Inorganic precursors

Mercury, tin, lead, arsenic, and antimony form toxic lipophilic organometallic compounds, which have a potential for bioaccumulation/bioconcentration in food chains. Apart from anthropogenic organometallic compounds, methyl derivatives of mercury and arsenic are biosynthesized from inorganic precursors in the natural environment. 

One potential solution to these problems, suggested some 20 years ago by Chantrell and Popper (1), involves the use of inorganic or organo-metallic polymers as precursors to the desired ceramic material. The concept (2) centers on the use of a tractable (soluble, meltable or malleable) inorganic precursor polymer that can be shaped at low temperature (as one shapes organic polymers) into a coating, a fiber or as a matrix (binder) for a ceramic powder. Once the final shape is obtained, the precursor polymer can be pyrolytically transformed into the desired ceramic material. With careful control of the pyrolysis conditions, the final piece will have the appropriate physical and/or electronic properties. 

Preparation of chiral mesoporous materials has become a great interest for material scientists. Normally chiral property is introduced into chiral mesoporous material via an organic chiral templating component. But, by using a sonochemical method, Gabashvili et al. [36] have prepared mesoporous chiral titania using a chiral inorganic precursor and a non-chiral dodecylamine as a template. Size of the pores was 5.5 nm. 

Gabashvili A, Major DT, Perkas N, Gedanken A (2010) The sonochemical synthesis and characterization of mesoporous chiral titania using a chiral inorganic precursor. Ultrason Sonochem 17 605-609... 

Organic block copolymer micelles serve as structure-directing reagents in a sol-gel mixture with inorganic precursors to form mesoporous inorganic structures... 

The huge variety of different monolithic supports being introduced for HPLC applications can generally be divided into two main classes monoliths based on organic precursors and monoliths based on inorganic precursors. 

Oxyhalides are another type of volatile inorganic precursors, which have been used in only a few studies, however. For instance, timgsten oxyfluo-ride (WO F ) and H2O have been used as precursors in the deposition of WO3 [48], while Cr02Cl2 together with CH3OH as an oxygen source have been used in the deposition of chromium oxide [49]. 

Afomic layer deposifion (ALD) is now a mature and accepted technique for depositing thin films and overlayers for various applicafions in modern fechnology. ALD is a chemical process where fhe precursor chemisfry plays a very important role and offers many possibilities. Conventional inorganic precursors have been used since the beginning of the ALD era over 30 years ago. To replace the classical precursors, e.g. volatile halides and... 

In 1995, Tanev and Pinnavaia [1] have reported the synthesis of a new type of mesoporous molecular sieve designated as the hexagonal mesoporous silica (HMS). Instead of using the ionic inorganic precursor and surfactant as in the case of MCM-41 [2], HMS is manufactured by hydrolysis reaction between a neutral inorganic precursor, tetraethyl-orthosilicate (TEOS) and a neutral primary amine surfactant (8-18 carbons). HMS possesses numerous favourable characteristics, but, like MCM-41, its synthesis process can only be concluded by the removal of the surfactant. This was reportedly done either by calcination at 630°C or by warm ethanol extraction [1]. 

The formation of the cubic phase is related to the presence of phenyl groups under the same synthesis conditions, with TEOS as unique inorganic precursor, only hexagonal phases have been prepared. But it also depends on other parameters since for a given PTES/TEOS molar ratio, the hydrolysis step plays a major role. We have thus tried to better understand the parameters that control the formation of the cubic phase, by changing the PTES/TEOS as well as the EtOH/Si molar ratios. 

Apart from cetyltrimethylammonium bromide (CTAB), the classical surfactant in M41S syntheses, a variety of differently sized cationic, anionic and neutral surfactants exists (figure 1), which can be used in order to mesostructure various inorganic precursors. 

PCH materials offer new opportunities for the rational design of heterogeneous catalyst systems, because the pore size distributions are in the supermicropore to small mesopore range (14-25A) and chemical functionality (e.g., acidity) can be introduced by adjusting the composition of the layered silicate host. The approach to designing PCH materials is based on the use of intercalated quaternary ammonium cations and neutral amines as co-surfactants to direct the interlamellar hydrolysis and condensation polymerization of neutral inorganic precursor (for example, tetraethylorthosilicate, TEOS) within the galleries of an ionic lamellar solid. 

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