Thermogravimetry applied to characterization of SBA-15 nanostructured material

Nanoporous silica with narrow pore size distribution has attracted increasing attention as a novel material for separations and reactions involving large molecules. SBA-15 has been synthesized in an acidic medium using a triblock copolymer as template. In this work, the SBA-15 was synthesized by the hydrothermal treatment at 373 K for 48 h, of a gel with the following overall molar composition: 1.0TEOS:0.017P123:5.7HCl:193H₂O, where TEOS is tetraethyl orthosilicate and P123 is poly(ethylene oxide, propylene oxide and 1,4-dioxane). The obtained material was characterized by thermogravimetry, X-ray diffraction, infrared spectroscopy and BET surface area. A kinetic study using the model free model was accomplished in the stage of decomposition of the template (P123). The obtained value of the apparent activation energy was ca. 131 kJ mol^–1.     

Ag/SBA-15表面催化过程的现场SERS研究

以三嵌段共聚物P₁₂₃为模板剂, 正硅酸乙酯为硅源, 水热合成了介孔分子筛SBA-15, 通过对SBA-15内外表面修饰, 使用银氨溶液和硝酸银溶液作为金属源合成Ag/SBA-15, 透射电镜(TEM)研究表明在SBA-15孔道内较好地分散了颗粒状和棒状的Ag纳米粒子. 以苯硫酚作为探针分子, 研究了负载Ag纳米粒子的SBA-15的SERS效应, 结果表明Ag/SBA-15具有良好的SERS活性. 另外, 该材料对催化硼氢化钠还原对硝基苯酚具有良好的催化效果, 通过结合现场SERS技术, 研究了该催化过程的机理.     

Synthesis and characterization of surface modified SBA-15 silica materials and their application in chromatography

Hexagonally ordered SBA-15 mesoporous silica spheres with large uniform pore diameters are obtained using the triblock copolymer, Pluronic P123, as template with a cosurfactant cetyltrimethylammonium bromide (CTAB) and the cosolvent ethanol in acidic media. A series of surface modified SBA-15 silica materials is prepared in the present work using mono- and trifunctional alkyl chains of various lengths which improves the hydrothermal and mechanical stability. Several techniques, such as element analysis, nitrogen sorption analysis, small angle X-ray diffraction, scanning electron microscopy (SEM), FTIR, solid-state (29)Si and (13)C NMR spectroscopy are employed to characterize the SBA-15 materials before and after surface modification with the organic components. Nitrogen sorption analysis is performed to calculate specific surface area, pore volume and pore size distribution. By surface modification with organic groups, the mesoporous SBA-15 silica spheres are potential materials for stationary phases in HPLC separation of small aromatic molecules and biomolecules. The HPLC performance of the present SBA-15 samples is therefore tested by means of a suitable test mixture.     

Adsorption and structural properties of channel-like and cage-like organosilicas

Channel-like and cage-like mesoporous silicas, SBA-15 (P6mm symmetry group) and SBA-16 (Im3m symmetry group), were modified by introducing single ureidopropyl surface groups, mixed ureidopropyl and mercaptopropyl surface groups, and single bis(propyl)disulfide bridging groups. These hexagonal and cubic organosilicas were prepared under acidic conditions via co-condensation of tetraethyl orthosilicate (TEOS) and proper organosilanes using poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) amphiphilic block copolymer templates, P123 (EO₂₀PO₇₀EO₂₀) and F127 (EO₁₀₆PO₇₀EO₁₀₆). The modified SBA-15 and SBA-16 materials were synthesized by varying the molar ratio of organosilane to TEOS in the initial synthesis gel. The removal of polymeric templates, P123 and F127, was performed with ethanol/hydrochloric acid solution. In the case of SBA-15 the P123 template was fully extracted, whereas this extraction process was less efficient for the removal of F127 template from the SBA-16-type organosilicas; in the latter case a small residue of F127 was retained. The adsorption and structural properties of the resulting materials were studied by nitrogen adsorption-desorption isotherms at −196^∘C (surface area, pore size distribution, pore volumes), powder X-Ray diffraction, CHNS elemental analysis and high-resolution thermogravimetry. The structural ordering, the BET specific surface area, pore volume and pore size decreased for both channel-like and cage-like mesoporous organosilicas with increasing concentration of incorporated organic groups.     

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.     

Synthesis, characterization, and luminescence properties of the ternary europium complex covalently bonded to mesoporous SBA-15

A novel mesoporous SBA-15 type of hybrid material (phen-SBA-15) covalently bonded with 1,10-phenanthroline (phen) ligand was synthesized by co-condensation of tetraethoxysilane (TEOS) and the chelate ligand 5-[N,N-bis-3-(triethoxysilyl)propyl]ureyl-1,10-phenanthroline (phen-Si) in the presence of Pluronic P123 surfactant as a template. The preservation of the chelate ligand structure during the hydrothermal synthesis and the surfactant extraction process was confirmed by Fourier transform infrared (FTIR) and (29)Si MAS NMR spectroscopies. SBA-15 consisting of the highly luminescent ternary complex Eu(TTA)(3)phen (TTA = 2-thenoyltrifluoroacetone) covalently bonded to a silica-based network, which was designated as Eu(TTA)(3)phen-SBA-15, was obtained by introducing the Eu(TTA)(3).2H(2)O complex into the hybrid materials via a ligand exchange reaction. XRD, TEM, and N(2) adsorption measurements were employed to characterize the mesostructure of Eu(TTA)(3)phen-SBA-15. For comparison, SBA-15 doped with Eu(TTA)(3).2H(2)O and Eu(TTA)(3)phen complexes and SBA-15 covalently bonded with a binary europium complex with phen ligand were also synthesized, and were named SBA-15/Eu(TTA)(3), SBA-15/Eu(TTA)(3)phen, and Eu-phen-SBA-15, respectively. The detailed luminescence studies on all the materials showed that, compared with the doping sample SBA-15/Eu(TTA)(3)phen and binary europium complex functionalized sample Eu-phen-SBA-15, the Eu(TTA)(3)phen-SBA-15 mesoporous hybrid material exhibited higher luminescence intensity and emission quantum efficiency. Thermogravimetric analysis on Eu(TTA)(3)phen-SBA-15 demonstrated that the thermal stability of the lanthanide complex was evidently improved as it was covalently bonded to the mesoporous SBA-15 matrix.     

HCl对有序介孔氧化硅结构与形貌的影响

以三嵌段共聚物P123为有机模板导向剂、正硅酸乙酯TEOS为无机硅源, 在HCl存在的强酸性环境下, 采用水热法合成了有序介孔分子筛SBA-15. 采用XRD、SEM、TEM、N2吸附-脱附等手段对产物的结构与形貌进行了分析, 考察了HCl用量对有序介孔材料结构及形貌的影响. 结果表明, 在合成有序介孔氧化硅时, HCl发挥了催化和中间离子的双重作用, 促使棒状胶束形成六方有序排列, 降低SBA-15中微孔的数量, 而且对合成有序介孔氧化硅SBA-15的形貌有显著影响. 适宜的HCl用量对形成“珍珠链状”形貌的、热稳定性优良的SBA-15介孔材料具有重要作用.     

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.     

SBA-15负载CeO2纳米晶的溶胶-凝胶一步合成

以P123为模板剂, 正硅酸乙酯和硝酸铈为前驱体, 通过溶胶-凝胶路线在酸性条件下合成了SBA-15负载氧化铈(CeO2与SiO2质量比为28.7%)有序介孔材料. 采用热重/差热分析(TGA/DTA)、X射线衍射(XRD)、透射电镜(TEM)和氮气吸附等手段对所合成材料进行了表征. 结果表明, 合成的材料具有类似于SBA-15的结构, 孔径、孔容和比表面积分别为38.7 Å, 0.46 cm3/g和570 m2/g. X射线衍射(XRD)、透射电镜(TEM)、X射线能谱(EDS)和选区电子衍射花样联合表征证实了铈物种以高分散的CeO2纳米晶的形式分布在介孔基体中.     

表面含磺酸基的介孔分子筛催化剂SBA-15-SO3H的制备及其催化性能

采用直接和后合成两种方法制备出含磺酸基的介孔分子筛SBA-15-SO₃H,用XRD和红外光谱分析制备过程中催化剂结构和组成的变化.结果表明,两种方法制备出的含磺酸基的催化剂都保持了SBA-15分子筛的完整晶体结构,并含有质子酸中心-SO₃H;固体核磁共振表征结果证明,两种方法都使MPTMS存在于分子筛的表面;用N₂吸附-脱附测定了它们的比表面积、孔径和孔容;TGA分析认为,MPTMS在分子筛表面的热稳定性大于300℃,酸碱滴定结果说明,直接法获得的催化剂的酸中心多于后合成法.酯化反应结果表明,直接法合成的催化剂比后合成法具有更高的稳定性,且简便、快捷、高效.     

一步法直接合成有机季铵功能修饰的介孔分子筛SBA-15

以P123 嵌段共聚物为模板剂, 3-三甲基丙基氯化铵三甲氧基硅烷(TMAPS)为修饰剂, 酸性条件下一步法直接合成了有机季铵基团功能修饰的SBA-15, 并通过XRD、TEM、N2吸附-脱附、Raman 光谱等对功能化样品的结构和性质进行了表征, 对一步法合成TMAPS 修饰的SBA-15 的可能反应机理进行了探讨. 修饰后的SBA-15 仍然保持了二维六方特征介孔结构, 随着TMAPS负载量的增大, SBA-15 孔道有序度下降, 孔径、孔容和比表面积也随之下降. 有机季铵基团在SBA-15 孔道表面均匀分散, 可与HAuCl4通过快速离子交换制备Au 颗粒高度分散的Au-SBA-15.     

PW_(11)/SBA-15介孔杂化材料的直接合成与表征

采用三嵌段共聚物EO20PO70EO20(P123)为模板剂,正硅酸乙酯(TEOS)和缺位Keggin型多金属氧酸盐Na7PW11O39(PW11)为无机前驱体,由共缩合法一步合成了PW11/SBA-15介孔杂化材料.通过红外(IR)光谱、紫外-可见漫反射光谱(UV-Vis/DRS)、X射线衍射(XRD)、低温N2吸附、透射电子显微镜(TEM)等手段对杂化材料和合成过程进行了表征.结果表明:杂化材料中不仅多金属氧酸盐的Keggin单元保留完整,且共价键联于介孔孔道内部,而且样品基本具有规整有序的六方介孔结构.TEOS预水解时间的长短对有序结构的构筑有明显影响,随预水解时间延长,样品的介观有序性增加.这是因为多金属氧酸盐对模板剂P123有盐析作用,其作用大小与多金属氧酸盐前驱物的溶解度有关.     

Direct synthesis and catalytic applications of ordered large pore aminopropyl-functionalized SBA-15 mesoporous materials

SBA-15 mesoporous silica has been functionalized with aminopropyl groups through a simple co-condensation approach of tetraethyl orthosilicate (TEOS) and (3-aminopropyl)triethoxysilane (APTES) using amphiphilic block copolymers under acidic conditions. The organic-modified SBA-15 materials have hexagonal crystallographic order, pore diameter up to 60 A, and the content of aminopropyl groups up to 2.3 mmol g(-1). The influences of TEOS prehydrolysis period and APTES concentration on the crystallographic order, pore size, surface area, and pore volume were examined. TEOS prehydrolysis prior to the addition of APTES was found essential to obtain well-ordered mesoporous materials with amino functionality. The amount of APTES incorporated in the silica framework increased with the APTES concentration in the synthesis gel, while the ordering of the mesoporous structure gradually decreased. Analysis with TG, IR, and solid state NMR spectra demonstrated that the aminopropyl groups incorporated in SBA-15 were not decomposed during the preparation procedure and the surfactant P123 was fully removed through ethanol extraction. The modified SBA-15 was an excellent base catalyst in Knoevenagel and Michael addition reactions.     

介孔SBA-15中有机模板剂的紫外/臭氧法脱除

紫外/臭氧法用于脱除有序介孔材料SBA-15中有机模板剂. 该方法是一种非加热光化学降解法, 简单、易操作, 可在温和条件下彻底除去SBA-15中三嵌段共聚物有机模板剂P123. 通过XRD, TEM, FT-IR和BET等对SBA-15经不同方法脱除模板剂前后的详细表征, 表明紫外/臭氧法在彻底脱除SBA-15中有机模板剂后, 保留了很好的骨架有序性, 比表面积更大, 孔道更加开放, 克服了高温焙烧脱除模板剂造成的孔道收缩.     

一种合成六方板状Zr-Ce-SBA-15介孔材料的新方法

以P123为模板剂, 正硅酸乙酯为硅源, 氯化氧锆和硝酸亚铈为无机前驱盐, 在不外加无机酸的条件下, 利用无机前驱盐自身水解产生的弱酸性环境, 通过水热合成路线一步合成了具有大的径轴比、短孔道、六方板状形貌的Zr-Ce-SBA-15介孔材料. 利用粉末X射线衍射(XRD)、透射电子显微镜(TEM)、扫描电子显微镜(SEM)、电感耦合等离子体原子发射光谱(ICP-AES)和氮气吸附等手段对所合成的样品进行了表征. 结果表明, 合成的材料具有类似于SBA-15的二维六方介孔结构, 孔径、孔容和比表面积分别为5.6 nm, 0.96 cm3/g和776 m2/g. 与常规SBA-15相比, 这种短孔道、大径轴比的六方板状介孔材料在吸附、分离及催化等领域中能更有效地促进分子的扩散传递.     

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.     

Synthesis and lysozyme adsorption of rod-like large-pore periodic mesoporous organosilica

Highly ordered rod-like large-pore periodic mesoporous organosilica (PMO) was successfully synthesized at low acid concentration with the assistance of inorganic salt using triblock copolymer P123 as a template. The roles of inorganic salt and acidity in the production of highly ordered mesostructure and the morphology control of PMOs were investigated. It was found that the inorganic salt can significantly widen the range of the synthesis parameters to produce highly ordered 2D hexagonal pore structure of p6mm symmetry. However, the uniform rod-like PMOs can only be synthesized in a narrow range of acid and salt concentrations, which were sensitive to induction time. The adsorption of lysozyme on PMO was studied at different pH values in comparison with adsorption on pure silica material under controlled morphology and pore structure. It was found that the adsorption capacity of lysozyme on the PMO was lower than that on pure SBA-15 silica material and the adsorption amounts are larger at pH 9.6 than at 7.0 for both materials. The results show that the electrostatic interaction between lysozyme and PMO/SBA-15 surface is more dominant than the hydrophobic forces and the interaction of neighboring lysozyme molecules also plays an important role.     

MOR/SBA-15复合分子筛的合成、表征及其催化性能评价

采用MOR纳米晶和正硅酸四乙酯为硅源,P123三嵌段共聚物为模板剂水热合成MOR/SBA-15复合分子筛催化剂。采用XRD、SEM、TEM和EDX等手段对催化剂进行了表征,在固定床反应器中评价二甲醚制乙醇催化性能。结果表明,通过控制合适的MOR纳米晶种及MOR纳米晶种在SBA-15水热合成体系中的添加量,可以成功地将MOR纳米晶作为SBA-15的结构单元嫁接到SBA-15的介孔骨架中,水热合成的MOR/SBA-15复合分子筛催化剂同时具有MOR和SBA-15的XRD特征衍射峰,相比于SBA-15,其比表面积和总孔体积由756 m2·g~(-1),1.07 cm3·g~(-1)降低至628 m2·g~(-1),0.85 cm3·g~(-1),平均孔径由8.1 nm提高到9.3nm,Cu修饰的MOR/SBA-15复合分子筛催化剂同时具有Cu MOR羰基化和Cu SBA-15加氢的双功能催化性能,其催化剂评价结果显示二甲醚转化率为43.6%左右,乙醇选择性为95.3%,Cu MOR/SBA-15复合分子筛催化剂实现了二甲醚到乙醇的一步转化。     

有机胺修饰具有较大孔径介孔材料的二氧化碳吸附性能

以非离子表面活性剂P123为模板剂,正硅酸甲酯为硅源,通过加入不同的扩孔剂制得具有较大孔径的SBA-15类介孔材料,并采用粉末X射线衍射(XRD)、低温氮气吸附-脱附、扫描电镜(SEM)、傅里叶变换红外(FTIR)光谱等手段对所得样品进行了表征.加入扩孔剂可以明显增大介孔材料的孔容和孔径,而异辛烷为扩孔剂的扩孔效果明显优于四氯化碳.经四乙烯五胺(TEPA)镀饰后,这些样品均表现出良好的CO2吸附性能.其中对于除去模板剂后再镀胺的样品,其CO2吸附能力与介孔材料孔道结构关系不大,而对于未除模板剂的原粉镀胺样品,CO2吸附能力则随孔道的变大而增强.此外,通过吸附等温线和CO2-程序升温脱附(TPD)手段比较了温度和压力对CO2吸附的影响,发现在较高温度下吸附时CO2的吸附能力随压力的变化存在显著差别,因而在这类TEPA修饰的介孔材料上可通过变压吸附的途径来实现对环境气流中CO2的吸附和分离.     

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.