A Sol-gel Method

Very few examples have been described for the non-covalent immobilization of chiral porphyrin complexes (Fig. 26). In the first case, the porphyrin-dichlororutheninm complex was encapsulated in silica, which was prepared around the complex by a sol-gel method [78], in an attempt to prevent deactivation observed in solution in the epoxidation of different alkenes with 2,6-dichloropyridine N-oxide. In fact, the heterogeneous catalyst is much more active, with TON up to 10 800 in the case of styrene compared to a maximum of 2190 in solution. Enantioselectivities were about the same imder both sets of conditions, with values aroimd 70% ee. 

Recently, it is reported that Xi02 particles with metal deposition on the surface is more active than pure Ti02 for photocatalytic reactions in aqueous solution because the deposited metal provides reduction sites which in turn increase the efficiency of the transport of photogenerated electrons (e ) in the conduction band to the external sjistem, and decrease the recombination with positive hole (h ) in the balance band of Xi02, i.e., less defects acting as the recombination center[l,2,3]. Xhe catalytic converter contains precious metals, mainly platinum less than 1 wt%, partially, Pd, Re, Rh, etc. on cordierite supporter. Xhus, in this study, solutions leached out from wasted catalytic converter of automobile were used for precious metallization source of the catalyst. Xhe XiOa were prepared with two different methods i.e., hydrothermal method and a sol-gel method. Xhe prepared titanium oxide and commercial P-25 catalyst (Deagussa) were metallized with leached solution from wasted catalytic converter or pure H2PtCl6 solution for modification of photocatalysts. Xhey were characterized by UV-DRS, BEX surface area analyzer, and XRD[4]. 

In order to obtain a nano-hybrid with higher mechanical properties, PDMS was replaced with poly(tetramethylene oxide) (PTMO) [41]. PTMO-Ti02 nano-hybrids were prepared by a sol-gel method from triethoxysilane functionalized PTMO (Si-PTMO) and tetraisopropyltitanate with weight ratios of 30/70, 40/60 and... 

Miyazaki et al. [43] reported that a sol-gel-derived Ta2Os gel shows hydroxyapatite-forming ability in SBF even in the amorphous state. Therefore, PTM0-Ta205 nano-hybrids prepared by a sol-gel method can be expected to form hydroxyapatite in SBF without any treatment. PTMO-CaO-Ta2Os nano-hybrids were prepared by... 

Preparation of a bioactive and degradable poly(epsilon-caprolactone) / silica hybrid through a sol-gel method. Biomaterials, 23, 4915-4921. 

The Stober method is also known as a sol-gel method [44, 45], It was named after Stober who first reported the sol-gel synthesis of colloid silica particles in 1968 [45]. In a typical Stober method, silicon alkoxide precursors such as tetramethylorthosili-cate (TMOS) and tetraethylorthosihcate (TEOS), are hydrolyzed in a mixture of water and ethanol. This hydrolysis can be catalyzed by either an acid or a base. In sol-gel processes, an acidic catalyst is preferred to prepare gel structure and a basic catalyst is widely used to synthesize discrete silica nanoparticles. Usually ammonium hydroxide is used as the catalyst in a Stober synthesis. With vigorous stirring, condensation of hydrolyzed monomers is carried out for a certain reaction time period. The resultant silica particles have a nanometer to micrometer size range. 

Guizard et al. (1986), Cot, Guizard and Larbot (1988) and Larbot et al. (1989) used a sol-gel method to prepare zirconia membrane top layers on an alumina support. The water necessary for the hydrolysis of the Zr-alkoxide was obtained from an esterification reaction. The complete hydrolysis was done at room temperature and resulted in a hydrated oxide. The precipitate was peptized with nitric or hydrochloric acid at pH <1.1 and the final sol... 

LDHs with Ni/Al molar ratio of 2.5 have been synthesized by a sol-gel method using nickel acetylacetonate and aluminium isopropylate as precursors. The sol-gel synthesized samples exhibited lower crystalhte dimensions and greater BET surface areas compared with coprecipitated samples prepared from an aqueous solution of nickel and aluminium nitrates [19,172]. 

Navvio, J.A., Testa, J.J., Djedjeian, P., Padron, J.R., Rodriguez, D., Litter, M.I. 1999. Iron-doped titania powders prepared by a sol-gel method. Appl Catal A General 178 191-203. 

Kohno M, Ogura S, Inoue Y (1996) Preparation of BaTi40g by a sol-gel method and its photocatalytic activity for water decomposition. J Mater Chem 6 1921-1924... 

New high-surface-area zirconia-carbon composites were prepared by a sol-gel method followed by a high-temperature treatment in inert gas.420 The samples proved to be very active and selective in the aromatization of Cg+ alkanes (n-hexane and n-octane). From n-octane, as main products, only ethylbenzene and o-xylene were formed. The catalysts have low acidity due to significant dehydration of the zirconia surface, and high surface area since the carbon matrix prevents sintering of the Zr02 particles. 

The new material is obtained through a sol-gel method followed by a thermal treatment at very high temperatures, so the material has a high thermal stability. 

ICI Co. uses a sol-gel method to produce silica-stabilized alumina (Saffil) and calcia-stabilized zirconia fibre [15], The saffil fibre is a 8-alumina short staple fibre that has about 4% Si02 and a very fine diameter (3 pm). 

Fig. 5.1. Scanning electron micrographs of continuous-bed columns prepared from ODS-silica particles packed in a capillary. Prepared from (a) 75 pm capillary packed with silica particles by sintering in the presence of NaHC03 [9], and (b) large pore (left) and small-pore (right) ODS particles by a sol-gel method [10]. Reproduced from refs. 9 and 10, with permission.

With fluorosulfonate ionomers other than Nation, the specifications for the GDL has to be changed. More recently, Nishikawa et al. [79] developed GDLs for novel organic-inorganic hybrid electrolytes. They mixed Triton and PTFE dispersions with carbon black and coated the mixture on to carbon paper that had been wet-proofed with FEP copolymer. A nanohybrid electrolyte was prepared by a sol-gel method and formed over the GDL. Addition of uncatalyzed carbon black to the cathode GDL was found to enhance the performance at high current densities. 

In addition [103,104], a new type of composite that combines DNA with silica components via a sol-gel method was described. The DNA-silica hybrid material is advantageous with respect to its mechanical and chemical stability in both aqueous and organic solvents. Similar to the previously described hybrids, the specific functions of the DNA molecules were retained and maintained the DNA-silica hybrid materials adsorb DNA-interactive chemicals from diluted aqueous solution. In another series of reports [105-109], DNA-loaded PSf microspheres were fabricated by means of a liquid-liquid phase separation technique. The release rate of DNA from the microspheres can be controlled by manipulating the microsphere structure. Increasing the polymer concentration causes lower porosity and smaller pores on the outer surface of the microspheres, and leads to a low release rate of DNA from the microspheres. The DNA-loaded PSf microspheres could effectively accumulate harmful DNA-intercalating pollutants and endocrine disruptors, as described in previous reports. 

Fu L., Zhang H., Wang S., Meng Q., Yang K. and Ni J. Preparation and luminescence properties of the ternary europium complex incorporated into an inorganic/polymer matrix by a sol-gel method, J. Sol-Gel Set. Technol. 15 (1999) pp. 49-55. 

Yan B., Zhang H., Lin J., Wang S. and Ni. J. Luminescence properties of the ternary rare earth complexes with P-diketones and 1,10-phenanthroline incorporated in silica matrix by a sol- gel method. Mater. Chem. Phys. 51 (1997) pp.92-95. 

YBOsiEu vary with the synthetic route. The YBOaiEu powder synthesized through a sol-gel method exhibit three Eu sites identified by site selective excitation. The Eu concentration dependence of emission intensity and Eu luminescence decay from 300 to 15 K prove that the energy migration is phononassisted. (Boyer et al., 2003). 

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