Synthesis Of Mesoporous Silica Materials Research Articles

Surfactant-free synthesis of mesoporous silica materials (Using tetraetylorthosilicate and oleic acid): Preparation, characterization, and catalytic applications

Mesoporous silica nanoparticles (MSNs), one of the important porous materials, have attracted enormous interest due to their exceptional physical and chemical properties. The present study describes a non-surfactant templating route to mesoporous silica materials with large surface areas (617 m2 g−1) and pore volumes (0.6374 cm3 g−1) using the oleic acid template that plays two important roles: as a catalyst for hydrolysis of silicon alkoxide and well-defined three-dimensional arrangement of silica nanospheres (as a natural). The silica was calcined and studied using several techniques such as FE-SEM, FT-IR, XRD, TEM, and BET. Afterward, the surfaces of the mesoporous silica nanoparticles (MSNs) were modified and used as a catalyst for synthesizing pyrazolopyranopyrimidines and pyrido[2,3-d:6,5-d]dipyrimidines.

A comparative life cycle assessment of the synthesis of mesoporous silica materials on a small and a large scale

LCA of the most common mesoporous silica materials MCM-41, MCM-48, UVM-7, Stober particles, SBA-15, SBA-16, HMS, KIT-5, KIT-6, MSU, and FDU.

Review on Template Removal Techniques for Synthesis of Mesoporous Silica Materials

The key step in the preparation of mesoporous silica materials is the removal of organic templates occluded inside the pores including nonionic, cationic, anionic surfactants and even ionic liquid (IL). The most common method to remove templates is conventional calcination under air at 550 °C. Although templates can be completely removed from the pores, calcination suffers many serious drawbacks including significant framework shrinkage, the collapse of the ordered structure, reduction of silanol concentrations on the pore wall (which are of high importance for postmodification), generation of large amounts of CO2 and organic amine compounds, the presence of carbon deposits or coke as a contaminant, elimination of organic functionalities (such as organoalkoxysilanes with amino groups), and the inability to recover or reuse expensive organic templates. That is why many attempts have been reported in the literature to develop novel methods for removing organic templates that are favorable from both economic and environmental standpoints for potentially large-scale applications. The current study reviews the recent development methods for template removal from various types of mesoporous silica materials. We have divided the template removal approaches into two categories: physical method and chemical method. The effects of those methods are discussed in detail on the textural and structural properties of mesoporous silica materials along with the template removal mechanism and their pores and coins.

Singlet oxygen-promoted one-pot synthesis of highly ordered mesoporous silica materials via the radical route

Compared with ˙OH in an acid-free synthesis system, 1O2 plays a more important role in the hydrolysis of TEOS to meet the targeted assembly rate for templates, which is crucial for the one-pot synthesis of mesoporous silica materials.

Influence of the Template Removal Method on the Mechanical Stability of SBA-15.

Removing the template from the pores after the polycondensation of the silica precursor is a necessary step in the synthesis of mesoporous silica materials. In our previous work, we developed a method for the efficient and spatially controlled functionalization of SBA‐15. First, the silanol groups on the particle surface and in the pore entrances were passivated. After extraction of the template, a pretreatment step in N2 converted the silanol groups to the single and geminal state. Afterwards, an azide functionality was introduced exclusively into the mesopores. This ensured that the catalyst could afterwards be immobilized unambiguously in the mesopores. The mechanical stability of a material functionalized in such a spatially controlled manner is studied and compared to other template removal methods. Even though several studies investigated the influence of the calcination temperature, the presence or the absence of oxygen during the template removal, the specific conditions used during the herein reported selective functionalization procedure have not been covered yet.

Mechanisms and Intermediates in the True Liquid Crystal Templating Synthesis of Mesoporous Silica Materials

Mesoporous silica materials (MSMs) produced by true liquid crystal templating (TLCT) are often considered as direct inverted replicas of the initial lyotropic liquid crystal (LLC) phase. However, the predictive design of tailor-made MSMs requires the full knowledge of the TLCT process, which is still incomplete. Here, we tackle this issue by monitoring the structural evolution during the templating process by small-angle X-ray scattering, showing that after the addition of the silica source the reaction mixture is first isotropic and then an intermediary liquid crystal phase appears, which is the key to the success of the templating process, namely the formation of ordered MSMs. We analyze the structure and the formation dynamics of this intermediary phase and present a simple theoretical model, which allows us to connect the structural parameters of the initial LLC and the MSM. These results provide an enhanced understanding of the TLCT process and are an important step toward the predictable synthesis of new MSMs in the future.

TAILORING THE PORE STRUCTURE OF MESOPOROUS SILICA BY USINGAMPHIPHILIC BLOCK COPOLYMER AND CONTROLOF AGING TEMPERATURE

Synthesis of mesoporous silica materials has been studied using Pluronic triblock copolymer F127 nonionic amphiphilic triblock copolymer (EO106 PO70 EO106) as high molecular weight structure-directing agent and TEOS as a silica source. The mesostructure of the silica material obtained, as determined by High Resolution Transmission electron microscopy (HRTEM), Atomic Force Microscopy (AFM), and nitrogen adsorption–desorption isotherm. Changing the amount of surfactant has effect on the porosity of the material, where increasing the amount of surfactant has effect on the hydrophobic surface curvature of the micelle and correspondingly the particle morphology. The particle morphology has changed from hexagonal to cubic Fm3m symmetry, with different pore sizes. Some samples with the same molar ratio have different unit cell size according to the change in aging temperature. HRTEM-ED shows cubic and cage structure of pores under optimum conditions of synthesis. The structural transformation is limited.

Simple Synthesis and Characterization of Hexagonal and Ordered Al–MCM–41 from Natural Perlite

Silica reagents are expensive and toxic for use in the synthesis of mesoporous silica materials. It is imperative to take an interest in green silicon sources. In this paper, we report the synthesis of hexagonal and ordered aluminum-containing mesoporous silica materials (Al–MCM–41) from natural perlite mineral without addition of silica or aluminum reagents. A pretreatment process involving acid leaching, alkali leaching, and strongly acidic cation exchange resins treatment was critical to obtain silicon and aluminum sources from natural perlite mineral. The Al–MCM–41 material was synthesized via a hydrothermal reaction with hexadecyl trimethyl ammonium bromide (CTAB) as the template and subsequent calcination. The resulting mesophase had a hexagonal and ordered mesoporous structure, confirmed by small-angle X-ray diffraction (SAXRD) and transmission electron microscopy (TEM). Al–MCM–41 material had a high Brunauer–Emmet–Teller (BET) surface area of 1024 m2/g, pore volume of 0.72 cm3/g and an average pore diameter of 2.8 nm with a pore size distribution centered at 2.5 nm. The thermal behavior of the as-synthesized samples during calcination was investigated by thermogravimetry (TG) and differential thermogravimetry (DTG) analysis. The Al–MCM–41 material showed a negative surface charge in aqueous solution with the pH value ranging from 2 to 13. The variations of chemical structures from natural perlite to Al–MCM–41 were traced by wide-angle X-ray diffraction (WAXRD) and Fourier-transform infrared spectroscopy (FTIR). A proposed mechanism for the synthesis of hexagonal and ordered mesoporous silica materials from natural perlite is discussed.

Synthesis of Mesoporous Silica Materials from Incineration Bottom Ash for the Removal of Toluene

Synthesis of Mesoporous Silica Materials from Incineration Bottom Ash for the Removal of Toluene

Catalytic oxidative desulfurization of DBT using green catalyst (Mo/MCM-41) derived from coal fly ash

Current study presents the synthesis of mesoporous silica material (MCM-41) derived from coal fly ash as a catalyst support material for the catalytic oxidative desulfurization (ODS) of liquid fuels. In this work, molybdenum active species were incorporated into the mesoporous silica (Mo/MCM-41) by the incipient wet-impregnation process. The obtained Mo/MCM-41 was characterized by FESEM, HRTEM, XRD, and FT-IR to confirm its structure and functional groups present on the catalyst. Characterization study revealed that mesoporous silica was successfully synthesized from coal fly ash. Desulfurization of dibenzothiophene (DBT) containing model fuel was investigated by using synthesized catalyst, approximately 94% of DBT removal was achieved by optimizing the influencing parameters of ODS process. The ODS results proved that Mo/MCM-41 could be the potential catalyst for reduction of DBT from liquid fuels. Oxidative reaction of DBT follows the pseudo first order reaction kinetic. DBT oxidation mechanism was proposed.

Tetraalkylammonium acetates and tetraalkylammonium tetrafluoroborates as new templates for room-temperature synthesis of mesoporous silica spheres

Six surface active compounds containing: hexadecyltrimethylammonium [HDTMA], dodecyltrimethylammonium [DDTMA] or didecyldimethylammonium [DDA] cation and tetrafluoroborate [BF4] or acetate [OAc] anion were synthesized, purified and characterized, and subsequently applied for the synthesis of mesoporous silica materials of MCM-41 type. The materials were characterized using X-ray diffraction, Scanning Electron microscopy, and nitrogen physisorption method. Their structures were compared with that of reference MCM-41 material obtained with the conventional template [HDTMA][Br]. Nanosized silica spheres with size distribution in the range of 200–800 nm are obtained with the novel templates. The pore size of the obtained materials was in the range of 2.1–3.1 nm, and it was dependent only on the cation structure of the templates. The MCM-41 materials obtained with the acetate-based templates were characterized with a higher specific surface area in comparison with the reference material. On the basis of SEM, XRD and nitrogen physisorption data could be concluded that all tetraalkylammonium acetates used as templates lead to mesoporous silica nanospheres with very good textural characteristics, while in case of tetraalkylammonium tetrafluoroborates the best results in terms of particle uniformity and surface properties are obtained with [DDTMA][BF4]. MCM-41-[HDTMA][OAc] exhibited excellent loading capacity (374.1 mg/g) for the cyclic peptide antibiotic bacitracin, and moderate to good loading capacity for larger peptide and proteins such as insulin (70.3 mg/g) and lipase from porcine pancreas (70.8 mg/g).

Synthesis of lamellar mesoporous silica materials using LCs as templates

ABSTRACTThe study focuses on the synthesis of mesoporous silica materials using liquid crystals (LCs) formed in an aqueous mixture of cationic cetyltrimethylammonium bromide (CTAB) and anionic sodium dodecyl sulfate (SDS) as templates and tetrathoxysilane (TEOS) as precursor. For this purpose, the phase behavior and range of LC areas were determined at different temperatures, concentrations, and ratios of CTAB/SDS. It was found that LCs became denser with the increased of concentration of surfactants. The mesoporous materials were synthesized using LCs as templates at various temperatures, surfactant concentrations, and pH values. The mesoporous samples were characterized using SEM and nitrogen sorption analysis. The research results showed that the structure of synthesized samples were lamellar and their surface areas increased significantly with the increase of temperature in the temperature range of LCs, reaching about 900 m2/g at 60°C. The surfactant concentrations affect the thickness of pore wall and thereby the specific surface area of products. The specific surface area and the order of mesoporous sample increased gradually with the decrease of pH.

Synthesis of mesoporous silica materials (MCM‐41) using silica fume as the silica source in a binary surfactant system assisted by post‐hydrothermal treatment and its Pb2+ removal properties

AbstractMesoporous silica materials (MCM‐41) were successfully prepared by substituting silica fume for silicate in different surfactant systems. The effects of binary surfactant systems and post‐hydrothermal treatment on the morphology and structural properties of MCM‐41 were investigated based on X‐ray diffraction (XRD), N2 sorption/desorption, and transmission electron microscopy analyses (TEM). The results confirmed that polyethylene glycol (PEG‐6000) is an effective additive template in a binary surfactant system for the synthesis of mesoporous silica materials. Meanwhile, the hydrothermal stability of the mesoporous silica materials can be improved by post‐hydrothermal treatment and the optimal experimental parameters are a temperature of 140 °C and a treatment time of 48 h. The formation of high‐quality MCM‐41 is based on the balance between the ordered assembly of the inorganic anionic species and cationic surfactant, in accordance with the electrostatic interactions and hydrogen bonds between PEG‐6000 and the inorganic species. Meanwhile, Pb(II) removal from aqueous solution has also been examined using MCM‐41 as an adsorbent. The results of adsorption showed that the as‐synthesized MCM‐41 demonstrated a high capacity of Pb2+.

A facile and novel route for dual-template method synthesis of mesoporous silica material Al-Ce-SBA-15

A kind of ordered mesoporous material Al-Ce-SBA-15 was successfully prepared by the method of dual-templates CTAB and P123 with adding appropriate amount of Al through a one-step hydrothermal synthesis. The prepared Al-Ce-SBA-15 material was characterized by XRD, EDX, HRTEM, SEM, FT-IR and N2 adsorption-desorption isotherm technique. The results showed that the heteroatoms Al and Ce highly dispersed on the surface of SBA-15 and the prepared Al-Ce-SBA-15 material still retained a desirable ordered mesoporous structure, high specific surface area, large pore volume and narrow pore size distribution. Especially, a uniform coating layer was formed on SBA-15, and the aggregation of metal Ce was avoided by adding appropriate amounts of Al.

Nanostuctured mesoporous materials from different silica sources using fluorinated surfactants as templates

We report here the synthesis of mesoporous silica materials from various fluorinated-based systems using as the inorganic precursor either sodium silicate solution or silicate ions produced from the dissolution of silica under basic conditions. The properties of the materials are compared with the ones of the mesostructures prepared from tetramethoxysilane as silica source. Results show that whatever the silica source, well-ordered hexagonal materials with a narrow pore size distribution are obtained. Nevertheless, the pH has a great influence on the properties of the recovered materials since it governs the interactions between the surfactant and the inorganic precursor and the pH range for which the hexagonal mesopore ordering is obtained, depends on the silica source. Using sodium silicate, hexagonal mesostructured materials with high specific surface area (≥800m2/g) and narrow pore size distribution (4nm) are recovered for pH from 0.3 to 5. It should be noted that the formation of organized mesoporous silica under acidic conditions with this precursor is barely reported in literature. Replacing sodium silicate by silica fumed, the pH range leading to a hexagonal mesopore ordering is reduced to 0.3–1.5. When the organosilane is used the ordered mesoporous materials are recovered regardless the pH. In addition in that case a better control of the self assembly between the surfactant and the silica species allows tuning the particles’ morphology. Under acidic conditions tetramethoxysilane gives rise to gyroids or toroids and favors the formation of submicrometer particles, while irregularly shaped particles are produced with sodium silicate or silica fumed under alkaline conditions. Results also show that neither the specific surface area, nor the cell parameter strongly depend on the silica precursor as long as the hexagonal structure is kept.

Synthesis of mesoporous silica material with ultra-large pore sizes and the HDS performance of dibenzothiophene

Ultra-large mesoporous silica materials using different micelle expanders including hexane, cyclohexane, 1,3,5-triisopropylbenzene and 1,3,5-triethylbenzene, have been successfully synthesized by the template of polymer surfactant of P123 (Aldrich, EO20PO70EO20). Among all the used micelle expanders, highly ordered cubic mesoporous silica material (SBA-16@hexane) with ultra-large pore size was obtained by using hexane. All the obtained samples were well characterized by small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), nitrogen adsorption–desorption, UV–vis diffuse reflectance spectroscopy (DRS), H2-TPR, pyridine-FTIR, 27Al MAS NMR, GC–MS and Raman. The synthesis mechanism was also proposed. Compared with the conventional SBA-16 (6.31 nm) synthesized taking polymer surfactant of F127 (propylene oxide block copolymer) as the template, the as-synthesized SBA-16@hexane had a pore diameter of 15.1 nm with a highly ordered mesostructure, which was the largest one among all the reported pore sizes of SBA-16 materials. The corresponding hydrodesulfurization (HDS) catalysts of NiMo/Al-SBA-16@hexane, NiMo/γ-Al2O3, and NiMo/Al-SBA-16 were prepared by using different supports respectively, furthermore, their HDS performances were evaluated adopting dibenzothiophene (DBT) as the probe reactant. The DBT HDS efficiencies over these catalysts followed the order: NiMo/Al-SBA-16@hexane > NiMo/γ-Al2O3 > NiMo/Al-SBA-16. The high activity of NiMo/Al-SBA-16@hexane can be attributed to the superior diffusivity of the novel support of SBA-16@hexane with ultra-large pore size.

Fast synthesis of mesoporous silica materials via simple organic compounds templated sol–gel route in the absence of hydrogen bond

As simple organic compounds that contain no hydroxyl, amino or carboxyl groups cannot assemble with the siliceous species through hydrogen bond or electrostatic force, they have not been applied as templates to prepare mesoporous silica materials before. However, in this work it was found that only if the organic compound can form homogeneous solution with ethanol and water can it successfully lead the formation of mesopores under the catalysis of 5% ammonium hydroxide (NH4OH) solution. The effects of template type, template amount and NH4OH solution concentration on the pore structure of the prepared porous silica were comprehensively studied. The pore size had no direct correlation with the molecular size of the template, but it could be easily adjusted in the range of 2.4–6.6 nm through changing the template amount. When using 5% NH4OH solution as the catalyst, the gelation time of siliceous species was ultrashort and therefore the template aggregates could be trapped in the three-dimensional SiO2 matrixes to function as the pore-forming agents. However, when the concentration of NH4OH solution was excessive high, like 15%, the gelation reaction was over intense and mesopores cannot be formed in the prepared silica. The mesoporous silica materials prepared in this new sol–gel route can be used as good supports of CO2 adsorbents. Through loading PEI into the mesopores of the silica materials, the solid amine adsorbents could be easily prepared, and they can keep remarkable CO2 adsorption ability even after 10 adsorption–desorption cycles.

Amphiphilic ABC triblock terpolymer templating for mesoporous silica

Self-assembled triblock terpolymers have attracted intense attention in recent years because of their abundant variety of assembly mesostructure. We reported the synthesis of mesoporous silica materials with the amphiphilic ABC triblock terpolymer polyethylene-poly(ethylene oxide)-polycaprolactone(PE-PEO-PCL) as a template and tetraethoxysilane(TEOS) as a silica source. Increasing the hydrophilic head group(PEO) led to the decrease of packing parameter g, which gave rise to the mesophase transformation from a cylindrical two-dimensional hexagonal P6mm structure to a cage-type face centered cubic closed-packing mesostructure. This new templating route provided a new insight into the template factor governed inorganic-organic self-assembly mesophases.

Adsorption characterization of gaseous volatile organic compound on mesoporous silica particles prepared from spent diatomaceous earth.

This study used spent diatomaceous earth (SDE) from drink processing as source of Si and cationic surfactant (CTAB) as a template for the synthesis of mesoporous silica Materials (MSM) through hydrothermal method. The MSM was characterized by Small-angle X-ray Diffraction (SXRD), Scanning Electron Microscopy (SEM), Thermo Gravimetric Analysis (TGA), Fourier Transform Infrared (FT-IR) spectroscopy and N2 adsorption-desorption analyzer. The results showed that the surface area, pore volume and pore size was roughly ranged from 880 to 1060 m2 g(-1), 1.05 cm3 g(-1) and 4.0 nm, respectively. The properties of the synthesized MSM were also compared with those prepared from pure silica sources (MCM-41) and got almost the same characteristics. The synthesized MSM was used as adsorbent at 25 degrees C with carrier gas of air. The adsorption equilibrium revealed that adsorption capacity of MSM was 59.6, 65.7, 69.6, 84.9 mg g(-1) while the acetone concentration was 600, 800, 1000 ppm, 1600 ppm respectively. Results showed that breakthrough curves correlate to the challenge vapor concentration, adsorbent loading, and the flow rate. The results obtained in the present work demonstrated that it was feasibility of using the SDE as a potential source of silica to prepare MSM.

Synthesis of mesoporous silica materials from municipal solid waste incinerator bottom ash

Incinerator bottom ash contains a large amount of silica and can hence be used as a silica source for the synthesis of mesoporous silica materials. In this study, the conditions for alkaline fusion to extract silica from incinerator bottom ash were investigated, and the resulting supernatant solution was used as the silica source for synthesizing mesoporous silica materials. The physical and chemical characteristics of the mesoporous silica materials were analyzed using BET, XRD, FTIR, SEM, and solid-state NMR. The results indicated that the BET surface area and pore size distribution of the synthesized silica materials were 992m2/g and 2–3.8nm, respectively. The XRD patterns showed that the synthesized materials exhibited a hexagonal pore structure with a smaller order. The NMR spectra of the synthesized materials exhibited three peaks, corresponding to Q2 [Si(OSi)2(OH)2], Q3 [Si(OSi)3(OH)], and Q4 [Si(OSi)4]. The FTIR spectra confirmed the existence of a surface hydroxyl group and the occurrence of symmetric Si–O stretching. Thus, mesoporous silica was successfully synthesized from incinerator bottom ash. Finally, the effectiveness of the synthesized silica in removing heavy metals (Pb2+, Cu2+, Cd2+, and Cr2+) from aqueous solutions was also determined. The results showed that the silica materials synthesized from incinerator bottom ash have potential for use as an adsorbent for the removal of heavy metals from aqueous solutions.