predictable synthesis of noble-Metal Nanocrystals.
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Colloidal Metal Nanocrystals with Metastable Crystal Structures.
Angewandte Chemie (International ed. in English), 2021Co-Authors: Annemieke Janssen, Quynh N Nguyen, Younan XiaAbstract:In addition to the conventional knobs such as composition, size, shape, and defect structure, the crystal structure (or phase) of Metal Nanocrystals offers a new avenue for engineering their properties. Various strategies have recently been developed for the fabrication of colloidal Metal Nanocrystals in metastable phases different from their bulk counterparts. With a focus on noble Metals, we begin with a brief introduction to their atomic packing, followed by a discussion about five major synthetic approaches to their colloidal Nanocrystals in unconventional phases. We then highlight the success of synthesis in terms of mechanistic insights and experimental controls, as well as the enhanced catalytic properties. We end this Minireview with perspectives on the remaining issues and future opportunities.
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Physical Transformations of Noble-Metal Nanocrystals upon Thermal Activation
Accounts of chemical research, 2020Co-Authors: Zhiheng Lyu, Ruhui Chen, Manos Mavrikakis, Younan XiaAbstract:ConspectusThe last two decades have witnessed the successful development of noble-Metal Nanocrystals with well-controlled properties for a variety of applications in catalysis, plasmonics, electron...
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surface capping agents and their roles in shape controlled synthesis of colloidal Metal Nanocrystals
Angewandte Chemie, 2020Co-Authors: Tung-han Yang, Younan Xia, Annemieke Janssen, Yifeng ShiAbstract:Surface capping agents have been extensively used to control the evolution of seeds into Nanocrystals with diverse but well-controlled shapes. Here we offer a comprehensive review of these agents, with a focus on the mechanistic understanding of their roles in guiding the shape evolution of Metal Nanocrystals. We begin with a brief introduction to the early history of capping agents in electroplating and bulk crystal growth, followed by discussion of how they affect the thermodynamics and kinetics involved in a synthesis of Metal Nanocrystals. We then present representative examples to highlight the various capping agents, including their binding selectivity, molecular-level interaction with a Metal surface, and impacts on the growth of Metal Nanocrystals. We also showcase progress in leveraging capping agents to generate Nanocrystals with complex structures and/or enhance their catalytic properties. Finally, we discuss various strategies for the exchange or removal of capping agents, together with perspectives on future directions.
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Noble-Metal Nanocrystals with Controlled Shapes for Catalytic and Electrocatalytic Applications.
Chemical reviews, 2020Co-Authors: Yifeng Shi, Quynh N Nguyen, Ming Zhao, Zhiheng Lyu, Ruhui Chen, Younan XiaAbstract:The successful synthesis of noble-Metal Nanocrystals with controlled shapes offers many opportunities to not only maneuver their physicochemical properties but also optimize their figures of merit in a wide variety of applications. In particular, heterogeneous catalysis and surface science have benefited enormously from the availability of this new class of nanomaterials as the atomic structure presented on the surface of a nanocrystal is ultimately determined by its geometric shape. The immediate advantages may include significant enhancement in catalytic activity and/or selectivity and substantial reduction in materials cost while providing a well-defined model system for mechanistic study. With a focus on the monoMetallic system, this review article provides a comprehensive account of recent progress in the development of noble-Metal Nanocrystals with controlled shapes, in addition to their remarkable performance in a large number of catalytic and electrocatalytic reactions. We hope that this review article offers the impetus and roadmap for the development of next-generation catalysts vital to a broad range of industrial applications.
Shuifen Xie - One of the best experts on this subject based on the ideXlab platform.
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shape controlled synthesis of colloidal Metal Nanocrystals by replicating the surface atomic structure on the seed
Advanced Materials, 2018Co-Authors: Kyle D. Gilroy, Younan Xia, Ming Zhao, Shuifen Xie, Xuan Yang, Dong QinAbstract:Controlling the surface structure of Metal Nanocrystals while maximizing the utilization efficiency of the atoms is a subject of great importance. An emerging strategy that has captured the attention of many research groups involves the conformal deposition of one Metal as an ultrathin shell (typically 1-6 atomic layers) onto the surface of a seed made of another Metal and covered by a set of well-defined facets. This approach forces the deposited Metal to faithfully replicate the surface atomic structure of the seed while at the same time serving to minimize the usage of the deposited Metal. Here, the recent progress in this area is discussed and analyzed by focusing on the synthetic and mechanistic requisites necessary for achieving surface atomic replication of precious Metals. Other related methods are discussed, including the one-pot synthesis, electrochemical deposition, and skin-layer formation through thermal annealing. To close, some of the synergies that arise when the thickness of the deposited shell is decreased controllably down to a few atomic layers are highlighted, along with how the control of thickness can be used to uncover the optimal physicochemical properties necessary for boosting the performance toward a range of catalytic reactions.
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well faceted noble Metal Nanocrystals with nonconvex polyhedral shapes
Chemical Society Reviews, 2016Co-Authors: Qiaoli Chen, Shuifen Xie, Yanyan Jia, Zhao-xiong XieAbstract:Precise engineering of noble-Metal Nanocrystals (NCs) is not only an important fundamental research topic, but also has great realistic significance in improving their performances required by the poor reserve and high cost of noble Metals. Well-faceted noble-Metal NCs with nonconvex polyhedral shapes could be promising candidates to optimize their performance and thus minimize their usage, as they may integrate a well-defined surface structure and a large surface area together, enabling them to have outstanding performance and high efficiency of atomic utilization. Moreover, undesirable aggregation and ripening phenomena could be avoided. This review provides a comprehensive summary of the unique characteristics and corresponding models of well-faceted nonconvex polyhedral noble-Metal NCs by classifying the cases into four distinct types, namely the concave polyhedral structure, excavated polyhedral structure, branched structure and nanocage structure, respectively. Due to the complexity of nonconvex morphologies and the thermodynamic antipathy for the growth of nonconvex shaped NCs, we firstly demonstrate the structure characterization and synthetic methodology in detail. Subsequently, typical applications in electrocatalysis and plasmonic fields are presented to demonstrate the unique surface and morphological effects generated from the well-faceted nonconvex NCs. To promote further development in this field, the perspectives and challenges concerning well-faceted noble-Metal NCs with nonconvex shapes are put forward in the end.
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Defect‐Rich Metal Nanocrystals in Catalysis
ChemCatChem, 2015Co-Authors: Shuifen Xie, Xiaoqing HuangAbstract:Metal Nanocrystals with high concentrations of surface defects are well known to material scientists, but have been given less attention by the catalysis community. In this concept, we advocate that engineered Metal Nanocrystals with rich defects could be a new platform for exploration as highly active heterocatalysts. Metal Nanocrystals with rich defects are analyzed in detail to illustrate the structural features, including twin boundaries (TBs) and grain boundaries (GBs). We also discuss the recent advances in synthetic methods for making Metal Nanocrystals with rich TBs/GBs to provide inspiration for a further rational synthesis. Typical catalytic measurements are highlighted to stress the positive correlation between the concentration of surface defects and the catalytic performances of Metal Nanocrystals.
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On the role of surface diffusion in determining the shape or morphology of noble-Metal Nanocrystals
Proceedings of the National Academy of Sciences of the United States of America, 2013Co-Authors: Xiaohu Xia, Hsinchieh Peng, Shuifen Xie, Maochang Liu, Jinguo Wang, Moon J. Kim, Younan XiaAbstract:Controlling the shape or morphology of Metal Nanocrystals is central to the realization of their many applications in catalysis, plasmonics, and electronics. In one of the approaches, the Metal Nanocrystals are grown from seeds of certain crystallinity through the addition of atomic species. In this case, manipulating the rates at which the atomic species are added onto different crystallographic planes of a seed has been actively explored to control the growth pattern of a seed and thereby the shape or morphology taken by the final product. Upon deposition, however, the adsorbed atoms (adatoms) may not stay at the same sites where the depositions occur. Instead, they can migrate to other sites on the seed owing to the involvement of surface diffusion, and this could lead to unexpected deviations from a desired growth pathway. Herein, we demonstrated that the growth pathway of a seed is indeed determined by the ratio between the rates for atom deposition and surface diffusion. Our result suggests that surface diffusion needs to be taken into account when controlling the shape or morphology of Metal Nanocrystals.
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Shape-controlled synthesis of Metal Nanocrystals
Mrs Bulletin, 2013Co-Authors: Younan Xia, Xiaohu Xia, Yi Wang, Shuifen XieAbstract:The ability to control the shape of Metal Nanocrystals is central to advances in many areas of modern science and technology, including catalysis, plasmonics, electronics, and biomedicine. This article provides a brief overview of our recent efforts toward the development of solution-phase methods for shape-controlled synthesis of Metal Nanocrystals. While the synthetic methods only involve simple redox reactions, we have been working diligently to understand the complex nucleation and growth mechanisms leading to the formation of Metal Nanocrystals with desired shapes and related properties. We hope this review will inspire new ideas and concepts in the general area of nanomaterial synthesis, expand our ability to engineer the properties of Metals for various applications, and contribute to the realization of sustainable use for some of the scarcest materials.
Kyle D. Gilroy - One of the best experts on this subject based on the ideXlab platform.
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Synthesis of Colloidal Metal Nanocrystals: A Comprehensive Review on the Reductants.
Chemistry (Weinheim an der Bergstrasse Germany), 2018Co-Authors: Thenner S. Rodrigues, Kyle D. Gilroy, Tung-han Yang, Ming Zhao, Anderson G. M. Da Silva, Pedro H. C. Camargo, Younan XiaAbstract:There is a growing interest in controlling the synthesis of colloidal Metal Nanocrystals and thus tailoring their properties toward various applications. In this context, choosing an appropriate combination of reagents (e.g., salt precursor, reductant, capping agent, and stabilizer) plays a pivotal role in enabling the synthesis of Metal Nanocrystals with diversified sizes, shapes, and structures. Here we present a comprehensive review that highlights one of the key reagents for the synthesis of Metal Nanocrystals via chemical reduction: the reductants. We start with a brief introduction to the compounds commonly employed as reductants in the colloidal synthesis of Metal Nanocrystals by showing their oxidation half-reactions and the corresponding oxidation potentials. Then we offer specific examples pertaining to the controlled synthesis of Metal Nanocrystals, followed by some fundamental aspects covering the general mechanisms of Metal ion reduction based on the Marcus Theory. Afterwards, we present a case-by-case discussion on a wide variety of reductants, including their major properties, reduction mechanisms, and additional effects on the final products. We illustrate these aspects by selecting key examples from the literature and paying close attention to the underlying mechanism in each case. At the end, we conclude by summarizing the highlights of the review and providing some perspectives on future directions.
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shape controlled synthesis of colloidal Metal Nanocrystals by replicating the surface atomic structure on the seed
Advanced Materials, 2018Co-Authors: Kyle D. Gilroy, Younan Xia, Ming Zhao, Shuifen Xie, Xuan Yang, Dong QinAbstract:Controlling the surface structure of Metal Nanocrystals while maximizing the utilization efficiency of the atoms is a subject of great importance. An emerging strategy that has captured the attention of many research groups involves the conformal deposition of one Metal as an ultrathin shell (typically 1-6 atomic layers) onto the surface of a seed made of another Metal and covered by a set of well-defined facets. This approach forces the deposited Metal to faithfully replicate the surface atomic structure of the seed while at the same time serving to minimize the usage of the deposited Metal. Here, the recent progress in this area is discussed and analyzed by focusing on the synthetic and mechanistic requisites necessary for achieving surface atomic replication of precious Metals. Other related methods are discussed, including the one-pot synthesis, electrochemical deposition, and skin-layer formation through thermal annealing. To close, some of the synergies that arise when the thickness of the deposited shell is decreased controllably down to a few atomic layers are highlighted, along with how the control of thickness can be used to uncover the optimal physicochemical properties necessary for boosting the performance toward a range of catalytic reactions.
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Autocatalytic surface reduction and its role in controlling seed-mediated growth of colloidal Metal Nanocrystals
Proceedings of the National Academy of Sciences of the United States of America, 2017Co-Authors: Tung-han Yang, Kyle D. Gilroy, Shan Zhou, Legna Figueroa-cosme, Yi-hsien Lee, Younan XiaAbstract:The growth of colloidal Metal Nanocrystals typically involves an autocatalytic process, in which the salt precursor adsorbs onto the surface of a growing nanocrystal, followed by chemical reduction to atoms for their incorporation into the nanocrystal. Despite its universal role in the synthesis of colloidal Nanocrystals, it is still poorly understood and controlled in terms of kinetics. Through the use of well-defined Nanocrystals as seeds, including those with different types of facets, sizes, and internal twin structure, here we quantitatively analyze the kinetics of autocatalytic surface reduction in an effort to control the evolution of Nanocrystals into predictable shapes. Our kinetic measurements demonstrate that the activation energy barrier to autocatalytic surface reduction is highly dependent on both the type of facet and the presence of twin boundary, corresponding to distinctive growth patterns and products. Interestingly, the autocatalytic process is effective not only in eliminating homogeneous nucleation but also in activating and sustaining the growth of octahedral Nanocrystals. This work represents a major step forward toward achieving a quantitative understanding and control of the autocatalytic process involved in the synthesis of colloidal Metal Nanocrystals.
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Reduction rate as a quantitative knob for achieving deterministic synthesis of colloidal Metal Nanocrystals.
Chemical science, 2017Co-Authors: Tung-han Yang, Kyle D. Gilroy, Younan XiaAbstract:Despite the incredible developments made to the synthesis of colloidal Metal Nanocrystals, it is still challenging to produce them in a reproducible and predictable manner. This drawback can be attributed to the fact that the protocols continue to be built upon qualitative observations and empirical laws. Because of the vast number of intricately entangled experimental parameters in a synthesis, it is almost impossible to predict and control the outcome by knowingly alternating these parameters. In this Perspective article, we discuss the recent efforts in pushing nanocrystal synthesis towards a deterministic process based upon quantitative measurements. In particular, we focus on how the reduction rate of a salt precursor can be used as a quantitative knob for predicting and controlling the outcomes of both nucleation and growth. We begin with a brief introduction to the techniques that have been used to extract the kinetic information of a synthesis and then discuss how the reduction rate is correlated with the defect structure, shape/morphology, and elemental distribution of the resultant Nanocrystals. We conclude by highlighting some of the recent advances related to in situ probing of nanocrystal synthesis, with an emphasis on the real-time, quantitative aspects with regard to both nucleation and growth.
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thermal stability of Metal Nanocrystals an investigation of the surface and bulk reconstructions of pd concave icosahedra
Nano Letters, 2017Co-Authors: Kyle D. Gilroy, Tung-han Yang, Manos Mavrikakis, Ahmed O Elnabawy, Luke T Roling, Jane Y Howe, Younan XiaAbstract:Despite the remarkable success in controlling the synthesis of Metal Nanocrystals, it still remains a grand challenge to stabilize and preserve the shapes or internal structures of metastable kinetic products. In this work, we address this issue by systematically investigating the surface and bulk reconstructions experienced by a Pd concave icosahedron when subjected to heating up to 600 °C in vacuum. We used in situ high-resolution transmission electron microscopy to identify the equilibration pathways of this far-from-equilibrium structure. We were able to capture key structural transformations occurring during the thermal annealing process, which were mechanistically rationalized by implementing self-consistent plane-wave density functional theory (DFT) calculations. Specifically, the concave icosahedron was found to evolve into a regular icosahedron via surface reconstruction in the range of 200–400 °C, and then transform into a pseudospherical crystalline structure through bulk reconstruction when fu...
Tung-han Yang - One of the best experts on this subject based on the ideXlab platform.
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surface capping agents and their roles in shape controlled synthesis of colloidal Metal Nanocrystals
Angewandte Chemie, 2020Co-Authors: Tung-han Yang, Younan Xia, Annemieke Janssen, Yifeng ShiAbstract:Surface capping agents have been extensively used to control the evolution of seeds into Nanocrystals with diverse but well-controlled shapes. Here we offer a comprehensive review of these agents, with a focus on the mechanistic understanding of their roles in guiding the shape evolution of Metal Nanocrystals. We begin with a brief introduction to the early history of capping agents in electroplating and bulk crystal growth, followed by discussion of how they affect the thermodynamics and kinetics involved in a synthesis of Metal Nanocrystals. We then present representative examples to highlight the various capping agents, including their binding selectivity, molecular-level interaction with a Metal surface, and impacts on the growth of Metal Nanocrystals. We also showcase progress in leveraging capping agents to generate Nanocrystals with complex structures and/or enhance their catalytic properties. Finally, we discuss various strategies for the exchange or removal of capping agents, together with perspectives on future directions.
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Surface Capping Agents and Their Roles in Shape‐Controlled Synthesis of Colloidal Metal Nanocrystals
Angewandte Chemie (International ed. in English), 2020Co-Authors: Tung-han Yang, Annemieke Janssen, Yifeng Shi, Younan XiaAbstract:Surface capping agents have been extensively used to control the evolution of seeds into Nanocrystals with diverse but well-controlled shapes. Here we offer a comprehensive review of these agents, with a focus on the mechanistic understanding of their roles in guiding the shape evolution of Metal Nanocrystals. We begin with a brief introduction to the early history of capping agents in electroplating and bulk crystal growth, followed by discussion of how they affect the thermodynamics and kinetics involved in a synthesis of Metal Nanocrystals. We then present representative examples to highlight the various capping agents, including their binding selectivity, molecular-level interaction with a Metal surface, and impacts on the growth of Metal Nanocrystals. We also showcase progress in leveraging capping agents to generate Nanocrystals with complex structures and/or enhance their catalytic properties. Finally, we discuss various strategies for the exchange or removal of capping agents, together with perspectives on future directions.
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Synthesis of Colloidal Metal Nanocrystals: A Comprehensive Review on the Reductants.
Chemistry (Weinheim an der Bergstrasse Germany), 2018Co-Authors: Thenner S. Rodrigues, Kyle D. Gilroy, Tung-han Yang, Ming Zhao, Anderson G. M. Da Silva, Pedro H. C. Camargo, Younan XiaAbstract:There is a growing interest in controlling the synthesis of colloidal Metal Nanocrystals and thus tailoring their properties toward various applications. In this context, choosing an appropriate combination of reagents (e.g., salt precursor, reductant, capping agent, and stabilizer) plays a pivotal role in enabling the synthesis of Metal Nanocrystals with diversified sizes, shapes, and structures. Here we present a comprehensive review that highlights one of the key reagents for the synthesis of Metal Nanocrystals via chemical reduction: the reductants. We start with a brief introduction to the compounds commonly employed as reductants in the colloidal synthesis of Metal Nanocrystals by showing their oxidation half-reactions and the corresponding oxidation potentials. Then we offer specific examples pertaining to the controlled synthesis of Metal Nanocrystals, followed by some fundamental aspects covering the general mechanisms of Metal ion reduction based on the Marcus Theory. Afterwards, we present a case-by-case discussion on a wide variety of reductants, including their major properties, reduction mechanisms, and additional effects on the final products. We illustrate these aspects by selecting key examples from the literature and paying close attention to the underlying mechanism in each case. At the end, we conclude by summarizing the highlights of the review and providing some perspectives on future directions.
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Autocatalytic surface reduction and its role in controlling seed-mediated growth of colloidal Metal Nanocrystals
Proceedings of the National Academy of Sciences of the United States of America, 2017Co-Authors: Tung-han Yang, Kyle D. Gilroy, Shan Zhou, Legna Figueroa-cosme, Yi-hsien Lee, Younan XiaAbstract:The growth of colloidal Metal Nanocrystals typically involves an autocatalytic process, in which the salt precursor adsorbs onto the surface of a growing nanocrystal, followed by chemical reduction to atoms for their incorporation into the nanocrystal. Despite its universal role in the synthesis of colloidal Nanocrystals, it is still poorly understood and controlled in terms of kinetics. Through the use of well-defined Nanocrystals as seeds, including those with different types of facets, sizes, and internal twin structure, here we quantitatively analyze the kinetics of autocatalytic surface reduction in an effort to control the evolution of Nanocrystals into predictable shapes. Our kinetic measurements demonstrate that the activation energy barrier to autocatalytic surface reduction is highly dependent on both the type of facet and the presence of twin boundary, corresponding to distinctive growth patterns and products. Interestingly, the autocatalytic process is effective not only in eliminating homogeneous nucleation but also in activating and sustaining the growth of octahedral Nanocrystals. This work represents a major step forward toward achieving a quantitative understanding and control of the autocatalytic process involved in the synthesis of colloidal Metal Nanocrystals.
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Reduction rate as a quantitative knob for achieving deterministic synthesis of colloidal Metal Nanocrystals.
Chemical science, 2017Co-Authors: Tung-han Yang, Kyle D. Gilroy, Younan XiaAbstract:Despite the incredible developments made to the synthesis of colloidal Metal Nanocrystals, it is still challenging to produce them in a reproducible and predictable manner. This drawback can be attributed to the fact that the protocols continue to be built upon qualitative observations and empirical laws. Because of the vast number of intricately entangled experimental parameters in a synthesis, it is almost impossible to predict and control the outcome by knowingly alternating these parameters. In this Perspective article, we discuss the recent efforts in pushing nanocrystal synthesis towards a deterministic process based upon quantitative measurements. In particular, we focus on how the reduction rate of a salt precursor can be used as a quantitative knob for predicting and controlling the outcomes of both nucleation and growth. We begin with a brief introduction to the techniques that have been used to extract the kinetic information of a synthesis and then discuss how the reduction rate is correlated with the defect structure, shape/morphology, and elemental distribution of the resultant Nanocrystals. We conclude by highlighting some of the recent advances related to in situ probing of nanocrystal synthesis, with an emphasis on the real-time, quantitative aspects with regard to both nucleation and growth.
Hsinchieh Peng - One of the best experts on this subject based on the ideXlab platform.
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Seed-Mediated Growth of Colloidal Metal Nanocrystals.
Angewandte Chemie (International ed. in English), 2016Co-Authors: Younan Xia, Hsinchieh Peng, Kyle D. Gilroy, Xiaohu XiaAbstract:Seed-mediated growth is a powerful and versatile approach for the synthesis of colloidal Metal Nanocrystals. The vast allure of this approach mainly stems from the staggering degree of control one can achieve over the size, shape, composition, and structure of Nanocrystals. These parameters not only control the properties of Nanocrystals but also determine their relevance to, and performance in, various applications. The ingenuity and artistry inherent to seed-mediated growth offer extensive promise, enhancing a number of existing applications and opening the door to new developments. This Review demonstrates how the diversity of Metal Nanocrystals can be expanded with endless opportunities by using seeds with well-defined and controllable internal structures in conjunction with a proper combination of capping agent and reduction kinetics. New capabilities and future directions are also highlighted.
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Shape-Controlled Metal Nanocrystals for Heterogeneous Catalysis.
Annual review of chemical and biomolecular engineering, 2016Co-Authors: Aleksey Ruditskiy, Hsinchieh Peng, Younan XiaAbstract:The ability to control the shape of Metal Nanocrystals allows us to not only maneuver their physicochemical properties but also optimize their activity in a variety of applications. Heterogeneous catalysis, in particular, would benefit tremendously from the availability of Metal Nanocrystals with controlled shapes and well-defined facets or surface structures. The immediate benefits may include significant enhancements in catalytic activity and/or selectivity along with reductions in the materials cost. We provide a brief account of recent progress in the development of Metal Nanocrystals with controlled shapes and thereby enhanced catalytic performance for several reactions, including formic acid oxidation, oxygen reduction, and hydrogenation. In addition to monoMetallic Nanocrystals, we also cover a biMetallic system, in which the two Metals are formulated as alloyed, core-shell, or core-frame structures. We hope this article will provide further impetus for the development of next-generation heterogeneous catalysts essential to a broad range of applications.
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shape controlled synthesis of colloidal Metal Nanocrystals thermodynamic versus kinetic products
Journal of the American Chemical Society, 2015Co-Authors: Younan Xia, Xiaohu Xia, Hsinchieh PengAbstract:This Perspective provides a contemporary understanding of the shape evolution of colloidal Metal Nanocrystals under thermodynamically and kinetically controlled conditions. It has been extremely challenging to investigate this subject in the setting of one-pot synthesis because both the type and number of seeds involved would be changed whenever the experimental conditions are altered, making it essentially impossible to draw conclusions when comparing the outcomes of two syntheses conducted under different conditions. Because of the uncertainty about seeds, most of the mechanistic insights reported in literature for one-pot syntheses of Metal Nanocrystals with different shapes are either incomplete or ambiguous, and some of them might be misleading or even wrong. Recently, with the use of well-defined seeds for such syntheses, it became possible to separate growth from nucleation and therefore investigate the explicit role(s) played by a specific thermodynamic or kinetic parameter in directing the evolution of colloidal Metal Nanocrystals into a specific shape. Starting from single-crystal seeds enclosed by a mix of {100}, {111}, and {110} facets, for example, one can obtain colloidal Nanocrystals with diversified shapes by adjusting various thermodynamic or kinetic parameters. The mechanistic insights learnt from these studies can also be extended to account for the products of conventional one-pot syntheses that involve self-nucleation only. The knowledge can be further applied to many other types of seeds with twin defects or stacking faults, making it an exciting time to design and synthesize colloidal Metal Nanocrystals with the shapes sought for a variety of fundamental studies and technologically important applications.
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Shape-controlled Metal Nanocrystals for catalytic applications
Mrs Bulletin, 2014Co-Authors: Aleksey Ruditskiy, Hsinchieh Peng, Sang-il Choi, Younan XiaAbstract:The implication of shape control in nanocrystal synthesis goes far beyond aesthetic appeal. For Metal Nanocrystals, the shape not only determines their physicochemical properties but also their technological relevance for catalytic, plasmonic, photonic, and electronic applications. In particular, heterogeneous catalysis is a fi eld that can benefi t tremendously from the availability of Metal Nanocrystals with well-controlled shapes, which may serve to signifi cantly increase reaction effi ciency while decreasing material cost. This article provides a brief overview of our recent progress in generating shape-controlled Nanocrystals with enhanced catalytic activity toward oxygen reduction and formic acid oxidation, two reactions that are crucial for the successful commercialization of fuel cell technology. The impact on other industrially important reactions will be discussed as well. We hope that this article provides a roadmap for further development of Metal nanocrystal-based catalysts with enhanced performance through shape-controlled synthesis.
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On the role of surface diffusion in determining the shape or morphology of noble-Metal Nanocrystals
Proceedings of the National Academy of Sciences of the United States of America, 2013Co-Authors: Xiaohu Xia, Hsinchieh Peng, Shuifen Xie, Maochang Liu, Jinguo Wang, Moon J. Kim, Younan XiaAbstract:Controlling the shape or morphology of Metal Nanocrystals is central to the realization of their many applications in catalysis, plasmonics, and electronics. In one of the approaches, the Metal Nanocrystals are grown from seeds of certain crystallinity through the addition of atomic species. In this case, manipulating the rates at which the atomic species are added onto different crystallographic planes of a seed has been actively explored to control the growth pattern of a seed and thereby the shape or morphology taken by the final product. Upon deposition, however, the adsorbed atoms (adatoms) may not stay at the same sites where the depositions occur. Instead, they can migrate to other sites on the seed owing to the involvement of surface diffusion, and this could lead to unexpected deviations from a desired growth pathway. Herein, we demonstrated that the growth pathway of a seed is indeed determined by the ratio between the rates for atom deposition and surface diffusion. Our result suggests that surface diffusion needs to be taken into account when controlling the shape or morphology of Metal Nanocrystals.