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Water pollution is a major environmental issue, which mankind is facing in modern times. Pollutants (especially dyes, antibiotics and bacteria) released by human activity into wastewater are harmful to humans, animals and water bodies. Therefore, it is urgent to remove these pollutants from wastewater. Amongst conventional wastewater tertiary treatment techniques, there are adsorption and advanced oxidation processes (AOPs) including photocatalysis. These two methodologies can have important benefit from the use of nanomaterials. Despite the plethora of reports about adsorption or photocatalysis for wastewater treatment, there are still some issues in this field, i.e.: (1) In photocatalysis, one of the most common photocatalysts, titanium dioxide (TiO2), has been widely used to degrade organic pollutants in water, but it has the limitation to be operated by ultraviolet (UV) light and, therefore, by means of a non-sustainable and high associated cost methodology. (2) Most of the literature presented one material to remove only one kind of pollutant at a time. However, as we all know, wastewater is a complex matrix comprising several species. (3) Most researchers have used only one technique, e.g. adsorption or photocatalysis, to treat wastewater. However, adsorption or photocatalysis has its own limitations, which may be overcome by their combined use. Only few researchers combined adsorption and photocatalysis for wastewater treatment and this field is still in its infancy. (4) Few research reports deal with nanocomposites simultaneously possessing antibacterial activity and the ability to remove organic pollutants of different chemical composition and properties, such as dyes and antibiotics. (5) After wastewater treatment, the recovery and the reuse of the photocatalytic materials used as slurry photocatalysts are generally problematic. The aim of this thesis is to tackle some of these issues by developing new multifunctional nanocomposites capable of removing different kinds of pollutants – namely dyes, antibiotics and bacteria – from wastewater through a sustainable and cost-effective treatment. Moreover, the new nanocomposites will have to be easy to recover and reusable. In this context, different kinds of polymer-based magnetic nanocomposites comprising a core of Fe3O4/poly(N-isopropylacrylamide-co-methacrylic acid) (Fe3O4/P(NIPAM-co-MAA)) microspheres were prepared. To reach this aim, the different kinds of nanomaterials to be combined in the composites were synthesized and thoroughly studied. The first material is silver-titanium dioxide nanoparticles (Ag-TiO2 NPs), which were prepared by synthesizing Ag NPs on the surface of commercial TiO2 P25 via a photochemical reduction method. Compared with TiO2 P25, the prepared Ag-TiO2 NPs showed enhanced visible light photocatalytic degradation of the two antibiotics ciprofloxacin (CIP) and norfloxacin (NFX). Besides, the visible light photocatalytic mechanism of Ag-TiO2 NPs underlying the photodegradation of CIP was studied. Moreover, recycling experiments of Ag-TiO2 NPs demonstrated that Ag-TiO2 NPs could be reused. Last but not least, Ag-TiO2 NPs displayed an excellent ability to inhibit the growth of Escherichia coli (E. coli). Subsequently, Fe3O4/P(NIPAM-co-MAA) microspheres were prepared and characterized according to a previously published procedure. After the single components were obtained, studied and characterized, a large part of the thesis was devoted to the preparation of the Fe3O4/P(NIPAM-co-MAA)/Ag-TiO2 nanocomposites, which showed excellent adsorption, photocatalytic and antibacterial activities. The new multifunctional nanocomposites could not only adsorb dyes like basic fuchsin (BF), but also degrade antibiotics like CIP and NFX under visible light irradiation. More importantly, the nanocomposites could adsorb and degrade the pollutants mixture (BF and CIP) in water under visible light irradiation and showed good antibacterial activity towards E. coli. Due to the superparamagnetic properties of Fe3O4 NPs, the nanocomposites could be easily reused. Finally, another material, polyamidoamine (PAMAM) dendrimer-grafted Fe3O4/P(NIPAM-co-MAA) nanocomposite, was prepared by combining the previously prepared Fe3O4/P(NIPAM-co-MAA) microspheres with dendrimers. The obtained nanocomposites showed excellent adsorption activities towards differently charged dyes. In particular, thanks to the carboxylic groups on MAA in the Fe3O4/P(NIPAM-co-MAA) microspheres, the nanocomposites could adsorb positively charged dyes (e.g. BF), while, thanks to the amino groups on PAMAM dendrimers, also negatively charged dyes such as methyl orange (MO) could be adsorbed. Due to the superparamagnetic properties of the Fe3O4 NPs, the nanocomposites could be easily reused. In conclusion, these multifunctional nanocomposites in this thesis work overcame some current limitations, which hinder the use of nanomaterials in wastewater treatment applications, thereby providing an ecologically promising and effective method for reducing water pollution.:Declaration of primary authorship iii Acknowledgments v Abstract vii Kurzfassung ix List of figures xvii List of tables xxiii Nomenclature xxv Chapter 1: Introduction 1 1.1 Motivation 1 1.2 Challenges 1 1.3 Aim of the thesis 2 1.4 Outline of the thesis 3 Chapter 2: Fundamentals 5 2.1 Pollutants in wastewater 5 2.2 Adsorption technique for wastewater treatment 6 2.2.1 Activated carbon 7 2.2.2 Zeolites 7 2.2.3 Polymers 8 2.3 Photocatalysis 11 2.3.1 History of TiO2 in photocatalysis 12 2.3.2 TiO2 crystalline phases 12 2.3.3 TiO2 photocatalytic mechanism under UV light irradiation 13 2.3.4 Parameters influencing the photocatalytic efficiency of TiO2 16 2.4 Development of visible light-responsive TiO2 photocatalysts 19 2.4.1 Non-metal doping 20 2.4.2 Metal doping 20 2.4.3 Dye sensitization 21 2.4.4 Coupled semiconductors 22 Chapter 3: Materials and experimental methods 23 3.1 Materials 23 3.2 Protocols 27 3.2.1 Preparation of Ag-TiO2 NPs 27 3.2.2 Preparation of Fe3O4/P(NIPAM-co-MAA)/Ag-TiO2 nanocomposites 27 3.2.3 Preparation of PAMAM dendrimer-grafted Fe3O4/P(NIPAM-co-MAA) nanocomposites 28 3.3 Characterization methods 29 3.3.1 High Resolution Transmission Electron Microscopy (HRTEM) 30 3.3.2 Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy 30 3.3.3 X-ray powder Diffraction (XRD) 30 3.3.4 UV-Vis Diffuse Reflectance Spectroscopy (UV-Vis DRS) 30 3.3.5 Fluorometer 31 3.3.6 Brunauer-Emmett-Teller (BET) surface area analysis 31 3.3.7 Vibrating Sample Magnetometer (VSM) 31 3.3.8 Thermal Gravimetric Analysis (TGA) 31 3.4 Photocatalytic activity measurements 31 3.4.1 Visible light photocatalytic activity of TiO2 P25 and Ag-TiO2 NPs 32 3.4.2 Visible light photocatalytic investigations of Fe3O4/P(NIPAM-co-MAA)/Ag-TiO2 nanocomposites 33 3.5 Adsorption capacity measurements 34 3.5.1 Adsorption capacity of Fe3O4/P(NIPAM-co-MAA)/Ag-TiO2 nanocomposites 34 3.5.2 Adsorption capacity of PAMAM dendrimer-grafted Fe3O4/ P(NIPAM-co-MAA) nanocomposites 35 3.6 Antibacterial activity tests 37 3.6.1 Ag-TiO2 NPs antibacterial activity investigations 38 3.6.2 Fe3O4/P(NIPAM-co-MAA)/Ag-TiO2 nanocomposites antibacterial activity investigations 38 Chapter 4: Ag-TiO2 NPs 41 4.1 Characterization of Ag-TiO2 NPs 42 4.2 Photocatalytic activity of Ag-TiO2 NPs 47 4.2.1 Assessment of the photocatalytic activity of Ag-TiO2 NPs 47 4.2.2 Reusability of Ag-TiO2 NPs 50 4.2.3 Photocatalytic mechanism of Ag-TiO2 NPs 51 4.3 Antibacterial properties of Ag-TiO2 NPs 53 4.4 Summary 54 Chapter 5: Fe3O4/P(NIPAM-co-MAA)/Ag-TiO2 nanocomposites 57 5.1 Characterization of Fe3O4/P(NIPAM-co-MAA)/Ag-TiO2 nanocomposites 58 5.2 Adsorption of dyes by Fe3O4/P(NIPAM-co-MAA)/Ag-TiO2 nanocomposites 64 5.3 Degradation of antibiotics by Fe3O4/P(NIPAM-co-MAA)/Ag-TiO2 nanocomposites 68 5.4 Reusability of Fe3O4/P(NIPAM-co-MAA)/Ag-TiO2 nanocomposites 72 5.5 Antibacterial activity of Fe3O4/P(NIPAM-co-MAA)/Ag-TiO2 nanocomposites 74 5.6 Adsorption and degradation of a mixture of pollutants by Fe3O4/P(NIPAM-co-MA A)/Ag-TiO2 nanocomposites 75 5.6.1 Adsorption and degradation of BF by Fe3O4/P(NIPAM-co-MAA)/Ag-TiO2 nanocomposites 75 5.6.2 Adsorption and degradation of CIP by Fe3O4/P(NIPAM-co-MAA)/Ag-TiO2 nanocomposites 78 5.6.3 Adsorption and degradation of a mixture of BF and CIP by Fe3O4/P(NIPAM-co-MAA)/Ag-TiO2 nanocomposites 80 5.7 Summary 86 Chapter 6: PAMAM dendrimer-grafted Fe3O4/P(NIPAM-co-MAA) nanocomposites 89 6.1 Characterization of PAMAM dendrimer-grafted Fe3O4/P(NIPAM-co-MAA) nanocomposites 89 6.2 Adsorption capacity of different nanocomposites towards dyes 95 6.2.1 Adsorption of positively charged dye BF by different nanocomposites 96 6.2.2 Adsorption of negatively charged dye MO by different nanocomposites 97 6.2.3 Adsorption of BF and MO by G51P0.8 and G51P0.5 nanocomposites 98 6.2.4 Adsorption kinetics and isotherm of G51P1 nanocomposites 101 6.3 Reusability 105 6.4 Summary 106 Chapter 7: Conclusions and outlook 109 7.1 Conclusions 109 7.2 Outlook 111 Appendix 113 A1 Calibration curves 113 A2 Assessment of the photocatalytic activity of Ag-TiO2 NPs 114 References 117 Scientific output 141 Curriculum vitae 143 |
