Structural Transformations Of Multimetallic Nanoparticles

Atomic-level understanding of the structural transformations of multimetallic nanoparticles (NPs) triggered by external stimuli is of vital importance to the enhancement of our capabilities to precisely fine-tailor the key structural parameters and thereby to fine-tune the catalytic properties of the NPs. In this work, I firstly show that Au-Cu bimetallic NPs demonstrate stoichiometry-dependent architectural evolutions during chemical dealloying processes and nanoporosity-evolving percolation dealloying only occurs for Au-Cu alloy NPs with Cu atomic fractions above the parting limit. The electrochemically active surface area and the specific activity of the dealloyed nanoframes can be systematically tuned to achieve the optimal electrocatalytic activity. Both the stability and the activity of the dealloyed Au nanoframes could be remarkably enhanced by incorporation of residual Ag into Au nanoframes through percolation dealloying of Au-Ag-Cu ternary alloy NPs. In addition, the catalytic selectivity of dealloyed porous Au NPs could be realized by precise control over of the surface atomic coordination numbers through percolation dealloying of Au-Cu bimetallic alloys with interior compositional gradients. Besides, nanoscale galvanic replacement reaction induced structural evolutions of Au-Cu bimetallic NPs has also been investigated in this dissertation. I have demonstrated the compositional stoichiometry and the structural ordering function as two key factors dictating the resulting architectures. More sophisticated and intriguing nanostructures have been achieved by coupling galvanic replacement with percolation dealloying or co-reduction. The electrocatalytic activity and the stability of the resulting NPs with controllable geometries have been pushed to a new level. Lastly, I extend the investigation to Au-Ni system with huge lattice mismatch. The success in geometry-controlled syntheses of a series of Au-Ni bimetallic heteronanostructures represents a significant step toward the extension of nanoscale interfacial heteroepitaxy to the ones exhibiting large lattice mismatches and even dissimilar crystalline structures. In summary, the goal of this dissertation is to gain new insights on structural transformations of multimetallic NPs which serve as a central design principle that guides the development of synthetic approaches to controllably fabricate architecturally sophisticated and compositionally diverse multimetallic nanostructures and build the structure-composition-property relationships and eventually optimize their performances

An Analysis Method of Symplectic Dual System for Decagonal Quasicrystal Plane Elasticity and Application

The symplectic solution system of decagonal quasicrystal elastic mechanics is considered. Hamiltonian dual equations together with the boundary conditions are investigated by utilizing the principle of minimum potential energy. Then the symplectic eigenvectors are given on the basis of the variable separation method. As application, analytical solution for decagonal quasicrystal cantilever beam with concentrated load is discussed. The analytical expressions of the stresses and displacements of the phonon field and phason field are obtained. The present method allows for the exploration of new analytic solutions of quasicrystal elasticity that are difficult to obtain by other analytic method

Eshelby Tensors for Two-Dimensional Decagonal Piezoelectric Quasicrystal Composites

The Eshelby tensor for two-dimensional (2D) piezoelectric quasicrystal composites (QCs) is considered. The explicit expressions of Eshelby tensors for 2D piezoelectric QCs are given using the Green’s function method and the interior polarization tensor method, respectively. On this basis, numerical examples of the Eshelby tensor for 2D piezoelectric QCs with ellipsoidal inclusions are discussed in detail

Residual Silver Remarkably Enhances Electrocatalytic Activity and Durability of Dealloyed Gold Nanosponge Particles

Percolation dealloying of multimetallic alloys entangles the selective dissolution of the less-noble elements with nanoscale restructuring of the more-noble components, resulting in the formation of spongelike, nanoporous architectures with a unique set of structural characteristics highly desirable for heterogeneous catalysis. Although the dealloyed nanoporous materials are compositionally dominated by the more-noble elements, they inevitably contain residual less-noble elements that cannot be completely removed through the percolation dealloying process. How to employ the less-noble elements to rationally guide the structural evolution and optimize the catalytic performances of the dealloyed noble metal nanocatalysts still remains largely unexplored. Here, we have discovered that incorporation of Ag into Au–Cu binary alloy nanoparticles substantially enhances the Cu leaching kinetics while effectively suppressing the ligament coarsening during the nanoporosity-evolving percolation dealloying of the alloy nanoparticles. The controlled coleaching of Ag and Cu from Au–Ag–Cu ternary alloy nanoparticles provides a unique way to optimize both the surface area-to-mass ratios and specific activities of the dealloyed nanosponge particles for the electrocatalytic oxidation of alcohols. The residual Ag in the fully dealloyed nanosponge particles plays crucial roles in stabilizing the surface active sites and maintaining the nanoporous architectures during the electrocatalytic reactions, thereby greatly enhancing the durability of the electrocatalysts. The insights gained from this work shed light on the underlying roles of residual less-noble elements that are crucial to the rational optimization of electrocatalysis on noble-metal nanostructures

General synthesis and atomic arrangement identification of ordered Bi–Pd intermetallics with tunable electrocatalytic CO2 reduction selectivity

Abstract Intermetallic compounds (IMCs) with fixed chemical composition and ordered crystallographic arrangement are highly desirable platforms for elucidating the precise correlation between structures and performances in catalysis. However, diffusing a metal atom into a lattice of another metal to form a controllably regular metal occupancy remains a huge challenge. Herein, we develop a general and tractable solvothermal method to synthesize the Bi-Pd IMCs family, including Bi2Pd, BiPd, Bi3Pd5, Bi2Pd5, Bi3Pd8 and BiPd3. By employing electrocatalytic CO2 reduction as a model reaction, we deeply elucidated the interplay between Bi-Pd IMCs and key intermediates. Specific surface atomic arrangements endow Bi-Pd IMCs different relative surface binding affinities and adsorption configuration for *OCHO, *COOH and *H intermediate, thus exhibiting substantially selective generation of formate (Bi2Pd), CO (BiPd3) and H2 (Bi2Pd5). This work provides a comprehensive understanding of the specific structure-performance correlation of IMCs, which serves as a valuable paradigm for precisely modulating catalyst material structures

Proteome characterization of developing grains in bread wheat cultivars (<it>Triticum aestivum</it> L.)

Abstract Background The analyses of protein synthesis, accumulation and regulation during grain development in wheat are more complex because of its larger genome size compared to model plants such as Arabidopsis and rice. In this study, grains from two wheat cultivars Jimai 20 and Zhoumai 16 with different gluten quality properties were harvested at five development stages, and were used to displayed variable expression patterns of grain proteins. Results Proteome characterization during grain development in Chinese bread wheat cultivars Jimai 20 and Zhoumai 16 with different quality properties was investigated by 2-DE and tandem MALDI-TOF/TOF-MS. Identification of 117 differentially accumulated protein spots representing 82 unique proteins and five main expression patterns enabled a chronological description of wheat grain formation. Significant proteome expression differences between the two cultivars were found; these included 14 protein spots that accumulated in both cultivars but with different patterns and 27 cultivar-different spots. Among the cultivar-different protein spots, 14 accumulated in higher abundance in Jimai 20 than in Zhoumai 16, and included NAD-dependent isocitrate dehydrogenase, triticin precursor, LMW-s glutenin subunit and replication factor C-like protein. These proteins are likely to be associated with superior gluten quality. In addition, some proteins such as class II chitinase and peroxidase 1 with isoforms in developing grains were shown to be phosphorylated by Pro-Q Diamond staining and phosphorprotein site prediction. Phosphorylation could have important roles in wheat grain development. qRT-PCR analysis demonstrated that transcriptional and translational expression patterns of many genes were significantly different. Conclusions Wheat grain proteins displayed variable expression patterns at different developmental stages and a considerable number of protein spots showed differential accumulation between two cultivars. Differences in seed storage proteins were considered to be related to different quality performance of the flour from these wheat cultivars. Some proteins with isoforms were phosphorylated, and this may reflect their importance in grain development. Our results provide new insights into proteome characterization during grain development in different wheat genotypes.</p

Intertwining Roles of Silver Ions, Surfactants, and Reducing Agents in Gold Nanorod Overgrowth: Pathway Switch between Silver Underpotential Deposition and Gold–Silver Codeposition

The past two decades have witnessed great success achieved in the geometry-controlled synthesis of metallic nanoparticles using the seed-mediated nanocrystal growth method. Detailed mechanistic understanding of the synergy among multiple key structure-directing agents in the nanocrystal growth solutions, however, has long been lagging behind the development and optimization of the synthetic protocols. Here we investigate the foreign ion- and surfactant-coguided overgrowth of single-crystalline Au nanorods as a model system to elucidate the intertwining roles of Ag⁺ foreign ions, surface-capping surfactants, and reducing agents that underpin the intriguing structural evolution of Au nanocrystals. The geometry-controlled nanorod overgrowth involves two distinct underlying pathways, Ag underpotential deposition and Au–Ag electroless codeposition, which are interswitchable upon maneuvering the interplay of the Ag⁺ ions, surfactants, and reducing agents. The pathway switch governs the geometric and compositional evolution of nanorods during their overgrowth, allowing the cylindrical Au nanorods to selectively transform into a series of anisotropic nanostructures with interesting geometric, compositional, and plasmonic characteristics. The insights gained from this work shed light on the mechanistic complexity of geometry-controlled nanocrystal growth and may guide the development of new synthetic approaches to metallic nanostructures with increasing architectural complexity, further enhancing our capabilities of fine-tuning the optical, electronic, and catalytic properties of the nanoparticles

Controlled Dealloying of Alloy Nanoparticles toward Optimization of Electrocatalysis on Spongy Metallic Nanoframes

Atomic-level understanding of the structural transformations of multimetallic nanoparticles triggered by external stimuli is of vital importance to the enhancement of our capabilities to fine-tailor the key structural parameters and thereby to precisely tune the properties of the nanoparticles. Here, we show that, upon thermal annealing in a reducing atmosphere, Au@Cu₂O core–shell nanoparticles transform into Au–Cu alloy nanoparticles with tunable compositional stoichiometries that are predetermined by the relative core and shell dimensions of their parental core–shell nanoparticle precursors. The Au–Cu alloy nanoparticles exhibit distinct dealloying behaviors that are dependent upon their Cu/Au stoichiometric ratios. For Au–Cu alloy nanoparticles with Cu atomic fractions above the parting limit, nanoporosity-evolving percolation dealloying occurs upon exposure of the alloy nanoparticles to appropriate chemical etchants, resulting in the formation of particulate spongy nanoframes with solid/void bicontinuous morphology composed of hierarchically interconnected nanoligaments. The nanoporosity evolution during percolation dealloying is synergistically guided by two intertwining structural rearrangement processes, ligament domain coarsening driven by thermodynamics and framework expansion driven by Kirkendall effects, both of which can be maneuvered by controlling the Cu leaching rates during the percolation dealloying. The dealloyed nanoframes possess large open surface areas accessible by the reactant molecules and high abundance of catalytically active undercoordinated atoms on the ligament surfaces, two unique structural features highly desirable for high-performance electrocatalysis. Using the room temperature electro-oxidation of methanol as a model reaction, we further demonstrate that, through controlled percolation dealloying of Au–Cu alloy nanoparticles, both the electrochemically active surface areas and the specific activity of the dealloyed metallic nanoframes can be systematically tuned to achieve the optimal electrocatalytic activities