User:Sketchc89/mesoporousedit

Mesoporous Organosilica
''1. The title explains what the article is about. Can't get much better than that.''--Sketchc89 (talk) 22:50, 12 October 2011 (UTC)

''2. The background and significance is a bit too wordy. This might just be due to the requirements of the assignment. There are a few points where the choice of past vs. present tense is awkward.''--Sketchc89 (talk) 22:50, 12 October 2011 (UTC)

''3.It does, but it needs to be stated more clearly. Significance is the most important thing and should come right after the definition. Always try to put yourself in the shoes of you user. Your user doesn't care about zeolites enough to put them in the second sentence. He/she cares about why is this important.'' --Sketchc89 (talk) 22:50, 12 October 2011 (UTC)

''4. Yes. No. Awesome job you nailed it''--Sketchc89 (talk) 22:50, 12 October 2011 (UTC)

''5. Pictures are worth a thousand words. Helpful images are worth a million. A great image can deliver all the content I need in a few seconds.''--Sketchc89 (talk) 22:50, 12 October 2011 (UTC)

''6. You did your homework. Hurray! The articles were relevant and recent''--Sketchc89 (talk) 22:50, 12 October 2011 (UTC)

''7. The synthesis section of the article was written very well. The rest of the article was verbose. Try asking what the point of each sentence is. Consider reducing the use of words like that, which, however, also.''--Sketchc89 (talk) 22:50, 12 October 2011 (UTC)

''One thing I would keep in mind is that you can link to other articles, so instead of having to explain parts of sentences you can just link out to the relevant article.

Good luck, you're doing great so far. Cheers.

Trying to read through references in the edit mode is making my eyes bleed. Wikipedia seriously needs a color coded IDE or something.''--Sketchc89 (talk) 22:50, 12 October 2011 (UTC)

Background and Significance
Mesoporous materials --Sketchc89 (talk) 22:15, 12 October 2011 (UTC)are have been defined as porous materials with pore size ranging from between--Sketchc89 (talk) 22:15, 12 October 2011 (UTC) 2 nm - 50 nm. Unlike zeolites, which are a much older family of porous materials, mesoporous materials owing to their larger pore size, allow for interaction with large molecules and polymers, nanoscale clusters and wires, and enhanced diffusion rates of molecules within the pores. The first breakthrough in the field of mesoporous materials was in 1992 when the Mobil Corporation researchers synthesized a family of materials with ordered mesoporosity, tunable pore diameter (2–30 nm), and high surface area (>700 m2 g-1). The synthesis involved co-assembly of surfactant micelles and a silica precursor, tetraethyl orthosilicate (TEOS). The early mesoporous materials designed were pure silicates (PMS) and aluminosilicates. However, their noncrystalline nature result ing ed--Sketchc89 (talk) 22:15, 12 October 2011 (UTC) in lower thermal and mechanical stability and broader pore-size distributions compared to zeolites was a major shortcoming. S oon s ynthesis of modified siliceous mesoporous materials expand ing ''ed'--Sketchc89 (talk) 22:15, 12 October 2011 (UTC)' their applications to other diverse areas such as drug delivery, separation, sensing, adsorption, and catalysis became a major focus in the area. Various types of modifications have been studied such as addition of key metallic or molecular species into or onto the siliceous mesoporous framework, and the synthesis of various other mesoporous transition metal oxide materials (eg TiO2). A lot of interest also emerged in incorporating organic groups into the PMS materials and yield--Sketchc89 (talk) 22:15, 12 October 2011 (UTC)ed useful properties by tuning the hydrophobicity/hydrophilicity of the surfaces. The most common approaches have been to covalently bind organic species to preformed silica by a post-synthetic grafting approach, co-condensation one-pot synthesis or direct condensation of bis-silanes. However, the limitation of these synthetic methods is that the distribution of the organic groups within the pores is not always homogenous. Also, the need for the co-assembly of silsesquioxane precursors with terminal organic groups with TEOS to form a stable periodic mesoporous structure limits the organic content of the material usually to around 25% with respect to the silicon wall sites. In 1999, Ozin et al and Stein et al, independently developed a class of organic-inorganic composites known as periodic mesoporous organosilicas (PMOs) in which the organic groups were located within the channel walls as bridges between Si centers,. The use of bridged organosilane precursors of the type (CH3 (CH2)nO)3Si–R–Si(O(CH2)nCH3)3 allows for the homogeneous integration of organic species into the walls of the mesoporous matrix through covalent Si–C bonds compared to the organosilica materials obtained via the grafting method. Such materials can be prepared with a high degree of order and uniformity of pores, using a silsesquioxane of the type (EtO)3Si-R-Si-(OEt)3 as the sole precursor. To date many inorganic-organic hybrid materials with interesting applications in biocatalysis, separation and decontamination, chromatography and drug delivery have been synthesized by covalently immobilizing organoalkoxysilanes (R–Si(OR’)) onto mesoporous silica materials.

Nanonaninano (talk) 02:52, 6 October 2011 (UTC)

Synthesis
Surfactant-mediated synthesis has been widely used for the production of mesoporous materials in general, and periodic mesoporous organosilicas (PMOs) specifically,. It involves the addition of a surfactant or copolymer to a specific molecular precursor. The surfactant directs the structure of the material by interacting with the precursor in such a way that is dependent on the properties of the precursor. After the bulk structure is assembled, the surfactant is removed, leaving pores, or channels, embedded in the material framework. The surfactant template can be removed by solvent extraction or ion-exchange mechanisms. An aging process is usually performed at high temperature before removal of the surfactant. During surfactant-mediated synthesis, hydrolysis and polycondensation, or co-condensation, are used to fuse precursor molecules in a framework. Acidic or basic conditions are used for the hydrolysis depending on the precursor being introduced pH is dependent on the precursor--Sketchc89 (talk) 22:15, 12 October 2011 (UTC).

Mesoporous organosilicate materials have been made using bridged organic precursors, in which an organic fragment is positioned between silicon-containing fragments. Single precursor syntheses are typically done with bridged organosilane groups. When only one bridged organic precursor is used, there is a homogeneous distribution of the molecule in the framework. This phenomenon is referred to as molecular-scale periodicity. Chiral precursors can also be introduced into the material framework, and using acidic conditions in the hydrolysis and condensation process proves better for chiral precursors because no racemization occurs. Co-condensation of multiple organosilane precursors can create multi-functional organosilica materials. Tetraethoxysilane (TEOS) is a common silicon precursor used in co-condensation reactions. Post-synthetic grafting is often used to functionalize the framework with organic groups. However, post-synthetic grafting can create uneven distribution of organic groups in the framework in contrast to co-condensation.

Depending on the synthetic conditions used to make mesoporous organosilicas, the mesoscale structure can either be amorphous or crystalline. Amorphous structures typically arise from functionalizing organic groups rather than directly integrating the functional groups in the framework, which produces a periodic structure. Organosilica materials can be precipitated from an aqueous phase to form powders, and evaporation-induced self-assembly can be used to create transparent materials. Evaporation-induced self-assembly usually causes random alignment of the material pores. This method of synthesis uses the difference in vapor pressure of solvents to vary the rate of evaporation and therefore the assembly of the organosilica framework. The synthesis section is written very well--Sketchc89 (talk) 22:15, 12 October 2011 (UTC)

Applications
The obvious most common, not obvious to everyone--Sketchc89 (talk) 22:15, 12 October 2011 (UTC) applications of high-surface area, highly porous compounds are catalysis, adsorption , and separation. These applications have been the roles of zeolites, but their small pore size limits them to work with small molecules. The larger pore size (2-50 nm) of mesoporous materials gives them wider application – larger molecules can be admitted, and guest molecules can migrate faster. To effect affect, I confuse this all the time--Sketchc89 (talk) 22:15, 12 October 2011 (UTC) catalytic transformations using mesoporous organosilicas, it is necessary to functionalize them. The two major methods are to add a group or heteroatom, such as a metal center, to the organic framework, and to anchor  an organic or organometallic group to the pore surface.

Incorporating catalytically active sites into the pore framework has the advantage--Sketchc89 (talk) 22:15, 12 October 2011 (UTC)The advantage of incorporating active sites into the pore framework is that it does not block the pores, so guest molecules travel more freely. However, the active sites that can be incorporated this way have low specificity. The major applications of this type of catalytically active mesoporous organosilicas are for acid catalysis and oxidation catalysis. Acid catalysis is very industrially important. Many reactions (such as Friedel-Crafts) are still carried out using conventional acids, a less environmentally friendly reaction condition than a heterogeneous catalyst. An oxide catalysis example would be good too. --Sketchc89 (talk) 22:15, 12 October 2011 (UTC)

Anchoring a homogeneous catalyst onto a mesoporous organosilicas framework has two primary disadvantages: the bulky group in the pore can block travel of guest molecules through it, and preparation of candidate molecules for anchoring to the framework is difficult. However, anchoring can create heterogeneous catalysts for a wide variety of chemical transformations: acid catalysis, base catalysis , coupling and condensation reaction catalysis , and even asymmetric catalysis. Good points but I would discuss the advantages before the disadvantages

Outline
''What a fabulous outline. I'm seeing stars!''--Sketchc89 (talk) 22:15, 12 October 2011 (UTC) other refs
 * Structure and types
 * Synthesis
 * Characterisation
 * Applications
 * Catalysis
 * Incorporation
 * advantages / disadvantages
 * acid catalysis
 * oxidation catalysis
 * Anchoring
 * advantages / disadvantages
 * acid catalysis
 * asymmetric catalysis
 * basic catalysis
 * other investigated reactions (e.g. coupling)
 * Adsorption
 * Separation