Synthesis and photocatalytic properties of highly crystalline and ordered mesoporous TiO2 thin films

Highly crystalline and ordered mesoporous TiO2 thin films have been synthesized by stabilization of the mesostructure with confined carbon; the films exhibit 2.5% photoconversion efficiency for the water photolysis at zero-bias and Xe lamp illumination of 40 mW cm(-2).     

Synthesis of ordered mesoporous Fe3O4 and gamma-Fe2O3 with crystalline walls using post-template reduction/oxidation

Ordered mesoporous Fe(3)O(4) with crystalline walls (inverse spinel structure) has been synthesized for the first time, representing to the best of our knowledge, the first synthesis of a reduced mesoporous iron oxide. Synthesis was achieved by reducing ordered mesoporous alpha-Fe(2)O(3) (corundum structure) to Fe(3)O(4) spinel then to gamma-Fe(2)O(3) by oxidation, while preserving the ordered mesostructure and crystalline walls throughout. Such solid/solid transformations demonstrate the stability of the mesostructure to structural phase transitions from the hexagonal close packed oxide subarray of alpha-Fe(2)O(3) (corundum structure) to the cubic close packed subarray of Fe(3)O(4) spinel and gamma-Fe(2)O(3). Preliminary magnetic measurements reveal that the spins in both Fe(3)O(4) and gamma-Fe(2)O(3) are frozen at 295 K, despite the wall thickness (7 nm) being less than the lower limit for such freezing in corresponding nanoparticles (>8 nm).     

Nanocomposite based on epoxy and MWCNTs modified with NiFe2O4 nanoparticles as efficient microwave absorbing material

In order to make a microwave absorbent material with good dielectric and magnetic properties, well dispersed microwave absorbing hybrid epoxy polymer composites containing nickel doped Fe₃O₄ nanocrystals coated on carbon nanotubes (NiFe₂O₄‐MWCNTs/epoxy) were synthesized by the combined precipitation‐hydrothermal method in 1‐30 wt.% of nanoparticles. Nickel possess well interaction with microwave radiation and represents fine electromagnetic interference (EMI) shielding and by dopping it into ferrite spinel structures, does not show any tendency to oxidation. Well‐dispersed NiFe₂O₄–MWCNTs/epoxy nanocomposite prepared by new in‐situ polymerization method. First, NiFe₂O₄–MWCNT nanoparticles ultrasonicated in acetone and after mixing with epoxy resin ultrasonicated again. Finally, hardner added to the composite and tuned temperature for evaporating solvent. X‐ray diffraction (XRD) and energy dispersive spectroscopy (EDS) confirmed the synthesizing NiFe₂O₄ nanoparticles. Saturation magnetization value of NiFe₂O₄‐MWCNTs is about 29 emu/g with very low remanence and coercivity content, which revealed that the NiFe₂O₄‐MWCNTs is ferromagnetic nanocrystal. Transmission electron microscopy (TEM) used to characterize the distribution of NiFe₂O₄ nanocrystals on the surface of MWCNTs. The TEM images show that NiFe₂O₄ nanocrystals have a mean size of 12 nm, and completely coated on the exterior surface of MWCNTs. The obtained results of reflection loss revealed that the maximum values of reflection loss of the NiFe₂O₄‐MWCNTs/epoxy increase by enhancing the content of nanoparticles until 10 wt.% and decreases in 30 wt.%.     

Synthesis of highly ordered mesoporous crystalline WS(2) and MoS(2) via a high-temperature reductive sulfuration route

A high-temperature reductive sulfuration method is demonstrated to synthesize highly ordered mesoporous metal sulfide crystallites by using mesoporous silica as hard templates. H2S gas is utilized as a sulfuration agent to in situ convert phosphotungstic acid H3PW12O40.6H2O to hexagonal WS2 crystallites in the silica nanochannels at 600 degrees C. Upon etching silica, mesoporous, layered WS2 nanocrystal arrays are produced with a yield as high as 96 wt %. XRD, nitrogen sorption, SEM, and TEM results reveal that the WS2 products replicated from the mesoporous silica SBA-15 hard template possess highly ordered hexagonal mesostructure (space group, p6mm) and rodlike morphology, analogous to the mother template. The S-W-S trilayers of the WS2 nanocrystals are partially oriented, parallel to the mesochannels of the SBA-15 template. This orientation is related with the reduction of the high-energy layer edges in layered metal dichalcogenides and the confinement in anisotropic nanochannels. The mesostructure can be 3-D cubic bicontinuous if KIT-6 (Iad) is used as a hard template. Mesoporous WS2 replicas have large surface areas (105-120 m2/g), pore volumes ( approximately 0.20 cm3/g), and narrow pore size distributions ( approximately 4.8 nm). By one-step nanocasting with the H3PMo12O40.6H2O (PMA) precursor into the mesochannels of SBA-15 or KIT-6 hard template, highly ordered mesoporous MoS2 layered crystallites with the 2-D hexagonal (p6mm) and 3-D bicontinuous cubic (Iad) structures can also be prepared via this high-temperature reductive sulfuration route. When the loading amount of PMA precursor is low, multiwalled MoS2 nanotubes with 5-7 nm in diameter can be obtained. The high-temperature reductive sulfuration method is a general strategy and can be extended to synthesize mesoporous CdS crystals and other metal sulfides.     

Bi2O3 deposited on highly ordered mesoporous carbon for supercapacitors

A simple route has been employed to prepare nanosized Bi₂O₃ deposited on highly ordered mesoporous carbon. The electrochemical measurements reveal that, by loading only 10% Bi₂O₃ on the mesoporous carbon, the specific capacitance of the composite is improved by 62%, with the maximum value reaching 232 F g^?1 at a sweep rate of 5 mV s^?1. The specific capacitance of Bi₂O₃ is calculated and reaches 1305 F g^?1 at 1 mV s^?1. It is found that the mass transfer in the framework of the crystalline oxide is still difficult in spite of its nanosize, as evidenced by the decline of the specific capacitance of the Bi₂O₃ with the increase of the sweep rate. The cyclic life of composite materials is also measured and the capacitance only declines 21% after 1000 cycles.     

Synthesis of ordered mesoporous crystalline carbon-anatase composites with high titania contents

A direct-triblock-copolymer templating method is demonstrated to synthesize ordered mesoporous crystalline C-TiO(2) (MCT) composites using phenolic resins and acid-base pairs [acidic TiCl(4) and basic counterpart Ti(OC(4)H(7))(4)] as carbon and titanium sources, respectively. The composites possess highly crystalline anatase pore walls that are "glued" by amorphous carbon, ordered mesostructure, high surface areas (approximately 200 m(2)/g), and large pore volumes (approximately 0.15 cm(3)/g). The titania content is as high as 87 wt%. MCT composite favors the immobilization of proteins and enhances the electrocatalytic properties in relation to the reduction of hydrogen peroxide.     

Synthesis of highly dispersed ceria-zirconia supported on ordered mesoporous alumina

Highly dispersed ceria-zirconia supported on ordered mesoporous alumina, showing higher thermal stability up to 900 °C, has been successfully synthesized via a sol-gel process associated with P123 as the template in ethanol solvent.     

Synthesis and characterization of highly ordered Ni-MCM-41 mesoporous molecular sieves

Highly ordered Ni-MCM-41 samples with nearly atomically dispersed nickel ions were prepared reproducibly and characterized. Similar to the Co-MCM-41 samples, the pore diameter and porosity can be precisely controlled by changing the synthesis surfactant chain length. Nickel was incorporated by isomorphous substitution of silicon in the MCM-41 silica framework, which makes the Ni-MCM-41 a physically stable catalyst in harsh reaction conditions such as CO disproportionation to single wall carbon nanotubes or CO2 methanation. X-ray absorption spectroscopy results indicate that the overall local environment of nickel in Ni-MCM-41 was a tetrahedral or distorted tetrahedral coordination with surrounding oxygen anions. Hydrogen TPR revealed that our Ni-MCM-41 samples have high stability against reduction; however, compared to Co-MCM-41, the Ni-MCM-41 has a lower reduction temperature, and both the H2-TPR and in situ XANES TPR reveal that the reducibility of nickel is not clearly correlated with the pore radius of curvature, as in the case of Co-MCM-41. This is probably a result of nickel being thermodynamically more easily reduced than cobalt. The stability of the structural order of Ni-MCM-41 has been investigated under SWNT synthesis and CO2 methanation reaction conditions as both require catalyst exposure to reducing environments leading to formation of metallic Ni clusters. Nitrogen physisorption and XRD results show that structural order was maintained under both SWNT synthesis and CO2 methanation reaction conditions. EXAFS results demonstrate that the nickel particle size can be controlled by different prereduction temperatures but not by the pore radius of curvature as in the case of Co-MCM-41.     

Facile synthesis of highly ordered mesoporous ZnTiO3 with crystalline walls by self-adjusting method

Highly ordered mesoporous ZnTiO(3) with crystalline walls was directly prepared by a sol-gel process combined with evaporation induced self-assembly in ethanol, using amphiphilic triblock copolymers as structure directing agents. The whole process is self-adjusting to organize the network-forming metal oxide species without additional acid or base. The mesoporous material is pure cubic-phase ZnTiO(3) and has large surface area (up to 134 m(2)/g), large pore volume (0.17 cm(3)/g), and narrow pore size distribution (3-4.5 nm). The optic behavior was systematically studied, which is very helpful to understand the mesoporous ZnTiO(3) material either in fundamental study or for potential applications in optics and catalysis. This work provides a "self-adjusting" approach to fabricate the mesoporous functional materials with diverse compositions: the diverse hydrolysis-condensation kinetics of various metal oxides is homogenized to yield stable multicomponent precursors. The development of such a simple, versatile, and reproducible method is important for applications in practice.     

Pseudomorphic transformation of highly ordered mesoporous Co3O4 to CoO via reduction with glycerol

In this report, we describe the exploration of possibilities for a pseudomorphic reduction of ordered mesoporous metal oxides by high temperature treatment with glycerol, which was most thoroughly studied as an example of the reaction of Co3O4 to CoO. It was found that the glycerol process is a gentle reduction procedure, which maintains the framework topology on the mesoscale while changing the oxidation state and the structure at the atomic scale.     

Synthesis of ordered mesoporous NiO with crystalline walls and a bimodal pore size distribution

A mesoporous solid with crystalline walls and an ordered pore structure exhibiting a bimodal pore size distribution (3.3 and 11 nm diameter pores) has been synthesized. Previous attempts to synthesize solids with large ordered mesopores by hard templating focused on the preparation of templates with thick walls (the thick walls become the pores in the target materials), something that has proved difficult to achieve. Here the large pores (11 nm) do not depend on the synthesis of a template with thick walls but instead on controlling the microporous bridging between the two sets of mesopores in the KIT-6 template. Such control determines the relative proportion of the two pore sizes. The wall thickness of the 3D cubic NiO mesopore has also been varied. Preliminary magnetic characterization indicates the freezing of uncompensated moments or blocking of superparamagnetism.     

红外光谱技术在纳米NiFe2O4制备过程中的应用

采用溶胶-凝胶法制备NiFe2O4纳米粉末,并经不同温度热处理.测定了制备过程中各阶段的红外吸收光谱和不同温度处理样品的红外漫反射光谱.结果表明,红外吸收光谱较好地反映了溶胶-凝胶法制备NiFe2O4纳米粉末过程中结构的变化,为确定热处理温度提供了实验依据,彻底消除有机物,热处理需在400℃以上;红外漫反射谱可以较好地反映粉末的尺寸效应和形态效应,粉末粒径越小,漫反射函数(K-M)值越大;当粒径达到一定尺寸时,红外漫反射的尺寸效应消失.     

Phosphotungestic acid supported mesoporous MCM-41 coated NiFe2O4 magnetic nanoparticles as highly effective green nanocatalysts for coumarin and xanthene synthesis

Journal of Sol-Gel Science and Technology - Phosphotungestic acid (PWA) supported on mesoporous MCM-41 coated NiFe2O4 magnetic nanoparticles were prepared to be used as efficient and recyclable...     

Synthesis of NiFe2O4 Powders Well Defined in Size and Morphologies

The uniform NeFe2O4 powders with different particle size and morphologies (octahedral, cubic and spherical) have been prepared from different precursors via hydrothermal process. The nanocrystallines derived from precursor B in the weak alkali solution (pH≥10) are superparamagnetic.     

Synthesis and characterization of highly ordered functional mesoporous silica thin films with positively chargeable -NH2 groups

Highly ordered mesoporous organic-inorganic hybrid silica thin films with covalently bonded, positively chargeable -NH2 terminal groups were synthesized by evaporation induced self-assembly of tetraethoxysilane, 3-aminopropyl-triethoxysilane, and a nonionic surfactant under acid conditions and characterized using TEM, GISAXS, FTIR, SAW-based N2 sorption, and TGA.     

Microwave absorption properties and infrared emissivities of ordered mesoporous C-TiO2 nanocomposites with crystalline framework

Ordered mesoporous C-TiO₂ nanocomposites with crystalline framework were prepared by the evaporation-induced triconstituent co-assembly method. The products were characterized by XRD, TEM, N₂ adsorption-desorption and TG. Their microwave absorption properties were investigated by mixing the product and epoxy resin. It is found that the peak with minimum reflection loss value moves to lower frequencies and the ordered mesoporous C-TiO₂ nanocomposite possesses an excellent microwave absorbing property with the maximum reflection loss of −25.4 dB and the bandwidth lower than −10 dB is 6.6 GHz. The attenuation of microwave can be attributed to dielectric loss and their absorption mechanism is discussed in detail. The mesoporous C-TiO₂ nanocomposites also exhibit a lower infrared emissivity in the wavelength from 8 to 14 μm than that of TiO₂-free powder.     

Synthesis and characterization of highly ordered mesoporous thin films with -COOH terminated pore surfaces

Highly ordered mesoporous inorganic-organic hybrid thin films with covalently bonded carboxylic acid (-COOH) terminal groups on the pore surfaces were synthesized by evaporation induced self-assembly of tetraethoxysilane, organosilanes, and a nonionic surfactant followed by acid hydrolysis and characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, surface acoustic wave (SAW) based N2 sorption, and thermogravimetric analysis (TGA) techniques.     

Synthesis and structural identification of a highly ordered mesoporous organosilica with large cagelike pores

Using 1,2-bis(trimethoxysilyl)ethane as organosiloxane precursor and a triblock copolymer surfactant, Pluronic F127, as template, a highly ordered mesoporous organosilica with large cagelike pores has been successfully synthesized. Its structure was resolved to be 3-D cubic Fmm by high-resolution transmission electron microscopy. The intergrowth of hexagonal close-packed and cubic close-packed phases was observed in this material. The effect of different siliceous precursors on the mesostructure was also investigated.     

Morphogenesis of highly ordered mixed-valent mesoporous molybdenum oxides

Control of the size, shape, and structure of mesoporous transition metal oxide materials is important in their correlations with corresponding optoelectronic and photocatalytic properties. Highly ordered cubic phases of mixed-valent mesoporous molybdenum oxides have been prepared by the reduction and decomposition of aqueous molybdenum precursor solution in the presence of poly(ethylene oxide) under ultrasonic irradiation. Large-scale uniform molybdenum oxide particles with well-defined crystal-like morphologies (ball-like, rhombic dodecahedral, and cubic shapes) were synthesized and found to be controllable by modifying the molecular chain length of the polymeric additive. Molybdenum oxides with an average oxidation state of 4.8 form a cubic lattice of open mesoporous structures.     

Ordered mesoporous Fe2O3 with crystalline walls

Alpha-Fe(2)O(3) has been synthesized with an ordered mesoporous structure and crystalline walls that exhibit a near-single crystal-like order. The unique magnetic behavior of the material, distinct from bulk nanoparticles of alpha-Fe(2)O(3) or mesoporous Fe(2)O(3) with disordered walls, has been established. Magnetic susceptibility, M?ssbauer, and neutron diffraction data show that the material possesses the same long-range magnetic order as bulk alpha-Fe(2)O(3), despite the wall thickness being less than the 8 nm limit below which magnetic ordering breaks down in nanoparticulate alpha-Fe(2)O(3), yet the Morin transition of bulk alpha-Fe(2)O(3) is absent. It is also shown by TEM, PXRD, and EXAFS that alpha-Fe(2)O(3) with the same ordered mesoporous structure but disordered walls contains small crystalline domains. M?ssbauer and magnetic susceptibility data demonstrate that this material exhibits no long-range magnetic order but superparamagnetic behavior.