New insights into the photocatalytic properties of RuO2/TiO2 mesoporous heterostructures for hydrogen production and organic pollutant photodecomposition

Photocatalytic activities of mesoporous RuO2/TiO2 heterojunction nanocomposites for organic dye decomposition and H2 production by methanol photoreforming have been studied as a function of the RuO2 loading in the 1 10 wt % range. An optimum RuO2 loading was evidenced for both kinds of reaction, the corresponding nanocomposites showing much higher activities than pure TiO2 and commercial reference P25. Thus, 1 wt % RuO2/TiO2 photocatalyst led to the highest rates for the degradation of cationic (methylene blue) and anionic (methyl orange) dyes under UV light illumination. To get a better understanding of the mechanisms involved, a comprehensive investigation on the photogenerated charge carriers, detected by electron spin resonance (ESR) spectroscopy in the form of O, Ti3+, and O2 trapping centers, was performed. Along with the key role of superoxide paramagnetic species in the photodecomposition of organic dyes, ESR measurements revealed a higher amount of trapped holes in the case of the 1 wt % RuO2/TiO2 photocatalyst that allowed rationalizing the trends observed. On the other hand, a maximum average hydrogen production rate of 618 μmol h1 was reached with 5 wt % RuO2/TiO2 photocatalyst to be compared with 29 μmol h1 found without RuO2. Favorable band bending at the RuO2/TiO2 interface and the key role of photogenerated holes have been proposed to explain the highest activity of the RuO2/TiO2 photocatalysts for hydrogen production. These findings open new avenues for further design of RuO2/TiO2 nanostructures with a fine tuning of the RuO2 nanoparticle distribution in order to reach optimized vectorial charge distribution and enhanced photocatalytic hydrogen production rates.