Non-aqueous sol-gel synthesis through a low-temperature solvothermal process of anatase showing visible-light photocatalytic activity


A novel, facile method based on a non-aqueous sol-gel solvothermal process has been developed to synthesise spherical TiO2 nanoparticles (NPs) in one pot. The reaction between titanium(IV) tert-butoxide (Ti[OC(CH3)(3)](4)) and benzyl alcohol was a simple process, which resulted in the formation of highly crystalline titania NPs with a small size of only 6 nm, and with a correspondingly high surface area. The chemical formation mechanism of the metal oxide NPs has been proposed, and the degree of surface hydroxyls (-OH groups) has been examined. The products of the synthesis were characterised by X-ray powder diffraction (XRPD) using the advanced whole powder pattern modelling (WPPM) method, high-resolution transmission electron microscopy (HR-TEM), thermo-gravimetric analysis (TGA), UV-visible diffuse reflectance spectroscopy (DRS), Fourier transform infrared spectroscopy (FT-IR), and nuclear magnetic resonance (NMR) spectroscopy. The photocatalytic activity (PCA) was evaluated in both the liquid-solid phase, by monitoring the degradation of an organic dye (methylene blue (MB)) under UV-light irradiation, and in the gas-solid phase, by following the degradation of 2-propanol under UV and visible-light exposures. The synthesized titania powders not only exhibited excellent photocatalysis in the liquid-solid phase (under UV irradiation), but also possessed a superior PCA in the gas-solid phase under a visible-light exposure. The effects on the PCA of the very small crystalline domain size, surface composition and the presence of organic molecules due to the synthesis process of the TiO2 NPs were shown to account for this behaviour.



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Karmaoui, M; Tobaldi, DM; Skapin, AS; Pullar, RC; Seabra, MP; Labrincha, JA; Amaral, VS

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Mohamed Karmaoui thanks N. J. O. Silva and Prof. A. M. S. Silva (University of Aveiro, Portugal), the former for the contribution to the study of the TiO2 NPs, the latter for the NMR measurements and his fruitful discussions. D. M. Tobaldi is grateful to the ECO-SEE project (funding from the European Union's Seventh Framework Programme for research, technological development and demonstration under grant agreement no. 609234. Note: the views expressed are purely those of the authors and may not in any circumstances be regarded as stating an official position of the European Commission). The authors would also like to acknowledge M. Ferro for microscopy analysis, which was supported by RNME-Pole University of Aveiro FCT Project REDE/1509/RME/2005. PEst-C/CTM/LA0011/2013 programme is also acknowledged. M. P. Seabra and R. C. Pullar wish to thank the FCT Ciencia 2008 programme for supporting this work.

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