Mesoporous silica MCM-41 with rod-shaped morphology: Synthesis and characterization

A new synthesis route has been established to prepare highly pure mesoporous silica material (Si-MCM-41) with rod-like morphology. To improve the stability and to bring about the long range ordering in the mesoporous material, a series of tetra-alkylammonium salts has been employed in the new procedure in addition to the surfactant, cetyl-trimethylammonium bromide. The mesoporous silica materials have been characterized by small-angle X-ray diffraction (SAX), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ sorption and solid state ²⁹Si NMR measurements. The XRD study revealed that an excellent long range structural ordering of mesoporous material can be achieved using tetra-butylammonium bromide as a promoter. SEM study showed that rod-shaped single crystal like particles were formed in hydrothermal synthesis. TEM study revealed the presence of hexagonal voids on the face of the rod-shaped particles while nitrogen sorption study establishes the mesoporosity of the material. A high degree of cross-linking of -Si-O-Si- networks in the mesoporous silica has been evidenced in ²⁹Si NMR study.     

Novel synthesis of ordered mesoporous materials Al-MCM-41 from bentonite

This paper reports the synthesis of ordered mesoporous materials Al-MCM-41 with a specific surface area of 1018 m²/g from bentonite. Pretreated bentonite was simultaneously used as silica and aluminum sources without addition of silica or aluminum reagents. Orthogonal experiments were adopted to optimize the processing parameters. The samples were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), N₂ adsorption–desorption measurements and Fourier transform infrared spectra (FTIR) techniques. The obtained materials were hexagonal Al-MCM-41. Calcination removed the surfactant while new bonds increased the crosslinking of the frameworks. Proper Si/Al molar ratio was critical for the formation of highly ordered mesoporous materials.     

Highly dispersed zinc phosphate microdomains in mesoporous silica

In situ immobilization of crystalline zinc phosphate nuclei in the mesoporous silica material resulted in a highly ordered 2D-hexagonal mesoporous material with evenly dispersed crystalline NaZnPO₄ microdomains in its matrix using the self-assembly of cationic surfactant under hydrothermal synthesis condition. Four samples with different Si:Zn:P:Na mole ratios have been prepared. X-ray diffraction (XRD) patterns of the as-synthesized as well as template-free samples indicated the presence of mesophase in each case. N₂ adsorption data indicated mesoporosity in the samples together with the existence of crystalline NaZnPO₄ phase for the materials synthesized with Si/Zn mole ratio 5-12. ²⁹Si MAS NMR results showed high value of the Q⁴/Q³ ratio in these materials suggesting highly crosslinked structure.     

Direct synthesis of CeO2/SiO2 mesostructured composite materials via sol–gel process

A series of CeO₂/SiO₂ mesostructured composite materials was synthesized by sol–gel process using Pluronic P123 as template, tetraethylorthosilicate as silica source and hexahydrated cerium nitrate as precursor under acid condition. The as-synthesized materials with Ce/Si molar ratio ranging from 0.03 to 0.3 were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), laser Raman spectroscopy (LRS), and N₂ adsorption. Characterization revealed that all samples possess ordered hexagonal mesoporous structure similar to SBA-15 and possess high surface area, large pore volume and uniform pore size. The fact that cerium species are present as highly dispersed CeO₂ nanocrystals in hexagonal matrix was confirmed by XRD combined with high-resolution TEM and selected area electron diffraction (SAED) analysis. Introduction of ceria to silica matrix can cause a distortion of hexagonal ordering structure and decrease pore diameter and increase the wall thickness of mesopores. Moreover, it can be found that this sol–gel route is a feasible, effective and simple method for templating synthesis of CeO₂/SiO₂ composite materials.     

Synthesis and characterization of mesoporous carbon through inexpensive mesoporous silica as template

Mesoporous silica materials have been synthesized through sol–gel reaction using inexpensive sodium silicate as source of silica and low cost hydroxy carboxylic acid compounds as templates/pore forming agents. The material measured surface area of 1014 m²/g, pore diameter of 65 Å and pore volume of 1.4 cc/g when parameters like time and temperature of synthesis along with mole ratio of TA/SiO₂ were optimized. Here TA stands for tartaric acid. Carbonization of sucrose inside the pores of above silica material at 900 °C followed by removal of silica framework using aqueous ethanoic solution of NaOH gave rise to mesoporous carbon material. The resulting materials were characterized by N₂-sorption, FTIR spectroscopy, X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, thermal analysis and cyclic voltammetry. Three dimensional interconnecting wormhole channel arrangement of mesoporous silica template leads to mesoporous carbon replica with surface area of 1200 m²/g. X-ray photoelectron spectroscopic study (XPS) of the mesoporous carbon material shows the concentration of carbon atom in the range of 97–98% with 1–2% oxygen and negligible amount of silica. The electrochemical double layer capacitance behavior of carbon material with the specific capacitance value of 88.0 F/g at the scan rate of 1 mV/s appears to be promising.     

Synthesis and characterization of tungsten-incorporated mesoporous molecular sieve MCM-48 by one step

Tungsten-substituted mesoporous MCM-48 materials are successfully synthesized at 393 K by a one-step co-condensation sol–gel method. The prepared samples with different Si/W ratios are characterized by X-ray diffraction (XRD), nitrogen adsorption, high-resolution transmission electron microscopy (HRTEM), diffuse reflectance UV–visible spectroscopy and FT-IR, and the results indicate the presence and good dispersion of tungsten species inside the silica pores, the Si/W ratio is controlled above 28. When the Si/W ratio is less than 28, though no bulk tungsten is detected outside the MCM-48 mesoporous silica, the pore structure order becomes worse.     

Preparation of monolithic silica-based aerogels with high thermal stability by ambient pressure drying

A monolithic silica-based aerogels were successfully synthesized via a sol-gel process using tetraethoxysilane and inexpensive inorganic aluminium salt Al(H₂O)₉(NO₃)₃ as precursors. The gels were dried at ambient pressure and the molar ratio of Al/Si was varied from 0 to 0.1. The structure and morphology of the aerogels were investigated by field-emission scanning electron microscopy, high-resolution transmission electron microscopy, Fourier transform infrared spectrometry, and N₂ adsorption-desorption. The microstructural images showed that a three-dimensional nanoscale structure formed in the as-prepared aerogels. The specific surface areas of the samples were in the range of 769–821?m²/g. Furthermore, when the Al/Si mole ratio was 0.1, its specific surface area and total pore volume remained at 103.5?m²/g and 0.25?cm³/g respectively after heating at 1100?°C for 2?h, exhibiting the best thermal stability of all aerogels fabricated in this study. The addition of the aluminium salt not only slowed the sintering of the silica, but also crystallization was restrained.     

Synthesis of Ti-containing mesoporous silicates from inorganic titanium sources

Titanium-containing mesoporous molecular sieves including periodic mesoporous silicas (SBA-15-type) and organosilicas (PMO-type) can be assembled by using mixed inorganic acid–base pairs (TiCl₄ and tetrabutyl titanate) or a single inorganic TiCl₃ as the titanium sources and tetraethoxysilane and/or 1,2-bis(triethoxysilyl)ethane as the silica sources and triblock copolymer as the structure-directing agent in acidic media through the hydrothermal method. Characterization using XRD, nitrogen sorption isotherms, UV–vis, FT-IR and NMR techniques reveals that the Ti-containing mesoporous materials possess ordered 2D hexagonal mesostructures, high surface areas (421–1070 m²/g), uniform pore sizes (5.1–8.0 nm), large pore volumes (0.5–1.3 cm³/g), and tetrahedrally incorporated titanium (IV) species in the silica network. The maximum incorporated Ti content is about 0.34 wt% for the ordered mesostructure regardless of the titania and silica sources and the initial Si/Ti ratio.     

Synthesis of mesoporous Si/SiC with three-dimensional structure derived from C/silicalite-1 via magnesiothermic reduction

C/silicalite-1 composites were successfully synthesized by using industrial silica sol as silica source and multiwalled carbon nanotube (MWCNTs) as carbon source under hydrothermal method. Then, C/silicalite-1 composites were transformed into mesoporous Si/SiC through magnesiothermal reduction at relatively low temperature (650 °C). The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM) and Brunauer–Emmett–Teller analysis (BET). The XRD patterns and TEM micrographs exhibit that C/silicalite-1 composites are transformed into Si/SiC. The SEM images exhibit that Si/SiC keeps the three-dimensional structure of silicalite-1. BET analysis shows that the specific surface areas and mesoporous distribution of Si/SiC are 274 m²/g and 4.69 nm, respectively.     

Synthesis and characterization of hollow zeolite microspheres with a mesoporous shell by O/W/O emulsion and vapor-phase transport method

Hollow microspheres of ZSM-5 with a mesoporous shell have been synthesized through formation of amorphous hollow SiO₂/Al₂O₃ microspheres by sol–gel process in multiple oil–water–oil emulsions and transformation of the amorphous species into zeolite by water–organic vapor-phase transport treatment at 160 °C for 8 days. The morphology of the amorphous and zeolite spheres observed by scanning electron microscopy shows no significant change whereas the molar ratio of Si/Al increases from 6 to 20 during the transformation. The structural feature of zeolite was characterized by X-ray diffraction and ²⁹Si and ²⁷Al magic-angle spinning nuclear magnetic resonance. Transmission electron microscopy and N₂ adsorption–desorption isotherms indicate that uniform mesopores in the shell of zeolite spheres arise from the interstices among zeolite crystallites.     

Rapid Room Temperature Synthesis of Hexagonal Mesoporous Silica Using Inorganic Silicate Sources and Cationic Surfactants under Highly Acidic Conditions

The room-temperature synthesis of mesoporous silica was investigated by using cationic surfactants and inorganic Si sources, like sodium silicate and colloidal silica. Mesoporous silica analogous to the hexagonal MCM-41 could be obtained over a wide range of pH below ca. 11 within short synthesis time (3 h), when the Q⁴-state Si was absent in the Si source solution prior to mixing with an aqueous solution of cationic surfactants. It was suggested that the strongly acidic conditions (pH < 1) were favorable to give mesoporous silica materials with higher surface area and larger mesopore volume.     

One‐step synthesis of ordered Sn‐substituted SBA‐16 mesoporous materials using prepared silica source of rice husk and their selectively catalytic activity

Highly ordered SBA‐16 silica mesoporous materials were synthesised hydro‐solvothermally under the acidic medium using SiO₂/F127/BuOH/HCl/H₂O gel. Pure SiO₂ powders were prepared from inexpensive and environmentally friendly silica source of rice husk. The pore size of the materials could be optimised by using a blend of P123 and F127 templates. Sn‐substituted SBA‐16 mesoporous materials were yielded via the direct injection of stannic chloride into the fixed gel in acidic medium. X‐ray diffraction, N₂ adsorption, scanning electron microscope/transmission electron microscope results suggest that tin ions were incorporated into the Si‐SBA‐16 framework by isomorphous substitution between Sn and Si ions. Elemental analysis indicates that tin can be substituted in the range of Si/Sn = 21.4–10.5. UV–vis, XPS, TPR‐H₂, TPD‐NH₃ results reveal that tin atoms are highly dispersed in 4+ oxidation state and mostly occupy in the silica framework. The degree of tin incorporation into silica framework can easily be controlled by a simply adjustment of the H₂O and HCl molar ratios. The mesoporous Sn‐SBA‐16 materials were an active benzylation catalyst with almost 100% selectivity to monoalkylated product in alkylation of aromatics with benzyl chloride. © 2011 Canadian Society for Chemical Engineering     

Salt-induced synthesis of sheet-like SBA-15 under neutral conditions

In a neutral buffer system (Tris–HCl), the sheet-like mesoporous silica SBA-15 with regular hexagonal array was synthesized in the presence of the triblock copolymer P123 and the organic salt Na₂EDTA. The small angle X-ray scattering, N₂ adsorption–desorption, SEM, and TEM techniques were used to investigate the topology and morphology of the synthesized mesoporous silica, which shows a well-ordered hexagonal mesostructure and a sheet-like morphology. The mesopore channels in the synthesized material are perpendicular to the sheet plane. The strategy via the addition of the organic salt Na₂EDTA provides an alternative to synthesize SBA-15 with a sheet-like morphology under mild conditions.     

Effects of templating surfactant concentrations on the mesostructure of ordered mesoporous anatase TiO2 by an evaporation-induced self-assembly method

We prepared ordered hexagonal mesoporous TiO₂ by an evaporation-induced self-assembly (EISA) method using Pluronic P123 and tetrabutyl orthotitanate (Ti(OBuⁿ)₄, TBOT) as the templating agent and the titanium source, respectively. The main purpose of this study was to elucidate the effects of surfactant concentrations on the pore arrangement, pore size, specific surface area and structure of mesoporous TiO₂ by the EISA method. The mesostructures of mesoporous TiO₂ were characterized with X-ray diffraction (XRD), nitrogen adsorption/desorption isotherms, and transmission electron microscopy (TEM). By varying the concentration of the block copolymer, mesoporous TiO₂ of various pore sizes and pore ordering were prepared. Because the mesostructure is governed by the concentration of P123 surfactant at gelation of the solution, a higher P123/TBOT mole ratio favored the formation of highly ordered mesoporous TiO₂ with a maximum pore volume of 0.26 cm³/g, a high specific surface area of 244 m²/g, and a BJH average pore size of 4.7 nm.     

Hexagonal mesoporous fluorescent hybrid materials with electron acceptor viologen units in the framework

Mesoporous MCM-41-type fluorescent hybrid materials with methylene viologen units in the framework have been synthesized via the co-hydrolysis and -condensation of dichloride of N,N′-bis(triethoxysilylmethyl)-4,4′-bipyridinium (VP) and tetraethoxysilane (TEOS). The obtained hybrid materials are characterized by the small-angle X-ray diffraction (SAXRD), high-resolution transmission electron microscope (HR-TEM), Fourier transform infrared spectrometer (FTIR), solid-state ²⁹Si NMR spectrum, nitrogen adsorption/desorption analyse, diffuse reflectance UV–VIS (DR UV-Vis), and confocal laser scanning fluorescence microscopy (CLSFM). The results show that the VP units are covalently bonded into the silica framework to form mesoporous hybrid materials. The obtained hexagonal mesoporous hybrid materials are found to emit fluorescence at ca.380 nm and 420 nm. The fluorescent intensity enhances with increasing the amount of the VP occupied in the silica framework, and it is not affected by the hexagonal or cubic array of the pore channels. It could be prospected that such hybrid materials would present great potential applications in drug delivery and fluorescence probing for medical diagnosis and synchronous therapy.     

Fe3O4 encapsulated mesoporous silica nanospheres with tunable size and large void pore

Magnetic Fe₃O₄ and mesoporous silica core-shell nanospheres with tunable size from 110–800 nm were synthesized via a one step self-assembly method. The morphological, structural, textural, and magnetic properties were well-characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, N₂ adsorption-desorption and magnetometer. These nanocomposites, which possess high surface area, large pore volume and well-defined pore size, exhibit two dimensional hexagonal (P6mm) mesostructures. Interestingly, magnetic core and mesoporous silica shell nanocomposites with large void pore (20 nm) on the shell were generated by increasing the ratio of ethanol/water. Additionally, the obtained nanocomposites combined magnetization response and large void pore, implying the possibility of applications in drug/gene targeting delivery. The cell internalization capacity of NH₂-functionalized nanocomposites in the case of cancer cells (HeLa cells) was exemplified to demonstrate their nano-medicine application.     

Effects of surfactant/silica and silica/cerium ratios on the characteristics of mesoporous Ce-MCM-41

Using the surfactant CTMABr (cetyltrimethyl ammonium bromide) and cerium(IV) sulfate, mesoporous Ce-MCM-41 molecular sieves were produced under a hydrothermal condition with various surfactant/silica (surfactant/Si) and silica/cerium (Si/Ce) ratios. Changes to the structural traits caused by changing the molar ratios of both surfactant/Si and Si/Ce were investigated. XRD (X-ray diffraction), FT-IR (fourier transform infrared spectroscopy), and SEM (scanning electro microscopy) were used for the characterization of prepared mesoporous samples. Among the tested molar ratios, surfactant/Si ratio of 0.5 and 0.2 showed highest values of d_1 0 0 and intensity, respectively, for the Si-MCM-41. XRD analysis also identified a quintessential hexagonal structure of Ce-MCM-41 for the Si/Ce molar ratio higher than 40 (maintaining the surfactant/Si ratio at 0.2). When cerium content was increased to have the Si/Ce molar ratio of 20, the hexagonal structure of Ce-MCM-41 was collapsed due to the structural stress of substituted cerium. FT-IR results confirmed calcination of Ce-MCM-41 and the incorporation of Ce⁴⁺ ions of cerium sulfate into the silica surface with proper removal of the surfactant. Rod-like shape with rounded edges of the prepared Ce-MCM-41 samples was identified by SEM. These results suggest surfactant/Si ratio of 0.2 and Si/Ce ratio of 40 for the production of Ce-MCM-41 with the highest level of crystallinity.     

Catalytic applications of sulfonic acid functionalized mesoporous organosilicas with different fraction of organic groups in the pore wall

Organosulfonic acid functionalized mesoporous organosilicas with different fraction of organic groups in the pore wall was synthesized in the presence of P123 (EO₂₀PO₇₀EO₂₀) by controlling the molar ratio of tetramethoxysilane (TMOS) to 1,2-bis(trimethoxysilyl)ethane (BTME) in the initial mixture during the co-condensation process of silane precursors in acidic medium. Structural characterizations (X-ray diffraction, nitrogen sorption analysis, and transmission electron microscopy) show that all materials have ordered hexagonal mesoporous structure with large pore diameter (7–9 nm). The existence of ethane and sulfonic acid groups in the material was verified by ²⁹Si MAS and ¹³C CP MAS NMR and X-ray photoelectron spectroscopy (XPS). The mesoporous solid acids can adsorb both water and hexane (the adsorption capacity for water and hexane is 240 and 600 mg/g, respectively) due to the existence of surface hydroxyl groups, propyl sulfonic acid group, and the ethane moiety. These mesoporous solid acids are efficient catalysts for the dehydration of 1-butanol and the hydration of propylene oxide (PO).     

An organic/inorganic hybrid mesoporous silica membrane: preparation and characterization

An organic/inorganic hybrid mesoporous silica membrane composed of mesoporous silica materials inside the channels of polycarbonate filtration membrane (PC) was synthesized by using aspiration-induced infiltration method, and the surfactant in as-prepared membrane was removed by employing template-extraction method. The obtained materials were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD),transmission electron microscopy (TEM) and N₂ adsorption–desorption measurement. The SEM images and EDS elemental analyses show that as-synthesized materials in PC are one-dimensional silica rods estimated as 200 nm in diameter and 9 μm in length. Moreover, the results of XRD, TEM and N₂ adsorption–desorption analysis clearly demonstrate that such silica rods are mesoporous materials with two-dimensional hexagonal mesostructure and the average mesopore diameter is about 3.0 nm. In addition, the porosity of organic/inorganic hybrid mesoporous silica membrane was further examined by molecule permeation. It is found that small molecule, such as rhodamine B, can transport across the membrane, but relatively large molecule, such as horse radish peroxidase, can not transport across the membrane, indicating that it is size-selectivity of such a membrane for molecule permeation, which has the potential application in the molecule filters to separate bio-macromolecule from small molecule.     

Characteristics of vanadium-substituted mesoporous silica with wormhole framework structure: effects of vanadium content

Vanadium-substituted wormhole framework structure (V-WMS) mesoporous silicas (V-WMS) with various Si/V ratios in the range of 15 and 200 were prepared at ambient temperature by neutral surfactant templating pathway. The materials were synthesized by using dodecylamine as a template and tetraethylorthosilicate as a silicon source. They were characterized by energy dispersive X-ray spectroscopy (EDS), powder X-ray diffraction (XRD), N₂ adsorption–desorption, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared absorption spectroscopy (FT-IR) and ultraviolet-visible absorption spectroscopy. V-WMS samples shown characters of larger framework wall thickness, small crystallite domain sizes, and complementary textural mesoporosities in comparison with M41S materials. These mesoporous V-WMS samples exhibited irregularly shaped mesoscale fundamental particles which aggregated into larger particles. They also demonstrated better thermal stability than MCM-41. An absorption band of FT-IR at ca. 960 cm⁻¹ was assigned to the vibration of Si–O–V linkages. These samples also showed one strong UV–visible absorbance with overlapping maxima at about 255 nm. The results show that vanadium was incorporated into the structure of wormhole mesoporous silica (WMS). However, for V-WMS with high vanadium content (Si/V < 25), a broad shoulder in XRD pattern was observed at about 3–4°, suggesting the presence of impurity phase of vanadium species in the sample. The efforts in preparing V-WMS specimens by neutral-template synthesis route had led to new mesoporous silica molecular sieves with catalytically active vanadium centers.