Vapor-surface sol -gel deposition

Guo, W., H. Y. Lu, and N. F. Hu, 2006. Comparative bioelectrochemical study of two types of myoglobin layer-by-layer films with alumina Vapor-surface sol-gel deposited AI2O3 films versus AIO3 nanoparticle films. Electrochim Acta 52 123-32. 

Wang, G., Lu, H. and Hu, N. (2007) Electrochemically and catalytically active layer-by-layer films of myoglobin with zirconia formed by vapor-surface sol-gel deposition. Journal of Electroanalytical Chemistry, 599, 91-9. 

After etching, a carbonaceous coating can be applied by chemical vapor deposition [6] or carbonaceous sol-gel deposit methods [7] deemed capable of further decreasing the internal resistances of ES cells as low as 0.4 fl.cm. Therefore, new and modified current collector surface treatment techniques can promise to further decrease internal cell resistance and improve the overall performance of modern ESs. 

The damaged surface of a ceramic after finishing is sometimes healed by coating. Coating methods include (1) sol—gel, (2) laser gazing, (3) chemical vapor deposition (CVD), (4) sputtering, (5) plasma spraying,... 

Other approaches to reducing the membrane pore size are being investigated. Many of them are based on the sol-gel process or chemical vapor deposition as discussed in Chapter 3. An example is the preparation of small-pore silica membranes. Amorphous silica membranes have been prepared from solutions of silicate-based polymers. More specifically, some strategies are employed aggregation of fractal polymeric clusters, variation of sol composition, the use of organic molecular templates and modification of pore surface chemistry [Wallace and Brinker, 1993]. 

In many studies the separation factor, which is indicative of the membrane s ability to separate two gases in a mixture, is predominantly governed by Knudsen diffusion. Knudsen diffusion is useful in gas separation mostly when two gases are significantly different in their molecular weights. In other cases, more effective uansport mechanisms are required. The pore size of the membrane needs to be smaller so that molecular sieving effects become operative. Some new membrane materials such as zeolites and other molecular sieve materials and membrane modifications by the sol-gel and chemical vapor deposition techniques are all in the horizon. Alternatively, it is desirable to tailor the gas-membrane interaction for promoting such transport mechanisms as surface diffusion or capillary condensation. 

Metal oxide nanostructures have been fabricated using different methods and preparation conditions. The most promising technique is sol-gel processing in combination with dipcoating technique.This method enables us to prepare spinel oxide thin film electrodes at ambient temperature with high level of doping and large surface area [117,118], The physical and chemical vapor deposition is another technique for metal oxide preparation [119,120],... 

Vapor-phase epoxidation of propylene using H2 and O2 was carried out over gold catalysts supported on mesoporous ordered (MCM-41) and disordered titanosilicates prepared hydrothermally or by modified sol-gel method. Gold nanoparticles were homogeneously dispersed on the titanosilicate supports by deposition-precipitation (DP) method. The catalysts and support materials were characterized by XRD, UV-Vis, surface area measurements (N2 adsorption) and TEM. NaOH was found to be the best precipitant to prepare Au catalysts with optimum propylene oxide yields and H2 efficiency. The extent of catalysts washing during preparation was found to affect the activity of the catalyst. The activity and hydrogen efficiency was found to depend on the type of mesoporous support used. 

Si02 surface modified Nafion membranes could be prepared by in situ surfactant-templated sol-gel reaction [38] or by plasma enhanced chemical vapor deposition [45]. Ti02-coated Nafion membranes were prepared by dip coating from a titania sol [85]. 

The catalytic wall reactor with channel diameters in the range 50-1000 pm and a length dependent on the reaction time required circumvents these shortcomings. However, in most cases, the catalytic surface area provided by the wall alone is insufficient for the chemical transformation and therefore the specific surface area has to be increased by chemical treatment of channel walls or by coating them with highly porous support layers. This can be done by using a variety of techniques such as sol-gel, electrophoretic and chemical or physical vapor deposition [8, 9]. 

Several methods for the incorporation of catalysts into microreactors exist, which differ in the phase-contacting principle. The easiest way is to fill in the catalyst and create a packed-bed microreactor. If catalytic bed or catalytic wall microreactors are used, several techniques for catalyst deposition are possible. These techniques are divided into the following parts. For catalysts based on oxide supports, pretreatment of the substrate by anodic or thermal oxidation [93, 94] and chemical treatment is necessary. Subsequently, coating methods based on a Uquid phase such as a suspension, sol-gel [95], hybrid techniques between suspension and sol-gel [96], impregnation and electrochemical deposition methods can be used for catalyst deposition [97], in addition to chemical or physical vapor deposition [98] and flame spray deposition techniques [99]. A further method is the synthesis of zeoUtes on microstructures [100, 101]. Catalysts based on a carbon support can be deposited either on ceramic or on metallic surfaces, whereas carbon supports on metals have been little investigated so far [102]. 

---