Ordered Mesopore Structure Research Articles

Fabrication of hollow mesoporous SiO2-BiOCl@PANI@Pd photocatalysts to improve the photocatalytic performance under visible light

A facile method was developed to synthesize a series of hollow mesoporous SiO2-BiOCl@PANI@Pd (HBPP) photocatalysts with super adsorption performance, plasmonic effect and fast interfacial charge migration. The samples were characterized by XRD, FETEM, FT-IR, XPS, DRS, etc. Photocatalytic degradation of methyl orange (MO) by HBPP composites was investigated.Results showed that the photocatalytic property of HBPP composite was superior to that of hollow mesoporous SiO2-BiOCl@PANI (HBP) composite under visible light irradiation, and the HBPP5wt% photocatalyst synthesized under 140°C exhibits the highest photocatalytic activity. In this photocatalysis system, the orderly mesoporous opening structure of the hollow mesoporous SiO2 sphere could effectively facilitate the transfer of reactant molecules, and the existence of the internal cavities would effectively prolong the action time of the irradiated light for the multiple reflections. Moreover, the formation of interacted interfaces between the semiconductor BiOCl and conducting polymer (polyaniline) could effectively improve the separation of the photogenerated electron-hole pairs, and the palladium nanoparticles (Pd NPs) with strong localized surface plasmon resonance (LSPR) absorption band in the near-UV region could effectively induce the generation of the photoexcited electron-hole pairs in BiOCl, thus the as-obtained photocatalyst exhibits superior photocatalytic activity under visible light irradiation. The work may set foundation for application of the new photocatalyst of HBPP-based LSPR and make an important step forward remedying environmental pollution.

Removing Nano Particles by Filtration Using Materials with Ordered Mesoporous Structure

The usage of porous materials to remove Nano Particles (Nanoparticles, NPs) is one of the critical ways to purify the air. The present study employed three typical mesoporous structures, CMK-3, SBA-15 and MCM-41 to conduct removal experiments, in which NPs were generated, ranging from 2 nm to 20 nm, aiming at exploring the practical feasibility and relative theory foundation about the filtration of mesoporous structures towards NPs. Based on the physical and chemical characterization of the three mesoporous structures above, coupled with the adsorption experiments, the results acquired indicated that the most probable pore size of mesoporous structures coupled with certain mesoporous capacity of a mesoporous structure are the key to remove NPs. However, the distribution of micropore contributed hardly to the removal of NPs. Based on this, exploration was made to observe the effect that different flow rates and thicknesses had on the efficiency of NPs removal. The consequences showed that most penetrating particle size (MPPS) of NPs decreased with the increase of flow rates. Meanwhile, the corresponding removal efficiency of MPPS decreased. Furthermore, MPPS did not change with the change of thicknesses. This study provided technical evidence for the removal of NPs on mesoporous structures.

Preparation and magnetic characteristics of mesoporous nickel oxide–silica composites

Mesoporous NiO–SiO2 (MCM-41) silica-matrix composites with various nickel oxide concentrations (NiO : SiO2 = 0.025 : 1 to 0.2 : 1) have been produced by oxide cocondensation under hydrothermal synthesis conditions in the presence of cetyltrimethylammonium bromide as a template and (2-cyanoethyl) triethoxysilane as an organosubstituted trialkoxysilane additive. X-ray diffraction data have been used to evaluate the maximum nickel(II) oxide concentration (NiO : SiO2 = 0.1 : 1) that allows the ordered mesopore structure of MCM-41 to persist in the silica-matrix composites. We have studied the magnetic properties of this material as functions of temperature and magnetic field. The results demonstrate that the magnetic properties of the nanocomposite with NiO : SiO2 = 0.1 : 1 at low temperatures (T < 20 K) are determined by incomplete spin compensation in the matrix and on the surface of the NiO nanoparticles.

Enhanced Stability of Spatially Confined Copper Nanoparticles in an Ordered Mesoporous Alumina for Dimethyl Ether Synthesis from Syngas

A spatial confinement effect of copper nanoparticles in an ordered mesoporous γ-Al2O3, which is synthesized by an evaporation induced self-assembly (EISA) method, was investigated to verify the enhanced catalytic activity and stability with less aggregation of copper crystallites during direct synthesis of dimethyl ether (DME) from syngas. The surface acidity of the mesoporous Al2O3 and the metallic copper surface area significantly altered catalytic activity and stability. The ordered mesopore structures of Al2O3 were effective to suppress the aggregation of copper nanoparticles even under reductive CO hydrogenation conditions through the spatial confinement effect of the ordered mesopores of Al2O3 as well as the formation of strongly interacted copper nanoparticles with the mesoporous Al2O3 surfaces by partial formation of the interfacial CuAl2O4 species. The aggregation of copper nanoparticles on the bifunctional Cu/meso-Al2O3 having an ordered mesoporous structure was effectively suppressed due to the...

High-efficiency non-thermal plasma-catalysis of cobalt incorporated mesoporous MCM-41 for toluene removal

The destruction of low concentrations of toluene in air streams using a non-thermal plasma catalysis system has been investigated in this study. A series of highly active cobalt incorporated MCM-41 (Co-MCM-41) catalysts were synthesized by a hydrothermal method. For comparison, cobalt-impregnated MCM-41 (Co-MCM-41_imp) catalysts were prepared via an impregnation method. The synthesized samples were characterized by X-ray diffraction (XRD), nitrogen adsorption-desorption isotherms, UV–vis diffuse reflection spectrum (UV–vis DRS), H2-temperature-programmed reduction analyses (H2-TPR) and transmission electron microscopy (TEM). The results showed that the cobalt modified samples retained the highly ordered mesopore structure of MCM-41. In addition, the cobalt species on Co-MCM-41 was highly dispersed in the silica framework of MCM-41 molecular sieves, while the cobalt on Co-MCM-41_imp was present as cobalt oxide clusters or Co3O4 nano-particles on the external surface of MCM-41. The non-thermal plasma catalytic performance of the catalysts was evaluated by toluene oxidation using a dielectric barrier discharge (DBD) reactor. The results showed that the Co-MCM-41 exhibited better catalytic activity and stability than Co-MCM-41_imp. The main reason for the enhanced catalytic performance and stability was attributed to the well dispersion of cobalt species, good ozone decomposition activities and the high ability to degrade organic intermediates on catalyst surface.

Synthesis and OER activity of NiO coatings with micelle–templated mesopore structure

AbstractCatalysts based on nickel oxide are some of the most active catalysts for the oxygen evolution reaction (OER) in alkaline media. However, preparing catalytic coatings with high surface area and good accessibility of the active sites remains challenging. We present a new approach for the synthesis of homogeneous and binder‐free nickel oxide coatings comprising a highly accessible ordered mesopore structure. The synthesis is achieved via evaporation induced self assembly utilizing PEO‐PB‐PEO triblock copolymers as pore template and a chemical complex of Ni2+ and citric acid as precursor. Excessive crystallization behaviour of NiO is avoided by thermal conversion of the precursor into an amorphous Ni carbonate intermediate, followed by transition of the carbonate into the metal oxide. We present a comprehensive analysis of the obtained materials in terms of morphology, crystallinity, surface area, composition, and OER activity of differently calcined catalysts. Retaining a low crystallinity and high surface area during the synthesis proofs to be the most important factor in obtaining a highly active OER catalyst.

ZnO Coatings with Controlled Pore Size, Crystallinity and Electrical Conductivity

Zinc oxide is a wide bandgap semiconductor with unique optical, electrical and catalytic properties. Many of its practical applications rely on the materials pore structure, crystallinity and electrical conductivity. We report a synthesis method for ZnO films with ordered mesopore structure and tuneable crystallinity and electrical conductivity. The synthesis relies on dip-coating of solutions containing micelles of an amphiphilic block copolymer and complexes of Zn 2+ ions with aliphatic ligands. A subsequent calcination at 400°C removes the template and induces crystallization of the pore walls. The pore structure is controlled by the template polymer, whereas the aliphatic ligands control the crystallinity of the pore walls. Complexes with a higher thermal stability result in ZnO films with a higher content of residual carbon, smaller ZnO crystals and therefore lower electrical conductivity. The paper discusses the ability of different types of ligands to assist in the synthesis of mesoporous ZnO and relates the structure and thermal stability of the precursor complexes to the crystallinity and electrical conductivity of the zinc oxide. DOI: http://dx.doi.org/10.5755/j01.ms.22.1.8634

Plasma-catalysis of metal loaded SBA-15 for toluene removal: Comparison of continuously introduced and adsorption-discharge plasma system

The destruction of low concentrations of toluene using two non-thermal plasma catalytic systems has been investigated in this study. Metals (Ag, Mn and AgMn) loaded SBA-15 catalysts were prepared by an impregnation method and further characterized by X-ray diffraction (XRD), N2 adsorption–desorption isotherm and H2-temperature-programmed reduction (H2-TPR). In our research, two types of plasma catalytic system, including continuously introduced and adsorption-discharge plasma system, were studied. The results showed that the loaded metals retained the highly ordered mesopore structure of SBA-15. The activities of as-prepared catalysts for the toluene conversion and carbon balance in both catalytic systems decreased in the following order: AgMn/SBA-15>Ag/SBA-15>Mn/SBA-15>SBA-15, which were consistent with the ozone decomposition activities. Compared to traditional continuously introduced plasma system, the adsorption-discharge plasma system slightly increased toluene conversion and significantly improved the carbon balance. The reaction intermediates and products in two plasma systems were detected by the GC–MS and in situ FT-IR analyses. The results showed that the types of organic byproducts detected in the adsorption-discharge system greatly decreased compared to continuously introduced system. Moreover, the different mechanisms of two systems were discussed.

Hollow Mesoporous SiO2–BiOBr Nanophotocatalyst: Synthesis, Characterization and Application in Photodegradation of Organic Dyes under Visible-Light Irradiation

In this paper, a novel visible-light-driven hollow mSiO2–BiOBr (H-mSiO2–BiOBr) nanophotocatalyst was successfully synthesized by a facile three-step method. First, the hollow mesoporous silica submicrospheres with orderly mesoporous opening structure and an independent internal cavity were synthesized by combining Stober hydrolysis and chemical etching. Second, the hollow mesoporous silica submicrospheres were functionalized by 3-triethoxysilylpropylamine (APTES), then the amino-groups were successfully introduced into the surface of this material. Third, the BiOBr nanophotocatalyst with size of about 8–15 nm was successfully synthesized on the surface of the aforementioned amino-functionalized hollow mesoporous silica submicrospheres by solvothermal synthesis with the aid of the oriented function of the surface amino-groups. After several characterizations of the materials, the photocatalytic degradation of RhB by this H-mSiO2–BiOBr nanophotocatalyst under visible-light irradiation was investigated. The ...

Hierarchically porous monoliths of carbon and metal oxides with ordered mesopores

Hierarchically porous carbon and metal oxide materials offer great benefits in separations, catalysis and renewable energy. We have here used hierarchically porous silica monoliths with ordered mesopores as hard templates to produce nanocast carbon, Co3O4, and NiO monoliths with similar structures. Besides providing the materials with more well-defined physicochemical properties, the ordered mesopore structure also offers an excellent model system for investigating the nanocasting process in detail. The mesopores of the silica monoliths were first infiltrated with furfuryl alcohol or metal nitrate precursor solutions, which subsequently could be thermally converted to carbon or the corresponding metal oxides. After the silica scaffolds have been removed by etching in base solutions, the resulting replica monoliths display macroscopic morphology and macropore structure similar to the original silica template. However, while the carbon and Co3O4 materials both display a well-organized nanowire structure, giving rise to high surface area and narrow pore size distribution, the NiO monoliths exhibit a significantly lower surface area and less well-defined mesopore structure implying that only part of the silica mesopores has been replicated. We believe this apparent difference between the two metal oxides is a consequence of differences in mass transport.

Synthesis of two-dimensional transition-metal phosphates with highly ordered mesoporous structures for lithium-ion battery applications.

Materials with ordered mesoporous structures have shown great potential in a wide range of applications. In particular, the combination of mesoporosity, low dimensionality, and well-defined morphology in nanostructures may exhibit even more attractive features. However, the synthesis of such structures is still challenging in polar solvents. Herein, we report the preparation of ultrathin two-dimensional (2D) nanoflakes of transition-metal phosphates, including FePO4, Mn3(PO4)2, and Co3(PO4)2, with highly ordered mesoporous structures in a nonpolar solvent. The as-obtained nanoflakes with thicknesses of about 3.7 nm are constructed from a single layer of parallel-packed pore channels. These uniquely ordered mesoporous 2D nanostructures may originate from the 2D assembly of cylindrical micelles formed by the amphiphilic precursors in the nonpolar solvent. The 2D mesoporous FePO4 nanoflakes were used as the cathode for a lithium-ion battery, which exhibits excellent stability and high rate capabilities.

Synthesis of Two‐Dimensional Transition‐Metal Phosphates with Highly Ordered Mesoporous Structures for Lithium‐Ion Battery Applications

AbstractMaterials with ordered mesoporous structures have shown great potential in a wide range of applications. In particular, the combination of mesoporosity, low dimensionality, and well‐defined morphology in nanostructures may exhibit even more attractive features. However, the synthesis of such structures is still challenging in polar solvents. Herein, we report the preparation of ultrathin two‐dimensional (2D) nanoflakes of transition‐metal phosphates, including FePO4, Mn3(PO4)2, and Co3(PO4)2, with highly ordered mesoporous structures in a nonpolar solvent. The as‐obtained nanoflakes with thicknesses of about 3.7 nm are constructed from a single layer of parallel‐packed pore channels. These uniquely ordered mesoporous 2D nanostructures may originate from the 2D assembly of cylindrical micelles formed by the amphiphilic precursors in the nonpolar solvent. The 2D mesoporous FePO4 nanoflakes were used as the cathode for a lithium‐ion battery, which exhibits excellent stability and high rate capabilities.

One-step synthesis of three-dimensionally ordered macro–mesoporous silica–alumina composites

In this work, three-dimensional (3D) ordered macro–mesoporous silica–alumina composites were synthesized for the first time in an acid solution, using an effective dual-templating approach. The material with a high surface (i.e., 509m2g−1) possesses spherical macropores with an ordered mesopore structure wall. The strong diffraction peak and the pore size distribution curves reveal the presence of relatively uniform mesopores (3.5nm pore width). The synthesized aluminosilicate materials with tailorable macro–mesoporous structure hold promise in select applications as catalysts, catalyst supports, or adsorbents. This synthesis method also has the potential to make other macro–mesoporous composites with different compositions.

In situ observation of sintering of nickel nanoparticles during nanocasting into mesoporous silica

Hierarchically porous metals are of interest in several application fields, including heterogeneous catalysis. Here, we report the nanocasting of nickel metal into hierarchically porous SBA-15 type monoliths containing ordered arrays of mesopores. Upon removal of the silica template, nickel replicas showed no evidence of an ordered mesopore structure. TEM images and XRD measurements of the nickel–silica composite show that nickel nanoparticles larger than the silica mesopores have formed. In situ heated stage TEM measurements indicate that sintering of nickel nanoparticles occurs, which leads to rapid disruption of the silica template in vacuum. This disruption appears to occur more rapidly in vacuum than under hydrogen atmosphere.

Catalytic dehydrogenation of isobutane over ordered mesoporous Cr2O3–Al2O3 composite oxides

Abstract A series of ordered mesoporous Cr 2 O 3 –Al 2 O 3 composite oxides synthesized via improved one-pot evaporation induced self-assembly strategy were investigated as the catalysts for catalytic dehydrogenation of isobutane. These mesoporous catalysts with good structural properties and thermal stability performed excellent catalytic properties. Besides, the effect of the ordered mesopore structure on improving catalytic properties was also studied. Compared with non-mesoporous catalyst, the current mesoporous catalyst could accommodate the gaseous reactant with more “accessible” active sites. Therefore, the present materials were considered as promising catalyst candidates for catalytic dehydrogenation of isobutane.

General Information to Obtain Spherical Particles with Ordered Mesoporous Structures

Conditions for the synthesis of aluminum organophosphonate (AOP) and aluminophosphate (AlPO) spheres containing periodic mesopores were optimized and demonstrated to be general morphological controls for the surfactant-assisted synthesis of mesoporous materials. High-quality AOP and AlPO spheres with uniform mesopores were obtained at low and high temperatures, respectively. The aerosol-assisted synthesis of materials with uniform mesopores was categorized by using the difference in relative density of soluble AOP and AlPO oligomers that interact with ethylene oxide (EO) units in EO(n)PO(m)EO(n) triblock copolymer (PO=propylene oxide). Then, ordered mesoporous structures are constructed with the adequate amount of species in resultant frameworks, and the number of interactive points in soluble species determines the resultant density of the frameworks after self-assembly. Consequently, temperature-dependent synthesis, which allows controlled infiltration of soluble species to match the density of resultant frameworks, is required for the formation of ordered mesoporous structures under morphological control.

Helical Al- and Ce-MCM-41 materials as novel catalyst for acid and redox processes

Helical mesoporous silicas containing aluminium or cerium into their framework have been synthesized via hydrothermal method. The synthesized materials were extensively characterized to understand their physico–chemical properties in view of their future catalytic applications. Low-angle powder XRD patterns of calcined samples showed a hexagonally ordered mesopore structure. NMR spectra of aluminium materials exhibited two signals at 50 and 0ppm assigned to tetracoordinated and octahedrally coordinated Al3+. DR-UV–vis and XPS spectrum of cerium content materials show that cerium was incorporated as Ce3+ and Ce4+ into the helical mesoporous material. Materials with molar ratios Si/Al=95 and Si/Ce=500 were found to be catalytically active in acid (oxathioacetalisations and alkylations) or redox (epoxidation of cyclohexene) catalyzed processes, respectively.

Formation and Shrinkage of Necks in Microporous Silica Molecular Sieve with Ordered Mesoporous Structure

We examined the relationship between the removal of the triblock copolymer template and the formation of necks available for molecular sieving in microporous silica molecular sieve that is composed...

Synthesis of cerium-doped MCM-41 for ozonation of p-chlorobenzoic acid in aqueous solution

Cerium-doped MCM-41 (Ce-MCM-41) was prepared by a hydrothermal method and its catalytic activity for ozonation of p-chlorobenzoic acid (p-CBA) in aqueous solution was studied. For comparison, cerium-loaded MCM-41 (Ce/MCM-41) was prepared by a dipping method. Ce-MCM-41 was characterized by the low and wide angle X-ray powder diffraction (XRD), nitrogen adsorption–desorption, transmission electron microscopy (TEM) and ultraviolet–visible diffuse reflection spectrum (UV–vis DRS). The results showed that the material retained the highly ordered mesopore structure of MCM-41 and had a surface area of 852m2g−1. Cerium was incorporated into the framework of MCM-41, locating at tetrahedrally coordinated sites. The cerium doping content, initial pH of aqueous solution and reaction temperature played important roles in catalytic ozonation of p-CBA. Under the chosen conditions (1.39mgl−1 ozone dosage, 10mgl−1p-CBA solution and 1gl−1 catalyst dosage), the high mineralization rate (86%) was achieved by Ce-MCM-41/O3 process at 60min reaction time, only 52% by O3 alone. The combination of Ce-MCM-41 and O3 exhibited a significant synergetic effect. Ce-MCM-41 showed the better activity and stability than cerium-loaded MCM-41(Ce/MCM-41) during catalytic ozonation of p-CBA, its cerium leaching was greatly reduced (only 0.085mgl−1) and below detection limit after being reused, compared with that of Ce/MCM-41 (0.44mgl−1) with the presence of the same theoretical cerium content. TOC removal rate slightly decreased from 86% to 81% and kept stable after Ce-MCM-41 being re-utilized two times, which illustrated that Ce-MCM-41 was a kind of promising catalyst for ozonation of p-CBA. The addition of Ce-MCM-41 significantly improved ozone decomposition into HO in aqueous solution and reduced ozone concentration in equilibrium.

Aerosol-Assisted Production of Mesoporous Titania Microspheres with Enhanced Photocatalytic Activity: The Basis of an Improved Process

An aerosol-based process was used to prepare mesoporous TiO(2) microspheres (MTM) with an average diameter in the range of 0.5-1 microm. The structural characteristics and photocatalytic properties of the synthesized materials were determined. As-prepared MTM materials and those heated in air from 400 to 600 degrees C exhibited mesoporous texture with a narrow size distribution and an inorganic framework that consisted of 4-13 nm anatase crystallites. Pore volumes for the MTM materials were in the range of 0.17-0.34 cm(3) g(-1). Microspheres heated to 400 degrees C presented a locally ordered mesopore structure and possessed X-ray diffraction d spacings between 9.8 and 17.3 nm. Heating above 400 degrees C resulted in a loss of the mesoscopic order, a decrease of the surface area, retention of the porosity, and an increase of the anatase nanoparticle size to 13 nm. The accessibility of the pore volume was measured by monitoring the uptake of gallic acid (GA) using Fourier transform IR. The MTM materials made excellent catalysts for the photodegradation of GA, with the performance being higher than that of an equivalent sample of Degussa P25. The present MTM materials are advantageous in terms of their ease of separation from the aqueous phase, and hence a novel photocatalytic process is proposed based on separate adsorption and photocatalytic decomposition steps with an improved and more rational use of both catalyst and sunlight.