Formation of titanium nitride nanoparticles within mesoporous silica SBA-15

We report the first synthesis of titanium nitride (TiN) nanoparticles inside the nanoscale channels of mesoporous silica SBA-15. The TiN precursor, Ti(NMe(2))(4) in toluene, was incorporated into the methyl group-modified channels of the SBA-15 powder. The functionalization of pore surfaces with methyl groups generates hydrophobic surfaces that facilitate impregnation with Ti(NMe(2))(4) and minimizes reactions between the TiN precursor and the hydroxyl groups on the surface of SBA-15. Formation of TiN nanoparticles inside the mesoporous channels of SBA-15 was carried out by subsequent ammonolysis at high temperatures (700-750 degrees C). The final products have been characterized by TEM and EELS images, powder XRD patterns, FTIR spectra, UV-vis absorption spectra, and nitrogen adsorption isotherm measurements to confirm the presence and distribution of TiN nanoparticles in the SBA-15 samples.     

Synthesis of Cu nanoparticles in mesoporous silica SBA-15 functionalized with carboxylic acid groups

In this study, the mesoporous silica SBA-15 materials containing carboxylic acid groups were used as an effective support to synthesize Cu nanoparticles. Various Cu loading levels from 4% to 13% on SBA-15 catalysts produced an average particle size of 2.8 to 3.1 nm, regardless of the Cu content.     

Vanadium silicalite-1 nanoparticles deposition onto the mesoporous walls of SBA-15. Mechanistic insights from a combined EPR and Raman study

Continuous Wave (CW) and pulsed Electron Paramagnetic Resonance (EPR) spectroscopy in conjunction with Raman spectroscopy are used to investigate the properties of Vanadium Silicalite-1 (VS-1) nanoparticles dispersed onto the mesoporous walls of SBA-15 silica. The properties of the deposited zeolite nanoparticles are found to be remarkably different from those of the full grown VS-1 zeolite. Monitoring of the local VO(2+) environment in the noncalcined nanoparticles in SBA-15 reveals that, in contrast to the full grown zeolite case, these sites are highly hydrophilic. Also, the stability of the TPAOH template is found to be affected by acidification of the nanoparticles. These results promise to be of great importance in elucidating the formation mechanism of TPAOH-templated zeolitic nanoparticles and their incorporation in mesoporous silica materials.     

Assembly of heteropoly acid nanoparticles in SBA-15 and its performance as an acid catalyst

Keggin‐type 12‐tungstophosphoric acid (TPA) nanocrystals have been assembled inside the pores of mesoporous silica through a vacuum impregnation method by using large‐pore SBA‐15 as a nanoreactor. The product was characterized by Brunauer–Emmet–Teller particle size distribution (BET‐PSD), NMR and FT‐IR spectroscopy, X‐ray diffraction (XRD), tranmsission electron microscopy (TEM), differential thermal analysis (DTA) and FT‐IR of adsorbed pyridine. The experimental results illustrate that the TPA nanocrystals are excellent Brønsted acid catalytic materials at room temperature.     

Au-Cu Alloy nanoparticles confined in SBA-15 as a highly efficient catalyst for CO oxidation

Au-Cu Alloy nanoparticles with sizes of approximately 3 nm were prepared in the confined space of SBA-15 and showed much better performance than monometallic particles in catalyzing CO oxidation even with the rich presence of H(2).     

Controlled synthesis of highly dispersed TiO2 nanoparticles using SBA-15 as hard template

Highly dispersed TiO2 nanoparticles were successfully synthesized by a wet impregnation method using SBA-15 as hard template for confining the growth of TiO2 nanocrystals, and then calcined at 550 degrees C in muffle furnace for 2 h. The as-synthesized samples were characterized with Fourier transform infrared spectra (FTIR), Raman spectroscopy, diffuse reflectance UV-visible spectroscopy (UV-vis), powder X-ray diffraction (XRD), small-angle X-ray diffraction (SAXRD), nitrogen adsorption, transmission electron microscopy (TEM) and photoluminescence spectra (PL). It was found that SBA-15 contained abundant silanol groups after removal of triblock copolymers by ethanol extraction and could easily adsorb a great number of titanium alkoxide via chemisorption. After subsequent hydrolysis of the anchored Ti complexes and calcination of the amorphous TiO2, anatase TiO2 nanocrystals with spherical shape and uniform particle diameter of about 6 nm were formed. A blue shift was observed in UV-vis absorption spectra due to the quantum size effect of TiO2 nanoparticles. Moreover, the as-prepared TiO2 nanoparticles showed a high PL intensity due to an increase in the recombination rate of photogenerated electrons and holes under UV light irradiation.     

Iron oxide nanoparticles supported on NH2- and COOH-functionalized SBA-15

Iron modified NH₂- or COOH- functionalized SBA-15 is characterized by XRD, N₂-physisorption, TPR-TG, FTIR, M?ssbauer spectroscopy and methanol decomposition. The material obtained from COOH-functionalized silica exhibits the highest catalytic activity.     

A 3D-TEM study of the shape of mesopores in SBA-15 and modified SBA-15 materials

The mesopores in SBA-15 are curved on a mesoscopic length scale and even more so in the case of modified SBA-15, which implies that using the particle size of these types of materials in diffusion studies may strongly underestimate the path length relevant for intraparticle diffusion.     

Structure sensitivity of vibrational spectra of mesoporous silica SBA-15 and Pt/SBA-15

The vibrational properties of mesoporous silica (SBA-15) were investigated by deep ultraviolet (UV) Raman and infrared spectroscopies with and without the presence of platinum nanoparticles in the mesopores that were incorporated by sonication. Raman and IR spectral line assignments were made by comparison to amorphous silicas. This procedure permitted identification of vibrations of longitudinal (LO) and transverse (TO) optical lattice modes, the presence of Si-OH, and vibrational modes associated with the presence of three-, four-, and six-membered siloxane rings. Hydraulic pressing of the mesoporous silica with pressure in the range 3-7 tons cm(-2) destroys the X-ray diffraction pattern and strongly decreases the Raman peak (D2) associated with three-membered rings at the surface. In the presence of platinum nanoparticles in the silica mesopores, a peak attributed to a Pt-O stretching vibration appears at between 530 and 580 cm(-1) in the UV-Raman spectrum, which can be used to monitor the presence of the platinum particles and their interaction with the support. The D2 feature in the UV-Raman spectra also decreases with increasing Pt loading, which is attributed to interactions of the Pt nanoparticles with the silica surface.     

SBA-15 silicas containing sucrose

Mesoporous silicas were synthesized by condensation of tetraethoxysilane (TEOS) in the presence of Pluronic P123 as a structure-forming agent, and sucrose as an auxiliary agent, to investigate the effect of sucrose and aging temperature on the final properties, particularly structure-adsorption characteristics. Obtained materials have been characterized by XRD, nitrogen sorption measurements SEM-EDX, TEM, thermogravimetry, and FT-IR. The obtained materials have well-developed porous structure??values of the specific surface area (S _BET) are in the range of 300?C950?m²/g and the sizes of primary mesopores are in the range of 9?C11?nm. It was established that S _BET and ordering significantly decreases with an increasing content of sucrose in the initial mixture.     

Strategic synthesis of SBA-15 nanorods

A simple synthesis of homogeneously sized, ordered mesoporous silica nanorods (SBA-15), spanning about 10 porous channels in width and ranging from 300 to 600 nm in length is reported.     

Physicochemical properties of Ti-grafted SBA-15

Partial oxidation of n-heptane to syngas at 400–450°C was investigated over Rh and Rh-Ni based catalysts. The Rh/-Al₂O₃ catalyst exhibited much better catalytic activity than the Rh-Ni/-Al₂O₃ catalyst. A combination of the Rh-based catalyst with the WGS reaction catalyst (Fe₃O₄—Cr₂O₃) increases the hydrogen selectivity but has no distinct effect on shifting the balance of the partial oxidation of n-heptane.This revised version was published online in December 2005 with corrections to the Cover Date.     

Mechanism for the formation of tin oxide nanoparticles and nanowires inside the mesopores of SBA-15

The formation of polycrystalline tin oxide nanoparticles (NP) and nanowires was investigated using nanocasting approach included solid-liquid strategy for insertion of SnCl₂ precursor and SBA-15 silica as a hard template. HR-TEM and XRD revealed that during the thermal treatment in air 5 nm tin oxide NP with well defined Cassiterite structure were formed inside the SBA-15 matrix mesopores at 250 °C. After air calcination at 700 °C the NP assembled inside the SBA-15 mesopores as polycrystalline nanorods with different orientation of atomic layers in jointed nanocrystals. It was found that the structure silanols of silica matrix play a vital role in creating the tin oxide NP at low temperature. The pure tin chloride heated in air at 250 °C did not react with oxygen to yield tin oxide. Tin oxide NP were also formed during the thermal treatment of the tin chloride loaded SBA-15 in helium atmosphere at 250 °C. Hence, it is well evident that silanols present in the silica matrix not only increase the wetting of tin chloride over the surface of SBA-15 favoring its penetration to the matrix pores, but also react with hydrated tin chloride according to the proposed scheme to give tin oxide inside the mesopores. It was confirmed by XRD, N₂-adsorption, TGA-DSC and FTIR spectra. This phenomenon was further corroborated by detecting the inhibition of SnO₂ NP formation at 250 °C after inserting the tin precursor to SBA-15 with reduced silanols concentration partially grafted with tin chloride.     

Synthesis and characterization of SBA-3, SBA-15, and SBA-1 nanostructured catalytic materials

A highly ordered large pore mesoporous silica molecular sieve SBA-3, SBA-15, Al-SBA-15, and SBA-1, were developed and characterized by XRD, BET, FTIR, SEM, and NMR-MAS. The catalytic materials were synthesized using different raw materials and operation conditions. These materials contain a regular arrangement of uniform channels with diameters between 1.8 and 10 nm, high specific surface area and high specific pore volume. The designed methods were effective for the synthesis, presenting each mesostructured materials, patterns of XRD and other characteristics corresponding to the reported ones in literature. The new route employed to synthesize Al-SBA-15, generates a catalyst with only aluminum in tetrahedral form, according to the data of (27)Al NMR-MAS. However, several reports indicated that the coordination of the Al atoms changes below the Si/Al ratio of 45, presenting peaks corresponding to penta and hexa-coordinated aluminum, which are absent in our samples (Si/Al = 50 and 33).     

Sonosynthesis of spiroindolines using functionalized SBA-15

Functionalized SBA-15 (immobilization of Pd on the modified SBA-15) has been used as an efficient catalyst for the preparation of spiroindolines by multi-component reactions of isatins, cyclic-1,3-diketones, and 6-amino-1,3-dimethyluracil under ultrasonic irradiation in water. The catalyst has been characterized by X-ray diffraction spectroscopy (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), N₂ adsorption analysis, temperature-programmed desorption (TPD), and thermogravimetric analysis (TGA). The advantages of this method include the reusability of the catalyst, low catalyst loading, excellent yields in short reaction times and easy separation of products, and use of ultrasonic irradiation as a valuable and powerful technology.

     

Synthesis monitoring of SBA-15 nanostructured materials

The SBA-15 materials were synthesized by the hydrothermal method using tetraethyl orthosilicate as silica source and P123 as template agent. The synthesis process was accomplished varying the time during the hydrothermal processing. For the synthesis monitoring, a small amount of sample was removed at different times, and analyzed by thermal analysis in order to determine the temperature ranges related to water desorption, template decomposition and silanol condensation for the SBA-15 nanostructured materials, as well as to estimate their quality. The samples were characterized by X-ray diffraction, infrared absorption spectroscopy, scanning electron microscopy, BET surface area and pore size distribution. The activation energy relative to decomposition of P123 template was determined from TG curves, using multiple heating rates and applying the model free kinetics. From the obtained data, it is possible to monitor the hydrothermal synthesis of SBA-15 in order to control the properties and conditions to prepare ordered materials.     

Investigation of the morphology of the mesoporous SBA-16 and SBA-15 materials

Mesoporous SBA-16 and SBA-15 were studied in order to control their possible morphologies. SBA-16 is synthesized using a silicon source (tetraethoxysilane, TEOS) and a ternary system consisting of surfactant F127 (EO106PO70EO106), water, and butanol. The same ternary system, with higher butanol concentration, is used to form SBA-15 material as well. An increase of the TEOS concentration results in a morphology shift of SBA-16 from micron-sized spheres, over randomly shaped aggregated particles, to macrospheres with a size of 15 mm. An identical increase in TEOS concentration also results in the formation of SBA-15 macrospheres, which can be controlled in size. Micron-sized spheres of SBA-15 were formed using a quaternary system of surfactant P123 (EO20PO70EO20), cetyltrimethylammonium bromide (CTAB), ethanol, and water. All mesoporous silica materials were characterized using SEM, XRD, and N2 sorption techniques.     

SBA-15介孔分子筛的乙基化修饰

20世纪90年代初,美孚公司的研究者们用烷基季铵盐阳离子表面活性剂作模板剂,在碱性条件下合成出M41S系列介孔分子筛。近几年,合成出了MCM,HMS,MSU、SBA等硅基分子筛系列。由于介孔材料表面有许多端羟基,可用来固定活性基团,使其在吸附、分离、催化和主客体化学等方面具有广泛的潜在应用价值。对介孔材料孔道进行有机改性的无机-有机复合材料的研究正在兴起,本文采用分步合成法,以乙基三乙氧基硅烷为偶联剂,