When a semiconductor absorbs energetic photons, electron-hole pairs are created in the material and generate free radicals on its surface that can react with nearby molecules. This is the principle of photocatalysis. However, this process can be thwarted by the rapid recombination of electron-hole pairs.
Iramis researchers have been studying the imogolite (OH)3Al2O3Si(OH) – an aluminosilicate naturally present in volcanic soils – synthesized in the form of nanotubes with a very uniform diameter (2-3 nm), and coated with hydrophilic hydroxyl groups (OH) on the surface. Their picosecond pulse radiolysis experiments in the presence of water show the spontaneous separation of charges (electrons and holes) formed under radiation and the associated production of hydrogen. Computer simulations suggest that the very strong curvature of the nanotubes facilitates charge separation because it induces an electric field in the wall of the nanotubes, which makes the electrons migrate towards the outside and the holes towards the inside of the nanotubes.
These results pave the way for the development of affordable photocatalysts. Imogolites can be produced at low cost and without environmental damage, and their surface can be functionalized to treat different types of pollutants, whether hydrophilic or hydrophobic. The researchers are now working on modifying these nanotubes, for example to decrease the activation energy of the process, in order to extend their efficiency over a wider range of wavelengths.
This work, conducted with the Institut de Chimie Physique (CNRS - Université Paris Saclay) and the Laboratoire de Chimie Physique et Microbiologie pour les Matériaux et l'Environnement (CNRS - Université de Lorraine), is part of a project funded by the ANR in collaboration with the Université Paris Diderot and the Institut Charles Gerhardt Montpellier.