Polymeric materials, such as carbon nitrides, are emerging as a new-class of metal-free photocatalysts suitable for H2 evolution from water under visible light irradiation. However, to date, appreciable amount of H2 can only be produced in presence of a sacrificial electron donor and small loads of co-catalyst (Pt). Moreover, the actual H2 evolution rates are not competitive with those achieved with more conventional photocatalysts. Despite the notable synthetic efforts made to ameliorate the photoactivity of these materials, no real breakthrough has been done yet. This fact is mostly due to a lack of mechanistic insight into the H2 evolution process with polymeric photocatalysts, ranging form a classical semicondutor-based mechanism to a photochemical molecular reaction. A possible strategy for addressing, at the molecular level, the H2 evolution mechanism, would be to develop a surface science approach for building-up well-defined water/photocatalysts interfaces to be exploited in surface photochemistry experiments. To this aim, ultra-high-vacuum (UHV) sublimation methods and surface mediated mechanisms will be used for growing structurally, chemically and electronically defined thin organic films, based both on non-covalent assemblies of the carbon nitrides building blocks and more condensed phases thereof (oligoemrs and 2D polymers). The water/chromophore interface and its evolution under UV/vis irradiation will be studied both in UHV and near ambient pressure environments by mostly using X-ray photoemission spectroscopy (XPS) and scanning tunnelling microscopy (STM) techniques.
