Development of a Photo-Fenton Catalyst Supported on Modified Polymer Films

The work presented in this thesis is a part of the European project INNOWATECH. The global objective of this project was to provide effective technological solutions for the treatment of industrial wastewater, to propose new concepts in wastewater treatment with potential benefits for the protection of the environment. In particular photo-assisted Fenton oxidation was investigated. It is a promising technology to decontaminate industrial wastewater as it makes use of the natural energy that provides the sun, abundant chemicals (iron ions and hydrogen peroxide) and does not produce toxic waste. Apart from short detour about homogenous photo-Fenton reaction (chapter 2) where the influence of pollutant physico-chemical properties on reactivity is studied, this thesis focuses on photo-Fenton treatment using a new solid catalysis. The immobilization of iron oxide on a suitable support is a strategy proposed to overcome the practical limitation related to homogeneous photo-Fenton treatment (i.e. the limited operational pH range and the problems caused by the separation of catalyst from the effluent). The preparation and the surface characterization of new photo-Fenton catalysts based on iron oxide supported on modified polymer films is described in chapters 3 and 4. The photocatalytic activities of prepared materials were evaluated mainly toward organic pollutant degradation both at laboratory (chapter 3-5) and at pilot (chapter 6) scales. In detail, chapter 2 focuses on the effect of contaminant physico-chemical properties on the reactivity via photo-assisted Fenton catalysis. Several para-substituted phenols were used in order to cover a wide range of electronics effects. Many physico-chemical descriptors were correlated with the initial Fenton and photo-Fenton degradation rates (r0). Electronic descriptors such as calculated zero point energy (Ezero) and energy of the highest occupied orbital were found to be the most adequate to predict Fenton and photo-assisted Fenton reactivity. The preparation of iron oxide-coated polymer films is described in chapter 3. Polyvinyl fluoride (PVF) film surface was functionalized by different methods, either by Vacuum-UV radiation, radio-frequency plasma, photo-Fenton oxidation or TiO2 photocatalysis. These pre-treatments were performed to increase iron oxide adhesion to polymer surface. Afterward the functionalized polymers films were immersed in an aqueous solution for the deposition of iron oxide layer by hydrolysis of FeCl3. The catalytic activities of resulting materials were compared during hydroquinone degradation in presence of H2O2 and under simulated solar light illumination. The most efficient and stable catalyst obtained was prepared by means of TiO2 photocatalytic functionalization of polymers followed by iron oxide coating (leading to so called Pf-TiO2-Fe oxide), therefore this preparation procedure was selected in chapters 4-6. Chapter 4 focuses on the study of the mechanisms involved during the preparation and use of Pf-TiO2-Fe oxide. In particular, the modifications induced by TiO2 photocatalysis on polymer surface such as oxygen group formation and deposition of TiO2 particles were characterized by x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and UV-visible spectrophotometry. The photocatalytic activity of Pf-TiO2-Fe oxide in presence of H2O2 and under simulated solar light radiation was evaluated toward HQ degradation. The occurrence of important synergistic effects between TiO2 and iron oxide was discussed. Finally, the effect of preparation parameters on photocatalytic activity of Pf-TiO2-Fe oxide/H2O2/light system was determined allowing the optimization of preparation procedure. Hence highly efficient photocatalysts for hydroquinone degradation and E. Coli inactivation were obtained. The degradation of hydroquinone and nalidixic acid (NA) mediated the system Pf-TiO2-Fe oxide/H2O2/light was examined (chapter 5). The contribution of homogeneous photo-Fenton oxidation in the degradation process was determined and the mechanisms involved in iron leaching are discussed. Besides, the effect of operational parameters on degradation rates was assessed. The rates are independent on initial pH and NaCl presence but were enhanced by increasing temperature. Long-term stability of Pf-TiO2-Fe oxide was evaluated by repetitive nalidixic acid degradation runs. The adaptation of Pf-TiO2-Fe oxide to pilot scale in a compound parabolic collector (CPC) solar photoreactor is described in chapter 6: solar photocatalytic degradation of phenol, nalidixic acid, mixture of pesticides, and another of emerging contaminants, in water was investigated. The influences of operational pH and pollutant structure on the degradation rates were evaluated. It was found that compounds with chelating moieties (or carboxylic acids) were the most quickly removed by Pf-TiO2-Fe oxide/H2O2/light and allowed the photo-Fenton catalyst to be efficient at higher pH values.