Incorporating Strong Polarity Minerals of Tourmaline with Semiconductor Titania to Improve the Photosplitting of Water

This paper describes a method for increasing the quantum efficiency in the photosplitting of water by integrating the Degussa P25 titania photocatalyst with a polar mineral tourmaline having surface electrical fields due to the pyroelectric effect. The amount of hydrogen produced from the photosplitting of water increased considerably with a tourmaline-integrated P25 titania photocatalyst compared to that with P25 titania in systems containing pure water as well as solutions of different pH values. It is proposed that the enhancement in the photocatalytic performance is due to a reduction in the Schottky barrier for electrons to migrate to the surface of the semiconductor. The surface electric fields of tourmaline lower the barrier by reducing the band bending in the space charge layer and increasing the chemical potential ( E F ) of the electrons in titania. The increase in the amount of hydrogen produced at a lower pH is attributed to the decrease in the overpotential of the hydrogen evolution reaction at lower pH values. In contrast to photocatalytic reduction, tourmaline has very little effect on titania for the photocatalytic oxidation of acetaldehyde. It is proposed that the surface electric fields present on tourmaline crystals reduce the band bending in the semiconductor and thus decrease the oxidation potential of the photogenerated holes. The results have important implications for enhancing the photocatalytic activity of titania for environmental remediation, increasing the quantum efficiency in photovoltaic (PV) solar cells, and other photoassisted processes.