Photocatalytic degradation of perfluorooctanoic acid with β-Ga_2O_3 in anoxic aqueous solution

摘要

Perfluorooctanoic acid(PFOA) is a new-found hazardous persistent organic pollutant,and it is resistant to decomposition by hydroxyl radical(HO·) due to its stable chemical structure and the high electronegativity of fluorine.Photocatalytic reduction of PFOA with β-Ga 2 O 3 in anoxic aqueous solution was investigated for the first time,and the results showed that the photoinduced electron(e cb) coming from the β-Ga 2 O 3 conduction band was the major degradation substance for PFOA,and shorter-chain perfluorinated carboxylic acids(PFCAs,C n F 2n+1 COOH,1 n 6) were the dominant products.Furthermore,the concentration of F was measured by the IC technique and defluorination efficiency was calculated.After 3 hr,the photocatalytic degradation efficiency was 98.8% and defluorination efficiency was 31.6% in the presence of thiosulfate and bubbling N 2.The degradation reaction followed first-order kinetics(k = 0.0239 min 1,t 1/2 = 0.48 hr).PFCAs(C n F 2n+1 COOH,1 n 7) were detected and measured by LC-MS and LC-MS/MS methods.It was deduced that the probable photocatalytic degradation mechanism involves e cb attacking the carboxyl of C n F 2n+1 COOH,resulting in decarboxylation and the generation of C n F 2n+1 ·.The produced C n F 2n+1 · reacted with H 2 O,forming C n F 2n+1 OH,then C n F 2n+1 OH underwent HF loss and hydrolysis to form C n F 2n+1 COOH.