Facile method to synthesize platelet SBA-15 silica with highly ordered large mesopores

Highly ordered mesoporous SBA-15 silica with large pore diameter of 18 nm (nominal BJH pore diameter ~22 nm) and short pore length (~500 nm) was synthesized using a micelle expander 1,3,5-triisopropylbenzene in the absence of ammonium fluoride by employing short initial stirring time at 17 °C followed by static aging at low temperature. Scanning and transmission electron microscopies revealed that the material comprised of platelet particles in which large mesopores were nearly flawlessly arranged within uniform domains up to 3 μm in size. The platelet SBA-15 had the (100) interplanar spacing of 17 nm, high surface area (~470 m(2) g(-1)) and large pore volume (~1.6 cm(3) g(-1)). The hydrothermal treatment at 130 °C for 2 days was employed to eliminate constrictions from the pore channels. The control experiment showed that a sample prepared with prolonged stirring had very similar mesoporous properties, but the particle size was smaller and the domains were irregular, proving that the static conditions facilitate the formation of SBA-15 with platelet particle morphology. The absence of ammonium fluoride was also critical in attaining the platelet particle shape.     

Evaluation of thermoporometry for characterization of mesoporous materials

The accuracy of thermoporometry (TPM) in terms of the characterization of SBA-15 is examined based on a model that classifies the water in the mesopores into two different types: freezable pore water, which can form cylindrical ice crystals, and nonfreezable pore water, which cannot undergo a phase transition during a differential scanning calorimetry (DSC) measurement. Applying the empirical relationship between the sizes of the ice crystals formed in the mesopores and the solidification temperature of the freezable pore water to a thermogram (a recording of the heat flux during the solidification of the freezable pore water) yielded a size distribution of the ice crystals. The size of the ice crystals increased slightly with repetitive freezing, indicating that the mesopores were enlarged by formation of the ice crystals. Adding the thickness, t(nf), of the nonfreezable pore water layer to the ice crystal-size distribution calculated from the thermogram allowed for the determination of the porous properties of SBA-15. The porous properties attained from TPM experiments were compared with the results attained through the combination of Ar gas adsorption experiments and nonlocal density functional theory (NLDFT) analysis. The porous properties determined by TPM were confirmed to be quite sensitive to the t(nf) value.     

Phase transitions of octamethylcyclotetrasiloxane confined inside aluminosilicate and silicate nanoporous matrices

We report the melting behaviour of a dipolar cyclic siloxane liquid: octamethylcyclotetrasiloxane (OMCTS) confined in three mesoporous silica matrices: Al-SBA-15, SBA-15 and CPG glasses, using differential scanning calorimetry and dielectric spectroscopy. We investigate the influence of acid sites on the adsorptive properties of mesoporous silica materials, which were synthesized by applying Pluronic-type polymers as pore-creating agents. Aluminosilicate matrices have been synthesized by direct synthesis procedure using aluminium chloride. These materials characterized by N₂ sorption measurements, and the small-angle X-ray scattering data exhibit the same hexagonal P6 mm structure with a mean mesopores size of 4.6 nm (Al-SBA-15) and 4.9 nm (SBA-15). The controlled pore glasses used in this experiment have pores of mean diameter of 7.5 nm. For all systems studied, the OMCTS melting point in pores has been found to decrease with decreasing pore diameter. This result is in qualitative agreement with that obtained in molecular simulation where the adsorbate-wall interactions are weak compared to the adsorbate–adsorbate interactions.     

利用ＳＢＡ-１５介孔内纳米碳合成含介孔的ＺＳＭ-５分子筛

SBA-15介孔分子筛内填充蔗糖并炭化后, 分别在碱性和弱酸性条件下, 用含铝源及TPABr的溶液浸渍,将SBA-15分子筛孔壁的无定形结构转化成ZSM-5分子筛的晶体结构, 除碳后得到含介孔的ZSM-5分子筛. 用X射线衍射、 N_2吸附-脱附、 ~(27)Al MAS NMR、 NH_3-TPD、 TEM、 SEM等对样品进行了表征, 考察了晶化时间等参数对样品的影响. 结果表明, 碱性条件下合成的ZSM-5分子筛晶体中含有少量孔径约3.2～4.2 nm的介孔孔道, 其酸强度接近与常规ZSM-5分子筛的酸强度;弱酸性条件下合成的ZSM-5分子筛晶体中含有大量孔径约1.4～1.6 nm的孔道, 其酸强度明显低于常规ZSM-5分子筛的酸强度.     

Aqueous dye adsorption on ordered mesoporous carbons

Ordered mesoporous carbons (OMCs) with varying pore size, and microporous carbon, CFY, were synthesized using ordered mesoporous silica SBA-15 and NaY zeolite as hard templates, respectively. N(2) adsorption tests show that the synthesized OMCs possess abundant mesopores and centralized mesopore distribution. Methylene blue (MB) and neutral red (NR) were used as probe molecules to investigate their adsorption behaviors on OMCs and CFY. As evidenced by adsorption tests, the volume of mesopores of which the pore size is larger than 3.5 nm is a crucial factor for the adsorption capacity and adsorption rate of MB on OMCs. However, the most probable pore diameter of OMCs was found to be vital to the adsorption capacity and adsorption rate of NR. Theoretical studies show that the adsorption kinetics of MB and NR on OMCs can be well depicted by using pseudo-second-order kinetic model.     

Iron oxide nanoparticles within the pore system of mesoporous SBA-15 in different acidity: the synthesis and characterization

Direct hydrothermal method is employed for incorporating iron into the pore structure of SBA-15. The resultant materials were analyzed by X-ray diffraction (XRD) patterns, N₂ sorption isotherm and X-ray photoelectron spectroscopy (XPS). The characterizations of XRD patterns and XPS revealed that iron nanoparticles were present as highly dispersed nanoclusters in the well-ordered mesoporous channels of SBA-15. The characterizations of t-plot reveal only microporous channels of SBA-15 are confirmed to be filled with iron nanoparticles, leaving the mesopores unaffected. The supported material still maintained its ordered mesoporous structure similar to SBA-15 and possessed high surface area, large pore volume and uniform pore size.     

Synthesis, structure and adsorption properties of nanoporous SBA-15 materials with framework and surface functionalities

Highly ordered SBA-15 nanoporous silica containing ethylene, phenylene bridges or/and amine, thiol, vinyl and phenyl surface groups were synthesized by using amphiphilic block copolymer as the structure-directing agent. The XRD data shows high degree of the order of the final structures. Obtained materials have well-developed porous structure—values of specific surface area are in the range 700–1050 m²/g and the sizes of cylindrical mesopores are in the range 6.5–9.5 nm. It was determined that size of the mesopores strongly depends even on small amounts of co-monomers co-condensing with TEOS. A new technique to introduce some amount of pendant amine groups by co-condensation of proper monomers has been proposed. Tetragonal structure was obtained when small amount of vinyl groups was introduced to the system. A new approach of determining pore size based only on the XRD measurements was compared with KJS method, confirming full usefulness of the former for calculation of the size of mesopores in SBA-15 materials. Dedicated to Professor Mietek Jaroniec on the occasion of his 60th birthday.     

Pore size tailoring in large-pore SBA-15 silica synthesized in the presence of hexane

Large-pore SBA-15 silicas were synthesized using poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymer Pluronic P123 as a template and hexane as a micelle expander. The reaction was initially carried out at 15 degrees C, followed by the heating of the synthesis gel at temperatures from 40 to 130 degrees C. Small-angle X-ray scattering data indicate that highly ordered two-dimensional hexagonal material (SBA-15 structure) formed at 15 degrees C and was preserved even after 5 days of heating at 130 degrees C. The unit-cell parameter for as-synthesized SBA-15 silicas was about 16.5 nm and increased only slightly after the heat treatment, whereas the unit-cell parameter after calcination was appreciably larger (16 vs 14 nm) for materials that were subjected to the thermal treatment. The pore size distribution of SBA-15 formed at 15 degrees C was narrow and centered at approximately 9.5 nm, which is close to the upper limit of pore diameters typically reported for SBA-15. The presence of constrictions in the pores of this material was evident. The heat treatment led to the elimination of the constrictions and to the pore diameter increase to 15 nm or more, tailored by the selection of appropriate treatment temperature and time. The pore size increase was the fastest during the first day of treatment, but it continued for at least 5 days. The pore size distribution broadened as the time of the treatment increased beyond 1 day. The pore size increase appears to be primarily related to the decrease in the degree of shrinkage during the calcination (removal of the template) and the decrease in the pore wall thickness.     

Mechanism of freezing of water in contact with mesoporous silicas MCM-41, SBA-15 and SBA-16: role of boundary water of pore outlets in freezing

The freezing mechanism of water contacted with mesoporous silicas with uniform pore shapes, both cylindrical and cagelike, was studied by thermodynamic and structural analyses with differential scanning calorimetry (DSC) and X-ray diffraction (XRD) together with adsorption measurements. In the DSC data extra exothermic peaks were found at around 230 K for water confined in SBA-15, in addition to that due to the freezing of pore water. These peaks are most likely to be ascribed to the freezing of water present over the micropore and/or mesopore outlets of coronas in SBA-15. Freezing of water confined in SBA-16 was systematically analysed by DSC with changing the pore size. The freezing temperature was found to be around 232 K, close to the homogeneous nucleation temperature of bulk water, independent of the pore size when the pore diameter (d) < 7.0 nm. Water confined in the cagelike pores of SBA-16 is probably surrounded by a water layer (boundary water) at the outlets of channels to interconnect the pores and of fine corona-like pores, which is similar to that present at the outlet of cylindrical pores in MCM-41 and of cylindrical channels in SBA-15. The presence of the boundary water would be a key for water in SBA-16 to freeze at the homogeneous nucleation temperature. This phenomenon is similar to those well known for water droplets in oil and water droplets of clouds in the sky. The XRD data showed that the cubic ice I(c) was formed in SBA-16 as previously found in SBA-15 when d < 8.0 nm.     

Improvement of the Kruk-Jaroniec-Sayari method for pore size analysis of ordered silicas with cylindrical mesopores

In this work, the X-ray diffraction structure modeling was employed for analysis of hexagonally ordered large-pore silicas, SBA-15, to determine their pore width independently of adsorption measurements. Nitrogen adsorption isotherms were used to evaluate the relative pressure of capillary condensation in cylindrical mesopores of these materials. This approach allowed us to extend the original Kruk-Jaroniec-Sayari (KJS) relation (Langmuir 1997, 13, 6267) between the pore width and capillary condensation pressure up to 10 nm instead of previously established range from 2 to 6.5 nm for a series of MCM-41 and to improve the KJS pore size analysis of large pore silicas.     

Effects of Morphology and Structural Characteristics of Ordered SBA-15 Mesoporous Silica on Release of Ibuprofen

Three kinds of highly ordered SBA-15 mesoporous materials with different pore sizes and morphologies denoted as LPS-SBA-15 (stick-like with pore size 7.28 nm), CPS-SBA-15 (stick-like with pore size 5.96 nm) and T-SBA-15 (tablet-like with pore size 4.64 nm) have been prepared, characterized and employed as carrier materials. The release behaviors of the ibuprofen in a simulated body fluid from these mesoporous silica materials were studied. The influences of pore size and exterior morphologies of mesoporous silica on the release behaviors of ibuprofen have been investigated. It has been found that the release becomes fast with increasing of pore size and slow with extending of transport pathway, and that the release rate of ibuprofen from the three kinds of SBA-15 is LPS-SBA-15 > T-SBA-15 > CPS-SBA-15. The results show that the inner structure as well as the exterior morphologies of SBA-15 mesoporous silica can seriously affect the release behaviors of ibuprofen.     

Understanding effect of wall structure on the hydrothermal stability of mesostructured silica SBA-15

Mesostructured silica SBA-15 materials with different structural parameters, such as pore size, pore volume, and wall thickness, etc., were prepared by varying the postsynthesis hydrothermal treatment temperature and adding inorganic salts. The hydrothermal stabilities of these materials in steam (100% water vapor) were systematically investigated using a variety of techniques including powder X-ray diffraction, transmission electron microscopy, nitrogen sorption, and (29)Si solid-state NMR. The effect of the pore size, microporosity or mesoporosity, and wall thickness on the stability was discussed. The results show that all of the SBA-15 materials have a good hydrothermal stability under steam of 600 degrees C for at least 24 h. N(2) sorption measurements show that the Brumauer-Emmett-Teller surface area of SBA-15 materials is decreased by about 62% after treatment under steam at 600 degrees C for 24 h. The materials with thicker walls and more micropores show relatively better hydrothermal stability in steam of 600 degrees C. Interestingly, we found that the microporosity of the mesostructured silica SBA-15 is a very important factor for the hydrothermal stability. To the materials with more micropores, the recombination of Si-O-Si bonds during the high-temperature steam treatment may not cause direct destruction to the wall structure. As a result, SBA-15 materials with more micropores show better stability in pure steam of 600 degrees C. Nevertheless, these materials are easily destroyed in steam of 800 degrees C for 6 h. Two methods to effectively improve the hydrothermal stability are introduced here: one is a high-temperature treatment, and another is a carbon-propping thermal treatment. Thermal treatment at 900 degrees C can enhance the polymerization degree of Si-O-Si bonds and effectively improve the hydrothermal stability of these SBA-15 materials in 800 degrees C steam for 12 h. But, this approach will cause very serious shrinkage of the mesopores, resulting in smaller pore diameter and low surface area. A carbon-propping thermal treating method was employed to enhance the polymerization of Si-O-Si bonds and minimize the serious shrinkage of mesopores at the same time. It was demonstrated to be an effective method that can greatly improve the hydrothermal stability of SBA-15 materials in 800 degrees C steam for 12 h. Furthermore, the SBA-15 materials obtained by using the carbon-propping method possess larger pores and higher surface area after the steam treatment at 800 degrees C compared to the materials from the direct thermal treatment method after the steam treatment.     

载体焙烧温度对Rh-Mn-Li/SBA-15催化CO加氢性能的影响

SBA-15分别于550、700、800和900℃进行焙烧,然后以等体积共浸渍法将Rh、Mn和Li负载其上。催化剂的性能用CO加氢反应进行评价。催化剂分别用N₂物理吸附、X射线衍射、透射电子显微镜、H₂化学吸附和傅里叶变换红外光谱进行表征。即使在900℃下进行焙烧,SBA-15的结构仍得到保持。但是,当焙烧温度从550℃升高到900℃,SBA-15的比表面积、孔径和总孔容分别从842.6 m²·g^-1、9.57 nm和1.18 cm³·g^-1降到246.4 m²·g^-1、5.62 nm和0.34 cm³·g^-1。此外,Rh颗粒的尺寸都在1.5-4.0 nm范围内,并且随着载体的焙烧温度增加而增加。另外,Rh颗粒更倾向位于高温焙烧载体的介孔内,这可能是因为经过高温焙烧,载体微孔下降。所以,H₂和CO更易与负载在高温焙烧后的载体上的Rh颗粒接触。因此,当载体焙烧温度达到900℃时,Rh-Mn-Li/SBA-15催化剂有非常高的C₂₊含氧化合物的活性和选择性。     

Large-pore mesoporous SBA-15 silica particles with submicrometer size as stationary phases for high-speed CEC separation

A new mesoporous sphere-like SBA-15 silica was synthesized and evaluated in terms of its suitability as stationary phases for CEC. The unique and attractive properties of the silica particle are its submicrometer particle size of 400 nm and highly ordered cylindrical mesopores with uniform pore size of 12 nm running along the same direction. The bare silica particles with submicrometer size have been successfully employed for the normal-phase electrochromatographic separation of polar compounds with high efficiency (e.g., 210,000 for thiourea), which is matched well with its submicrometer particle size. The Van Deemeter plot showed the hindrance to mass transfer because of the existence of pore structure. The lowest plate height of 2.0 microm was obtained at the linear velocity of 1.1 mm/s. On the other hand, because of the relatively high linear velocity (e.g., 4.0 mm/s) can be generated, high-speed separation of neutral compounds, anilines, and basic pharmaceuticals in CEC with C18-modified SBA-15 silica as stationary phases was achieved within 36, 60, and 34 s, respectively.     

Schiff碱改性法制备SBA-15型介孔分子筛负载的纳米氧化镍

基于Schiff碱功能单体的改性作用,采用共缩聚方法,制备了SBA-15型介孔分子筛负载的氧化镍纳米粒子。 采用小角X射线散射（small angle XRD）、广角X射线衍射（wide angle XRD）、紫外-可见光谱（UV-Vis）、高分辨透射电子显微镜（HRTEM）和N2吸附-脱附测定对制得的样品进行了表征。 结果表明,制得的样品具有SBA-15型介孔分子筛典型的二维六方有序结构,NiO纳米粒子主要分布于SBA-15型介孔分子筛的孔道内。 当功能单体的含量不超过10%时,SBA-15型介孔分子筛的孔径在6~8 nm范围内;而当功能单体的含量达到15%时,SBA-15型介孔分子筛的孔道被严重堵塞,孔径降为3.8 nm。 NiO纳米粒子的尺寸随着功能单体含量的增加而增大。     

Synthesis of stearic acid triethanolamine ester over solid acid catalysts

<正>The synthesis of stearic acid triethanolamine ester over solid acid catalysts was investigated.The results showed that the catalytic activity and selectivity of zirconium sulfate supported on SBA-15(6)(pore diameter 6 nm) is better than that of commonly used hypophosphorous acid,zirconium sulfate supported on MCM-41 and zirconium sulfate supported on SBA-15(9)(pore diameter 9 nm).     

Adsorption of bulky molecules of nonylphenol ethoxylate on ordered mesoporous carbons

Ordered mesoporous carbons (OMCs) with varying pore sizes were prepared using ordered mesoporous silica SBA-15 as hard templates. The OMCs possess abundant mesopores with narrow pore size distribution, on which the adsorption behavior of bulky molecules of nonylphenol ethoxylate (NPE) were investigated. The isotherms of NPE on OMCs can be fitted by Langmuir adsorption model, evidenced by the adsorption data. The surface area of the pores larger than 1.5 nm is a crucial factor to the adsorption capacity of NPE, whereas the most probable pore diameter of OMCs is crucial to the adsorption rate of NPE. The adsorption temperature has more significant effects on adsorption rate than the adsorption capacity. Theoretical studies show that the adsorption kinetics of NPE on OMCs can be depicted with the pseudo-second-order kinetic model. In addition, thermodynamic parameters of adsorption were evaluated based on the equilibrium constants related to the equilibrium of adsorption at different temperatures.     

Quantitative Distinction between Noble Metals Located in Mesopores from Those on the External Surface

We compare three methods for quantitatively distinguishing the location of noble metal (NM) particles in mesopores from those found on the external support surface. MCM-41 and SBA-15 with NM located in mesopores or on the external surface were prepared and characterized by TEM. ³¹P MAS NMR spectroscopy was used to quantify arylphosphines in complexes with NM. Phosphine/NM ratios drop from 2.0 to 0.2 when increasing the probe diameter from 1.08 to 1.54 nm. The reaction between NM and triphenylphosphine (TPP) within 3.0 nm MCM-41 pores takes due to confinement effects multiple weeks. In contrast, external NM react with TPP instantly. A promising method is filling the pores by using the pore volume impregnation technique with tetraethylorthosilicate (TEOS). TPP loading revealed that 66 % of NMs are located on the external surface of MCM-41. The pore filling method can be used in association with any probe molecule, also for the quantification of acid sites.     

纯硅介孔分子筛SBA-15表面的手性移植

聚环氧乙烯醚-聚环氧丙烯醚-聚环氧乙烯醚(EO20PO70EO20)三嵌段高分子为模板剂制备了SBA-15分子筛. 用3-氨丙基-三乙氧基硅烷对SBA-15进行改性, 改性后SBA-15表面上的氨基再与(+)-O,O'-二苯甲酰基-L-酒石酸酐(DBTA)进行酰化反应, 以酰胺键将该手性羧酸连接在SBA-15表面上. XRD和氮气吸附结果表明, 材料经过处理后仍然保持良好的孔性质; 13C和29Si魔角旋转核磁共振(MAS NMR)谱图表明, SBA-15与氨丙基化合物的作用是共价成键, 表面修饰度达25%; 从傅里叶变换红外(FTIR) 光谱可见, 有部分修饰氨基与DBTA成功地进行了酰化反应, 以一个羧基裸露的形式将该二元羧酸化合物连接在表面上; 从孔径分布图可知, 胺丙基修饰之后孔减小了1.5 nm, 与DBTA修饰后孔尺寸又减少0.5 nm, 说明胺丙基化合物是头对头垂直连接在Si表面上, 而酒石酸分子是采取平行方式侧卧在氨基表面.     

Pt-doped semiconductive oxides loaded on mesoporous SBA-15 for gas sensing

SBA-15-based solids combining semiconductive oxides (Sn and In) and noble metal (Pt) were prepared by an incipient wet impregnation method in order to obtain materials for gas sensing. The materials were characterized by XRD, BET adsorption, SEM, and TEM. The BET analysis allowed obtaining details about the specific surface areas, pore size, and modifications due to the indium and/or tin oxides followed by the Pt deposition. XRD data revealed that In₂O₃ did not enter the mesopores of SBA-15, preventing also the entrance of the Pt nanoparticles in the mesopores. On the other hand, SnO₂ nanoparticles further doped with Pt could enter the mesoporous network, affording a SBA-15 material loaded with SnO₂ and very small Pt nanoparticles with high dispersion. Tablets obtained by pressing the modified SBA-15 were tested as sensitive materials for propene and hydrogen detection.