The photocatalytic production of H2 from water as well as from a 1:1 methanol:water solution employing pre–treated TiO2 and various Pt–TiO2 photocatalysts was studied by using an Nd:YAG laser as irradiation source. The photocatalysts (0.5–, 1–, 1.5– and 2 wt% Pt–TiO2) were prepared by utilizing a photocatalytic reduction method after which characterisation by various analytical techniques, i.e. XRD, TEM, ICP, SEM, and EDX, were conducted. XRD clearly indicated that platinum was not present in the crystal structure of TiO2, but was rather loaded onto the surface of TiO2. TEM analysis confirmed the presence of Pt on the surface with a particle/cluster size between 11 nm and 22 nm. SEM showed that repeatable results in respect of surface appearance were obtained. ICP and EDX indicated that the loading method was successful with only a slight deviation between the actual amount loaded and the calculated amount loaded. The impact of the loaded Pt on the band gaps of the different photocatalysts was investigated by diffuse reflectance spectroscopy (DRS) and calculated by employing the Kubelka–Munk method. The band gap values shifted sequentially from 3.236eV to 3.100 eV as the loading increased, moving closer to the absorbance region for visible light. The amount of hydrogen produced from the individual photocatalysts dispersed in both pure water and aqueous methanol solutions, was measured manually with a gas chromatograph. As soon as irradiation was initiated, a distinct colour change from shades of grey to dark blue–grey was observed for all the photocatalysts. XRD confirmed that it was due to the anatase phase transforming to produce more rutile phase. No H2 was detected for the various photocatalysts suspended in water, i.e. in the absence of methanol. The amount of hydrogen produced from the various Pt photocatalysts suspended in the aqueous methanol solution was found to be the highest for the 0.5wt%– and 1.5wt% Pt–TiO2 photocatalysts and the lowest for the 2wt% Pt–TiO2. This could be due to loading Pt above the optimum amount to such an extent, preventing sufficient light from reaching the TiO2 surface. Pt particles can also touch and overlap which will decrease Pt contact with TiO2 thus decreasing effective charge transfer. / Thesis (M.Sc. (Chemistry))--North-West University, Potchefstroom Campus, 2012.

The photocatalytic production of H2 from water as well as from a 1:1 methanol:water solution employing pre–treated TiO2 and various Pt–TiO2 photocatalysts was studied by using an Nd:YAG laser as irradiation source. The photocatalysts (0.5–, 1–, 1.5– and 2 wt% Pt–TiO2) were prepared by utilizing a photocatalytic reduction method after which characterisation by various analytical techniques, i.e. XRD, TEM, ICP, SEM, and EDX, were conducted. XRD clearly indicated that platinum was not present in the crystal structure of TiO2, but was rather loaded onto the surface of TiO2. TEM analysis confirmed the presence of Pt on the surface with a particle/cluster size between 11 nm and 22 nm. SEM showed that repeatable results in respect of surface appearance were obtained. ICP and EDX indicated that the loading method was successful with only a slight deviation between the actual amount loaded and the calculated amount loaded. The impact of the loaded Pt on the band gaps of the different photocatalysts was investigated by diffuse reflectance spectroscopy (DRS) and calculated by employing the Kubelka–Munk method. The band gap values shifted sequentially from 3.236eV to 3.100 eV as the loading increased, moving closer to the absorbance region for visible light. The amount of hydrogen produced from the individual photocatalysts dispersed in both pure water and aqueous methanol solutions, was measured manually with a gas chromatograph. As soon as irradiation was initiated, a distinct colour change from shades of grey to dark blue–grey was observed for all the photocatalysts. XRD confirmed that it was due to the anatase phase transforming to produce more rutile phase. No H2 was detected for the various photocatalysts suspended in water, i.e. in the absence of methanol. The amount of hydrogen produced from the various Pt photocatalysts suspended in the aqueous methanol solution was found to be the highest for the 0.5wt%– and 1.5wt% Pt–TiO2 photocatalysts and the lowest for the 2wt% Pt–TiO2. This could be due to loading Pt above the optimum amount to such an extent, preventing sufficient light from reaching the TiO2 surface. Pt particles can also touch and overlap which will decrease Pt contact with TiO2 thus decreasing effective charge transfer. / Thesis (M.Sc. (Chemistry))--North-West University, Potchefstroom Campus, 2012.

The packaging does not serve as a mere containment but also can be designed to play a key role in preserving the product from quality-deteriorating factors, including oxygen, light irradiation, and foodborne pathogenic microorganisms (e.g., Escherichia coli). There has been a growing interest in employing ultra-porous metal-organic frameworks (MOF) with visible light-responsive antibacterial mechanisms to generate reactive oxygen species (ROS) that can eliminate bacteria via an oxidative burst. MOF is made of inorganic metal ions/nodes/clusters/secondary building units linked by organic bridge ligands, where titanium dioxide (TiO2) and tetrakis(4-carboxyphenyl)porphyrin) (TCPP) were selected for these components, respectively. TiO2 is an exceptional UV-A/B/C-blocker; meanwhile, TCPP dye performs a remarkable photocatalytic ability even under visible light, on top of its macro-heterocyclic structure that is ideal as a MOF linker. Both have good compatibility but suffer from the notorious tendency to self-quench/aggregate. The incorporation of MOF-based conjugates into a polymeric matrix, like cellulose, is among the proven-successful solutions. Cellulose is the Earth's most abundant and naturally biodegradable, and cellulose nanofibril (CNF) was particularly chosen for its high specific surface area and surface activity. However, a straightforward, cheap, and environmentally friendly approach of multicycle homogenization (0-25 passes) was conducted to solve neat cellulose's challenge of natural hydrophilicity, where low pressure (<10 MPa) was applied to prevent the common over-shearing effect. The antibacterial efficacy of CNF films functionalized with TiO2-TCPP conjugate on inhibiting E. coli growth was analyzed with and without light of different intensities (3000 and 6000 lux). The positive impacts of CNFs' promoted fibrillation and subsequent inter/intra-molecular hydrogen bonding post-homogenization were evidenced in an array of functional properties, i.e., crystallinity, TiO2-TCPP conjugate dispersion, surface smoothness, mechanical properties, thermal stability, hydrophobicity, oxygen barrier (comparable to ethylene-vinyl alcohol (EVOH), a commercial high-barrier polymer), and 100%-antibacterial rate (under 6000 lux after 72 hours). Varying optimum cycles of homogenization demonstrated the prospect of the proposed homogenization approach in preparing CNF with diverse processability and applicability. These findings also exhibited a promising potential for a myriad of high-barrier, UV-blocking, and/or visible light-responsive antibacterial film applications, including food packaging and biomedical. / Doctor of Philosophy / Packaging is useful not only as a container but can also be designed to help prevent products from being spoiled due to various reasons such as oxidation, light, and bacterial contamination. Researchers have discovered the promising antibacterial feature of the metal-organic framework (MOF). Packaging made with MOF technology can harness light and oxygen in the environment to produce a special form of oxygen called reactive oxygen species (ROS) that can kill unwanted bacteria. MOF is an extremely porous sponge-like material made of two ingredients: an inorganic metal cluster and an organic linker; in this study, titanium dioxide (TiO2) and a porphyrin called TCPP were selected, respectively. TiO2 is an excellent ultraviolet blocker, while TCPP has a unique, ring-like geometry that is ideal for use as a linker and an antimicrobial feature that works well under the visible light spectrum. The pair are compatible but still suffer from MOF's notorious challenge, where it tends to clump together because of its tiny size. To resolve this problem, TiO2-TCPP MOF can be deposited evenly in a cast made of polymer. Cellulose has been proven to work effectively as a polymeric cast; moreover, it is natural, biodegradable, and in abundant supply. A type of nanosized cellulose—cellulose nanofibril (CNF)—was specifically chosen because its high surface area and activity are useful when blended with other materials. However, cellulose is naturally a poor water-repellant that is not ideal for packaging applications. As a solution, cellulose can be treated with a homogenization technique by passing the material through a very narrow hole under high pressure. Homogenization can be problematic as it possibly damages the cellulose's structure, and its high pressure can also be expensive and energy consuming. Therefore, low pressure with multiple cycles was applied in this work. CNF-TiO2-TCPP films were tested for their ability to slow down E. coli bacteria growth with and without light of varying brightness to compare its light-sensitive antimicrobial feature. Homogenization was found helpful in producing higher-quality CNF, which improved several of the film's final characteristics, including an even material dispersion, structural order, smoothness, strength, heat resistance, and water repellency. Most importantly, it produced films with oxygen barrier ability comparable to commercial high-barrier plastics and completely eliminated bacteria after 72 hours. The optimum number of homogenization cycles was found to be dependent on the desired characteristics and application. Overall, these findings carry a promising potential for a variety of applications, including food packaging and the biomedical field.

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.

<p>In this research project, nanostructured composites based on Tin dioxide (SnO2) and Titanium dioxide (TiO2) with poly-4-styrene sulfonic acid (PSSA) doped polyaniline (PANI) conducting polymer has been investigated based on their structural, electrical and electrochemical properties. The synthesis of conducting polymers and their metal oxide or composites have been carried out chemically or electrochemically according to methods modified from the literature. Layer-by-layer construction of nano-Metal Oxide/PSSA doped polyaniline composites were successfully constructed by electroanalytical methods on the surface of a glassy carbon working electrode (GCE).</p>

<p>In this research project, nanostructured composites based on Tin dioxide (SnO2) and Titanium dioxide (TiO2) with poly-4-styrene sulfonic acid (PSSA) doped polyaniline (PANI) conducting polymer has been investigated based on their structural, electrical and electrochemical properties. The synthesis of conducting polymers and their metal oxide or composites have been carried out chemically or electrochemically according to methods modified from the literature. Layer-by-layer construction of nano-Metal Oxide/PSSA doped polyaniline composites were successfully constructed by electroanalytical methods on the surface of a glassy carbon working electrode (GCE).</p>

Magister Scientiae - MSc / In this research project, nanostructured composites based on Tin dioxide (SnO2) and Titanium dioxide (TiO2) with poly-4-styrene sulfonic acid (PSSA) doped polyaniline (PANI) conducting polymer has been investigated based on their structural, electrical and electrochemical properties. The synthesis of conducting polymers and their metal oxide or composites have been carried out chemically or electrochemically according to methods modified from the literature. Layer-by-layer construction of nano-Metal Oxide/PSSA doped polyaniline composites were successfully constructed by electroanalytical methods on the surface of a glassy carbon working electrode (GCE). / South Africa

Submitted by Onia Arantes Albuquerque (onia.ufg@gmail.com) on 2018-10-26T15:10:46Z No. of bitstreams: 2 Dissertação - Yagly Grasielle dos Santos Gomes - 2018.pdf: 4358810 bytes, checksum: 03c5c38a49fbef4f529827141eb0fdab (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2018-10-29T10:29:49Z (GMT) No. of bitstreams: 2 Dissertação - Yagly Grasielle dos Santos Gomes - 2018.pdf: 4358810 bytes, checksum: 03c5c38a49fbef4f529827141eb0fdab (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2018-10-29T10:29:50Z (GMT). No. of bitstreams: 2 Dissertação - Yagly Grasielle dos Santos Gomes - 2018.pdf: 4358810 bytes, checksum: 03c5c38a49fbef4f529827141eb0fdab (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2018-10-10 / Fundação de Amparo à Pesquisa do Estado de Goiás - FAPEG / In recent years, titanium dioxide TiO2 has been well studied due to its various interesting physical and chemical properties, especially with regard to the application in processes of photocatalytic discoloration. These processes have always attracted the interest of the scientific community, mainly because it is possible to use sunlight as a source of energy for the reaction to happen. The present work had the objective of studying the influence of pH on the hydrothermal crystallization of the amorphous (TiO2) gel obtained by the complex decomposition method by two different routes varying temperature and time of synthesis, where in one of the routes the materials were crystallized in a reactor metal and on the other synthetic route was used a glass reactor. Such routes were used as a relatively new, promising and efficient processing method for obtaining this type of material. The obtained samples were characterized by different techniques: the X-ray diffraction confirmed the obtaining of monophasic materials and also in mixtures of phases, with tetragonal structure for the polymorphs anatase and rutile, proving that the hydrothermal method is efficient in the synthesis of the samples of interest having energy expenditure when compared to conventional crystallization methods. Using the X-ray diffraction data, the sizes of crystallites (TC), and the percentage values of phases present in each sample were measured. The (MEV/FEG) scanning electron microscopy characterization and (TEM) transmission, evidenced the changes in the size and morphology of the materials obtained, especially between anatase and rutile when single-phase. The photocatalytic tests showed the best performance of some materials, especially for the sample crystallized in pH 7 in the glass reactor, which decoloured the study dye in 99.7% due to its morphology as well as anatase / rutile composition in percentage terms. / Nos últimos anos, o dióxido de titânio TiO2 vem sendo bastante estudado devido as suas várias propriedades físicas e químicas interessantes, principalmente no que se diz respeito à aplicação em processos fotocatalíticos. Esses processos sempre atraíram o interesse da comunidade científica, principalmente por ser possível a utilização da luz solar como fonte de energia para que a reação aconteça. O presente trabalho teve como objetivo estudar a influência do pH na cristalização hidrotérmica do gel amorfo de (TiO2) obtido pelo método de decomposição de complexos por duas rotas distintas variando temperatura e tempo de síntese, onde em uma das rotas os materiais foram cristalizados em um reator de metal e na outra rota utilizou-se um reator de vidro. Tais rotas foram utilizadas por ser um método de processamento relativamente novo, promissor e eficaz para a obtenção desse tipo de material. As amostras obtidas foram caracterizadas por diferentes técnicas: a difração de raios X confirmou a obtenção de materiais monofásicos e também em misturas de fases, com estrutura tetragonal para os polimorfos anatase e rutilo comprovando que o método hidrotérmico é eficiente no controle da síntese das amostras de interesse tendo gastos energéticos bem menores quando comparados a métodos convencionais de cristalização. Utilizando os dados referentes à difração de raio X, foram aferidos os tamanhos de cristalitos (TC) e os valores percentuais de fases presentes em cada amostra. A caracterização por microscopia eletrônica de varredura (MEV/FEG) e de transmissão (MET), evidenciaram as mudanças no tamanho e na morfologia dos materiais obtidos, especialmente, entre anatase e rutilo quando monofásicos. Os ensaios fotocatalíticos mostraram o melhor desempenho de alguns materiais, principalmente para a amostra cristalizada em valor de pH 7 no reator de vidro, que descoloriu em 99,7% o corante em estudo, isso devido à sua morfologia bem como à composição anatase/rutilo em termos percentuais.

The present thesis deals with the beneficial influence of nanostructuring on electrochemical performance of certain promising electrode and electrolyte materials for lithium-ion batteries (LIBs). Electrochemical performances of chosen electrodes and electrolytes have been presented in a systematic and detailed manner via studies related to both transport and lithium storage. Titanium dioxide (TiO2) or titania, a promising non-carbonaceous anode material for LIBs was chosen for the study. As part of the study, variety of nanostructured titania were synthesized. In general, all materials exhibited high lithium storage ( theoretical value for lithium storage in titania) and some of them showed exemplary rate capability, typically desired for modern lithium-ion batteries. Studies related to performance of these materials and mechanistics of lithium storage and kinetics are presented in Chapters 2-5. “Soggy sand” electrolyte, a promising soft matter electrolyte for LIBs was studied on the electrolyte side. Ion transport, mechanical strength and electrochemical properties of “soggy sand” electrolytes synthesized via dispersion of various surface chemically functionalized silica particles dispersed in model as well as LIB relevant electrolytes were studied in this thesis. Extensive physico-chemical and battery performance studies of “soggy sand” electrolytes are discussed in Chapters 6-8. A brief discussion of the contents and highlights of the individual chapters are described below: Chapter 1 briefly discusses the importance of electrochemical power sources as a viable green alternative to the combustion engine. Various facets of rechargeable LIBs, one of the most important electrochemical storage devices, are presented following the general discussion on electrochemical power devices. The importance of nanostructuring of electrodes with special emphasis on anodes for high lithium storage capacities and rate capabilities are also discussed in the opening chapter. The various advantages and disadvantages of the most commonly used electrolytes in LIB i.e. the liquid electrolytes are also discussed in Chapter 1. Suggestions for improvement of the physico-chemical properties of liquid electrolytes especially via nanostructuring (demonstrated via dispersions of fine oxide particles in liquid electrolytes in Chapters 6-8) using the concept of Heterogeneous doping are discussed in detail. A brief description on the importance of rheology for comprehension of soft matter microstructure is also provided in this chapter. Chapter 2 discusses composite of anatase titania (TiO2) nanospheres and carbon grown and self-assembled into micron-sized mesoporous spheres via a solvothermal synthesis route as prospective anode for rechargeable lithium-ion battery. The morphology and carbon content and hence the electrochemical performance are observed to be significantly influenced by the synthesis parameters. Synthesis conditions resulting in a mesoporous arrangement of an optimized amount of carbon and TiO2 exhibited the best lithium battery performance. The first discharge cycle capacity of carbon-titania mesoporous spheres (solvothermal reaction at 150 oC at 6 h, calcination at 500 oC under air, BET surface area 80 m2g-1) was 334 mAhg-1 (approximately 1 Li) at current rate of 66 mAg-1. High storage capacity and good cyclability is attributed to the nanostructuring (i.e. mesoporosity) of TiO2 as well as due to formation of a percolation network of carbon around the TiO2 nanoparticles. The micron-sized mesoporous spheres of carbon-titania composite nanoparticles also show good rate cyclability in the range (0.066-6.67) Ag-1. The electrochemical performance of the mesoporous carbon-TiO2 spheres has been compared with nonporous TiO2 spheres, normal mesoporous TiO2 and bulk TiO2. Implications of nanostructuring and conductive carbon interface on lithium insertion/removal capacity and insertion kinetics in nanoparticles of anatase polymorph of titania is discussed in Chapter 3. Sol-gel synthesized nanoparticles of titania (particle size ~ 6 nm) were hydrothermally coated ex situ with a thin layer of amorphous carbon (layer thickness: 2-5 nm) and calcined at a temperature much higher than the sol-gel synthesis temperature. The carbon-titania composite particles (resulting size  10 nm) displayed immensely superior cyclability and rate capability (higher current rates  4 Ag-1) compared to unmodified calcined anatase titania. The conductive carbon interface around titania nanocrystals enhances the electronic conductivity and inhibits crystallite growth during electrochemical insertion/removal thus preventing detrimental kinetic effects observed in case of un-modified anatase titania. The carbon coating of the nanoparticles also stabilized the titania crystallographic structure via reduction in the accessibility of lithium ions to the trapping sites. This resulted in decrease in the irreversible capacity observed in case of nanoparticles without any carbon coating. Chapter 4 discusses the morphology and electrochemical performance of mixed crystallographic phase titania nanotubes and nanosheets for prospective application as anode in rechargeable lithium-ion batteries. Hydrothermally grown nanotubes/nanosheets of titania (TiO2) and carbon/silver-titania (C/Ag-TiO2) comprise a mixture of both anatase and TiO2(B) crystallographic phases. The first cycle capacity (at current rate = 10 mAg-1) for bare TiO2 nanotubes was 355 mAhg-1 (approximately 1.06 Li), which is higher than both the theoretical capacity (335 mAhg-1) as well as reported values for pure anatase and TiO2(B) nanotubes. Higher capacity is attributed to a combination of presence of mixed crystallographic phases of titania as well as trivial size effects. The surface area of bare TiO2 nanotubes was very high being equal to 340 m2g-1. Surface modification of the TiO2 nanotubes via amorphous carbon and Ag nanoparticles resulted in significant improvement in battery performance. The first cycle irreversible capacity loss can be minimized via effective coating of the surface. Carbon coated TiO2 nanotubes showed superior performance than Ag nanoparticle coated TiO2 nanotubes in terms of long term cyclability. Unlike Ag nanoparticles which are randomly distributed over the TiO2 nanotubes, the effective homogeneous carbon coating forms an efficient percolation network for the conducting species thus exhibiting better battery performance. The C-TiO2 and Ag-TiO2 nanotubes showed a better rate capability i.e. higher capacities compared to bare TiO2 nanotubes in the current range 0.055-2 Ag-1. Although titania nanosheets retains mixed crystallographic phases, the lithium battery performance (first cycle capacity = 225 mAhg-1) is poor compared to TiO2 nanotubes. It is attributed to lower surface area (22 m2g-1) which resulted in lesser electrode/electrolyte contact area and inefficient transport pathways for Li+ and e-. Implications of iron on electrochemical lithium insertion/removal capacity of iron (Fe3+) doped anatase TiO2 is discussed in Chapter 5. Iron doped anatase TiO2 nanoparticles with different doping concentrations were synthesized by simple sol-gel method. The electrochemistry of anatase TiO2 is observed to be a strong function of concentration of iron (Fe3+). A high 1st cycle discharge capacity of 704 mAhg−1 (2.1 mol of Li) and 272 mAhg−1 (0.81 mol of Li) at the 30th discharge cycle with Coulombic efficiency greater than 96% has been observed for 5% iron (Fe3+) doped TiO2 at a current density of 75 mAg−1. Additional increase in the iron (Fe3+) concentrations deteriorates the lithium storage of TiO2. An improvement in lithium storage of more than 50% is noticed for 5% iron (Fe3+) doped TiO2 compared to pure anatase TiO2 which shows an initial discharge capacity of 279 mAhg−1. The anomalous lithium storage behavior in all the iron (Fe3+) doped TiO2 has been accounted, in addition to homogeneous Li insertion in the octahedral sites, on the basis of formation of metallic Fe and Li2O during initial lithiation process and subsequent heterogeneous interfacial storage between Fe and Li2O interface. Chapter 6 discusses in a systematic manner the crucial role of oxide surface chemical composition on ion transport in “soggy sand” electrolytes. A “soggy sand” electrolytic system comprising of aerosil silica functionalized with various hydrophilic and hydrophobic moeities dispersed in lithium perchlorate ethylene glycol solution ( = 37.7) was used for the study. Detailed rheology studies show that the attractive particle network in case of the composite with unmodified aerosil silica (with surface silanol groups) is most favorable for percolation in ionic conductivity as well as rendering the composite with beneficial elastic mechanical properties. Though weaker in strength compared to the composite with unmodified aerosil particles, attractive particle networks are also observed in composites of aerosil particles with surfaces partially substituted with hydrophobic groups. However, ionic conductivity is observed to be dependent on the size of the hydrophobic moiety. No spanning attractive particle network was formed for aerosil particles with surfaces modified with stronger hydrophilic groups (than silanol) and as a result no percolation in ionic conductivity was observed. The composite with hydrophilic particles was a sol contrary to gels obtained in case of unmodified aerosil and partially substituted with hydrophobic groups. Chapter 7 also discusses the influence of oxide surface chemical composition but additionally the role of solvent on ion solvation and ion transport of “soggy sand” electrolytes. Compared to the liquid electrolyte in Chapter 6, a lower dielectric constant liquid electrolyte was employed for the study in this chapter. A “soggy sand” electrolyte system comprising of dispersions of hydrophilic/hydrophobic functionalized aerosil silica in lithium perchlorate-methoxy polyethylene glycol solution ( = 10.9) was employed for the study. Static and dynamic rheology measurements again showed formation of an attractive particle network in case of the composite with unmodified aerosil silica (i.e. with surface silanol groups) as well as composites with hydrophobic alkane groups. While particle network in the composite with hydrophilic aerosil silica (unmodified) were due to hydrogen bonding, hydrophobic aerosil silica particles were held together via van der Waals forces. The network strength in the latter case (i.e. for hydrophobic composites) were weaker compared with the composite with unmodified aerosil silica. Both unmodified silica as well as hydrophobic silica composites displayed solid-like mechanical strength. However, this time around no enhancement in ionic conductivity compared to the liquid electrolyte was observed in case of the unmodified silica. This is attributed to the existence of a very strong particle network which leads to the “expulsion” of all conducting entities from the interfacial region between adjacent particles. The ionic conductivity for composites with hydrophobic aerosil particles displayed ionic conductivity as a function of the size of the hydrophobic chemical moiety. No spanning attractive particle network was observed for aerosil particles with surfaces modified with stronger hydrophilic groups (than silanol). The composite resembled a sol and no percolation in ionic conductivity was observed. Chapter 8 describes the influence of dispersion of uniformly sized mono-functional or bi-functional (“Janus”) particles on ionic conductivity in lithium battery solutions and it’s implications on battery performance. Mono-functionalized (hydrophilic or hydrophobic) and bi-functionalized Janus (hydrophilic and hydrophobic) particles form physical gels of varying strength over a wide range of concentration (0.1    0.4; , oxide volume fraction). While the composites with mono-functionalized particles display shear thinning typical of gels (due to gradual breaking up spanning particle network held together by hydrogen/van der Walls force), the bi-functionalized “Janus” particles exhibit both complementary properties of gel and sol. The latter observation is interpreted in terms of existence of both hydrogen and van der Waals force arising out of the particle arrangement which get perturbed under the influence of external shear. Composites with homogeneous hydrophilic surface group show the highest ionic conductivity whereas the homogeneous hydrophobic surfaces exhibit superior electrode/electrolyte interface stability and battery cyclability. The Janus particles did not show any enhancement in ionic conductivity however, battery performance is highly satisfactory taking intermediate values between the homogeneously functionalized hydrophilic and hydrophobic particle composites.

Les ressources en eau sont menacées par diverses formes de pollution et les procédés de traitement proposés sont souvent complexes avec des résultats qui ne sont pas toujours satisfaisants. Cette étude vise à développer un traitement, simple et peu coûteux pour réduire au maximum la présence dans l’eau des acides humiques (AH), un polluant organique. L’approche adoptée est la mise en place d’un procédé hybride combinant l’adsorption et la photocatalyse hétérogène réalisée avec le dioxyde de titane. La méthode d’adsorption a été réalisée d’une part avec du charbon actif et d’autre part avec trois argiles provenant de la Côte d’Ivoire. Le charbon actif a été préparé à partir des coques de coco selon une procédure assez simplifiée, sans additifs chimiques, dans le souci d’obtenir un adsorbant économique et écologique. Les trois argiles brutes (Dabou, Yamoussoukro et Katiola) ont chacune subi des opérations de purification pour obtenir des fractions pures. Des tests de caractérisation réalisés par diverses techniques (analyse élémentaire, DRX, adsorption d’azote, IR, etc.) ont été effectués sur les adsorbants obtenus. Les essais d’adsorption réalisés avec le charbon ont montré qu’aucune élimination des AH n’a été observé. La raison principale serait le manque de groupements fonctionnels sur la surface du charbon préparé. Les tests d’adsorption conduit avec les argiles ont montré que ces matériaux sont capables d’éliminer les AH. Les résultats ont révélé que l’argile la plus riche en kaolinite (celle de Yamoussoukro) a une capacité d’adsorption maximale largement supérieure (115 mg/g) par rapport aux autres (20 et 15 mg/g pour Dabou et Katiola respectivement). Cette différence trouve son explication dans la composition minéralogique et structurale de chacune des argiles. Les tests de photocatalyse menés ont montré une dégradation des macromolécules d’AH en des composés de plus petites tailles. La minéralisation de la matière organique a été observée avec une réduction du carbone organique total de l’ordre de 72 et 82 % respectivement aux pH 7 et 3. En mettant en série à pH 3, les deux procédés à savoir l’adsorption suivie de la photocatalyse, une réduction de 95% du carbone organique total des AH est obtenue. Le procédé hybride ainsi réalisé montre un avantage certain car il permet d’éliminer la quasi-totalité de la pollution organique initiale. / Water resources are threatened by various forms of pollution and the proposed treatment processes are often complex with results that are not always satisfactory. This study aims to develop a simple and inexpensive treatment to minimize the presence of humic acids (HA), an organic pollutant, in water. The approach adopted is the establishment of a hybrid process combining adsorption and heterogeneous photocatalysis performed with titanium dioxide. The adsorption method was carried out primary with activated carbon and secondary with three clays from Ivory Coast. Activated carbon was prepared from coconut shell by a simplified procedure, without chemical additives, in order to obtain an economic and ecological adsorbent. The three raw clays (Dabou, Yamoussoukro and Katiola) each underwent purification operations to obtain pure fractions. Characterization tests including various techniques (elemental analysis, XRD, nitrogen adsorption, IR, etc.) were carried out on the adsorbents obtained. Adsorption tests carried out with the coal showed that no elimination of HA was observed. The main reason is the lack of functional groups on the surface of the prepared coal. The adsorption tests conducted with the clays have shown that these materials are capable of removing HA. The results revealed that the clay richest in kaolinite (Yamoussoukro) has a much higher maximum adsorption capacity (115 mg/g) compared to the others (20 and 15 mg/g for Dabou and Katiola respectively). This difference found its explanation in the mineralogical and structural composition of each of the clays. Photocatalysis tests showed a degradation of the macromolecules of HA into smaller sizes compounds. The mineralization of the organic matter was observed with total organic carbon reduction rate equal to 72 and 82% at pH 7 and 3 respectively. By placing in series the two processes namely adsorption followed by photocatalysis, the removal percentage of HA obtained at pH 3, is about 95%. This hybrid process shows an advantage since it makes it possible to eliminate almost all of the initial organic pollution.