Yanyan Jia

Unique Excavated Rhombic Dodecahedral PtCu3 Alloy Nanocrystals Constructed with Ultrathin Nanosheets of High-Energy {110} Facets

Ultrathin crystalline nanosheets give an extremely high surface area of a specific crystal facet with unique physical and chemical properties compared with normal three-dimensionally polyhedral nanocrystals (NCs). However, the ultrathin metal nanosheets tend to curl themselves or assemble with each other sheet by sheet, which may reduce the effective surface area and accordingly the catalytic activity to a great extent. Here we report a facile wet-chemical route that allows the fabrication of novel excavated rhombic dodecahedral (ERD) PtCu3 alloy NCs with ultrathin nanosheets of high-energy {110} facets. The surface area was measured to be 77 m(2) g(-1) by CO stripping, although the particle size is about 50 nm. Electrochemical characterizations showed that the ERD PtCu3 NCs exhibit excellent electrocatalytic performance and high antipoisoning activity in comparison with commercial Pt black and PtCu3 alloy NCs with {111} surfaces.

Surfactant-concentration-dependent shape evolution of Au-Pd alloy nanocrystals from rhombic dodecahedron to trisoctahedron and hexoctahedron

The surface structure-controlled synthesis of noble metal nanocrystals (NCs) bounded by high-index facets has become a hot research topic due to their potential to significantly improve catalytic performance. This study reports the preparation of monodisperse Au-Pd alloy NCs with systematic shape evolution from rhombic dodecahedral (RD) to trisoctahedral (TOH), and hexoctahedral (HOH) structures by varying the concentration of surfactant in the surfactant-mediated synthesis. The as-prepared three kinds of alloy NCs possess almost the same size and composition as each other. It is suggested that the surfactant containing long-chain octadecyltrimethyl ammonium (OTA(+)) ions plays a key role in the formation of high index facets, and the crystal growth kinetics may also have an effect on the formation of different nanocrystal morphologies. In addition, the catalytic activities of these NCs are evaluated by structure-sensitive reactions, including ethanol electro-oxidation and the catalytic reduction of 4-nitrophenol (4-NPh). These three types of Au-Pd alloy NCs exhibit different catalytic selectivities towards these two reactions. The catalytic activities toward electro-oxidation of ethanol are in the order of HOH > RD > TOH, which follows the order of their corresponding surface energies. However, the activities toward catalytic reduction of 4-NPh are in the order of RD > TOH > HOH, which should be related to the local structure of the surfaces.

Efficient and Ultrafast Formation of Long-Lived Charge-Transfer Exciton State in Atomically Thin Cadmium Selenide/Cadmium Telluride Type-II Heteronanosheets

Colloidal cadmium chalcogenide nanosheets with atomically precise thickness of a few atomic layers and size of 10-100 nm are two-dimensional (2D) quantum well materials with strong and precise quantum confinement in the thickness direction. Despite their many advantageous properties, excitons in these and other 2D metal chalcogenide materials are short-lived due to large radiative and nonradiative recombination rates, hindering their applications as light harvesting and charge separation/transport materials for solar energy conversion. We showed that these problems could be overcome in type-II CdSe/CdTe core/crown heteronanosheets (with CdTe crown laterally extending on the CdSe nanosheet core). Photoluminesence excitation measurement revealed that nearly all excitons generated in the CdSe and CdTe domains localized to the CdSe/CdTe interface to form long-lived charge transfer excitons (with electrons in the CdSe domain and hole in the CdTe domain). By ultrafast transient absorption spectroscopy, we showed that the efficient exciton localization efficiency could be attributed to ultrafast exciton localization (0.64 ± 0.07 ps), which was facilitated by large in-plane exciton mobility in these 2D materials and competed effectively with exiton trapping at the CdSe or CdTe domains. The spatial separation of electrons and holes across the CdSe/CdTe heterojunction effectively suppressed radiative and nonradiative recombination processes, leading to a long-lived charge transfer exciton state with a half-life of ∼ 41.7 ± 2.5 ns, ∼ 30 times longer than core-only CdSe nanosheets.

Underpotential Deposition-Induced Synthesis of Composition-Tunable PtCu Nanocrystals and Their Catalytic Properties

Pt-Cu alloy octahedral nanocrystals (NCs) have been synthesized successfully by using N,N-dimethylformamide as both the solvent and the reducing agent in the presence of cetyltrimethylammonium chloride. Cu underpotential deposition (UPD) is found to play a key role in the formation of the Pt-Cu alloy NCs. The composition in the Pt-Cu alloy can be tuned by adjusting the ratio of metal precursors in solution. However, the Cu content in the Pt-Cu alloy NCs cannot exceed 50%. Due to the fact that Cu precursor cannot be reduced to metallic copper and the Cu content cannot exceed 50%, we achieved the formation of the Pt-Cu alloy by using Cu UPD on the Pt surface. In addition, the catalytic activities of Pt-Cu alloy NCs with different composition were investigated in electrocatalytic oxidation of formic acid. The results reveal that the catalytic performance is strongly dependent on Pt-Cu alloy composition. The sample of Pt(50)Cu(50) exhibits excellent activity in electrocatalytic oxidation of formic acid.

Wet chemical synthesis of intermetallic Pt3Zn nanocrystals via weak reduction reaction together with UPD process and their excellent electrocatalytic performances

Platinum based alloy nanocrystals are promising catalysts for a variety of important practical process. However, it remains a great challenge to synthesize platinum-based intermetallic compound nanocrystals with well-defined surface structures. In this communication, taking the synthesis of concave cubic intermetallic Pt3Zn nanocrystals with {hk0} facets as an example, we proposed a new synthesis strategy for intermetallic compounds by reduction of noble metal precursors via a slow reduction process and reduction of transition metal ions via an underpotential deposition (UPD) process in wet chemical synthesis. The as-prepared intermetallic Pt3Zn nanocrystals exhibited superior CO poisoning tolerance and high electro-catalytic activity in both methanol and formic acid oxidation reactions in comparison with solid solution Pt3Zn nanocrystals and Pt/C.

Synthesis of spatially uniform metal alloys nanocrystals via a diffusion controlled growth strategy: The case of Au-Pd alloy trisoctahedral nanocrystals with tunable composition

AbstractRational synthesis of bimetallic alloy nanocrystals (NCs) is still a great challenge. Especially, spatially uniform alloy NCs are very difficult to achieve because of the different reduction rates of the individual alloy components. Herein we propose a facile wet chemical synthetic strategy to prepare uniform bimetallic alloy NCs with tunable composition by controlling the growth of alloy NCs under diffusion controlled conditions. Using this strategy, we successfully synthesized trisoctahedral (TOH) Au-Pd alloy NCs enclosed by {hhl} high-index facets with uniform spatial distributions and different compositions. Significantly, using our strategy, the composition of the as-prepared Au-Pd alloy NCs is identical to the ratio of the two metal precursors in the reaction solution over a wide range. Investigation of the composition-dependent electrochemical behavior of the as-prepared TOH Au-Pd alloy NCs showed that the TOH Au-Pd alloy NCs containing 14.1 atom% Pd exhibited the best activity.

A facile surfactant-free synthesis of Rh flower-like nanostructures constructed from ultrathin nanosheets and their enhanced catalytic properties

Rh is an important catalyst that is widely used in a variety of organic reactions. In recent years, many efforts have focused on improving its catalytic efficiency by fabricating catalyst nanoparticles with controlled size and morphology. However, the frequently employed synthesis route using organic compounds either as the reaction medium or capping agent often results in residual molecules on the catalyst surface, which in turn drastically diminishes the catalytic performance. Herein, we report a facile, aqueous, surfactant-free synthesis of a novel Rh flowerlike structure obtained via hydrothermal reduction of Rh(acac)3 by formaldehyde. The unique Rh nanoflowers were constructed from ultrathin nanosheets, whose basal surfaces comprised {111} facets with an average thickness of ~1.1 nm. The specific surface area measured by CO stripping was 79.3 m2·g−1, which was much larger than that of commercial Rh black. More importantly, the Rh nanoflower catalyst exhibited excellent catalytic performance in the catalytic hydrogenation of phenol and cyclohexene, in contrast to the commercial Rh black and polyvinyl pyrrolidone (PVP)-capped Rh nanosheets exposed by similar {111} basal surfaces.

Composition-tunable synthesis of Pt–Cu octahedral alloy nanocrystals from PtCu to PtCu3 via underpotential-deposition-like process and their electro-catalytic properties

Bimetallic alloy nanocrystals (NCs) have received great attention because their physical and chemical properties greatly depend on their composition and structure. However, simultaneous control of the composition and surface structure (or morphology) of metal alloy NCs is challenging due to differences in standard redox potential (SRP). According to our previous research, well-shaped and composition-tunable Pt–Cu alloy NCs can be controlled in mild reduction conditions. However, the content of Cu in the as-prepared Pt–Cu alloy NCs cannot exceed 50% using N,N-dimethylformamide (DMF) as the weak reductant. In this paper, we reported a successful synthesis of the octahedral Pt–Cu bimetallic alloy NCs with a molar ratio of Cu ranging from 50% to 75% via introducing a slightly stronger reductant (n-butylalcohol) to improve the reducing ability and tune the sequential reaction kinetics. It is found that n-butylalcohol can solely reduce the Cu precursor to metallic copper. The UPD-like process ensures the formation of the Pt–Cu alloy due to the strong binding energy between Cu atoms and the Pt crystal surface. Owing to the successful control of Cu, the content in Pt–Cu alloy increased from 50% to 75%, and the relationship between the composition and the properties of the electro-catalytic oxidation of formic acid were further investigated. The results reveal that the electro-catalytic performance of the Pt–Cu alloy is enhanced along with Cu content, and that PtCu3 exhibits excellent catalytic activity and anti-poisoning ability.