Titanium Dioxide (TiO2) emerged as one of the most popular photocatalysts since 1970's. However, its photocatalytic activity requires UV irradiation due to its large band gap unless further functionalization or modifications are performed. Furthermore, recovery issue has always been a major drawback, if the more effective form nano particles are utilized. The key objectives of this research were synthesizing new TiO2 based photocatalyst systems that are effective with both the UV and the visible light while utilizing novel superior environmentally friendly techniques enabling development of nano-structured photocatalysts that can be easily recovered. In this dissertation research, highly porous nano-structured TiO2/WO3/Fe3+ aerogel composite photocatalyst are prepared, characterized, and tested for model photocatalytic reactions. The photocatalyst structure is tailored to capture environmental pollutants and enable their decomposition in-situ under both UV and visible light through photodecomposition to smaller benign substances. A novel and green method is applied to prepare unique surfactant templated aerogel photocatalysts with highly porous nano-structure, high surface area, and tailored pore size distribution. Sol-gel process followed by supercritical fluids extraction and drying allowed synthesis of highly porous composite TiO2/WO3 aerogel. The surfactant template was completely removed with the aid of a supercritical solvent mixture followed with heat treatment. Fe3+ ion was incorporated within the composite aerogel photocatalyst as dopant either at the sol-gel co-precipitation step or at a subsequent supercritical impregnation process. Supercritical drying followed with heat treatment results in titanium dioxide with the most profound anatase crystal structure. Neutral templates were used to further enhance retention and tuning of the nano-pore structure and the surface properties. The Nitrogen adsorption-desorption isotherms methods were used to follow the removal of solvents and templates as well as tracking the textural properties of the synthesized aerogel. Surfactant-templated aerogels, which show remarkable thermal stability and uniform pore size distribution, exhibit specific surface areas three times more than the highly optimized commercial nano-particles, industry standard TiO2 photocatalyst Degussa P-25, even after heat treatment. The synthesized catalysts were characterized by using SEM, FIB, EDS, XRD, XPS and porosimetry prior to post photocatalytic activity evaluation through a model photocatalytic reaction. The band gaps of the catalysts were also determined by using diffuse reflectance spectroscopy. The model reaction employed Methylene Blue (MB) photo-oxidation under UV and visible light. Resulting aerogel TiO2/WO3/Fe3+ photocatalyst exhibited comparable photocatalytic capability to Degussa P25 under UV light exposure and offered much superior photocatalytic capability under visible light exposure.

Semiconductor photocatalysis has received considerable attention in recent years as an alternative for treating water polluted with hazardous organic chemicals. The process, as a means of removal of persistent water contaminants such as pesticides, which exhibit chemical stability and resistance to biodegradation, has attracted the attention of many researchers. To a lesser extent, it has also been studied for decontamination of water containing toxic metals. Precious and common metals enter waters through washing, rinsing, pickling and surface treatment procedures of industrial processes, such as hydrometallurgy, plating and photography. As a result we are living in an environment with a multitude of potentially harmful toxic metal ions. In contrast, the demand for metals increases significantly with the development and growth of industry. Even though research on the photocatalytic recovery of waste and noble metals has escalated in the past 10 years, the practical implementation of these processes is not yet justified. The successful implementation of large scale reactors, for industrial application, has to consider several reactor design parameters that must be optimised, such as reactor geometry and the utilization of radiated energy. In this study the effect of various parameters such as initial platinum(IV)chloride concentrations, initial sacrificial reducing agent (ethanol) concentrations, catalyst (TiO2) concentration, pH, temperature and light intensity has been investigated as a first step towards optimising a photocatalytic batch and photocatalytic flow reactor. Langmuir–Hinshelwood kinetics has been applied to calculate the photocatalytic rate constant kr as well as the adsorption equilibrium constant Ke for both the initial platinum(IV) dependency as well as the initial ethanol concentration dependency. The results in this study may be used in future work for the optimisation and comparison of both batch and flow reactors towards the industrial implementation of these processes. / Thesis (M.Sc. (Chemistry))--North-West University, Potchefstroom Campus, 2012.

PdCl2/Bi2WO6 and Pd/Bi2WO6 composite photocatalysts were synthesized via a template free hydrothermal process and the respective photocatalytic activities were investigated by degradation of Rhodamine B. The new catalyst composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and ultraviolet visible (UV-vis) light diffuse reflectance spectra, respectively. By XRD, it was found that the loaded Pd species did not alter the crystal lattice of Bi2WO6 photocatalyst. Through the XPS spectra, it was found that the PdCl2/Bi2WO6 was successfully reduced by chemical reducing agents CH2O and N2H4, respectively, and palladium was present in the form of both metallic Pd and Pd ion spe-cies (Pd0 and Pd2+), while the Pd species in a NaBH4-reduced composite exhibited only metallic Pd species (Pd0). For the SEM images, it was observed that both classes of composites were constructed from plenty of nanoplates, which were closed packed with hierarchical structures. Furthermore, the removal efficiency of Rhodamine B was found to be influenced by parameters such as catalyst dosage, pollutant concentration and solution pH.

Semiconductor photocatalysis has received considerable attention in recent years as an alternative for treating water polluted with hazardous organic chemicals. The process, as a means of removal of persistent water contaminants such as pesticides, which exhibit chemical stability and resistance to biodegradation, has attracted the attention of many researchers. To a lesser extent, it has also been studied for decontamination of water containing toxic metals. Precious and common metals enter waters through washing, rinsing, pickling and surface treatment procedures of industrial processes, such as hydrometallurgy, plating and photography. As a result we are living in an environment with a multitude of potentially harmful toxic metal ions. In contrast, the demand for metals increases significantly with the development and growth of industry. Even though research on the photocatalytic recovery of waste and noble metals has escalated in the past 10 years, the practical implementation of these processes is not yet justified. The successful implementation of large scale reactors, for industrial application, has to consider several reactor design parameters that must be optimised, such as reactor geometry and the utilization of radiated energy. In this study the effect of various parameters such as initial platinum(IV)chloride concentrations, initial sacrificial reducing agent (ethanol) concentrations, catalyst (TiO2) concentration, pH, temperature and light intensity has been investigated as a first step towards optimising a photocatalytic batch and photocatalytic flow reactor. Langmuir–Hinshelwood kinetics has been applied to calculate the photocatalytic rate constant kr as well as the adsorption equilibrium constant Ke for both the initial platinum(IV) dependency as well as the initial ethanol concentration dependency. The results in this study may be used in future work for the optimisation and comparison of both batch and flow reactors towards the industrial implementation of these processes. / Thesis (M.Sc. (Chemistry))--North-West University, Potchefstroom Campus, 2012.

Σκοπός της παρούσας εργασίας είναι η κινητική μελέτη της αντίδρασης παραγωγής υδρογόνου μέσω φωτοκαταλυτικής αναμόρφωσης της μεθανόλης και η ανάπτυξη μοντέλου για την περιγραφή του πεδίου της ακτινοβολίας στον πειραματικό φωτοαντιδραστήρα. Τα αποτελέσματα μπορούν να χρησιμοποιηθούν για τον υπολογισμό των κινητικών παραμέτρων της αντίδρασης και τον προσδιορισμό των σχεδιαστικών παραμέτρων που απαιτούνται για την ανάπτυξη και βελτιστοποίηση κατάλληλου φωτοαντιδραστήρα. Η φωτοκαταλυτική διάσπαση του νερού με χρήση ημιαγωγών και ηλιακής ακτινοβολίας αποτελεί μια από τις πλέον υποσχόμενες διεργασίες για τη φωτοχημική μετατροπή και αποθήκευση της ηλιακής ενέργειας. Η αντίδραση μπορεί να λάβει χώρα μέσω διέγερσης ενός ημιαγωγού (π.χ. TiO2) από φωτόνια με ενέργεια ίση ή μεγαλύτερη από το ενεργειακό του χάσμα. Το αποτέλεσμα είναι η προώθηση ενός ηλεκτρονίου από τη ζώνη σθένους (VB) στη ζώνη αγωγιμότητας (CB) του υλικού και η δημιουργία μιας οπής στην ζώνη αγωγιμότητας: (1) Η συνήθης τύχη των φωτοπαραγόμενων φορέων φορτίου είναι η (μη επιθυμητή) επανασύνδεσή τους, που συνοδεύεται από έκλυση της αποθηκευμένης ενέργειας με τη μορφή θερμότητας: (2) Οι φωτοπαραγόμενες οπές και τα ηλεκτρόνια που καταφέρνουν να φθάσουν στην επιφάνεια του ημιαγωγού μπορούν, υπό ορισμένες προϋποθέσεις, να εκκινήσουν αντιδράσεις για την παραγωγή οξυγόνου και υδρογόνου μέσω οξείδωσης και αναγωγής του νερού, αντίστοιχα: (3) (4) Το πρόβλημα είναι ότι ο ρυθμός παραγωγής υδρογόνου είναι πολύ μικρός, κυρίως λόγω της εγγενώς μικρής κβαντικής απόδοσης της διεργασίας, η οποία καθορίζεται από την αντίδραση επανασύνδεσης ηλεκτρονίου-οπής (Εξ.2). Η αντίδραση επανασύνδεσης μπορεί να κατασταλεί παρουσία κατάλληλων “θυσιαζόμενων” ενώσεων στο διάλυμα, οι οποίες αντιδρούν ταχέως και μη αντιστρεπτά με τις φωτοπαραγόμενες οπές. Με τον τρόπο αυτό αυξάνεται ο χρόνος ζωής των ηλεκτρονίων και, επομένως, ο ρυθμός παραγωγής υδρογόνου μέσω της Εξ. 4. Ως θυσιαζόμενες ενώσεις μπορούν να χρησιμοποιηθούν χαμηλού ή “αρνητικού” κόστους οργανικές ενώσεις, όπως παραπροϊόντα και παράγωγα βιομάζας. Οι ενώσεις αυτές οξειδώνονται προοδευτικά από τις οπές προς CO2, με αποτέλεσμα τα φωτοπαραγόμενα ηλεκτρόνια να ανάγουν αποδοτικά το νερό προς παραγωγή Η2. Η συνολική διεργασία μπορεί να περιγραφεί από την ακόλουθη γενική αντίδραση αναμόρφωσης: (5) Χαρακτηριστικά πλεονεκτήματα της μεθόδου αποτελούν ο σχετικά υψηλός ρυθμός παραγωγής υδρογόνου και το γεγονός ότι, σε αντίθεση με τις συνήθεις θερμοκαταλυτικές αντιδράσεις αναμόρφωσης, η αντίδραση πραγματοποιείται σε συνθήκες περιβάλλοντος. Επιπροσθέτως, η παραγωγή υδρογόνου μπορεί να λάβει χώρα με ταυτόχρονη αποικοδόμηση οργανικών ρύπων, με προφανή περιβαλλοντικά οφέλη. Ένα άλλο σημαντικό πρόβλημα που σχετίζεται με τις περιορισμένες εφαρμογές των φωτοκαταλυτικών μεθόδων σε πιλοτική και βιομηχανική κλίμακα οφείλεται στη δυσκολία σχεδιασμού και ανάπτυξης αποδοτικών φωτοαντιδραστήρων. Το πρόβλημα του σχεδιασμού έγκειται στο γεγονός ότι, σε αντίθεση με τους συμβατικούς καταλύτες, η ενεργοποίηση ενός φωτοκαταλύτη δε γίνεται θερμικά αλλά μέσω απορρόφησης φωτονίων κατάλληλης ενέργειας. Επομένως, για την μοντελοποίηση ενός φωτοαντιδραστήρα απαιτείται, εκτός από τη χρήση των συνήθων εξισώσεων για τα ισοζύγια μάζας, θερμότητας και ορμής, μια επιπλέον εξίσωση για την περιγραφή του ισοζυγίου της ενέργειας της ακτινοβολίας στο σύστημα. Η εξίσωση αυτή χρησιμοποιείται για τον υπολογισμό του “τοπικού ογκομετρικού ρυθμού απορρόφησης ενέργειας” (local volumetric rate of energy absorption, LVREA), ο οποίος αποτελεί μια από τις σημαντικότερες σχεδιαστικές παραμέτρους ενός φωτοαντιδραστήρα διότι περιγράφει την ποσότητα των φωτονίων που απορροφούνται ανά μονάδα όγκου σε κάθε σημείο του αντιδραστήρα. Για τον σχεδιασμό του αντιδραστήρα είναι επίσης απαραίτητη και μία έκφραση του ρυθμού της αντίδρασης. Για την εξαγωγή αυτής της έκφρασης απαιτείται η εύρεση του ρυθμού του βήματος ενεργοποίησης μέσω ακτινοβολίας, ο οποίος εκφράζεται συναρτήσει του LVREA. Εφόσον ο ρυθμός αυτός είναι γνωστός μπορεί να εισαχθεί στο κινητικό μοντέλο της αντίδρασης ενώ οι διάφορες κινητικές παράμετροι μπορούν να υπολογιστούν πειραματικά. Μεταξύ των προσεγγίσεων που έχουν προταθεί για τον υπολογισμό του LVRΕA, οι πιο ακριβείς περιλαμβάνουν την αριθμητική επίλυση της εξίσωσης μεταφοράς ακτινοβολίας (radiation transfer equation, RTE). Στην παρούσα εργασία χρησιμοποιείται η μέθοδος των “φασματικών στοιχείων” (spectral elements) για την επίλυση ενός μονοδιάστατου μοντέλου για την περιγραφή του πεδίου της ακτινοβολίας και τον υπολογισμό του LVREA σε έναν πειραματικό αντιδραστήρα, στον οποίο περιέχεται ο φωτοκαταλύτης σε μορφή αιωρήματος. Η αντίδραση που μελετάται είναι η παραγωγή υδρογόνου μέσω της φωτοκαταλυτικής αναμόρφωσης της μεθανόλης (Εξ. 6) σε αιώρημα καταλύτη 0.5%Pt/TiO2, το οποίο ακτινοβολείται με φως στη περιοχή που απορροφά το TiO2. (6) Σύμφωνα με το μοντέλο που αναπτύχθηκε, ο ρυθμός της φωτοκαταλυτικής αντίδρασης εξαρτάται από τη συγκέντρωση του καταλύτη στο αιώρημα, την ειδική ένταση ακτινοβολίας και τη συγκέντρωση του αντιδρώντος στο διάλυμα. Για τον σκοπό αυτό, μελετήθηκε στην παρούσα εργασία η επίδραση των λειτουργικών παραμέτρων της αντίδρασης, όπως η ένταση της προσπίπτουσας ακτινοβολίας (Ι0), η συγκέντρωση του φωτοκαταλύτη (Ccat) και η συγκέντρωση της μεθανόλης, (CMeOH) στο ρυθμό παραγωγής Η2 (rH2). Από τα αποτελέσματα προκύπτει ότι ο ρυθμός παραγωγής υδρογόνου εξαρτάται ισχυρά από τη συγκέντρωση του οργανικού υποστρώματος και αυξάνει κατά σχεδόν δύο τάξεις μεγέθους με αύξηση της CMeOH από 0 σε 1 mol L-1. Επιπλέον, αύξηση του ρυθμού επιτυγχάνεται με αύξηση του Ι0. Τα αποτελέσματα των φωτοκαταλυτικών πειραμάτων μπορούν να χρησιμοποιηθούν για τη μοντελοποίηση του συστήματος και το σχεδιασμό φωτοκαταλυτικού αντιδραστήρα για την παραγωγή υδρογόνου. / Heterogeneous photocatalytic reactions occurring at the surface of illuminated semiconductors, especially TiO2, have been the subject of extensive investigation in the last few years. This is because of the high potential of photocatalytic processes for a wide range of applications, which include mineralization of organic pollutants, disinfection of water and air, production of renewable fuels, and organic syntheses. Although remarkable progress has been made in fundamental research, applications in pilot and industrial scale are still in their infancy. This is mainly due to the lack of efficient solar photocatalysts and the difficulty of designing photoreactors able to integrate maximum light efficiency and mass transfer within one piece of equipment. Regarding photoreactor design, complications arise from the mode of photocatalyst activation, which involves excitation of the semiconductor photocatalyst by photons of appropriate energy. Thus, in addition to the usual equations for mass, heat and momentum balances, photoreactor modelling requires an additional equation to describe the balance of radiation energy in the system. This equation is used to calculate the "local volumetric rate of energy absorption" (LVREA) which describes the amount of photons absorbed per unit volume at each point of the reactor and provides one of the major photoreactor design parameters. The LVREA depends on the characteristics of the incident radiation, the optical properties of the system, the type and concentration of the photocatalyst and the geometry of the reactor. Therefore, calculation of the LVREA requires knowledge of the distribution of the radiation field inside the reactor. Among the various approaches proposed to calculate the LVREA, the most accurate ones are those that solve numerically the “radiation transfer equation” (RTE). This requires the development of a mathematical model that describes the emission model of the radiation source and the radiation field inside the reactor. In the present work, we have developed a one-dimensional spectral element algorithm for the description of the radiation field and the calculation of the LVREA in an experimental photoreactor containing the photocatalyst (Pt/TiO2) in suspension. The target reaction investigated was the photocatalytic reforming of methanol for hydrogen production (CH3OH+H2O→3H2+CO2). The radiation source used was a light emitting diode (LED), which emits radiation at wavelengths (λmax=390 nm) corresponding to the bandgap of TiO2 (3.2 eV). Our results refer to the effect of operating parameters such as incident light intensity (I0), photocatalyst content (CTiO2), and methanol concentration (CMeOH) on the rate of H2 production (rH2). They show that rH2 depends strongly on methanol concentration and increases by almost 2 orders of magnitude when CMeOH is increased from 0 to 1 mol L-1. A substantial enhancement of rH2 is also observed with increasing I0 or CTiO2. Results of photocatalytic experiments and photoreactor modelling are used to extract kinetic parameters for the methanol photoreforming reaction.

98 f. / Submitted by Ana Hilda Fonseca (anahilda@ufba.br) on 2013-10-03T14:59:45Z No. of bitstreams: 1 Dissertação_Jefferson_Silva_2012_Quimica.pdf: 1947075 bytes, checksum: 25582d9f2d2ee577efefaac8a9ab46e1 (MD5) / Approved for entry into archive by Ana Hilda Fonseca(anahilda@ufba.br) on 2013-10-03T15:01:11Z (GMT) No. of bitstreams: 1 Dissertação_Jefferson_Silva_2012_Quimica.pdf: 1947075 bytes, checksum: 25582d9f2d2ee577efefaac8a9ab46e1 (MD5) / Made available in DSpace on 2013-10-03T15:01:12Z (GMT). No. of bitstreams: 1 Dissertação_Jefferson_Silva_2012_Quimica.pdf: 1947075 bytes, checksum: 25582d9f2d2ee577efefaac8a9ab46e1 (MD5) Previous issue date: 2012 / A fotocatálise heterogênea tem sido apontada como uma alternativa efetiva para o tratamento de efluentes industriais de difícil degradação, a fim de minimizar o impacto ambiental associado ao seu descarte ineficiente. Neste trabalho foi avaliada a atividade de catalisadores TiO2, sintetizados pelo método Pechini variando-se a razão molar (ácido cítrico)/(cátion metálico) de 2:1 (P21), 3:1 (P31), 4:1 (P41) e 5:1 (P51) em três sistemas fotocatalíticos: fotodegradação do azo-corante alaranjado de metila (CI Acid Orange 52) em solução aquosa, fotorredução do íon mercúrio (II) em solução aquosa, separadamente, e no sistema binário fotodegradação do alaranjado de metila/ fotorredução do mercúrio (II). Dentre as reações fotocatalíticas envolvendo o sistema contendo solução aquosa de alaranjado de metila, foi observada a alta eficiência do catalisador P21 na descoloração total da solução em 90 minutos, provavelmente devido à formação da fase anatásio pura. Além disso, os resultados mostraram que o corante pode ser degradado por fotocatálise sem a dissolução de O2 e que o catalisador P21 possuiu bom desempenho no estudo da desativação ao manter o mesmo comportamento em três ciclos reacionais de 240 minutos. Foi observado também, uma representativa degradação da molécula do azo-corante atingindo Demanda Química de Oxigênio (DQO) < 40 mgO2.L-1 em 90 minutos de reação. No estudo da atividade fotocatalítica dos catalisadores na fotorredução do mercúrio (II) foi observada a maior atividade cinética do catalisador P21 demonstrada pela significativa diminuição da concentração do mercúrio em 10 minutos de reação. A maior capacidade de adsorção deste corante pode ter influenciado neste resultado. Foi avaliada a variação de alguns parâmetros reacionais nas reações tais como: pH (4 ou 7), concentração inicial do cátion Hg+2 (10, 20 ou 40 mg.L-1) e concentração do catalisador (1 ou 2 g.L-1) utilizando os catalisadores P21 e P51. Os resultados mostraram que o conjunto de parâmetros que proporcionou a maior taxa de redução foi: pH 7, concentração inicial 10 mg.L-1 e 1 g.L-1 de catalisador. Neste teste, foi possível a redução da concentração de mercúrio (II) para valores menores do que os aceitos pela maioria das instituições de regulamentação ambiental. Foi realizado, também, o estudo do efeito da adição de três compostos orgânicos (etanol, ácido oxálico e ácido cítrico) e NaCl nos sistemas reacionais com os catalisadores P21 e P51 e com a variação do pH (4 ou 7). Foi observado que as taxas de adsorção foram maiores nas soluções com pH 7 o que, de forma geral, influenciou diretamente na maior taxa de fotorredução destes sistemas. Por fim, nos sistemas fotocatalíticos binários (alaranjado de metila/Hg+2) foi possível observar que a presença de íons metálicos diminui a taxa de descoloração do corante, provavelmente, devido à desativação do catalisador provocada pela deposição de mercúrio metálico na superfície do catalisador. / Salvador

Water pollution has become an environmental catastrophe due to the rapid urbanization. The treatment of dumping of waste chemicals in water bodies has contributed to the increase in pollution. In addition to the pollution caused by waste chemicals, faecal bacteria such as Escherichia, Staphylococcus, Pseudomonas etc., can cause serious health issues. Techniques such as filtration and chlorination provide clean water but are associated with disadvantages such as toxic by-products. Although clean water can be still obtained by these techniques, the development of resistance by microorganisms with such conventional treatments of antibiotics is inevitable and poses a new threat. Various researches have taken place in the past few decades to provide clean drinking water. Photocatalysis is considered to be a promising viable alternative for the existing methods to solve the menace of water pollution. It is an advanced oxidation process where the reactive oxygen species are generated by using nanomaterials that can cause degradation of chemicals and pathogens. Particularly, photocatalysis using semiconductors and their composites have been tested for their use in the destruction of contaminants. Several methods have been used in the synthesis of nanomaterials and the variations in their morphologies have resulted in different applications such as photocatalysis and electrocatalysis. Among all semiconductors, TiO2 has been widely used in this application owing to their non-toxicity and abundance in availability. However, TiO2 can be activated only in the presence of UV light. Therefore, the formation of heterojunctions, doping of metals/no- metals in TiO2 has enabled the activation of TiO2 in the visible region. The former approach has also been studied with ceria and silver salts combination. Besides conventional metal oxides, other transitional metal oxides such as copper oxide and bismuth oxide have also been studied owing to its conducting property and facile growth on substrates respectively for enhanced photocatalysis. All the above tweaking has enabled efficient charge separation, band gap reduction, and prevention of recombination. In this thesis, all the nanomaterials and their composites have been synthesized using simple methods such as solution combustion, hydrothermal, solution co-precipitation, and chemical deposition. The primary aim of this thesis is to synthesize various effective nanomaterials with different morphologies, bandgap engineered nanocomposites, metal or non-metal doped metal oxides for efficient waste water treatment of dyes, antibiotics, phenols, and bacteria. Besides, relying on photocatalytic ability, the photoconductivity and intrinsic conducting properties of nanomaterials were exploited to perform photoelectrocatalysis that enhances the rate of decontamination to several orders than photocatalysis. In addition to focusing on increasing the rate of degradation, the main drawback of photocatalysis which is catalyst retrieval has been overcome using conducting substrates and nanomaterial coated substrates for efficient photocatalytic and photoelectrocatalytic decontamination of waste water. All the structural, morphological, chemical and optical properties were thoroughly studied using various characterization techniques such as XRD, SEM, TEM, XPS, UV-DRS, PL respectively. The rate kinetics of dye, antibiotic and phenol degradation was examined. Experimental data was tested with the proposed model in the case of photoelectrocatalytic degradation. The photocatalysts were also studied for its reusability for many cycles. All the proposed works have analyzed the reason for the enhanced activity by performing scavenger reactions to determine the responsible reactive oxygen species. Thus, this thesis exhibits a thorough understanding of how to design and engineer nanomaterials for photocatalytic and photoelectrocatalytic water remediation. The following are the chapters discussed in this thesis. Chapter 1 discusses the drawbacks associated with the current waste water treatment methods and the possibilities of photocatalysis to replace the existing treatments. The advantages of certain transition metals, conventional methods of synthesis and various other properties of the nanomaterials have been discussed. Chapter 2 explains the synthesis of TiO2 nanobelts using combustion synthesized TiO2 under UV and solar irradiation. The catalyst has been characterized for its structural, morphological, chemical and optical properties. The degradation of anionic and cationic dyes and their activity against E.coli bacteria have been evaluated. The efficiency of this catalyst has been compared with commercial Degussa P25. This study shows the morphological influence of nanomaterials on photocatalytic activity. Chapter 3 describes the synthesis of Ag3PO4 impregnated combustion synthesized TiO2 nanobelts using co-precipitation technique. The activity of this material has been studied under solar light. The catalyst has been characterized for its structural, morphological, chemical and optical properties. Similar to the previous chapter, the degradation of dyes and the antibacterial activity of this catalyst has been compared with commercial Degussa P25. This study explains the importance of morphology and charge carrier facilitation in the case of heterojunction formation. Chapter 4 explains the synthesis of ceria nanoflakes by solution combustion method using ascorbic acid as fuel and PEG assisted sonochemical method. The catalyst has been characterized for its structural, morphological, chemical and optical properties. The effect of silver salts such as AgBr on ceria/Ag3PO4 under visible region for degradation of dyes and antibacterial activity has been evaluated. This work elucidates the effect of band engineering in the charge carrier dynamics between interfaces of components within the catalysts. Chapter 5 elucidates the synthesis of vanadium, nitrogen co doped TiO2 catalysts for the simultaneous degradation of microbes and antibiotics. The primary aim of this work is to understand whether interstitial or substituted doped nitrogen will be effective in the presence of vanadium. The photoactivity of this novel catalyst was studied for its synergistic degradation of antibiotics and bacteria simultaneously towards the prevention of microbial resistance towards antibiotics. Chloramphenicol and E.coli were subjected to photodegradation under visible light. Chapter 6 explains the synthesis of copper oxide based nanomaterial for antibiotic and bacterial degradation by photoelectrocatalysis. In order to enhance the rate of photodegradation, photocatalysis has been upgraded with the application of a potential to photocatalytic systems that possess better charge conducting capability. Highly network like copper oxide has been synthesized using conventional combustion synthesis method and compared with copper oxide nanorods synthesized by hydrothermal method. The rate kinetics of photocatalytic and photoelectrocatalytic degradation of antibiotics has been examined thoroughly and validated based on a cyclic network model. This work demonstrates the synergistic rate enhancing capacity upon combining photocatalysis and electrocatalysis. Chapter 7 discusses the fabrication of Cu/CuO/FTO (fluorine doped tin oxide) based substrates for bacterial degradation. Considering the difficulties in photocatalyst retrieval processes and realizing the importance of electrocatalysis, conducting substrates such as Cu strip, FTO were subjected to antibacterial treatment. Formation of copper oxide onto copper strip during the course of reaction forced us to develop CuO/Cu and CuO/FTO interfaces to examine the photocatalytic and photoelectrocatalytic killing of E.coli. Chapter 8 investigates the fabrication of Bi2O3/Ag based material for photocatalytic and photoelectrocatalytic degradation for phenols and substituted phenols. This work starts with fabrication of Bi2O3 working electrodes by chemical deposition. Photodegradation experiments were conducted under UV irradiation and enhancement of the rate of degradation was observed when the working electrode was deposited with silver nanoparticles via chemical reduction method. Formation of the intermediate Bi(OH)x on Bi2O3 or Bi2O3/Ag has resulted in better hydroxyl radical generation upon excitation. Similarly, surface plasmon resonance due to silver nanoparticles was found to be responsible for augmentation in degradation efficiency of phenol. Chapter 9 briefly summarizes the work and provides future directions. The research work thus attempts to design and engineer photocatalytic nanomaterials that are better than the existing materials and emphasizes the importance towards water remediation.

Made available in DSpace on 2014-06-11T19:30:18Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-07-22Bitstream added on 2014-06-13T20:40:10Z : No. of bitstreams: 1 kataoka_fp_me_bauru.pdf: 2231157 bytes, checksum: 41333d9fadeec00b484d0df4442b5ebd (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Os problemas ambientais gerados pelo crescimento das atividades humanas e industriais têm aumentado a necessidade pelo desenvolvimento de tecnologias alternativas para a remediação de sistemas aquáticos contaminados. A fotocatálise heterogênea, utilizando dióxido de titânio, tem se mostrado eficiente neste aspecto. Neste trabalho, foram sintetizadas nanoestruturas de TiO2 utilizando como precursor o isopropóxito de titânio pela rota hidrotérmica. Os materiais obtidos foram caracterizados por DRX, FT-Raman, FTIR, BET e MEV. A fim de avaliar a atividade fotocatalítica das amostras produzidas, foram realizados testes de degradação do corante rodomina B sob irradiação UV, luz branca e luz solar. A medida da degradação da molécula foi mensurada por espectroscopia UV-Vis. Os resultados das caracterizações mostraram que a rota de síntese utilizada foi eficiente na produção de nanoestruturas cristalinas de TiO2 com morfologias diferentes e os ensaios de degradação revelaram que a propriedade fotocatalítica dos materiais esta diferente relacionada com a morfologia, a área superficial e a presença de grupos químicos ligados à superfície / The environmental problems generated by tye growth of human and industrial activities have increased the need for the development of alternative technologies for the remediation of contaminated aquatic systems. The heterogeneous photocatalysis using titanium dioxide, has been show effective in this respect. In this work, nanoestructures have been synthesized as a precursor of TiO2 using titanium isopropóxido by the hydrothermal route. The materials were characterized by XRD, FT-Raman, FTIR, BET and SEM. In order to evaluate the photocatalytic activity of the samples produced, tests were performed using degradation of the dye rhodamine B under UV, white light and sunlight. The measurements of the degradation of the molecule was measured by UV-Vis spectroscopy. The results of the characterizations showed that the synthetic route used was efficient in the production of crystalline nanostructured TiO2 with different morphologies and degradation testing revealed that the photocatalytic properties of materials is directly associated to the morphology, surface area and the presence of chemical groups bound to the surface

Nos últimos anos, óxidos metálicos têm sido amplamente estudados para uma série de aplicações na indústria eletrônica e metalúrgica, sendo empregados em revestimentos anticorrosivos, sensores químicos, em dispositivos optoeletrônicos sensíveis, entre outros. Dentre os óxidos metálicos, o TiO2 (óxido de Titânio) tem enorme potencial em aplicações como sensor de gás, sensor de pH e em dispositivos fotossensíveis como células solares sensibilizadas por corante e para degradação fotocatalítica de compostos orgânicos. Há várias morfologias que podem ser obtidas para o TiO2, porém a de maior interesse atualmente é a de arranjos ordenados de nanotubos de TiO2 produzidos pelo processo de anodização do Ti, que por terem maior área superficial que outras morfologias como por exemplo, filmes finos, nanopilares e nanobastões, apresenta também maior sensibilidade à presença dos gases e/ou soluções a serem analisados, assim como maior absorção de fótons, além de uma menor recombinação de pares elétron-lacuna no material. Apesar destas várias vantagens, a atividade fotocatalítica do TiO2 é limitada por absorver apenas radiação ultravioleta devido a seu largo gap de aproximadamente 3,2 eV. Assim, neste trabalho foram produzidos nanotubos de TiO2 pelo processo de oxidação anódica do Ti, com diferentes parâmetros, correlacionando-os com a morfologia resultante. Com isso foi possível observar que o comprimento e diâmetro externo dos nanotubos de TiO2 crescem proporcionalmente com o aumento da tensão, sendo aproximadamente linear até um dado valor de saturação. A exceção a isto refere-se a nanotubos de TiO2 crescidos a partir de Ti depositado e substratos de vidro, no qual, há uma limitação de Ti a ser anodizado, de modo que após a conversão total do Ti em óxido não há mais o crescimento de nanotubos, porém os diâmetros gerados respeitam os mesmos valores para os casos em que não há essa limitação. Os nanotubos de TiO2 crescidos foram submetidos a processos de nitretação em um reator de deposição química a vapor assistida por plasma e os parâmetros foram avaliados com o intuito de encontrar as melhores condições para diminuição de seu gap, afim de aumentar sua atividade fotocatalítica. Pressão e potência de rádio frequência foram variados de 0,66 a 2,66 mBar (0,50 a 2,00 Torr) e 0,22 a 3,51 W/cm2 respectivamente. A maior diminuição no valor do gap, para 2,80 eV, foi obtida usando-se a pressão de 1,33 mBar (1,00 Torr), 1,75 W/cm2 de potência de rádio frequência durante um processo de 2 h a 320 °C, levando a uma diminuição de 14% no valor do gap e a um aumento de 25% na atividade fotocatalítica (redução de Azul de Metileno). Essa diminuição no valor do gap óptico dobra a abrangência de absorção de fótons de 5% para 10% do espectro solar. Os nanotubos de TiO2 nitretados produzidos com gap de 2,80 eV foram facilmente integrados a um microcanal de polidimetilsiloxano, produzindo um dispositivo fotocatalítico para estudo na fotodegradação de compostos orgânicos, podendo ser usado inclusive para redução de poluentes. O dispositivo fotocatalítico reduziu completamente 5 µL de solução de Azul de Metileno em cerca de 12 min, com uma taxa aproximadamente linear de 130 µM/h, enquanto os nanotubos de TiO2 como preparados apresentaram taxa de cerca de 115 µM/h. Logo, o dispositivo com nanotubos de TiO2 nitretados teve um aumento de 13% em sua eficiência de redução. / In recent years, metal oxides have been widely studied for a number of applications in the electronics and metallurgical industry, being used in anticorrosive coatings, chemical sensors, sensitive optoelectronic devices, among others. Among the metal oxides, TiO2 (titanium oxide) has enormous potential in applications such as gas sensor, pH sensor and in photosensitive devices such as dye sensitized solar cells and for photocatalytic degradation of organic compounds. There are several morphologies that can be obtained for TiO2, but the most interesting one today is ordered arrangements of TiO2 nanotubes produced by the Ti anodization process, which have a larger surface area than other morphologies such as thin films, nanopillars and nanobastones, also presents greater sensitivity to the presence of the gases and/or solutions to be analyzed, as well as greater absorption of photons, besides a smaller recombination of electron-hole pairs in the material. Despite these several advantages, the photocatalytic activity of TiO2 is limited by absorbing only ultraviolet radiation due to its wide gap of approximately 3.2 eV. Thus, in this work, TiO2 nanotubes were produced by the anodic oxidation process of Ti, with different parameters, correlating them with the resulting morphology. With this, it was possible to observe that the length and external diameter of the TiO2 nanotubes grow proportionally with the increase of the voltage, being approximately linear up to a given value of saturation. The exception to this relates to TiO2 nanotubes grown from Ti deposited and glass substrates, in which, there is a limitation of Ti to be anodized, so that after the total conversion of Ti to oxide, there is no longer growth of nanotubes, but the diameters generated respect the same values for cases in which there is no such limitation. The as grown TiO2 nanotubes were submitted to nitriding processes in a plasma assisted chemical vapor deposition reactor and the parameters were evaluated in order to find the best conditions to decrease their gap in order to increase their photocatalytic activity. Pressure and radio frequency power were varied from 0.66 to 2.66 mBar (0.50 to 2.00 Torr) and 0.22 to 3.51 W/cm2 respectively. The largest decrease in the gap value, to 2.80 eV, was obtained using the pressure of 1.33 mbar (1.00 Torr), 1.57 W/cm2 of radio frequency power during a process of 2 h in 320 °C, leading to a 14% decrease in gap value and a 25% increase in photocatalytic activity (reduction of Methylene Blue). This decrease in the value of the optical gap doubles the absorption range of photons from 5% to 10% of the solar spectrum. The nitrided TiO2 nanotubes produced with a gap of 2.80 eV were easily integrated into a microchannel of polydimethylsiloxane, producing a photocatalytic device for the study of photodegradation of organic compounds, and could be used to reduce pollutants. The photocatalytic device completely reduced 5 µL of Methylene Blue solution in about 12 min, with an approximately linear rate of 130 µM/h, whereas the TiO2 nanotubes as grown presented a rate of about 115 µM/h. Therefore, the device with nitrided TiO2 nanotubes had a 13% increase in its reduction efficiency.

PdCl2/Bi2WO6 and Pd/Bi2WO6 composite photocatalysts were synthesized via a template free hydrothermal process and the respective photocatalytic activities were investigated by degradation of Rhodamine B. The new catalyst composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and ultraviolet visible (UV-vis) light diffuse reflectance spectra, respectively. By XRD, it was found that the loaded Pd species did not alter the crystal lattice of Bi2WO6 photocatalyst. Through the XPS spectra, it was found that the PdCl2/Bi2WO6 was successfully reduced by chemical reducing agents CH2O and N2H4, respectively, and palladium was present in the form of both metallic Pd and Pd ion spe-cies (Pd0 and Pd2+), while the Pd species in a NaBH4-reduced composite exhibited only metallic Pd species (Pd0). For the SEM images, it was observed that both classes of composites were constructed from plenty of nanoplates, which were closed packed with hierarchical structures. Furthermore, the removal efficiency of Rhodamine B was found to be influenced by parameters such as catalyst dosage, pollutant concentration and solution pH.