Academic literature on the topic 'Visible-light responsive photocatalyst'

Kyoto University (京都大学)<br>0048<br>新制・課程博士<br>博士(工学)<br>甲第13834号<br>工博第2938号<br>新制||工||1434(附属図書館)<br>26050<br>UT51-2008-C750<br>京都大学大学院工学研究科物質エネルギー化学専攻<br>(主査)教授 井上 正志, 教授 江口 浩一, 教授 田中 庸裕<br>学位規則第4条第1項該当

The development of sustainable and green technologies powered by renewable energy sources is highly desired to address the growing global energy need and water scarcity problems. Heterogeneous photocatalysis emerged in the past decades as promising solar-powered technology for environmental remediation applications such as wastewater treatment. The photoactivity of the materials is believed to be governed by complex mechanisms, still it was shown that it may be critically dependent on the following material properties (i) ability and effectiveness to absorb incident photons, (ii) charge separation efficiency, (iii) charge utilization efficiency, (iv) morphology including the size and shape of the nanostructure and its distribution and (v) the crystal structure, phase composition and crystallinity ... etc. Hence, most strategies aiming to improve the performance of photocatalytic materials may focus on one or more of the aforementioned aspects. Beside developing new materials or modifying existing systems, the development of sustainable, easy-to-operate systems are highly desired for developing countries such as Africa where almost half of the population are affected by water scarcity of some sort. For this motivation the immobilization of powder catalyst could be one attractive solution. In this thesis three experimental systems are presented. In the first two the effect of material properties on the photoactivity whereas in the third chapter the immobilization of powder catalyst was investigated. The first experimental project aimed to study the effect of synthesis parameters of WO3 nanostructures on its morphology, phase composition, optical properties and ultimately on the photoactivity. Understanding the role of process parameters to gain control over the material properties is still a challenge but is of great interest in photocatalysis. Here, a hydrothermal synthesis method was employed to synthesize WO3 nanostructures with various morphologies, crystal phases and optical properties. The effect of the solution pH, the polymeric surface modulator and the added EtOH was investigated on the material properties and on the photocatalytic activities. It was found that the crystal structure and the morphology of WO3 was influenced by the solution pH in the first place. It was proposed that stabilization effects between the crystal phase and the morphology could also influence the crystallization process beside supersaturation. It was revealed that despite the highest surface area of W-2.01-P20E, reduced oxidation state did not promote high photo-response. Instead the photoactivity of WO3 was seen as the compromise of the material properties including the optical, structural properties and the oxidation state. In the second experimental project the effect of Ag co-catalysis was studied on TiO2- Cu2O heterostructure formation. Coupling a wide band gap (TiO2) and a narrow band gap (Cu2O) semiconductor could benefit from extended light absorption properties and additionally from enhanced charged separation. In this study a facile wet chemical synthesis method was coupled with a UV treatment step to fabricate TiO2-Ag-CuxO ternary hybrid nano-materials. The effect of the Ag loading (1-5%) and the synthesis sequence of the Ag deposition step was evaluated on the material properties as well as on the visible photocatalytic activity. It was revealed that both the amount and the order of the Ag-deposition altered the material properties considerably. Typically TiO2/CuxO/Ag (TCA) catalysts had better visible light absorption properties but reduced affinity to adsorb methyl orange (MO) to their surface. Whereas, TiO2/Ag/CuxO (TAC) catalysts in general had better dye adsorption properties relative to TCA and had more efficient decoloration properties under visible light. TOC and HPLC-MS analysis revealed that MO and possibly its degradation products were mainly mineralized and/or adsorbed to the surface of TAC catalyst with 5% nominal Ag content in the visible process generating limited amount of byproducts in the final solution. The third experimental project focused on the immobilization of the previously prepared powder TiO2-Cu2O nanostructure. In this work a fluorine-doped tin oxide (FTO) glass sheet was used as a substrate and the doctor-blade coating technique has been employed to make TiO2-Cu2O thin films. Although this technique has a widespread use in the fabrication of solar cells to the best of our knowledge this is the first report on supported TiO2-Cu2O photocatalytic systems prepared by this method. To optimize the performance of the TiO2- Cu2O thin film under visible light irradiation, the chemical composition of the doctor-blading paste and the temperature of the final thermal treatment step was studied. It was found that both the paste composition and the heat treatment step played an important role in the material properties. When the film contained ethyl cellulose the minimum temperature to remove organic additives was 350 °C. Whereas for the films containing only alpha terpineol 300 °C was sufficient. It was revealed that the higher temperature treatment resulted in more oxidized films which were also shown in their deeper colour. The most effective film under visible light irradiation was TC-0-300 which contained no cellulose and was treated at the lowest temperature.

Along with many other solar energy conversion processes, research on photocatalytic water splitting to generate hydrogen and oxygen has experienced rapid major development over the past years. Developing an efficient visible-light-responsive photocatalyst has been one of the targets of such research efforts. In this regard, nitride materials, particularly Ta3N5, have been the subject of investigation due to their promising properties. This dissertation focuses on the fundamental parameters involved in the photocatalytic processes targeting overall water splitting using Ta3N5 as a model photocatalyst. The discussion primarily focuses on relevant parameters that are involved in photon absorption, exciton separation, carrier diffusion, carrier transport, and catalytic efficiency. A collection of theoretical and experimental studies of properties associated with Ta3N5 have been utilized to obtain a comprehensive understanding of this material. The fundamental structural and optoelectronic properties of Ta3N5 have been addressed. From the electronic properties, the dielectric constant and effective masses have been calculated. Because of its high dielectric constant and relatively low effective masses, Ta3N5 is promising for photocatalytic reaction applications. Studies of lattice dynamics, optical properties, and band positions have been able to clearly show that the synthesized Ta3N5 is essentially non-stoichiometric and that a truly pure phase of Ta3N5 has never been achieved, even though XRD has shown a pure phase sample. The photophysical properties of Ta3N5, such as the absorption coefficient, carrier mobility, and carrier lifetime, have been experimentally measured by synthesizing Ta3N5 thin films. Very low kinetic properties with very low transport properties and fast carrier recombination explained why overall water splitting has never been achieved with Ta3N5 as a photocatalyst to date. The extent to which the surface states of Ta3N5 photocatalysts affect photocatalytic performance has been investigated. The surface topmost layer is demonstrated to play a critical role in the photocatalytic activity of Ta3N5; further research on the surface properties of Ta3N5 should be conducted to understand and improve charge separation and the resulting photocatalytic activity. Finally, a remarkable improvement in the photocatalytic OER has been achieved with the addition of cobalt as a cocatalyst. There is a trade-off between the optimum contact of hole transfer from bulk Ta3N5 to the surface of the cobalt cocatalyst and providing active sites for the electrochemical reaction. Knowing the characteristics of cobalt on the Ta3N5 surface, further improvement was attempted by adding a noble metal to the CoOx/Ta3N5 photocatalyst system, where a synergetic effect of CoOx and noble metals was observed.

碩士<br>國立高雄應用科技大學<br>化學工程與材料工程系<br>99<br>Electrospinning display tremendous functions in some of the domain of sciences, such as, electrochemistry, gas storage, drug release, and environmental protection. In this study, precursor solution contains polyvinylpyrrolidone (PVP), titanium tetraisopropoxide (TTIP), alcohol, and appropriate templates. The precursor was ejected through a needle under a high voltage electric field and then collected the micro/nano organic-titanium fibers. Following calcination process was adopted to remove the polymer parts. The visible-light-responsive TiO2-XNX mesoporous hollow tubular photocatalysts were characterized by wide angle x-ray diffraction (WAXD), field emission scanning electron microscopy (FE-SEM), isotherm nitrogen sorption measurement, x-ray photoelectron spectroscopy (XPS). The photocatalytic activity of TiO2-XNX mesoporous hollow tubular photocatalysts were evaluated by measuring the degradation of methylene blue (MB) under visible light irradiation. The change of MB concentration was measured by ultraviolet and visible spectroscopy (UV-Vis). The experimental results show that the crystalline phase of TiO2-XNX mesoporous hollow tubular photocatalyst is anatase. The specific surface area of mesoporous hollow tubular photocatalysts using PS, Mineral oil, or silica as templates are 37.5 m2/g, 11~31 m2/g, 150~225 m2/g, respectively. The nitrogen (N) doped of TiO2-XNX mesoporous hollow tubular photocatalyst contains 2% N and the P doped of TiO2-XNX mesoporous hollow tubular photocatalyst contains 0.1% P. The photocatalytic activity was evaluated by measuring the degradation of MB under visible light irradiation. The phosphorus doped photocatalyst show superior photodegradation efficiency than nitrogen doped photocatalyst and commercial P-25.

碩士<br>國立中興大學<br>土壤環境科學系所<br>105<br>According to the investigation report from World Health Organization (WHO) and the United Nations Environment Program (UNEP), with the number of bacteria being ∼139 CFU cm-2 in the countryside and 72,110 CFU cm-2 in an urban environment(Peng, et al. 2008). Among them, some pathogenic strains such as Escherichia coli, Staphylococcus aureus, Klebsiella pneumoniae were caused infectious diseases ; some fungus such as Aspergillus niger and Aspergillus flavus are easy to caused food and environmental pollution (Zhang, et al. 2012). Due to traditional disinfection techniques produce toxic and carcinogenic substances in sterilization and antibacterial processes, such as iodide, derivatives of phenol, dibutyl phthalate, trihalomethanes and haloacetic acids. Therefore, development of new anti-bacteria (fungus) green materials is the top priority issue for today. In this research, homemade N-TiO2, N-T-TiO2, C-TiO2 and Pd-C-TiO2 were carried out photocatalytic deactivated under visible light irradiation. The inactivation reaction parameters including photocatalyst dose, the bacteria initial concentration and light intensity. The bioindicators were Klebsiella pneumoniae and Aspergillus niger. The experimental data were used to simulate the deactivation efficiency of the above-mentioned indicators strain by using the (Chick-Waston model, Modified Hom model, Light Chick-Waston model and Light Modified Hom model). The results showed that when the four photocatalytic materials were 1.0 g L-1 and 0.5%, the light intensity was 7.32 mW cm-2, and the initial bacterial concentrations were 105 CFU mL-1 and 105 spore # mL-1 can effectively make Klebsiella pneumoniae (1440 minutes) and Aspergillus niger (168 hours) reach 99.999% of the antibacterial rate. The antibacterial efficiency of each material on Klebsiella pneumoniae / Aspergillus niger was Pd-C-TiO2> C-TiO2> N-T-TiO2> N-TiO2. Effects of different microbial species on anti-photocatalytic deactivation with these four kinds of photocatalytic materials, Klebsiella pneumoniae (Pd-C-TiO2, 210 min) was lower than that of Aspergillus niger (Pd-C-TiO2, 96 hours). According to the electron micrograph of this study and predecessors studies, it was found that the cell wall of Aspergillus niger was thicker than Klebsiella pneumoniae, so the efficiency of inactivation was lower than that of Klebsiella pneumoniae under the same conditions. Chick-Waston model, Modified Hom model, Light-Chick-Waston model, and Light-Modified Hom model showed the potential to fit the experimental data and k values are regular, if the use of Modified Hom model for Klebsiella pneumoniae and Aspergillus niger simulation operation, showing the two photocatalytic deactivation reaction of the three-phase parameter changes are consistent. The trend of the first stage (buffer period) inactivation rate constant (k1) tends to rise; the second stage (logarithmic period) inactivation rate constant (k2) tends to rise; the third stage (lag phase) inactivation rate Constant (k3) value tends to decline. In this research, SEM, TEM, TXM and AFM were used to investigate the changes of cell surface and morphology in the photocatalytic deactivation of Klebsiella pneumoniae and Aspergillus niger during photocatalytic deactivation of modified titanium dioxide, and the mechanism of photocatalytic deactivation were explored by the release of K+, CoA, MDA, DNA and protein. The results of this research show that the homemade photocatalyst titanium dioxide has a high efficiency of antibacterial activity with the bioindicators such as Klebsiella pneumoniae and Aspergillus niger can reach 99.999% antibacterial rate and no traditional energy consumption, resulting in toxic byproducts and other shortcomings. In the future, these four materials can be widely used in anti-(fungi) and environmental anti-bacterial technology level and a high potential for development.

碩士<br>逢甲大學<br>生醫資訊暨生醫工程碩士學位學程<br>100<br>The goal of this study is aimed at fabrication of titania naopartices by sol-gel process and production of Ag/TiO2 compsoite nanoparticles by depositing Ag nanoparticle onto the surface of TiO2 via the chemical reduction of silver nitrate solution for enhancing the antibacterial capability. In addition, the nitrogen doped TiO2 fine powder was attempeted by gas doping route at elvated temperature to improve the photocatalytic ability of titania powder in the visible range. In the sol-gel process, titanium tetraisopropoxide (TTIP) was used as presurcour in aqueous acetone solution with adding NaOH and HNO3 to adjust the acidity (pH = 3~9) to synthesize TiO2 nanoparticles. At pH = 7, the average size of titania particles was minimized with much marrower size distribution. The crystllainity of titania powder which was calcined at 600oC appeared to be with anatase phase. The size and dispersion behavior of Ag/TiO2 powder was tuned by using different concentration of sliver nitrate (0.5~5.0 mM) and amount if PEG surfactant (0.2~5.0 wt%). The photocatalytic efficiency of sol-gel derived titania powder after calcining at 600oC was 51% under the test of methyl blue solution by UV radiation. The photocatalytic efficiency of Ag/TiO2 nanopowder was incrased to 58% when 0.2 mM PEG surfactant was employed. The Ag/TiO2 composite nanoparticles have much improved photocatalytic efficiency (72%) when higher amount of sliver nitrate was applied (5 mM), as compared to commercially available P25 (Degussa) TiO2 nanoparticles. A gaseous doping method was used to obtain nitrogen containing titania powder to increase its photocatalytic efficiency in the visible range. The pure TiO2 nanoparticles were heat treated in the tube furnace by flowing the nitrogen and ammonia gases to remove oxygen and to thermal decomposition, respectively. Thereby the N-TiO2 powder can be generated by doping nitrogen atoms into the TiO2 lattices to decrease its semiconductor band-gap. The results showed that both commercially available P25 and sol-gel derived TiO2 powders after nitrogen doping had increased photocatalytic efficiency in the visible range by 2~5 times as compared to the undoped TiO2 powders.

碩士<br>國立中興大學<br>環境工程學系所<br>106<br>A visible-light-driven graphitic carbon nitride/reduced graphene oxide/α-Sulfur composite (CNRGOS8) was synthesized as efficient photocatalysts for environmental applications. The photocatalytic reactivity of the fabricated CNRGOS8 was determined by the degradation of Rhodamine B (RhB) and tetracycline (TC). The effects of pH, mixed ratio of catalysts, dosage of photocatalyst were optimized, and the reaction kinetics and reaction pathway were studied. The results indicated the optimized pH values for RhB and TC degradation was 3 and 7, respectively. In addition, no deterioration of the efficiency was found for CNRGOS8 (70:5:25) after 5 cycles of operation. Such a result was indicative of a prolonged lifetime of the CNRGOS8 (70:5:25). With probing by the scavengers, 2-Propanol (·OH capture reagent), benzoquinone (O2•－ capture reagent) and sodium oxalate (h+ capture reagent), the major reactive species were identified as superoxide radicals and hydroxyl radicals. The abundant natural organic matter such as humic acid (HA) oftentimes coexists with the pollutants in the aquatic environment, which may affect the efficiency and alter reaction pathways of photodegradation of the pollutants. An enhanced electron transfer and reactive oxide species production were found for CNRGOS8 (70:5:25) in the presence of humic acid. However, the overall removal efficiency of the pollutants was suppressed due to the competition between CNRGOS8 (70:5:25) and the coexisting HA for the active sites.

碩士<br>東海大學<br>環境科學與工程學系<br>95<br>Metal modified titania nano-photocatalysts were prepared by sol-gel method using inorganic precursor copper(II) nitrate 2.5 hydrate, chrom(III) nitrate nonahydrate and iron(III) nitrate nonahydrate. We expect that this modification can enhance the light absorption in blue spectral region. Photo-degradation of methylene blue under irradiation of blue light (450 nm) was studied. SEM and TEM micrographs show that the size of metal modified TiO2 particles was approximatly 20 nm. XRD results indicate the prevailing existence of high dispersive anatase titania photocatalyst. BET surface area results show that specific surface area of the catalysts is 69.0-83.7 m2/g. As indicated by UV-Vis spectra, an increase in metal content results in greater absorption of blue light. The greatest photocatalytic activity in this study is obtained by using 0.1 at. % Cu-TiO2 catalyst under blue light illumination for 36 hours.

碩士<br>國立清華大學<br>化學工程學系<br>100<br>ZnFe2O4 is a magnetic and visible light response photocatalyst material, but was rarely studied in photocatalytic water splitting for hydrogen production. In this study, we first used ZnFe2O4 aerogels and ZnFe2O4/CdS composites as the photocatalyst for photocatalytic water splitting under visible light irradiation. The high surface area, 3-D connected pore structure, and large porosity are the advantageous for aerogels to serve as the photocatalyst. We prepared ZnFe2O4 aerogels under different annealing conditions and tried to find out the relationship between the hydrogen production rate and annealing condition. In the part of composite material, we utilized the magnetic property of ZnFe2O4 and the compatible energy band structure of ZnFe2O4 and CdS for our photocatalytic water splitting purposes. We also used varius catalyst material analyses to interpret the experimental results. The photocatalytic water splitting reaction of ZnFe2O4 aerogels was carried out in a methanol solution under 400W high pressure Hg light source. The methanol served as the sacrificial agent. Under the full spectrum of radiation, the hydrogen evolution rate of ZnFe2O4 aerogels, calcined at 500 ° C for 10 hours, was 9840μmol / g • hr. The data showed that the rates of hydrogen evolution increased as the crystallinity improved. In our experiments, a co-catalyst, Pt, was loaded via a photodeposition method to give a Pt/ZnFe2O4 aerogels photocatalyst (1 wt %), but it did not show significant improvements in the rate of hydrogen evolution. In the part of visible light irradiation, 1M NaNO2 was circulated through the reactor jacket to filter out the UV light (λ<400 nm). After 6 hours of continuous light irradiation, the hydrogen evolution became saturated. The best performance was achieved by the ZnFe2O4 aerogels calcined at 500 ° C and held for 10 hours, and the hydrogen evolution rate was 7.43μmol/g•hr. Another part of this research focused on the performance of CdS/ZnFe2O4 composite materials in photocatalytic water splitting. In this part, we used a Na2S /Na2SO3 solution as the sacrificial reagent. About 20wt.% of CdS was loaded onto the ZnFe2O4 aerogel. Here, aerogels provided high specific surface area and appropriate pore sizes for loading CdS, leading to 25.8μmol/g•hr in hydrogen evolution rate under visible light irradiation, and showed good stability in the cycle experiment. The photocatalyst of 20wt.% ZnFe2O4 decorated on CdS nanorods were characterized by XRD, BET, XPS, SEM, PL, and TEM. The result proved that ZnFe2O4 was successfully decorated on CdS nanorods, and made the photocatalyst magnetic for easy recycle. The conduction band of ZnFe2O4 is more negative than that of CdS, and thus the electron can move from ZnFe2O4 to CdS for hydrogen reduction. The valence band of ZnFe2O4 is less positive than that of CdS, so that the holes generated in CdS can move to ZnFe2O4 to protect CdS from photocorrosion. In the long term experiment, the ZnFe2O4 decoration not only hampered the photocorrosion of CdS, but also improved the activity of hydrogen evolution. The highest hydrogen production rate of 20wt.% ZnFe2O4 decorating on CdS nanorod was 2811μmol/g•hr.

碩士<br>東海大學<br>環境科學與工程學系<br>96<br>Abstract Metal modified TiO2 catalysts nano-photocatalysts were prepared by sol-gel process using inorganic copper nitrate 2.5 hydrate, chrom nitrate nonahydrate, and iron nitrate nonahydrate, under acidic condition. This modification results in catalysts with enhanced visible light absorbance in blue light region. These catalysts were characterized by the use of UV-vis spectroscopy, BET surface area analyzer, TEM, SEM, and XAS. The SEM and TEM images show that the catalysts particle size is approximately 10─15 nm. The BET surface area of the catalysts is in 77.7─100.5 m2/g range. From XRD results, the pure and modified TiO2 calcined at 500 ◦C are in anatase form. The UV/Vis absorption spectra indicate that the metal modified TiO2 can absorb more visible light in blue region. The XAS results from the metal modified catalysts indicate that the prevailing coppor species is Cu2+ and the iron species is Fe3+. Photocatalytic activity of modified TiO2 catalysts was higher than that of non-modified TiO2 under blue light irradiation. After photocatalytic reaction for 36 hours, the greatest photocatalytic activity in this study is obtained by using 0.1% Cu/TiO2 under blue light illumination. Keywords: Sol-gel method, Photodegradation of methylene blue, Blue light absorption, Metal modified TiO2.