Photosynthetic Solar Fuels and Chemicals Production with Hybrid Inorganic Semiconductor Nanostructures

In the present thesis hybrid inorganic semiconductor nanostructures are investigated for solar-to-chemical (STC) energy conversion purposes. Among the family of fuel-forming reactions, hydrogen production is targeted by means of mild and sustainable synthetic routes. Traditional water splitting poses, to this extent, stringent kinetics and technological limitations, hampering overall photochemical performance. Leveraging on the superior hydrogen forming quantum efficiency expressed by core-shell CdSe@CdS seeded-rod (SR) nanostructures, we develop alternative anodic organic transformations to realise closed redox cycle solar chemicals syntheses. Notably, this approach circumvents the use of sacrificial reagents, promoting instead value-added oxidative chemistries. We find that fluorescence quenching screening allows for rigorous selection of such reactions, defining optoelectronic rules bridging between materials properties and photosynthetic performance. We observe that, for aldehyde forming transformations, extensive chemical potential is stored by the concomitant generation of hydrogen fuel, up to remarkable 4.2% STC conversion efficiencies, doubling state-of-the art solar-to-hydrogen benchmark values. The ability of SR to promote concerted electron transfer is then tested for additional photo-redox reactions. The oxidative potential of SR allows access to photo-polymerisation and photo-reforming processes whilst the proton reducing capability in organic media allows for in situ photo-hydrogenations. Furthermore, initial address of chemo-selective radical coupling reactions has leveraged on the nanometric distance between reduction- and oxidation-active sites, providing a promising outlook for future optimisation. Finally, attempts to integrate these photocatalysts into microfluidic chips targeted prompt application of the system to a scalable device. The flow conditions offered by such photoreactors promise to soften current limits and further upgrade STC energy conversion. Not only could turnover number be nourished by continuous reagent replenishment, but photocatalyst recyclability will also be attained at successful chemical anchoring of nanorods to reactor walls. The work presented in this thesis therefore endows Ciamician’s dream of the photochemistry of the future with bright forthcoming perspectives.