Photochemical Reaction Mechanism of Environmental Pollutants

Dear Colleagues,

The degradation and control of persistent, highly toxic organic pollutants, especially those accumulated in different waters, are pivotal to global ecological security. Advanced oxidation technologies (AOTs) are playing a more and more important role in both source treatment (high concentration) and extensive watershed treatment (low concentration) of these organic pollutants, because they aim to convert organic pollutants into CO₂, H₂O and mineralized inorganic ions. However, for many years, AOTs have remained difficult to achieve application on a large scale; the main obstacles are high energy consumption and high cost. As a result, photocatalytic degradation and photooxidative degradation by utilizing solar energy are the only feasible ways to thoroughly solve the bottleneck of AOT. To this end, researchers focus on designing more efficient photocatalysts through varying composition, structure, morphology and so on. Among them, the reaction mechanism between various photocatalysts (or sensitizers), reactive sites or reactive species and pollutant molecules is of vital importance during the process of photo-induced degradations. In addition, there are many chemical reactions of environmental pollutants in the natural world, including soil, water, atmosphere and even plant media forced by solar irradiation. Therefore, the in-depth understanding of mechanisms of environmental pollutants transformation, degradation and mineralization under light irradiation is critical to the design and development of high-efficiency and high-performance photo-induced degradation systems. 

The mechanism of photochemical reaction for current AOTs eliminating organic pollutants in water mainly includes the following aspects: (1) the processes of organic pollutant molecules being oxidized, reduced, hydrolyzed and finally broken into CO₂, H₂O and inorganic ion X^-; (2) photo-induced catalyst (or sensitizer) activates molecular oxygen O₂, O₃, H₂O₂, S₂O₈^2-, Cl₂, ClO₂ etc. and the influence factors of the solution; (3) generation pathway and characterization of various species of reactive oxygen species and photo-generated holes/electron pairs in homogeneous or heterogeneous systems; (4) analysis and characterization of intermediate products in degradation of organic pollutants; (5) relaxation, lifetime and reaction path of photo-excited states in homogeneous and heterogeneous system. The mechanisms of photocatalysis, sensitization and direct photolysis are very complex and involve multidisciplinary intersections, especially the spectral characterization of steady and transient states. However, this Special Issue only encompasses five aforementioned aspects and mainly focuses on the studies of homogeneous and heterogeneous photodegradation mechanisms of environmental organic pollutants.

Prof. Dr. Wanhong Ma
Guest Editor

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• Photo-degradation of organic pollutants in waters
• Homogeneous photo-catalytized or sensitized mechanisms
• Hetergenous photo-catalytized mechanisms
• Intermediate fragments and intermediate process
• Reactive oxygen species (ROS)