The photoelectrochemical response and catalytic efficiency towards phenol photooxidation of mesoporous titania particles with spherical morphology have been explored. The catalysts were synthesized in two different arrangements using carbon spheres in a dual role as support and morphology director: hollow spherical titania particles and dense structures where the titania shell is surrounding a carbon core. Although the synthesized titania hollow spheres exhibited a similar photoelectrochemical behavior and optical properties than commercial P25, they showed a better photocatalytic response towards phenol photo-oxidation in terms of pollutant mineralization. This behavior cannot be explained in terms of the crystallinity (found to be higher for P25) and has been attributed to both confinement effects in the mesoporosity of these catalysts as well as to the spherical morphology of titania particles. The spherical arrangement of the titania surface would favor the fast motion of the charge carriers and minimize recombination processes. On the other hand, no clear contribution of the carbon phase to the enhanced photocatalytic response, since quite similar performance is observed for the hollow spheres and the core/shell composite. However, separation and filtration of the catalysts become easier for the carbon/titania composite, thereby improving the so-called practical efficiency. 1. Introduction Triggered by the rising interest in the development of advanced oxidation processes (AOP) for wastewater remediation, heterogeneous photocatalysis has received much attention in the last years [1, 2]. Particularly, extensive research is being carried out on the development of novel synthetic routes to improve the photocatalytic activity of conventional semiconductors—mostly TiO2 and ZnO—and ideally achieving the complete degradation (mineralization) of recalcitrant pollutants both in liquid and gas phase. The low efficiency of AOP based on heterogeneous photocatalysis is mainly due to high surface recombination rates of the charge carriers, low efficiency under visible light, separation (filtration), and recovery and reutilization of the fine photocatalyst powders [3, 4]. To overcome all these issues, different approaches are being considered such as doping with transition metal and nonmetal ions, surface sensitization of dyes, design of nanostructured photocatalysts with controlled morphology, or immobilization on appropriate substrates [2, 5–8]. In this regard, the enhanced photocatalytic performance of carbon/semiconductor composites has been reported over a
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