Direct synthesis of CeO2/SiO2 mesostructured composite materials via sol–gel process

A series of CeO₂/SiO₂ mesostructured composite materials was synthesized by sol–gel process using Pluronic P123 as template, tetraethylorthosilicate as silica source and hexahydrated cerium nitrate as precursor under acid condition. The as-synthesized materials with Ce/Si molar ratio ranging from 0.03 to 0.3 were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), laser Raman spectroscopy (LRS), and N₂ adsorption. Characterization revealed that all samples possess ordered hexagonal mesoporous structure similar to SBA-15 and possess high surface area, large pore volume and uniform pore size. The fact that cerium species are present as highly dispersed CeO₂ nanocrystals in hexagonal matrix was confirmed by XRD combined with high-resolution TEM and selected area electron diffraction (SAED) analysis. Introduction of ceria to silica matrix can cause a distortion of hexagonal ordering structure and decrease pore diameter and increase the wall thickness of mesopores. Moreover, it can be found that this sol–gel route is a feasible, effective and simple method for templating synthesis of CeO₂/SiO₂ composite materials.     

Promotion effect of cerium and lanthanum oxides on Ni/SBA-15 catalyst for ammonia decomposition

CeNi/SBA-15 and LaNi/SBA-15 catalysts were prepared by deposition–precipitation (DP) method and characterized by N₂ physical adsorption, XRD, H₂-TPR, H₂-chemisorption and TEM. Their catalytic performances in the ammonia decomposition reaction were tested and compared with Ni/SBA-15 catalyst. Addition of cerium and lanthanum oxides to the Ni/SBA-15 catalyst caused some decrease of BET surface area and pore volume of the catalysts, but led to a promotion effect to their catalytic activity which was closely related to the ratio of Ce (La)/Ni. The highest conversion of ammonia could be obtained when the Ce (La)/Ni ratio was around 0.3. The promotion effect is more evident on CeNi/SBA-15(0.3) than on LaNi/SBA-15(0.3) catalyst under identical reaction conditions. The CeNi/SBA-15 and LaNi/SBA-15 catalysts show smaller nickel particle size and easier reducibility in comparison with the Ni/SBA-15 catalysts.     

Pd/SBA-15 nanocomposite: Synthesis, structure and catalytic properties in Heck reactions

Pd nanoparticles supported in mesoporous silica SBA-15 (or Pd/SBA-15 nanocomposites) were prepared by ion-exchange with cationic Pd precursor in an alkaline solution on an uncalcined silica. The high Pd loading in these nanocomposites can be achieved up to 5.21 wt.% by adjusting the pH value of the solution. The surface area and the pore volume decrease with increasing Pd loading. The Pd nanoparticles equal to or smaller than 6 nm in size in the nanocomposites are distributed in the channels of the mesoporous SBA-15. The Pd/SBA-15 nanocomposites exhibit excellent catalytic activities and high reuse ability in air for the Heck carbon-carbon coupling reactions.     

Ce-SBA-15六方介孔分子筛的合成与表征

采用浸渍法和沉积-沉淀法对有序六方介孔氧化硅分子筛SBA-15进行铈改性。通过X射线衍射、Fourier红外光谱、透射电镜、N2吸附-脱附、X射线光电子能谱和感应耦合等离子体原子发射光谱等对复合材料Ce-SBA-15的介孔结构、铈元素的含量及其化学态进行了表征。结果表明:以硫酸铈为铈源的沉积-沉淀法即使在小的负载量下,铈元素在载体中的分散性很差;而以醋酸铈为铈源的浸渍法能使铈元素在载体中均匀分散,得到的复合材料保持载体SBA-5高度有序的二维六方孔道结构,未检测到氧化铈晶相峰。以醋酸铈为铈源时,当铈负载量达到10.74%时,浸渍法制备的载体的比表面积为368.3m2/g。分子筛中引入的铈元素主要以正四价态形式存在。     

Template synthesis of large pore ordered mesoporous carbon

Nanocast carbon (NCC-1) with large pores and ordered structure was synthesized via a nanocasting process using aluminum-containing SBA-15 as template and furfuryl alcohol (FA) as carbon precursor. This carbon has several interesting features, such as two steps with distinguished hystereses in the nitrogen sorption isotherm, high surface area of 2000 m²/g and large pore volumes of 3.0 cm³/g. It was found that the key factors in the synthesis of such carbons are the aging temperature of the SBA-15 template, the concentration of furfuryl alcohol (dissolved in trimethylbenzene), and the carbonization temperature. The optimal conditions for materials with high surface area and pore volumes are SBA-15 starting materials aged at 140 °C, 25 vol% of FA solution and 850–1100 °C carbonization temperatures. Moreover, it has been demonstrated that such nanocast carbon can be synthesized in a more facile way than previously reported. Purely siliceous SBA-15 without the need of Al³⁺-incorporation can be directly used as template. In this case, the polymerization catalyst—oxalic acid and FA were simultaneously introduced into the pore space of SBA-15.     

Synthesis of functionalized SBA-15 with ordered large pore size and its adsorption properties of BSA

SBA-15, mesoporous material, is a very excellent candidate for drug delivery system because its pore size is easy to control according to synthesis conditions and the presence of swelling agent. In this study, a known swelling agent, 1,3,5-trimethylbenzene (TMB), was used to increase the pore size with increased aging temperature and prolonged aging time. Furthermore, 3-aminopropyltriethoxysilane (APTES) was incorporated on SBA-15 surface via post synthesis method to separate protein effectively. The samples were characterized by X-ray diffraction (XRD), nitrogen adsorption and desorption analyses, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier Transform Infrared (FT-IR). Adsorption capacity increased with temperature at the isoelectric point (pI) of bovine serum albumin (BSA) regardless of the pore size of SBA-15 samples. Release studies were carried out in the range of pH from neutral to basic solution on unmodified and amine-modified samples. In addition, the adsorption mechanism was investigated by employing the pseudo-first order, pseudo-second order, and intraparticle diffusion models.     

Co掺杂对Ce/MCM-41和Ce/SBA-15催化剂催化氧化甲苯性能的影响

以分子筛为载体,采用等体积浸渍法制备Ce/SBA-15、Ce/MCM-41、Ce Co/SBA-15和Ce Co/MCM-41催化剂。用N2吸附-脱附、X射线衍射、扫描电子显微镜、H2程序升温还原、X射线光电子能谱和傅立叶变换红外光谱等对载体和催化剂进行表征,并考察催化剂催化氧化甲苯的活性。结果表明,与载体相比,随着Ce和Co的浸渍,催化剂的比表面积和孔容下降,但仍然保持了载体的有序介孔结构。引入的Ce和Co没有进入分子筛骨架,而是以立方相固溶体形式存在于分子筛表面和孔道中。催化剂催化氧化甲苯活性顺序依次为:Ce Co/SBA-15>Ce Co/MCM-41>Ce/MCM-41>Ce/SBA-15。共浸渍Ce和Co的催化剂活性明显优于只浸渍Ce的催化剂,活性与其还原性能直接相关,Ce Co/SBA-15催化剂具有最低的还原温度和最好的供氧能力,从而表现出最优的催化性能。     

Effect of different synthesis methods on the structural and catalytic performance of SBA-15 modified by aluminum

Two different aluminum-containing mesoporous Al/SBA-15 were prepared by post-synthesis method and direct synthesis method using P123 as structure directing agent and aluminum isopropoxide as the aluminum source. Samples were characterized in detail by XRD, N₂ adsorption, TEM,²⁷Al MAS NMR, and the acidic properties were performed by FT-IR of pyridine adsorption (Py-IR). The results show that Al/SBA-15 prepared by the direct synthesis method possessed higher BET surface area and larger pore volume. The acidic properties were investigated in Friedel–Crafts alkylation of phenol tert-butylation. The different synthesis method leads to distinct coordination of Al and intensity of acidity. Kinetics of the alkylation over Al/SBA-15 was also investigated. These results indicated that Al/SBA-15, prepared by post-synthetic grafting method, has more activity ability than the corresponding one synthesized by direct method since they contain more Lewis acid sites and Brönsted acid sites. The catalysts preserved almost their initial catalytic activity after four reuses.     

Synthesis of mesoporous silica from bottom ash and its application for CO<Subscript>2</Subscript> sorption

A supernatant solution of silicate species extracted from bottom ash in a power plant was used to prepare a mesoporous silica by the synthesis protocol of SBA-15. XRD, N₂ adsorption-desorption, and TEM confirmed a disordered mesopore structure. The pore volume and average pore size of the product were significantly larger than SBA-15 prepared using pure chemicals, and complementary textural mesoporosity was detected. When the mesoporous silica was tested for carbon dioxide sorption after polyethyleneimine (PEI) impregnation, substantially higher CO₂ sorption capacity (169 mg CO₂/g-sorbent) was achieved than that of PEI-impregnated pure SBA-15 under the same test conditions. High CO₂ sorption capacity was maintained when the gas composition was changed to 15% CO₂, and the hybrid material exhibited satisfactory performances during the 10 recycle runs.     

Ce/SBA-15联合Oxone去除水中染料RhB的试验研究

将负载型的Ce/SBA-15与过硫酸氢钾复合盐(Oxone)联合,考察了该联合体系对染料罗丹明B(RhB)的去除效果。结果表明:该体系中RhB的去除符合准一级动力学方程,提高Ce/SBA-15和Oxone投加量,降低初始RhB浓度和提高反应温度会增强RhB的去除效果,未调节溶液初始pH值时,RhB的去除效果最好。制备的Ce/SBA-15在5次循环使用后仍具有约80%的RhB去除率,RhB的去除机制为表面吸附催化。Ce/SBA-15与Oxone联合产生以硫酸根自由基为主的处理技术对难降解污染物质具有潜在的实际应用价值。     

聚甲基丙烯酸-介孔氧化硅复合材料的制备及释药研究

采用自由基聚合的方法合成了pH敏感性聚甲基丙烯酸(PMAA)/介孔分子筛SBA-15纳米复合物。用XRD、FTIR、TG、低温N2吸附-脱附、TEM等对复合物进行了表征,并以阿司匹林为模型药物分子,进行了药物释放测试。结果表明,复合材料仍然保持有序六方结构,但比表面积、孔容、孔径有所降低;在pH=7.4的释放介质中,12 h内释放了72%的药物,而在pH=1.0的释放介质中,12 h药物释放量为30%。该纳米复合材料对阿司匹林的释放具有pH敏感性,有望在药物控制释放领域得到应用。     

Characterization and synthesis of Ce-incorporated mesoporous molecular sieves under microwave irradiation condition

Ce-incorporated MCM-41 mesoporous molecular sieves (CeMCM-41) were synthesized by microwave irradiation method from sodium silicate and ammonium cerium (IV) nitrate precursors and using cetyltrimethyl ammonium bromide (CTAB) as template. The resulting samples were characterized by means of XRD, TEM, FT-IR, UV-Vis, XPS and N₂ physical adsorption, respectively. The effect of the Si/Ce molar ratio on the textural properties of CeMCM-41 was investigated. The results reveal that the CeMCM-41 was successfully synthesized. The resultant mesoporous materials have specific surface areas in the range of 602–1,216 m²/g and pore sizes in the range of ca. 2.6–2.9 nm. The structural properties are related to the amount of cerium incorporation. The surface area and pore volume of the resulting CeMCM-41 were gradually reduced as the cerium content in the sample increased, and the mesoporous ordering diminished.     

中微双孔分子筛SBA-15的合成

采用P123(PEO20PPO70PEO20)为模板剂,正硅酸乙酯(TEOS)为硅源试剂,在强酸溶液中采用水热晶化法合成中微双孔分子筛SBA-15,并考察模板剂浓度、反应温度,离子导向剂和共溶剂对中微双孔分子筛SBA-15的影响.结果表明:控制合成温度可以精确调控SBA-15的介孔孔径;引入离子导向剂后合成的SBA-15具有更好的介孔有序性;加入共溶剂N,N-二甲基酰胺(DMF)会破坏SBA-15孔道的有序性,孔壁变薄,但可以提高分子筛的比表面积和孔容,大幅度提高孔径;采用乙醇后处理分子筛SBA-15有利于保持分子筛骨架.合成中微双孔分子筛SBA-15的合适条件为P123,TEOS,NaCl,HCl与H2O物质的量之比0.017∶1∶1.5∶9.86∶137,反应温度40℃,P123自组装反应时间4 h,与硅源组装老化时间24 h,晶化温度100℃,晶化48 h,在此条件下得到高质量的中微双孔分子筛SBA-15对苯吸附量接近1 000mg/g.     

Morphological control of mesoporous silica SBA-15 synthesized at low temperature without additives

Fiber-like or rod-like mesoporous SBA-15 silicas with different lengths and diameter of macrostructures and pore diameter could be synthesized by the self-assembly of silica-surfactant (commonly used Pluronic P123 (EO₂₀-PO₇₀EO₂₀) as a structure-directing agent) through careful control of the synthetic temperature and stirring time without any additives. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and nitrogen adsorption–desorption isotherms are used to characterize these mesoporous silica materials. Compared with those reports on conventional SBA-15, our work is focused on one-step synthesis and the morphological control of ordered mesoporous silica synthesized at low temperature under low concentration of P123 (0.67 wt%) without the addition of inorganic salts, where pre-hydrolyzed silica species may favor the self-assembly of silica-polymer hybrid micelles. Moreover, the pore diameter of fiber-like SBA-15 synthesized at 40 °C is slightly smaller than that of conventional SBA-15, revealing that the average micellar radius of P123 micelles in this low concentration of P123 solution was almost same as that for the conventional synthesis of SBA-15.     

Template synthesis of CMK-3 nanostructured carbon material and study of its properties

Mesostructured carbon has been obtained by template synthesis. SBA-15 mesostructured silicate has been used as a template. The effect of the properties of a template on the ordering of a replica has been studied. It has been shown with the use of X-ray diffraction, gas adsorption, and electron microscopy that there are evident correlations of the conditions of synthesis of a template with the ordering of a carbon replica, which can be guided by the synthesis of materials. The ordering of a replica significantly depends on the mesopore volume of the initial template and thickness of the pore wall. One should use templates with the highest possible mesopore volume and minimal wall thickness to obtain highly ordered replicas. These templates can be prepared during the treatment of synthesized materials at temperatures close to 100°C. It has been determined that, when there is SBA-15, the presence of micropores is a necessary condition for the preparation of carbon replicas that retain the structure of the template.     

调控表面活性剂浓度制备单分散SBA-15介孔材料

采用溶胶-凝胶水热法,调控反应参数和反应工艺制备SBA-15介孔材料。通过扫描电镜、透射电镜、X射线衍射以及氮气吸附-脱附分析表征表明,在一定范围,随着表面活性剂浓度增加,介孔材料SBA-15形貌出现由球形、陀螺形到米粒状的变化,介观有序度提高。在反应物料P123与Si物质的量比为0.012时,介孔材料的物性常数如晶面间距、比表面积、孔体积和最可几孔径较小。采用静态陈化-水热法研究不同表面活性剂浓度对介孔材料形貌演变的影响,为有效调控SBA-15介孔材料形貌提供必要依据。     

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.     

A simple aqueous solution based chemical methodology for synthesis of Ag nanoparticles dispersed on mesoporous silicate matrix

A simple chemical method has been developed for preparation of Ag nanoparticles dispersed on mesoporous silicate matrix, SBA-15. Ag nanoparticles were uniformly dispersed on SBA-15 matrix by using the reduction reaction of AgNO₃ with trisodium citrate. The synthesized materials were characterized by using room temperature powder XRD analysis, N₂ adsorption-desorption isotherm, high resolution TEM and SEM. It was observed that the synthesized SBA-15 and Ag-SBA-15 have a surface area of 778 and 151 m²/g respectively. The synthesized materials have long range ordering of pores with narrow pore size distribution centered at ∼ 7 nm. Pore structure of SBA-15 remains preserved even after deposition of Ag nanoparticle. This chemical route reported here offers a simple method for preparation of Ag-SBA-15, where unagglomerated Ag nanoparticles (∼ 20 nm) are uniformly dispersed on SBA-15.     

An overview of ordered mesoporous material SBA-15: synthesis,functionalization and application in oxidation reactions

Ordered mesoporous materials are attracting wide concern because of their applications in the field of catalysis, adsorption, separations, drug delivery systems and gas sensors owing of their extremely high surface area combined with well-defined pore structures with narrow pore size distributions. Various mesoporous materials such as MCM-41, MCM-48, SBA-15 and SBA-16 have been reported in past two decades. Synthesis of mesoporous materials involves the concept of aggregation of surfactants as structure directing agents under acidic or basic conditions. The dimensions of these mesopores can be obtained by type of surfactant, auxiliary chemicals and synthesis conditions. At present, SBA-15 has attracted more attention among different mesoporous silica structures due to their desirable properties such as thick pore wall and hexagonal mesopores (4–12 nm), high surface area, ease of synthesis and functionalization and high thermal and mechanical stability. In last few years, great effort has been made on the development of various methods for the synthesis of mesoporous materials as support for oxidation reactions. The aim of this review article is to focus mainly on mesoporous SBA-15 together with its application as support for various oxidation reactions.     

组装法制备巯基改性磁性SBA-15

采用热分解法制备了单分散、平均粒径约15nm的锰铁氧体磁性纳米粒子。通过正硅酸乙酯与磁性纳米粒子表面油酸盐的配体交换将磁性纳米粒子锚定在SBA-15表面。并且将负载过程与巯基改性过程耦合制备了巯基改性的磁性SBA-15。考察了合成SBA-15过程中干燥方式对其结构和性质的影响,研究了负载磁性纳米粒子和巯基改性顺序对巯基改性磁性SBA-15的结构和性能的影响。结果表明,喷雾干燥法合成的SBA-15介孔孔壁较薄,但具有更大的比表面积、孔体积和平均孔径。以其为载体时磁性纳米粒子负载量更大,所得磁性SBA-15的饱和磁强度更高。当将巯基改性和负载磁性纳米粒子分为前后两步时,巯基改性SBA-15的表面疏水环境有利于吸附疏水磁性纳米粒子,所得磁性SBA-15负载磁性纳米粒子量更大,饱和磁强度更高。磁性纳米粒子粒径大于SBA-15孔径,其主要负载于SBA-15外表面,有利于得到介孔孔道通畅的磁性SBA-15。巯基改性的磁性SBA-15的孔体积介于0.56~0.6cm³/g,比表面积介于353~432m²/g,饱和磁强度最高达到0.91emu/g,可作为一种大容量的吸附材料用于吸附分离、药物缓释等领域。