03/31/2016: A recent publication, "Pressure Dependent Polymorphism and Bandgap Tuning of Methylammonium Lead Iodide Perovskite", was chosen as a Hot article and has been featured in the online collection of "Nanoscale".

 

Author: Sarah Millar

Published Date: 18 January 2014

Source / Publisher: Chemistry - A European Journal/Wiley-VCH

Copyright: Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

10/17/2012: Hydrogenation of olefins is often used to test new heterogeneous catalysts, especially noble metals, such as Pt, Pd, and Au. Each crystallographic facet of such catalysts has its own role in the catalysis. For example, {111} planes of Au preferentially activate C=O groups, whereas low-coordinated sites at corners and edges favor the breaking of C=C bonds. It has also been shown that hydrogenation of styrene takes place on defect sites (high-index kinks and steps) of Pd catalysts, rather than their low-index terraces. Thus, the fabrication of nanocatalysts with high-index crystallographic facets could lead to more efficient catalysts.

We recently report the simple synthesis of high-quality Pt3Co nanocubes (NCs) with a concave structure. The NCs were prepared through a wet-chemical approach, in which the ratio of oleyl amine (OAM)/oleic acid (OA) was finely tuned. The NCs are terminated with high-index crystallographic planes containing a combination of several sub-facets.The team proposes that the formation of Pt3Co seeds is dependent on the concentration of free metallic atoms during the reaction, whereas the final morphology of NCs was controlled by selective binding with the appropriate OAM/OA ratio during the crystal-growth stage.Using hydrogenation of styrene as a model reaction, the NCs showed enhanced catalytic activity in comparison with low-indexed surface terminated Pt3Co nanocubes of similar size owing to their more open structure, more stable composition/morphology, and the increased number of active atomic sites located on their high-index crystallographic planes.

The manuscript (DOI: 10.1002/chem.201301724) has been chosen to be highlighted on the ChemistryViews website. The short news article is available at this link.

 

 

10/17/2012: Watching Nanoscale Octahedra Crystallize: Assembly of nanoparticles into ordered superlattices opens up many potential applications such as sensors, catalysts, and novel optical materials. Unlike spherical particles, which can normally self-assemble into a close-packed fcc superlattice, systems containing non-spherical building blocks are much less known. We have recently demonstrated how to synthesize monodisperse non-spherical nanocrystals, including nanocubes and nanoctahedra. In recent experiments at D1 station of Cornell High Energy Synchrotron Source (CHESS) at Cornell University, together with CHESS staff scientist Dr. Detlef-M. Smilgies we determined an extremely low packing density superstructure consisting of Pt3Cu2 nanotahdera. Furthermore, for the first time, we observed reversible Kirkwood-Alder transition occurred in this system. The details were just highlighted on CHESS web site http://news.chess.cornell.edu/articles/2012/Fang10172012.html   as well as reported in our recent publication [JACS 134 (34), 14043-14049 (2012)].



12/10/2011: TOC of our recent publication, "Reversal of Hall-Petch Effect in Structural Stability of PbTe Nanocrystals and Associated Variation of Phase Transformation", has been selected and posted as one of "rolling pictures" on Nano Letters.


05/10/2011: Our review paper, "self-Assembly of Lead Chalcogenide Nanocrystals" (Chem. Asian J. 6(5)/2011, page 1126), was recently published, and its art-work was chosen as a cover picture.


1/18/2011: Our previous synthesis methodology of Pt nanocubes was cited in Gelest catalog (click show details), "Metal-Organics" p. 176-177.

Are shape-controlled nanocrystals of Pt-based alloy promising electrocatalysts?

11/22/2010: Our previous work, Pt3M (M=Fe, Co, Ni and Pt) nanocube synthesis and ORR study on Pt3Ni nanoctahedra, has been highlighted by Xia's paper, " Shaping a Bright Future for Platinum-Based Alloy Electrocatalysts" which will be published soon.

Can an electrocatalytic investigation be conducted on a particle shape-controlled level?

08/16/2009: Our new paper, "Enhancing by Weakening: Electrooxidation of Methanol on Pt3Co and Pt Nanocubes" was just published in Angew. Chem. Int. Ed. In this work, Pt3Co and Pt nanocubes were comparatively prepared and studied. The enhanced catalytic activity on Pt3Co nanocubes was explained by the slower and weaker adsorption of CO onto the surface of Pt3Co.


8/12/2010: We just receive word that our communication "Enhancing by Weakening: Electrooxidation of Methanol on Pt3Co and Pt Nanocubes" has been chosen as a "Hot Paper" by the Editors of Angewandte Chemie for its importance in a rapidly evolving field of high current interest.

This announcement will be published in the table of contents entry on Angewandte's homepage prior to publication of the full paper as soon as possible.

4/27/2010: It is now possible to assemble binary nanosphere superlattice patterns with various structures, and it was determined that opposite electrical charges are the major driving force to result in such patterns. With a success of various nanopolyhedron syntheses, the question has been extended to a non-spherical nanoparticle colloidal system: What is the dominant driving force to induce a superlattice assembly in a non-spherical-particle system? With our recent advances in preparation of shape- and size-controlled nonspherical nanoparticles, we answered this question in the current issue of ACS Nano (4/4). In this work, we reported our observation of two-dimensional (2D) superlattices consisting of c-In2O3 nanoctahedra and Pd nanospheres, and identified three types of c-In2O3 skeleton structures in the 2D octahedral c-In2O3-spherical Pd nanoparticle supercrystal patterns. In collaboration with Dr. Luo at TAMU, we concluded that (1) the vertices of c-In2O3 nanoctahedra could have higher electrical charge density than that on edge or plane; (2) most of the Pd nanoparticles locate on the middle plane of the c-In2O3 nanoctahedra well above the substrate surface (support film) rather than sitting on it in the 2D supercrystal assembly patterns; (3) the orientation of c-In2O3 nanoctahedra dominates the structure of a nonspherical 2D supercrystal pattern. On the basis of these investigations in a non-spherical nanoparticle colloidal system, we confirmed that Coulomb forces resulted from opposite electrical charges on nanopolyhedra (c-In2O3) and metal nanospheres (Pd) are the major driving forces to induce such assemblies. Read more.

Highlight: Shape DOES affect the electrochemical catalytic activity.

01/06/2010: We successfully synthesized high-quality Pt3Ni nanopolyhedra (geometric tiny solids with flat facets and straight edges) using a recently developed wet-chemical approach, and investigated their shape-dependent oxygen reduction activity which is a significant reaction in the cathode of proton exchange membrane fuel cells. Amazingly, we determined that the activity on Pt3Ni nanoctahedra (terminated with {111} facets) is ~5 folds higher than that of nanocubes (bounded with {100} facets) with a similar size. This discovery is important for developing new type of electrocatalyst with a superior oxygen reduction activity used in the real world of fuel cells. This result will be published in Nano Letters soon.

12/1/2009: For the first time, we found that W(CO)6 can control the morphology of Pt-3d-transition alloy nanoparticles and we have developed a general approach for preparation {100}-terminated Pt3M nanocubes (M = Pt or Co, Fe, and Ni). This result was published in JACS.


11/25/2009: We released a facile and general synthetic method for preparation of high-quality, {100}-terminated Pt3M nanocubes (M = Pt or 3d-transition metals Co, Fe, and Ni). We realize that addition of W(CO)6 is crucial for control of the nucleation process when the metallic precursors are reduced, whereas an optimized ratio of the solvent pair, oleylamine and oleic acid, is the key to enabling the lowest total surface energy on {100} facets in order to develop such cubic nanocrystals in the present system. This novel method was published in the last issue of JACS this year.



04/30/2009: Shape-controlled catalysis: High-quality Pt-Cu nanocubes with an average size of about 8 nm were synthesized from a high-temperature organic solution system in the presence of various capping ligands. These cubic Pt-Cu nanocrystals terminated with {100} facets demonstrated a superior catalytic activity towards methanol oxidation compared to similar sized Pt-Cu and Pt nanospheres. This result was published in Angew. Chem. Int. Ed. on 4/29/2009. This publication was highlighted as "VIP" (Very Important Paper).


03/5/2009: We just received an invitation from Chem. Eur. J. that our accepted manuscript, Soluble InP and GaP Nanowires: Self-Seeded, Solution-Liquid-Solid Synthesis and Electrical Properties, has been highlighted with a frontispiece in a forthcoming issue.


02/20/2009: We have controlled growth parameters and self-assembled various PbSe QD arrays on flat gold surface for scanning tunneling spectroscopy measurements. The current-voltage curves of the arrays were analyzed using double-barrier tunnel junction model to acquire the shunt capacitance between the array and the gold substrate. This article will be published in J. Phys. Chem. C on 5/7/2009, and the Cover Art will show up on issue 18, 2009.


02/04/2009: Zhaoping's article, "Soluble InP and GaP Nanowires: Self-Seeded, Solution-Liquid-Solid Synthesis and Electrical Properties" was accepted by Chem. Eur. J. In recent years, a solution-based approach supported by a solution-liquid-solid (SLS) mechanism has been developed to enable the quality-control in addition to previous physical processing methods. Nevertheless, there still has a large room to improve the wet-chemical synthesis of III-V nanowires. Our modified strategy presented in this publication avoids some issues that exist in the SLS method, such as heterogeneous phase of catalyst and potential metallic contamination in nanowires. We also demonstrate excellent quality of the as-prepared InP and GaP nanowires, including low native point defects for carrier concentrations and few structural defects (especially for InP). The scientific impacts of this work lie in the fact that in this relatively facile solution-based approach developed in our group the catalyst seeds can be in-situ generated by the decomposition of the metalorganic precursor, In(CH3)3 or Ga(C2H5)3, at an appropriately high temperature without using any special surfactant. Moreover, this synthetic approach may be promising in readily extending to a preparation strategy of other high-quality III-V nanowires including GaAs, GaSb, InAs, InSb, and their (Ga/In)(P/As/Sb) alloys.

09/22/2008: Jun's research article, " Simple Cubic Super Crystals Containing PbTe Nanocubes and Their Core-Shell Building Blocks", was published in JACS. In this full paper, we report a preparation of high-quality cubic PbTe nanocrystals, their square-array assemblies in two-dimensional patterns, as well as simple cubic super crystals. The influence of oleylamine in nanocrystal synthesis and core-shell formation through an anion-exchange mechanism was also studied. The simple cubic super crystals together with two-dimensional assembly patterns containing PbTe nanocubes and their core-shell building blocks were fully characterized. Such super crystals consisting of structural building blocks may allow engineering of more complex materials from which novel properties may emerge.



09/09/2008: Jun's research communication, entitled "p-Type Field-Effect Transistors of Single-Crystal ZnTe Nanobelts", was published in Angewandte Chemie Int. Ed. In this work, we have been succeeded, for the first time, in preparation of straight ZnTe nanobelts with extremely low thickness (< 6 nm). We further determined a crystal growth direction of < (-2)0 0 > in the growth of the belts, which has never been reported previously. We also demonstrated these single-crystal ZnTe nanobelts as p-type field-effect transistors, revealing a bright future of applications in nanodevice engineering.

03/19/2008: Our self-assembly paper, entitled "Super-Crystal Structures of Octahedral c-In2O3 Nanocrystals", was published in JACS. Three-dimensional (3D) self-assembly of nanocrystal (NC) superlattice, i.e. super crystal (SC), has attracted increasing attention. The small building blocks for assemblies are usually spherical nanocrystals. Recent progress indicates that it is possible to achieve a super crystal using non-spherical NCs, such as cubic NCs.

In this article, we describe and analyze 2D and some 3D assemblies of uniform cubic-phase In2O3 NCs with octohedral shapes. We demonstrate our amazing observations on this kind of super crystals (or superlattices) as a model system, exposing largeness at least in tens of microns scale and other unique features such as steps, terraces, kinks and vacancies which are similar to those from a single crystal. Based on the EM observations, three types of well-defined octahedral NC packing structures in such super crystal system are also identified.

02/13/2008: Zhaoping's III-V QD paper was published in Angewandte Chemie and highlighted as VIP very important paper on Feb. 13, 2007.

III-V semiconductors are very important materials and are of great interest for new generation of microelectronics. Colloidal III-V semiconductor nanocrystals have also been a subject of intensive studies because of their rich phenomena associated with quantum-confinement effects. However, studies of III-V nanocrystals are largely restrained due to the difficulty of their synthetic chemistry. The scientific impacts of this work lie on that we have introduced a new concept, co-reduction, to understand the formation of InP. We believe that this report may provide the following breakthroughs: (1) We demonstrate an great improvement of the synthetic conditions using a novel approach, e,g, shortening the period of reaction time and reducing the cost of precursor; (2) This novel method has skipped expensive or more hazardous P-sources, such as tris(trimethylsilyl)phosphine in the process of InP nanocrystal synthesis, making this synthetic strategy noticeably "greener" and more economical. (3) The present work may benefit the further scale-up of such III-V chemical synthesis as well, creating a new direction in extending this achievement to the preparations of InAs and InSb nanocrystals using AsCl3 and SbCl3 as the pnicogen sources, respectively.