Advanced Oxidation Processes (AOPs) – Utilization of Hydroxyl Radical and Singlet Oxygen

Abstract

Considering the nature of organic contaminants in water, methods of their oxidative decomposition seem to be most appropriate for their removal from contaminated water. There are a lot of methods of chemical oxidation, however, Advanced Oxidation Processes (AOPs) seem to be the most suitable technologies for organic contaminants removal. AOPs belong to a group of processes that efficiently oxidize organic compounds towards harmless inorganic products such as water or carbon dioxide. The processes have shown great potential in treatment of pollutants of low or high concentrations and have found applications for various types of contamination. The hydroxyl radical (•OH) is oxidizing agent used at AOPs to drive contaminant decomposition. It is a powerful, non-selective chemical oxidant, which reacts very rapidly with most organic compounds. Another strong oxidizing agent, singlet oxygen, can be generated by photosensitization of phthalocyanines. Phthalocyanines are molecules based on pyrrol structures connected mainly with methionine groups (–CH=) having a metallic central atom. Illumination upon specific wavelengths initiates formation of singlet oxygen that attack organic contaminants.

A Multipurpose Metallophore and Its Copper Complexes with Diverse Catalytic Antioxidant Properties to Deal with Metal and Oxidative Stress Disorders: A Combined Experimental, Theoretical, and In Vitro Study

“…On the contrary, there is no enzymatic natural protection against one of the most dangerous ROS, the hydroxyl radical ( • OH). The main reason for this may be its high reaction rate constant (10 9 mol –1 L –1 s –1 ) . Such species may be formed by different natural or synthetic processes (Fenton reaction, Haber–Weiss reaction, TiO 2 photocatalytic process, ozone irradiation, hydrogen peroxide photolysis, etc.)…”

“…The main reason for this may be its high reaction rate constant (10 9 mol −1 L −1 s −1 ). 183 Such species may be formed by different natural or synthetic processes (Fenton reaction, Haber−Weiss reaction, TiO 2 photocatalytic process, ozone irradiation, hydrogen peroxide photolysis, etc.). 183 From a biological point of view, the • OH radical can readily oxidize DNA, lipids, and proteins.…”

Review of emerging technologies for nutrient removal in wastewater treatment

“…UV/H2O2 systems utilize hydrogen peroxide as a source of hydroxyl radicals, which are generated via UV-induced decomposition of hydrogen peroxide molecules (Guo, et. al., 2022, Krystynik, P. (2021, Lei, et. al., 2021.…”

Titanium Dioxide as the Most Used Photocatalyst for Water Purification: An Overview

“…Exciting species are formed by irradiating TiO 2 semiconducting particles with a light of energy higher than the energy gap [108][109][110][111][112][113][114][115]. Namely, electron-hole (e − -h + ) pairs are formed (reaction (1)), together with holes in VB and electrons in CB, representing the initial phase of the photocatalytic process (Figure 4) [115].…”

“…Reactions (2) and (3) are thermodynamically possible since the aforementioned condition is fulfilled for the TiO 2 . Since newly formed • OH are powerful oxidizing agents whose standard redox potential is +2.8 V [112][113][114], they can practically oxidize all organic compounds to mineral products (Figure 4) [115].…”