Effects of the Brookite Phase on the Properties of Different Nanostructured TiO ₂ Phases Photocatalytically Active Towards the Degradation of N‐Phenylurea

Abstract

Different sol‐gel synthesis methods were used to obtain four nanostructured mesoporous TiO ₂ samples for an efficient photocatalytic degradation of the emerging contaminant N‐phenylurea under either simulated solar light (1 Sun) or UV light. Particularly, two TiO ₂ samples were obtained by means of as many template‐assisted syntheses, whereas other two TiO ₂ samples were obtained by a greener template‐free procedure, implying acidic conditions and, then, calcination at either 200 °C or 600 °C. In one case, anatase was obtained, whereas in the other three cases mixed crystalline phases were obtained. The four TiO ₂ samples were characterized by X‐ray powder diffraction (followed by Rietveld analysis); Transmission Electron Microscopy; N ₂ adsorption/desorption at −196 °C; Diffuse Reflectance UV/Vis spectroscopy and ζ‐potential measurements. A commercial TiO ₂ powder (i. e., Degussa P25) was used for comparison. Differences among the synthesized samples were observed not only in their quantitative phase composition, but also in their nanoparticles morphology (shape and size), specific surface area, pore size distribution and pH _IEP (pH at isoelectric point), whereas the samples band‐gap did not vary sizably. The samples showed different photocatalytic behavior in terms of N‐phenylurea degradation, which are ascribed to their different physico‐chemical properties and, especially, to their phase composition, stemming from the different synthesis conditions.

Abstract

Three different sol‐gel synthesis methods were adopted to produce four TiO ₂ samples with different phase composition. A greener template‐free method working under acidic conditions led to the formation of high‐brookite content mixed phases. Under solar light, these substances revealed a fair photocatalytic activity towards the degradation of a pollutant of environmental concern.