Photomineralization process

Up to now hundreds of organic and inorganic compounds have been successfully degraded in the photomineralization process [60,65], Photodegradation processes may be useful for either water or air purification. There are several reports also on photocatalyzed removal of selected inorganic ions such as CN [66], NO3... 

Several years ago, it was pointed out that both O2 and H2O are essential species in the photomineralization process of 4-chlorophenol in the presence of irradiated Ti02 [23]. No photodegradation occurs in the absence of either O2 or H2O, or both [23,24]. Adsorbed oxygen traps e (eqn.8) thereby delaying electron/hole recombination (eq.2). 

While the relative importance of direct and sensitized photolysis has to be assessed case by case, it is very likely that these two processes play a substantial role in phototransformation of most organic solutes in surface waters, together with the photolysis of species that can act as ligands for Fe(III) (e.g. carboxylates). Indeed, the photolysis of Fe(III)-carboxylate complexes plays a major role in natural DOM photomineralization [75-78],... 

Figure 1. Conceptual diagram showing the role of CDOM in regulating solar radiation and temperature regimes in aquatic ecosystems, as well as the processes by which UV alters CDOM biolability, photolability, and photomineralization. The width of the arrows approximates the strength of the effects.

PROBABLE FATE photolysis reported in experiments, but environmental significance is unknown, aqueous photolytic half-life 4 days, release to the environment can decrease due to photolysis and reaction with hydroxyl radicals oxidation too slow to be an important process, photooxidation half-life in water 84.5 days, in air 5.1-51.4 days hydrolysis not an important process first-order hydrolytic half-life >8x10 yrs volatilization not an important process, may contribute to losses at the surface of the soil sorption high potential for sorption by organic materials, rate is unknown biological processes biodegradation very important, but exact rate uncertain due to variations between data photomineralization may contribute to losses at the surface of the soil... 

TABLE 19.1 Primary Processes and Associated Characteristic Time Domains in the Ti02-Sensitized Photomineralization of Organic Pollutants... 

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