Decomposition of Environmentally Persistent Perfluorinatied Acids by Use of Metal Complex Photocatalysis

研究了环境持久性全氟羧酸(PFCA)在紫外可见光下、H_2O_2紫外可见光照射下、钨杂多酸(多金属氧酸盐)光催化剂和过硫酸盐作用下对水中环境持久性全氟羧酸的分解。在长链全氟辛烷磺酸的情况下，直接光解缓慢地生成CO_2、F~(2-)离子和短链全氟辛酸。与直接光解相比，H_2O_2对PFCA的降解效果较差。另一方面，杂多酸光催化剂能有效地分解PFCA，生成F~+和CO_2，并抑制了短链PFCA在反应溶液中的积累。浓度为1.35 mM的全氟辛烷磺酸在200 W氙灯照射下，在24 h内被催化剂完全分解，不伴随催化剂降解。气相色谱/质谱仪(GC/MS)检测结果表明，没有发现CF4等环境有害物质的踪迹，CF4具有很高的全球变暖潜力。当使用过硫酸盐作为光化学氧化剂时，PFCA的分解速度更快。浓度为1.35 mM的全氟辛酸在50 mM的S_2O_8光化学体系中完全降解，光照4h后，全氟辛酸的初始分解速率是单独光解的11倍。

The decomposition of environmentally persistent perfluorocarboxylic acids (PFCAs, typically perfluorooctanoic acid ; PFOA) in water by UV-visible light irradiation, by H_2O_2 with UV-visible light irradiation, by a tungstic heteropolyacid (polyoxometalate) photocatalyst, and by persulfate was examined. In the case of long-chain PFCAs such as PFOA, direct photolysis proceeded slowly to produce CO_2, F^- ions and short-chain PFCAs. Compared to the direct photolysis, H_2O_2 was less effective in PFCA decomposition. On the other hand, the heteropolyacid photocatalyst led to efficient PFCA decomposition and the production of F^- ions and CO_2. The photocatalyst also suppressed the accumulation of short-chain PFCAs in the reaction solution. PFOA in the concentrations of 1.35 mM was completely decomposed by the catalyst within 24 h of irradiation from a 200-W xenon-mercury lamp, with no accompanying catalyst degradation. Gas chromatography/mass spectrometry (GC/MS) measurements showed no trace of environmentally undesirable species such as CF_4, which has a very high global-warming potential. When persulfate was used as a photochemical oxidant, the PFCA decomposition proceeded more rapidly. PFOA at a concentration of 1.35 mM was completely decomposed by a photochemical system using 50 mM S_2O_8^<2-> and 4 h of irradiation and the initial PFOA decomposition rate was 11 times higher than with photolysis alone.