Campbell Tammy Y, Vecitis Chad D, Mader Brian T, Hoffmann Michael R
W. M. Keck Laboratories, California Institute of Technology, Pasadena, California 91125, USA.
J Phys Chem A. 2009 Sep 10;113(36):9834-42. doi: 10.1021/jp903003w.
The sonochemical degradation kinetics of the aqueous perfluorochemicals (PFCs) perfluorobutanoate (PFBA), perfluorobutanesulfonate (PFBS), perfluorohexanoate (PFHA), and perfluorohexanesulfonate (PFHS) have been investigated. Surface tension measurements were used to evaluate chain-length effects on equilibrium air-water interface partitioning. The PFC air-water interface partitioning coefficients, KeqPF, and maximum surface concentrations, Gamma(max)PF, were determined from the surface pressure equation of state for PFBA, PFBS, PFHA, and PFHS. Relative KeqPF values were dependent upon chain length KeqPFHS approximately equal to 2.1KeqPFHA approximately equal to 3.9KeqPFBS approximately equal to 5.0KeqPFBA, whereas relative GammamaxPF values had minimal chain length dependence Gamma(max)PFHS approximately equal to Gamma(max)PFHA approximately equal to Gamma(max)PFBS approximately equal to 2.2Gamma(max)PFBA. The rates of sonolytic degradation were determined over a range of frequencies from 202 to 1060 kHz at dilute (<1 microM) initial PFC concentrations and are compared to previously reported results for their C8 analogs: perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA). Under all conditions, the time-dependent PFC sonolytic degradation was observed to follow pseudo-first-order kinetics, i.e., below kinetic saturation, suggesting bubble-water interface populations were significantly below the adsorption maximum. The PFHX (where X = A or S) sonolysis rate constant was observed to peak at an ultrasonic frequency of 358 kHz, similar to that for PFOX. In contrast, the PFBX degradation rate constants had an apparent maximum at 610 kHz. Degradation rates observed for PFHX are similar to previously determined PFOX rates, kapp,358PFOX approximately equal to kapp,358PFHX. PFOX is sonolytically pyrolyzed at the transiently cavitating bubble-water interface, suggesting that rates should be proportional to equilibrium interfacial partitioning. However, relative equilibrium air-water interfacial partitioning predicts that KeqPFOX 5KeqPFHX. This suggests that at dilute PFC concentrations, adsorption to the bubble-water interface is ultrasonically enhanced due to high-velocity radial bubble oscillations. PFC sonochemical kinetics are slower for PFBS and further diminished for PFBA as compared to longer analogs, suggesting that PFBX surface films are of lower stability due to their greater water solubility.
已对全氟化合物（PFCs）全氟丁酸（PFBA）、全氟丁烷磺酸（PFBS）、全氟己酸（PFHA）和全氟己烷磺酸（PFHS）在水中的声化学降解动力学进行了研究。通过表面张力测量来评估链长对平衡气-水界面分配的影响。根据PFBA、PFBS、PFHA和PFHS的表面压力状态方程确定了PFC的气-水界面分配系数KeqPF和最大表面浓度Gamma(max)PF。相对KeqPF值取决于链长，KeqPFHS约等于2.1KeqPFHA约等于3.9KeqPFBS约等于5.0KeqPFBA，而相对Gamma(max)PF值对链长的依赖性最小，Gamma(max)PFHS约等于Gamma(max)PFHA约等于Gamma(max)PFBS约等于2.2Gamma(max)PFBA。在初始PFC浓度较低（<1 microM）的情况下，在202至1060 kHz的频率范围内测定了声解降解速率，并与先前报道的其C8类似物全氟辛烷磺酸（PFOS）和全氟辛酸（PFOA）的结果进行了比较。在所有条件下，观察到随时间变化的PFC声解降解遵循准一级动力学，即在动力学饱和以下，这表明气泡-水界面的数量显著低于吸附最大值。观察到PFHX（其中X = A或S）的声解速率常数在358 kHz的超声频率处达到峰值，与PFOX的情况类似。相比之下，PFBX的降解速率常数在610 kHz处有一个明显的最大值。观察到的PFHX的降解速率与先前测定的PFOX的速率相似，kapp,358PFOX约等于kapp,358PFHX。PFOX在瞬时空化的气泡-水界面处发生声解热解，这表明速率应与平衡界面分配成正比。然而，相对平衡气-水界面分配预测KeqPFOX>5KeqPFHX。这表明在低浓度PFC时，由于高速径向气泡振荡，对气泡-水界面的吸附在超声作用下增强。与较长的类似物相比，PFBS的PFC声化学动力学较慢，而PFBA的则进一步降低，这表明PFBX表面膜由于其较高的水溶性而稳定性较低。
