Reactivity of Inorganic Radicals and Excited Triplet States in Colloidal Silica Suspensions.

ARCE, VALERIA; CAREGNATO, PAULA; GONZALEZ, MÓNICA C.; MÁRTIRE DANIEL O.

Series: Nanotechnology Science and Technology, Chemical Engineering Methods and Technology.

Nova Publishers

Lugar: New York; Año: 2011; p. 39 - 80

Aquatic photochemistry studies the degradation of contaminants induced by light (either terrestrial sunlight or artificial light used in engineered water treatment systems). In addition to the ?direct photolysis? or ?direct phototransformation? route there exist a variety of photochemical reactions involving chromophores already present in natural waters and producing reactive species that initiate the degradation of the target contaminant (?indirect phototransformation?). Since the main absorber of light in natural waters is colored dissolved natural organic matter (CDOM), the excited triplet states of CDOM are involved in the indirect phototransformation of contaminants. However, irradiation of CDOM leads to the formation of other species, such as singlet molecular oxygen, solvated electrons, hydrogen peroxide, and hydroxyl radicals among others. Most of these species are able to initiate chemical reactions in which undesirable organic components are attacked and ultimately destroyed, thus providing a mechanism for self-cleansing of the water sources. Silica is a ubiquitous material in the environment, which is present in great amounts in natural waters. This material is an excellent sorbent of contaminants, as well as reactive species involved in their degradation. Thus, it is relevant to know the mechanisms of the reactions that take place at the silica/water interfaces. Because colloidal silica has a very high specific surface area and is optically transparent in the in the near-infrared, visible and ultraviolet regions, it is very appropriate for investigating interfacial reaction kinetics involving photochemically generated species. This chapter reviews recent research concerned with the kinetic behavior of two kinds of reactive species in colloidal silica suspensions. On one hand, excited triplet states, mainly those of benzophenone, and on the other hand inorganic radicals, such as SO4.-, Cl., Cl2.-, HPO4.-, (SCN)2.-.