Synthesis, characterization, optimization and application of TiO2-based photocatalytic materials for environmental applications related to emerging pollution

This PhD thesis deals with the exploitation of heterogeneous photocatalysis, as an Advanced Oxidation Process, for environmental issues related to the emerging pollution: in particular for wastewater remediation and bacterial decontamination purposes. During this project, several photocatalytic materials have been synthesized by coupling semiconductor (TiO2) nanoparticles (both bare and doped) to different supporting materials, e.g. persistent luminescence materials (3ZnO:Ga2O3:2GeO2: Cr3+; CaAl2O4: (La, Nd)3+), magnetic and porous materials (ferrite nanoparticles, magnetic zeolite obtained from industrial waste) and polymeric materials (based on polydimethylsiloxane “PDMS”). In addition, an analytical approach to the study on the abatement and the quantification of emerging pollutants was considered, an important part of which was carried out at the Water Lab of the Environmental Engineering Department at Technical University of Crete, under the supervision of Professor Elia Psillakis. Specifically, TiO2 was synthesized through the sol-gel technique, both in the undoped and doped form (for example with Cu and N), while its crystallization on several supporting materials was obtained with different synthetic techniques such as: sol-gel synthesis, solid-state synthesis, hydrothermal/solvothermal synthesis and electrospinning technique. Some of the synthesized materials were investigated using a chemometric approach, that is the possibility to exploit an Experimental Design mathematical model in order to investigate the optimal synthetic conditions to get enhanced photocatalytic efficiency (within the experimental domain) for the materials. All samples synthesized within the current project were subjected to a physical-chemical characterization, by means of: X-Ray Diffraction “XRD” and crystallographic refinements (Rietveld, Pair Distribution Function “PDF”, Williamson-Hall plot), Scanning and Transmission Electron Microscopy-Energy Dispersive X-Ray Spectrometry “SEM-EDS”, “TEM”, Porosimetry Brunauer-Emmett-Teller “BET”, Dynamic Light Scattering “DLS”, Differential Scanning Calorimetry “DSC”, Diffuse Reflectance (Kubelka-Munk plots for Energy Gap “Eg”), Rheological Measurements, Luminescence Properties, Turbidimetry, Inductively Coupled Plasma – Atomic Emission Spectroscopy “ICP-AES”, Diffuse Reflectance Infrared Fourier Transform Spectroscopy “DRIFTS” and antibacterial properties with E. Coli cultures. Above all, a kinetic characterization in terms of photocatalytic efficiency evaluation was always performed for synthesized samples. In particular, kinetic behaviour of the photocatalysts was evaluated by means of Methylene Blue “MB” aqueous solutions degradation, studied as a function of time, with different initial concentrations (as required by ISO NORM 10678:2010). For MB quantification, a UV-Vis spectrophotometer was used, and experiments were usually performed in triplicate. Furthermore, during the first part of the project, a Pilot Plant Prototype was assembled (with a processing volume equal to 1L) and used for preliminary evaluations on a potential industrial scale-up. All tests and characterizations achieved were adapted according to the specific supporting material employed. Eventually, considering the nature of emerging micro-pollutants, an analytical approach to the determination of their concentration in aqueous systems was employed. Specifically, chromatographic tests were performed with liquid and gas chromatography techniques, often coupled with mass spectrometry, for some specific emerging pollutants (Ofloxacin, Parabens, Nicotine, Salbutamol). Matrix effects were also considered in the evaluation of the pollutants’ degradation during the advanced oxidation tests. This task wouldn’t have been possible without valuable National and International collaborations, which gave an essential help to the development of the project for what concerns a part of the reported characterization. My acknowledgements are directed to: Department of Chemistry and Industrial Chemistry - University of Genova (Analytical, Industrial, Physical Sections), Analytic and Photochemistry Section of the Department of Chemistry - University of Pavia; Department of Chemistry - University of Kuwait; Department of Environmental Engineering - Technical University of Crete; Institute of Methodologies of Environmental Analysis, Institute of Matter and Institute of Superconducting and other Innovative Materials and Devices - National Research Council. Each individual contribute will be highlighted in each dedicated section, throughout the manuscript.