PROS AND CONS OF NANOMATERIALS: STUDY OF HALLOYSITE-BASED NANOCOMPOSITES FOR BIOMEDICAL OR CATALYTIC PURPOSES AND EVALUATION OF ENVIRONMENTAL AQUATIC TOXICITY OF CEO2 NANOPARTICLES

My Ph.D. dealt mainly with the study of halloysite nanotubes (HNT), and their interaction with molecules and nanoparticles as potential for potential applications either in biomedicine or in catalysis. A minor part of my Ph.D work was dedicated to the preparation and characterization of Ceria nanoparticles stabilized with polymers of different charge, to investigate, in collaboration with the group of prof Della Torre and Binelli, their effect on various animal and bacterial models relative to their possible toxic effects especially in the aquatic environment. I started the first part of my thesis by introducing the clay material HNT. HNT is a unique natural nanomaterial composed of double-layered aluminosilicate with a hollow tubular structure in the micro range. A preliminary literature survey revealed that HNT, due to their physical and chemical features, could be suitable for many application fields like medicine and catalysis (Chapter 1). We started our aim by synthesizing some HNT adducts possibly suitable for hyperthermia applications by selectively load superparamagnetic iron oxides (SPIONs) into the inner lumen of HNT. The magnetic properties of the loaded SPIONs did not change after their trapping inside the HNT lumen. The SPION-in-HNT nanocomposite was synthesized through the pre-modification of the HNT inner lumen such that it becomes suitable to be suitable to load the apolar SPION as synthesized by thermal decomposition method without a further step of ligand exchange (Chapter 2). To extend the loading to another kind of NP for hyperthermia applications, we tried to load gold nanoparticles. The gold NPs can be synthesized in various shapes; we synthesized spherical and star shapes of gold for our purpose. Gold can be loaded inside the inner lumen in the studied shapes, but the low concentration of gold suspension hampered a massive loading into the HNT lumen. (Chapter 3). The second part of the work with Halloysites was devoted to the preparation and characterization of HNT adducts with luminescent molecules able to act as photosensitizers for photodynamic therapy (PDT). For this purpose, we were interested in loading perfluorinated porphyrin, in their non-coordinated- and Zn-coordinated form, inside the lumen of HNT. The release of the photosensitizer by the inner lumen was slowed down compared to the release of the perfluorinated drugs adsorbed in the outer surface of HNT. (Chapter 4). To use HNT as a dual vector for drug delivery, we synthesized HNT-Ru photosensitizer. The photosensitizer was covalently bonded to the silica part of the outer surface of HNT, leaving the inner lumen free for potentially an extra loading with another drug. The photophysical properties of synthesized nanocomposite were then tested (Chapter 5). Finally, concerning HNT, we aimed to synthesize a new synthetic Au-Pt nanoparticle supported over HNT with different Au-to-Pt molar ratios via a sol immobilization method for catalytic purposes. The synthesized catalyst showed that the activity toward hydrogenation of C=O of cinnamaldehyde increased with increasing the molar ratio of Au/Pt (Chapter 6). Unfortunately, the product potentially useful for biomedical purposes were not tested at least at cellular level, and this lack to the work was essentially due to the COVID-19 pandemic situation that slowed down a lot of collaboration especially with biologist collaborators. The last part of my thesis was devoted to synthesizing nanoceria and covering it with natural polymer available in the aquatic system as alginate and chitosan. Ceria NPs surrounded by both Alginate and Chitosan showed no acute toxicity effects at the average environmental concentration level of the two tested natural macromolecules (Chapter 7).