TiO2-anatase films made by sol-gel processing and their photodegradation activity towards pollutants in water

Titanium dioxide has become the material of choice for hydrophilic photocatalytic surfaces and the sol-gel technique has emerged as one of the most promising techniques for growing TiO2 thin films. This chapter describes our sol-gel preparation and utilization of thin titania films on glass substrates as catalysts for photodegradation of organic pollutants, such as azo dyes and pesticides in aqueous solutions. The good photoefficiency of the as-prepared films relies on their high contact surface area and nanocrystalline structure, which facilitates efficient photoinduced electron-hole pair generation. Transparent TiO2-anatase films on soda-lime glass supports were produced by two different sol-gel processing routes: (i) dip coating from alcoholic sols containing surfactants and followed by heat treatment at 500\ub0C; (ii) dip coating from aqueous sols after extended refluxing treatment and followed by heating at ~100\ub0C. In both cases the starting precursor was titanium alkoxide and the final coating consisted of a dominant anatase crystalline phase. In case of the high-temperature processing route, the detrimental effect of interdiffused sodium ions from the glass substrate during heat treatment was prevented by depositing a thin silica barrier layer prior to titania deposition. The intermediate barrier layer was not needed in case of the lowtemperature processing route, where the crystallization of anatase has been already promoted during the formation of the sol. X-ray absorption spectroscopy and X-ray diffraction were applied to determine the structure development at different stages from the precursor solution to the solid thin film. Surface morphology, characterized by monodispersed or joint nanoparticles and variable roughness, was investigated with atomic force microscopy, while the surface and indepth composition of films were analyzed by X-ray photoelectron spectroscopy. A photocatalytic activity of the as-prepared films was studied in two different tailor-made photoreactors filled with an aqueous solution of certain pollutant. In case of an azo dye, the films were immersed in its colored solution and photobleaching was followed in-situ with the help of UV-VIS spectroscopy. The degradation of the pesticide was monitored by HPLC analysis and its mineralization by ionic chromatography. The insecticide thiacloprid was stable under irradiation (wavelength range 310-400 nm) in the absence of TiO2 films during 8 hours long period, whereas in the presence of best-performing titania films the half time of the parent molecule was typically 15 minutes. The titania catalyst can be easily removed from the solution, which is one of the principal advantages of using the immobilized films as catalysts rather than powders

Photocatalytic TiO2 Coatings: Effect of Substrate and Template

Transparent TiO2 films with a high photodegradation activity towards an azo dye in aqueous solution were prepared by sol\u2013gel processing. Films on soda\u2013lime glass supports protected with a thin silica barrier layer exhibited better crystallization and monodisperse nanoparticles, higher absorption of light below 370\u2009nm, and higher photocatalytic activity than those films deposited on bare glass supports proving the detrimental effect of interdiffused sodium ions on the development of the anatase nanostructure. The effect of substrate was more pronounced in thinner films (300\u2009nm) than in thicker ones (1200\u2009nm), which were achieved by adding a template (i.e. Pluronic F127) to the sol

Low-temperature synthesis and characterization of TiO2 and TiO2-ZrO2 photocatalytically active thin films

Transparent TiO2 and TiO2\u2013ZrO2 (molar ratio Zr/Ti = 0.1) thin films were produced by low-temperature sol\u2013gel processing from nanocrystalline aqueous based solutions. The structural features and compositions of the films treated at room temperature, 100 \ub0C and 500 \ub0C were investigated by X-ray diffraction, X-ray photoelectron spectroscopy and thermal analysis. Addition of zirconia increased specific surface area (140\u2013230 m2 g 121) and hindered the growth of anatase crystallites, exhibiting a constant size of 6\u20137 nm in the whole temperature range. These significant changes with respect to pure TiO2 in anatase crystalline form did not result in significantly and systematically different photocatalytic activity, which was evaluated in terms of aqueous pollutant degradation (azo-dye in water) and self-cleaning ability (fatty contaminant deposit). The films treated at only 100 \ub0C showed excellent photocatalytic activity towards azo-dye degradation. Contact angle measurements of aged and contaminated surfaces revealed a fast or sharp hydrophilicity gain under UVA illumination. Accordingly, the results of this study confirmed the potential application of advantageous low-temperature films in water treatment as well as for self-cleaning surfaces

Understanding controlled drug release from mesoporous silicates: Theory and experiment.

Based on the results of carefully designed experiments upgraded with appropriate theoretical modeling, we present clear evidence that the release curves from mesoporous materials are significantly affected by drug-matrix interactions. In experimental curves, these interactions are manifested as a non-convergence at long times and an inverse dependence of release kinetics on pore size. Neither of these phenomena is expected in non-interacting systems. Although both phenomena have, rather sporadically, been observed in previous research, they have not been explained in terms of a general and consistent theoretical model. The concept is demonstrated on a model drug indomethacin embedded into SBA-15 and MCM-41 porous silicates. The experimental release curves agree exceptionally well with theoretical predictions in the case of significant drug-wall attractions. The latter are described using a 2D Fokker-Planck equation. One could say that the interactions affect the relative cross-section of pores where the local flux has a non-vanishing axial component and in turn control the effective transfer of drug into bulk solution. Finally, we identify the critical parameters determining the pore size dependence of release kinetics and construct a dynamic phase diagram of the various resulting transport regimes

COLLEGIUM ANTROPOLOGICUM

In this volume the results of the research program “Evolution of the Human peopling in Italy:paleobiology, behaviour and substistence strategies” financed by the MIUR (Ministry of Education, Universities and Research) and coordinated by Prof. F. Facchini were published

Vitrification from solution in restricted space: Formation and stabilization of amorphous nifedipine in a nanoporous silica xerogel carrier.

Purpose: The goal was to find thermodynamic criteria that must be satisfied in order to prevent formation of crystalline state of drugs within a confined space (e.g., nanopores of inorganic solid). Similarly, criteria that lead to stabilization of amorphous drug within such pores were investigated. Methods: In the theoretical part, the classical thermodynamics of nucleation is applied to the conditions of a restricted space. The theoretical findings are verified using porous silica as a carrier and nifedipine as a model drug. The amorphicity of the latter is checked using XRD and thermal analysis (DTA, DSC) in combination with BET measurements. Results: It is shown that there exists a critical pore radius of a host below which the entrapped substance will solidify in an amorphous form. There also exists a critical pore radius below which the entrapped amorphous solid will not be able to crystallize. Specifically, incorporation of NIF into a silica xerogel with an average pore diameter of about 2.5 nm produces and stabilizes its amorphous form. Conclusion: Entrapment of drugs into solid nanoporous carriers could be regarded as a potentially useful and simple method for production and/or stabilization of non-crystalline forms of a wide range of drugs