Photocatalysis Ppt Download UPD
Edilio Jetlife
The earliest mention came in 1911, when German chemist Dr. Alexander Eibner integrated the concept in his research of the illumination of zinc oxide (ZnO) on the bleaching of the dark blue pigment, Prussian blue.[2][3] Around this time, Bruner and Kozak published an article discussing the deterioration of oxalic acid in the presence of uranyl salts under illumination,[3][4] while in 1913, Landau published an article explaining the phenomenon of photocatalysis. Their contributions led to the development of actinometric measurements, measurements that provide the basis of determining photon flux in photochemical reactions.[3][5] After a hiatus, in 1921, Baly et al. used ferric hydroxides and colloidal uranium salts as catalysts for the creation of formaldehyde under visible light.[3][6]
In 1938 Doodeve and Kitchener discovered that TiO
2 , a highly-stable and non-toxic oxide, in the presence of oxygen could act as a photosensitizer for bleaching dyes, as ultraviolet light absorbed by TiO
2 led to the production of active oxygen species on its surface, resulting in the blotching of organic chemicals via photooxidation. This was the first observation of the fundamental characteristics of heterogeneous photocatalysis.[3][7]
In homogeneous photocatalysis, the reactants and the photocatalysts exist in the same phase. The process by which the atmosphere self-cleans and removes large organic compounds is a gas phase homogenous photocatalysis reaction.[24] The ozone process is often referenced when developing many photocatalysts:
Micro-sized ZnO tetrapodal particles added to pilot paper production.[29] The most common are one-dimensional nanostructures, such as nanorods, nanotubes, nanofibers, nanowires, but also nanoplates, nanosheets, nanospheres, tetrapods. ZnO is strongly oxidative, chemically stabile, with enhanced photocatalytic activity, and has a large free-exciton binding energy. It is non-toxic, abundant, biocompatible, biodegradable, environmentally friendly, low cost, and compatible with simple chemical synthesis. ZnO faces limits to its widespread use in photocatalysis under solar radiation. Several approaches have been suggested to overcome this limitation, including doping for reducing the band gap and improving charge carrier separation.[31]
Elucidating the origin of light-induced reaction rate enhancement in plasmonic photocatalysis is very challenging. Now, bimetallic supercrystals are reported to boost photocatalytic hydrogen evolution from formic acid with the sole aid of intensified electric fields.
Contrary to photocatalysis, the use of photochemical energy solely to initiate reactions is underexplored. Here, the authors demonstrate light initiated synthesis of functionalized organosilanols, silanediols, and polymeric siloxanol under ambient reaction conditions.
There has been a considerable amount of research in the development of sustainable water treatment techniques capable of improving the quality of water. Unavailability of drinkable water is a crucial issue especially in regions where conventional drinking water treatment systems fail to eradicate aquatic pathogens, toxic metal ions and industrial waste. The research and development in this area have given rise to a new class of processes called advanced oxidation processes, particularly in the form of heterogeneous photocatalysis, which converts photon energy into chemical energy. Advances in nanotechnology have improved the ability to develop and specifically tailor the properties of photocatalytic materials used in this area. This paper discusses many of those photocatalytic nanomaterials, both metal-based and metal-free, which have been studied for water and waste water purification and treatment in recent years. It also discusses the design and performance of the recently studied photocatalytic reactors, along with the recent advancements in the visible-light photocatalysis. Additionally, the effects of the fundamental parameters such as temperature, pH, catalyst-loading and reaction time have also been reviewed. Moreover, different techniques that can increase the photocatalytic efficiency as well as recyclability have been systematically presented, followed by a discussion on the photocatalytic treatment of actual wastewater samples and the future challenges associated with it.
Photocatalysis is generally referred to as the acceleration of a photoreaction by the presence of a semiconductor catalyst such as titanium dioxide (TiO2) or zinc oxide (ZnO). Photocatalytic materials can be prepared by using various methods such as a sol-gel process, solution processing, microwave-assisted synthesis, electrochemical, hydrothermal and solvothermal synthesis. These materials can be applied to a range of surfaces as they possess many desirable properties such as decontamination, disinfection and self-cleaning. Improvements in the properties of photocatalysts can be achieved by doping the semiconductor with both metal and non-metal species. Various mechanisms involving photocatalysis are discussed in detail. UV, solar and visible light-induced photocatalysis and its applications in the treatment of water in general and for contaminants of emerging concerns in particular are also described. Additionally, applications of nanotubular TiO2-based materials for water and air purification are detailed with a number of recent examples. Discussion is also provided on materials such as spinel ferrites that possess a narrow band gap and serve as magnetically separable photocatalysts. Moreover, a number of recent examples regarding approaches to improve the photocatalytic process by using metal and non-metal-doped TiO2, materials with metal/inorganic hetero-structures, nano-heterojunctions, graphitic carbon nitride, and graphene composites are discussed. These novel photocatalytic materials offer excellent potential for various future environmental applications. However, extensive research will be required to address the stability and robustness of these catalysts under various environmental conditions. It is concluded that the rapid growth in the discoveries of novel photocatalytic materials offers great promise for the future of advanced oxidation processes (AOPs).
NASA has explored the beneficial applications of a process called photocatalysis for use both in space and on Earth. Photocatalysis is essentially the opposite of photosynthesis, the process used by plants to create energy. In photocatalysis, light energizes a mineral, triggering chemical reactions that result in the breakdown of organic matter at the molecular level, producing primarily carbon dioxide and water as byproducts.
NASA has studied the benefits of photocatalysis for purifying water during space missions, and plant growth chambers featuring photocatalytic scrubbers have flown on multiple NASA missions, using the photocatalytic process to preserve the space-grown crops by eliminating the rot-inducing chemical ethylene. (The scrubber technology resulted in a unique air purifier, featured in Spinoff 2009, now preserving produce and sanitizing operating rooms on Earth.)
Photocatalysis has recently become a common word and various products using photocatalytic functions have been commercialized. Among many candidates for photocatalysts, TiO2 is almost the only material suitable for industrial use at present and also probably in the future. This is because TiO2 has the most efficient photoactivity, the highest stability and the lowest cost. More significantly, it has been used as a white pigment from ancient times, and thus, its safety to humans and the environment is guaranteed by history. There are two types of photochemical reaction proceeding on a TiO2 surface when irradiated with ultraviolet light. One includes the photo-induced redox reactions of adsorbed substances, and the other is the photo-induced hydrophilic conversion of TiO2 itself. The former type has been known since the early part of the 20th century, but the latter was found only at the end of the century. The combination of these two functions has opened up various novel applications of TiO2, particularly in the field of building materials. Here, we review the progress of the scientific research on TiO2 photocatalysis as well as its industrial applications, and describe future prospects of this field mainly based on the present authors' work.
Since Matsunaga et al. first reported the inactivation of bacteria using TiO2 photocatalysis in 1985 [9] there have been more than 1000 research papers published in the area. The effectiveness of photocatalysis against microorganisms, including bacteria (cells [10,11], spores [12] and biofilms [11]), viruses [13], protozoa [14], fungi [15] and algae [16] has been investigated, and this work has been reviewed by McCullagh et al. [17], Malato et al. [8], and Robertson et al. [18]. In general photocatalytic disinfection in water requires minutes or tens of minutes of direct UVA exposure (using TiO2 as the photocatalyst) and it is considered to be quite a slow microbial inactivation process, as compared to e.g., UVC disinfection (seconds of direct exposure). The mechanism of photocatalytic inactivation is different from that of UVC disinfection. Whilst the majority of papers published in the area focus on the assessment of novel materials, new reactor systems or the effect of experimental parameters on the rate of inactivation, a significant number of studies have specifically investigated ROS interaction with the biological structures within microorganisms in an attempt to elucidate the mechanism resulting in the loss of organism viability. A review of the mechanisms involved in photocatalytic disinfection was conducted by Dalrymple et al. [19], however, the exact sequence of events leading to loss of viability is not completely understood. Continued insight into the mechanisms of attack of ROS on microorganisms will allow researchers to optimize materials and reactor design to improve the rate and efficacy of photocatalytic disinfection [20].
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