Doped Silicon Nanocrystal Plasmonics

Doped semiconductor nanocrystals represent an exciting new type of plasmonic material with optical resonances in the infrared. Unlike noble metal nanoparticles, the plasmon resonance can be tuned by altering the doping density. Recently, it has been shown that silicon nanocrystals can be doped using phosphorus and boron resulting in highly tunable infrared plasmon resonances. Due to the band structure of silicon, doping with phosphorus contributes light (transverse) and heavy (longitudinal) electrons, while boron contributes light and heavy holes and one would expect two distinct plasmon branches. Here we develop a classical hybridization theory and a full quantum mechanical TDLDA approach for two-component carrier plasmas and show that the interaction between the two plasmon branches results in strongly hybridized plasmon modes. The antibonding mode where the two components move in phase is bright and depends sensitively on the doping densities. The low energy bonding mode with opposite charge alignment can only be observed in the quantum regime when strong Coulomb screening is present. The theoretical results are in good agreement with the experimental data

Flexible 2D Boron Imidazolate Framework for Polysulfide Adsorption in Lithium–Sulfur Batteries

The “polysulfide shuttle,” a process initiated by the dissolution of polysulfides, is recognized to be one of the major failure mechanisms of lithium–sulfur (Li–S) batteries. Much research effort has been dedicated toward efficient cathode additives and host materials to suppress the leaching of polysulfide species. Herein, we report a new 2D metal–organic framework constituted by a tritopic ligand, boron imidazolate ([BH(Im)3]−, Im = imidazole), and Co2+ ions for lithium polysulfide adsorption. The cobalt imidazolate framework (CoN6-BIF) contains octahedrally coordinated Co centers that form two-dimensional layers in the a,b plane. Composite cathodes containing CoN6-BIF exhibited high sulfur utilization and capacity retention, resulting in improved specific capacity and cycle life compared to sulfur/carbon controls. Density functional theory (DFT) calculations suggest that CoN6-BIF linkers are rotationally flexible, allowing the framework to accommodate polysulfide in the expanded pores. This unusual property of BIFs opens up new avenues for exploring flexible metal–organic frameworks (MOFs) and their applications to energy storage

Flexible 2D Boron Imidazolate Framework for Polysulfide Adsorption in Lithium–Sulfur Batteries

The “polysulfide shuttle,” a process initiated by the dissolution of polysulfides, is recognized to be one of the major failure mechanisms of lithium–sulfur (Li–S) batteries. Much research effort has been dedicated toward efficient cathode additives and host materials to suppress the leaching of polysulfide species. Herein, we report a new 2D metal–organic framework constituted by a tritopic ligand, boron imidazolate ([BH(Im)3]−, Im = imidazole), and Co2+ ions for lithium polysulfide adsorption. The cobalt imidazolate framework (CoN6-BIF) contains octahedrally coordinated Co centers that form two-dimensional layers in the a,b plane. Composite cathodes containing CoN6-BIF exhibited high sulfur utilization and capacity retention, resulting in improved specific capacity and cycle life compared to sulfur/carbon controls. Density functional theory (DFT) calculations suggest that CoN6-BIF linkers are rotationally flexible, allowing the framework to accommodate polysulfide in the expanded pores. This unusual property of BIFs opens up new avenues for exploring flexible metal–organic frameworks (MOFs) and their applications to energy storage

Flexible 2D Boron Imidazolate Framework for Polysulfide Adsorption in Lithium–Sulfur Batteries

The “polysulfide shuttle,” a process initiated by the dissolution of polysulfides, is recognized to be one of the major failure mechanisms of lithium–sulfur (Li–S) batteries. Much research effort has been dedicated toward efficient cathode additives and host materials to suppress the leaching of polysulfide species. Herein, we report a new 2D metal–organic framework constituted by a tritopic ligand, boron imidazolate ([BH(Im)3]−, Im = imidazole), and Co2+ ions for lithium polysulfide adsorption. The cobalt imidazolate framework (CoN6-BIF) contains octahedrally coordinated Co centers that form two-dimensional layers in the a,b plane. Composite cathodes containing CoN6-BIF exhibited high sulfur utilization and capacity retention, resulting in improved specific capacity and cycle life compared to sulfur/carbon controls. Density functional theory (DFT) calculations suggest that CoN6-BIF linkers are rotationally flexible, allowing the framework to accommodate polysulfide in the expanded pores. This unusual property of BIFs opens up new avenues for exploring flexible metal–organic frameworks (MOFs) and their applications to energy storage

Exploiting Localized Surface Binding Effects to Enhance the Catalytic Reactivity of Peptide-Capped Nanoparticles

Peptide-based methods represent new approaches to selectively produce nanostructures with potentially important functionality. Unfortunately, biocombinatorial methods can only select peptides with target affinity and not for the properties of the final material. In this work, we present evidence to demonstrate that materials-directing peptides can be controllably modified to substantially enhance particle functionality without significantly altering nanostructural morphology. To this end, modification of selected residues to vary the site-specific binding strength and biological recognition can be employed to increase the catalytic efficiency of peptide-capped Pd nanoparticles. These results represent a step toward the <i>de novo</i> design of materials-directing peptides that control nanoparticle structure/function relationships

Direct Synthetic Control over the Size, Composition, and Photocatalytic Activity of Octahedral Copper Oxide Materials: Correlation Between Surface Structure and Catalytic Functionality

We report a synthetic approach to form octahedral Cu₂O microcrystals with a tunable edge length and demonstrate their use as catalysts for the photodegradation of aromatic organic compounds. In this particular study, the effects of the Cu²⁺ and reductant concentrations and stoichiometric ratios were carefully examined to identify their roles in controlling the final material composition and size under sustainable reaction conditions. Varying the ratio and concentrations of Cu²⁺ and reductant added during the synthesis determined the final morphology and composition of the structures. Octahedral particles were prepared at selected Cu²⁺:glucose ratios that demonstrated a range of photocatalytic reactivity. The results indicate that material composition, surface area, and substrate charge effects play important roles in controlling the overall reaction rate. In addition, analysis of the post-reacted materials revealed photocorrosion was inhibited and that surface etching had preferentially occurred at the particle edges during the reaction, suggesting that the reaction predominately occurred at these interfaces. Such results advance the understanding of how size and composition affect the surface interface and catalytic functionality of materials

Light-Activated Tandem Catalysis Driven by Multicomponent Nanomaterials

Transitioning energy-intensive and environmentally intensive processes toward sustainable conditions is necessary in light of the current global condition. To this end, photocatalytic processes represent new approaches for H₂ generation; however, their application toward tandem catalytic reactivity remains challenging. Here, we demonstrate that metal oxide materials decorated with noble metal nanoparticles advance visible light photocatalytic activity toward new reactions not typically driven by light. For this, Pd nanoparticles were deposited onto Cu₂O cubes to generate a composite structure. Once characterized, their hydrodehalogenation activity was studied via the reductive dechlorination of polychlorinated biphenyls. To this end, tandem catalytic reactivity was observed with H₂ generation via H₂O reduction at the Cu₂O surface, followed by dehalogenation at the Pd using the <i>in situ</i> generated H₂. Such results present methods to achieve sustainable catalytic technologies by advancing photocatalytic approaches toward new reaction systems

Elucidation of Peptide-Directed Palladium Surface Structure for Biologically Tunable Nanocatalysts

Peptide-enabled synthesis of inorganic nanostructures represents an avenue to access catalytic materials with tunable and optimized properties. This is achieved <i>via</i> peptide complexity and programmability that is missing in traditional ligands for catalytic nanomaterials. Unfortunately, there is limited information available to correlate peptide sequence to particle structure and catalytic activity to date. As such, the application of peptide-enabled nanocatalysts remains limited to trial and error approaches. In this paper, a hybrid experimental and computational approach is introduced to systematically elucidate biomolecule-dependent structure/function relationships for peptide-capped Pd nanocatalysts. Synchrotron X-ray techniques were used to uncover substantial particle surface structural disorder, which was dependent upon the amino acid sequence of the peptide capping ligand. Nanocatalyst configurations were then determined directly from experimental data using reverse Monte Carlo methods and further refined using molecular dynamics simulation, obtaining thermodynamically stable peptide-Pd nanoparticle configurations. Sequence-dependent catalytic property differences for C–C coupling and olefin hydrogenation were then elucidated by identification of the catalytic active sites at the atomic level and quantitative prediction of relative reaction rates. This hybrid methodology provides a clear route to determine peptide-dependent structure/function relationships, enabling the generation of guidelines for catalyst design through rational tailoring of peptide sequences

Effects of Metal Composition and Ratio on Peptide-Templated Multimetallic PdPt Nanomaterials

It can be difficult to simultaneously control the size, composition, and morphology of metal nanomaterials under benign aqueous conditions. For this, bioinspired approaches have become increasingly popular due to their ability to stabilize a wide array of metal catalysts under ambient conditions. In this regard, we used the R5 peptide as a three-dimensional template for formation of PdPt bimetallic nanomaterials. Monometallic Pd and Pt nanomaterials have been shown to be highly reactive toward a variety of catalytic processes, but by forming bimetallic species, increased catalytic activity may be realized. The optimal metal-to-metal ratio was determined by varying the Pd:Pt ratio to obtain the largest increase in catalytic activity. To better understand the morphology and the local atomic structure of the materials, the bimetallic PdPt nanomaterials were extensively studied by transmission electron microscopy, extended X-ray absorption fine structure spectroscopy, X-ray photoelectron spectroscopy, and pair distribution function analysis. The resulting PdPt materials were determined to form multicomponent nanostructures where the Pt component demonstrated varying degrees of oxidation based upon the Pd:Pt ratio. To test the catalytic reactivity of the materials, olefin hydrogenation was conducted, which indicated a slight catalytic enhancement for the multicomponent materials. These results suggest a strong correlation between the metal ratio and the stabilizing biotemplate in controlling the final materials morphology, composition, and the interactions between the two metal species