Synthesis Of Mesoporous Metal Oxides Research Articles

A Novel Molten Salt Mediated Synthesis of Mesoporous Metal Oxides with High Crystallization.

The controlled synthesis of mesoporous metal oxides remains a great challenge because the uncontrolled assembly process and high-temperature crystallization can easily destroy the mesostructure. Herein, we develop a facile, versatile, low-cost, and controllable molten salt assisted assembly strategy to synthesize mesoporous metal oxides (e.g., CeO2, ZrO2, SnO2, Li2TiO3) with high surface area (115-155 m2/g) and uniform mesopore size (3.0 nm). We find this molten salt mediated assembly enables the desolvation of the precursors and forms bare metal ions, enhances their coordination interaction with the surfactant, and promotes their assembly into a mesostructure. Furthermore, the molten salt assisted crystallization process can lower the collision probability of the target metal atom, inhibit its further growth into large crystals, and achieve a well-maintained mesostructure with high crystallization. Furthermore, this method can be expanded to synthesize various structured mesoporous metal oxides, including hollow spheres, nanotubes, and nanosheets by introducing the carbon template. The obtained mesoporous CeO2 microspheres loaded with Cu species exhibit excellent antibacterial performance and superior catalytic activity for the hydrogenation of nitrophenol with high conversion and cycling stability.

Solvent-pair surfactants enabled assembly of clusters and copolymers towards programmed mesoporous metal oxides

Organic-inorganic molecular assembly has led to numerous nano/mesostructured materials with fantastic properties, but it is dependent on and limited to the direct interaction between host organic structure-directing molecules and guest inorganic species. Here, we report a “solvent-pair surfactants” enabled assembly (SPEA) method to achieve a general synthesis of mesostructured materials requiring no direct host-guest interaction. Taking the synthesis of mesoporous metal oxides as an example, the dimethylformamide/water solvent pairs behave as surfactants and induce the formation of mesostructured polyoxometalates/copolymers nanocomposites, which can be converted into metal oxides. This SPEA method enables the synthesis of functional ordered mesoporous metal oxides with different pore sizes, structures, compositions and tailored pore-wall microenvironments that are difficult to access via conventional direct organic-inorganic assembly. Typically, nitrogen-doped mesoporous ε-WO3 with high specific surface area, uniform mesopores and stable framework is obtained and exhibits great application potentials such as gas sensing.

Stoichiometric metal nitration based novel green synthesis of mesoporous metal oxides and their enhanced heterogeneity

In this work, a general and novel method for the green synthesis of mesoporous metal oxides via stoichiometric metal nitration has been demonstrated. Pluronic surfactants and their effect on synthesis procedures in terms of surface area have been experimentally studied in detail. Contrary to the traditional synthesis procedure, water has been utilized as the solvent and in several cases, such as tin oxide, manganese oxide, aluminum oxide, antimony oxide, zinc oxide, cobalt oxide, copper oxide, yttrium oxide, lanthanum oxide, and silver either the highest or comparable surface areas have been successfully synthesized. Through XRD, and TEM, all materials were observed to be crystalline except silver and magnesium oxide. SEM shows that with an increase in surfactant molar mass agglomeration decreases. Ammonia chemisorption on acidic materials gives quantitative amounts of ammonia chemical bonding with catalysts, whereas carbon dioxide chemisorption gives a quantitative value of CO2 chemical binding with basic sites. As high as 1901.8 μmol/g and 994.6 μmol/g ammonia chemisorption values for oxides of vanadium and tin were achieved. Amphoteric materials give both acidic and basic enhanced adsorption. Finally, all synthesized materials are studied under organic catalytic transformations. Benzyl bromide is theoretically more active compared with benzylamine and benzyl alcohol which was also experimentally shown through the conversion.

General Surface-Casting Synthesis of Mesoporous Metal Oxides with Hollow Structures and Ultrahigh Surface Areas

General Surface-Casting Synthesis of Mesoporous Metal Oxides with Hollow Structures and Ultrahigh Surface Areas

Recent advances in mechanochemical synthesis of mesoporous metal oxides

This review presents advances and challenges in the mechanochemical synthesis of mesoporous metal oxides with uniform porosity.

Synergistic effect of mesoporous metal oxides and PtO2 nanoparticles in aerobic oxidation of ethanol and ionic liquid induced acetaldehyde selectivity

We report on the catalytic performance of mesoporous metal oxides (MMOs) as catalysts and as potential supports for platinum (Pt) nanoparticles in aerobic oxidation of ethanol. Synthesis of MMOs was achieved through the hard-template method and the resulting MMOs resembled the 3-D structure of the templating KIT-6. The Pt nanoparticles were templated and stabilized using poly(amidoamide), PAMAM, dendrimer to achieve dendrimer-encapsulated Pt nanoparticles (Pt-DENs) with an average size of 3.5 ± 0.4 nm. All the components of the catalysts (Pt-DENs and MMOs) were first characterized separately and thereafter, followed the preparation of MMO-immobilized Pt nanoparticles. Upon characterization of the MMO-immobilized Pt nanoparticles, the Pt nanoparticle size increased as determined from hydrogen-chemisorption and organothiol-adsorption technique. Furthermore, X-ray photoelectron spectroscopy (XPS) revealed that Pt has an oxidation state of 4+ after removal of the dendrimer at 550 °C signifying an oxide state (PtO2). The hydrogen temperature-programmed reduction (H2-TPR) revealed a change in electronic structure of MMOs as reduction peaks shifted to lower temperatures upon immobilization of PtO2 nanoparticles. This change in electronic structure of the mesoporous metal oxides upon immobilization of PtO2 nanoparticles is found to be one of the reasons for enhanced catalytic activity. Improved selectivity towards acetaldehyde was induced by introduction of an ionic liquid layer in a solid catalyst with ionic liquid layer, SCILL concept. Furthermore, the amount of ionic liquid coating plays a pivotal role in impacting selectivity and has an impact in the reaction turnover frequency.

Solvent-Free Self-Assembly for Scalable Preparation of Highly Crystalline Mesoporous Metal Oxides.

Mesoporous metal oxides (MMOs) have been demonstrated great potential in various applications. Up to now, the direct synthesis of MMOs is still limited to the solvent induced inorganic-organic self-assembly process. Here, we develop a facile, general, and high throughput solvent-free self-assembly strategy to synthesize a series of MMOs including single-component MMOs and multi-component MMOs (e.g., doped MMOs, composite MMOs, and polymetallic oxide) with high crystallinity and remarkable porous properties by grinding and heating raw materials. Compared with the traditional solution self-assembly process, the avoidance of solvents in this method not only greatly increases the yield of target products and synthesis efficiency, but also reduces the environmental pollution and the consumption of cost and energy. We believe the presented approach will pave a new avenue for scalable production of advanced mesoporous materials for various applications.

Aluminum hydroxide-mediated synthesis of mesoporous metal oxides by a mechanochemical nanocasting strategy

A mechanochemical nanocasting strategy using aluminum hydroxide as the mesoporous structure-directing agent to fabricate mesoporous metal oxides.

Synthesis of Mesoporous Metal Oxides by Structure Replication: Thermal Analysis of Metal Nitrates in Porous Carbon Matrices

A variety of metal nitrates were filled into the pores of an ordered mesoporous CMK-3 carbon matrix by solution-based impregnation. Thermal conversion of the metal nitrates into the respective metal oxides, and subsequent removal of the carbon matrix by thermal combustion, provides a versatile means to prepare mesoporous metal oxides (so-called nanocasting). This study aims to monitor the thermally induced processes by thermogravimetric analysis (TGA), coupled with mass ion detection (MS). The highly dispersed metal nitrates in the pores of the carbon matrix tend to react to the respective metal oxides at lower temperature than reported in the literature for pure, i.e., carbon-free, metal nitrates. The subsequent thermal combustion of the CMK-3 carbon matrix also occurs at lower temperature, which is explained by a catalytic effect of the metal oxides present in the pores. This catalytic effect is particularly strong for oxides of redox active metals, such as transition group VII and VIII metals (Mn, Fe, Co, Ni), Cu, and Ce.

One-step nanocasting synthesis of crystalline mesoporous CoO without using reducing agent

Ordered mesoporous crystalline CoO material was synthesized by a simple one-step nanocasting synthesis method using mesoporous silica as a hard template and cobalt nitrate Co(NO3)2·6H2O as the metal precursor. The cobalt nitrate precursor was impregnated inside the mesopore space of the hard template and was in-situ converted to Co3O4 in the first stage. Then it was further converted to CoO by directly heating up the intermediate to 740–780°C for 2h in an tube furnace under a constant nitrogen gas flow. No hydrogen or organic reducing agent was used. The obtained mesoporous CoO possesses ordered mesostructure and crystalline framework. This method provides a new facile and green strategy for the synthesis of mesoporous metal oxides with lower oxidation states.

Catalytic Decomposition of N<SUB>2</SUB>O on Ordered Crystalline Metal Oxides

The synthesis of mesoporous metal oxides using mesoporous silicas or carbons as hard templates has attracted growing interest recently, but the catalytic application of mesoporous metal oxides has not been studied sufficiently. In addition, few publications have compared the catalytic performance of a series of mesoporous metal oxides in the same reaction, and little is known about the influence of preparation details of mesoporous metal oxides on catalytic activity. Herein, ordered crystalline mesoporous metal oxides (i.e., CeO2, Co3O4, Cr2O3, CuO, alpha-Fe2O3, beta-MnO2, Mn2O3, Mn3O4, NiO) prepared using mesoporous SiO2 (KIT-6) as a hard template were tested in the decomposition of N2O, an environmental pollutant, and the catalytic performance was compared with that of commercial metal oxides with low surface areas. In particular, mesoporous Co3O4, beta-MnO2, and NiO showed high N2O conversions at 350 degrees C. The influence of preparation parameters of mesoporous Co3O4 on catalytic activity was then studied in more detail. Mesoporous Co3O4 samples with different pore sizes and wall thicknesses were prepared using KIT-6 synthesized under different hydrothermal or calcination temperatures. Interestingly, the catalytic activities of different mesoporous Co3O4 samples were found to be influenced by these preparation details.

Synthesis of Mesoporous Metal Oxide by the Thermal Decomposition of Oxalate Precursor

A synthesis method was newly developed to prepare mesoporous transition metal oxides by thermal decomposition of transition metal oxalates, and the method was advantageous in its versatility, low cost, and environmental friendliness. Various mesoporous transition metal oxides were successfully synthesized by the newly developed method, such as magnetic γ-Fe2O3, CoFe2O4, and NiFe2O4, MnxOy, Co3O4, and NiO. Morphology, structure, and magnetic property of the synthesized mesoporous transition metal oxides were characterized by XRD, TG-DTA, SEM, TEM, quantum design SQUID, and N2 sorption techniques. From the dependency of the heating rate, calcination time, and calcination temperature on the metal oxide structures, it was revealed that the calcination temperature was the major factor to determine the final mesoporous structure of the metal oxides. The mesoporous structures were well constructed by their corresponding metal oxide nanoparticles resulting from oxalate thermal decomposition.

A general synthesis of mesoporous metal oxides with well-dispersed metal nanoparticles via a versatile sol–gel process

The design and preparation of efficient, stable and economical metal nanoparticles supported on mesoporous metal oxides (MNPs/MMOs) has been a major direction in many applications especially in the catalysis area. The conventional synthesis methods for MNPs/MMOs are complex and lack high-degree control over different compositional/structural parameters. Herein, we reported a general synthesis of MNP/MMO composites via a one-step, versatile sol–gel process under strongly acidic conditions. The successful introduction of stable, PVP-capped MNPs into the AcHE sol–gel system (Ac, H, and E represent acetic acid, HCl, and EtOH, respectively) allows us to synthesize a large variety of MNPs/MMOs (M = Pt, Au, Pd, and MMOs = TiO2, SiO2, ZrO2, Al2O3). In addition to the compositional variation, the preformed PVP-capped MNPs in the AcHE sol–gel system decouple the particle nucleation and inorganic–organic co-assembly processes, permitting a stabilization of the MNPs in the nano-scale range over a wide particle concentration. Meanwhile, structural regulation can also be achieved by variation of the block copolymer concentration. The high-degree control over different compositional/structural parameters of MNPs/MMOs provides a useful material candidate platform to further study their structure–property relationship for the design of a better catalyst for a specific reaction. The best Pt/Si–TiO2 catalyst for n-hexane combustion obtained in this study serves as an example to show that the control of the adsorption and diffusion of reactants and products may be achieved by the optimization of composition and structure of the MNP/MMO catalysts, which may provide valuable insights for a detailed understanding of the structure- or composition-dependent chemical reactivity of the catalysts.

Container Effect in Nanocasting Synthesis of Mesoporous Metal Oxides

We report a general reaction container effect in the nanocasting synthesis of mesoporous metal oxides. The size and shape of the container body in conjunction with simply modifying the container opening accessibility can be used to control the escape rate of water and other gas-phase byproducts in the calcination process, and subsequently affect the nanocrystal growth of the materials inside the mesopore space of the template. In this way, the particle size, mesostructure ordering, and crystallinity of the final product can be systemically controlled. The container effect also explain some of the problems with reproducibility in previously reported results.

Synthesis of mesoporous metal oxides by structure replication: Strategies of impregnating porous matrices with metal salts

Various measures to optimise the impregnation of mesoporous CMK-3 carbon and SBA-15 silica matrices with metal nitrates for the synthesis of mesoporous metal oxides by structure replication are investigated. The effect of surface modification of the matrix pores, the choice of a solvent with suitable polarity, and the concentration of the metal nitrate solution are studied in detail. The efficiency of pore loading is monitored by nitrogen physisorption measurements. The creation of polar functions at the pore surface of CMK-3 carbon is shown to increase the impregnation efficiency substantially while maximizing the pore wall polarity of SBA-15 silica by increasing the amount of free silanol groups does not have any significant impact. The choice of a less polar solvent (THF instead of water) has a positive effect on the wettability of CMK-3 carbon in the first impregnation cycle but turns out to be disadvantageous in the second cycle; a similar trend is observed for variation of the metal salt concentration.

Sonochemistry as a tool for preparation of porous metal oxides

Abstract The porous metal oxides are an important class of materials, because the surface area/volume ratio of a material is increased by many fold, making them very useful in surface-related applications. The mesoporous materials were discovered in the 1990s, and since then they have been excellent candidates for materials science research. These mesoporous materials are prepared by hydrolyzing the inorganic precursor (usually metal alkoxide) in an acid, basic, or neutral medium in the presence of an organic structure-directing agent, the surfactant, in a conventional method. Recently, we have demonstrated that the sonochemical technique can be employed for the synthesis of mesoporous metal oxides. The sonochemical method reduced the time period required for such synthesis by many fold, and also produced more stable structures. We got excellent results with silica, titania, yittria-stabilized zirconia (YSZ), and Fe2O3. We also used an inorganic precursor other than an alkoxide for the preparation of mesoporous metal oxides. In this article, we present some of the recent results on this topic.