Synthesis of morphology-controllable mesoporous Co3O4 and CeO2

Recently, extensive works have been devoted to the morphology control of mesoporous materials with respect to their use in various applications. In this paper, we used two kinds of mesoporous silica, SBA-15 rods and spheres as hard templates to synthesize morphology-controllable mesoporous metal oxides. By carefully controlling the loading of metal precursors in the mesopores of the hard template, mesoporous Co₃O₄ and CeO₂ with different morphologies, such as micrometer-sized rod, hollow sphere, saucer-like sphere, and solid sphere were conveniently obtained. The structural properties of these materials were characterized by XRD, BET, SEM and TEM. In addition, it is found that the differences observed in the textural properties of the two mesoporous metal oxides nanocasted from the same template can be attributed to the properties of metal precursors and the interaction between metal oxide and SiO₂. Thus-obtained mesoporous metal oxides with such special morphologies may have a potential application in the field of environmental catalytic oxidation.     

Fabrication of hollow spheres of metal oxide using fructose-derived carbonaceous spheres as sacrificial templates

In this report, fructose-derived carbonaceous spheres were utilized as sacrificial templates for the fabrication of metal oxide hollow spheres (MOHSs) by a facile hydrothermal approach. Hollow spheres of a series of crystalline metal oxides (α-Fe₂O₃, Cr₂O₃, Co₃O₄, NiO, and ZnO) have been fabricated, utilizing the metal chloride as the oxide precursors. Heating of an aqueous solution of the metal chloride and fructose to moderate temperature in an autoclave affords a spherical composite consisting of a metal precursor shell sheathing a carbonaceous core. Subsequent removal of the interior carbonaceous cores by thermal treatment through oxidation in air produces free-standing crystalline oxides hollow spheres. The MOHSs were characterized by means of SEM, TEM, XRD, IR spectroscopy, energy dispersive X-ray (EDX) and sorption measurements. The results show convincingly that using fructose as a sacrificial template after application of a hydrothermal synthesis route could be a favourable sacrificial template for the fabrication of various MOHSs.     

介孔金属氧化物/复合物的合成方法

介孔金属氧化物及其复合物由于其特有的组成与结构, 在催化、传感、光、电、磁等领域有着广泛的应用, 是近年来国内外跨学科领域研究的热点。本文对近几年来介孔金属氧化物及其复合物的合成方法进行了归纳总结, 其合成途径大致可以分为软模板法、硬模板法及纳米晶粒组装法。     

Impact of film thickness on the morphology of mesoporous carbon films using organic-organic self-assembly

Mesoporous polymer and carbon thin films are prepared by the organic-organic self-assembly of an oligomeric phenolic resin with an amphiphilic triblock copolymer template, Pluronic F127. The ratio of resin to template is selected such that a body-centered cubic (Im3m) mesostructure is formed in the bulk. However, well-ordered mesoporous films are not always obtained for thin films (<100 nm), and this behavior is found to be directly correlated with the initial phenolic resin to template ratio. Furthermore, the symmetry of ordered phases is highly dependent on the number of layers of spheres in the film: Monolayers and bilayers are characterized by hexagonal close-packed (HCP) symmetry, while films with approximately 5 layers of spheres exhibit a mixture of HCP and face-centered orthorhombic (FCO) structures. Ultrathick films having more than 30 layers of spheres are similar to the bulk body-centered cubic symmetry with a preferential orientation of the closest-packed (110) plane parallel to the substrate. Film thickness and initial composition of the carbonizable precursors in the template are critical factors in determining the morphology of mesoporous carbon films. These results provide insight into why difficulties have been reported in producing ultrathin ordered mesoporous carbon films using cooperative organic-organic self-assembly.     

Single‐Crystal‐like Nanoporous Spinel Oxides: A Strategy for Synthesis of Nanoporous Metal Oxides Utilizing Metal‐Cyanide Hybrid Coordination Polymers

Development of a new method to synthesize nanoporous metal oxides with highly crystallized frameworks is of great interest because of their wide use in practical applications. Here we demonstrate a thermal decomposition of metal‐cyanide hybrid coordination polymers (CPs) to prepare nanoporous metal oxides. During the thermal treatment, the organic units (carbon and nitrogen) are completely removed, and only metal contents are retained to prepare nanoporous metal oxides. The original nanocube shapes are well‐retained even after the thermal treatment. When both Fe and Co atoms are contained in the precursors, nanoporous Fe?Co oxide with a highly oriented crystalline framework is obtained. On the other hand, when nanoporous Co oxide and Fe oxide are obtained from Co‐ and Fe‐contacting precursors, their frameworks are amorphous and/or poorly crystallized. Single‐crystal‐like nanoporous Fe?Co oxide shows a stable magnetic property at room temperature compared to poly‐crystalline metal oxides. We further extend this concept to prepare nanoporous metal oxides with hollow interiors. Core‐shell heterostructures consisting of different metal‐cyanide hybrid CPs are prepared first. Then the cores are dissolved by chemical etching using a hydrochloric acid solution (i.e., the cores are used as sacrificial templates), leading to the formation of hollow interiors in the nanocubes. These hollow nanocubes are also successfully converted to nanoporous metal oxides with hollow interiors by thermal treatment. The present approach is entirely different from the surfactant‐templating approaches that traditionally have been utilized for the preparation of mesoporous metal oxides. We believe the present work proves a new way to synthesize nanoporous metal oxides with controlled crystalline frameworks and architectures.     

A Rational Repeating Template Method for Synthesis of 2 D Hexagonally Ordered Mesoporous Precious Metals

A repeating template method is presented for the synthesis of mesoporous metals with 2D hexagonal mesostructures. First, a silica replica (i.e., silica nanorods arranged periodically) is prepared by using 2D hexagonally ordered mesoporous carbon as the template. After that, the obtained silica replica is used as the second template for the preparation of mesoporous ruthenium. After the ruthenium species are introduced into the silica replica, the ruthenium species are then reduced by a vapor‐infiltration method by using the reducing agent dimethylamine borane. After the ruthenium deposition, the silica is chemically removed. Analysis by transmission and scanning electron microscopies, a nitrogen‐adsorption–desorption isotherm, and small‐angle X‐ray scattering revealed that the mesoporous ruthenium had a 2D hexagonal mesostructure, although the mesostructural ordering is decreased compared to that of the original mesoporous carbon template. This method is widely applicable to other metal systems. By changing the metal species introduced into the silica replica, several mesoporous metals (palladium and platinum) can be synthesized. Ordered mesoporous ruthenium and palladium, which are not easily attainable by the soft‐templating methods, can be prepared. This study has overcome the composition variation limitations of the soft‐templating method.     

一步制备高比表面积介孔Co3O4-CeO2及其表征

以有序介孔二氧化硅KIT-6为硬模板,硝酸钴、硝酸铈为金属源,分别在真空辅助条件和普通搅拌条件下制备了介孔CoCeOx复合氧化物。采用XRD、SEM、TEM、N2吸脱附等技术表征了复合氧化物的物化性质,并评价其氧化甲苯的性能。结果表明,在真空辅助和搅拌条件下制备的CoCeOx氧化物是由Co3O4和CeO2组成的介孔Co3O4-CeO2复合氧化物,其比表面积分别为141和89 m^2·g^-1,平均孔径分别为8.7和9.6 nm。真空辅助纳米复制过程有利于金属盐的前驱体充分填充到模板的孔隙中,去除模板后,可以得到有序的介孔复合金属氧化物。所制备介孔钴铈复合氧化物具有孔道有序性好、比表面积大的特点,在挥发性有机化合物的氧化去除方面具有一定的应用前景。     

Fabrication of nanocapsules with Au particles trapped inside carbon and silica nanoporous shells

Carbon capsules with hollow cores and mesoporous shells (HCMS) containing entrapped Au particles were prepared by template replication from solid core/mesoporous shell silica spheres with encapsulated Au particles. The resulting HCMS carbon capsules were then nanocast one step further to generate Au-trapping hollow core silica capsules with nanostructured shells.     

Bicontinuous ceramics with high surface area from block copolymer templates

Mesoporous polymers with gyroid nanochannels can be fabricated from the self-assembly of degradable block copolymer, polystyrene-b-poly(L-lactide) (PS-PLLA), followed by hydrolysis of PLLA block. Well-defined polymer/ceramic nanohybrid materials with inorganic gyroid nanostructures in a PS matrix can be obtained by using the mesoporous PS as a template for sol-gel reaction. Titanium tetraisopropoxide (TTIP) is used as a precursor to give a model system for the fabrication of metal oxide nanostructures from reactive transition metal alkoxides. By controlling the rates of capillary-driven pore filling and sol-gel reaction, the templated synthesis can be well-developed. Also, by taking advantage of calcination, bicontinuous TiO(2) with controlled crystalline phase (i.e., anatase phase) can be fabricated after removal of the PS template and crystallization of TiO(2) by calcination leading to high photocatalytic efficiency. This new approach provides an easy way to fabricate high-surface-area and high-porosity ceramics with self-supporting structure and controlled crystalline phase for practical applications. As a result, a platform technology to fabricate precisely controlled polymer/ceramic nanohybrids and mesoporous ceramic materials can be established.     

Wrapping and inclusion of organic molecules with ultrathin,amorphous metal oxide films

In this review, we overview metal oxide nanostructures in which organic molecules play important roles as templates, as structural units, and, in some cases, as hosts. Their structural precision and diversity are discussed from the viewpoint of the topology of a metal-oxygen network. Supramolecular capsules of metal oxides are prepared by the self-assembly of polyoxometalates. Zeolites and mesoporous materials are synthesized by using organic molecules with their assemblies acting as templates. The topological networking of silsesquioxanes makes it possible to produce novel nanocomposites and microporous materials. In the final section, we demonstrate our recent studies into molecular imprinting, the encapsulation of a fluorescent dye, and the wrapping of individual polymer chains. Ultrathin, amorphous metal oxide films can retain the shape of organic molecules and can be used to create molecular composites by precisely wrapping individual molecules. These films are also effective in insulating molecular functions from external environments. The advantages of amorphous metal oxides are discussed in relation to the properties of the corresponding crystalline metal oxides and their potential prospects in nanotechnology.     

Synthesis of nanoporous metal oxides through the self-assembly of phloroglucinol-formaldehyde resol and tri-block copolymer

A versatile route to synthesize nanoporous crystalline metal oxides has been developed through the self-assembly of phloroglucinol-formaldehyde resol and tri-block copolymer templates. Materials were characterized by a complementary combination of X-ray diffraction, nitrogen sorption, and transmission electron microscopy. Metal oxides synthesized using this route have remarkably high surface area when compared with the commercial samples. The surface area of metal oxides decreased upon calcination at higher temperatures. However, the surface area was still much higher when compared with the commercial samples. TEM investigation reveals that upon calcination at higher temperature, the size of the crystal increased but the short range order was merely disturbed. The analyses show that the present method is suitable as a direct route to synthesize crystalline nanoporous metal oxides. Hydrogen bonding plays a key role in the preferential arrangement of porous metal-carbon structure in the domain of tri-block copolymer. The nanoporous metal oxides with ordered mesoporous structure, high surface area, and crystalline framework are expected to show significant improvement in catalysis and nano-technology.     

Ordered mesoporous alumina-supported metal oxides

The one-pot synthesis of alumina-supported metal oxides via self-assembly of a metal precursor and aluminum isopropoxide in the presence of triblock copolymer (as a structure directing agent) is described in detail for nickel oxide. The resulting mesoporous mixed metal oxides possess p6 mm hexagonal symmetry, well-developed mesoporosity, relatively high BET surface area, large pore widths, and crystalline pore walls. In comparison to pure alumina, nickel aluminum oxide samples exhibited larger mesopores and improved thermal stability. Also, long-range ordering of the aforementioned samples was observed for nickel molar percentages as high as 20%. The generality of the recipe used for the synthesis of mesoporous nickel aluminum oxide was demonstrated by preparation of other alumina-supported metal oxides such as MgO, CaO, TiO 2, and Cr 2O 3. This method represents an important step toward the facile and reproducible synthesis of ordered mesoporous alumina-supported materials for various applications where large and accessible pores with high loading of catalytically active metal oxides are needed.     

Highly crystalline inverse opal transition metal oxides via a combined assembly of soft and hard chemistries

A combined assembly of soft and hard chemistries is employed to generate highly crystalline three-dimensionally ordered macroporous (3DOM) niobia (Nb2O5) and titania (TiO2) structures by colloidal crystal templating. Polystyrene spheres with sp2 hybridized carbon are used in a reverse-template infiltration technique based on the aqueous liquid phase deposition of the metal oxide in the interstitial spaces of a colloidal assembly. Heating under inert atmosphere as high as 900 degrees C converts the polymer into sturdy carbon that acts as a scaffold and keeps the macropores open while the oxides crystallize. Using X-ray diffraction it is demonstrated that for both oxides this approach leads to highly crystalline materials while heat treatments to lower temperatures commonly used for polymer colloidal templating, in particular for niobia, results in only weakly crystallized materials. Furthermore it is demonstrated that heat treatment directly to higher temperatures without generating the carbon scaffold leads to a collapse of the macrostructure. The approach should in principle be applicable to other 3DOM materials that require heat treatments to higher temperatures.     

Hollow Mesoporous Carbon Spheres with Magnetic Cores and Their Performance as Separable Bilirubin Adsorbents

Hollow mesoporous carbon spheres with magnetic cores are directly replicated from hollow mesoporous aluminosilicate spheres with hematite cores by a simple incipient‐wetness impregnation technique. The amount of magnetic cores and the saturation magnetization value can be easily tuned by changing the concentration of iron nitrate solution used in the synthesis procedure. As‐prepared hollow mesoporous carbon spheres with magnetic cores are used as separable bilirubin adsorbents and show very good adsorptive properties. The characteristics of as‐prepared composites are examined by XRD, N₂ sorption, TEM, vibrating‐sample magnetometry, and UV/Vis spectroscopy.     

Facile synthesis and characterization of novel mesoporous and mesorelief oxides with gyroidal structures.

In this paper, we bring forward an effective strategy, solvothermal postsynthesis, to prepare ordered mesoporous silica materials with highly branched channels. Structural characterizations indicate that the titled mesoporous materials basically have the cubic double gyroidal (space group Ia-3d) structure with small fraction of distortions. The mesopore sizes and surface areas can be up to 8.8 nm and 540 m2/g, respectively, when microwave digestion is employed to remove the organic templates. A phase transition model is proposed, and possible explanations for the successful phase transition are elucidated. The results show that the flexible inorganic framework, high content of organic matrix, and nonpenetration of poly(ethylene oxide) segments may facilitate the structural evolution. This new synthetic strategy can also be extended to the preparation of other double gyroidal silica-based mesoporous materials, such as metal and nonmetal ions doped silica and organo-functionalized silica materials. The prepared 3D mesoporous silica can be further utilized to fabricate various ordered crystalline gyroidal metal oxide "negatives". The mesorelief "negatives" (Co3O4 and In2O3 are detailed here) prepared by impregnation and thermolysis procedures exhibit undisplaced, displaced, and uncoupled enantiomeric gyroidal subframeworks. It has been found that the amount of metal oxide precursors (hydrated metal nitrates) greatly influence the (sub)framework structure and single crystallinity of the mesorelief metal oxide particles. The single crystalline gyroidal metal oxides are ordered both at mesoscale and atomic scale. However, these orders are not commensurate with each other.     

One-step synthesis of ordered mesoporous carbonaceous spheres by an aerosol-assisted self-assembly

Ordered mesoporous carbonaceous spheres with variable structures have been successfully prepared by using phenolic oligomers as a carbon precursor and amphiphilic triblock copolymers as a template via a one-step aerosol-assisted organic-organic self-assembly method.     

General Synthesis of Multi‐Shelled Mixed Metal Oxide Hollow Spheres with Superior Lithium Storage Properties

Complex hollow structures of transition metal oxides, especially mixed metal oxides, could be promising for different applications such as lithium ion batteries. However, it remains a great challenge to fabricate well‐defined hollow spheres with multiple shells for mixed transition metal oxides. Herein, we have developed a new “penetration–solidification–annealing” strategy which can realize the synthesis of various mixed metal oxide multi‐shelled hollow spheres. Importantly, it is found that multi‐shelled hollow spheres possess impressive lithium storage properties with both high specific capacity and excellent cycling stability. Specifically, the carbon‐coated CoMn₂O₄ triple‐shelled hollow spheres exhibit a specific capacity of 726.7 mA h g^?1 and a nearly 100 % capacity retention after 200 cycles. The present general strategy could represent a milestone in design and synthesis of mixed metal oxide complex hollow spheres and their promising uses in different areas.     

Aerosol assisted synthesis of silica/phenolic resin composite mesoporous hollow spheres

Hollow spheres of phenolic resin/silica composite are synthesized by macroscopic phase separation of a sorbitan monooleate surfactant Span 80 during aerosol-assisted spraying. The cavity can be evolved from multiple compartments to single hollow cavity with the increase of Span 80 content. The composite shell becomes mesoporous due to the release of small molecules after thermal treatment above 350 °C. After further thermal treatment at a higher temperature for example 900 °C in nitrogen or 1,450 °C in argon, the carbon/silica composite hollow spheres or crystalline silicon carbide hollow spheres are derived, respectively. Compared to the pure phenolic resin-based carbon spheres, thermal stability of the carbon-based composite spheres in air is essentially improved by the introduction of inorganic component silica. The carbon-based composite hollow spheres combine both performances of easy mass transportation through macropores and high specific surface area of mesopores, which will be promising to support catalysts for fuel cells. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

规则中孔氧化铈的纳米铸型合成及作为高CO氧化活性金催化载体的应用(英文)

以有序的中孔炭材料CMK-3为模板,以硝酸铈为前体,利用纳米铸型法合成了具有规则结构的中孔氧化铈,考察了模板脱除温度对中孔氧化铈微结构的影响.热重、元素分析、X射线衍射、透射电镜和氮气物理吸附结果表明,炭模板的脱除温度可低至350℃,所得氧化铈具有二维六方规则结构,比表面积高达167 m~2/g,孔径分布集中在3～5nm.采用胶体沉积法将2-5nm的金溶胶粒子沉积到所得氧化铈表面制得了Au/CeO_2催化剂,考察了Au/CeO_2在CO氧化反应中的活性.结果表明,该催化剂的活性较常规氧化铈制备的金催化利有明显提高,这可能与载体的规则结构有关.     

An ordered mesoporous aluminosilicate with completely crystalline zeolite wall structure

An ordered mesoporous aluminosilicate with completely crystalline zeolite pore wall structure, denoted as OMZ-1, was successfully synthesized by recrystallization of SBA-15 using in situ formed CMK-5 as the hard template. The role of carbon material not only serves as a hard template to preserve ordered mesoporous structure but also kinetically controls the crystallization process to form large crystals.