This work investigates the possibility of using LaMn Fe O @mSiO as oxygen carriers for chemical looping combustion (CLC). CLC is a new combustion technique with inherent separation of CO from atmospheric N . LaMn Fe O @mSiO core-shell materials were prepared by coating a layer of mesostructured silica around the agglomerated perovskite particles. The oxygen carriers were characterized using different methods, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N sorption, hydrogen temperature-programmed reduction (H -TPR), and temperature- programmed desorption of oxygen (TPD-O ). The reactivity and stability of the carrier materials were tested in a special reactor, allowing for short contact time between the fluidized carrier and the reactive gas [Chemical Reactor Engineering Centre (CREC) fluidized riser simulator]. Multiple reduction-oxidation cycles were performed. TEM images of the carriers showed that a perfect mesoporous silica layer was formed around samples with 4, 32, and 55 nm in thickness. The oxygen carriers having a core-shell structure showed higher reactivity and stability during 10 repeated redox cycles compared to the LaMn Fe O core. This could be due to a protective role of the silica shell against sintering of the particles during repeated cycles under CLC conditions. The agglomeration of the particles, which occurred at high temperatures during CLC cycles, is more controllable in the core-shell-structured carriers, as confirmed by SEM images. XRD patterns confirmed that the crystal structure of all perovskites remained unchanged after multiple redox cycles. Methane conversion and partial conversion to CO were observed to increase with the contact time between methane and the carrier. Indeed, more oxygen from the carrier surface, grain boundaries, and even from the bulk lattice was released to react with methane. Upon rising the contact time, less CO was formed, which is desirable for CLC application. Increasing the reaction temperature and methane partial pressure lead to enhanced conversions of CH under CLC conditions. © 2012 American Chemical Society.

Sarshar Zahra    Zhenkun Sun    赵东元     Serge Kaliaguine   

Energy and Fuels

2012

Lanthanide-doped upconversion nanoparticles have shown considerable promise in solid-state lasers, three-dimensional flat-panel displays, and solar cells and especially biological labeling and imaging. It has been demonstrated extensively that the epitaxial coating of upconversion (UC) core crystals with a lattice-matched shell can passivate the core and enhance the overall upconversion emission intensity of the materials. However, there are few papers that report a precise link between the shell thickness of core/shell nanoparticles and their optical properties. This is mainly because rare earth fluoride upconversion core/shell structures have only been inferred from indirect measurements to date. Herein, a reproducible method to grow a hexagonal NaGdF shell on NaYF :Yb,Er nanocrystals with monolayer control thickness is demonstrated for the first time. On the basis of the cryo-transmission electron microscopy, rigorous electron energy loss spectroscopy, and high-angle annular dark-field investigations on the core/shell structure under a low operation temperature (96 K), direct imaging the NaYF :Yb,Er@NaGdF nanocrystal core/shell structure at the subnanometer level was realized for the first time. Furthermore, a strong linear link between the NaGdF shell thickness and the optical response of the hexagonal NaYF :Yb,Er@NaGdF core/shell nanocrystals has been established. During the epitaxial growth of the NaGdF shell layer by layer, surface defects of the nanocrystals can be gradually passivated by the homogeneous shell deposition process, which results in the obvious enhancement in overall UC emission intensity and lifetime and is more resistant to quenching by water molecules. © 2012 American Chemical Society.

张凡    车仁超    Xiaomin Li    Chi Yao    杨建平    Dengke Shen    Hu Pan    李炜    赵东元    

Nano Letters

2012

A series of core-shell-structured composite molecular sieves comprising zeolite single crystals (i.e., ZSM-5) as a core and ordered mesoporous silica as a shell were synthesized by means of a surfactant-directed sol-gel process in basic medium by using cetyltrimethylammonium bromide (CTAB) as a template and tetraethylorthosilicate (TEOS) as silica precursor. Through this coating method, uniform mesoporous silica shells closely grow around the anisotropic zeolite single crystals, the shell thickness of which can easily be tuned in the range of 15-100 nm by changing the ratio of TEOS/zeolite. The obtained composite molecular sieves have compact meso-/micropore junctions that form a hierarchical pore structure from ordered mesopore channels (2.4-3.0 nm in diameter) to zeolite micropores (≈0.51 nm). The short-time kinetic diffusion efficiency of benzene molecules within pristine ZSM-5 (≈7.88×10 m s ) is almost retainable after covering with 75 nm-thick mesoporous silica shells (≈7.25×10 m s ), which reflects the greatly opened junctions between closely connected mesopores (shell) and micropores (core). The core-shell composite shows greatly enhanced adsorption capacity (≈1.35 mmolg ) for large molecules such as 1,3,5-triisopropylbenzene relative to that of pristine ZSM-5 (≈0.4 mmolg ) owing to the mesoporous silica shells. When Al species are introduced during the coating process, the core-shell composite molecular sieves demonstrate a graded acidity distribution from weak acidity of mesopores (predominant Lewis acid sites) to accessible strong acidity of zeolite cores (Lewis and BrÃ?nsted acid sites). The probe catalytic cracking reaction of n-dodecane shows the superiority of the unique core-shell structure over pristine ZSM-5. Insight into the core-shell composite structure with hierarchical pore and graded acidity distribution show great potential for petroleum catalytic processes. Esprit de core: Meso-/microporous core-shell composite molecular sieves with hierarchical pore structures (see figure), from opened mesopore channels (2.4-3.0 nm) to accessible micropores (≈0.51 nm), and graded acidity distributions, from weakly acidic mesopores to accessible strongly acidic ZSM-5 cores, have been synthesized. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Xufang Qian    Bin Li    Yuanyuan Hu    牛国兴    Zhang Dan    车仁超    唐颐    苏党生    Abdullah Asiri    赵东元    

Chemistry - A European Journal

2012

张凡    施益峰    Sun Xiaohong    赵东元     Galen Stucky   

Chemistry of Materials

2012

Ordered 2-D hexagonal mesoporous TiO-SiO nanocomposites consisted of anatase TiO nanocrystals and amorphous SiO nanoparticles, with large mesochannels and high specific surface areas, have been extensively and detailedly evaluated using various cationic dyes (methylene blue, safranin O, crystal violet, brilliant green, basic fuchsin and rhodamine-6G), anionic dyes (acid fuchsin, orange II, reactive brilliant red X3B and acid red 1) and microcystin-LR. We use mesoporous 80TiO-20SiO-900 for the degradation of cationic dyes and MC-LR, due to the dominant adsorption of SiOH groups and synergistic role of coupled adsorption and photocatalytic oxidation. For anionic dyes, due to the adsorption results predominantly from TiOH groups, our strategy realizes the enhanced photocatalytic oxidation by strong surface acids and larger available specific surface area. Based on this, we prepared 90TiO-10SiO-700 to degrade them. The results show that our samples exhibit excellent degradation activities to all the contaminants, which are much higher than that of P25 photocatalyst. The dyes are not only decolorized promptly but degraded readily as well. It is strongly indicated that our mesoporous nanocomposites are considerably stable and reusable. These results demonstrate that our mesoporous TiO-SiO nanocomposites present extensive and promising application in the fast and highly efficient degradation of various organic pollutants. © 2012 Elsevier B.V.

董维阳    Yaojun Sun    Qingwei Ma    Zhu Li    华伟明    Lu Xinchun    庄国顺    张士成    郭志刚    赵东元    

Journal of Hazardous Materials

2012

The development of a simple and reproducible route to prepare uniform core@TiO structures is urgent for realizing multifunctional responses and harnessing multiple interfaces for new or enhanced functionalities. Here, we report a versatile kinetics-controlled coating method to construct uniform porous TiO shells for multifunctional core-shell structures. By simply controlling the kinetics of hydrolysis and condensation of tetrabutyl titanate (TBOT) in ethanol/ammonia mixtures, uniform porous TiO shell core-shell structures can be prepared with variable diameter, geometry, and composition as a core (e.g., α-Fe O ellipsoids, Fe O spheres, SiO spheres, graphene oxide nanosheets, and carbon nanospheres). This method is very simple and reproducible, yet important, which allows an easy control over the thickness of TiO shells from 0 to ∼25, ∼45, and ∼70 nm. Moreover, the TiO shells possess large mesoporosities and a uniform pore size of ∼2.5 nm, and can be easily crystallized into anatase phase without changing the uniform core-shell structures. © 2012 American Chemical Society.

李炜    杨建平    吴张雄    Jinxiu Wang    Bin Li    Shanshan Feng    邓勇辉    张凡    赵东元    

Journal of the American Chemical Society

2012

Titania is one kind of important materials, which has been extensively investigated because of its unique electronic and optical properties. A large number of efforts have been made to synthesize mesoporous TiO materials with high surface area and uniform pore size, as well as apply them in many fields. In this review paper, we focus on the ordered mesoporous TiO materials. We summarize the synthesis pathways, morphology, doping, as well as crystallization of the mesoporous TiO in synthesis section. And we introduce the applications in photocatalysis, solar cells, lithium-ion batteries, sensors and catalyst supports. Besides, we also mention several nanostructured TiO materials. © 2012 Elsevier Ltd. All rights reserved.

张任远    Ahmed Elzatahry    Salem salem Al-Deyab    赵东元    

Nano Today

2012

Ordered mesoporous MgO/carbon composites have been synthesized for the first time via a "one-pot" assembly strategy associated with a direct carbonization process by using phenolic resol as a carbon source, inorganic salt magnesium nitrate as a precursor and amphiphilic triblock copolymer Pluronic F127 as a template. The obtained mesoporous MgO/carbon composites exhibit uniform pore sizes (3.9-4.9 nm), high specific surface areas (510-780 m g), and high pore volumes (0.30- 0.53 cm g). In addition, a phase transformation from hexagonal (p6m) to body-centred cubic mesostructure (Im3m) occurs as the magnesium content increases. To the best of our knowledge, this is the first time the synthesis of ordered mesoporous carbon nanocomposites with cubic symmetry has been reported. With this facile "one-pot" assembly approach, one can incorporate as high as 37 wt % of MgO in the composites. Especially, the increased magnesium content induces the enlarged particle sizes of the MgO nanocrystals, which can be tuned in the size range from more than 4 nm to around 13 nm, together with a high dispersion in the amorphous carbon framework. When the MgO particles have sizes larger than the mesopore wall thickness, they can extend from the carbon walls into mesopore channels, and hence bring a rougher pore surface and a lower degree of mesostructure regularity. For the application test, such mesoporous MgO/carbon nanocomposites show excellent solid base property as proved by CO adsorption.

She Lan    李静    万颖    姚向东    屠波    赵东元    

Journal of Materials Chemistry

2011

In this work, we report a detailed investigation on the surface topology of ordered mesoporous WS nanoarrays nanocast from the silica SBA-15 template. Using a high-resolution scanning electron microscopy (HRSEM) technique, we acquire distinguishably clear images of the WS surface. A large number of small nanorods are found to be evenly distributed among the nanowire arrays, supporting their ordered mesostructures. Based on these observations, tunnel-like connecting pores are proposed to have a similar distribution in the mother mesoporous silica SBA-15 template. Interestingly, we observe the atomic crystal lattices of the layered WS on the HRSEM image. To the best of our knowledge, this is the first time that atomic crystal lattices have been directly observed using a SEM technique. In addition, both materials show good adsorption-desorption capabilities with hydrogen, and the maximum amount of hydrogen that can be taken up is 0.34 wt% for mesoporous WS and 0.52 wt% for mesoporous MoS at a pressure of 10 bar, indicating that both are potential hydrogen storage materials. © 2011 IOP Publishing Ltd.

She Lan    李静    顾栋    施益峰    车仁超    赵东元    

Nanotechnology

2011

Ordered mesoporous carbon-supported calcium oxide materials have been rationally synthesized for the first time. Large specific surface area, high content of nanosized calcium oxides can be easily obtained and tuned. The structure, porosity and the particle size evolution as a function of calcium content and carbonization temperature are extensively characterized and well correlated with their CO sorption properties. The composite materials are of significance for CO physisorption at ambient temperatures with high capacity and selectivity over N. Meanwhile, the nanocrystalline calcium oxides are highly active for CO chemisorption, with tuneable and high CO capacity at 200-500 °C. An almost complete initial conversion and fast reaction kinetics at a low temperature (450 °C) and low CO pressure can be achieved within minutes. Cyclic stability is also substantially improved due to the confinement effect of the CaO nanoparticles within the mesopores. These materials would be suitable for CO separation over a wide range of temperatures. © 2011 the Owner Societies.

吴张雄    Na Hao    Gongkui Xiao    刘丽英    Paul Webley    赵东元    

Physical Chemistry Chemical Physics

2011