A template carbonization strategy to synthesize ordered mesoporous silica microspheres with trapped sulfonated carbon nanoparticles for efficient catalysis

Ordered mesoporous materials have attracted much attention since their discovery owing to their outstanding properties, such as tunable pore sizes and mesostructures, variable morphologies, high surface areas, and large pore volumes. These features make them promising candidates for applications including catalysis, adsorption and separation, chemical sensing, and biomedicine. To date, significant advances have been achieved in the synthesis of mesoporous materials, particularly in the soft templating approach using surfactants or block copolymers as the templates (structuredirecting agents), and enormous ordered mesoporous materials with variable pore structures, pore sizes, and framework compositions have been prepared. Apart from exploring the methods of synthesis and strategies, considerable efforts have been devoted to designing functional ordered mesoporous materials by introducing functional nanomaterials or organic groups for practical applications. For example, using sol–gel chemistry, many functional mesoporous composites have been synthesized by coating functional nanoparticles. Furthermore, functional organic groups or nanoparticles have been introduced into mesopores, resulting in various functional mesoporous materials that are useful in drug delivery, chemical sensing, and catalysis. Particularly the immobilization of sulfonic acid groups (-SO3H) in mesopores have aroused great research interest because the mesoporous materials can provide a large accessible surface area for supporting high density of acidic sites, thus serving as efficient solid Bronsted acids. Compared to traditional homogeneous acid catalysts (such as H2SO4, AlCl3, BF3), the novel heterogeneous catalysts are environmentally benign and can be readily recycled from reaction medium, thus reducing the energy consumption for the production of chemicals. To introduce sulfonic acid groups on the pore walls of mesoporous silica materials, typical methods involve the attachment of sulfur-containing organic silanes (for example SH, S S ) by post-grafting or co-condensation and subsequent oxidation with hydrogen peroxide. Van Rhijn et al. first reported the synthesis of ordered mesoporous silicas functionalized with SO3H groups using co-condensation or post-modification. The obtained SO3H-functionalized mesoporous silicas exhibited good performance in catalyzing the condensation of 2-methylfuran with acetone with high conversion (85%) and selectivity (96%) toward the target product 2,2-bis(5-methylfuryl)propane. By contrast, traditional microporous solid acids, such as H-b and H-US-Y zeolites, exhibited much lower conversion (ca. 60%) and selectivity (ca. 70%) owing to the undesired fast formation and adsorption of tarry oligomeric compounds in the narrow zeolite pores and subsequent catalyst deactivation. This result suggests that the immobilization of SO3H groups in mesoporous silicas with larger pore is more favorable for catalysis. Although mesoporous silicas functionalized with the SO3H groups can be easily synthesized by the post-grafting or cocondensation, these methods allow for only a limited amount of functional silanes to be used so as to avoid the damage of ordered mesostructure or pore blocking, resulting in a low density of sulfonic acid groups anchored in the pore walls. Recently, Nakajima et al. synthesized sulfonated carboncontaining mesoporous silica SBA-15 fibers by carbonization of the impregnated glucose in the pores of SBA-15, followed with a sulfonation treatment. The mesoporous carbon/silica functionalized with SO3H groups exhibited a good catalytic performance in the dimerization of a-methylstyrene; however, through this post impregnation, it is difficult to control the sulfonated carbon distribution and avoid pore blocking. Therefore, development of novel approaches and strategies to the synthesis of functionalized mesoporous heterogeneous solid acidic catalysts is of great importance and interest. Herein, we demonstrate a facile template carbonization strategy to synthesize ordered large-pore mesoporous silica microspheres with sulfonated carbon nanoparticles trapped inside the accessible mesopores through a solvent-evaporation-induced aggregating assembly (EIAA) approach. In this approach, amphiphilic poly(ethylene oxide)-b-polystyrene (PEO-b-PS) and tetraethylorthorsilicate (TEOS) were used [*] Q. Yue, M. H. Wang, J. Wei, Prof. Dr. Y. H. Deng, T. Y. Liu, Prof. Dr. R. C. Che, Prof. Dr. B. Tu, Prof. Dr. D. Y. Zhao Department of Chemistry, Advanced Materials Laboratory Key Laboratory of Smart Drug Delivery, Ministry of Education Fudan University, Shanghai 200433 (China) E-mail: yhdeng@fudan.edu.cn dyzhao@fudan.edu.cn Homepage: http://www.mesogroup.fudan.edu.cn/