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.     

Hierarchical mesoporous silica microspheres as unique hard-template for preparation of hierarchical mesoporous TiO2 microspheres with trimodal mesoporosities via nanocasting

This work for the first time reported that hierarchical meso-mesoporous SBA-15 silica microspheres (HMM-SiO₂-MSs) can serve as a unique and suitable hard-template for the nanocasting preparation of mesoporous TiO₂ with both hierarchical mesostructures and well-preserved microsphere particle morphology. A two-step impregnation (TSI) method was developed and customized and its effectiveness was studied in comparison with the single-step impregnation method. Trimodal mesoporosities and their origin are newly recognized and analyzed. The materials were examined by various techniques, including the FE-SEM, N₂ sorption, TEM and XRD. Under optimized conditions, the hierarchical mesostructures and spherical particle morphology of HMM-SiO₂-MSs can be replicated for HMM-TiO₂-MSs. The high surface area and pore volume of HMM-TiO₂-MSs reach 194 m² g^-1 and 0.68 cm³ g^-1, respectively, with the latter more than twice those templated by conventional SBA-15s. Besides HMM-TiO₂-MSs, such HMM-SiO₂-MSs as hard-template might be extended to the preparation of other materials with hierarchical mesostructures.     

Inorganic–organic hybrid materials based on functionalized silica and carbon: A comprehensive understanding toward the structural property and catalytic activity difference over mesoporous silica and carbon supports

Inorganic–organic hybrid materials based on functionalized silica and carbon were synthesized by anchoring molybdovanadophosphoric acid (H₅[PMo₁₀V₂O₄₀] · 32.5H₂O) onto amine-functionalized SBA-15, ethane-bridged SBA-15 and mesoporous carbon, respectively. Small angle X-ray diffraction, N₂ sorption analysis, HRTEM, SEM, FT-IR, CP-MAS NMR were used to diagnose the mesoporous structure of inorganic–organic hybrid materials. The structural integrity of molybdovanadophosphoric acid has been found to be retained after immobilization over mesoporous materials. These inorganic–organic hybrid materials were tested in the environmentally friendly oxidation of 2-methylnaphthalene (2MN) with 30% aqueous hydrogen peroxide. Molybdovanadophosphoric acid containing mesoporous organosilica hybrid material (ethane-bridged SBA-15) exhibited higher catalytic activities in the oxidation of 2MN to give a clean product 2-methy-1,4-naphthoquinone (menadione vitamin K3 precursor), because of the improved hydrophobicity of the material. The correlation between structural properties and catalytic activities of these hybrid materials has been well addressed in our present studies.     

Highly accessible SnO2 nanoparticle embedded SBA-15 mesoporous silica as a superior photocatalyst

We address the accessibility of tin oxide (SnO₂) nanoparticles synthesized inside the pores of mesoporous silica (SBA-15) host. On using a low-temperature route for in situ synthesis of SnO₂ and hence eliminating interparticle aggregation, SnO₂ nanoparticles of diameter much smaller (3.5 nm) than the cylindrical pore diameter (6.3 nm) of the SBA-15 could be synthesized. This enables molecules diffusing into the SBA-15 pores to access the very high specific surface area of SnO₂; enabling the diffusing species to react easily with the latter. This is demonstrated by an enhanced photocatalytic degradation rate constant of an aqueous solution of rhodamine B dye, on contacting the latter with the SnO₂-SBA-15 composite.     

New mesoporous carbon materials synthesized by a templating procedure

The new porous carbon materials were obtained by templating procedure using mesoporous silica (SBA-15) as template. The ordered mesoporous silica materials were synthesized by using Pluronic P123 (non-ionic triblock copolymer, EO₂₀PO₇₀O₂₀). SBA-15/cryogel carbon composites were obtained by sol–gel polycondenzation of resorcinol and formaldehyde in the presence of different amount of SBA-15. The polycondenzation was followed by freeze drying and subsequent pyrolysis. One set of SBA-15/sucrose carbon composites was prepared by using sucrose as carbon source. The silica template was eliminated by dissolving in hydrofluoric acid (HF) to recover the carbon material. The obtained carbon replicas were characterized by nitrogen adsorption–desorption measurements, X-ray diffraction and scanning electron microscopy (SEM). It was revealed that the samples have high specific surface (533–771 m² g^?1), developed meso- and micro-porosity and amorphous structure. Porous structure of carbon replicas was found to be a function of the carbon source, properties of SBA-15 and silica/carbon ratio. Room temperature adsorption of nitrogen and adsorption of phenol from aqueous solutions were investigated.     

Synthesis of mesoporous materials SBA-15 and CMK-3 from fly ash and their application for CO2 adsorption

A supernatant solution of silicate species extracted from coal fly ash in a power plant by alkali fusion was used in acidic condition to prepare a mesoporous silica SBA-15. The SBA-15 was used as a template for the synthesis of a mesoporous carbon CMK-3 using sucrose as a carbon source. Characterization of the produced mesoporous materials by XRD, N₂ adsorption-desorption, SEM, and TEM confirmed the formation of well-ordered hexagonal mesostructures. Textural properties were found close to those prepared by pure chemicals. SBA-15 after polyethyleneimine impregnation and CMK-3 were tested for carbon dioxide adsorption, successfully demonstrating the possibility of recycling the industrial waste product in a power plant into a useful adsorbent.     

Sulfonic acid functionalized mesoporous SBA-15 for selective synthesis of 4-phenyl-1,3-dioxane

Mesoporous SBA-15 silica has been functionalized with propylsulfonic acid groups post-synthetically using 3-mercaptopropyltrimethoxysilane as sulfur source. The materials before and after functionalization have been characterized by BET surface area and pore size distribution by BJH method, powder X-ray diffraction and temperature programmed desorption (TPD) of NH₃. The resultant mesoporous material (solid acid catalyst) exhibited hexagonal mesoscopic ordering, which possess 1.3 meq H⁺ g⁻¹ SiO₂ exchange capacity, 96 Å mesopore size diameter, and 660 m² g⁻¹surface area. Sulfonic acid groups anchored to SBA-15 silica pore surfaces are thermally stable up to 653 K, hydrothermally robust in boiling water and resistant to leaching in organic and aqueous solvents under mild conditions. XRD results indicate that there is no change in the structure after anchoring SBA-15 with SO₃H group. SBA-15-SO₃H catalyst has been found to be highly active and selective for the Prins condensation of styrene with formaldehyde. Both the conversion of styrene and the selectivity to 4-phenyl-1,3-dioxane are nearly 100%. Presence of more number of acid sites in SBA-15-SO₃H catalyst helps in achieving high yields. Furthermore, the conversion and the selectivity to 4-phenyl-1,3-dioxane are found to be consistent in four repeated cycles.     

Metal oxides nanoparticles on SBA-15: Efficient catalyst for methane combustion

Catalysts based on crystalline nanoparticles of Mn and Co metal oxides supported on mesoporous silica SBA-15 have been developed. These materials were characterized by XRD, BET and transmission electron microscopy (TEM) techniques. SBA-15 mesoporous silica was synthesized by a conventional sol–gel method using a tri-block copolymer as surfactant. Supported Mn₃O₄ and Co₃O₄ nanoparticles were obtained after calcination of as-impregnated SBA-15 by a metal salt precursor. The catalytic activity was evaluated in the combustion of methane at low concentration.Co₃O₄/SBA-15 (7 wt.%) exhibits the highest performance among the different oxides. Furthermore, this novel generation of catalysts appeared as active as conventional LaCoO₃ perovskite, usually taken as reference for this reaction. Thanks to its organized meso-structures, SBA-15 material creates peculiar diffusion conditions for reactants and/or products.     

Influence of polyhydric solvents on the catalytic &; adsorption properties of self-oriented mesoporous SBA-15 silica

Mesoporous materials (2–50 nm) have generated much interest due to its multi-faceted applications as catalysts, adsorbents and drug delivery systems. This study is the first of its kind to systematically investigate the effect of polyhydric solvents on the morphology, catalytic and adsorption properties of self-oriented mesoporous silica. Three different mesoporous SBA-15 silica materials were synthesized using Water (SW), Glycerol (SG) and Ethylene Glycol (SEG) as solvent. They were characterized using FE-SEM, HR-TEM, small angle XRD, FT-IR, BET and solid state NMR. Morphological studies such as pore characteristics, surface area and the functionalization were carried out by comparing their catalytic and adsorption properties. Each mesoporous sample was used to catalyze biodegradable aliphatic polyester synthesis namely poly (butylene succinate), poly (butylene pimelate) and poly (butylene sebacate) and compared with a conventional homogeneous catalyst SnCl₂·2H₂O. The results offered higher purity and yield of polyesters and they took the order as SW > SG > SEG. The adsorption efficiency of each mesoporous sample was compared using the fluorescent dye Rhodamine-B and it took a reverse order (SEG > SG > SW) to that of the catalytic efficiency. This difference may be attributed to the difference in free active sites, ordered morphology of pores and surface area. The synthesized polyesters were characterized using FT-IR, ¹H NMR, XRD, GPC, DSC and the adsorption studies, using UV–Visible spectrophotometer.     

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.     

Adsorption of phosphate and nitrate anions on ammonium-functionnalized mesoporous silicas

Surface modified mesostructured silica materials represent potential adsorbents offering an opportunity to remediate several important water pollutants. In the present work, ammonium-functionnalized MCM-41, MCM-48 and SBA-15 mesoporous silica materials were synthesized via post-synthesis grafting and co-condensation. Their efficiency to remove nitrate and phosphate anions in aqueous solutions was investigated. The adsorbent materials showed high adsorption capacities reaching 46.5 mg NO₃⁻/g and 55.9 mg H₂PO₄⁻/g under the operating conditions explored. The mesoporous silica materials functionalized via post-synthesis grafting method exhibited higher performances in terms of percentage pollutant removal and adsorption capacities if compared to their analogs synthesized according to the co-condensation strategy.     

Cooperative self-assembly of silica-based mesostructures templated by cationic fluorocarbon/hydrocarbon mixed-surfactants

In this work, we have systematically studied the influences of reaction temperature, silica sources, and nature of surfactant templates on cooperatively self-assembled mesostructures. Both positively charged hydrocarbon (HC) surfactant cetyltrimethylammonium bromide (CTAB) and fluorocarbon (FC) surfactant FC-4 were used as the templates, and four silica sources tetramethyl orthosilicate (TMOS), tetraethyl orthosilicate (TEOS), 1,2-bis (trimethoxysilyl) ethane (BTME) and 1,2-bis (triethoxysilyl) ethane (BTEE) were used as the precursors. When CTAB and FC-4 were applied as mixed templates and BTME or BTEE as the silica source, it was found that ordered mesostructure with a hollow morphology can be successfully obtained only at temperatures higher than the demixing temperature (T_d) of two surfactants. When FC-4 was used as a single template, generally vesicular structures were obtained regardless of the silica sources. In the case of CTAB/FC-4 co-templates, the utilization of pure silica sources (TEOS and TMOS) gave rise to nano-particles with neither hollow morphology nor the ordered mesostructure. The above results can be understood by the interactions between the templates and the silica sources considering the hydrophobic sequences of surfactants (CTAB < FC-4) and different silica precursors (TMOS < TEOS < BTME < BTEE). It is anticipated that by carefully tuning the interaction between surfactant templates and silica species, novel mesoporous materials with controlled composition, structure and morphology can be designed and fabricated.     

Metal (Co,Mn)-amine-functionalized mesoporous silica SBA-15: synthesis,characterization and catalytic properties in hydroxylation of benzene

Mesoporous silica SBA-15 was synthesized using H₃PO₄ and functionalized with ethylendiaminopropyltrimethoxysilane (H₂N–(CH₂)₂–NH–(CH₂)₃–) by grafting method. A variety of transition metals such as Co and Mn have been coordinated with amine-functionalized silica SBA-15. The materials have been characterized by XRD, FT-IR, BET, TGA, ¹³C-NMR, DR UV–Vis, atomic absorption spectroscopy (AAS) and back titration using NaOH (0.1 N). The catalytic performance of obtained catalyst was determined for hydroxylation of benzene using H₂O₂ as oxidant in the presence of O₂ atmosphere. At optimized conditions, the Mn-amine-functionlized mesoporous silica SBA-15 exhibited high catalytic activity at room temperature in the absence of solvent.     

Propane oxidative dehydrogenation over vanadia catalysts supported on mesoporous silicas with varying pore structure and size

The structural characteristics and the performance of vanadia catalysts (0.7–8 wt.% V) supported on mesoporous (MCM-41, HMS, MCF, SBA-15), microporous (silicalite) and non-porous (SiO₂) silicas in oxidative dehydrogenation of propane were investigated. The structure of vanadia species, the redox and the acidic properties of the catalysts were studied using in situ Raman spectroscopy, TPD- NH₃ and H₂-TPR. The only vanadia species detected on the surface of HMS and MCM-41 for V loadings up to 8 wt.% were isolated monovanadates indicating high vanadia dispersion. Additional bands ascribed to V₂O₅ nanoparticles were evidenced in the case of SBA-15 and MCF supported catalysts while these bands were the only ones identified on the surface of the catalysts supported on silicalite and non-porous silica. The catalysts supported on mesoporous HMS and MCM-41 materials showed the best performance achieving high propane conversions (35–40%) with relatively high propene selectivities (35–47%). Lower activity due to the lower degree of vanadia dispersion, caused by the partial destruction of the pore structure was observed for the SBA-15 and MCF supported catalysts. The degree of dispersion of the V species on the catalyst surface and not the pore size and structure of the mesoporous support or the acidity/reducibility characteristics mainly determine the catalytic activity towards propene production. In addition, it was shown that the pore structure and size of the mesoporous supports did not have any significant effect in the turnover rates (TOF values) of propane conversion (and propene formation at low propane conversion, below ca. 10%). However, the highest propene yield (up to 19%) and stable catalytic behavior was attained for catalysts supported on HMS mesoporous silica, and especially for those combining framework mesoporosity and textural porosity (voids between primary nanoparticles).     

Progesterone inclusion into cyclodextrin-functionalized mesoporous silica

SBA-15 type mesoporous silica has been modified to produce a covalent bond with β-cyclodextrin by two different synthetic approaches to obtain an hybrid system able to work as a drug delivery system for progesterone. In the first approach, SBA-15 silica was first let to react with 3-glycidyloxypropyltrimethoxysilane to produce an epoxide ring functional group on mesoporous silica. The latter was then reacted under basic conditions with mono-6-deoxy-6-mercapto-β-cyclodextrin (β-CDCH₂SH), prepared in its turn in two steps from β-cyclodextrin (β-CD) through monotosylation to give β-CDCH₂OTs followed by thiolation with thiourea. In the second approach, a silica suitably functionalized with a terminal thiol group (obtained by the reaction of SBA-15 silica with 3-mercaptopropyltrimethoxysilane) was reacted with β-CDCH₂OTs. The obtained materials were characterized by X-Ray powder diffraction, nitrogen adsorption, ¹³C Cross Polarization Magic Angle Spin Nuclear Magnetic Resonance (¹³C CP/MAS NMR). Progesterone was loaded on the materials producing complete filling of mesopores and cyclodextrin cavities. Its release was studied at different pH values. Only one of the two progesterone-loaded delivery device is able to retain the drug in the system during the first period at acid pH (2 h) and release it after pH increase.     

Functionalized Mesoporous SBA-15 with CeF<Subscript>3</Subscript>: Eu<Superscript>3+</Superscript> Nanoparticle by Three Different Methods: Synthesis,Characterization, and Photoluminescence

Luminescence functionalization of the ordered mesoporous SBA-15 silica is realized by depositing a CeF₃: Eu³⁺ phosphor layer on its surface (denoted as CeF₃: Eu³⁺/SBA-15/IS, CeF₃: Eu³⁺/SBA-15/SI and CeF₃: Eu³⁺/SBA-15/SS) using three different methods, which are reaction in situ (I-S), solution impregnation (S-I) and solid phase grinding synthesis (S-S), respectively. The structure, morphology, porosity, and optical properties of the materials are well characterized by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, N₂ adsorption, and photoluminescence spectra. These materials all have high surface area, uniformity in the mesostructure and crystallinity. As expected, the pore volume, surface area, and pore size of SBA-15 decrease in sequence after deposition of the CeF₃: Eu³⁺ nanophosphors. Furthermore, the efficient energy transfer in mesoporous material mainly occurs between the Ce³⁺ and the central Eu³⁺ ion. They show the characteristic emission of Ce³⁺ 5d → 4f (200–320 nm) and Eu^{3+ 5}D₀ → ⁷F _J (J = 1–4, with ⁵D₀ → ⁷F₁ orange emission at 588 nm as the strongest one) transitions, respectively. In addition, for comparison, the mesoporous material CeF₃: Eu³⁺/SBA-15/SS exhibits the characteristic emission of Eu³⁺ ion under UV irradiation with higher luminescence intensity than the other materials.     

Synthesis of hexagonal and cubic mesoporous silica using power plant bottom ash

An alkali fusion method was adopted to extract silicate species from coal bottom ash in a power plant and the supernatant solution was used for the synthesis of MCM-41, SBA-15, and SBA-16 mesoporous silica materials. The minor impurities present in the bottom ash were not found to be detrimental to the successful formation of mesoporous silica phases. Additional silica from sodium metasilicate was introduced to improve the textural properties for SBA-15 and SBA-16. According to SEM analyses, particle morphology of the samples gradually approaches those prepared using pure chemical as the amount of external silica source increases. XRD analyses confirmed well-ordered mesostructures in all of these silica materials. N₂ adsorption–desorption isotherms of MCM-41 prepared using bottom ash showed a type IV isotherm with a region of steep increase due to capillary condensation, whilst SBA-15 and SBA-16 showed type IV isotherm with H1 and H2 hysteresis loops, respectively. ²⁷Al MAS NMR analysis of MCM-41 synthesized from the supernatant solution reveals that the extracted Al species from bottom ash were tetrahedrally incorporated in the framework. TEM clearly showed the uniform pore structure of the materials prepared using the industrial waste.     

Application of Cs salt of 12-tungstophosphoric acid supported on SBA-15 mesoporous silica in NO x storage

Cs salt of 12-tungstophosphoric acid (HPW) was deposited simultaneously at the external surface of the SBA-15 silica microcrystals and inside its mesoporous channels at loading of 60 wt% and Cs/W ratio in the range between 0.9 and 2, followed by impregnation of 1 wt% Pt. The performance of the Pt/CsHPW/SBA-15 composite materials was tested in the NO _x storage. The optimal NO _x storage capacity and efficiency were achieved at Cs/W of 1.5. The dispersion of CsHPW on SBA-15 led to a significant decrease of its crystal size (5–13 nm) compared with bulk HPW and HPW supported on titania (28–29 nm). Pt/CsHPW/SBA-15 displayed lower NO _x absorption capacity but much higher absorption and desorption efficiency than the reference Pt/HPW and Pt/HPW/TiO₂ materials. Consequently, Pt/CsHPW/SBA-15 displayed a better performance in short lean (2 min)—rich (1 min) absorption-desorption cycles. The novel Pt/CsHPW/SBA-15 nanocomposites presents the basis for improved storage material for NO _x removal from lean exhaust gases in highly dynamic aftertreatment technologies.     

Synthesis of mesoporous SnO2 spheres via self-assembly and superior lithium storage properties

This paper firstly reported a simple route to prepare SnO₂ mesoporous spheres for lithium ion battery. Mesoporous SnO₂ spheres in range of 100–300 nm were prepared by primary reaction at 353 K for 30 min, and calcination process at 773 K, which could be scaled up for manufacturing. The nano-size effect of the small particle and the 3D mesoporous structure promoted the electrolyte and lithium ion transfer and suppressed the volume changes, which greatly enhanced the cycle performances. As the anode material, it could deliver 761 mAh g⁻¹ capacity after 50 cycles at the current density of 200 mA g⁻¹. Even at 2 A g⁻¹, it retained 480 mAh g⁻¹ after 50 cycles. Furthermore, we suggested that the high stability of the structure was responsible for the improved cycle properties.     

Novel low-κ polyimide/mesoporous silica composite films: Preparation,microstructure, and properties

A series of novel low-dielectric constant (low-κ) polyimide (PI) composite films containing the SBA-15 or the SBA-16-type mesoporous silica were successfully prepared via in situ polymerization and following thermal imidization. Their morphologies, dielectric constants, and thermal and dynamic mechanical properties were investigated. It is found that the dielectric constants of the composite films can be reduced from 3.34 of the pure PI to 2.73 and 2.61 by incorporating 3 wt% SBA-15 and 7 wt% SBA-16, respectively. The reduction of the dielectric constant is attributed to the incorporation of the air voids (κ = 1) stored within the mesoporous silica materials, the air volume existing in the gaps on the interfaces between the mesoporous silica and the PI matrix, and the free volume created by introducing large-sized domains. The PI/mesoporous silica composite films prepared in this study also present stable dielectric constants across the wide frequency range and a good phase interconnection. The improvement of the thermal stability and dynamic mechanical properties of the PI film is achieved by incorporation of the mesoporous silica materials. The enhanced interfacial interaction between the surface-treated mesoporous silica and the PI matrix has led to the minimization of the deterioration of the mechanical properties. The incorporation of the mesoporous silica materials is a promising approach to prepare the low-κ PI films.