Effect of alcohol on morphology and mesostructure control of anionic-surfactant-templated mesoporous silica (AMS)
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AbstractAbstractMesoporous materials have been paid much attention in both scientific researches and practical applications. In this review, we focus on recent developments on preparation and functionalization of new families of mesoporous materials, especially non-siliceous mesoporous materials invented in our research group. Replica synthesis is known as the method to synthesize mesoporous materials composed of various elements using originally prepared mesoporous replica. This strategy has been applied for the syntheses of novel mesoporous materials such as carbon nanocage and mesoporous carbon nitride. Carbon nanocage has a cage-type structure with huge surface area and pore volume, which exhibits superior capabilities for biomolecular adsorption. Mesoporous carbon nitride was synthesized, for first time, by using mixed material source of carbon and nitrogen simultaneously. As a totally new strategy for synthesis of mesoporous materials, the elemental substitution method has been recently proposed by us. Direct substitution of component elements in original mesoporous materials, with maintaining structural regularity, provided novel mesoporous materials. According to this synthetic strategy, mesoporous boron nitride and mesoporous boron carbon nitride have been successfully prepared, for first time. In addition to these material inventions, hybridization of high functional materials, such as biomaterials, to mesoporous structure has been also developed. Especially, immobilization of proteins in mesopores was systematically researched, and preparation of peptidehybridized mesoporous silica was demonstrated. These new families of mesoporous materials introduced in this review would have high potentials in future practical applications in wide ranges from electronics and photonics to environmental and medical uses.Key Words: Mesoporous materialTemplate synthesisReplica synthesisElemental substitutionBiomaterial
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Methyl orange
Photodegradation
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The discovery of siliceous mesoporous materials made the possible of catalysis,adsorption,and separation processes involving large molecules,which were rather difficult in small pore systems of zeolites.Internal/external surface properties and pore size of siliceous mesoporous materials can be precisely tuned via physical and/or chemical modifications.Moreover,proper modifications can enhance hydrothermal stability of siliceous mesoporous materials.Nowadays,modified mesoporous silicas showed better activity,selectivity,and/or stability than that of pristine mesoporous silicas in many catalysis and adsorption processes.Synthetic mechanisms of siliceous mesoporous materials and recent progress in synthesis and application of organo-functionalized mesoporous silicas were reviewed.
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Infinite, beautiful, and functional: Functionalized porous materials represent an exciting and ever expanding area of catalytic materials. This Special Issue describes the wide ranging uses of these materials and expresses their awesome potential. During the last two decades, the synthesis of new mesoporous materials has been one of the most active and successful areas of research in chemistry and materials science.1 The use of surfactants to template the structure of mesoporous materials has produce a myriad of new solids, with narrow and controllable pore size distribution and tunable pore structure.2 Also, different bio-inspired strategies have helped to further expand the palette of porous materials that scientists and industry have at their disposal.3 In most cases, however, mesoporous materials are used only as catalysts supports. Their large surface area and open pore structure are used to accommodate a wide variety of nanoparticles or to anchor homogeneous catalysts to the porous surface. The benefits of supporting catalytically active phases on porous materials are well-known, but also their current limitations, such as partial pore blocking, inhomogeneous distribution of the active phase throughout the particle, and numerous preparation steps.4 Although smartly tuning the synthesis conditions can greatly limit these drawbacks, an ideal catalyst should incorporate the active phase in their structure, which will dramatically improve the dispersion and homogeneity of the active phase while minimizing pore blocking. Functional mesoporous materials provide many opportunities in a wide variety of fields, from optics to sensing and from drug delivery to adsorption, but also in catalysis.5 They represent the evolution of catalysts from a composite material made of a support plus a supported phase to a new functional solid, which comprises the right chemistry and an optimized porous structure for a given chemical reaction. In this sense, functional mesoporous catalysts can be compared to natural bio-catalysts (enzymes), which possess an optimized tridimensional structure and chemical functionality, defined by their molecular composition (amino acid sequence). The use of building blocks that contain both of these components to produce new catalysts using a bottom up strategy, as in nature, is a new avenue that is still largely unexplored. Indeed, there are many previous and well-known examples of mesoporous materials that contain an active phase in their structure. A good example of this would be Al-MCM-41 in which the incorporation of aluminum in the structure of the otherwise catalytically inert silica-based MCM-41 makes it active for some acid-catalyzed reactions.6 However, in the last few years the field of functional mesoporous materials—many examples of which have been prepared with other applications in mind—has grown considerably opening-up new opportunities for some challenging and important catalytic chemical process. This Special Issue of ChemCatChem provides an up-to-date and comprehensive vision of the new synthetic strategies for the incorporation of chemical functionalities in mesoporous materials, their characterization and some relevant, and in some cases surprising examples of the use of functional mesoporous catalysts in important chemical reactions. Periodic mesoporous organosilicas (PMOs) are excellent examples of a functional mesoporous material with many catalytic applications. Some of the organic moieties that can be incorporated into the framework of PMO present good catalytic activity, especially sulfonic acid groups, which have been widely used in a wide range of acid-catalyzed reactions (figure 1).7 Another, example of the potential of PMO in catalysis is the amination of phenylene moieties in crystal-like mesoporous silica hybridized with phenylene. The modified PMO successfully catalyzed the Knöevenagel condensation reaction as a solid-base catalyst recently reported by S. Inagaki et al. (Figure 2).8 The same group described the synthesis of a mesoporous biphenyl-silica followed by coordination of a rhenium precursor. The PMO containing a rhenium(I) in its framework was then used for the enhancement of photocatalytic CO2 reduction, which displays the potential of modified PMOs as a light- harvesting antenna in photoreaction systems.9 Enhanced photocatalytic CO2 reduction over a rhenium(I) complex embedded in the framework of a PMO. Figure reproduced with permission from Ref. 7b. The crystal-like structure of an aminated phenylene-bridged mesoporous organosilica (PMO), used as a solid base catalyst in the Knöevenagel condensation reaction. Figure reproduced with permission from Ref. 8. Various metal complexes with catalytic activity have been recently used as building blocks for the preparation of functional mesoporous materials, by using ligands with alkoxysilane terminal groups, which are hydrolyzed in the presence of a surfactant, to produce silica materials with controlled porosity and the metal complex in their framework. The accessibility of the active phase and reusability of the catalyst have been confirmed for same commercially relevant reactions.10 A recent milestone in this field has been recently achieved by the commercialization of hierarchical zeolites as a new class of FCC catalysts, overcoming one of the major limitations of zeolites, i.e. the diffusion of large molecules to their interior, in their most significant commercial application. These functional mesoporous materials, which combine in the same phase controlled mesoporosity (introduced by surfactant-templating) and zeolitic crystallinity, are being used in refineries in USA, and display the practical and enormous potential of more accessible catalysts with chemical functionality, strong Brönstead acidity in this case, in their framework.11 The new bottom-up synthetic strategies, widely used in the preparation of nanomaterials, can be now applied to the fabrication of better functional catalysts, which should not be limited to the deposition of an active phase on a support (a strategy with well-known limitations), but thought in a different more holistic way, in which both chemical function and pore structure should be integrated in the same material. The creativity shown in the last years by synthetic chemists in the preparation of new mesoporous materials can be now further expanded to create new catalysts with both optimized porous structures and chemical functionality. Please enjoy this Special Issue. Rafael Luque and Javier Garcia Martinez This Special Issue would have not been possible without the contributions from many people who are leading this field and have found the time to contribute to this overview of the main developments of the last few years. The guest editors would like to thank especially the whole ChemCatChem editorial team for their effort in making this Special Issue a success. Javier Garcia Martinez is Professor of Inorganic Chemistry and Director of the Molecular Nanotechnology Lab at the University of Alicante, Spain. He has published extensively in the areas of nanomaterials and energy and is the author of more than twenty five patents. Javier is co-founder of Rive Technology Inc. (Boston, MA), a VC-funded MIT spin-off commercializing hierarchical zeolites for diffusion-limited applications. Javier is the editor of "Nanotechnology for the Energy Challenge" (Wiley-VCH, 2011) and "Mesoporous Zeolites" (Wiley-VCH, 2013). In 2005, Javier was awarded the Europa Medal and he received the Silver Medal of the European Young Chemist Award in 2006. In 2007, Javier received the TR 35 Award from MIT's Technology Review magazine (USA). Since 2010, he has been a member of the Council on Emerging Technologies of the World Economic Forum, which recognized him as Young Global Leader. Javier is a Fellow of the Royal Society of Chemistry, a member of the Global Young Academy, and a Bureau member of the International Union for Pure and Applied Chemistry. Dr. Rafael Luque has a significant experience on biomass and waste valorisation practises to materials, fuels and chemicals over the past 10 years. He has also published over 150 research articles, filed 3 patent applications and edited 5 books, as well as numerous contributions to book chapters in the areas of (nano)materials science, heterogeneous (nano)catalysis, microwave and flow chemistry, biofuels and green chemical methods in synthetic organic chemistry. Rafael is also an Editorial Advisory Board member of several internationaly recognized journals. Among his recent awards, Rafael was awarded the Marie Curie Prize from the Instituto Andaluz de Quimica Fina in Spain (2011), the Green Talents award from the Federal Ministry of Education and Research in Germany (2011), and the TR35 Spain 2012 from MIT (USA). He has also been recently honoured as a Distinguished Engineering Fellow (2013) by Hong Kong University of Science and Technology (HKUST). Dr. Luque combines his academic duties with his activities as young entrepreneur after co founding the spin-off companies Starbon Technologies at York, UK (2011) and Green Applied Solutions S.L. in Cordoba, Spain (2012).
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PREFACE INTRODUCTION SYNTHESIS APPROACH OF MESOPOROUS MOLECULAR SIEVES Synthesis Hydrothermal Synthesis Removal of Template Basic Synthesis Acidic Synthesis Nonaqueous Syntheses Postsynthesis Treatment Stability of Mesoporous Materials Pore-Size Control MECHANISMS FOR FORMATION OF MESOPOROUS MATERIALS Introduction Synthesis Pathways Mesophase Tailoring Hard-Templating Approach STRUCTURAL CHARACTERIZATION METHODS XRD Electron Microscopy NMR Physical Sorption REPRESENTATIVE MESOPOROUS SILICA MOLECULAR SIEVES D Mesostructures 3D Hexagonal Phases Cubic Phases Disordered Mesostructures DOPING IN MESOPOROUS MOLECULAR SIEVES Aluminum Doping Boron Doping Gallium and Indium Doping Germanium and Tin Doping Transition-Metal Doping MORPHOLOGY CONTROL The Methods and Techniques Typical Morphologies Magnetically Responsive Ordered Mesoporous Materials MESOPOROUS NONSILICA MATERIALS Mesoporous Carbon Mesoporous Polymers Mesoporous Nonsiliceous Oxides Mesoporous Metals Mesoporous Metal Chalcogenides Ordered Mesoporous Nonoxide Ceramic Materials Mesoporous Metal Nitrides, Carbides and Fluorides ORGANIC GROUP FUNCTIONALIZED MESOPOROUS SILICAS Synthetic Approaches Combinatorial Synthesis Accessibility to the Active Site and Applications Conclusions APPLICATIONS OF MESOPOROUS MOLECULAR SIEVES Catalysts and Carriers Biology, Separation and Adsorption Photoelectric Applications High-Tech Fields Such as Electromagnetism OUTLOOK INDEX
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Mesoporous materials with the characteristics of high surface area, ordered pore arrangements and good uniformity of pore size have a wide prospect of application in many fields such as electronics, optics, magnetics, sensors and catalysis etc. and are extensively investigated at home and abroad.The recent progress in studies of non-siliceous mesoporous materials including mesoporous aluminophosphates (AlPOs), mesoporous carbon and mesoporous metal oxides are reviewed.
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Since the discovery of silicate and aluminumsilicate ordered materials in the early 1900s, they display a periodic array of mesopores of tailored and narrowly distributed size, have attracted the attention of many research groups due to their special properties. Much work has been devoted to the studies of the synthesis, application of such materials and siliceous ordered mesoporous materials, they have been well-investigated and covered by several excellent reviews. However, less work has been done for non-siliceous mesoporous materials and mesoporous composites, although they could have more interesting properties and wide range applications in the areas such as optics, electricity, magnetics, catalysis and sensors. The latest progress in the study of non-siliceous mesoporous materials, mesoporous composites is reviewed and the basic concepts, mechanisms, properties and applications are introduced. Based on the existing problems in this field, the development trend, application and research directions are discussed.
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Ordered mesoporous silicas with 2-dimensional hexagonal arrays of closed cylindrical pores were synthesized via templating with block copolymer surfactant followed by calcination at appropriately high temperatures. Precursors to closed-pore silicas, including SBA-15 silicas and organosilicas, were selected based on the existence of narrow passages to the mesopores. The increase in calcination temperature to 800–950 °C led to a dramatic decrease in nitrogen uptake by the materials, indicating the loss of accessible mesopores, whereas small-angle X-ray scattering (SAXS) indicated no major structural changes other than the framework shrinkage. Since SAXS patterns for ordered mesoporous materials are related to periodic arrays of mesopores, the existence of closed mesopores was evident, as additionally confirmed by TEM. The formation of closed-pore silicas was demonstrated for ultralarge-pore SBA-15 and large-pore phenylene-bridged periodic mesoporous organosilicas. The increase in the amount of tetraethyl orthosilicate in standard SBA-15 synthesis also allowed us to observe the thermally induced pore closing. It is hypothesized that the presence of porous plugs in the cylindrical mesopores and/or caps at their ends was responsible for the propensity to the pore closing at sufficiently high temperatures. The observed behavior is likely to be relevant to a variety of silicas and organosilicas with cylindrical mesopores.
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