Reversible Solubilization Of Typical Polycyclic Aromatic Hydrocarbons (PAHs) By A Nonionic Switchable Surfactant

An investigation has conducted on the nonionic switchable surfactant:11-ferrocenylundecyl polyoxyethylene ether (FPEG).In this paper, we mainly investigated the reversible electrochemical behaviors, the micellization process and micelle particle size distribution of surfactants solutions, the solubilization abilities and releasing regularity of polycyclic aromatic hydrocarbons(PAHs) by single FPEG solutions,we also reported the FPEG solutions mixed with a conventional surfactants SDS in differents mass ratio, to investigate the solubilization abilities of PAHs, in the mixed solutions, the AS is used to evaluate the synergistic solubilization ability. We have drawn several original conclusions based on the experimental data:(1)The main object of study in this paper, a novel nonionic switchable surfactant11-ferrocenylundecyl polyoxyethylene ether (FPEG) was synthesized and characterized by means of1H-NMR and13C-NMR to confirm the molecular structure. The electrochemical behavior of reduction and oxidation states of FPEG solutions was investigated by cyclic voltammograms, glassy carbon electrode, platinum wire and saturated calomel electrode(SCE) as the working, counter and reference electrodes, respectively.The results showed that the anodic peak potential(Epa) and cathodic peak potential (Epc)were0.2555V and0.1807V,respectively, AEp=Epa-Epc=74.8mV and the ratio of Ipa/Ipc=1.28, which reveals the reversible reduction-oxidation characteristics of FPEG solution. A three-electrode oxidation-reduction system was used to transfer the reduced form to oxidized and re-reduced forms, the efficiency of oxidation can be reach as78%. Surface tension of the reduced, oxidized and re-reduced forms of FPEG solution were measured at25℃by adopting the platinum plate method, the critical micelle concentration(CMC) of the reduced, oxidized and re-reduced forms were15mg/L,30mg/L and16mg/L, respectively, the CMC of FPEG solution changed significantly while the reduced form oxidized to oxidation state, whereas the CMC of re-reduced form dropped to16mg/L, which was almost similar to the reduced form, this indicated that micelle formation and disruption could be reversibly controlled by oxidation-reduction reaction of the ferrocenyl group in the FPEG molecular structure.(2)We investigated the surface tension of FPEG solutions with different inorganic salts(0.1mol·L-1NaCl and0.1mol·L-1CaCl2), the CMC dropped to12and8mg/L, respectively, with the addition of inorganic salts,which means that the addition of inorganic salts improved the surface activities of FPEG solutions and made the micelle formation in a lower concentration. The thermodynamic process of micelle formation was investigated by measuring the CMCs of FPEG solution in different temperature,the results showed that with the increasing temperature,the surface tension decreased and corresponded to the decreased CMCs,the thermodynamic parameters standard entropy change (⊿Smθ), standard enthalpy change (⊿Hmθ) and standard Gibbs free energy change (⊿Gmθ) were calculated and the results indicated that the micelle formation was a entropy-driven process, and the micelle formation process spontaneous. Dynamic light scattering (DLS) and steady-state fluorescence probe technique were used to study the micelle size distribution and micelle aggregation numbers of FPEG solutions. The mean value of hydrodynamic diameters of FPEG solutions was9.9nm which was calculated by a NNLS (non-negatively constrained least square) algorithm,at the concentration of500mg/L, in the steady-state fluorescence probe research, pyrene was used as probe and cetylpyridinium chloride(CPC) was quencher, the excitation wavelength and emission wavelength were set at335nm and373nm,respectively, the results showed while the quencher concentrations ranged from0.25to0.40mmol’L"1that the micelle aggregation number(N) increased linearly with the concentration ranged from5to12times CMC of FPEG solutions, The critical micelle aggregation number(Nm) which mean that the aggregation number of surfactant at the concentration of CMC was extrapolated by N-cs curve to be66.(3) The solubilization and releasing regularities of single FPEG solutions to PAHs were also investigated,and the results revealed that the solubilization abilities was a function of FPEG concentrations, FPEG solutions had solubilization abilities both before and after CMC,whereas,the solubilization capacity improved enormously while the concentration far above CMC. The solubilization abilities of pyrene, phenanthrene and acenaphthene fellow the order pyrene> phenanthrene>acenaphthene,which was mainly attributed to the partition coefficients of solutes in the FPEG solutions.The solubilization capacity of oxidized FPEG solutions was also conducted, which was used to compare with the solubilization capacity of reduced form, the results showed the release efficiency of pyrene, phenanthrene and acenaphthene were40%,this could be explained that while the micelles of FPEG oxidized to monomers,the molecular still had interactive with solutes,meanwhile, the micelles were not disrupted completely in the solutions,the release abilities comply with the order acenaphthene> phenanthrene> pyrene,which was on the contrary with the solubilization abilities.The influence of inorganic salts on the solubilization abilities was investigated as the same, and the results showed the the addition of inorganic salts(NaCl,CaCl2)could improve the solibization abilities significantly.(4) The CMCs of FPEG solutions mixed with SDS changed in different mass ratio, while FPEG:SDS=9:l,the CMC was the lowest,and the mixed solutions had the best solubilization ability.The solubilization behaviors of mixed FPEG solutions were explored at the mass ration2:8,3:7,4:6,7:3.8:2,9:1,respectively.The results showed that the synergistic solubilization effect of pyrene happened at the mass ratio7:3,8:2and9:1,the synergistic abilities improved with the increasing mole fraction of FPEG;while the synergistic abilities of phenanthrene only happened at the ration8:2and9:1,whereas,there has no significant synergistic solubilization abilities at any ratio in the solubilization of acenaphthene, this mainly attributed to the different distribution abilities of pyrene, phenanthrene and acenaphthene in the mixed solutions. As for pyrene and phenanthrene, the increasing mole fraction of FPEG in the mixed solutions could make pyrene and phenanthrene solubilized to micelle phase more smoothly.