Thesis of Joëlle El Aseel

Defense of thesis Joëlle Al Aseel  - Laboratory PhLAM

Abstract :

The warming trend observed in the recent years has raised significant concerns due to the observable impacts of climate change, which include intensified forest fires, stronger hurricanes and rising sea levels. Human activities, especially burning biomass and coal, industrial emissions and vehicular pollution, are major contributors to this warming.
Particulate matter (PM), such as soot or black carbon, poses immediate health risks, impacting respiratory and cardiovascular health. Carbonaceous PM exhibits large surface area where pollutants such as polycyclic aromatic hydrocarbons (PAHs) adsorb. Nonetheless, carbon-based materials like activated carbon, carbon nanotubes, and graphene showcase diverse applications (filtration, electronics, sensors …) due to their unique properties (conduction, stiffness, refractoriness …). By unravelling the interactions between pollutants, notably PAHs, and carbon surfaces, it is possible to address environmental issues more effectively and advance in industrial development. This interaction is predominantly influenced by the surface chemical composition and the nature of the adsorbate, and can be evaluated based on experimental and theoretical methods.
For this purpose, this thesis presents an innovative experimental methodology that combines laser irradiation of a carbonaceous surface (HOPG) with fast space-resolved detection of the laser-induced incandescence (LII). The adsorption/desorption processes are driven by the surface temperature, which is therefore a crucial parameter in determining the adsorption energy. The space-time evolution of the surface temperature was estimated previously using simulation methods. In this work, we put specific emphasis on the experimental determination of the temporal and spatial profiles of temperature with nanosecond time resolution and micrometre space resolution. Understanding these profiles allows for a subsequent determination of the desorption rates of PAH molecules adsorbed at sub-monolayer coverage on HOPG surfaces.
The experimental work was complemented by a molecular-level theoretical approach to investigate the interaction between PAHs and several forms of carbonaceous surfaces. This complementary method relies on force field based molecular dynamics (FF-MD) and periodic density functional theory (DFT) calculations. Using these methods, it was possible to ascertain the adsorption energies of various PAHs on pristine and defective carbon-based surfaces. In this thesis, systems of different PAHs adsorbed on graphite and HOPG were investigated, and the results from both calculation methods exhibit a very good agreement with the experimentally determined adsorption energies reported in literature.
In conclusion, this work presents substantial experimental development, enabling the determination of adsorption energies based on actual temperature measurements, and molecular-scale calculations on representative carbonaceous surfaces and adsorbed molecules. Both the experimental and theoretical approaches open up prospects for studies of various adsorbent-adsorbate systems.

Keywords : Adsorption,Laser-induced incandescence,Carbon,Theoretical modelling,Classical molecular dynamics,Density Functional Theory