Non-free radicals based advanced oxidation processes: Research progress and future prospects

Due to the strong oxidizing ability of free radicals, advanced oxidation processes (AOPs) are almost considered to be the 'universal key' for organic wastewater treatment, but they cannot be perfect. AOPs has always been built on the basis of strong oxidizing free radicals (free radicals based AOPs, FAOPs), which are difficult to resist the interference of common magazines (inorganic anions and dissolved organic matters) in practical wastewater, and their selectivity is not satisfactory. The above problems seem to be well solved in the non-free radicals based AOPs (NFAOPs) system, because non-radicals represented by singlet oxygen exhibit strong anti-interference ability and selectivity to benzene compounds with electron donating groups. However, the current understanding of NFAOPs does not match their application potential. Therefore, this work attempts to make a detailed review on the types, identification, advantages and disadvantages of NFAOPs, in order to provide some guidance for the subsequent research on their mechanism, initiation and performance optimization.