Preparation Of Ordered Mesoporous TiO₂Thin Film And Its Application In Methanol Catalytic Combustion

For the last two decades, highly ordered mesoporous oxide materials havereceived widespread attention due to their promising applications such asheterogeneous catalysis, adsoption, separation, sensors, host guest chemistry,molecular electronic device, medicine and novel nanomaterials design, etc. Andmesoporous oxide thin film material on flat substrates becomes a very importantelement of the microelectronic and photoelectronic products, including plat paneldevices and integrated circuit. Among all kinds of metal oxides materials, titania isof particular interest owing to its unique physicochemical properties, making itpossess higher application value in the fields of photovoltaic cells, optical waveguide,photo-or chemical sensors and catalysis.In this paper, we combined sol-gel technology and evaporation inducedself-assembly process, which offers an effective way for inorganic species to formmesoporous structure. In the case of mesoporous TiO₂thin film preparation,titianium precursors are dispersed in water/ethanol/surfactant system to obtain asol-gel solution, then the film is deposited on flat and clean substrates by dip-coatingof the solution, followed by humidity aging and the removal of templates. In order tofurther improve the structure and performance, we used the rare metal Ce and noblemetal Pt to modify the mesoporous TiO₂thin film, respectively, and also investigatedits application in methanol catalytic combustion. The synthesized film catalyst hasbroken through the application restriction of current powder catalysts, providing awider application area. The main contents are summarized as follows:1. Mesoporous TiO₂thin film has been succefully synthesized throughevaporation induced self-assembly method, using triblock copolymer P123as thetemplate, titanium（Ⅳ） isopropoxide as the inorganic precursor, hydrochloric acid asthe stabilizer, ethanol as the solvent. The influence of several experimentalparameters, including aging humidity, aging temperature, substrate properties, and calcination temperature, on the mesostructure of titania thin films was investigated indetails. The morphology structure and phase structure were tested by SEM and XRD.The results comfirmed that TiO₂thin film with highly-ordered mesochannels in ahexagonally close-packed system was obtained under the aging temperature of25℃, relative humidity of55-75%, using silicon as the substrate and applyingcalcination of350℃for organic template removal. And the sample calcined at350℃has good anatase.2. To expand the application potential of mesoporous TiO₂thin film in themicroelectronic and photoelectronic field, we adopted low temperature plasmatreatment instead of traditional calcination temperature to remove template P123forpreparation of mesoporous TiO₂thin film. The morphology structure and phasestructure were tested by SEM and XRD. The results showed3D hexagonally orderedmesoporous TiO₂thin film was obtained either by argon plasma or oxygen plasma.Further invstigations demonstrated higher plasma power and longer process timewould produce mesoporous TiO₂thin films with lower surface porosity and thinnerthickness to a certain degree.3. By changing the compositional rations of Ce and Ti species, variousmesoporous TiO₂thin films with different amount of Ce content were prepared. Themorphology structure and phase structure were tested by SEM and XRD. The resultsshowed well-developed anatase crystallization in the frameworks and retention ofthe highly ordered mesoporous structure could be realized by optimizing the amountof Ce dopant.4. Mesoporous titinia thin film supported platinum catalysts were synthesized bymicrodrop dispension method and its application in methanol catalytic combustionwas also investigated in details. The evaluation results showed that the catalyticactivity of argon plasma etching catalyst was much better than the one of methanolreduction sample, which was explained by the fact that the percentage compositionof reduced Pt in the former sample was55.6%higher than the latter’s. Besides, the mesostructure ordering and nanocrystalline phase of thin film were the two miancasues for influencing the catalytic activity. The best methanol catalytic combustionreactivity was obtained when used silicon wifer as substrate and optimized Cecontent as2mol%, which yielded73%methanol conversion at room temperature.