||The proponents of the present project synthesized very recently a new highly efficient nanostructured composite photocatalyst. This photocatalyst is made of TiO2 nanoparticles chemically bonded to graphene platelets. The new photocatalyst proved to have a much higher photocatalytic activity compared to the standard P25 from Evonik, or to the state-of-the-art photocatalysts such as vlp7000 from Kronos or PC500 from Millenium.
When a TiO2 nanoparticle is illuminated with photons with energy equal or larger than the band gap, electrons (e-) are injected from the valence band into the conduction band leaving a positive hole (h+). The injected electrons can move to the semiconductor surface and originate a reduction reaction or they can recombine with holes originating heat only. On the other hand, holes that reach the surface of the semi-conductor, driven by the so-called Helmholtz layer, can originate oxidation reactions. Due to the strong oxidation potential of the TiO2 (anatase), ca. 3 V, compared to the relatively small reduction one, ca. -0.2 V, titania is used mostly in photooxidation reactions. The large band gap of titania, 3.2 V, allows that only photons with a wavelength smaller than 386 nm can be absorbed; this corresponds to around 5 % of the solar spectrum energy. To increase the activity of a photocatalyst various strategies can be used: a) increasing its surface area, b) decreasing the recombination rate of the photo generated electron-hole pairs, c) extending the light absorption range to longer wavelengths and d) providing better access to the reactants and preventing the adsorption of the reaction products. Activated carbon has a large surface area and is a great adsorbent for many chemical species. It was observed that when used together with titania it has the ability to improve the photooxidation of certain chemical species. The photooxidation reaction is well described by the Langmuir-Hinshelwood mechanism. This means that the pollutants