Photocatalysis process

Photocatalysis processes are environmental friendly, heading for sustainable development because their driving force is sunlight, their oxidizing agent is atmospheric molecular oxygen and most photodegradations result in complete mineralization of the DOM without any pollution by risky side-products. 

Table 20. Removal of pollutants using chitosan-ri02 catalyst through adsorption-photocatalysis process. 

Iron-containing boron nitride-based composites have good prospects in photocatalysis processes of deep degradation of dissolved organic matter (DOM) including processes with simultaneous hydrogen release. 

Ti02 is generally one of the most widely used photocatalysts due to its chemical stability, non-toxicity, low cost and high efficiency in the photocatalysis process. But it has many disadvantages, including (i) it is difficult and expensive to... 

Due to the fact that the photocatalyst is typically a non-toxic substance (titanium dioxide in most of the applications) and that no chemical additive is needed, alongside the low energy demand which can be satisfied by the solar radiation, it is evident that an integrated pervaporation-photocatalysis process can absolutely satisfy the requirements of sustainable chemistry. 

Chin S S, Chiang K and Fane A G (2006), The stability of polymeric membranes in a TiOj photocatalysis process , J Membrane Sci, 275,202-211. 

Heterogeneous Ti02 photocatalysis and homogeneous photo-Fenton, are the AOPs for which the solar technologies have been most extensively studied and developed (13). In the last few years, solar photocatalysis processes have shown to be an important alternative for pesticide degradation in the field of AOPs (14, 15) with extended research performed at pilot-plant scale (16, 17). The renewed interest of researchers (18) in the photo-assisted Fenton processes (classic old reactive system, discovered by Fenton (19) in the last century) is today underlined by a significant number of studies devoted to wastewater treatment... 

Until now, there are many references relevant to electron- and energy-transfer processes occurring in photocatalysis. Many books and reviews can be referred. Here, we only emphasis on the unusual property of photocatalysis processes different from common catalysis processes whether heterogeneous system or homogeneous system. 

A photocatalyst is a semiconducting substance which can be chemically activated by light radiation that results in oxidation-reduction (redox) reaction, i.e., it has a photocatalysis action or photoactivity. As illustrated in Fig. 1.1 [16, p. 147 24, p. 10], photocatalysis is similar to the photosynthesis in plants in the mechanism, in which chlorophyl acts as a catalyst to produce oxygen from carbon dioxide and water. Chlorophyl is a very powerful photocatalysL The photocatalyst in the photocatalysis process corresponds to the chlorophyl in the photosynthesis process. 

There are three steps in the photocatalysis process. Step 1 Photon with energy above 1.23 eV K < -1000 nm) is absorbed Step 2 photoexcited electrons and holes separate and migrate to the surface as shown in Figure 13.8b and Step 3 the adsorbed species (water) is reduced and oxidized by the electrons and holes. 

Fig. 11.7 Important processes in the surface photocatalysis processes photoexcitation of electron-hole pair, charge transfer processes, bulk and surface recombination processes, and electron- and charge-induced chemistry at surfaces (Reproduced with permission from Ref [27]. Copyright 1995 American Chemical Society)...

The mechanism for a whole photocatalysis process is usually quite complicated. In this section, we will describe recent studies of detailed photocatalytic reactions of two important molecules on various Ti02 surfaces oxygen (electron scavenger) and methanol (hole scavenger), which are representative photooxidation and photoreduction reactions oti Ti02. 

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