UV photolysis of perfluorooctanoic acid (PFOA) in dilute aqueous solution

摘要

Perfluorooctanoic acid (PFOA) is very persistent in the environment and widely detected in thenwater environment. Only some advanced methods with extreme reaction conditions are shown tonbe capable of degrading the compound efficiently, and almost all the earlier investigations usednvery high PFOA concentrations. The compound is detected normally at very low concentrations innthe water environment, while mild reaction conditions for its degradation are preferable. Thisnarticle aimed to elucidate photodegradation of PFOA in dilute aqueous solutions by combined UVnwavelengths (185 nmt254 nm) and 254 nm using a newly designed UV jacket. PFOA degradationnwas greatly enhanced with the combined wavelengths with almost one hundred percent PFOAnremovals in four-hour reaction. The removals were well described by the first-order reactionnkinetic. The removal efficiencies and rate values significantly decreased with smaller initial PFOAnconcentrations. But defluorination was greatly enhanced with smaller PFOA concentrationsnpossibly due to accelerated decomposition of fluorinated intermediates of PFOA. Formic acid andnacetic acid were two tentatively identified intermediates of PFOA photolysis while the former wasna major intermediate predominantly controlling solution pH during the oxidation. The resultsndemonstrated that PFOA photolysis by the combined wavelengths with mild reaction conditionsncan be greatly enhanced by proper design of UV jacket and reactor system.