Influence of water temperature on the photocatalytic activity of titanium dioxide (original) (raw)
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Mechanism of the OH Radical Generation in Photocatalysis with TiO2 of Different Crystalline Types
Journal of Physical Chemistry C, 2014
The difference in the OH radical generation through photocatalytic reaction with distinct crystalline types of TiO 2 in aqueous suspension was explored by means of a fluorescence probe method. By employing two kinds of probe molecules with different adsorptivities, that is, coumarin and coumarin-3-carboxylic acid, we could detect OH radicals located near the TiO 2 surface and those in the bulk solution individually. The amount of the OH radicals near the TiO 2 surface was much larger than that in the solution, which diffused from the TiO 2 surface to the bulk solution. Rutile TiO 2 produced a much smaller amount of OH radicals as compared to anatase and anatase-contained TiO 2. On the addition of H 2 O 2 , the OH radical generation for pure anatase TiO 2 decreased but increased for rutile and rutile-contained TiO 2. This difference could be explained as follows: at the surface of anatase TiO 2 , trapped holes become adsorbed OH radicals, while at the rutile surface, Ti-peroxo (Ti-OO-Ti) produced by the combination of two trapped holes which correspond to the adsorbed H 2 O 2 , could work as a catalyst for the OH radical generation from water.
Photocatalysis of Titanium Dioxide for Water Disinfection: Challenges and Future Perspectives
International Journal of Photochemistry
The performance of metal oxides such as titanium dioxide (TiO2), in the conversion of solar energy into chemical energy, is determined by semiconducting properties. The conversion process is closely related to the light-induced reactivity between oxide semiconductors and water, which may lead to partial water oxidation and consequently water disinfection. Key performance-related properties are considered here, including light absorption, light-induced ionisation over the band gap, charge separation, charge transport, charge transfer, and the chemical reactions taking place at anodic and cathodic sites. Optimisation of these interconnected performance-related properties is discussed, along with the photocatalytic application in water disinfection.
Photocatalytic Water Treatment by Titanium Dioxide: Recent Updates
Photocatalytic water treatment using nanocrystalline titanium dioxide (NTO) is a well-known advanced oxidation process (AOP) for environmental remediation. With the in situ generation of electron-hole pairs upon irradiation with light, NTO can mineralize a wide range of organic compounds into harmless end products such as carbon dioxide, water, and inorganic ions. Photocatalytic degradation kinetics of pollutants by NTO is a topic of debate and the mostly reporting Langmuir-Hinshelwood kinetics must accompanied with proper experimental evidences. Different NTO morphologies or surface treatments on NTO can increase the photocatalytic efficiency in degradation reactions. Wisely designed photocatalytic reactors can decrease energy consumption or can avoid post-separation stages in photocatalytic water treatment processes. Doping NTO with metals or non-metals can reduce the band gap of the doped catalyst, enabling light absorption in the visible region. Coupling NTO photocatalysis with other water-treatment technologies can be more beneficial, especially in large-scale treatments. This review describes recent developments in the field of photocatalytic water treatment using NTO.
Revista Facultad …, 2011
In this work, TiO 2 photocatalysts were synthesized using a conventional sol-gel and hydrothermal synthesis methods with steam pressure treatment. Photocatalysts were characterized by X-ray diffraction (XRD), diffuse reflectance spectra (DRS) and N 2 adsorption-desorption. The photoactivity of the samples was analyzed towards the photooxidation of the azo dye Orange II (Or-II) and phenol using different illumination setups to compare the activity features of photocatalysts. The effect of the synthesis variables such as the synthesis route, water/alcoxide and alcohol/alcoxide ratios, as well as the alcohol type was analyzed. TiO 2 photocatalysts obtained by hydrothermal synthesis have a better photoactivity than the particles synthesized by the chosen sol-gel route, reaching the Or-II degradation photoactivity of the commercial TiO 2 P25. On the other hand, the water/alcoxide ratio and alcohol type have a marked effect on the photoactivity of the hydrothermal synthesized TiO 2 , whereas the alcohol/alcoxide ratio does not have a relevant effect on the Or-II degradation photoactivity.
A review on the visible light active titanium dioxide photocatalysts for environmental applications
Fujishima and Honda (1972) demonstrated the potential of titanium dioxide (TiO2) semiconductor materials to split water into hydrogen and oxygen in a photo-electrochemical cell. Their work triggered the development of semiconductor photocatalysis for a wide range of environmental and energy applications. One of the most significant scientific and commercial advances to date has been the development of visible light active (VLA) TiO2 photocatalytic materials. In this review, a background on TiO2 structure, properties and electronic properties in photocatalysis is presented. The development of different strategies to modify TiO2 for the utilization of visible light, including non metal and/or metal doping, dye sensitization and coupling semiconductors are discussed. Emphasis is given to the origin of visible light absorption and the reactive oxygen species generated, deduced by physicochemical and photoelectrochemical methods. Various applications of VLA TiO2, in terms of environmental remediation and in particular water treatment, disinfection and air purification, are illustrated. Comprehensive studies on the photocatalytic degradation of contaminants of emerging concern, including endocrine disrupting compounds, pharmaceuticals, pesticides, cyanotoxins and volatile organic compounds, with VLA TiO2 are discussed and compared to conventional UV-activated TiO2 nanomaterials. Recent advances in bacterial disinfection using VLA TiO2 are also reviewed. Issues concerning test protocols for real visible light activity and photocatalytic efficiencies with different light sources have been highlighted.
Rev. Fac. Ing. Univ. Antioquia, 2011
In this work, TiO 2 photocatalysts were synthesized using a conventional sol-gel and hydrothermal synthesis methods with steam pressure treatment. Photocatalysts were characterized by X-ray diffraction (XRD), diffuse reflectance spectra (DRS) and N 2 adsorption-desorption. The photoactivity of the samples was analyzed towards the photooxidation of the azo dye Orange II (Or-II) and phenol using different illumination setups to compare the activity features of photocatalysts. The effect of the synthesis variables such as the synthesis route, water/alcoxide and alcohol/alcoxide ratios, as well as the alcohol type was analyzed. TiO 2 photocatalysts obtained by hydrothermal synthesis have a better photoactivity than the particles synthesized by the chosen sol-gel route, reaching the Or-II degradation photoactivity of the commercial TiO 2 P25. On the other hand, the water/alcoxide ratio and alcohol type have a marked effect on the photoactivity of the hydrothermal synthesized TiO 2 , whereas the alcohol/alcoxide ratio does not have a relevant effect on the Or-II degradation photoactivity.-Keywords: TiO 2 , photocatalytic oxidation, sol-gel, hydrothermal synthesis, orange II Resumen En este trabajo, se sintetizó TiO 2 usando los métodos sol-gel convencional y el hidrotérmico con un tratamiento a presión de vapor. Los fotocatalizadores se caracterizaron por difracción de rayos X (DRX), espectroscopía de reflectancia difusa (ERD) y con base en las isotermas de adsorción-desorción de N 2 se hizo el análisis textural. La fotoactividad de las muestras de TiO 2 se evaluó frente a la degradación del colorante Orange II (Or-II) y del fenol bajo irradiación con diferentes sistemas de iluminación. Se analizó el efecto de las variables de síntesis del TiO 2, tales como el método de síntesis, las relaciones agua/alcóxido, alcohol/alcóxido y el tipo de alcohol, sobre su fotoactividad. Los resultados muestran que el TiO 2 sintetizado por el método hidrotérmico alcanzó la fotoactividad del TiO 2 de referencia Degussa P25, mientras que el proceso sol-gel escogido condujo a un TiO 2 menos activo. Adicionalmente, se encontró que la relación agua/alcóxido y el tipo de alcohol tienen un marcado efecto sobre la degradación del Or-II mientras que la relación alcohol/alcóxido no presentó un efecto significativo. -Palabras clave: TiO 2 , oxidación fotocatalítica, síntesis hidrotérmica, síntesis sol-gel, orange II
J Mod Green Energy , 2024
The term "photocatalysis" has recently gained high popularity, and various products using photocatalytic functions have been commercialized. Of all the materials that may be used as photocatalysts, titanium dioxide (TiO 2) is virtually the only one that is now and most likely will remain appropriate for industrial application. Water and air purification systems, sterilization, hydrogen evolution, self-cleaning surfaces, and photoelectrochemical conversion are just a few of the products and applications in the environmental and energy domains that make extensive use of TiO 2 photocatalysis. This is due to the fact that TiO 2 has the lowest cost, most stability, and most effective photoactivity. Furthermore, history attests to its safety for both people and the environment because it has been used as a white pigment since antiquity. This review discusses some important aspects and issues concerning different synthesis methods and their influence on the structure and properties of TiO 2 , as well as the concept of photocatalysis based on it as a promising biocompatible functional material that has been widely used in recent years. The advantages of TiO 2 applications in various fields of science and technology are discussed, including environmental protection, photocatalysis including self-cleaning surfaces, water and air purification systems, hydrogen liberation, photovoltaic energy, cancer diagnosis and therapy, coatings and dental products, etc. Information on the structure and properties of TiO 2 phases is presented, as well as modern methods of synthesizing functional materials based on it. A detailed review of the basic principles of TiO 2 photocatalysis is then given, with a brief introduction to the modern concept of TiO 2 photocatalysis. Recent advances in the fundamental understanding of TiO 2 photocatalysis at the atomic-molecular level are highlighted, and advances in TiO 2 photocatalysis from the perspective of design and engineering of new materials are discussed. The challenges and prospects of TiO 2 photocatalysis are briefly discussed.
Modified Titanium Dioxide for Photocatalytic Applications
Photocatalysts - Applications and Attributes [Working Title]
Titanium dioxide (TiO 2 ) has been widely used as a photocatalyst in many environmental and energy applications due to its efficient photoactivity, high stability, low cost, and safety to the environment and humans. However, its large band gap energy, ca. 3.2 eV limits its absorption of solar radiation to the UV light range which accounts for only about 5% of the solar spectrum. Furthermore, the photocatalytic activity of TiO 2 is also limited by the rapid recombination of the photogenerated electron-hole pairs. When used in water treatment applications, TiO 2 has a poor affinity toward organic pollutants, especially hydrophobic organic pollutants. Several strategies have been employed to reduce its band gap energy, its electron-hole recombination rates as well as enhance its absorption of organic pollutants. In this chapter, we review some of the most recent works that have employed the doping, decoration, and structural modification of TiO 2 particles for applications in photocatalysis. Additionally, we discuss the effectiveness of these dopants and/or modifiers in enhancing TiO 2 photoactivity as well as some perspective on the future of TiO 2 photocatalysis.
Materials Science in Semiconductor Processing, 2016
During recent years there has been a growing tendency to study new photocatalysts for water and air treatment. To large extent this endeavor is part of a more general effort searching for efficient conversion of solar energy into electricity and into chemical energy stored in hydrogen. Yet, despite the so many man-years invested in this search titanium dioxide is still considered to be the photocatalyst of choice. This paper discusses the current status of research with non-TiO 2 photocatalysts for water decontamination. It suggests that developing of new, highly photoactive photocatalysts for water and air treatment is hindered by a combination of reasons, reflecting the tendency of the scientific community to "search under the streetlight". This includes the overemphasis on bandgap values while overlooking the importance of band positions, the use of dyes as model contaminants under visible light, the ignoring of the importance of transient phenomena, the under-emphasis of the role of surface area and the lack of implementation of theoretical tools in the developing of new photocatalysts. Stepping out of the comfort zone is not only possible but essential.