Investigation of TiO2 and InVO4-TiO2 Semiconductors for the Photocatalytic Degradation of Aqueous Organics PDF Download
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Author: Sandra L. Pettit
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Parametric studies of the visible spectrum photodegradation of methyl orange, an azo dye, and 2-chlorophenol provide a basis for analysis. Methyl orange was utilized to ascertain the effect of pure and mixed phase titania in the semiconductor composites. The TiO2 photodegradation of geosmin and MIB has been previously demonstrated in small-scale batch slurry reactions. Slurry systems require the downstream separation of catalyst from the liquid. Laboratory trials use centrifugation or micro-filtration. Alternatively, immobilization of the photocatalyst could allow scale-up of the process. Here, titania was immobilized on glass plate substrates using an ethanol spray technique. Finally, naturally tainted waters may contain a number of constituents in addition to the target compounds. In recirculating aquaculture systems, the water contains natural organic matter (NOM), ammonia, nitrite/ nitrate, and carbonate species. These constituents may block light penetration, block reaction sites, scavenge hydroxyl radicals, or affect the surface chemistry of the catalyst. Further, geosmin and MIB concentrations are extremely low, in the ppt range. Naturally tainted waters from MOTE Marine Laboratory Aquaculture Research Park are treated in the laboratory and in situ to demonstrate TiO2 degradation efficiency for trace concentration geosmin and MIB degradation in a complex water matrix.
Author: Sandra L. Pettit
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Parametric studies of the visible spectrum photodegradation of methyl orange, an azo dye, and 2-chlorophenol provide a basis for analysis. Methyl orange was utilized to ascertain the effect of pure and mixed phase titania in the semiconductor composites. The TiO2 photodegradation of geosmin and MIB has been previously demonstrated in small-scale batch slurry reactions. Slurry systems require the downstream separation of catalyst from the liquid. Laboratory trials use centrifugation or micro-filtration. Alternatively, immobilization of the photocatalyst could allow scale-up of the process. Here, titania was immobilized on glass plate substrates using an ethanol spray technique. Finally, naturally tainted waters may contain a number of constituents in addition to the target compounds. In recirculating aquaculture systems, the water contains natural organic matter (NOM), ammonia, nitrite/ nitrate, and carbonate species. These constituents may block light penetration, block reaction sites, scavenge hydroxyl radicals, or affect the surface chemistry of the catalyst. Further, geosmin and MIB concentrations are extremely low, in the ppt range. Naturally tainted waters from MOTE Marine Laboratory Aquaculture Research Park are treated in the laboratory and in situ to demonstrate TiO2 degradation efficiency for trace concentration geosmin and MIB degradation in a complex water matrix.
Author: Innocent Udom
Publisher:
ISBN:
Category : Chemical engineering
Languages : en
Pages : 116
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Book Description
This research investigated the supported semiconductor photocatalysts (TiO2 and ZnO), particularly ZnO nanorods and nanowires, their synthesis methods, properties and corresponding effectiveness in photocatalysis. The effect of transition metal co-catalysts on the photocatalytic properties of TiO2 was investigated. Although TiO2 is the most extensively studied photocatalyst for water decontamination, ZnO, as presented in this work, could be a substitute because of its lower cost, relative energy bandgap and higher visible light photoactivity. Both photocatalysts were doped and screened for the decomposition of model contaminates, rhodamine B (RhB), phenol and methyl orange, under ultraviolet and/or visible light irradiation. In the photodegradation of RhB, TiO2/Ru 1% showed a superior photocatalytic activity relative to P25-TiO2 under broad-band irradiation, while doped ZnO-Ag resulted in better photodegradation of methyl orange, compared to P25-TiO2, under visible light irradiation.
Author: Dessy Ariyanti
Publisher:
ISBN:
Category : Graywater (Domestic wastewater)
Languages : en
Pages : 122
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Book Description
Wastewater consists of various colloidal particulates, pathogenic microorganisms, and organic pollutants. The discharge of untreated wastewater with a large quantity of organic pollutants does not only lead to the eutrophication and human health risks, but also contributes significantly to Green House Gas (GHG) emissions in the form of nitrous oxide and methane. To date, the most feasible technology in the research of organic wastewater treatment is photocatalysis using semiconductor metal oxide TiO2. By the illumination of UV light, TiO2 generate hydroxyl radicals (•OH) which can further assist the decomposition and mineralization of organic compound. Although the superiority of TiO2 among photoactive materials has been established, there are still some space related to its performance and efficiency that can be improved further such as the process optimization, morphology modification and improvement of their optical properties. In this thesis, the research mainly focuses on the application of TiO2 for organic degradation and the development of TiO2 photocatalyst, which include: (1) investigation on TiO2 photocatalysis for mixed dyes degradation in a photo-reactor (PR) and in a submerged membrane photo reactor (SMPR) and (2) investigation on the morphology modification by employing alkaline hydrothermal process and surface modification through chemical reduction to the improvements of material properties and photocatalytic activity of TiO2. The results of the study on TiO2 photocatalysis for dyes degradation in a binary system indicate that in the binary or even more complex systems, except for the degradation kinetics, the mechanism, and pathway follow those of in a single system. The reactions will eventually end up with total mineralization of organic dyes, showing the effectiveness of TiO2 photocatalysis. As the effectiveness of TiO2 photocatalysis for dyes degradation has been proven, further improvement in the TiO2 catalyst recovery obviously added more value to the process technically and economically. This is developed by integrating the photo-reactor with membrane filtration system (SMPR) for simultaneous dyes degradation and TiO2 catalyst recovery. Compared to the conventional photo-reactor, SMPR offer additional hydrodynamic force in the solution by its catalyst recovery activity that can improve photocatalytic activity up to 20%. In addition, by applying low flux (66 L/m2h), low concentration of catalyst (0.5 g/L), and aeration (1.3 L/min) can give an optimum photocatalytic performance as well as optimum membrane filtration performance. On the development of TiO2 catalyst, morphology modification via hydrothermal methods with operating condition 180oC for 20 h followed by annealing at 500oC has successfully produced TiO2 nanoribbon with dimensions 200-300 nm in width and several microns in length and possessed relatively high surface area and pore volume that improve the photocatalytic activity. This nanostructured can be used to develop multifunction membrane material for effective photocatalysis. Another important work in the TiO2 photocatalyst development is that the surface modification have been successfully introduced to pristine TiO2 via NaBH4 treatment and its concentration can be controlled by appliying different temperatures. The modified TiO2 (X300-450) has a good visible light absorption. Additionally, for the black TiO2 treated via NaBH4 reduction in 400 and 450oC, it shows low charge recombination compared to the pristine TiO2. Furthermore, in the application for dye degradation, it was found that those properties are not linear to the photocatalytic activity, as it has mainly bulk defects, which play the role of swallow traps for the electron and hole recombination, thus reducing the amount of charge migrated to the surface for photocatalytic reaction.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 307
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Book Description
Photocatalysis with semiconductor has recently emerged as an advanced oxidation process for environmental decontamination. It is safe and versatile, and consumes only light. It is very promising for solving the environmental problems in the most economic way. TiO2 of anatase phase has proven to be the most promising semiconductor photocatalyst for widespread environmental applications because it shows a high reactivity under ultraviolet (UV) light and it is nontoxic, stable and inert chemically. However, anatase TiO2 has a band gap of 3.2eV. This limits its application under sunlight as well as providing its high reactivity because the light with the energy larger than 3.2eV (corresponding to a wavelength of 387nm) constitutes only 3︢︣4% of the energy of solar light reaching the earth. TiO2 of rutile phase is claimed as catalytically inactive or much less active for organic compound photodegradation although it has a smaller band gap (3.0eV) corresponding to a wavelength of 413nm. Therefore, modifications of TiO2 are needed to allow TiO2 to efficiently utilize the solar spectrum. The present dissertation aims at developments of the photocatalysts which can work under visible light. One method used in the study was modification of rutile TiO2 by surface platinization. The experimental results indicate that Pt can act as a bridge for electrons created in rutile TiO2 to transfer to O2, which enables rutile TiO2's photoactivity under visible light. Roles of Pt deposited on anatase and anatase-rutile TiO2 for aqueous organic photooxidation were also investigated experimentally and theoretically. The other method used was modification of TiO2 with transition metal ions. MCM-41, a kind of mesoporous material, was used as a host for incorporation of transition metal ions (Cr, V, Fe, Cu, Mn, Co, Ni, Mo and La) and TiO2 loading. Only Cr6+ was found to be able to sensitize TiO2 for organic degradatoin under visible light. Two other mesoporous materials (MCM-48, and SBA-15) with different pore sizes and dimensionalities were also studied as supports for Cr6+ and TiO2. MCM-41 was found to be the best for visible light photocatalyst development. Cr6+ concentration in TiO2-loaded Cr-incorporated MCM-41 was parametrically investigated and the optimal atomic ratio of Si to Cr was 20. The catalyst deactivates with reation time; the deactivated catalyst can be 100% reactivated by recalcination under 450 C. Cr leaching is minimal when the catalyst deactivates completely after reaction. What is more, the synergistic effect between anatase and rutile titanias named in the literature was investigated with different kinds of titanias. A technique was discovered for removal of organics containing acid and/or phenolic groups under visible light by using commercial pristine TiO2. Conclusively, it has been shown that visible light utilization for aqueous organic oxidation can be achieved by modification of TiO2 with surface platinization or Cr6+ incorporation.
Author: Vincenzo Augugliaro
Publisher: Royal Society of Chemistry
ISBN: 1849732035
Category : Science
Languages : en
Pages : 283
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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: Mohamed A. Barakat
Publisher: Springer
ISBN: 3319242717
Category : Science
Languages : en
Pages : 39
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Book Description
In this brief, a comprehensive review of the UV/visible-TiO2 photocatalytic oxidation process is presented with an insight into the mechanisms involved, the role of titanium dioxide as a catalyst, irradiation sources, types of reactors, and a comparison between various modes of TiO2 application. An overview of the development and enhancement of the activity of TiO2 nanoparticles in photocatalysis is presented. The topics covered include a detailed look at the unique properties of the TiO2 nanoparticles and their relationship to photocatalytic properties. The utilization of the TiO2 nanoparticles as photocatalysts, in the non-doped and doped forms is also reviewed. Finally, the use of modified TiO2 nanoparticles has made a significant contribution in providing definitive mechanistic information regarding the visible light photocatalytic processes.
Author: Debjani Mukherjee
Publisher:
ISBN:
Category :
Languages : en
Pages : 320
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Comprising about 70% of the Earth's surface, water is undoubtedly the most precious natural resource. According to the W.H.O, around 3.5 million people are dying every year from different water related diseases. Different kinds of dyes and pharmaceutical products have been detected in drinking water, all over the world. These organic compounds being non removable by traditional water purification processes, made advanced oxidation processes come into existence. Among all kind of advanced oxidation processes, photocatalytic oxidation is the most promising one. The photocatalytic process is based on aqueous phase hydroxyl radical chemistry and couples low energy UV light with semiconductors acting as photocatalyst. The slurry form of TiO2 though being efficient has several disadvantages (particularly, post treatment expensive separation steps) which brings the immobilization of the catalysts on surfaces into existence. In this study, a TiO2-polymeric film photocatalyst was synthesized by reaction of gelatin, polyvinyl alcohol and polyvinyl pyrrolidone. TiO2 Degussa P25 powder was embedded into the polymeric matrix. The characterization of the film by OM, SEM, FTIR, revealed the topography of the catalyst films. Optimization of photocatalysts functionality was carried out by varying the cross linking methods and conducting several photodegradation reactions both under UV and solar light. Aspirin and methyl orange were chosen as model compounds, as traces of these compounds were detected in the drinking water of South-Western Ontario. The freeze-dried film photocatalyst was observed to degrade organic compounds efficiently, under both UV and solar illuminations. Degradation of high concentrated organic pollutants, was observed to follow Langmuir-Hinshelwood kinetics while at low concentration, first-order kinetics was observed. The effects of initial concentration, flow rate, pH, light intensity, photocatalyst loading, and thickness of the film on the degradation rates were studied. Mechanism of degradation of aspirin was studied from LC/MS analysis. The TOC analysis was carried out to analyse the organic carbon content of the intermediates formed during the course of degradation. Finally, photocatalytic degradation reaction was carried out in a continuous flow reactor under LED lights. film photocatalyst holds the potential of being an efficient and economical form of future photocatalyst for water purification.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 4
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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: Zakhele Siyanda Prince Khuzwayo
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Polychlorinated endocrine disrupting chemicals are environmental pollutants that are increasingly found in water sources. As a result of their hydrophobic properties, they generally accumulate in adipocytes of humans and wildlife when ingested. In this study, the feasibility of the advanced oxidation processes (AOPs) such as heterogeneous photocatalysis technology is investigated for the treatment of organochlorides in water systems. Titanium dioxide (TiO2) is the semiconductor catalyst of interest. The literature suggests that the most prominent organochlorides in the region are organochloride pesticides (OCPs). A group of 5 compounds were identified for the investigation: DDT, DDE, heptachlor, chlordane, and a polychlorinated biphenyl compound named 2,3,4-trichlorobiphenyl. Reverse phase solid phase extracted (RP-SPE) surface water organic analytes analysis was conducted using gas chromatography mass spectroscopy (GC-MS). Results from most sampling sites showed high concentration levels of the organochlorides in the environment. Heterogeneous photocatalysed mineralisation processes of organochlorides in aqueous systems were conducted in a batch reactor. Organochloride spiked solutions of differing catalyst concentrations are irradiated using a UV lamp for a period of 30 minutes. The reaction kinetics are determined and weighed against conventional photolysis. Results showed improved photo degradation of organochlorides under photocatalytic imposed conditions in comparison to photolysis. Results also suggest that photocatalytic degradation of organochlorides is less favoured with increased TiO2 catalyst concentrations. Enhanced catalyst performance studies through TiO2 surface property modification were conducted using copper nitrate (CuNO3) as a catalyst dopant. The doped catalyst showed slightly improved degradation of organochlorides at particular catalyst concentrations. Simulated photocatalytic rate of reaction kinetics results are in correlation with the modeled experimental results. They show variability of the degradation constant in the rate of reaction with varied catalyst concentrations. Catalyst concentration efficiency of each compound and the rate of the reactions were determined.
