Study On The Preparation, Characterization And Application Of The Novel Sensitive Materials Based On Silica Matrix

Silicon dioxide is a kind of excellent substrate material for the adulterated or adsorbed or embedded sensitive species, which has some advantages as the substate, such as inert to reactant, heat stability, high insulative ability and great transparency, and has been widely applied to research and industry as the important substrate of catalyst and the vivacious material at nanometer scale.Silica gel is an important kind of silicon oxide with porous structure and high adsorptive ability. Pure porous silica gel has been directly applied to humidity measurement and the detection of trace substance in solvent, after which had been adsorbed and condensed by silica gel. However, most of silica gels used in sensors have to load special sensitive species to detect the analytes. This thesis studied the fabrication of vanadia-silica xerogel and its application for chroma sensor and phosphorescence sensor. Synthesis and stabilization of pure and doped vanadia-silica xerogels, either in the shape of thin films or bulk materials, have attracted considerable attention due to their diverse applications in thermochromic, electrochromic and switching devices. In 1990's, researchers had developed humidity sensor with vanadia-silica xerogels as the sensitive element which could become red when adsorbing water vapour in air. In this study, it is first reported the fabrication of the sensor based on the color change of vanadia-silica xerogels slice due to the reduction of V5+ ions in the xerogel slice by ethanol with water's participation, which was used to detect the trace water in ethanol. The vanadia-siiica xerogels slice is low-cost, low toxic, mass produce, easy to fabricate and less chemicals consumption, prepared simply with 104.5 mL tetraethyl orthosilicate, 1.4259 g ammonium metavanadate, 117 mL ethanol and 108 mL redistilled water. During the gelation of colloid, no acidic or alkaline catalyst was employed, which ensures the purity of vanadia-silica xerogels and simplifys the analysis of chromophore and phosphorescence resource. It can be observed that the vanadia-silica xerogels slice heated at 500°C for 1 h is colorless and transparent. When the cooled slice expose to ambient air, it turn red within 3 seconds. This behavior suggests that the slice has ultra sensitivity and excellent response speed toward humidity. With thermogravimetric analysis experiment, it's discovered that the maximal weight of water adsorbed by the slice was about 21% (w/w) of that of slice and that the slice would be completely dehydrated when heated at 100°C, which indicates the humidity sensing ability of the slice is reproducible. The microscopic photograph of the slice reveals that the adsorption ability of the slice comes from its porous structure. The results of ESR measurement shows V5+ in the slice could be deoxidized to [VO(H2O)5]2+ which is green blue by ethanol on condition that water participated in the reaction. When the xerogel slices are soaked in ethanol solution containing water, the green blue [VO(H2O)5]2+ and the red pseudooctahedral oxovanadium(V) centers produced by the coordination of two water molecules to the vanadium metal center will be formed, and then the color of the slice will turn into green yellow whose complementary color is blue. In this reseach work, B values of the images captured by a commecial digital camera of the slices soaked in ethanol solution with diverse water content were collected by home made program based on MATLAB software, and then the relationship curve of B value and water content was achieved. It's found that the B value monotonously increased with water content decreasing. This relationship can be applied to the detection of trace water in ethanol solution with detection limit of 1 v/v %. The detection method of water content used in this work only need a family digital camera instead of expensive UV-Vis or IR. spectrophotometer, simultaneously owning a good measurement precision.Furthermore, it's found that the vanadia-silica xerogel slice could emit phosphorescence with the wavelength peaked at 527 nm and 537 nm after heated at 800°C and 1100°C for 1 hour respectively. Microscopic photograph shows the porous structure of the surface of the slice after heated at 800°C, while the surface of the slice is glassy after heated at 1100°C. Water, ether, sodium hyposulphite aqueous solution and hydrofluoric acid can penetrate into the slice heated at 800°C and quench its phosphorescence, suggesting that the slice heated at 800°C can be used as phosphorescence sensor for water, ether, sodium hyposulphite aqueous solution or hydrofluoric acid. The experiments demonstrated that the slice couldn't emit phosphorescence heated at 500°C, and that the phosphorescence intensity of the slice heated at 1100°C was larger than that of 800°C sample. A possible interpretation is presented based on the observation of V2O5 nanocrystal in the slice heated at 1100°C in TEM experiment. The quantum size effect of V2O5 nanocrystal leads to its phosphorescence emission, and the dielectric confinement effect of the SiO2 matrix surrounding V2O5 nanocrystal leads to the phosphorescence quenching.Since the end of 1980's, the novel physical and chemical properties of nanometer materials embedded in SiO2 matrix have been intensively studied. Ge nanocrystal embedded in SiO2 matrix has shown its potential applications due to its novel optical and electrical properties, and will be an important basic material of nanoelectronics and nanooptics components. So far, in the reported preparation methods of nano-crystalline Ge (nc-Ge) embedded in SiO2 matrix mainly inclouding magnetron co-sputtering, chemical vapor deposition (CVD), ion implantation and sol-gel method, heat process at temperature above 400°C is a necessary procedure for preducing nanocrystal, which will increase the preparation cost and difficulty. As to ion implantation method, because the ion fluence of 1×1017cm-2 has greatly exceeded a solid surface atomic density (～1×1015 cm-2),so the ion implantation with the fluence above 1×1017 cm-2 was less carried out for nano-crystalline Ge preparation. As a result, the density of nano-particles is low and the intensity of corresponding photoluminescence is weak. It has not been clarified whether Ge nanocrystal with high-intensity photoluminescence can be prepared by ion implantation with higher fluence than 1×1017 cm-2. In this thesis, a new preparation method is reported, by which, nc-Ge can be directly produced by high dose ion implantation without subsequent annealing. The mechanisms of the formation and the fluorescence emission of nc-Ge are discussed. The preparation technique of nc-Ge used in this reseach work can be applied to produce high quality nc-Ge, owning to the advantages of the precise control of the depth distribution and the required density of nc-Ge in matrix by changing ion energy and fluence. The photoluminescence property of nc-Ge can be applied to fluorescence sensor for radiation fluence detection.