Adsorption and photocatalytic degradation of per- and polyfluoroalkyl substances (PFAS) in water by nanostructured membranes

The aim of this thesis is to develop a nanostructured membrane designed for removing fluorinated compounds from water, specifically targeting perfluorooctanoic acid acid (PFOA). PFOA falls under Persistent Organic Pollutants (POPs) due to its remarkable chemical and thermal stability, posing significant risks to both human health and the environment. Among various proposed techniques for degrading these substances, advanced oxidation processes stand out for their efficacy. These processes leverage the potent oxidative properties of hydroxyl groups (via Fenton reactions) and sulfate groups (via persulfate activation processes) to break down pollutant molecules. Heterogeneous photocatalysis, facilitated by the incorporation of an additional catalyst in the membranes, is particularly promising. In this context, a nanostructured polymeric membrane serves as a support for the catalysts, including ferrous sulfate and hydrogen peroxide for Fenton reactions, potassium persulfate for persulfate activation processes, and titanium dioxide for heterogeneous catalysis. All of these methods are promoted by UV radiation. The membranes are made of polyimide, a polymer renowned for its outstanding chemical and physical properties, ensuring superior performance even under high temperatures and exhibiting resistance to UV irradiation without any adverse effects. Different techniques were used to characterize the membranes, some of them are Fourier-transformed infrared spectroscopy (FT-IR, to understand if the imidation process is taking place), thermo-gravimetric analysis (TGA, to know the catalyst content of the membrane) and environmental scanning electron microscope (ESEM, to observe the nanostructure of the membrane). In this experience, different polymer concentrations in solution were test for the membrane production: a high viscosity of the polymeric solution is necessary to spin it to produce a membrane, moreover, low viscosities lead to the production of defects in the membrane texture. In addition, both ambient and inert atmospheres were tested to analyze PAA solution production: inert ambient ensure a proper viscosity for electrospinning and low temperature during solution storage maintains a high viscosity for long time. Different tests were made to understand the distinct contribution related to the PFOA removal: adsorption of the pollutant in the membrane and degradation of it. Experiments performed confirmed that a UV lamp is necessary to accelerate and increase the degradation process of the contaminant, however, its removal is not yet satisfactory. Further future studies may be based on the degradation contribution of each individual reaction mechanism: Fenton, oxidation via persulphates and photocatalysis.