Photocatalytic activity

Keywords Antibacterial Antimicrobial Bacteria Biocide Contact-active Light-activated Photocatalytic Release Self-polishing Surface... 

The gel produced from this reaction is coated on an inert substrate, such as glass or stainless steel, and the sample is heated to 500 EC for 1 h in air. The hlms produced are characterized by thickness, grain size, pore size, surface area, and photocatalytic activity. Photocatalytic activity is determined by measuring the rate of discoloring of aqueous solution of methyl organge, a typical organic dye. 

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. 

A. Di Paola, M. Bellardita, R. Ceccato, L. Palmisano, F. Parrino, 2009, Highly active photocatalytic Ti02 powders obtained by thermohydrolysis of TiCU in water, J. Phys. Chem. C, 113,34, 15166-15174. 

Grandcolas M, Cottineau T, Louvet A, Keller N, Keller V (2013) Solar light-activated photocatalytic degradation of gas phase diethylsulfide on WOs-modified Ti02 nanotubes. Appl Catal Environ 138 128-140... 

Tobaldi D, Pullar R, Skapin AS, Seabra M, Labrincha J (2014) Visible light activated photocatalytic behaviour of rare earth modified commercial Ti02. Mater Res Bull 50 183-190... 

A debate centers on the mechanistic details of heterogeneous photocatalysis. The goal is to improve the photocatalytic activity of Ti02, and understand the role and importance of mineralisation by (/) free versus surface bound oxidising radicals, OH, and (2) by surface OH radicals versus direct hole oxidation. 

The photochemistry of transition metal 1,3-diketone chelate complexes has been known for some time [30,31], and their photophysical and photochemical properties and photocatalytic activity in different chemical reactions were reviewed in 1990 by Marciniak and Buono—Core [32]. Further discussion on the photochemistry of meta] chelate will not take place here since this subject is out of the scope of this chapter. 

It was observed leldivdy early that chonically labile compounds - such as vitamins, carotenes - decomixise, either on application to the TLC layer or during the TLC separation that follows. Ibis phenomenon was primarily ascribed to the presence of oxygen (oxidation) and exposure to light (photochemical reaction) in the presence of the active sorbents, which were assumed to exert a catalytic effect (photocatalytic reaction). 

The advantages of microreactors, for example, well-defined control of the gas-liquid distributions, also hold for photocatalytic conversions. Furthermore, the distance between the light source and the catalyst is small, with the catalyst immobilized on the walls of the microchannels. It was demonstrated for the photodegradation of 4-chlorophenol in a microreactor that the reaction was truly kinetically controlled, and performed with high efficiency [32]. The latter was explained by the illuminated area, which exceeds conventional reactor types by a factor of 4-400, depending on the reactor type. Even further reduction of the distance between the light source and the catalytically active site might be possible by the use of electroluminescent materials [19]. The benefits of this concept have still to be proven. 

Table 1 Surface area, band gap energies and photocatalytic activities for H2 evolution from an electrolsde solution over single CdS and CdS-based composite photocatalysts.

Hydrothermal synthesis of titanium dioxides using acidic and basic peptizing agents and their photocatalytic activity on the decomposition of orange II... 

Where C is initial concentration of the orange II and A is a rate constant related to the reaction properties of the solute which depends on the reaction conditions, such as reaction temperature, pH of solution. The photocatalytic activity increases with an increase in this value. 

Table 1. Physical properties of nanosized TiOj powders prepared at different HNO3 and TENOH concentration and their photocatalytic activity...

We have developed a compact photocatalytic reactor [1], which enables efficient decomposition of organic carbons in a gas or a liquid phase, incorporating a flexible and light-dispersive wire-net coated with titanium dioxide. Ethylene was selected as a model compound which would rot plants in sealed space when emitted. Effects of the titanium dioxide loading, the ethylene concentration, and the humidity were examined in batches. Kinetic analysis elucidated that the surface reaction of adsorbed ethylene could be regarded as a controlling step under the experimental conditions studied, assuming the competitive adsorption of ethylene and water molecules on the same active site. 

The photocatalytic activity of 20mesh wire-net photocatalyst was observed to be nearly equal to that of 350mesh one under the same amount of titanium dioxide loading (1.88 g). 

Kinetic analysis based on the Langmuir-Hinshelwood model was performed on the assumption that ethylene and water vapor molecules were adsorbed on the same active site competitively [2]. We assumed then that overall photocatalytic decomposition rate was controlled by the surface reaction of adsorbed ethylene. Under the water vapor concentration from 10,200 to 28,300ppm, and the ethylene concentration from 30 to 100 ppm, the reaction rate equation can be represented by Eq.(l), based on the fitting procedure of 1/r vs. 1/ Ccm ... 

In the presence of H2O2, Ti02/Cr-Ti-MCM-41 showed a marked increase in photocatalytic activity for decomposition of 4-NP over Ti02/Cr-Ti-MCM-41 in visible light. H2O2 increases the reaction rate by the promotion of adsorption of reactant and the removing of surface-trapped electrons. 

Recently, it is reported that Xi02 particles with metal deposition on the surface is more active than pure Ti02 for photocatalytic reactions in aqueous solution because the deposited metal provides reduction sites which in turn increase the efficiency of the transport of photogenerated electrons (e ) in the conduction band to the external sjistem, and decrease the recombination with positive hole (h ) in the balance band of Xi02, i.e., less defects acting as the recombination center[l,2,3]. Xhe catalytic converter contains precious metals, mainly platinum less than 1 wt%, partially, Pd, Re, Rh, etc. on cordierite supporter. Xhus, in this study, solutions leached out from wasted catalytic converter of automobile were used for precious metallization source of the catalyst. Xhe XiOa were prepared with two different methods i.e., hydrothermal method and a sol-gel method. Xhe prepared titanium oxide and commercial P-25 catalyst (Deagussa) were metallized with leached solution from wasted catalytic converter or pure H2PtCl6 solution for modification of photocatalysts. Xhey were characterized by UV-DRS, BEX surface area analyzer, and XRD[4]. 

The photocatalytic reactivity for TCE decomposition was increased by platinization and the photocatalytic activity of the catalysts prepared with leached solution fi-om wasted automobile catalyst was similar to that of the catalysts modified with H2PtCl6. 

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