Title : Photocatalysis and artificial photosynthesis with octahedral main group sulphides
After a brief survey of the current need of achieving the solar energy-aided photodissociation of water, a presentation will be first made of In2S3 and SnS2 as visible light active photocatalysts. Their spectral response in a simple reaction (photooxidation of aqueous HCOOH) will be analyzed, showing the superior activity and photo corrosion resistance of these sulphides compared with another suphide, the typical CdS photocatalyst. In the case of In2S3 it will be also shown that this spectral response, coupled with the different steps of the degradation of a typical dye (rhodamine B), allows obtaining mechanistic insight on the generation of the different radicals which control those steps.
Furthermore, it will be shown how hyperdoping In2S3 with vanadium is able to insert in the bandgap a narrow, partially occupied band which allows the excitation from the valence to conduction bands in two steps (the in-gap band concept shown to be relevant in photovoltaic materials), extending to lower photon energies the spectral response of the photocatalytic process in exactly the same range as the up-conversion process which is evidenced with photoluminescence tests.
Then it will be shown how coupling to these semiconductors electroactive enzymes, which contain only inexpensive metals and have shown the ability to generate electrochemically H2 and O2 from water, allows the photon-aided generation of both these gases either catalytically (with aid of a sacrificial agent) or electrochemically (with a decrease in overpotential). In the case of O2, in fact, this is the first example ever of a coupling between an enzyme and inorganic semiconductors to achieve the photon-aided generation of this molecule. This opens a way towards artificial photosynthesis.