Recently, researchers on nanoparticles and nanostructures has received a great deal of attention not only in the area of synthesis and characterization but also in their potential application in various high-technological applications. Nanomaterials are widely used not only for environmental and biological applications but also for electronic and sensing applications. Among various classes of nanomaterials, the metal oxide nanostructures possess particular important because of their significant physical and chemical properties which allowed them to be used for the fabrication of highly efficient nanodevices. The metal oxide nanomaterials are widely used for catalysis, sensing, and electronic devices, and so on. Due to the high-efficient applications, researchers have developed several synthesis strategies to prepare metal oxide nanostructures with tailored geometry and utilize them for a variety of applications. However, it is still desirable to prepare metal oxide nanomaterials with environment-friendly precursors and processes with varied size and morphology for their effective utilization in specific applications. This thesis focuses on the synthesis, characterizations and specific applications of two undoped and doped metal oxide nanostructures, i.e. zinc oxide (ZnO) and iron oxide (α-Fe2O3). The thesis highlights the development of novel synthesis techniques/procedures which are rapid, consume less energy and time, and are less cumbersome, more economical, especially because of the low temperature process. The other aspect of the thesis is to use the as-synthesized nanomaterials for several important applications such as sensors, photovoltaic, and photocatalysis. The thesis is divided into several chapters. Chapter 1 starts with a brief introduction of the metal oxide nanostructures and their various synthetic methods. In addition to this, a short review on the targeted applications, i.e. sensing, photovoltaic and photocatalytic, of this thesis was also discussed in this chapter. Finally, the chapter describes the objective and importance of the thesis. Chapter 2 deals with the details of the synthesis and characterization techniques used in this thesis. Two specific techniques, i.e. hydrothermal and thermal evaporation, have been used for the synthesis of various undoped and doped nanomaterials explored in this thesis. The synthesized nanomaterials were examined by variety of techniques in terms of the morphological, structural, optical, compositional and electrical properties. Moreover the prepared nanomaterials together were used for various applications such as sensing, photovoltaic and photocatalytic applications. In a word, this chapter provides all the detailed procedures for the synthesis, characterizations and applications of targeted nanomaterials in this thesis. Chapter 3 describes the main results and discussion of the thesis. This chapter is divided into several sections and each section describes the synthesis, detailed characterizations and particular application of a single metal oxide nanomaterial. Section 1 describes the growth, characterization and ammonia chemical sensing applications of well-crystalline ZnO nanopencils grown via facile and simple hydrothermal process using commonly used laboratory chemicals. Importantly, the fabricated ammonia chemical sensor exhibited ultra-high sensitivity. Section 2 demonstrates the use of ZnO balls made of intermingled nanocrystalline nanosheets for photovoltaic device application. Successful growth, characterizations and phenyl hydrazine chemical sensing applications based on Ag-doped ZnO nanoflowers was demonstrated in section 3 of this chapter. Section 4 describes the Ce-doped ZnO nanorods for the detection of hazardous chemical; hydroquinone. Section 5 exemplifies the facile growth and detailed structural and optical characterizations of In-Doped ZnO hollow spheres composed of nanosheets networks and nanocones. Finally, section 6 illustrates the utilization of α-Fe2O3 hexagonal nanoparticles for environmental remediation and smart sensor applications. Moreover the synthesized α-Fe2O3 hexagonal nanoparticles were characterized in detail in terms of their morphological, structural, compositional and optical properties. Chapter 4 briefly highlights the overall conclusion and an outlook for further investigations suggested by the work undertaken here for this thesis. / Τα τελευταία χρόνια τα νανοσωματίδια και οι νανοδομές έχουν προσελκύσει μεγάλο ερευνητικό ενδιαφέρον λόγω των σημαντικών δυνατοτήτων που προσφέρουν για εφαρμογές υψηλής τεχνολογίας. Τα νανοϋλικά χρησιμοποιούντα ευρέως τόσο για περιβαλλοντικές και βιολογικές εφαρμογές όσο και για εφαρμογές στην ηλεκτρονική και τους αισθητήρες. Μεταξύ των διάφορων κατηγοριών νανοϋλικών, οι νανοδομές μεταλλικών οξειδίων παρουσιάζουν ιδιαίτερο ενδιαφέρον λόγω των φυσικών και χημικών ιδιοτήτων τους, που τους επιτρέπουν να χρησιμοποιούνται για την κατασκευή νανοσυσκευών υψηλής απόδοσης, με χαρακτηριστικά πεδία εφαρμογών την κατάλυση, την ηλεκτρονική και τους αισθητήρες. Για τους σκοπούς αυτούς, έχει αναπτυχθεί πληθώρα μεθόδων για την σύνθεση και προετοιμασία νανοδομών μεταλλικών οξειδίων με επιθυμητές γεωμετρίες, ώστε να είναι κατάλληλα για διαφορετικές εφαρμογές. Παρόλα αυτά, εξακολουθεί να υπάρχει έντονο ενδιαφέρον για την παραγωγή τέτοιων υλικών σε διάφορα μεγέθη και μορφολογίες, με περιβαλλοντικά φιλικές μεθόδους, με απώτερο σκοπό την χρησιμοποίησή τους σε συγκεκριμένες εφαρμογές. Η παρούσα διατριβή εστιάζει στην σύνθεση, τον χαρακτηρισμό και τις εφαρμογές των νανοδομών δύο συγκεκριμένων μεταλλικών οξειδίων (ZnO και α-Fe2O3) με ή χωρίς προσμείξεις. Η διατριβή δίνει έμφαση σε νέες τεχνικές σύνθεσης, οι οποίες είναι γρήγορες, καταναλώνουν λιγότερη ενέργεια και είναι πιο οικονομικές κυρίως λόγω χαμηλότερης θερμοκρασίας επεξεργασίας. Οι δομές των νανοϋλικών που προκύπτουν, χρησιμοποιούνται σε διάφορες σημαντικές εφαρμογές, όπως είναι οι αισθητήρες, τα φωτοβολταϊκά και η φωτοκατάλυση. Η διατριβή χωρίζεται σε 4 κεφάλαια. Στο κεφάλαιο 1 δίνεται μία σύντομη εισαγωγή στις νανοδομές των μεταλλικών οξειδίων και τις διάφορες μεθόδους σύνθεσης. Παρουσιάζονται συνοπτικά τα είδη των εφαρμογών τα οποία θα αποτελέσουν αντικείμενο μελέτης και τέλος περιγράφονται οι αντικειμενικοί στόχοι και η σημασία της διατριβής. Το κεφάλαιο 2 πραγματεύεται λεπτομερώς τις τεχνικές σύνθεσης και χαρακτηρισμού που υιοθετούνται στο μεγαλύτερο μέρος της μελέτης. Συγκεκριμένα, για την σύνθεση των νανοϋλικών (με ή χωρίς προσμίξεις) χρησιμοποιούνται οι τεχνικές της υδροθερμικής και της θερμικής εξάχνωσης. Τα παραγόμενα νανοϋλικά μελετήθηκαν ως προς την σύνθεσή τους, καθώς επίσης και τις μορφολογικές, δομικές, οπτικές και ηλεκτρικές ιδιότητες. Στην συνέχεια, χρησιμοποιούνται για τα διάφορα είδη εφαρμογών που αναφέρθηκαν παραπάνω. Με άλλα λόγια, στο κεφάλαιο αυτό περιέχονται όλες οι λεπτομέρειες των διαδικασιών παραγωγής και των εφαρμογών. Το κεφάλαιο 3 περιλαμβάνει την παρουσίαση και συζήτηση των αποτελεσμάτων. Αποτελείται από διάφορες παραγράφους η κάθε μία εκ των οποίων περιγράφει την σύνθεση, τον χαρακτηρισμό και τις εφαρμογές ενός εκ των υλικών. Στην Παράγραφο 1 περιγράφονται η ανάπτυξη, ο χαρακτηρισμός των κρυσταλλικών ZnO νανομολυβδιών μέσω μίας απλής και εύκολης υδροθερμικής διαδικασίας, χρησιμοποιώντας συνηθισμένα εργαστηριακά υλικά, καθώς επίσης και η εφαρμογή τους ως χημικοί αισθητήρες αμμωνίας. Αξίζει να σημειωθεί ότι οι αισθητήρες που κατασκευάστηκαν επέδειξαν υπέρ-υψηλή ευαισθησία. Η παράγραφος 2 επιδεικνύει την χρήση ZnO σφαιρών που είναι κατασκευασμένες απο αναμιγμένα νανοκρυσταλλικά νανοφύλλα για φωτοβολταϊκές εφαρμογές. Η επιτυχής ανάπτυξη και χαρακτηρισμός ZnO νανολουλουδιών εμπλουτισμένα με Άργυρο καθώς επίσης και η χρήση τους σε εφαρμογές αισθητήρων φαινυλο-υδραζίνης παρουσιάζονται στην παράγραφο 3. Στην παράγραφο 4 περιγράφεται η χρήση ZnO νανοράβδων εμπλουτισμένων με Δημήτριο για την ανίχνευση της επικίνδυνης χημικής ουσίας υδροκινόνης. Στην Παράγραφο 5 παρουσιάζεται η ανάπτυξη και ο λεπτομερής δομικός και οπτικός χαρακτηρισμός κοίλων σφαιρών ZnO εμπλουτισμένων με Ίνδιο που αποτελούνται απο δίκτυα νανοφύλλων και νανοκώνους. Τέλος στην παράγραφο 6 περιγράφεται η χρήση εξαγωνικών νανοσωματιδίων α-Fe2O3 για περιβαλλοντική αποκατάσταση και εφαρμογές ευφυών αισθητήρων. Οι δομές αυτές χαρακτηρίστηκαν λεπτομερώς ως προς τη σύνθεση τις μορφολογικές, τις δομικές και τις οπτικές ιδιότητες. Στο κεφάλαιο 4 παρουσιάζονται τα συμπεράσματα της παρούσας διατριβής καθώς επίσης και προστάσεις για την περεταίρω διερεύνηση των υπό μελέτη συστημάτων.

Le travail de thèse porte sur les méthodes de synthèse de nanostructures de dioxyde de titane et de leurs études physicochimiques afin de préciser les corrélations entre la morphologie, le dopage métallique, les caractéristiques structurales avec l'efficacité photocatalytique. Le grand intérêt pour les nanomatériaux TiO2 réside dans la mise au point de nouvelles sources d'énergie ou la conservation de l’environnement par des processus photocatalytiques. Cependant, la limitation principale de TiO2 est du au large gap électronique (eV ~3,2) du polymorphe Anatase. Ainsi, un des objectifs importants pour l'amélioration de l’efficacité des nanomatériaux TiO2 est d'augmenter leur photoactivité en décalantla création de paires d'électron-trou de l’UV à la gamme du visible. D'ailleurs, on a montré que l'utilisation de nanostructures 1D de TiO2 (nanotubes) a amélioré la collection de charges, en favorisant leur transport dans les structures 1D, qui par conséquent réduit au minimum la recombinaison et prolonge les durées de vie des électrons.La première partie de ce travail est dédiée à la synthèse des nanopoudres TiO2 dopées par des ions métalliques (Ag, Cu, Eu) préparés par sol-gel. Même avec différents éléments de dopage qui apparemment peuvent adopter le même état de valence (2+) (Cu2+, Ag2+, Eu2+), différents comportements ont été démontrés pour l'incorporation efficace de ces ions dans la structure de TiO2. L'anomalie entre les rayons ioniques des différents éléments utilisés module le rapport du dopage substitutionnel. Ceci est en effet réalisé pour Cu2+ mais dans moins d'ampleur pour Ag2+ tandis que les ions d'europium forment une ségrégation de phase Eu2Ti2O7. La dégradation de colorants de bleu de méthylène (MB) a étéaméliorée légèrement avec les échantillons dopés Ag. La raison a été attribuée aux clusters métalliques Ag qui ont été en effet mis en évidence à travers leur bande d’absorption plasmonique. La deuxième partie porte sur des couches minces de TiO2 dopés (Cu, Ag, et Eu) qui ont été élaborés par sol-gel et spin-coating et dipcoating. Les paramètres optimaux ont été obtenus pour réaliser les films cristallins mais présentant une organisation mésoporeuse qui dépend également du processus de dopage. Des études de Photocatalyse ont été également réalisées et l'efficacité des films ont été comparées en fonction des éléments dopants. La troisième partie de la thèse est liée à la modification morphologique des nanoparticules pour former des nanotubes à l'aide de la méthode hydrothermale sous pression contrôlée. Un plan d'expérience basé sur la méthode Taguchi a été utilisé pour la détermination des paramètres optimaux.Les nanotubes TiO2 augmentent la surface spécifique en comparaison avec les nanoparticules. La dégradation de bleu deméthylène par les nanotubes a montré une efficacité photocatalytique plus élevée qu’avec les nanopoudres TiO2 pures etdopés Ag. / The thesis work is focused on the synthesis methods of titanium dioxide nanostructures and their physico-chemical studies in order to point out the correlations between the morphology, metal doping, structural features with the photocatalytic efficiency. The great interest on TiO2 nanomaterials deals with new sources of energy or in the environment preservation through the photocatalytic properties. However, the main limitations is due to the wide band gap (~3.2 eV) of the anatase polymorph. Thus, a major objective for improvement of the performance of TiO2 nanomaterials is to increase theirphotoactivity by shifting the onset of the electron-hole pairs creation from UV to the visible range. Moreover, it was found that using onedimensional (1-D) TiO2 (nanotubes) improved the charge collection by 1D nanostructures which consequently minimizes the recombination and prolongate the electron lifetimes. The first part of this work is focused on the synthesis of TiO2 nanopowders doped with metallic ions (Ag, Cu, Eu) prepared by Solgel. Even with different doping elements which apparently can adopt the same valence state (2+) such as (Cu2+, Ag2+,Eu2+), different behaviors were demonstrated for the effective incorporation of these ions in the host structure of TiO2. The discrepancy between ionic radii of the different used elements modulates the ratio of the substitutional doping. This is indeed achieved for Cu2+ but in less extent for Ag2+ while Europium ions form segregated phase as Eu2Ti2O7. The experiments on the degradation of methylene blue (MB)dyes have shown slight improvement with Ag-doped samples. The reason was tentatively attributed to the Ag clusters which were indeed demonstrated through their plasmon optical band. The second part of the work concerns thin films of TiO2 doped (Cu, Ag, and Eu) which were elaborated by spin coating and dip coating. The optimal parameters were obtained to achieve crystalline films but presenting mesoporous organisation which also depends on the doping process. Photocatalysis investigations were also realized and the efficiency of the films compared as function of the doping elements.The third part of the thesis is related to the morphological modification from nanoparticles to nanotubes by using the hydrothermal method with controlled pressure. An experimental design based on Taguchi Method was employed for the determination of the optimal parameters. TiO2 nanotubes increase the surface area in comparison with TiO2nanoparticles. TiO2 nanotubes were tested for the methylene blue degradation and show a higher photocatalytic efficiency than TiO2 nanopowders and TIO2 doped with Ag.

Afin de satisfaire la demande croissante des systèmes de traitement de l'air, des procédés commerciaux basés sur la photocatalyse par TiO2 ont été commercialisés. Récemment le problème de la désactivation de ces systèmes a attiré l'attention des industriels ainsi que des chercheurs. Les Siloxanes Méthyliques Volatils (SMVs) présents dans l'air auraient été identifiés comme une source majeure contribuant à cette désactivation. Par ailleurs, dans les centres de stockage des déchets, la valorisation du biogaz nécessite de recueillir et de traiter le biogaz issu des déchets organiques en vue de produire de l'énergie renouvelable et inoffensive pour l'environnement. A nouveau, les SMVs ont été identifiés comme un frein principal au développement de cette filière, ces derniers conduisant après oxydation à des dépôts de silice abrasifs dans le moteur. Les difficultés de mesure des SMVs aussi bien dans le biogaz que dans l'air ambiant ainsi que l'évaluation de leur impact sur les systèmes photocatalytiques ou dans les procédés de valorisation du biogaz constituent par conséquent un vrai défi. Afin de répondre à ces problématiques, ce travail comporte trois volets principaux : Le premier volet est dédié à la mise au point d'une méthode de mesure des siloxanes méthyliques volatils dans le biogaz et dans l'air ambiant. Pour ce faire nous avons choisi de mettre en place un système d'échantillonnage des SMVs basé sur leur piégeage et préconcentration sur un support solide suivi d'une désorption thermique ou chimique (extraction par solvant) avant leur analyse par GC-MS. Puisqu'aucune étude systématique sur le choix des supports n'est relatée dans la littérature, nous avons comparé plusieurs types d'adsorbants en déterminant le volume de perçage pour chacun des SMVs afin de choisir le (les) meilleur(s). Le second volet est consacré à l'évaluation des teneurs en SMVs dans le biogaz ainsi que dans l'air ambiant en différents endroits. Une méthode d'analyse des SMVs fiable a été développée qui a permis de confirmer les résultats précédents obtenus au laboratoire en ce qui concerne le choix des adsorbants pouvant piéger quantitativement les SMVs. Enfin, dans le troisième volet, l'impact des SMVs sur les systèmes photocatalytiques en choisissant comme molécule modèle l'octaméthylcyclotétrasiloxane (D4) a été étudié / In order to address the growing demand for indoor air treatment, many commercial systems based in the potocatalytic degradation using TiO2 have reached the market. Recently, deactivation of these systems has been observed. Some of the potentially most important deactivation pollutants are volatile methyl siloxanes (VMS), which are becoming more and more abundant indoor and in ambient air. Moreover, the increasing interest in the utilization of biogas to generate renewable energy (production of heat or electricity), has created significant concerns about the presence of VMS in the biogas. During biogas combustion, VMS are oxidized to abrasive microcrystalline silica that causes serious damage to gas engines, thus reducing the economic benefits of using biogas. Hence, it is essential to be able to measure the concentration of such VMS in ambient air and in biogas by a reliable method, as well as to study their impact on the photocatalytic systems. To address these issues, this work has three main parts: The first part is dedicated to the development of a method for measuring volatile methyl siloxanes in biogas and in ambient air. We have chosen sampling gas through sorbent tube followed by thermal desorption or chemical desorption (solvent extraction) and analysed using GC-MS. Since no systematic study on the choice of materials is related in the literature, we compared several types of adsorbents based on the determination of the VMS breakthrough volume (BV), in order to choose an appropriate adsorbent and to obtain accurate quantification of VMS. The second part is devoted to the evaluation of VMS in biogas and in ambient air at different sites. A reliable analytical method has been developed, and results are in agreement with the previous results obtained in the laboratory regarding the choice of adsorbents. Finally, in the third part, for a better understanding of the impact of VMS on photocatalytic systems, D4 was chosen as a VMS model compound as it is one of the most important VMS

El deterioro de las construcciones realizadas a base de cemento, producido en gran medida, por la exposición de estas a la emisión de gases tóxicos emanados por el creciente parque automotor hace que se busquen alternativas a fin de contrarrestar su efecto sobre los elementos más expuestos.  Un nuevo método para afrontar este problema es la incorporación del fotocatalizador dióxido de titanio TiO2 capaz de desarrollar propiedades controladas por la luz solar como son la purificación del aire y la autolimpieza. Este trabajo busca introducir este componente orgánico al mortero de cemento usado para el tarrajeo de fachadas y elementos estructurales, para ello se adicionan diferentes porcentajes (5%,7.5% y 10%) de dióxido de titanio (TiO2) y se evalúan las propiedades de los morteros modificados haciendo uso de [1] para los ensayos de compresión, [2] para los ensayos de fluidez, [3]para los ensayos de absorción y [4] para los ensayos de actividad fotocatalítica. Este estudio concluye que el mejor porcentaje de adición de dióxido de titanio es de 5% con el cual se otorga al mortero de cemento la propiedad de autolimpieza sin perjudicar sustancialmente sus propiedades mecánicas. / The deterioration of the surfaces of the constructions made with mortar c/a 1: 5 of portland cement, are produced by being exposed to the emission of toxic gases emanating from the growing automobile fleet, this problem causes alternatives to be sought in order to counteract its effect on buildings and the environment. A new method to deal this problem is the incorporation of the titanium dioxide photocatalyst (TiO2) into the Portland cement mortar, which is capable of developing self-cleaning and air purification properties to be in contact with sunlight. This work seeks to introduce this organic component to the Portland cement mortar, used for the facade charging and structural elements, for this purpose, different percentages (5%, 7.5% and 10%) of titanium dioxide (TiO2) are added and the properties of the modified mortars making use of [1] compression tests, [2] fluidity tests, [3] absorption tests and [4] photocatalytic activity tests with which the self-cleaning capacity was verified. This study concludes that the best percentage of titanium dioxide addition is 5%, with which the portland cement mortar is granted self-cleaning property without substantially damaging its mechanical properties. / Tesis

This master thesis deals with the topic of alternative production of hydrogen as the energy carrier of the future. The primary focus is on the production of hydrogen based on photocatalytical water splitting in the presence of semiconductor materials (especially modified and unmodified TiO2). The aim of the thesis is a synthesis of nanostructured oxide, graphene/graphene oxide particles and its composites, and a study of its structures and photocatalytical properties regarding photolysis of water. Products of the syntheses are described from the point of view of phase composition, surface area and photocatalytical activity. The main output of the thesis is a discussion of the influence of alkaline complex forming reagents on the hydrothermal low-temperature synthesis of biphasic TiO2, and a study of the influence of graphene/graphene oxide modification on photocatalytical activity of biphasic TiO2.

This work aims at modelling and evaluating a new type of photocatalytic reactors, named fixed-bed photocatalytic membrane reactor (FPMR). Such reactors are based on the deposition of a thin layer of photocatalysts on a permeable substrate by filtration. This layer serves as a photocatalytic membrane, named fixed-bed photocatalytic mem-brane (FPM), which is perpendicularly passed by the reactant solution and illuminated by a suitable light source. One advantage of FPMs is their renewability. The model, which was developed for this reactor, relates the overall reaction rate in the FPM with the intrinsic reaction kinetic at the catalyst surface and accounts for light intensity, structural and optical layer properties as well as the mass transfer in the pores. The concept of FPMR was realised by using a flat sheet membrane cell. It facilitated principal investigations into the reactor performance and the validity of the model. For this purpose, the photocatalytic degradation of organic compounds, such as meth-ylene blue and diclofenac sodium, was conducted at varying conditions. Pyrogenic ti-tania was used as a photocatalyst. The experimental data support the developed mod-el. They also indicate a significant impact of the flow conditions on the overall photo-catalytic activity, even though the Reynolds number in the FPM was very small; the to-tal mass transfer rate in the FPM amounted to more than 1.0 s−1. The experiments also showed a sufficient structural strength of the FPM and photocatalytic stability. In addi-tion, the renewal and regeneration of FPMs was successfully demonstrated. Furthermore, another FPMR was designed by means of submerged ceramic mem-branes. This reactor was mainly used to assess the effectiveness and efficiency of FPMRs at the example of the photocatalytic degradation of oxalic acid. The correspond-ing reactor was run closed loop and in continuous mode. The effectiveness of the reac-tor was evaluated based on common descriptors, such as apparent quantum yield, photocatalytic space-time yield and light energy consumption. The results showed that the FPMR based on submerged ceramic membrane had a higher efficiency than other reported photocatalytic reactors. The comparison of the different modes of operation revealed that the closed loop FPMR is most efficient with regard to light energy con-sumption. Finally, this work discusses the up-scaling of FPMRs for industrial applications and proposes a solution, which can e.g. be employed for wastewater treatment or CO2 conversion.:Abstract iii Kurzfassung v Acknowledgment vii Contents ix Nomenclature xiii 1 Introduction 1 1.1 Motivation 1 1.2 Aim and objectives of the work 3 1.3 Thesis outline 3 2 Heterogeneous photocatalytic reactors 5 2.1 Introduction to photocatalysis 5 2.2 Processes in heterogeneous photocatalysis 6 2.2.1 Optical phenomena 7 2.2.2 Mass transfer 8 2.2.3 Adsorption and desorption 9 2.2.4 Photocatalytic reactions 10 2.2.5 Factors affecting heterogeneous photocatalysis 12 2.3 Photocatalytic reactor systems towards water treatment 16 2.3.1 Introduction to photocatalytic reactors 16 2.3.2 Development of photocatalytic reactor designs 17 2.3.3 Quantitative criteria for evaluating photocatalytic reactor designs 21 2.4 Cake layer formation in membrane microfiltration 22 2.4.1 Suspension preparation 22 2.4.2 Cake layer formation 23 2.5 Fluid flow through a fixed bed of particles 25 2.5.1 Pressure drop through a fixed-bed 25 2.5.2 Liquid-solid mass transfer correlation in fixed-bed 25 3 Concept and mathematical modelling of FPMRs 29 3.1 Concept of fixed-bed photocatalytic membrane reactors 29 3.2 Modelling of fixed-bed photocatalytic membrane reactors 31 3.3 Model sensitivity analysis 37 3.4 Chapter summary 39 4 FPMR realised with flat sheet polymeric membrane 41 4.1 Introduction 41 4.2 Materials and set-up 41 4.2.1 Materials 41 4.2.2 Experimental set-up 43 4.3 Experiments and methods 48 4.3.1 Formation of fixed-bed photocatalytic membrane 48 4.3.2 Reactor performance 50 4.3.3 Parameters study and model verification 53 4.3.4 Catalyst layer characterisation 56 4.3.5 Measurement and evaluation of photocatalytic activity of FPM 59 4.4 Results and model verification 60 4.4.1 Reactor performance 60 4.4.2 Influence parameters 71 4.4.3 Model verification 79 5 FPMR realised with submerged ceramic membrane 92 5.1 Introduction 92 5.2 Materials and reactor set-up 93 5.2.1 Reactor set-up 93 5.2.2 Chemicals 97 5.3 Experiments and methods 97 5.3.1 Formation of fixed-bed photocatalytic membranes 97 5.3.2 Photocatalytic performance 97 5.3.3 Parameter study 98 5.3.4 Reactor model for calculating reaction rate constant of FPM 99 5.3.5 Comparison of different reactor schemes 102 5.4 Results and discussions 105 5.4.1 Reactor performance 105 5.4.2 Consistency of CPMR and LPMR data 107 5.4.3 Influence of catalyst loading 108 5.4.4 Influence of permeate flux and light intensity 109 5.4.5 Reactor efficiency 111 5.4.6 Comparison of different reactor schemes 113 5.5 Proposed up-scaled FPMR systems 113 5.6 Concluding remarks 116 6 Conclusion and outlook 118 6.1 Summary of thesis contributions 118 6.2 Discussion and outlook 120 References 122 List of Figures 134 List of Tables 138 Appendix A Calibration 139 A.1 Distribution of light intensity on the surface of catalyst layer 139 A.2 Concentration and absorbance of diclofenac 141 A.3 TOC concentration and electrical conductivity of oxalic acid 141 A.4 Concentration and absorbance of methylene blue 142 Appendix B Mathematical modelling 143 B.1 Influence of axial dispersion on the reaction rate 143 B.2 Special case 146 Appendix C Comparison the photocatalytic activity of TiO2 and ZnO 147 Appendix D Mathematical validation of model for LPMR and CPMR 148 D.1 Model for LPMR (cf. Eq. (5 12)):148 D.2 Model for CPMR (cf. Eq. (5 17)) 149 Appendix E Particle size distribution 151

M.Tech. (Department of Chemistry, Faculty of Applied and Computer Sciences), Vaal University of Technology. / To replace the conventional wastewater treatment technology, photocatalysis has the best potential due to its utilization of visible light to photodegrade organic and inorganic contaminants. However, agglomeration of nanoparticles leads to serious decrease in photocatalytic performance when applied in slurry form, due to hindrance effect. TiO2 semiconductor photocatalyst mediated advanced oxidation process is referred to as one of the most efficient technologies to degrade organic pollutants in water. However, TiO2 semiconductor for water purification hinders large scale applicability due to poor activity under visible light and the recombination of photogenerated electron and hole pairs. The modification of TiO2 semiconductor photocatalyst with carbon dots (CDs) is of high importance due to low toxicity, aqueous stability, enhanced surface area, economic feasibility, good biocompatibility and chemical inertness of CDs. Herein, strategies are highlighted to improve the activity of TiO2 semiconductor photocatalyst by coupling it with CDs and Fe2O3. In this study, we study the morphological influence of TiO2 nanostructures on photocatalytic degradation of tetracycline hydrochloride present in industrial wastewater. TiO2 nanostructures, nanotubes, nanospheres and nanofibers were Synthesized using the hydrothermal technique. TiO2 nanotubes, nanofibers and nanospheres were prepared by the hydrothermal treatment of TiO2 nanoparticles with different NaOH concentrations (5, 10 and 12 N) at 120 and 140 ˚C; afterwards, HCl was added until it reached pH 2. Both the crystalline phase and coordination of the TiO2 nanotubes, nanofibers and nanospheres were composed principally. Likewise, the surface area, pore volume and pore size of the TiO2 nanotubes, nanofibers and nanospheres changed with the NaOH rinsing treatment. The photocatalytic activity for tetracycline degradation were strongly enhanced by the nanofibers and nanotubes in the basic and acid media, respectively, showing a relationship between their structure and the medium. TiO2 nanostructures and the composite material were characterized by scanning electron microscope\SEM), X-Ray Diffraction (XRD), transmission electron microscope (TEM) and Fourier transform infrared (FTIR). BET surface area analysis was carried out using nitrogen adsorption desorption curves. The results show that TiO2 morphology had great influence on photocatalytic degradation of tetracycline hydrochloride due to difference in specific surface area and pore volume of nanostructures. The photocatalytic degradation experiments were carried out for three hours under visible-LED light. TiO2 nanofibers show better degradation performance than nanotubes and nanospheres due to presence of large surface area for reaction, higher porosity with dispersion of active sites at different length scales of pores and presence of oxygen vacancies. Agricultural biomass pine bark serves as a carbon source and was doped into TiO2-nanofibers (TNF) to fabricate the composite material (CD-TNF). CD-TNF composite nanofibers were prepared via a facile hydrothermal method. This study revealed that the photocatalytic efficiency of tetracycline (TC) under visible light irradiation of the composite nanofiber is higher than that of pure TiO2-nanofiber. The anchored CDs can both enhance the light absorption and suppress photogenerated electron hole recombination which results in the enhancement of catalytic and antibacterial properties. The CDs can better capture and transfer photogenerated electrons through the Ti-O-C and Fe-O-C bonds. Moreover, CDs can improve the utilization of photogenerated electrons and the electrons in CDs are captured by O2 to produce O2•- radicals and the role of O2•- radicals in the photocatalytic process is significantly improved. A new efficient photocatalyst consisting of TiO2/CD/Fe2O3 composite material was Synthesized by the hydrothermal treatment and applied in the photodegradation of 5 mg/L tetracycline hydrochloride (TC) under visible-LED light. The CDs/TiO2/Fe2O3 composite showed enhanced photocatalytic performance for tetracycline photodegradation when compared with TiO2/CDs and pure TiO2 under the visible light irradiation. The mechanism of the improved photocatalytic activity over CDs/TiO2/Fe2O3 was also investigated. The influence of the interface formation between Fe2O3 and TiO2/CDs affects severely the charges separation efficiency and enhances the electron transfer to keep on the existence of Fe3+/Fe2+ moieties that take significant role in the reaction mechanism.

Ph. D. (Department of Chemistry, Faculty of Applied and Computer Sciences), Vaal University of Technology. / Aromatic organic contaminants are difficult to biodegrade, and thus effective green technologies are required to remove these pollutants from the ecosystem. Tetracycline antibiotic, an organic water pollutant, can be degraded by heterogeneous photocatalysis using an appropriate catalyst, with capability in converting the visible light energy into active species. The thesis focused on silver nanoparticles anchored on silver bromide (Ag/AgBr) as a plasmonic catalyst dispersed on activated carbon (ACK), were used as a photocatalyst (AABR-ACK) in tetracycline removal. The aim is to develop a catalyst that is active in low intensity visible light, whilst the addition of activated carbon will increase the light absorption and separate the charge pairs, after the photocatalyst has been excited by the visible light. The activated carbons were derived from pinecone pyrolyzed in a microwave. The pinecone mass to potassium hydroxide impregnation ratio and microwave pyrolysis time influenced the activated carbon properties. An impregnation ratio of 2.24 and microwave pyrolysis time of 16 minutes at constant microwave power of 400 W yielded the activated carbon with the best-developed porous structure and electrochemical properties. This activated carbon was used during the optimisation of the Ag/AgBr activated carbon (AABR-ACK) catalysts preparation using a thermal polyol precipitation method and response surface methodology. The most active catalyst was the AABR-ACK 11 obtained by a preparation temperature of 140 ºC, time (17.50 minutes), mass of surfactant and activated carbon (0.26 g and 0.03 g) respectively. This catalyst had an ordered nanospheres morphology, reduced electron-hole recombination rate, better electrochemical properties and exhibited enhanced activity on the tetracycline antibiotic removal in comparison to other Ag/AgBr activated carbon catalysts. A percentage degradation of 92% was obtained in 180 minutes were obtained with the AABR-ACK 11 catalyst. The photocatalyst prepared using the best activated carbon derived from pinecone developed in this study was compared to photocatalysts prepared using commercial activated carbon and biochar. The Ag/AgBr activated carbon catalysts using pinecone-derived activated carbon degraded the tetracycline to 92%, which is significantly higher than the percentage degradations (80% and 74%) for the catalyst prepared using commercial activated carbon and biochar catalysts respectively. The higher activity of the Ag/AgBr activated carbon catalysts using pinecone-derived activated carbon was due to the conductive attributes of the catalyst support for accelerated transfer of photo-induced electrons. The Ag/AgBr activated carbon catalysts using pinecone- derived activated carbon also exhibited better performance on tetracycline removal when compared to photocatalysts reported in literature. Two catalyst preparation methods, thermal polyol and deposition precipitation, were compared. The thermal polyol method yielded a more active catalyst for the degradation of the tetracycline in comparison to the deposition precipitation method. The degradation reaction conditions such as pH, light intensity and degradation temperature influenced the rate of the reaction. The highest rate of degradation was obtained at a pH of seven, white light and 40 ºC temperature. The intermediate products formed because of hydroxylation, deamination, demethylation and dehydration during the photocatalytic degradation of tetracycline antibiotics were identified using liquid chromatography mass spectrometer. Quenching experiments with hydroxyl, hole, and superoxide anion species showed that the most important radical responsible for the tetracycline degradation was the superoxide anion radical.

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