ChemInform Abstract: Advances in Catalytic Oxidation of Organic Pollutants — Prospects for Thorough Mineralization by Natural Clay Catalysts.

Abstract

Abstract This review is devoted to oxidative water treatments, with emphasis on catalytic ozonation. The approach tackled herein resides in exposing a wide variety of oxidative treatments attempts as a basis for summarizing the main findings that allow envisaging improvements aiming towards total mineralization of organic pollutants. Comparison between specific operating conditions for specific pollutant-catalyst-oxidizing systems is quite difficult, and is not targeted in the present work. However, when deeply and judiciously analyzed, such a comparison allows demonstrating that, except for some works, most of these attempts seldom took into accounts basic requirements such as the parameter interactions, the role of cation mobility around a solid surface, if any, the multiple pollutant-catalyst-oxidizing species interactions and the significant contribution of adsorption, etc. Otherwise, how to explain that many experiments are still conducted with unsuitable catalysts under totally inadequate operating conditions? A better understanding of the essential requirements for a catalyst to achieve total mineralization of any organic molecules is the main objective of this work. The data summarized herein allow devoting a special interest to ozone, which is a powerful oxidizing agent and probably the most easily handleable, in spite of its low solubility in water. The use of catalysts is an ultimate strategy to improve the ozonation performance, by reducing the chemical oxygen demand (COD), even until total disappearance. However, solid catalysts, more particularly those developing high specific surface areas, such as silicates, aluminosilicates, zeolites, pseudozeolites, and clay minerals and derivatives are expected to display appreciable performances in ozonation. The latest findings show strong dependency of their catalytic activity on the chemical and physical characteristics of their surface, their concentration in the liquid media, the pH level of the reaction mixture and other parameters. The effects of these factors will be systematically examined in this review paper. The state-of-the-art in the catalytic ozonation of organic pollutants may be useful to understand the contribution of both surface and bulk ozonation reaction in the vicinity of the surface of a solid catalyst, and more particularly the role of the catalytic agent and its mobility near the solid surface. A rigorous data synthesis, made available in the present paper, allows understanding the ozone scavenging by the very species present in water, and correlating the highest effectiveness of ozone in the presence of optimum catalyst concentration at optimum pH. This supposes strong interactions between the main factors, which remain to be elucidated for each type of catalyst. The structure of this review makes emphasis on montmorillonite, which exhibits most of the required properties for effective ozonation catalysts. These are common features of natural clay minerals and zeolites, which appear as interesting candidates for large-scale water treatments, targeting complete mineralization of organic pollutants without generating persistent toxins.