Mesoporous materials morphology control

Mesoporous materials were originally synthesized in irregular bulk or powder forms, which could limit their applications in separation, optics, electronics, and so on. Thus, it is highly desirable to produce mesoporous materials with controllable macroscopic forms. So far, mesoporous materials have been synthesized in a variety of forms including thin films, spheres, fibers, monoliths, rods, single crystals, and nanoparticles. The acidic synthetic route (S+X I+) developed by Huo etal. appears to be the most appropriate for the morphological control of mesostmctures. 

The above results demonstrate that partially fluorinated nonionic surfactants, having a fluorinated hydrophobic chain and a nonfluorinated poly(ethylene oxide) polar chain, can be successfully used to obtain mesoporous materials with controlled morphology and pore size. The specific surface areas can be high, similar to MCM-41 materials obtained using hydrocarbon surfactants. 

Although studies on the subject of ordered mesoporous materials were started about 15 years ago, the unique structure and the properties of these materials attracted many scientists in different fields of research. Their efforts resulted in fruitful results that have been reported in thousands of publications. The flexibility and complexity of their synthesis and structure, and the extensive application potentials of mesoporous materials, create a huge opportunity for researchers and developmental scientists. This chapter will summarize the research results on mesoporous materials from syntheses, structures, formation mechanisms, compositions, morphologies, pore-size control, modifications, applications, challenges, and so on. 

Nevertheless, using preorganized organic assembly to control morphology and nucleation is a potentially powerful approach to mesoporous materials synthesis, particularly... 

For industrial applications, the particle size, morphology, and texture of the mesoporous material are important, which include several critical points such as mechanical stability and macroscopic shapes with well defined properties. Morphology control is one of the most interesting issues in the research field of mesoporous materials. It plays a very important role in understanding the basic synthesis mechanism. 

The control of morphology in mesoporous materials is thought to be governed by kinetic effects as the self-assembly of surfactant molecules and nucleation processes... 

Detailed control of the structural and properties such as pore topology, pore diameter, pore connectivity, controlled multiscale porosity, surface properties, reactivity, functionalization, morphology, and macroscopic shape are desirable to reach the ultimate goals of industrial and commercial applications. Make mesoporous materials able to compete with other current using materials (e.g., zeolites). 

Y. Saito, S. Kambe, T. Kitamura, Y. Wada, Shozo Yanagida Morphology control of mesoporous Ti02 nanocrystaUine films for performance of dye-sensitized solar cells , Solar Energy Materials and Solar Cells, 83, 1-13, (2004). 

Morphology control is indispensable in many of the advanced applications envisioned for functional mesoporous materials (54, 267). Permselective membranes, micro-spheres, or monoliths are important for sorption, separation, and chromatography purposes. Porous thin films or fibrous structures are relevant for electronics, optics, low fe-dielectrics, and sensing applications. Colloidal particles or nanospheres are preferred for biomedical systems to be used in drug delivery or magnetic resonance imaging (MRl) with contrast agents. 

The dimensions and accessibility of pores of zeohtes and microporous solids are confined to the subnanometer scale (<1.5 run), which hmits their applications when processing bulky molecules. Mesoporous materials with pore sizes ranging from 2 to 50 nm overcome these limitations. In contrast with microporous zeolites, these materials lack atomic ordering (crystallinity) in their silica walls as these are usually amorphous. The attractive properties of ordered mesoporous materials include well-defined pore system high surface area and pore sizes narrow pore size distribution tunable up to 100 nm existence of micropores in the amorphous wall (for thicker wall materials) existence of various wall (framework) compositions obtained from direct synthesis, or posttreatment or modification high thermal and hydrothermal stabilities if properly prepared or treated and various controllable regular morphologies on different scales from nanometers to micrometers. 

Morphology Control In Mesoporous Materials Mesoporous Nanoparticles... 

From their discovery in 1992, the field of mesoporous materials has grown in an exponential way with increasing successful synthetic methods for siHca, metal oxides, phosphates, and so on. The relatively low hydrothermal stabiHty of mesoporous phases is perhaps the most critical consideration for their appH-cation, in particular for heterogeneous catalysis. Likewise, the incorporation of chemical functionalities into mesoporous materials has enlarged their appHca-tions. Future research efforts will likely address the development of novel synthetic methods to better control such functionaHzation while avoiding the loss of textural and structural properties of these materials. The morphological control of mesoporous siliceous solids and the incorporation of chemical functionaHties are also of great interest to yield materials with novel properties and prospective applications. 

Ordered mesoporous materials synthesized using surfactant templates [60,61,99] have been widely used as hard templates to prepare various mesoporous carbons. Two Korean research groups were the first to independently demonstrate the use of ordered mesostructured silicas as hard templates [62,63]. Because they have larger pore sizes than zeolites, ordered mesoporous silicas with a 3-D pore system (e.g., MCM-48, SBA-15, and SBA-16) offer more flexibilities for control over the structural, morphological, and surface properties of templated mesoporous carbon. 

Control of morphological properties (particle size and shape) is critical in the behaviour of mesoporous materials in biological media. The interaction of SBA-15 and MCM-41 mesoporous silica particles with human red blood cells was investigated by Zhao et al. (2011). Larger SBA-15 particles ( 531 nm, characterised by... 

Mesoporous materials can be made in a variety of forms. These include bulk powders (the most common form), monolithic gels, and thin Aims, hierarchically ordered fi-brous/tubular forms, and hard spheres. The form obtained depends on the synthesis conditions and in particular the rate of precipitation of the inorganic species. For silica materials, low pH values are used to slow down the rate of silicate precipitation, thus making it easier to control the morphology and form. 

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