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Study on the coating of nano-scale SiO_2 film on the surface of nanocrystalline Mg-Al layered double hydroxides

Science China Chemistry 2005年第2期48卷 107-114页

作者： ZHANG Zejiang1,2,3, MEI Xiujuan2, XU Chenghua1 & QIU Fali1 1. Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences, Chengdu 610041, China 2. Sichuan Fire Research Institute of Public Security Ministry, Chengdu 611830, China 3. Graduate School of the Chinese Academy of Sciences, Beijing 100039, China Correspondence should be addressed to Zhang Zejiang (email: zzjzzjzz@***) 1. Chengdu Institute of Organic Chemistry Chinese Academy of Sciences 610041 Chengdu China 2. Sichuan Fire Research Institute of Public Security Ministry 611830 Chengdu China 3. Graduate School of the Chinese Academy of Sciences 100039 Beijing China

The coating process of a nano-scale SiO2 film on the nanocrystalline Mg-Al layered double hydroxides via a sol-gel process was investigated. The uniform and dense SiO2film with a thickness of about 5 nm on the nano-LDHs particles was characterized by the solubility test in the dilute HNO3 or HCl acid, TEM and FT-IR, XRD, TG and DSC. The chemical shifts of binding en- ergies of Al 2p, Mg 2p, Si 2s and O 1s on the coated particles indicate that the coating of the SiO2 nano-film on the surface of the nano-LDHs proceeds through the formation of Mg-O-Si and Al-O-Si bonds. The thermal analysis shows that both the SiO2-coated nano-LDHs and the nano-LDHs have a similar mass loss process, in which there are three obvious stages of mass loss in the temperature range of 40—700℃. Furthermore, the more the coatedamount of SiO2on the surface of the nano-LDHs is, the less the mass loss of the samples is at 700℃.The nano- LDHs have two obvious endothermic peaks at 244.67℃ and 430.13℃, whose corresponding heat absorption capacities are 412.28 J/g and 336.30 J/g, respectively. In contrast, the coated nano-LDHs have only one endothermic peak at 243.60℃ with a heat absorption capacity of 221.25 J/g.

关键词： layered double hydroxides, nanocrystalline, silica, coating.

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Preparation and characterization of highly photoactive nanocrystalline TiO_(2)powders by solvent evaporation-induced crystallization method

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Science China Chemistry 2003年第6期46卷 549-557页

作者：余家国余济美程蓓赵修建 State Key Laboratory of Advanced Technology for Materials Synthesis and Processing Wuhan University of TechnologyWuhan 430070 China Department of Chemistry The Chinese University of Hong KongHong Kong China

Highly photoactive bi-phase nanocrystalline TiO2 photocatalyst was prepared by a solvent evaporation-induced crystallization (SEIC) method, and calcined at different temperatures. The obtained TiO2 photocatalyst was characterized with X-ray diffraction (XRD), transmission electron microscopy (TEM) and BET surface areas. The photocatalytic activity was evaluated by the photocatalytic oxidation of acetone in air. The results show that solvent evaporation can promote the crystallization and phase transformation of TiO2 at 100°C. When calcination temperatures are below 600°C, the prepared TiO2 powders show bimodal pore size distributions in the mesoporous region. At 700°C, the pore size distributions exhibit monomodal distribution of the inter-aggregated pores due to the collapse of the intra-aggregated pores. At 100°C, the obtained TiO2 photocatalyst by this method shows good photocatalytic activity, and at 400°C, its photocatalytic activity exceeds that of Degussa P25. This may be attributed to the fact that the prepared TiO2 photocatalyst has higher specific surface areas, smaller crystallite size and bimodal pore size distribution.

关键词： nanocrystalline, TiO2, photocatalyst, preparation, solvent evaporation-induced crystallization method.

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Molecular dynamics simulation of thermal stability of nanocrystalline vanadium

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Science China(Technological Sciences) 2006年第4期49卷 400-407页

作者： WEI Mingzhi1, XIAO Shifang1, YUAN Xiaojian2 & HU Wangyu1,2 1. Material Science and Engineering College, Hunan University, Changsha 410082, China 2. Department of Applied Physics, Hunan University, Changsha 410082, China Material Science Engineering College Hunan University Changsha 410082 China Department of Applied Physics Hunan University Changsha 410082 China

The microstructure and thermal stability of nanocrystalline vanadium with an average grain size ranging from 2.86 to 7.50 nm are calculated by means of the analytic embedded-atom method and molecular dynamics. The grain boundary and nanocrystal- line grain atoms are differentiated by the common neighbor analysis method. The results indicate that the fraction of grain boundary increases with the grain size decreasing, and the mean energy of atoms is higher than that of coarse crystals. The thermal-stable tem- peratures of nanocrystalline vanadium are determined from the evolution of atomic energy, fraction of grain boundary and radial distribution function. It is shown that the stable tem- perature decreases obviously with the grain size decreasing. In addition the reasons which cause the grain growth of nanocrystalline vanadium are discussed.

关键词： nanocrystalline, embedded-atom method, molecular dynamics, thermal stability.

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A novel solar cell fabricated with spiral photo-electrode for capturing sunlight 3-dimensionally

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Science China(Technological Sciences) 2006年第6期49卷 663-673页

作者： LIU Yong SHEN Hui DENG Youjun Institute for Solar Energy Systems State Key Lab of Optoelectronic Materials and Technologies Sun Yat-sen University Guangzhou 510275 China Institute for Solar Energy Systems State Key Lab of Optoelectronic Materials and Technologies Sun Yat-sen University Guangzhou 510275 China Institute for Solar Energy Systems State Key Lab of Optoelectronic Materials and Technologies Sun Yat-sen University Guangzhou 510275 China

A novel solar cell fabricated with spiral photo-electrode for capturing sunlight 3-dimensionally (3D-cell) is proposed in this paper. We studied its performance both in solar simulator and in nature sunlight. Spiral photo-electrode of 3D-cell can receive sunlight from all directions and therefore can track the sun passively. And it is much insensitive to solar azimuth angle and shade. In addition, it increases the area to obtain scattered sunlight and reflected light. Compared with the dye-sensitized solar cells using sandwich structure, it would be more advantageous in the sealing technique.

关键词： solar cell, Titania, dye-sensitized, nanocrystalline, solar to electronic conversion efficiency.

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