Carbon mediated photoinduced reactions as a key factor in the photocatalytic performance of C/TiO2

We have explored the photoelectrochemical behavior of carbon/titania composites, aiming at understanding the mechanisms of the photoinduced processes occurring in such hybrid photocatalysts that lead to enhanced photocatalytic efficiencies of the pristine semiconductor for the photodegradation of refractory pollutants in water. In a first step, spectrometric techniques have been applied to investigate the structural and optical properties of the carbon/semiconductor composites compared to the intrinsic characteristics of the unsupported semiconductor. The second approach consisted in the preparation of thin film electrodes to explore the photoinduced reactions occurring at the interface under UV light and bias potential. The gathered results provided experimental evidence on the carbon-mediated photoinduced reactions, distinguishing different mechanisms: i) the carbon matrix acts as a charge trapping network that modifies the fate of the photogenerated charge carriers (avoiding recombination and thus enhancing the photocatalytic efficiency); ii) illumination of the carbon additive renders photogenerated carriers due to π-π* transitions, capable of participating in charge transfer reactions with electron donors present in the reaction medium. Our results point out that beyond the beneficial effect of the porosity of the support, the carbon matrix does play an important role in the photo-induced reactions of carbon-supported photocatalysts. Broader context The use of light energy is particularly useful for the degradation of refractory pollutants, since the excitation of electronic molecular states at energies provided by light may induce chemical bond breaking. Consequently, heterogeneous photocatalysis based on semiconductors is becoming one of the most promising green chemistry technologies in the environmental remediation arena. However major cornerstones of photocatalytic processes that prevent their large scale implementation are related to the photoelectrochemical properties of the semiconductor (low visible light activity, high recombination of photogenerated species, etc.). Coupling carbon materials as additives to semiconductor has long proved to be an attractive strategy to improve the photocatalytic efficiency of carbon/semiconductor composites on the photodegradation of a variety of recalcitrant pollutants, albeit the exact role of the carbon phase on the enhanced performance of the composites has not yet been fully understood. Aiming at understanding the mechanisms of the photoinduced processes occurring in such hybrid photocatalysts, we have investigated the photoelectrochemical response of carbon/titania thin film electrodes under UV light, and their efficiency for the photo-oxidation of phenol. Our findings show the key role of the carbon matrix on the photoinduced reactions occurring at the carbon/semiconductor interface, beyond the reported beneficial effect of porous supports. corresponding author, E-mail: [email protected] (CO Ania); Tel. +34 985 118846; Fax +34 985297662