Comparative study of different semiconductors for hydrogen production on the NIMBE photocatalysis platforms

Full description

The increasing global demand for energy, together with the need to reduce the use of fossil fuels in the context of climate change, has created a strong need to develop new clean energy technologies. Among the solutions being investigated, photocatalytic systems capable of producing molecules of interest (H₂ or CH₄) from water, CO₂, sunlight, and semiconductor materials are particularly promising. However, the results obtained depend strongly on the experimental conditions and on the reactor configuration, making the comparison of different systems difficult, and sometimes even impossible. Within NIMBE, several laboratories are developing both photocatalytic platforms (including illumination systems, sample environments, and analytical equipment) and semiconductor materials for use as photocatalysts.
More specifically, LIONS is working on a nanoclay called imogolite. Imogolite is a nanotube with the chemical composition (HO)₃Al₂O₃SiCH₃ (from the outer to the inner surface of the wall), with external and internal diameters of approximately 3 and 1.8 nm, respectively. It can be dispersed in water and contains a hydrophobic inner cavity. Imogolite is a semiconductor with a large band gap (> 5.5 eV, corresponding to illumination at wavelengths around 250 nm). By grafting gold nanoparticles onto the outer surface of the nanotubes, it is possible to significantly improve their photocatalytic properties compared with the ungrafted system, with H₂ production increased by a factor of 90. The resulting system also becomes active in the visible-light range. LEDNA, meanwhile, is developing different types of nanodiamonds for photocatalytic applications, with particle sizes ranging from approximately 5 to 50 nm. These materials are also wide-band-gap semiconductors, with a band gap of approximately 5.5 eV. Control of their surface chemistry and chemical impurities makes it possible to generate intermediate electronic states within the band gap, enabling photoexcitation in the visible-light range. Under solar-type illumination, these materials have therefore been used for H₂ production from water and for the complete photocatalytic degradation of pollutants such as PFOA. Nanodiamond/gold hybrid materials will also be investigated during the internship. Regarding the experimental facilities, each laboratory has dedicated equipment for characterizing gases produced under illumination, as well as different photocatalytic setups. At LIONS, the solutions are placed in quartz vials and illuminated using LEDs with wavelengths ranging from 250 to 530 nm. The setup is located inside a temperature-controlled enclosure. The gases produced are subsequently analyzed by micro-gas chromatography (µ-GC). LEDNA uses a temperature-controlled photoreactor equipped with an immersed lamp (medium-pressure Hg or Xe lamp) and connected to a mass spectrometer for online analysis of the gases produced.
The objective of the internship is to investigate the photocatalytic properties of the systems developed by the two laboratories using their respective experimental platforms, in order to understand how the geometry and configuration of the experimental setup influence the reactivity. TiO₂ P25 will be used as a reference material, and the target reaction will be H₂ production from a sacrificial molecule, isopropanol. Beyond simply comparing the performance of the materials and identifying the specific characteristics of each experimental setup, this combined study is expected to provide a better understanding of the photocatalytic systems investigated by both teams. Indeed, the LEDNA setup allows real-time analysis of the gases produced, providing access to the dynamics of the reactions. In contrast, the LIONS setup allows post-reaction analysis, which is better suited to evaluating overall production yields. Furthermore, the LIONS setup uses quasi-monochromatic light sources, whereas the LEDNA setup is equipped with polychromatic light sources. By combining the analyses performed on these two experimental platforms, more comprehensive information on the photoreactivity of the two semiconductor systems studied by the two teams can therefore be obtained.

Location

CEA Saclay, (91) Essonne, France

Internship conditions

• Internship duration: 5 months
• Level of study: Bac+5
• Training: Master 2
• Continuation in PhD thesis: No
• Application deadline: 1 février 2027

Useful methods and technics:
First, the samples will be synthesized and stabilized as colloidal suspensions in water, and then characterized by small-angle X-ray scattering (SAXS), infrared and UV–visible spectroscopy, electron microscopy, and other complementary techniques.
The photoelectronic properties of the samples will be characterized by diffuse reflectance spectroscopy in the UV–visible range and by X-ray photoelectron spectroscopy (XPS). Ultraviolet photoelectron spectroscopy (UPS) coupled with XPS would be more appropriate for investigating the electronic band structure, but this would be difficult to implement within the scope of an M2 internship.
Illumination experiments will be carried out using UV lamps, LEDs, and a solar simulator.
The gases produced during illumination will be identified and quantified by gas chromatography (micro-GC) or mass spectrometry, both during and after illumination, in order to determine the kinetics and yields of the reactions involved.

Computer languages and software:
Python, Microsoft Office (Word, Excel, PowerPoint)

Supervisor

Pierre Picot
Phone: 0611377908
Email :

Head of the laboratory NIMBE / LIONS

Valérie Geertsen
Phone: