Abstract
Titania nanocrystalline particles were synthesized by hydrolysis-condensation of titanium tetraisopropoxide in water-in-oil micellar solutions of water/cyclohexane/Triton X-100 system, and the effects of reflux time and water-to-surfactant molar ratio on the particle uniformity, crystallinity, and surface area were studied. Several characterization techniques including TEM and SEM, as well as X-ray diffraction and FT-IR spectroscopy, helium pycnometry, and nitrogen physisorption, were employed to evaluate the particle density and dimensions, crystallite size, surface area value, and the porosity features in the as-prepared condition and also after thermal treatment at 500°C. The results show that all treated samples are dense nanocrystalline anatase particles with BET surface area values over 100 m2·g−1 and primary particle size of 10–15 nm. However, for the as-prepared samples, as the reflux time increases, a better purification of particles from the synthesis environment is resulted, leading to denser and more crystalline powders with smaller particle size and higher BET surface area values culminating in 179 m2·g−1 for 24 hours of refluxing. Moreover, decreasing the water-to-surfactant molar ratio from 10 to 5 and 2 increases the particles surface area to 239 and 224 m2·g−1, respectively, at the expense of slight density and crystallinity degradation and considerable prolongation of surfactant removal step. Supportively, the comparison between photocatalytic activities of as-prepared samples also evidences the effectiveness of reflux time extension on improving the sample features and enhancing their functionality. This study can highlight how the earlier synthesis steps can influence the evolution of the structure of the final products.
Highlights
Titania nanocrystalline particles were synthesized by hydrolysis-condensation of titanium tetraisopropoxide in water-in-oil micellar solutions of water/cyclohexane/Triton X-100 system, and the effects of reflux time and water-to-surfactant molar ratio on the particle uniformity, crystallinity, and surface area were studied
TiO2 nanostructures are highly functional materials for solar energy conversion applications such as photocatalysis and photovoltaics owing to the superior optoelectrical properties and outstanding chemical stability [1, 2]. e results of previous investigations indicate that the solar energy conversion efficiency of the photovoltaic devices utilizing nanocrystalline TiO2 is critically dependent on the phase, morphology, and porosity features of the titania [3,4,5,6]
We investigate the effects of water-tosurfactant molar ratio, W, and the refluxing time, R, on the surface area, porosity features, and crystallite size of TiO2 nanoparticles synthesized through the reverse micelle method in water/cyclohexane/Triton X-100 system with the particular scope of obtaining higher quality as-prepared nanoparticles in terms of enhanced photocatalytic functionality
Summary
TiO2 nanostructures are highly functional materials for solar energy conversion applications such as photocatalysis and photovoltaics owing to the superior optoelectrical properties and outstanding chemical stability [1, 2]. e results of previous investigations indicate that the solar energy conversion efficiency of the photovoltaic devices utilizing nanocrystalline TiO2 is critically dependent on the phase, morphology, and porosity features of the titania [3,4,5,6]. In dye-sensitized solar cells (DSSCs), narrow size distributed mesoporous anatase nanoparticles with high values of surface area and pore volume are known to be much more effective in improving the charge transfer properties as well as providing sufficient dye absorption capacity and enough volume for the electrolyte diffusion, which result in enhanced energy conversion efficiency and superior performance [7, 8]. E sol-gel synthesis has been successfully applied for preparing nanocrystalline metallic oxide materials including TiO2. This method involves the hydrolysis and condensation of a metal alkoxide such as titanium(IV) isopropoxide and yielding intermediate oxo-hydroxide spices which eventually form the metal oxide [1, 9, 10]. The as-synthesized precipitates are generally amorphous and a postcalcination temperature over 300°C is required to obtain the anatase phase, whereby the inevitable particle enlargement due to the agglomeration causes collapse of the pore structure and surface area reduction [11].
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