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1. chinaXiv:201711.00002 [pdf]

Simultaneous Cu Doping and Growth of TiO2Nanocrystalline Array Film as a Glucose Biosensor.pdf

Yunyu Cai; Yixing Ye; Shouliang Wu; Jun Liu; Changhao Liang
分类: 材料科学 >> 材料化学

Doping additional ions into semiconductor is a potential strategy to modify the electronic structure of semiconductor materials. By using a highly reactive colloidal Cu clusters as doping precursor, we present here the successful doping of Cu ions into TiO2 nanocrystalline that simultaneously transformed from amorphous anodic TiO2 nanotubes during a dissolution and recrystallization process. The Cu-doped TiO2 nanoparticles (Cu-TNPs) film was characterized by X-ray diffraction, scanning and transmission electron microscopy and Raman spectroscopy. The Cu-TNPs show a rugby-like shape with exposed active {101}, {001} facets and the long-axis parallel to [001] lattice direction. The substitutional Cu2+ ions dopants in TiO2 nanocrystals caused the swelling of the crystalline unit cell. Such efficient doping design facilitate the improvement of nanostructured TiO2 as a potential biosensor for glucose molecules.

提交时间: 2017-11-01 点击量233, 下载量150

2. chinaXiv:201711.00003 [pdf]

Highly-dispersed ultrafine Pt nanoparticles on reduced graphene oxide nanosheets In situ sacrificial template synthesis and superior electrocatalytic performance for methanol oxidation.pdf

Shouliang Wu; Jun Liu ; Zhenfei Tian; Yunyu Cai; Yixing Ye; Qinglin Yuan; Changhao Liang
分类: 材料科学 >> 材料化学

We report a simple and environment-friendly route to prepare platinum/reduced graphene oxide (Pt/rGO) nanocomposites (NCs) with highly reactive MnOx colloids as reducing agents and sacrificial templates. The colloids are obtained by laser ablation of a metallic Mn target in graphene oxide (GO)-containing solution. Structural and morphological investigations of the as-prepared NCs revealed that ultrafine Pt nanoparticles (NPs) with an average size of 1.8 (± 0.6) nm are uniformly dispersed on the surfaces of rGO nanosheets. Compared with commercial Pt/C catalysts, Pt/rGO NCs with highly electrochemically active surface areas show remarkably improved catalytic activity and durability toward methanol oxidation. All of these superior characteristics can be attributed to the small particle size and uniform distribution of the Pt NPs, as well as the excellent electrical conductivity and stability of the rGO catalyst support. These findings suggest that Pt/rGO electrocatalysts are promising candidate materials for practical use in fuel cells.

提交时间: 2017-11-01 点击量261, 下载量183

3. chinaXiv:201711.00004 [pdf]

Co-doped Ni hydroxide and oxide nanosheet networks Laser-Assisted Synthesis Effective Doping, and Ultrahigh Pseudocapacitor Performance.pdf

Dewei Liang; Shouliang Wu; Jun Liu; Zhenfei Tian; Changhao Liang
分类: 材料科学 >> 材料化学

Morphology control and impurity doping are two widely applied strategies to improve the electrochemical performance of nanomaterials. Herein, we report an environmentally friendly approach to obtain Co-doped Ni(OH)2 nanosheet networks using a laser-induced cobalt colloid as a doping precursor followed by an aging treatment in a hybrid medium of nickel ions. The shape and specific surface area of the doped Ni(OH)2 can be successfully adjusted by changing the concentration of sodium thiosulfate. Furthermore, a Co-doped Ni(OH)2 nanosheet network was further converted into Co-doped NiO with its pristine morphology retained via facile thermal decomposition in air. The structure and electrochemical performance of the as-prepared samples are investigated with scanning and transmission electron microscopy, energy dispersive x-ray analysis, x-ray diffraction, Fourier transform infrared spectroscopy, the nitrogen adsorption-desorption isotherm technique, and electrochemical measurements. The Co-doped Ni(OH)2 electrode shows an ultrahigh specific capacitance of 1421 F/g at a current density of 6 A/g, and a good retention level of 76% after 1000 cycles, in sharp contrast with only a 47% retention level of the pure Ni(OH)2 electrode at the same current density. In addition, the Co-doped NiO electrode exhibits a capacitance of 720 F/g at 6 A/g and 92% retention after 1000 cycles, which is also superior to those values for relevant pure NiO electrodes. The Co2+ partially substitutes for Ni2+ in the metal hydroxide and oxide, resulting in an increase of free holes in the valence band, and, therefore, enhancement of the p-type conductivity of Ni(OH)2 and NiO. Moreover, such novel mesoporous nanosheet network structures are also able to enlarge the electrode-electrolyte contact area and shorten the path length for ion transport. The synergetic effect of these two results is responsible for the observed ultrahigh pseudocapacitor performance.

提交时间: 2017-11-01 点击量200, 下载量116

4. chinaXiv:201710.00078 [pdf]

Laser irradiation-induced Au-ZnO nanospheres with enhanced sensitivity and stability in ethanol sensing.pdf

Hao Zhang; Shouliang Wu; Jun Liu; Yunyu Cai; Changhao Liang
分类: 材料科学 >> 材料化学

Incorporating noble metal nanoparticles on the surface or inner side of semiconductors to form a hybrid nanostructure is an effective route to improve the gas sensing performance of these semiconductors. In this study, we present novel Au-decorated ZnO nanospheres (Au-ZnO NSs) obtained by laser irradiation of liquids. Structural characterization indicated that the Au-ZnO NSs consisted of single crystalline ZnO NSs with few Au nanoparticles decorated on their surfaces and abundant encapsulated Au nanoparticles with relatively small sizes. Laser irradiation-induced heating–melting–evaporating processes are responsible for the formation of unique Au-ZnO NSs. Gas sensing properties of the Au-ZnO NSs, as gas sensing materials, were investigated and compared with those of pure ZnO NSs. The former showed lower working temperature, higher sensitivity, better selectivity, and good reproducibility. The response values of Au-ZnO NSs and pure ZnO NSs sensors to ethanol of 100 ppm were 252 and 75 at working temperature of 320 °C and 360 °C, respectively. The significant enhancements in gas sensing performance should be attributed to the electronic sensitization induced by the depleted layers between encapsulated Au nanoparticles and ZnO and chemical sensitization originating from the catalytic effects of Au nanoparticles decorated on the surfaces that dissociated molecular oxygen.

提交时间: 2017-10-31 点击量172, 下载量124

5. chinaXiv:201710.00079 [pdf]

A general strategy toward transition metal carbidecarbon coreshell nanospheres and their application for supercapacitor electrode.pdf

Hemin Zhang; Jun Liu; Zhenfei Tian; Yixing Ye; Yunyu Cai; Changhao Liang; Kazuya Terabe
分类: 材料科学 >> 材料化学

A general and straightforward strategy was developed for fabricating transition metal carbide (TMC)/carbon (C) core/shell nanospheres (NSs) by laser ablation of transition metals in acetone/ethanol liquid. Various TMC/C core/shell NSs such as TaC/C, NbC/C, HfC/C, and MoC/C core/shell NSs were successfully fabricated, highlighting the generality of this method. Crucially, this approach is green, facile, catalyst-free, and especially can be operated under ambient environments. Interestingly, all of the as-synthesized TMCs in the NS cores showed a cubic phase and structures similar to that of NaCl-type. The cores were further encapsulated by amorphous carbon shell with different thickness. As an example of the functional properties of these compound materials, the TaC/C core/shell NSs obtained were investigated as a supercapacitor electrode, which showed a large specific capacitance, excellent rate capability and remarkable cycling ability, revealing that the NSs could be used as new electrode materials for electrochemical energy storage. The photoluminescence of TaC/C core/shell NSs exhibited strong emission under the specific excitation wavelength at room temperature, showing potential biomedical applications due to the good biocompatibility of carbon shell. Besides, the basic physical and chemical reactions involved in the unique formation mechanism under highly nonequilibrium states induced by ultrafast laser ablation were discussed.

提交时间: 2017-10-31 点击量201, 下载量159

6. chinaXiv:201709.00081 [pdf]

Porous TiO2 nanowires derived from nanotubes synthesis, characterzation and their enhanced photocatalytic properties.doc

金震
分类: 材料科学 >> 材料科学(综合)

Anatase porous TiO2 nanowires were synthesized via simple in situ hydrothermal treatment of the amorphous anodic TiO2 nanotubes in urea aqueous solution at 70 ºC. The morphology transformation process was also analyzed so that hydroxide induced dissolution-recrystallization mechanism was proposed. Due to the coarse surface and porous structure, the porous TiO2 nanowires possess a large surface area of 267.56 m2g-1, which is almost 4 times higher than that of amorphous anodic TiO2 nanotubes. The photocatalytic properties of the porous TiO2 nanowires towards MB, phenol and Rhodamine 6G were investigated. The porous TiO2 nanowires display better photocatalytic activity than that of TiO2 nanotubes or Degussa P25. The enhanced photocatalytic activity is attributed to the porous structure and the large specific surface area. Such porous TiO2 nanowires maybe considered as an ideal photocatalyst for the rapid photodegradation of organic pollutant in water. Furthermore, this facile, low-cost and environmentally friendly method is highly expected to innovate the design and fabrication of highly photoactive porous TiO2 nanowires, which have potential applications in photocatalysis and solar energy conversion.

提交时间: 2017-09-19 点击量107, 下载量84

7. chinaXiv:201708.00302 [pdf]

Electronic origin of strain effects on solute stabilities in iron

刘伟
分类: 材料科学 >> 金属与冶金

Nonuniform strain fields might induce the segregation of alloying solutes and ultimately lead to the mechanical performance degradation of body-centered-cubic (bcc) Fe based steels serving in extreme environments, which is worthy of investigation. In this paper, two typical volume conserving strains, shear strain (SS) and normal strain (NS), are proposed to investigate the strain effects on solute stabilities in bcc iron by first-principles calculations. For solutes in each transition metal group, the calculated substitution energy change due to SS exhibits a linear dependence on the valence d radius of the solutes, and the slope decreases in an exponential manner as a function of the absolute difference between the Watson’s electronegativity of iron and the averaged value of each transition metal group. This regularity is attributed to the Pauli repulsion between the solutes and the nearest neighboring Fe ions modulated by the hybridization of valence d bands and concluded to be originated from the characteristics of valence d bonding between the transition-metal solutes and Fe ions under SS. For main-group and post transition-metal solutes, the considerable drop of substitution energy change due to NS is concluded to be originated from the low-energy side shift of the widened valence s and p bands of the solutes. Our results indicate that the stabilities of substitutional solutes in iron under volume-conserving strain directly correlate with the intrinsic properties of the alloying elements, such as the valence d radius and occupancy, having or not having valence s and p bands.

提交时间: 2017-08-23 点击量99, 下载量78

8. chinaXiv:201708.00301 [pdf]

Clustering and segregation of small vacancy clusters near tungsten (0 0 1) surface

李祥艳
分类: 材料科学 >> 材料科学(综合)

Nanoporous metals have been shown to exhibit radiation-tolerance due to the trapping of the defects by the surface. However, the behavior of vacancy clusters near the surface is not clear which involves the competition between the self-trapping and segregation of small vacancy clusters (Vn) nearby the surface. In this study, we investigated the energetic and kinetic properties of small vacancy clusters near tungsten (0 0 1) surface by combining molecular statics (MS) calculations and object Kinetic Monte Carlo (OKMC) simulations. Results show that vacancies could be clustered with the reduced formation energy and migration energy of the single vacancy around a cluster as the respective energetic and kinetic driving forces. The small cluster has a migration energy barrier comparable to that for the single vacancy; the migration energy barriers for V1–5 and V7 are 1.80, 1.94, 2.17, 2.78, 3.12 and 3.11 eV, respectively. Clusters and become unstable near surface (0 0 1) and tend to dissociate into the surface. At the operation temperature of 1000 K, the single vacancy, V2, V3 and V4 were observed to segregate to the surface within a time of one hour. Meanwhile, larger clusters survived near the surface, which could serve as nucleating center for voids near the surface. Our results suggest that under a low radiation dose, surface (0 0 1) could act as a sink for small vacancy clusters, alleviating defect accumulation in the material under a low radiation dose. We also obtained several empirical expressions for the vacancy cluster formation energy, binding energy, and influence radius as a function of the number of vacancies in the cluster.

提交时间: 2017-08-23 点击量92, 下载量71

9. chinaXiv:201708.00300 [pdf]

Surface-structure dependence of healing radiation-damage mechanism in nanoporous tungsten

李祥艳
分类: 材料科学 >> 金属与冶金

Under nuclear fusion environments, displacement damage in tungsten (W) is usually caused by neutrons irradiation through producing large quantities of vacancies (Vs) and interstitials (SIAs). These defects not only affect the mechanical properties of W, but also introduce trap sites for implanted hydrogen isotopes and helium. Nano-structured W with high fraction of free surfaces has been developed to mitigate the radiation damage. However, the mechanism of the surface reducing defects accumulation is not well understood. Using multiscale simulation methods, we investigated the interaction of the SIA and V with different surfaces at across length and time scales. We found that, at a typical operation temperature of 1000K, surface (110) preferentially heals radiation damage of W compared with surface (100) and boundary (310). On surface (110), the diffusion barrier for the SIA is only 0.68eV. The annihilation of the SIA-V happens via the coupled motion of the V segregation towards the surface from the bulk and the two dimensional diffusion of the SIA on the surface. Such mechanism makes the surface (110) owe better healing capability. On surface (100), the diffusion energy barrier for the SIA is 2.48eV, higher than the diffusion energy barrier of the V in bulk. The annihilation of the SIA-V occurs via the V segregation and recombination. The SIA was found to migrate one dimensionally along a boundary (310) with a barrier of 0.21eV, leading to a lower healing efficiency in the boundary. This study suggested that the on-surface process plays an important role in healing radiation damage of NP W in addition to surface-enhanced diffusion and annihilation near the surface. A certain surface structure renders nano-structured W more radiation-tolerant.

提交时间: 2017-08-23 点击量99, 下载量79

10. chinaXiv:201703.00903 [pdf]

Preparation and electrochemical properties of high purity mixed-acid electrolytes for high energy density vanadium redox flow battery

Fan, Chuanlin; Yang, Haitao; Zhu, Qingshan
分类: 材料科学 >> 材料化学

All-vanadium redox flow battery (VRFB) is a large-scale electrochemical energy storage technology with numerous potential applications because of its inherent safety and long service life. In previous years, a novel mixed-acid electrolyte system, vanadium electrolytes with mixture of sulfuric acid and hydrochloric acid, has been developed by the Pacific Northwest National Laboratory (PNNL) to increase vanadium solubility, which can effectively raise the electrolyte energy density from 25 Wh/L to 40 Wh/L. To further improve mixed-acid VRFBs, in present work, high purity mixed-acid electrolytes were prepared using a novel direct dissolution – electrochemical reduction process from high purity vanadium oxytrichloride (VOCl3). And the purity and electrochemical properties were investigated, comparing with common mixed-acid electrolytes and regular sulfate electrolytes prepared from metallurgical grade vanadium pentoxide. It was found that the novel process demonstrated a great potential for the low cost and high efficiency production of high purity electrolytes with excellent electrochemical properties for mixed-acid VRFBs. Comparing the traditional high purity electrolytes preparation process, the present novel method will dramatically cut the cost by more than 90 percent, which will considerably facilitate the commercial application of high performance and high density VRFBs.

提交时间: 2017-08-15 点击量628, 下载量397

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