Physical Properties and Photocatalytic Degradation Studies of Chlorinated Hydrocarbons Using TiO2 Based Thin Films PDF Download
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Author: Sook Chuin Ng
Publisher:
ISBN:
Category : Organochlorine compounds
Languages : en
Pages : 146
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Author: Sook Chuin Ng
Publisher:
ISBN:
Category : Organochlorine compounds
Languages : en
Pages : 146
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Book Description
Author: Vincenzo Augugliaro
Publisher: Royal Society of Chemistry
ISBN: 1847558704
Category : Science
Languages : en
Pages : 259
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Book Description
The book deals with the environmentally friendly cleaning materials functionalized with TiO2, a widely known semiconductor giving rise to redox reactions under artificial or solar irradiation. The role of titanium dioxide in the worldwide community is introduced first. The fundamental working principles of heterogeneous photocatalysis follow and a critical section on the semiconductor bulk and surface properties open the way to the differences between TiO2 blend features with respect to analogous thin film layouts. Then Follows the main section of the book which deals with the techniques applied to manufactured commercial devices, ranging from glasses to textiles and from concrete and other construction materials to paintings. Also road asphalt and other devices, such as photocatalytic air conditioning machines are outlined. Last generation materials, not yet commercialized, and the deposition techniques applied to prepare them are also widely discussed. The final part of the book covers the difficult and modern topic of standardization and comparison of performance of photocatalytic processes and in particular the guidelines proposed by various worldwide organizations for standardization are discussed. The book covers the general matters as well as the practical applications with the supporting methods discussed in detail. This book brings together a team of highly experienced and well-published experts in the field, providing a comprehensive view of the applications of supported titanium dioxide.
Author: Dianlu Jiang
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages :
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Abstract: In this work, a series of simple, rapid and effective photoelectrochemical methodologies have been developed and successfully applied to the study of kinetic and thermodynamic characteristics of photocatalytic oxidation processes at TiO2 nanoparticulate films. As an application of the systematic studies of photocatalytic processes by photoelectrochemical techniques, a rapid, direct, absolute, environmental-friendly and accurate COD analysis method was successfully developed. In this work, the TiO2 nanoparticles colloid was prepared by the sol-gel method. The TiO2 nanoparticles were immobilized onto ITO conducting glass slides by dip-coating method. Thermal treatment was carried out to obtain nanoporous TiO2 films of different structures. At low calcination temperature (below 600 degrees C), nanoporous TiO2 films of pure anatase phase were prepared. At high calcination temperature (above 600 degrees C), nanoporous TiO2 films of mixed anatase and rutile phases were obtained. At these film electrodes, the work was carried out. By employing steady state photocurrent method and choosing phthalic acid as the model compound, the photocatalytic activity of the TiO2 nanoporous films calcined at various temperatures and for different lengths of time was evaluated. It was found that the films with mixed anatase and rutile phases calcined at high temperature exhibited high photocatalytic activity. Based on semiconductor band theory, a model was proposed, which explained well this finding. By employing linear sweep voltammetry (under illumination) and choosing glucose (an effective photohole scavenger) as a model compound, the characteristics of the photocatalytic processes at nanoparticulate semiconductor electrodes were investigated. Characteristics of the nanoporous semiconductor electrodes markedly different from bulk semiconductor electrodes were observed. That is, within a large range of electrode potentials above the flat band potential the electrodes behaved as a pure resistance instead of exhibiting variable resistance expected for bulk semiconductor electrodes. The magnitude of the resistance was dependent on the properties of the electrodes and the maximum photocatalytic oxidation rate at TiO2 surface determined by the light intensity and substrate concentration. A model was proposed, which explained well the special characteristics of particulate semiconductor electrodes (nanoporous semiconductor electrodes). This is the first clear description of the overall photocatalytic process at nanoparticulate semiconductor electrodes. The investigation set a theoretical foundation for employing photoelectrochemical techniques to study photocatalytic processes. By using the transient technique (illumination step method analogous to potential step method in conventional electrochemistry), the adsorption of a number of strong adsorbates on both low temperature and high temperature calcined TiO2 nanoporous films was investigated. Similar adsorption characteristics for different adsorbates on different films were observed. In all the cases, three different surface bound complexes were identified, which was attributed to the heterogeneity of TiO2 surface. The photocatalytic degradation kinetics of the pre-adsorbed organic compounds of different chemical nature was also studied by processing the photocurrent-time profiles. Two different photocatalytic processes, exhibiting different rate characteristics, were observed. This was, again, attributed to the heterogeneity of the TiO2 surface corresponding to heterogeneous adsorption characteristics. The catalytic first order rate constants of both fast and slow processes were obtained for different organic compounds. It was found that for different adsorbates of different chemical nature the magnitudes of rate constant for the slow kinetic process were very similar, while the magnitudes of rate constant for the fast process were significantly affected by the photohole demand characteristics of different adsorbates. Photohole demand distribution that depends on the size and structure of the adsorbed molecules was believed to be responsible for the difference. By employing steady state photocurrent method, the photocatalytic degradation kinetic characteristics of both strong adsorbates and weak adsorbates of different chemical structures were compared at pure anatase TiO2 nanoporous TiO2 films as well as at anatase/rutile mixed phase TiO2 nanoporous film electrodes. At the former electrodes for all the different organic compounds studied, the photocatalytic reaction rate increased linearly with concentration at low concentrations. Under such conditions, it was demonstrated that the overall photocatalytic process was controlled by diffusion and was independent of the chemical nature of organic compounds. However, the linear concentration range and the maximum photocatalytic reaction rate at high concentrations were significantly dependent on the chemical nature of the substrates. This was explained by the difference in the interaction of different organic compounds with TiO2 surface, the difference in their photohole demand distributions at the TiO2 surface and the difference in their nature of intermediates formed during their photocatalytic mineralization. In contrast, at the latter electrodes for the photocatalytic oxidation of different organic compounds the linear ranges (diffusion control concentration range) and the maximum reaction rates at high concentration were much larger than at the former electrodes and much less dependent on the chemical nature of the organic compounds. The spatial separation of photoelectrons and photoholes (due to the coexistence of rutile phase and anatase phase) and the increase in the lifetime of photoelectrons and photoholes are responsible for the excellent photocatalytic activity of the electrodes. By employing the thin-layer photoelectrochemical technique (analogous to the thin-layer exhaustive electrolytic technique), the photocatalytic oxidation of different organic compounds at the mixed phase TiO2 nanoporous electrodes were investigated in a thin layer photoelectrochemical cell. It was found that the charge derived from exhaustive oxidation agreed well with theoretical charge expected for the mineralisation of a specific organic compound. This finding was true for all the compounds investigated and was also true for mixtures of different organic compounds. The photocatalytic degradation kinetics of different organic compounds of different chemical identities in the thin layer cell was also investigated by the photoelectrochemical method. Two kinetic processes of different decay time constants were identified, which were attributed to the degradation of preadsorbed compounds and the degradation of compounds in solution. For the degradation of compounds in solution, a change in the overall control step from substrate diffusion to heterogeneous surface reaction was observed. For different organic compounds, the variation of the rate constant was determined by the photohole demand rather than by the chemical identities of substrates. The kinetics of the fast kinetic process, on the other hand, was greatly affected by the adsorption properties of the substrates. For the strong adsorbates, the rate was much larger than for weak adsorbates. However, the rate constant of the process was independent of the chemical identities of the substrates and the variation of the constant was also determined by the photohole demand. Based on the principles of exhaustive photoelectrocatalytic degradation of organic matter in a thin layer cell, a novel, rapid, direct, environmental-friendly and absolute COD analysis method was developed. The method was tested on synthetic samples as well as real wastewater samples from a variety of industries. For synthetic samples with given compositions the COD values measured by my method agree very well with theoretical COD value. For real samples and synthetic samples the COD values measured by my method correlated very well with those measured by standard dichromate COD analysis method.
Author: Troy Matthew Twesme
Publisher:
ISBN:
Category :
Languages : en
Pages : 172
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This investigation studied the photocatalytic oxidation of light alkanes using photocatalytic thin films. In the research presented, nearly complete oxidation of isobutane, n-butane and propane using ZrO2/TiO2 thin films in a single pass reactor was demonstrated. The importance of reactor design on the effectiveness of the photocatalytic reaction is discussed in terms of photocatalyst packing and adequate illumination for catalyst activation. The influence of relative humidity in the contaminant feed stream and the reactor operating temperature were evaluated to establish optimal operating conditions for the photocatalytic reactor. Further photocatalytic studies used propane as a probe compound to investigate metal-modification of photocatalytic thin films as a means to improve propane oxidation and mineralization. Six precious metals (Ag, Au, Pd, Pt, Rh, and Ru) were tested at 1 weight percent loadings in TiO2, SiO2/TiO2, and ZrO2/TiO2 thin films. The photocatalytic reactor was operated at temperatures up to 100 C with the expectation that a thermal catalytic enhancement due to the precious metals would be observed. Propane conversion data revealed that at 1% loading, the addition of metals to the thin films reduced the activity for conversion of propane, regardless of temperature. However, the reactor temperature iii significantly affected light irradiance. Reaction rates adjusted for the influence of temperature on reactor irradiance revealed the highest reaction rates occurred at 100 C, but evaluation of Langmuir-Hinshelwood-Hougen-Watson kinetics showed that temperature significantly reduced the surface adsorption of propane. Of the 21 materials tested, an unmodified ZrO2/TiO2 thin film had the best activity for propane conversion and mineralization. Lastly, a novel method to investigate the photoinduced change in surface potential of photocatalytic thin films was investigated.
Author:
Publisher:
ISBN:
Category : Photocatalysis
Languages : en
Pages : 7
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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Titanium dioxide (TiO2), a semiconductor metal oxide, has been used in heterogeneous photocatalysis for the destruction of organic, inorganic, and biological materials. The chief objectives of my doctoral research are to generate kinetic data and to develop engineering models for photocatalytic oxidation (PCO) using TiO2 thin films for current challenges in "solid"--Solid and air-solid environmental remediation. Three topics are studied in detail: i. TiO2 Photocatalytic Oxidation for Formaldehyde Removal from Air (Air-Solid) Formaldehyde (CH2O) is a toxic air contaminant present in industrial, commercial, and residential buildings. A novel rotating honeycomb adsorbent coupled with a PCO reactor was demonstrated by F. Shiraishi and coworkers for CH2O oxidation. They showed that their cyclic adsorbent D PCO reactor could oxidize CH2O to concentrations below the WHO guideline, but they made no attempt to model the system. In this project we modeled their batch system at transient and steady states. In addition, we applied the batch model kinetic parameters to design a continuous system for typical residential home challenges. ii. TiO2 Photobleaching of Dye Layers as a Field Analysis Method ("Solid"-Solid) Technological advances in the past decade allow glass manufacturers to deposit thin, photoactive, nano-sized TiO2 layers on glass billed as "self-cleaning" surfaces. Field installation of such "self-cleaning" window glass for office buildings or residential homes will require the creation of field analysis methods to characterize the initial and continuing catalyst activity variations with time and environmental conditions. In this project we characterized the PCO properties of commercial Pilkington Activ"!glass by oxidizing deposited organic dyes (a) to show visual decolorization and recovery of the aesthetic clarity of the glass and (b) to determine the light-driven reaction kinetics on Activ"!glass. i.
Author: Daniel Clark Gapen
Publisher:
ISBN:
Category :
Languages : en
Pages : 430
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Author: Tong-hyŏn Kim
Publisher:
ISBN:
Category :
Languages : en
Pages : 326
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Book Description
Author: Elisha B. Babatunde
Publisher: BoD – Books on Demand
ISBN: 9535103849
Category : Technology & Engineering
Languages : en
Pages : 498
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Book Description
The book contains fundamentals of solar radiation, its ecological impacts, applications, especially in agriculture, architecture, thermal and electric energy. Chapters are written by numerous experienced scientists in the field from various parts of the world. Apart from chapter one which is the introductory chapter of the book, that gives a general topic insight of the book, there are 24 more chapters that cover various fields of solar radiation. These fields include: Measurements and Analysis of Solar Radiation, Agricultural Application / Bio-effect, Architectural Application, Electricity Generation Application and Thermal Energy Application. This book aims to provide a clear scientific insight on Solar Radiation to scientist and students.
Author: Jesus Moreira del Rio
Publisher:
ISBN:
Category :
Languages : en
Pages : 434
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Book Description
Abstract Scaling up a photoreactor requires both knowledge of optical properties of the slurry medium and an established kinetic model. Measuring the scattering and absorption coefficients of particles suspended in water involves the use of specialized optical equipment, as well as the partial solution of the radiative transfer equation (RTE). In addition, modeling of the radiation field in photoreactors with complicated geometries offers special challenges. On the other hand, most of the kinetic models (KM) for phenol photodegradation reported in the literature were obtained for a single organic chemical species only. In fact, neglecting all the intermediate species generated during the photoreaction, is a common oversimplification that limits the KM application. As a result, once the radiation and kinetic models fully established, energy efficiencies can be obtained. In this PhD dissertation, the photocatalytic degradation of phenol over four different TiO2 catalysts is studied. It is proven that phenol yields hydroquinone, catechol, benzoquinone, and acetic and formic acids as main intermediate species. The radiation field inside photocatalytic reactors is predicted by solving the RTE. From the solution of the RTE, the local volumetric rate of energy absorption (LVREA) is also calculated. The radiation field inside an annular photoreactor is simulated using the Monte Carlo (MC) method for different TiO2 suspensions in water. All simulations are performed by using both the spectral distribution, and the wavelength-averaged scattering and absorption coefficients. The Henyey-Greenstein phase function is adopted to represent forward, isotropic and backward scattering modes. It is assumed that the UV lamp reflects the back-scattered photons by the slurried medium. It is proven, photo-absorption rates, using MC simulations and spectral distribution of the optical coefficients, agree closely with experimental observations from a macroscopic balance (MB). It is also found that the scattering mode of the probability density function, is not a critical factor for a consistent representation of the radiation field. iv When solving the RTE, two optical parameters are needed: (1) the absorption and scattering coefficients, and (2) the phase function. In this research work, the MC method, along with an optimization technique, is shown to be effective in predicting the wavelength-averaged absorption and scattering coefficients for different TiO2 powders. To accomplish this, the LVREA and the transmitted radiation (Pt) in the photoreactor are determined by using a MB. The optimized coefficients are calculated ensuring that they comply with a number of physical constrains, falling in between bounds established via independent criteria. The optimization technique is demonstrated by finding the absorption and scattering coefficients for different semiconductors that best fit the experimental values from the MB. The objective function in this optimization is given by the least-squared error for the LVREA. A photocatalyst is synthesized and its optical properties determined by the proposed method. This approach is a general and promising one; not being restricted to reactors of concentric geometry, specific semiconductors and/or particular photocatalytic reactor unit scale. Based on the proposed intermediate reactions, a phenomenological based unified kinetic model is proposed for describing the obtained experimental observations in phenol photodegradation. This Langmuir-Hinshelwood (L-H) kinetic model is based on a Series- Parallel reaction network. This reaction model is found to be applicable to the various TiO2 photocatalyst in the present study. This unified kinetic network is based on the identified and quantified chemical species in the photoconversion of phenol and its intermediates. In order to minimize the number of optimized parameters, the adsorption constants of the different intermediate species on the different catalysts configuration, are obtained experimentally. It is shown that the unified kinetic model requires a number of significant assumptions to be effective; avoiding overparametization. As a result, the unified kinetic model is adapted for each specific TiO2 photocatalyst under study. These different models adequately describe the experimental results. It is shown that this approach results in good and objective parameter estimates in the L-H kinetic model, which is typically applied to photocatalytic reactors. Finally, two efficiency factors, the quantum yield and the photochemical and thermodynamic efficiency factor, are obtained, in this PhD dissertation. These factors are based on the kinetic model proposed and the radiation being absorbed by the photocatalyst particles. The v efficiency calculations consider stoichiometric relationships involving observable chemical species and OH- groups. The obtained efficiency factors point toward a high degree of photon utilization and, as a result, the value of photocatalysis and Photo-CREC-Water reactors for the conversion of organic pollutants in water is confirmed.
