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  • SBA-15 Mesoporous Molecular Sieve
    Aug 16, 2018 | ACS MATERIAL LLC

    SBA-15 molecular sieve is prepared by the hydrothermal method with triblock polymer pluronic P123 (EO20-PO70EO20), hydrochloric acid, tetraethyl orthosilicate (TEOS) and deionized water as raw materials. SBA-15 has an ordered structure that contains uni-dimensional mesopores of uniform size ranging from about 4 to 30 nm.1 Unique properties of SBA-15 include uniform and adjustable pore size, thick pore walls, superior hydrothermal/thermal and mechanical stability, high surface area, high pore volume and open pore structure. All of these properties render it highly valuable in a wide variety of applications.

    Introduction

    Since the first discovery in 1998, SBA-15 ordered hexagonal mesoporous silica has received a significant amount of attention.2 SBA-15 has a two-dimensional, hexagonal, through-hole structure with a space group p6mm.3 SBA-15 shows three XRD diffraction peaks, which can be assigned to (100), (110) and (200) crystal face diffractions (Figure 1). Furthermore, the silica on the SBA-15 framework is generally amorphous and no significant diffraction peak is observed in wide-angle XRD diffraction. The particle size of SBA-15 is 1~4 um and the BET surface area is above 550 m2/g.

    Fig.1

    Figure 1. Typical XRD Analysis of ACS Material Mesoporous Silica Molecular Sieve SBA-15

    Synthesis

    SBA-15 molecular sieve is prepared by the popular hydrothermal method4. Triblock polymer pluronic P123 (EO20PO70EO20) is used as the structure-direction agent and tetraethyl orthosilicate (TEOS) as the silica source. The typical synthesis process starts by first dissolving a P123 triblock copolymer in a solution that contains water and 38 wt% HCl. After stirring for 3 hours at room temperature, TEOS is added to the solution. The solution is then vigorously stirred for 10 minutes and placed at 40oC for 24 hours under static condition, followed by aging at 100 oC for 24 hours. To remove the copolymers, 1.5 g of particles are added to a mixture of 38wt% HCl and methanol and refluxed for 24 hours. Final particles are then separated by centrifugation, washed with distilled water, dried at 70 oC for 12hours and calcined  at 550 oC. The molar composition of the mixture is SiO2 : 0.017P123 : 2.9HCl : 202.6H2O. The particle size and pore volume can be adjusted by the molar composition of the mixture, aging time and aging temperature.

    Fig.2

    Figure 2. XRD patterns of SBA-15 Mesoporous Molecular Sieve

    There are also alternative approaches for preparing SBA-15 catalysts such as substitution of Si4+ by changing different cations, functionalization with different groups, changing the active phase component or varying the preparation method.5

    Applications

    Mesoporous silica particles are good candidates for drug delivery because of their biocompatibility, uniform structure, tunable pore size with narrow distribution, large pore volume, large surface area and ease of surface functionalization. SBA-15 has been extensively studied for both drug and gene delivery because of its ordered structure. For drug delivery, the drug loading capacity is affected by the pore size, surface area and drug-surface affinity.6

    To expand the applications of SBA-15 mesoporous silica in catalysis, separation and sensor design, many researchers have focused on the preparation of organic-functionalized materials by the direct incorporation of organic groups through co-condensation or by grafting the organic groups onto the surface of the mesoporous silica. Aminopropyl-functionalized SBA-15 has been found to be useful for some base-catalyzed reactions including Knoevenagel reactions of carbonyl  compounds with ethyl cyanoacetate, reactions of aldol condensation and the intramolecular addition of benzaldehyde and 2-hydroxyacetophenone to flavanone.7

    SBA-15 can support various catalysts, including non-noble metal sulfides, metal phosphides, metal carbides and noble metals.8,9 Used in this manner, SBA-15 plays two main roles. First, it serves to disperse the active metal, which leads to higher metallic surface areas and subsequently higher catalyst activity. Second, it provides a method for influencing the selectivity of the products. In a test experiment, a series of Mo2C/SBA-15 catalysts with different Mo contents were prepared by temperature-programmed carburization of their oxide precursors and the Mo2C/SBA-15 catalysts exhibited excellent hydrodesulfurization (HDS) activity. Iron catalysts supported on SBA-15 and aluminum-containing SBA-15 were active toward the production of hydrocarbons via the Fischer-Tropsch process. Pt nanoparticles were embedded into the mesoporous silica SBA-15 using low power sonication. The Pt/SBA-15 catalysts demonstrated weak structure sensitivity with smaller particles demonstrating higher activity. Turnover rates for ethane hydrogenolysis of ethane on Pt particles increased monotonically with increasing metal dispersion. 

    Conclusion

    SBA-15 is a versatile mesoporous silica material possessing highly ordered nanopores and a large surface area. It is widely employed as a good candidate for drug delivery and it can be modified with different cations, heteroatoms and organic functional groups. SBA-15 has expanding applications in catalysis, separation, and sensor design. Furthermore, SBA-15 supports various catalysts, including non-noble metal sulfides, metal phosphides, metal carbides and noble metals.

    ACS Material Products:

    Molecular Sieves

     

    References 

    1. Huirache-Acuña, R., Nava, R., Peza-Ledesma, C.L., Lara-Romero, J., Alonso-Núez, G., Pawelec, B. and Rivera-Muñoz, E.M., 2013. SBA-15 mesoporous silica as catalytic support for hydrodesulfurization catalysts. Materials, 6(9), pp.4139-4167.

    2. Wang X, Lin K S K, Chan J C C, et al. Direct synthesis and catalytic applications of ordered large pore aminopropyl-functionalized SBA-15 mesoporous materials. Journal of Physical Chemistry B, 2005, 109(5):1763-1769.

    3. Chong A S M, Zhao X S. Functionalization of SBA-15 with APTES and characterization of functionalized materials. Journal of Physical Chemistry B, 2003, 107(46):12650-12657.

    4. Song S W, K. Hidajat A, Kawi S. Functionalized SBA-15 Materials as carriers for controlled drug  delivery: influence of surface properties on matrix-drug interactions. Langmuir, 2005, 21 (21): 9568-9575.

    5. D J K, B C D, Frank Huggins, et al. SBA-15-Supported iron catalysts for Fischer−Tropsch production of diesel fuel. Energy & Fuels, 2006, 20(6): 2608-2611.

    6. Hwang D H, Lee D, Lee H, et al. Surface functionalization of SBA-15 particles for ibuprofen delivery. Korean Journal of Chemical Engineering, 2010, 27(4):1087-1092.

    7. Wainwright S G, Parlett C M A, Blackley R A, et al. True liquid crystal templating of SBA-15 with reduced microporosity. Microporous and Mesoporous Materials, 2013, 172(2):112-117.

    8. Zhang H, Sun J, Ma D, et al. Unusual mesoporous SBA-15 with parallel channels running along the short axis. Journal of the American Chemical Society, 2004, 126 (24): 7440-7441.

    9. Nakahira A, Hamada T, Yamauchi Y. Synthesis and properties of dense bulks for mesoporous silica SBA-15 by a modified hydrothermal method. Materials Letters, 2010, 64(19):2053-2055.