The effect of particle shape on the activity of nanocrystalline TiO2 photocatalysts in phenol decomposition. Part 2: The key synthesis parameters influencing the particle shape and activity

Abstract

Nanosized TiO2 photocatalysts were synthesized via hydrogen–air flame hydrolysis by using two slightly different, home made diffusion flame burners (Burners A and B). Titanium(IV) chloride vapor was introduced into the flame via bubbling dry air throughout the precursor liquid. X-ray diffraction (XRD) measurements revealed that the particles are anatase–rutile mixtures with a phase composition ranging from 98:2 to 57:43 anatase to rutile weight ratio. The hydrogen–oxygen molar ratio in the flame, as well as the precursor vapor feeding rate were found to be the key parameters which determine both particle structure and morphology. Spherical and polyhedral particles with significantly varying photocatalytic activity were produced in Burner A by increasing the precursor vapor feeding rate at a constant hydrogen–oxygen molar ratio, the photocatalytic activity increased for samples synthesized. The differences in particle size, specific surface area and anatase–rutile composition were found to be marginal but the particle shape changed from spherical to polyhedral by increasing that parameter. From this, it was concluded that particle shape plays an important role in photocatalytic activity, the faceted particles are better photocatalysts than spherical ones. With Burner B, predominantly polyhedral particles were obtained, some of them with further improved photocatalytic activity. Synthesis parameters for obtaining maximum activity have been established for both burners. Our results prove, that bare (undoped) TiO2 photocatalysts with photocatalytic activity significantly better than that of P25 can routinely be prepared and their performance optimized via the fine-tuning of the synthesis parameters employed.