In this paper, CeO 2 nanocubes with the (200)terminated surface/graphene sheet composites have been prepared successfully by a simple hydrothermal method. It is found that the CeO 2 nanocubes with high crystallinity and specific exposed surface are well dispersed on well-exfoliated graphene surface. The (200)-terminated surface/graphene sheet composites modified electrode showed much higher sensitivity and excellent selectivity in its catalytic performance compared to a CeO 2 nanoparticle-modified electrode. The photoluminescence intensity of the CeO 2 anchored on graphene is about 30 times higher than that of pristine CeO 2 crystals in air. The higher oxygen vacancy concentration in CeO 2 is supposed to be an important cause for the higher photoluminescence and better electrochemical catalytic performance observed in the (200)-terminated surface/graphene sheet composites. Such ingenious design of supported well-dispersed catalysts in nanostructured ceria catalysts, synthesized in one step with an exposed high-activity surface, is important for technical applications and theoretical investigations.
High-pressure researches on nanostructural material have been of considerable interest because of the appearance of many novel high-pressure behaviors in the nanomaterials. 1À4 Previous highpressure studies on nanocrystalline materials show that the grain size, shape, and structure of the nanocrystals have significant effects on the phase transition pressure, compressibility, and even phase transition routines, 5,6 in which, the size effect of nanomaterials has been found to be the most important factor all along and has attracted great enthusiasm. Many typical nanomaterials have been studied, such as ZnO, 7 TiO 2 , 8 CeO 2 , 9 ZnS, 10 Si, 11 and so on, and the size effects are found to influence their high-pressure behaviors, including the mechanical properties and transformations under pressure. Swamy et al. 12 studied nanocrystalline anatase TiO 2 using the high-pressure method and found a size-dependent phase selectivity of anatase at high pressure. All of these results show that nanomaterials give birth to distinct, usually enhanced, properties compared with conventional bulk polycrystalline materials. Therefore performing high-pressure studies on nanomaterials is important not only for exploring the new structures and properties in materials but also for fundamental scientific contribution, for example, understanding the factors that lead to phase transitions in materials. Spinels with AB 2 O 4 formula are binary oxides, which have important technological applications, including use as magnetic materials, 13 superhard materials, 14 and high-temperature ceramics. 15 Various spinel structures result from the different cation distributions in the A (tetrahedral) and B (octahedral) sites. 16 Highpressure studies on this family (mainly on bulk materials) have found three proposed orthorhombic phases of CaMn 2 O 4 -, CaTi 2 O 4 -, and CaFe 2 O 4 -type structures as high-pressure polymorphs of spinels. 17 Recently, Mao et al. compared the compressional behaviors of bulk and nanorod LiMn 2 O 4 and revealed that nanostructured materials can accommodate more stress compared with their bulk counterparts and make the nanomaterials possibly have enhanced application in battery. To our knowledge, this is the first high-pressure study on AB 2 O 4 formula nanomaterials. Therefore it is also expected the nanosize effect could alter compressibility, transition pressures, and even phase transformation routines for other members in the AB 2 O 4 -type ABSTRACT: The size effect on structural transitions of Mn 3 O 4 has been investigated under pressures by in situ synchrotron X-ray diffraction and Raman technique in a diamond anvil cell. Compared with bulk Mn 3 O 4 , Mn 3 O 4 nanoparticles show an obvious elevation of phase transition pressure and different phase transformation routines with the occurrence of a new high-pressure phase at 14.5À23.5 GPa. The new phase most probably has an orthorhombic CaTi 2 O 4 -type structure, which is regarded as a metastable phase transforming to the higher pressure marokite-like structure. By ...
We report a synthesis of hydrogenated carbon nanospheres (HCNSs) via a facile solvothermal route at low temperatures (60-100 °C), using CHCl3 as the carbon source and potassium (K) as the reductant. Selective cleavage of the relatively lower stable C-Cl bonds (compared to C-H bonds) of the carbon precursor (CHCl3) by K metal results in the growth of HCNSs. The diameter of HCNSs ranges from 40 to 90 nm. The HCNSs have a graphite-like ordered carbon structure in spite of their high degree of hydrogenation. The HCNSs exhibit an average Brunauer-Emmett-Teller (BET) surface area of 43 m(2) g(-1), containing a small amount of mesopores and macropores in the structure. The nanospheres' sample as an anode material for lithium ion batteries (LIBs) has been studied. It exhibits a high discharge capacity (3539 mA h g(-1) in the first cycle, 978 mA h g(-1) after 50 cycles) and good cycling stability, demonstrating advantages as a promising candidate for anode materials in LIBs. The high capacity of the HCNSs is due to their unique nanostructures and high percentage hydrogenation, as well as hydrogenation induced structural defects.
The behavior of molecules and molecular chains confined in 1D nanochannels imposed by external interactions is a problem of fundamental interest. Here, we report structural manipulation of iodine confined inside zeolite (AFI) nanochannels by the application of high pressure. Structural transformations of the confined iodine under pressure have been unambiguously identified by polarized Raman spectroscopy combined with theoretical simulation. The length of the iodine chains and the orientation and intermolecular interaction of the confined iodine have been tuned at the molecular level by applied pressure. Almost all the confined iodine can be tuned into an axially oriented state upon compression, favoring the formation of long chains. The long iodine chains can be preserved to ambient pressure when released from intermediate pressures. ■ INTRODUCTIONStudies of the control and manipulation of atoms/molecules and their assemblies generate remarkable new insights into how physical and chemical systems function. They permit direct observation of molecular behavior that can be obscured by ensemble averaging and enables the study of important problems ranging from fundamental physics to the design of nanoscale electro-optical devices. In particular, much effort has been focused on the control of atomic/molecular chains due to their potential application as quantum wires. 1−9 By using simultaneous STM and TEM (transmission electron microscopy), gold nanowires composed of several atomic chains have been fabricated and show quantum conductance behavior. 2 Later, thinner nanowires have been fabricated in high vacuum with an electron beam thinning technique but the stability becomes lower with decreasing size and the length is still limited to a few nanometers (<6 nm). 3 On the other hand, filling materials into one-dimensional channels has been shown to be an efficient way to prepare atomic/molecular chains stable at ambient condition. 9−13 However, the atomic/molecular chains obtained usually show a mixture of different arrangements or have random orientations and are mixed with individual atoms/molecules in the channels due to size mismatch between the host channel and the filled species or because of inhomogeneous filling. 8−14 A typical example is that filling iodine into single wall carbon nanotubes (SWNTs) yields either helicoidal chains, polyiodides, discrete individual molecules, or new crystalline structures of iodine in the nanotube channels, depending on the tube diameter. 14−16 To obtain chains in a particular desired structural arrangement requires further manipulation. 17 For this purpose, understanding the transformation dynamics of the confined iodine imposed by external interactions becomes very important.High pressure serves as a powerful tuning parameter that has been used to tune the intermolecular interaction and structure of bulk materials. 18−23 In the confined environment, the configuration of the material is expected to be modified not only by the applied pressure but also by the evolution of the co...
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