The properties of a nanocrystal are heavily influenced by its shape. Shape control of a colloidal nanocrystal is believed to be a kinetic process, with high-energy facets growing faster then vanishing, leading to nanocrystals enclosed by low-energy facets. Identifying a surfactant that can specifically bind to a particular crystal facet is critical, but has proved challenging to date. Biomolecules have exquisite specific molecular recognition properties that can be explored for the precise engineering of nanostructured materials. Here, we report the use of facet-specific peptide sequences as regulating agents for the predictable synthesis of platinum nanocrystals with selectively exposed crystal surfaces and particular shapes. The formation of platinum nanocubes and nanotetrahedrons are demonstrated with Pt-{100} and Pt-{111} binding peptides, respectively. Our studies unambiguously demonstrate the abilities of facet-selective binding peptides in determining nanocrystal shape, representing a critical step forward in the use of biomolecules for programmable synthesis of nanostructures.

Surfactants with preferential adsorption to certain crystal facets have been widely employed to manipulate morphologies of colloidal nanocrystals, while mechanisms regarding the origin of facet selectivity remain an enigma. Similar questions exist in biomimetic syntheses concerning biomolecular recognition to materials and crystal surfaces. Here we present mechanistic studies on the molecular origin of the recognition toward platinum {111} facet. By manipulating the conformations and chemical compositions of a platinum {111} facet specific peptide, phenylalanine is identified as the dominant motif to differentiate {111} from other facets. The discovered recognition motif is extended to convert nonspecific peptides into {111} specific peptides. Further extension of this mechanism allows the rational design of small organic molecules that demonstrate preferential adsorption to the {111} facets of both platinum and rhodium nanocrystals. This work represents an advance in understanding the organic-inorganic interfacial interactions in colloidal systems and paves the way to rational and predictable nanostructure modulations for many applications.

Structure‐enhanced catalytic activity: An ultrathin platinum multiple‐twinned nanowire network is shown to be an efficient electrocatalyst (see picture). This material has a higher electrochemical surface area and exhibits a much improved activity toward both the oxygen reduction reaction and the methanol oxidation reaction relative to commercial Pt/C catalysts.

Metal nanocrystals enable new functionality in sensors, biomarkers, and catalysts while mechanisms of shape‐control in synthesis remain incompletely understood. This study explains mechanisms of biomolecule recognition and ligand‐directed growth of cubic platinum nanocrystals in atomic detail using molecular dynamics simulation (MD), synthesis, and characterization. Peptide T7 is shown to selectively recognize {100} bounded nanocubes through preferential adsorption near the edges as opposed to facet centers. Spatial preferences in peptide binding are related to differences in the binding of water molecules and conformational matching of polarizable atoms in the peptide to {100} epitaxial sites. Changes in peptide concentration also have profound impact on attraction versus repulsion on a given surface. As an example, the selective synthesis of cubes in the presence of peptide T7 demonstrates that only intermediate T7 concentration leads to high yield. High‐resolution transmission electron microscopy (HRTEM) shows concentration‐dependent changes in crystal shape, yield, and size. Large‐scale MD simulations explain associated differences in facet coverage and in adsorption energies of T7 peptides on cuboctahedral seed crystals, supporting a growth mechanism of adatom deposition. A similar analysis using a different peptide S7 is presented as well. Emerging computational opportunities to predict ligand binding to metal nanocrystals and rationalize growth preferences are summarized.

Structural defects/grain boundaries in metallic materials can exhibit unusual chemical reactivity and play important roles in catalysis. Bulk polycrystalline materials possess many structural defects, which is, however, usually inaccessible to solution reactants and hardly useful for practical catalytic reactions. Typical metallic nanocrystals usually exhibit well-defined crystalline structure with few defects/grain boundaries. Here, we report the design of ultrafine wavy nanowires (WNWs) with a high density of accessible structural defects/grain boundaries as highly active catalytic hot spots. We show that rhodium WNWs can be readily synthesized with controllable number of structural defects and demonstrate the number of structural defects can fundamentally determine their catalytic activity in selective oxidation of benzyl alcohol by O2, with the catalytic activity increasing with the number of structural defects. X-ray photoelectron spectroscopy (XPS) and cyclic voltammograms (CVs) studies demonstrate that the structural defects can significantly alter the chemical state of the Rh WNWs to modulate their catalytic activity. Lastly, our systematic studies further demonstrate that the concept of defect engineering in WNWs for improved catalytic performance is general and can be readily extended to other similar systems, including palladium and iridium WNWs.