Synthesis And Properties Of Mesoporous Materials

By Author: jayson elliot
Total Articles: 162
Comment this article

In Recent years, Nanosceience has been the most popular science in the research and industrial communities. The term Nano refers to one billionth (10-9) of a meter. As an example of nanoscale: The width of a human hair is 10.000 times higher than the width of a nano dot. Nanoparticles offer unique properties such as mechanical, good wetting, chemical, thermal and optical properties.
Generally, Nanoparticles can be synthesized either by Top-down approach or Bottom-up approach. Top-down methods include ball milling and attrition, while the bottom-up methods include colloidal dispersion or precipitation process. Though top-down approach is simple and easy to operate even for large scale production, but it suffers with imperfection of surface structure and inhomoginity in particle size distributions. However, the bottom-up methods offer to build nanoparticles atom-by-atom, molecule-by-molecule or cluster-by-cluster, which excludes the surface roughness and offer various physicochemical properties with a desired particle size distribution.
Nanoporous materials are considered to be special category of nanoparticles because ...
... of their unique synthesis routes and properties. A good cup of coffee cannot be prepared without the use of a filter paper, and hence the filter paper which possesses a specific pore size is an important aspect of brewing good coffee. The pores in the filter paper are on a micrometer (μm) scale. The science of making porous materials of molecular size is industrially important, as these are essential for gas separation, drug delivery, catalysis and other applications of great value to modern society.
Mesoporous materials are an important category of nanoporous materials due to their large pore size (2.0 - 50.0 nm). The synthesis of mesoporous materials is based on the use of surfactants as templates. The surfactant molecules self assemble to form micelle structures. The synthesis involves the replication of a surfactant liquid crystal structure by the polymerization of a metal oxide precursor (e.g. silica, alumina, titanium oxide, other metal oxides) around these structures. This is followed by removal of the organic surfactant through calcination. The procedure leads to a porous structure supported by a hard metal oxide framework.
Silica based nanoporous materials have shown to have potential for many applications, these include their use as catalyst supports, adsorbents and membrane separation as a result of their high specific surface areas, internal pore volumes, tailorable surfaces, and high chemical and thermal stabilities. In life science, nanoporous silica materials play an important role as drug delivery systems. Recent advances in technology have made it possible to tailor the porosity and other properties of silica nanoparticles, which make it particularly interesting as a drug delivery system.
Properties of nanoporous silica materials:
Uniform pore size distribution
High surface area and pore volume
Controlled particle shape and size
1D, 2D and 3D porous structures
High density of hydroxyl ( ESi-OH) groups
Anchoring various functional groups on the framework
Biocompatibility
In addition to the nanoporous silica materials, Nanoporous Alumina is an interesting and attractive material because of its applications as absorber or catalyst support in heterogeneous catalytic reactions. Classically, apart from zeolites, materials most commonly used for catalysis and catalyst supports have been those based on high surface nanoporous aluminas, owing to their thermal, chemical, and mechanical stability and their low cost. Synthesis of nanoporous alumina is rather difficult due to aluminum metal coordination and hence vapor phase deposition or sol gel methods are most commonly used. Initially the synthesis of aluminum nanoparticles employed simple top down approaches, most common being ball milling, but were shortly abandoned due to lack of control of the resulting particles. However, by using surfactant templates and structure directing agents and polymerization of aluminum oxide precursor, one can prepare high quality nanoporous aluminum nanoparticles. The precipitated nanoporous alumina powder can be filter and calcined at 500 oc for removal of organic templating agents.
Aluminum nanoparticles possess high surface areas and controlled pore size. The particle size and shape can be controlled by tuning the synthesis parameters such as temperature, pH, additives, solvents and drying methods. Nanoporous alumina particles are expected to play important roles in various applications such as in electronics, optoelectronics, catalysis, hydrogen storage and thin film coatings.
Jayson Elliot, For more information on Nanoporous Silica, Synthesis of nanoparticles, Nanoporous Alumina, silica nanoparticles, Aluminum nanoparticles.