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TiO2 nanoparticles are one of the most suitable materials for photocatalysis, specifically for water and air treatment and removal of a wide variety of organic pollutants such as dyes, aromatic compounds, and chlorinated aromatic compounds. Methods of synthesis of TiO2 are generally categorized in two main classes of wet chemical, and dry methods. Wet chemical methods generally provide a better control over size, size distribution, and shape; all of which significantly affect photocatalytic performance of the produced nanoparticles. Despite its advantages over other semiconductor photocatalysts, wide band-gap of titania restrains its photocatalytic activity to only UV light, which only makes up to 5% of the light reaching surface of the earth. To induce visible-light activity, titania has been doped by different dopants, including transition metal-dopants such as Fe, and Co and non-metal dopants such as N, and C. Nitrogen has been shown to be a better dopant, providing a suitably placed energy state within the band-gap of TiO2, and not suffering from issues related to transition-metal dopants such as low thermal and physical stability and high electron-hole recombination rates. To dope titania with nitrogen, one could add the nitrogen source together with other precursors during synthesis, referred to as wet chemical doping methods, or anneal the synthesized titania nanoparticles under a flow of ammonia at high temperatures, referred to as dry doping methods. While different doping methods have been studied individually, the author maintains that there has been an absence of research comparing the effectiveness of these methods, on photocatalytic performance of N-doped TiO2 within a consistent experiment. In this research TiO2 nanoparticles were synthesized by a facile, inexpensive sol-gel method, and doping was done by wet chemical methods, dry methods, and a combination of both these methods. Visible-light photocatalytic activity of these nanoparticles was evaluated by their efficiency in degradation of methyl orange. The results show wet doping methods increase the efficiency of titania nanoparticles more than dry doping, or combination of both. Further investigation showed that the main reason for higher activity of wet chemically doped nanoparticles is due to their higher available surface area of 131.7 m2.g-1. After normalizing the available surface area, measured by the BET method, it was shown that a combination of wet chemical doping, and dry doping at 600 °C result in the most active nanoparticles, but high temperature dry doping severely decreases the surface area, lowering the overall efficiency of the product. Additionally, N-doped TiO2 nanoparticles were synthesized using a simple hydrothermal method, in which the nitrogen source was used not only to dope, but also to control shape, size, size distribution, and morphology of the titania nanoparticles, and to induce aqueous colloidal stability. It was shown that addition of triethylamine during the synthesis, results in ultra-small, colloidally stable, cubic TiO2 nanoparticles, while using triethanolamine results in formation of TiO2 pallets, assembled into spherical, rose-like structures. The synthesized nanoparticles show impressive efficiency in visible-light removal of phenol, 4-chlorophenol, and pentachlorophenol, achieving 100% degradation of a 100-ppm phenol solution in 90 min, more than 98% degradation of a 20-ppm 4-chlorophenol solution in 90 min, and 97% degradation of a 10-ppm pentachlorophenol in 180 min with 500 ppm loading of the catalyst in all cases. Moreover, synthesized nanoparticles showed no sign of deactivation after 5 consecutive runs, removing 4-chlorophenol, showing their reusability. / Graduate

Nitrogen-doped TiO2 nanotubes with enhanced visible light photocatalytic activity have been synthesized using commercial titania P25 as raw material by a facile P25/urea co-hydrothermal method. Morphological and microstructual characteristics were conducted by transmission electron microscopy, powder X-ray diffraction, and nitrogen adsorption/desorption isotherms; chemical identifications were performed using X-ray photoelectron spectroscopy, and the interstitial nitrogen linkage to the TiO2 nanotubes is identified. The photocatalytic activity of all nitrogen-doped TiO2 nanotubes synthesized by different urea content, evaluated by the decomposition of rhodamine B dye solution under visible light using UV¡VVis absorption spectroscopy, is found to exhibit higher degradation rate than that of P25. Factors affecting the photocatalytic activity of RB were analyzed and a possible mechanism of photodegradation was also proposed. The high photocatalytic activity was attributed to the process of two different mechanisms, one was the direct degradation of the chromophoric system and the other was successive deethylation of the four ethyl groups.

Titanium dioxide(TiO2) is a stable, effective and well-known photocatalyst for degradation of pollutants. However, its practical applications are limited due to the need for energy higher than 3.2 eV, or a wavelength lower than 390 nm (high frequency waves, ultraviolet and above) hindering its ability to effectively work in the visible light region (about 400 nm to 700 nm). Nitrogen-doped TiO2 (N-TiO2) has garnered some attention as a photocatalyst as it appears to work even in the visible light region. This could allow the utilization of a larger part of the solar spectrum. This thesis presents the results of photocatalytic degradation of methylene blue (MB) carried out under simulated visible light by using TiO2 and N-TiO2(doped in the lab) to evaluate and compare their efficiencies under similar conditions.

Orientador: Claudia Longo / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-18T16:06:49Z (GMT). No. of bitstreams: 1 Santos_ReginaldodaSilva_D.pdf: 4843119 bytes, checksum: 3b7dd1f72628c75da40e0f76317b6cfa (MD5) Previous issue date: 2011 / Resumo: Nanopartículas de TiO2 foram preparadas por método sol-gel a partir da hidrólise de isopropóxido de titânio, tratamento hidrotérmico (200 °C, 8 h) e calcinação (450 °C, 30 min); amostras de TiO2 dopado com ferro (Fe:TiO2) foram obtidas pela mesma metodologia incluindo nitrato férrico nos precursores (razão molar Fe/Ti de 1, 3 e 5%). Para comparação, investigou-se também uma mistura de a-Fe2O3/TiO2 (Fe/Ti = 4 %). O intervalo de banda proibida, de 3,2 eV para o TiO2, diminuiu de 3,0 para 2,7 eV com o aumento do teor de Fe. Análises por difração de raios X e refinamento Rietveld revelaram que o TiO2 é constituído por anatasa (82 %) e brookita (18 %); para Fe:TiO2, observou-se 30 % de brookita e identificou-se 0,5; 1,0 e 1,2 wt % de hematita nas amostras com Fe/Ti de 1; 3 e 5%. Filmes porosos, com espessura de 1,5 mm, foram depositados em eletrodos de vidro a partir de suspensões com polietilenoglicol e calcinação. Em solução aquosa, irradiados com um simulador solar, os eletrodos apresentaram comportamento de semicondutor tipo-n: para o TiO2, fotopotencial de -0,95 V em circuito aberto e fotocorrente de 0,34 mA cm em 0,8 V; valores muito menores foram observados para Fe:TiO2 e a-Fe2O3/TiO2. O TiO2 também apresentou maior atividade fotocatalítica para degradação de fenol e, quando utilizado como foto-anodo em célula de dois compartimentos, polarizado a + 0,7 V por 4 h, promoveu a oxidação de formiato e a produção de 18 mmol de H2 sobre contra-eletrodo de Pt. Os eletrodos de Fe:TiO2 e a-Fe2O3/TiO2 apresentaram valores menores de corrente, impossibilitando a obtenção de H2 no catodo. Embora as amostras de Fe:TiO2 tenham apresentado maior aproveitamento da luz visível, a inserção do ferro como dopante e a hematita segregada podem dificultar a separação das cargas fotogeradas e o transporte de elétrons através dos contornos de grãos, resultando em menor atividade fotocatalítica nas aplicações decorrentes da conversão de energia solar / Abstract: TiO2 nanoparticles were synthesized by sol-gel method from hydrolysis of titanium isopropoxide followed by hydrothermal treatment (200 °C, 8 h) and annealing (450 °C, 30 min). Fe doped TiO2 (Fe:TiO2) samples were synthesized by similar methodology adding ferric nitrate, with Fe/Ti atomic ratio corresponding to 1, 3 and 5 %. A mixture of a-Fe2O3/TiO2 (with Fe/Ti = 4 at %) was also investigated. The band gap energy, estimated as 3.2 eV for TiO2, gradually ranged from 3.0 to 2.7 eV with increasing iron content. Rietveld refinement of X ray diffraction data revealed that TiO2 consisted of 82 % anatase and 18 % brookite; for Fe:TiO2, brookite increased to 30 % and hematite was also identified (0.5; 1.0 and 1.2 wt % for samples prepared with 1; 3 and 5 % of Fe/Ti). Porous films, 1.5 mm thick, were deposited on transparent electrodes from aqueous suspension with polyethylene glycol and annealing. In aqueous solution, irradiated by a solar simulator, the electrodes exhibited n-type semiconductor behavior: for TiO2 electrode, -0,95 V of photo-potential at open circuit condition and 0,34 mA cm of photocurrent when biased at 0.8 V; much lower values were observed for Fe:TiO2 and a-Fe2O3/TiO2 electrodes. TiO2 film also exhibited higher photocatalytic activity for phenol oxidation than other samples. The electrodes were also used as photo-anodes in a two-compartment electrochemical cell with Pt counter-electrode and HCOONa as hole scavenger. The cell assembled with irradiated TiO2 anode biased at + 0.7 V for 4 h produced 18 mmol of H2 at the cathodic compartment. H2 evolution was not detected and very low currents were observed for Fe:TiO2 or a-Fe2O3/TiO2 photo- anodes. Although Fe:TiO2 samples exhibited higher sunlight harvesting, inserted iron and segregated hematite can hinder the separation of photogenerated charges, as well as the electron transport across the grain boundaries, resulting in lower photocatalytic activity for solar energy conversion / Doutorado / Físico-Química / Doutor em Ciências

No description available.

Over the past few decades, inorganic nanostructured materials have elicited a lot of interest due to their high surface-to-volume ratio and many size dependent properties which stem from their nanoscale dimensions. Owing to these distinct properties, they have found applications in widespread fields like catalysis, energy storage, electronics, and biotechnology. In the field of biotechnology, nanotubes and mesoporous materials are attractive vehicles for drug delivery because of their hollow and porous structures and facile surface functionalization. Their inner void can take up large amounts of drug as well as act as gates for the controlled release of drug. These hollow structures can also be used for confining biomolecules like proteins and peptides. The study on protein conformation in biocompatible materials is very important in materials sciences for the development of new and efficient biomaterials(sensors, drug delivery systems or planted devices). Titania(TiO2)has been widely explored for applications in photovoltaic cells, batteries, desalination, sensing, and photocatalysis, to name only a few. The work presented in this thesis focuses on titania based nanostructures for drug delivery and protein confinement. First part of the work focusses on synthesis and characterization of Fe-doped TiO2 nanotubes. Fe-doped TiO2 nanotubes were demonstrated as controlled drug delivery agents. In vitro cytotoxic effects of Fe-doped titania nanotubes were assessed by MTT assay by exposing Hela cell line to the nanotubes. Second part of the work focusses on synthesis and characterization of TiO2 nanotubes by two synthesis procedures, namely hydrothermal and sol-gel template synthesis. Myoglobin, a model globin protein was encapsulated in hydrothermally synthesized TiO 2 nanotubes(diameter 5 nm) and sol-gel template synthesized TiO2 nanotubes(diameter 200 nm). Effect of encapsulating myoglobin these nanotubes was studied. The electrochemical activity and structure of myoglobin were studied by cyclic voltammetry and circular dichroism respectively. Direct electron transfer was found to be enhanced upon confinement in 200 nm diameter nanotubes. No such enhancement was observed upon encapsulation in hydrothermally synthesized nanotubes. In addition to this, the thermal stability of myoglobin was found to be enhanced upon confinement inside 200 nm diameter TiO 2 nanotubes.

After introducing fundamentals of catalysis with noble metal surfaces especially Pt metal for CO oxidation and subsequent developments on nano-crystalline Pt metals supported on oxide supports, an idea of Pt ion in reducible oxide supports acting as adsorption sites is proposed in chapter 1. Idea of red-ox cycling of an ion in an oxide matrix is presented taking Cu ion in YBa2Cu3O7 as an example. Noble metal ions in reducible oxides such as CeO2 or TiO2 acting as adsorption sites and hence a red-ox catalyst was arrived at from chemical considerations. Among several reducible oxide supports, TiO2 was chosen from crystal structure and electronic structure considerations. A good redox catalyst for auto exhaust and related applications should have high oxygen storage capacity (OSC). Any new material that can work as a redox catalyst should be tested for its OSC. Therefore we designed and fabricated a temperature programmed reduction by hydrogen (H2¬TPR) system to measure OSC. This is presented in chapter 2. We have synthesized a number of oxides by solution combustion method. Structures were determined by powder XRD and Rietveld refinement methods. Fe2O3, Fe2-xPdxO3-δ, Cu1-xMnAl1+xO4, LaCoO3, LaCo1-xPdxO3-δ, CeO2, Ce1¬xPdxO2-δ, TiO2, Ti1-xPdxO2-δ and many other oxide systems were synthesized and their structures were determined. OSC of these systems were determined employing the H2/TPR system. TPR studies were carried out for several redox cycles in each case. Except Pd ion substituted CeO2 and TiO2 other oxide systems decomposed during redox cycling. Pd ion substituted TiO2 gave highest OSC and also it was stable paving way to choose this system for further study. In chapter 3, we have described lattice oxygen of TiO2 activation by the substitution of Pd ion in its lattice. Ti1-xPdxO2-x (x = 0.01 to 0.03) have been synthesized by solution combustion method crystallizing in anatase TiO2 structure. Pd is in +2 oxidation state and Ti is in +4 oxidation state in the catalyst as seen by XPS. Pd is more ionic in TiO2 lattice compared to Pd in PdO. Oxygen storage capacity defined by ‘amount of oxygen that is used reversibly to oxidize CO’ is as high as 5100 μmol/g of Ti0.97Pd0.03O1.97. Oxygen is extracted by CO to CO2 in absence of feed oxygen even at room temperature. Rate of CO oxidation is 2.75 μmol.g-1.s-1 at 60 0C over Ti0.97Pd0.03O1.97 and C2H2 gets oxidized to CO2 and H2O at room temperature. Catalyst is not poisoned on long time operation of the reactor. Such high catalytic activity is due to activated lattice oxygen created by the substitution of Pd ion as seen from first-principles density functional theory (DFT) calculations with 96 atom supercells of Ti32O64, Ti31Pd1O63, Ti30Pd2O62 and Ti29Pd3O61. The compounds crystallize in anatase TiO2 structure with Pd2+ ion in nearly square planar geometry and TiO6 octahedra are distorted by the creation of weakly bound oxygens. Structural analysis of Ti31Pd1O63 which is close to 3% Pd ion substituted TiO2 shows that bond valence of oxygens associated with both Ti and Pd ions in the lattice is 1.87. A low bond valence of oxygen is characteristic of weak oxygen in the lattice compared to oxygens with bond valence 2 and above in the same lattice. Thus, the exact positions of activated oxygens have been identified in the lattice from DFT calculations. Pt has two stable valencies: +2 and +4. Ti ion in TiO2 is in +4 state. Is it possible to substitute Pt exclusively in +2 or +4 state in TiO2? Implications are that Pt in +2 will have oxide ion vacancies and Pt in +4 states will not have oxide ion vacancies. Indeed we could synthesize Pt ion substituted TiO2 with Pt in +2 and +4 states by solution combustion method. In chapter 4, we have shown the positive role of an oxide ion vacancy in the catalytic reaction. Ti0.97Pt2+0.03O1.97 and Ti0.97Pt4+0.03O2 have been synthesized by solution combustion method using alanine and glycine as the fuels respectively. Both are crystallizing in anatase TiO2 structure with 15 nm average crystallite size. X-ray photoelectron spectroscopy (XPS) confirmed Pt ions are only +2 state in Ti0.97Pt0.03O1.97 (alanine) and only in +4 state in Ti0.97Pt0.03O2 (glycine). CO oxidation rate with Ti0.97Pt2+0.03O1.97 is over 10 times higher compared to Ti0.97Pt4+0.03O2. The large shift in 100 % hydrocarbon oxidation to lower temperature was observed by Pt2+ ion substituted TiO2 from that by Pt4+ ion substituted TiO2. After reoxidation of the reduced compound by H2 as well as CO, Pt ions are stabilized in mixed valences, +2 and +4 states. The role of oxide ion vacancy in enhancing catalytic activity has been demonstrated by carrying out the CO oxidation and H2 + O2 recombination reaction in presence and in absence of O2. There is no deactivation of the catalyst by long time CO to CO2 catalytic reaction. We analyzed the activated lattice oxygens upon substitution of Pt2+ ion and Pt4+ ion in TiO2, using first-principles density functional theory (DFT) calculations with supercells Ti31Pt1O63, Ti30Pt2O62, Ti29Pt3O61 for Pt2+ ion substitution in TiO2 and Ti31Pt1O64, Ti30Pt2O62, Ti29Pt3O61 for Pt4+ ion substitution in TiO2. We find that the local structure of Pt2+ ion has a distorted square planar geometry and that of Pt4+ ion has an octahedral geometry similar to Ti4+ ion in pure TiO2. The change in coordination of Pt2+ ion gives rise to weakly bonded oxygens and these oxygens are responsible in high rates of catalytic reaction. Thus, the high catalytic activity results from synergistic roles of oxide ion vacancy and weakly bonded lattice oxygen. In chapter 5, we have shown high rates of H2 + O2 recombination reaction by Ti0.97Pd0.03O1.97 catalyst coated on honeycomb monolith made up of cordierite material. This catalyst was coated on γ¬Al2O3 coated monolith by solution combustion method using dip-dry-burn process. This is a modified conventional method to coat catalysts on honeycombs. Formation of Ti0.97Pd0.03O1.97 catalyst on monolith was confirmed by XRD. Form the XPS spectra of Pd(3d) core level in Ti1-xPdxO2-δ, Pd ion is the formed to be +2 state. Ti0.97Pd0.03O1.97 showed high rates of H2 + O2 recombination compared to 2 at % Pd(metal)/γ-Al2O3, Ce0.98Pd0.02O2-δ, Ce0.98Pt0.02O2-δ, Ce0.73Zr0.25Pd0.02O2-δ and Ti0.98Pd0.02O1.98. Activation energy of H2 + O2 recombination reaction over Ti0.97Pd0.03O1.97 is 7.8 kcal/mole. Rates of reaction over Ti0.97Pd0.03O1.97 are in the range of 10 – 20 μmol/g/s at 60 0C and 4174 h-1 space velocity. Rate is orders of magnitude higher compared to noble metal catalysts. From the industrial point of view, solvent-free hydrogenation of aromatic nitro compounds to amines at nearly 1 bar pressure is an important process. In chapter 6, we showed that Ti0.97Pd0.03O1.97 is a good –nitro to –amine conversion catalyst under solvent-free condition at 1.2 – 1.3 bar H2 pressure. Nitrobenzene, p-nitrotoluene and 2-chloro-4-nitrotoluene are taken for the catalytic reduction reaction. The amine products were analyzed by gas chromatography and mass spectrometry (GCMS). Further, confirmation of compounds was done by FTIR, 1H NMR and 13C NMR. In presence of alcohol as solvent, 100% conversion of aromatic nitro compounds to amines took place at higher temperature and it required more times. In n-butanol solvent, 100% conversion of nitrobenzene and p-nitrotoluene occurred within 10 h and 12 h at 105 °C respectively. We have compared solvent-free reduction of p-nitrotoluene over different catalysts at 90 °C. Catalytic activity for reduction of p¬nitrotoluene over Ti0.97Pd0.03O1.97 is much higher than that reaction over 3 atom % Pd on TiO2 and Pd metal. Turnover frequencies (TOF) for nitrobenzene and 2-chloro-4-nitrotoluene conversion are 217 and 20 over Ti0.97Pd0.03O1.97 respectively. With increase of temperature, TOF of aromatic nitro compound reduction is also increased. We have compared the solvent-free reduction of aromatic nitro compound over Ti0.97Pd0.03O1.97 with others in the literature. Upto 3 cycles of reduction reaction, there was no degradation of Ti0.97Pd0.03O1.97 catalyst and stability of catalyst structure was analyzed by XRD, XPS and TEM images. Catalyst is stable under reaction condition and the structure is retained with Pd in +2 state. Finally, we have proposed the mechanism of -nitro group reduction reaction based on the structure of Ti0.97Pd0.03O1.97. Instead of handling nano-crystalline materials we proceeded with coating our catalysts on cordierite honeycombs. In chapter 7, we have shown high catalytic activity towards Heck reaction over Ce0.98Pd0.02O2-δ and Ti0.97Pd0.03O1.97 coated on cordierite monolith. XRD patterns of Ce0.98Pd0.02O2¬δ coated on cordierite monolith were indexed to fluorite structure. Heck reaction of aryl halide with olefins over Ce0.98Pd0.02O2-δ and Ti0.97Pd0.03O1.97 coated on cordierite monolith were carried out at 120 °C. The products were first analyzed by GCMS and for the confirmation of compounds, we have recorded 1H NMR and 13C NMR. Heck reaction was carried out with different solvents and different bases for choosing the good base and a solvent. Hence, we have chosen K2CO3 as base and N,N¬dimethylformamide (DMF) as solvent. We have compared the rates of Heck reactions over these two catalysts and Ti0.97Pd0.03O1.97 catalyst showed much higher catalytic activity than Ce0.98Pd0.02O2-δ. With increase of temperature from 65 °C to 120 °C, the catalytic activity of Ti0.97Pd0.03O1.97 on Heck reaction is also increased. The catalyst was reused for next Heck reaction without significant loss of activity. A mechanism for Heck reaction of aryl halide with alkyl acrylate has been proposed based on the structure of Ti0.97Pd0.03O1.97. In chapter 8, we have provided a critical review of the work presented in the thesis. Critical issues such as noble metal ion doping in TiO2 vs noble metal ion substitution, difficulty of proving the substitution of low % noble metal ion in TiO2, need for better experimental methods to study noble metal ion in oxide matrix have been discussed. Finally, conclusions of the thesis are presented.