Mesoporous silica monoliths

S.A. El-Safty and T. Hanaoka, Microemulsion Liquid Crystal Templates for Highly Ordered Three-dimensional Mesoporous Silica Monoliths with Controllable Mesopore Structures. Chem. Mater., 2004, 16, 384 100. 

S.A. El-Safty, T. Hanaoka, and F. Mizukami, Large-sclae Design of Cubic Ia3d Mesoporous Silica Monoliths with High Order, Controlled Pores, and Hydrothermal Stability. Adv. Mater., 2005, 17, 47-53. 

Gold nanoparticles prepared within mesoporous silica monolith showed red-shift of the Mie-resonance absorption band with decreasing the Au particle size. Comparison with theoretical calculations of Mie-resonance for particles of... 

Monolithic carbons are easier to handle than powdered materials. Direct shaping of monolithic mesoporous carbons during their preparation is highly desirable. Mesoporous carbon monoliths may be fabricated by using mesoporous silica monoliths as template. Carbon monoliths with well-developed and accessible porosity have been produced using silica monoliths with a hierarchical structure containing macropores and meso-pores as templates and furfuryl alcohol or sucrose as a carbon precur-... 

Leventis N, Mulik S, Wang X, Dass A, Patil V U, Sotiriou-Leventis C, Lu H, Churu G, Capecelatro A (2(X)8) Polymer nano-encapsulation of templated mesoporous silica monoliths with improved mechanical properties. J Non-Cryst SoUds 354 632-644... 

The aim of this chapter is to provide details of a new class of nanosensor based on mesoporous silica monoliths with cage-like pores as carriers. Comprehensive up-to-date information is provided regarding the environmental chemistry and toxicity of mercury, antimony, cadmium and lead, in the quest to design simple, eco-friendly and smart sensing systems. A critical review of the literature is also provided in terms of the chemical toxicity of mercury, antimony, cadmium and lead, and their treatments with different processes and under varying environmental condihons. 

The growth of MOF nanoparticles inside porous silica monolith is a promising approach for catalysis applications. Sachse et al. demonstrated the successful formation of HKUST-1 crystals inside silica monolith [79]. Macro/mesoporous silica monolith was synthesized using TEOS as a Si02 precursor and ammonia as a catalyst. For the subsequent MOF formation, the as formed monolith was immersed in HKUST-1 precursor solution using DMSO as a solvent. The employment of DMSO instead of classical solvents (ethanol and water mixture) for the synthesis of HKUST-1 crystals led to slower nucleation of smaller crystals in the mesopores of monolith rather than at the outer surface. 

The major design concept of polymer monoliths for separation media is the realization of the hierarchical porous structure of mesopores (2-50 nm in diameter) and macropores (larger than 50 nm in diameter). The mesopores provide retentive sites and macropores flow-through channels for effective mobile-phase transport and solute transfer between the mobile phase and the stationary phase. Preparation methods of such monolithic polymers with bimodal pore sizes were disclosed in a US patent (Frechet and Svec, 1994). The two modes of pore-size distribution were characterized with the smaller sized pores ranging less than 200 nm and the larger sized pores greater than 600 nm. In the case of silica monoliths, the concept of hierarchy of pore structures is more clearly realized in the preparation by sol-gel processes followed by mesopore formation (Minakuchi et al., 1996). 

A rather limited range of mesopores in terms of size and volume were observed in the skeletons of polymer monoliths. The porosity of the polymer monolith seems to be lower than that of silica monolith. The total porosity of these monoliths is in the range of 0.61-0.73, whereas interstitial (through-pore) porosity and mesopore porosity are 0.28-0.70 and 0.03-0.24, respectively. In the case of poly(butyl methacrylate-co-ethylene dimethacrylate), the observed porosity is around 0.61-0.71, resulting in permeability 0.15-8.43 x 10 14 m2, whereas the observed porosity of silica monoliths prepared in a capillary is 0.86-0.96 and the permeability is 7-120 x 10 14 m2. Higher permeability will be advantageous for 2D applications, as mentioned later. 

Another recent trend focused on supports in the shape of monolithic columns having the goal to benefit from the high permeability and the improved mass transfer characteristics of such structures. With this goal in mind, Lubda and Lindner [75] prepared enantioselective silica monolith columns with tert-butylcarbamoylquinine surface modification. A commercial sol-gel-derived Chromolith Performance Si (100 X 4.6 mm ID) monolith (1.9 tim macropore diameter, 12.5 nm mesopore... 

Fig. 5 Relationship between the amount of graft polymers and Mn of free polymers. The graft polymerization was carried out under various conditions on silicon wafer (squares), silica particles with varying diameter (d = 12, 130, 290, 740, 1550 nm) (circles), and silica monolith with 50-nm mesopores (triangles). Two types of immobilized initiators, 2 and 5 (n = 6 and R" = CH3) in Fig. 2, two types of copper halides, CuBr and CnCl, and two types of ligands, spartein (Sp) and dipyridyl derivatives (4,4 -diheptyl-2,2 -dipyridyl (dHbipy) and 4,4 -dinonyl-2,2 -dipyridyl (dNbipy)), were used...

Usually, two 100 cm long monolithic columns were prepared from the same reaction mixture, and two-four 33 cm long columns were obtained from the two 100 cm long silica capillaries containing silica monolith. The capillary columns (100 pm I.D.) showed 10,000-12,000 theoretical plates for the effective length of 25 cm under optimized conditions in a pressure-driven mode, and up to 40,000 plates in the CEC mode. The use of smaller-sized capillaries, e.g., 50 pm I.D., and the modification of the preparation method of mesopores, resulted in a monolithic silica column of higher efficiency and higher mechanical stability [25-27], Under optimized conditions, 80,000 plates were obtained with a 25 cm column in CEC. 

A monolithic column can be defined as a column consisting of one piece of solid with a defined pore structure that possesses interconnected skeletons and interconnected flow paths (through-pores) and mesopores. A monolithic silica column consists of micron-sized skeletons (1-2pm), through-pores (up to 8pm), and mesopores (10-12nm). The mesopores provide the needed... 

Feng and coworkers prepared nanocrystalline tin oxide on monolithic mesoporous silica starting from Sn(acac)2Cl2 by simple immersing of the substrate in the precursor solution. Heat treatment (300-600 °C) leads to nanocomposites with a large specific surface area. The electrical properties of these nanocomposites were also investigated. The authors found an inverse correlation between the precursor concentration and the electrical resistivities of the samples. ... 

Figure 3. Three-dimensional AFM image of the surface of monolithic mesoporous silica. Taken from ref 39 - Reproduced by permission of The Royal Society of Chemistry.

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