Wenbo Yue

Crystal Structure and Growth Mechanism of Unusually Long Fullerene (C60) Nanowires

Exceptionally long C60 nanowires, with a length to width aspect ratio as large as 3000, are grown from a 1,2,4-trimethylbenzene solution of C60. They have been formed to possess a highly unusual morphology, with each nanowire being composed of two nanobelts joined along the growth direction to give a V-shaped cross section. The crystal structure of these nanowires is found to be orthorhombic, with the unit cell dimensions of a = 10.2 A, b = 20.5 A, and c = 25.6 A. Structural and compositional analyses enable us to explain the observed geometry with an anisotropic molecular packing mechanism that has not been observed previously in C60 crystal studies. The nanowires have been observed to be able to transform into carbon nanofibers following high-temperature treatment, but the original V-shaped morphology can be kept unchanged in the transition. A model for the nanowire morphology based upon the solvent-C60 interactions and preferential growth directions is proposed, and potentially it could be extended for use to grow different types of fullerene nanowires.

Sandwich-Structured Graphene-Fe3O4@Carbon Nanocomposites for High-Performance Lithium-Ion Batteries

Advanced anode materials for high power and high energy lithium-ion batteries have attracted great interest due to the increasing demand for energy conversion and storage devices. Metal oxides (e.g., Fe3O4) usually possess high theoretical capacities, but poor electrochemical performances owing to their severe volume change and poor electronic conductivity during cycles. In this work, we develop a self-assembly approach for the synthesis of sandwich-structured graphene-Fe3O4@carbon composite, in which Fe3O4 nanoparticles with carbon layers are immobilized between the layers of graphene nanosheets. Compared to Fe3O4@carbon and bulk Fe3O4, graphene-Fe3O4@carbon composite shows superior electrochemical performance, including higher reversible capacity, better cycle and rate performances, which may be attributed to the sandwich structure of the composite, the nanosized Fe3O4, and the carbon layers on the surface of Fe3O4. Moreover, compared to the reported graphene-Fe3O4 composite, the particle size of Fe3O4 is controllable and the content of Fe3O4 in this composite can be arbitrarily adjusted for optimal performance. This novel synthesis strategy may be employed in other sandwich-structured nanocomposites design for high-performance lithium-ion batteries and other electrochemical devices.

Porous crystals of cubic metal oxides templated by cage-containing mesoporous silica

Porous single crystals of cubic Co3O4, NiO, In2O3 and CeO2 were fabricated using cage-containing SBA-16 and FDU-12 as hard templates, and characterized by X-ray powder diffraction, high-resolution transmission electron microscopy and N2 adsorption/desorption. Unsuccessful synthesis of non-cubic metal oxides implies that the symmetries of the oxide structures have a significant effect on crystal growth inside the mesopore networks in these templates. A possible mechanism of crystal growth in the confined spherical cages is discussed.

Cubes of zeolite a with an amorphous core

Gefullte Mikrowurfel: Zeolith-A-Mikrowurfel mit einkristalliner Schale und amorphem Kern wurden durch In-situ-Kristallisation eines Natriumalumosilicatgels in unvernetztem Chitosanhydrogel synthetisiert. Die Bildung wurfelformiger Kern-Schale-Strukturen verlauft uber Partikelaggregation und Oberflache-zu-Kern-Kristallisation, die durch das Hydrogelnetzwerk induziert wurde, und liefert ein neues mechanistisches Modell fur Keimbildung und Wachstum von Zeolithen.

Sandwich-structural graphene-based metal oxides as anode materials for lithium-ion batteries

Graphene-based metal oxides commonly show outstanding electrochemical performance due to the superior properties of graphene. However, the as-formed metal oxides decorated on graphene prefer to disintegrate or aggregate together, and the graphene–metal oxide hybrids also randomly aggregate themselves, resulting in capacity fading and poor cycling stability. Herein, the graphene-based metal oxides are further protected by graphene nanosheets through a stepwise heterocoagulation method, producing a layered sandwich structure. Compared to the normal graphene-based metal oxides, the sandwich-like graphene-based composites exhibit higher reversible capacities, better cycle performances, and higher rate capabilities. Such sandwich structure can avoid the aggregation of the composites and also act as an ideal strain buffer to alleviate the volume change of metal oxides during cycles. Moreover, the electronic conductivity of the electrode can be further enhanced by the introduction of additional graphene nanosheets. This double layer protection strategy is very effective and may be extended to prepare other high-capacity electrode materials for lithium-ion batteries.

Facile synthesis of ZSM-5 composites with hierarchical porosity

Hierarchically structured composites (TUD-M) with ZSM-5 nanocrystals embedded in a well-connected mesoporous matrix were synthesized by employing only one organic templating/scaffolding molecule (TPAOH). Micro- and mesopores form separately under different synthesis conditions. Both the size of the zeolite crystals and the mesopore size in the amorphous matrix can be tuned. A lower Si/Al ratio results in a slower growth of zeolite crystals and improves the hydrothermal stability of this new type of composite. Solid state NMR reveals that the aluminium species are all tetrahedrally coordinated, and that silicon species condense further during crystal growth. A carbon replica of TUD-M proves that the mesopores are interconnected, and also hints at the similarities between the meso-structures of TUD-M and TUD-1. The scaffolding mechanism at the basis of the mesostructure is not limited to TPAOH. Other zeolite/meso-structure composites could also be synthesized based on the same concept.

Graphene-encapsulated mesoporous SnO2 composites as high performance anodes for lithium-ion batteries

Mesoporous metal oxides such as SnO2 exhibit a superior electrochemical performance as anode materials for lithium-ion batteries due to their large surface areas and uniform pores. However, they suffer from the capacity fading in varying degrees during cycles because their partial pores may collapse during the charge–discharge process. Herein, graphene-encapsulated mesoporous SnO2 composites have been simply synthesized using a modified stepwise heterocoagulation method. These graphene-based SnO2 composites exhibit not only higher capacities and better rate capabilities but also improved cycle performances, suggesting that the electrochemical performance of mesoporous SnO2 can be further enhanced by graphene encapsulation.

Mesoporous single-crystal Co3O4 templated by cage-containing mesoporous silica

Mesoporous single-crystal Co(3)O(4) was obtained using cage-containing mesoporous silicas, FDU-12 and SBA-16, as templates and characterised by XRD, HRTEM and nitrogen adsorption-desorption while SQUID magnetometry was used to probe the magnetic character.

Fabrication of graphene-porous carbon–Pt nanocomposites with high electrocatalytic activity and durability for methanol oxidation

Nobel metal catalysts (e.g., Pt) are mostly used as the electrode materials for fuel cells due to their high electrocatalytic activity. The electrocatalytic activity, durability and utilization efficiency of the catalysts strongly depend on the textural features of the support. In this work, a novel 2D porous carbon substrate, graphene-based porous carbon, is designed as the catalyst support. Highly dispersed Pt nanoparticles with a diameter of 2–3 nm can be controllably fabricated on graphene-based porous carbon, and show dramatically improved electrocatalytic activity and durability for methanol oxidation compared to Pt nanoparticles supported by porous carbon or graphene. The excellent electrocatalytic behavior can be attributed to the unique textural features of graphene-based porous carbon, which inherits the advantages of graphene and porous carbon, including a high surface area, high electronic conductivity, and high dispersion of catalysts with a controllable particle size.

Fabrication of graphene-encapsulated CoO/CoFe2O4 composites derived from layered double hydroxides and their application as anode materials for lithium-ion batteries

Bicomponent CoO/CoFe2O4 composites with tunable particle sizes are prepared using Co–Fe layered double hydroxides (LDHs) or Co–Fe hydroxides as precursors. Moreover, graphene-encapsulated CoO/CoFe2O4 composites (labeled as G-CoO/CoFe2O4) are fabricated by co-assembly of graphene oxide nanosheets and Co–Fe LDHs/hydroxides, and then thermal decomposition of Co–Fe LDHs/hydroxides. Compared to uncoated CoO/CoFe2O4, G-CoO/CoFe2O4 composites exhibit enhanced cycle performances and rate capabilities. The superior performance may be attributed to the graphene encapsulation that prevents the aggregation of CoO/CoFe2O4 particles, buffers the strain from the volume variation of CoO/CoFe2O4, and improves the electronic conductivity of the composite electrode. The electrochemical properties of G-CoO/CoFe2O4 can be further improved by reducing the particle size of CoO/CoFe2O4 due to the enlarged interface between graphene nanosheets and CoO/CoFe2O4 particles.