Influence of pH of sol-gel solution on phase composition and photocatalytic activity of TiO2 under UV and visible light

• Preparation of TiO2 at pH = 10 with NH4OH and HT in air at 400 °C causes narrowing of Eg.
• Such prepared TiO2 is active under visible light due to formation of Ti3+ and NO22−.
• High crystallinity of anatase and low value of ς extend lifetime of free charges.

Nanocrystalline TiO2 was prepared in the sol-gel method by hydrolysis of titanium (IV) isopropoxide (TIP) at the different pH: autogenic, pH = 10 (with ammonia solution) and pH = 3 (with acetic acid solution). The obtained materials were calcined at 400 °C. Time Resolved Microwave Conductivity (TRMC) analyses showed, that the highest lifetime of charge-carriers was obtained for sample prepared at pH = 10 calcined at 400 °C, which exhibited highly crystallised anatase phase and the lowest value of ς potential. Preparation of TiO2 with an ammonia solution and its further calcination at 400 °C caused reduction of Ti4+ to Ti3+ in the bulk, narrowing of the band gap with formation of an extra band above the valence band of TiO2 assigned to formed NO22− species. Such prepared photocatalyst showed extended lifetime of free charges under UV irradiation in comparison with the other prepared samples and activity under visible light.

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