Mesoporous ceramics

Pacific Northwest National Laboratory (PNNL) is researching the use of self-assembled monolayers on mesoporous supports (SAMMS) technology for the removal of metals and radionuclides from liquid and gaseous hazardous wastes. SAMMS combines two technologies—mesoporous ceramic material and functionalized monolayers. The ceramic material has pores that increase its surface area. This ceramic material is coated with functionalized monolayers that form stable, covalent bonds with the contaminants. 

J.M. Hofman-Ziiter, Chemical and Thermal Stability of (Modified) Mesoporous Ceramic Membranes , PhD Thesis, University of Twente, 1995. 

The porous structure of ceramic supports and membranes can be first described using the lUPAC classification on porous materials. Thus, macroporous ceramic membranes (pore diameter >50 nm) deposited on ceramic, carbon, or metallic porous supports are used for cross-flow microfiltration. These membranes are obtained by two successive ceramic processing techniques extrusion of ceramic pastes to produce cylindrical-shaped macroporous supports and slip-casting of ceramic powder slurries to obtain the supported microfiltration layer [2]. For ultrafiltration membranes, an additional mesoporous ceramic layer (2 nm<pore diameter <50 nm) is deposited, most often by the solgel process [11]. Ceramic nanofilters are produced in the same way by depositing a very thin microporous membrane (pore diameter <2 nm) on the ultrafiltration layer [4]. Two categories of micropores are distinguished the supermicropores >0.7 nm and the ultramicropores <0.7 nm. 

The most demanding support requirements are those for ultra thin micro-porous gas separation membranes, which are currently being developed in several research organisations worldwide including ECN (Petten, the Netherlands). In principle, a mesoporous Knudsen or UP membrane can serve as support for these membranes if the defect density in the substrate surface, i.e. the mesoporous layer, is low enough. Indeed, the quality of the Knudsen or UF membrane as support for a microporous gas separation membrane should be higher than is usually needed for the UF or Knudsen function [4]. This means that not every mesoporous ceramic membrane is a suitable support for micro-porous or dense amorphous gas separation membranes. 

Finally, organic additives can affect the thermal properties (phase transformation behaviour) of mesoporous ceramic membranes. Ziiter [15] reported the transformation from monoclinic to tetragonal particles and back as a function of the amount of PVA. 

J.M. Ziiter-Hofman, Chemical and thermal stability of (modified) mesoporous ceramic membranes. PhD Thesis, University of Twente, Enschede, the Netherlands. 

S. Roy Chowdhury, P. T. Witte, D. H. A. Blank, P. L. Alsters, J. E. ten Elshof, Recovery of homogeneous polyoxometalate catalysts from aqueous and organic media by a mesoporous ceramic membrane without loss of catalytic activity, Chem. Eur.. 12 (2006) 3061. 

All the mesoporous ceramic oxides obtained by this method are amorphous on the atomic level, but show periodicities on the nanometer length scale and narrow pore size distribution. The outcome of the process is very predictable, as the binary phase diagram of the surfactant can be used as a guideline towards the nanostructure design. The transmission electron microscopy images of siH-cas derived from three different LLC surfactant phases are shown in Fig. 3. 

The position of the hydrophilic poly(ethylene oxide) (PEO) headgroups in ABCs and nonionic surfactant templates bears important imphcations with respect to the overall pore structure of the resulting porous material. The PEO chains can be assumed to be firmly anchored and molecularly dispersed within the silica matrix, hence giving rise to substantial microporosity of the meso-porous system. The following section is aimed at describing the pore structure of nonionically templated mesoporous ceramics more exactly. 

The surfactant templated synthesis of mesoporous ceramics was first reported in 1992 [1], and since that time there has been a veritable explosion in the number of papers in the area. There has been particular interest in the functionalization of mesoporous ceramics [2-S]. As outlined in Figure 1, the original synthesis employed rod-shaped micelles composed of cationic surfactant molecules as the pore template (more recently, this methodology has been extended to a wide variety of other surfactant systems and reaction conditions). When exposed to routine sol-gel conditions, the cationic micelles undergo an anionic metathesis with silicate anions, resulting in a glass-coated log which... 

List the possible applications for zeolites and mesoporous ceramics. 

Kamperman M, Garcia WBC, Du P, Ow H, Wiesner U (2004) Ordered mesoporous ceramics stable up to 1500°C fiom diblock copolymer mesophases. J Am Chtan Soc 126 14708... 

S. Patil, S. S. Pancholi, S. Agrawal and G. P. Agrawal Surface-modified mesoporous ceramics as delivery vehicle for haemoglobin. Drug Deliv., 11,193-199 (2004). 

The pyrolysis process provides a fast and simple route for the preparation of mesoporous ceramic materials. While the spatial distribution of the nanoclusters in 2 is random, we are extending our research efforts to the design and synthesis of amphiphilic copolyferrocenylenesilynes, in the hope of converting self-assembled... 

Guizard C., Levy C., Dalmazio L., Julbe A. Preferential oxygen transport in nanophase mesoporous ceramic ion conducting membranes. MRS. Symp. Proc. 2003 752 131-142 Hamakawa S., Hayakawa T., Suzuki K., Murata K., Takehira K. Methane conversion with an electrochemical membrane reactor. In Proceeding of ICIM 5 (Inorganic Membranes), Nagoya, Japan. Nakao S., ed., 1998, pp. 350-353... 

Vallet-Regi, M., Manzano, M., and Colilla, M. (2013) Stimuli-responsive drug delivery systems based on mesoporous silica, in Biomedical Applications of Mesoporous Ceramics, CRC Press, New York, pp. 105-134. 

Figure 5.29 Strategy for developing inorganic nanoscale objects and mesoporous media from microphase-ordered block copolymer templates. In this case, an I-EO diblock copolymer is imbibed with a ceramic precursor such as 3-(glycidyloxypropyl)trimethoxysilane (GLYMO) and aluminum iec-butoxide so that the corresponding silicate can be subsequently formed within the confined environment of the copolymer matrix. Dissolution of the copolymer results in discrete, polymer-covered ( hairy ) objects, whereas calcination at elevated temperatures yields mesoporous ceramic materials. (Reprinted with permission from Simon, P. F. W., Ulrich, R., Spiess, H. W. and Wiesner, U. Chem. Mater. 13, 3464, 2001. Copyright (2001) American Chemical Society.)...

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