Xiao-Juan Ye

Large-Scale Synthesis of Carbon Nanomaterials by Catalytic Chemical Vapor Deposition: A Review of the Effects of Synthesis Parameters and Magnetic Properties

The large-scale production of carbon nanomaterials by catalytic chemical vapor deposition is reviewed in context with their microwave absorbing ability. Factors that influence the growth as well as the magnetic properties of the carbon nanomaterials are discussed.

The effect of nitrogen incorporation on the magnetic properties of carbon-doped ZnO

Samples of carbon-doped ZnO powders were prepared by the standard solid-state reaction method and sintered separately in argon and nitrogen atmospheres. According to the results of Raman spectroscopic investigation, the samples sintered in nitrogen showed lower D-bond (disordered) and G-bond (graphitic) concentrations, plausibly a result of nitrogen incorporation into the carbon-doped ZnO sample. All the samples are ferromagnetic at room temperature, and compared with those sintered in argon, those sintered in nitrogen have a lower magnetic moment. We found that the electrons-mediated mechanism is more suitable than the holes-mediated one for the explanation of ferromagnetism of carbon-doped ZnO materials.

Curvature and ionization-induced reversible hydrogen storage in metalized hexagonal B36

The synthesis of quasiplanar boron clusters (B36) with a central hexagonal hole provides the first experimental evidence that a single-atomic-layer borophene with hexagonal vacancies is potentially viable [Z. Piazza, H. Hu, W. Li, Y. Zhao, J. Li, and L. S. Wang, Nat. Commun. 5, 3113 (2014)]. However, owing to the hexagonal holes, tunning the electronic and physical properties of B36 through chemical modifications is not fully understood. Based on (van der Waals corrected-) density functional theory, we show that Li adsorbed on B36 and B36 (-) clusters can serve as reversible hydrogen storage media. The present results indicate that the curvature and ionization of substrates can enhance the bond strength of Li due to the energetically favorable B 2p-Li 2p orbitals hybridization. Both the polarization mechanism and the orbital hybridization between H-s orbitals and Li-2s2p orbitals contribute to the adsorption of H2 molecules and the resulting adsorption energy lies between the physisorbed and chemisorbed states. Interestingly, the number of H2 in the hydrogen storage medium can be measured by the appearance of the negative differential resistance behavior at different bias voltage regions. Furthermore, the cluster-assembled hydrogen storage materials constructed by metalized B36 clusters do not cause a decrease in the number of adsorbed hydrogen molecules per Li. The system reported here is favorable for the reversible hydrogen adsorption/desorption at ambient conditions.

Non-hexagonal symmetry-induced functional T graphene for the detection of carbon monoxide

Unlike on hexagonal graphene where Li atoms tend to cluster, using density functional theory, we demonstrate that Li atoms remain isolated on tetrasymmetrical T graphene due to a nonuniform charge distribution in T graphene. Furthermore, we examine the adsorption of several common gas molecules and find that Li-decorated T graphene exhibits a high sensitivity to CO. The CO adsorption strength can be manipulated by an external electric field, resulting in a short recovery time. Our results provide an insight to build promising nanosensors based on two-dimensional carbonic materials beyond hexagonal symmetry.

Metalized T graphene: A reversible hydrogen storage material at room temperature

Lithium (Li)-decorated graphene is a promising hydrogen storage medium due to its high capacity. However, homogeneous mono-layer coating graphene with lithium atoms is metastable and the lithium atoms would cluster on the surface, resulting in the poor reversibility. Using van der Waals-corrected density functional theory, we demonstrated that lithium atoms can be homogeneously dispersed on T graphene due to a nonuniform charge distribution in T graphene and strong hybridizations between the C-2p and Li-2p orbitals. Thus, Li atoms are not likely to form clusters, indicating a good reversible hydrogen storage. Both the polarization mechanism and the orbital hybridizations contribute to the adsorption of hydrogen molecules (storage capacity of 7.7 wt. %) with an optimal adsorption energy of 0.19 eV/H2. The adsorption/desorption of H2 at ambient temperature and pressure is also discussed. Our results can serve as a guide in the design of new hydrogen storage materials based on non-hexagonal graphenes.

Quantum-size effect on the electronic and optical properties of hybrid TiO2/Au clusters

Although TiO2/Au nanosystems exhibit high photocatalytic activities under solar radiation in the experiment, the quantum-size effect of TiO2 on the growth, electronic properties, and reactivity of Au clusters remains elusive. Using (time dependent) density functional theory, it is found that Au atoms attach to low-coordinated Ti and O atoms and serve as seeds for the growth of Au clusters, and the electronic (optical) properties of hybrid Au-TiO2 nano-clusters depend strongly upon the type of supported Au clusters. Interestingly, decorating TiO2 nano-particles with even-numbered Au clusters (Au8 or Au10) can enhance the photocatalytic activity by: (i) spatially separating electron and hole states and (ii) balancing redox strength and visible light absorption. Furthermore, the interactions between the Au-TiO2 clusters and a single water molecule have been studied. It will open up new avenues for exploring controlled photocatalysts in semiconductor-based quantum-confined systems.