Typical Reversible Surfactants: Synthesis, Characterazation And Application In The Solubilization Of Lnapls

Surfactant enhanced aquifer remediation (SEAR) technology is one of the most efficient, the least time-consuming, the wider areas and a promising technique among the remediation approaches for the contaminated soil and groundwater. However, it is difficult to recycle the surfactant in SEAR and the scale of application is limited. Therefore, it is the key point to use surfactant with special properties, which is the available way to settle this problem. Two kinds of reversible surfactant were synthesized, the structures were characterizated by elemental analysis and 1H NMR spectroscopy. The surfacial chemical properties, related to solubilization, reversible behavior of electrochemistry and mechanisms of solubilization were investigated. The application of reversible surfactant in remediation of polluted environment were also forecasted. The contents and conclusions of the work are as follows:(1)The structures of reversible surfactant were analyzed and confirmed by elemental analysis and 1H NMR spectroscopy. The principles of critical micelle concentration (CMC) and water enhanced solubility were investigated. The results indicated that values of CMC of straight cationic surfactant were higher than that of compounds through the comparison with their values of CMC. For example, The CMC values of traditional straight cationic surfactant are 1/30 and 1/25 times higher than that of N'-dodecy-N,N-dimethylacetamidine bicarbonate salts (DDAAB) and (ferrocenylmethyl) dodecyldimethylammonium bromide (Fc12) through comparison with theirs, which they exhibited good solubility enhancement.(2)The water solubility enhancements of typical LNAPLs (benzene, toluene and ethylbenzene) by reversible surfactant were investigated. The results suggested that ferrocenyl surfactant possessed solubility propertiy of traditional surfactant, the water solubility enhancements of pollutants by ferrocenyl surfactant were obvious around CMC. The values of Kmc of benzene, toluene and ethylbenzene by Fc12 were as follows:729,898 and 1875, the Kmc by Fc14 were as follows:1140,1628 and 3374, which indicated the water solubility enhancements of selected pollutants by Fc14 is stronger than that of Fc12. The solubility of benzene, toluene and ethylbenzene can be ranked as follows: ethylbenzene> toluene> benzene. Effects of ferrocenyl surfactant concentrations on removal efficiency of selected VOCs were significant and followed this series:benzene> toluene> ethylbenzene, there was a higher removal efficiency with a low ferrocenyl surfactant concentrations.(3)Effects of micellar on electrochemical behavior of ferrocenyl surfactant were studied using cyclic voltammetry as a major means. The results indicated that Fc14 and Fc12 possessed well reversible characteristic in O.lmol/L Na2SO4 acid solution and in O.lmol/L Li2SO4 solution around pH=2, respectively. When the reversible surfactants concentration was high, the electrochemical behavior was a diffusion-controlled reversible process. While the concentration was low, the characteristics of sorption was easily detected. Fc8 possessed well reversible characteristic in 0.1mol/L NaCl acid and neutral solution. Otherwise, based on the linear relation between the logarithm of peak current (Ipc) and the logarithm of scan rate with the values of slope around 0.5, which indicated that the electrochemical behavior of Fc8 was a diffusion-controlled reversible process. The Ipc and diffusion coefficient (D) changed abruptly around the critical micellar concentration (CMC) of the ferrocenyl surfactant, which the trendency was coincided with the change of surface tension and effects of micellar on Ipc and D were obvious.