The consortium develops two types of materials: on the one hand, TiO2-based thin films, and on the other hand, Cu2S-In2S3-Ga2S3 powders. The latter are layered metal sulfides named CIGSn (n=4, 5, 6, 7), with “n” corresponding to the total number of sulfur layer. The electronic structure engineering consists in tuning the “n” stoichiometry for the CIGSn during the micro-wave assisted synthesis, in introducing nitrogen into the TiO2 structure by Reactive Magnetron Sputtering (RMS) to form TiOxNy, and in depositing gold nanoparticles by magnetron sputtering at the surface of TiO2 thin films prepared by Plasma Enhanced Chemical Vapor Deposition (PECVD).
The OMATSOLFUEL project demonstrates that plasma-based techniques offer a wide range of parameters to finely tune the physicochemical properties of thin films. In one case, the N2/O2 ratio leads to numerous TiOxNy stoichiometries, and in another case, different sets of reactor pressure, plasma discharge power, and duration offer various morphologies for the Au nanoparticles in the Au/TiO2 heterostructure.
The size of the Au nanoparticles was estimated by an innovative multi-technique approach combining: (i) scanning and transmission electron microscopies with local information (few nm2) and high resolution with (ii) UV-Vis transmission and X-ray photoelectron spectroscopies with lower accuracy but probing a larger surface area (few mm2). To obtain morphological parameters in a mean-field approach, inelastic XPS backgrounds were fitted with QUASES.
Preliminary photocatalytic results were obtained for Au/TiO2 and TiOxNy thin films as well as CIGSn powders. Glucose photoconversion was tested, but further experiments are needed. Efforts were spent to demonstrate the photocatalytic activity of CIGSn through the simultaneous photoproduction of H2 and the photooxidation of ascorbic acid. The highest rate of hydrogen production was measured with CIGS4 (3.3 µmol/h). A photocatalytic test is currently set up with the particularity of working at controlled temperature and illumination conditions, and of analyzing both the gas phase to get the amount of the H2 produced, and the liquid phase to get the information relative to the high value-added sugar derivatives.
