Environmental self-cleaning

The crucial meanings of photosensitization for environmental self-cleaning processes and conversion of solar energy into a useful one are discussed in Chapters 9 (section 9.4) and 21 (section 21.4) [113-124]. 

Ciesla P, Mytych P, Kocot P, Stasicka Z. Role of iron and chromium complexes in environmental self-cleaning processes. Separation Sci Technol 2007 42 1651-66. 

Not only transition metal ions and complexes are active in the environmental self-cleaning, but also naturally occurring N02 and NO3 ions have recently been reported to contribute to the photodegradation of pesticides [13]. 

The role of photocatalysis by transition metal complexes in the environment is reviewed, and its influence on composition of the environmental compartments, transport between them, and activation of the environmental self-cleaning behavior is characterized. In description of atmospheric processes, the attention is paid to coordination compounds as photocatalysts of the transfer and redox reactions of nitrogen oxides. In the case of hydrosphere and soils, various mechanisms of organic pollutant photodegradations are presented in which the iron, copper, and chromium complexes play... 

The role of photochemistry in nature is difficult to overestimate especially when we consider conversion of solar energy into the chemical energy in natural photosynthesis or ozone production, which protects the Earth from hazardous UV radiation. Much less is known about the role of sunlight in environmental self-cleaning processes. 

Mor, G.K., Varghese, O.K., Pishko, M.V. and Grimes, C.A., A room-temperature Ti02-nanotube hydrogen sensor able to self-clean photoactively from environmental contamination, Journal of Materials Research, 19(2), 628, 2004. 

Already, a number of studies that have been carried out have demonstrated the effectiveness of these functions, oxidative decomposition and high hydrophilicity, in applications involving building materials. This approach promises to make both indoor and outdoor environmental cleaning possible, with antibacterial, stain-resistant, self-cleaning, and deodorizing functions. 

The most common sacrificial electron acceptor in the environment is molecular oxygen, whereas the main sacrificial donors are organic compounds. In consequence, the self-cleaning processes consist in oxidation of organic pollutants by molecular oxygen in its triplet ground state the reactions are driven by energy from solar radiation. In nature, many different photoinitiators or photosensitizers are reactive, but the most common environmental photosensitizers include hiunic substances (HS), whereas the best photoinitiators are transition metal complexes. 

The self-cleaning mechanisms by photocatalysis and photosensitization apply also to organic matter included in microorganisms, thus it can also lead to environmental self-disinfection. This is especially expected in the vicinity of a semiconductor (especially Ti02) and/or iron deposits, which are responsible for solar photogeneration of reactive oxygen substances capable of water disinfection (272-275). 

Obtaining insight into charge transfer processes is important in order to improve the photoconversion efficiencies in semiconductor-based nanoassemblies. The principles and mechanism of photocatalytic reactions in advanced oxidation processes can be found in earlier review articles [40-42]. Technological advances in this area have already led to the product development for a variety of day-to-day operations. Commercialization of products such as self-cleaning glass, disinfectant tiles and filters for air purification demonstrate the initial success of nanosystems for environmental applications [43]. 

The cements containing active photocatalytic titania nanoparticles have widespread applications to create environmentally clean surfaces. These applications include self-cleaning surfaces, anti-soiling, depollution of VOCs and NOx contaminants and antifungal/microbial activities [521-528]. The relevant photocatalytic processes may occur both at the air-solid interface and at the liquid-solid interface. 

Immobilization of NS-Ti02 on metallic materials such as stainless steel and aluminium plates opens up many new potential uses, because of their mechanical robustness, corrosion resistance, strength and shape-forming properties. These include architectural self-cleaning applications, antimicrobial coatings and many environmental applications including water and air purification [4, 5, 531] (see Tables 15-17). In this section, we describe the immobilization of NS-Ti02 on metallic materials as well as metal oxide substrates. 

Nanosheets, Nanofibers, NS-Ti02, Sol-gel process. Nanoclays, Doped-Ti02, Hydrothermal process. Photocatalysis, Electrocatalysis, Solar cell. Lithium batteries. Antibacterial surfaces. Self-cleaning surfaces, Photocatalytic cancer treatment, H2 production. Environmental remediation. Immobilized 7702. 

Where the coating itself does not provide all the desired properties, top coats or top finishes will be applied as a final environmental barrier, providing UV stability, durability, inertness and self-cleaning attributes. Top finish choices include acrylics, acryUcs/polyurethanes and PVF films. 

The top-coats are responsible for the durability and resistance to water and chemical impacts from the environment. Mainly acrylic and fiuori-nated polymers are used for top-coats on various base coats (PVC, PUR, PTFE, silicone rubber, etc.) to enhance resistance to soiling and ageing. Certain additives for UV protection can be added. Due to its self-cleaning non-adhesive surface the top-coat is often hard and brittle. On PVC coatings the top-coat gives not only protection against environmental infiuences but also a barrier against emission of plasticizer out of the PVC. 

Mor GK, Carvalho MA, Varghese OK, Pishko MV, Grimes CA (2004) A room-temperature TiOj-nanotube hydrogen sensor able to self-clean photoactively from environmental contamination. J Mater Res 19 628-634 Morio M, Hyodo T, Shimizu Y, Egashira M (2009) Effect of macrostructural control of an auxiliary layer on the CO sensing properties of NASlCON-based gas sensors. Sens Actuators B Chem 139 563-569 Nam CY, Tham D, Fischer JE (2005) Disorder effects in focused-ion-beam-deposited Pt contacts on GaN nanowires. Nano Lett 5 2029-2033... 

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