Synthesis and characterization of hyperbranched mesoporous silica SBA-15

Branched mesoporous silica SBA-15 materials have been prepared in a simple process using non-ionic surfactant in acidic conditions in the presence of metal ions.     

Temperature-programmed microwave-assisted synthesis of SBA-15 ordered mesoporous silica

The currently available microwave technology permits the development and implementation of a temperature-programmed microwave-assisted synthesis (TPMS) of ordered mesoporous silicas (OMSs). Unlike in previously reported syntheses of OMSs, in which only the final hydrothermal treatment was carried out under microwave irradiation, this work takes advantage of the existing capabilities of modern microwave systems to program the temperature and time for the entire synthesis of these materials. To demonstrate the flexibility of the proposed microwave-assisted synthesis, besides programming two consecutive steps involving initial stirring of the gel at a lower temperature and static hydrothermal treatment at a higher temperature, we explored the possibility of temperature programming of the latter step. A major advantage of microwave technology is the feasibility of temperature and time programming, which has been demonstrated by the synthesis of one of the most popular OMSs, SBA-15, over an unprecedented range of temperatures from 40 to 200 degrees C. Since the synthesis of OMSs has not yet been explored and reported at temperatures exceeding 150 degrees C, this work is focused on the SBA-15 samples prepared at higher temperatures (such as 160, 180, and even 200 degrees C). These SBA-15 samples show better thermal stability than those synthesized at commonly used temperatures either under conventional or microwave conditions. Moreover, a partial decomposition of the template during high-temperature microwave-assisted syntheses does not compromise the formation of well-ordered SBA-15 materials. This study shows that the simplicity and capability of temperature and time programming in TPMS allows one not only to tune the adsorption and structural properties of OMSs but also to easily screen a wide range of conditions in order to optimize and scale-up their preparation as well as to significantly reduce the time of synthesis from days to hours.     

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.     

Adsorption of C7 hydrocarbons on biporous SBA-15 mesoporous silica

In our recent studies (Vinh-Thang, H.; Huang, Q.; Eic, M.; Trong-On, D.; Kaliaguine, S. Langmuir 2005, 21, 2051-2057; Vinh-Thang, H.; Huang, Q.; Eic, M.; Trong-On, D.; Kaliaguine, S. Stud. Surf. Sci. Catal. 2005, in press), a series of synthesized SBA-15 materials were characterized using nitrogen adsorption/desorption isotherms at 77 K and SEM images. In the present paper, four of them (MMS-1-RT, MMS-1-60, MMS-1-80, and MMS-5-80) were further investigated with regard to their equilibrium characteristics using n-heptane and toluene as sorbates by the standard gravimetric technique. SBA-15 materials proved to have a broad pore size distribution within the micropore/small-mesopore range in the walls of their main mesoporous channels. The adsorption capacities for toluene were found to be higher than for n-heptane. The isosteric heats of adsorption, estimated by the Clausius-Clapeyron equation, are also higher for toluene compared to n-heptane. They were found to depend on framework microporosity of the relevant SBA-15 samples. The isosteric heats of adsorption for all sorbates decrease with increased loading and approach the heats of evaporation of the respective sorbate. The adsorption capacities of SBA-15 samples are significantly higher than those of silicalite, i.e., the MFI zeolite silica analogue. In contrast to that, the isosteric heats of adsorption in the mesopore channels of SBA-15 were found to be much smaller. This result also suggests that SBA-15 can potentially be a good candidate for separation of C(7) hydrocarbons.     

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.     

Formation of indium nitride nanorods within mesoporous silica SBA-15

We report the first formation of arrays of InN nanorods inside the nanoscale channels of mesoporous silica SBA-15. In(NO3)3 dissolved in methanol was incorporated into SBA-15 powder without prior pore surface functionalization. Formation of InN nanorod arrays was carried out by ammonolysis at 700 degrees C for 8 h. The final products have been characterized by FT-IR spectra, (29)Si MAS NMR spectra, Raman spectra, XRD patterns, TEM images, nitrogen adsorption-desorption isotherm measurements, and optical spectroscopy. The freestanding InN nanorods observed after silica framework removal with HF solution show diameters of 6-7.5 nm and lengths of 25-50 nm. Formation of a trace amount of In2O3 was also verified. The InN nanorods exhibit a broad band centered at around 550-600 nm, and a band gap energy of 1.5 eV was determined. No light absorption in the near-IR region was measured. The nanorods give a weak emission band centered at around 600 nm. These optical properties are believed to be related to the possible incorporation of oxygen during InN nanorod synthesis.     

Synthesis and characterization of large-pore vinyl-functionalized mesoporous silica SBA-15

Ordered mesoporous silicas SBA-15 with high loadings of pendant vinyl groups have been synthesized via co-condensation of tetraethoxysilane (TEOS) and triethoxyvinylsilane (TEVS) templated with a triblock copolymer.     

Iron-modified mesoporous SBA-15 silica: Preparation and characterization studies

Fe-SBA-15 materials with different Si/Fe ratios (Si/Fe = 100, 60, 15) have been synthesized by hydrothermal method and characterized by several spectroscopic techniques. Electron spin resonance and Mössbauer spectroscopy, along with electron microscopy and X-ray diffraction, allowed differentiation of several iron species. These species correspond to hematite particles, very small “isolated” or oligomeric Fe^III species possibly incorporated in the mesoporous silica wall, and Fe^III oxide clusters either isolated or agglomerated, forming “rafts” at the surface of the silica and exhibiting ferromagnetic ordering. Because of their agglomeration, these clusters appear with a two-peak size distribution, with one peak corresponding to the isolated clusters formed in the mesopores and still embedded in them and the other corresponding to the agglomerates spread on the surface of the mesoporous silica particles.     

Enhanced release of itraconazole from ordered mesoporous SBA-15 silica materials

This in vitro study reports on the enhanced release of the hydrophobic drug itraconazole from the ordered mesoporous SBA-15 silica material and on the existence of a critical mesopore diameter for enhancing release.     

Amino-functionalized SBA-15 type mesoporous silica having nanostructured hexagonal platelet morphology

Amino-functionalized SBA-15 type mesoporous silicas having unique hexagonal platelet morphologies with short channels (100-300 nm) running parallel to the thickness of the nanostructured hexagonal platelet type morphologies have been directly synthesized by co-condensation of aminopropyltriethoxysilane (APTES) and sodium metasilicate as a silica source in the presence of Pluronic P123 triblock copolymer as a structure directing agent.     

Direct synthesis of plugged SBA-15 type mesoporous silica using alcoholamines

Plugged mesoporous SBA-15 having a 2-D hexagonal pore structure could be directly synthesized under acidic conditions using P123 as a supramolecular template, sodium metasilicate and alcoholamines. The use of alcoholamines seemed to play roles as capturing agents for silica sources that could form internal porous plugs.     

Formation of arrays of gallium nitride nanorods within mesoporous silica SBA-15

We report the first formation of arrays of GaN nanorods inside the nanoscale channels of mesoporous silica SBA-15. GaCl3 dissolved in toluene was incorporated into the methyl group-functionalized SBA-15 powder. The pore surfaces functionalized with methyl groups should facilitate the impregnation with GaCl3. Formation of GaN nanorod arrays within SBA-15 was carried out by heating the powder to 700 degrees C for 3 h under nitrogen atmosphere, followed by ammonolysis at 900 degrees C for 5 h. epsilon-Ga2O3, an unusual phase for Ga2O3, formed after the first thermal process and was converted into wurtzite GaN during ammonolysis. The final products have been characterized by FT-IR spectra, powder XRD patterns, TEM images and SAED patterns, EDS analysis, and nitrogen adsorption-desorption isotherm measurements to confirm the presence of GaN nanostructures. The nanorods are 6-7.5 nm in diameter, and can be a few hundreds of a nanometer in length to exhibit nanowire structure. Free-standing GaN nanorod arrays were revealed upon removal of the silica framework with HF solution. Optical characterization of the isolated GaN nanorod arrays shows a strong and sharp near band-edge emission at 375 nm, and two phonon-assisted donor-acceptor peaks at 395 and 415 nm. A broad but weak emission in the region of 335-360 nm due to the quantum confinement effect of short nanorods was observed.     

Schiff-base-functionalized mesoporous silica SBA-15: Covalently bonded assembly of blue nanophosphors

Two kinds of Schiff-base-functionalized organic–inorganic mesoporous luminescent hybrid materials have been obtained by co-condensation of tetraethyl orthosilicate and the organosilane in the presence of Pluronic P123 surfactant as a template. N,N′-Bis(salicylidene)-1,3-propanediamine (BSPA) and N,N′,N″-tris(salicylidene)-(2-aminoethyl) amine (TSAEA), possessing two different representative structures, were firstly prepared and then functionalized with trialkoxylsilyl groups through the hydrogen transfer reactions between the active hydroxyl groups of the Schiff-base compounds and the internal ester group of isocyanate in 3-(triethoxysilyl)-propyl isocyanate (TESPIC). Schiff-base grafted to the coupling agent 3-(triethoxysilyl)-propyl isocyanate (TESPIC) was used as the precursor for the preparation of mesoporous materials. The luminescence properties of these resulting materials were characterized in detail, and the results reveal that they all have high surface area, uniformity in the mesostructure. The resulting materials (BSPA–SBA-15 and TSAEA–SBA-15) exhibit regular uniform microstructures and no phase separation happened because the organic and the inorganic compounds were covalently linked through Si–O bonds via a self-assembly process. Furthermore, these two materials have the similar luminescence range in the blue range.     

亚微米中孔SBA-15 棒状固定相在毛细管电色谱分离中的应用(英文)

采用中孔SBA-15棒状硅胶颗粒填充毛细管柱用于毛细管电色谱(CEC)分离。这一亚微米材料直径为400 nm并具有沿相同方向伸展的高度有序、均一的圆柱形中孔。棒状的特殊形态使得填充柱的通透性良好,简化了尺寸微小的CEC柱的填充过程。修饰后的棒状SBA-15填充毛细管柱成功应用于反相和离子交换电色谱分离非极性和极性样品,获得了较高柱效(140000理论塔板/m)。流速3.2cm/min时获得最低理论塔板高度为7.1 mm。范迪米特曲线说明了SBA-15孔结构的传质阻力特征。分别以芳香酸、人参、天麻提取物为样品,对亚微米固定相毛细管电色谱柱加以评价。该固定相显示出了较高的分离能力,为纳米材料在色谱固定相中的应用提供了一个新的思路。     

Retention of heavy metal ions on SBA-15 mesoporous silica functionalised with carboxylic groups

Three samples of SBA-15 functionalised with -(CH(2))(3)COOH groups have been prepared by co-condensation, starting from solutions of TEOS and 4-(triethoxysilyl)butyronitrile, acting as -(CH(2))(3)COOH precursor, of different molar compositions. Materials were characterised by X-ray diffraction, nitrogen adsorption, and FT-IR spectroscopy. The pK(a) and the acidic capacity were measured for all samples by potentiometric titration. The acidic capacity increases with increasing amount of -COOH precursor in the synthesis mixture only up to 10% molar of total alkoxysilane. The value for the pK(a)(4.75) is independent of the acidic capacity of the material. The sample prepared starting from an amount of -COOH precursor equal to 10% molar of total alkoxysilane was chosen to test selective interactions with heavy metals of environmental importance (Ag(+), Cd(2+), Fe(3+), Cu(2+), Zn(2+)) at different pH values and ionic strengths. The significant and selective adsorption exhibited by the material has been exploited in a preliminary cation-exchange chromatographic application showing the possibility of eluting the metal ions at different retention times.