Radially organized pillars in TiO2 and in TiO2/C microspheres: Synthesis, characterization and photocatalytic tests

Porous TiO2 microspheres with robust texture and high photoactivity were prepared by inflowing a TiO2 precursor in the confined space of polystyrene-co-divinyl benzene (PS-co-DVB) polymer, working as sacrificial scaffold. The impregnated polymer spheres, upon thermal treatments under N2, N2/air or pure air flow at temperatures in the 400–500 °C interval, are transformed into porous microspheres. Depending on the gas flow composition, the obtained microspheres are constituted by porous carbon, hybrid core–shell C/TiO2 or of cemented TiO2 nanoparticles assembled in elongated pillars. The composition of pure TiO2 microspheres ranges from pure anatase (400 °C) to the prevailing rutile phase (>475–500 °C). All samples have been extensively characterized by means of SEM/AFM microscopes, N2-volumetric porosimetry, XRD and UV–vis analyses. The photodegradation of NO has been used to check the photocatalytic activity of the TiO2 materials. It is concluded that they exhibit higher photoactivity than the classical benchmark material (Degussa P25). This property together with porous character of the microspheres, the tunable anatase–rutile ratio and the high crystallinity makes these microspheres very interesting materials for applications in photocatalysis. From a physical point of view, the large axial pores and the columnar nature of the spheres can produce the entrapment of the light into the material.

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► Synthesis of porous microspheres via template processes.
► Two kinds of materials: (1) porous core–shell C/TiO2 and (2) pure TiO2 mesoporous microspheres.
► The structure of the TiO2 phase is constituted by cemented anatase and rutile nanoparticles.
► By changing the temperature of treatment, tunable anatase/rutile composition is obtained.
► Materials exhibit high activity in the photocatalytic oxidation of NO.