Reduction of chlorinated methanes with nano-scale Fe particles: effects of amphiphiles on the dechlorination reaction and two-parameter regression for kinetic prediction.

The influences of amphiphiles, including humic acid (HA) and various types of surfactants, on dechlorination of carbon tetrachloride (CTC) and chloroform (CF) by the nano-scale Fe particles were investigated. Since the amphiphiles would modify the surface tension between the liquid-liquid and solid-liquid interface, in the presence of amphiphile matrix solution the Fe corrosion rate and the parent compound dechlorination rate would be different from those in the ultrapure water. Among the four amphiphile solutions, Fe corrosion rate was the highest in the anionic surfactant sodium dodecyl sulfate (SDS) solution, presumably due to the existence of chemisorption between the hydrophilic head of SDS and Fe particles. The dechlorination rates of CTC and CF could be described with the pseudo-first order kinetic model. The influences of amphiphiles on the dechlorination reaction rate were related to the species of parent compound and concentration of the matrix solution. The influences of HA on the dechlorination of CTC and CF were the most significant compared to other matrix solutions. At relatively low HA concentration (<0.1 g L(-1)), the HA molecules (serving as electron transfer mediator) would significantly accelerate the dechlorination rate of CF. The two-parameter regression with energy of the lowest unoccupied molecular orbital (E(LUMO)) and HA concentration as the descriptors was developed to predict the specific reduction rate constants of chlorinated methanes in HA solution. The analysis of variance (ANOVA) indicated the existence of significant relationship between the dechlorination rate constants and the two descriptors.