Dottorato in SCIENZE CHIMICHE

Titolo della tesi: Synthesis and characterizations of TiO2 and γ-Fe2O3 nanohybrids and their biological and environmental applications

This Ph.D. thesis focused on the synthesis and characterization of TiO2 and γ-Fe2O3 nanoparticles (NPs) for their potential antibacterial and environmental applications. For the TiO2NPs, a commercial TiO2 nanopowder was employed and functionalized with organic and alkoxysilane molecules. For the antibacterial and gas sensing applications, the TiO2 nanopowder was functionalized with a bifunctional silane linker, (3-mercaptopropyl)trimethoxysilane (MPTMS), bearing –O and –SH moieties in its opposing sites, to mediate the covalent attachment of TiO2- to AgNPs and enhance their colloidal stability as well. The synthesis was carried out by the two main steps: i) the commercially available TiO2NPs were functionalized with MPTMS through the formation of surface Ti–O–Si covalent bonds (TiO2NPs-MPTMS), and ii) the nanohybrid was prepared by decoration of AgNPs, modified with 3MPS (3-mercapto-1-propanesulfonate) i.e. AgNPs-3MPS, on the surface of TiO2NPs-MPTMS, to form TiO2NPs-MPTMS-AgNPs-3MPS, abbreviated as TiO2-Ag_2.5, TiO2-Ag_1, and TiO2-Ag_4. The silanization reaction was tested in different conditions in terms of solvent, time, use of ammonia (as catalyst), and the precursor ratios. The stability, size, morphology, and chemical composition of these nanoparticles were studied by extensive characterizations including FTIR-ATR (and far-IR), FESEM-EDS, TEM, ICP, DLS, ζ-potential, 1H-NMR, UV-Vis, and XPS. The colloidal stabilities of TiO2NPs-MPTMS and the nanohybrids were studied in both water and biological culture media. The results demonstrated both successful chemical silanization of the pristine TiO2NPs and the subsequent AgNPs decoration. Thanks to a multidisciplinary approach, antibacterial activities of these nanohybrids were investigated on multidrug resistance Gram-positive and Gram-negative bacteria and the results showed a synergic antibacterial effect of TiO2- and AgNPs in the nanohybrid, compared to the pristine TiO2NPs and control groups. Also, the nanohybrids have been employed for designing a solid-state chemoresistive sensor with the aim to detect H2S toxic gas. Deposition of the nanohybrids on the interdigitated electrodes could enhance the sensitivity of resistive sensor with high response. Also, direct loading of an anticancer prodrug, 5-aminolevolinic acid (ALA), onto the surface of the TiO2 nanopowder was studied, because of importance of this nanocomposite in photodynamic cancer therapy. Regarding the γ-Fe2O3 nanohybrid, a novel peptide-based magnetogel was synthesized through the encapsulation of γ-Fe2O3-polyacrylic acid (PAA) nanoparticles (γ-Fe2O3NPs) into a hydrogel matrix, used for enhancing the ability of the hydrogel to remove Cr(III), Co(II), and Ni(II) pollutants from water. Fmoc-Phe (fluorenylmethoxycarbonyl-phenylalanine) and diphenylalanine (Phe2) were used as starting reagents for the hydrogelator (Fmoc-Phe3) synthesis via an enzymatic method. The PAA-coated magnetic nanoparticles were synthesized in a separate step, using the co-precipitation method, and encapsulated into the peptide-based hydrogel. The resulting organic/inorganic hybrid system (γ-Fe2O3NPs-peptide) was characterized with different techniques, including FT-IR, Raman, UV-Vis, DLS, ζ-potential, XPS, FESEM-EDS, swelling ability tests, and rheology. Considering the application in heavy metals removal from water, the adsorption of this magnetogel was compared to its precursors and the effect of an external magnetic field was assessed. Four different systems were selected for this study including: 1) γ-Fe2O3NPs stabilized with PAA, (γ-Fe2O3NPs); 2) Fmoc-Phe3 hydrogel (HG); 3) γ-Fe2O3NPs embedded in peptide magnetogel (γ-Fe2O3NPs@HG); and 4) γ-Fe2O3NPs@HG in the presence of an external magnetic field. To quantify the removal efficiency of these four model systems, UV-Vis technique was employed as a fast, cheap, and versatile method. The results demonstrated that both Fmoc-Phe3 hydrogel and γ-Fe2O3NPs peptide magnetogel can efficiently remove all the tested pollutants from water. Interestingly, due to the presence of magnetic γ-Fe2O3NPs inside the hydrogel, the removal efficiency can be enhanced by applying the external magnetic field. The proposed magnetogel represents a smart multifunctional nanosystem with improved absorption efficiency and synergic effect upon applying the external magnetic field.