Investigation of interaction between phenol and cetylpyridinium chloride micelle in the absence and in the presence of electrolyte by 1H NMR spectroscopy

In recent years, the micellar enhanced ultrafiltration (MEUF) of phenol in wastewater using cetylpyridinium chloride (CPC) as surfactant has gained many attentions. However, so far no research has focused on the interaction between phenol and CPC micelle. In this study, the interaction between phenol and CPC micelle with and without electrolyte was investigated by using 1H NMR spectroscopy. In the absence of electrolyte, at low phenol concentrations (0.5 mM and 1 mM) phenol was solubilized at the micelle–water interface by the ion interaction between C6H6O− and C5H5N+, and in the hydrophilic head group region of CPC micelle by the polar interaction between phenol and CPC micelle. When phenol concentration range was from 1 mM to 8 mM, the micelle–water interface and the hydrophilic head group region of CPC micelle saturated with C6H5O− and phenol, then phenol penetrated into the palisade layer deeper but was still close to the hydrophilic head group of CPC micelle. The presence of NaCl and Na2SO4 had almost no influence on the solubilization of phenol in CPC micelle, however, the presence of Na2CO3 promoted the solubilization of phenol in CPC micelle significantly. In the presence of Na2CO3, more C6H5O− ions were solubilized at the water–micelle interface by the ion interaction between C6H6O− and C5H5N+. At low Na2CO3 concentration the micelle–water interface of CPC micelle saturated with C6H5O−, and benzene ring penetrated into the palisade layer of CPC micelle, but deeper penetration was not observed with the increase of Na2CO3 concentration. Excessive CO32− could make some C6H5O− transfer from CPC micelle to water, resulting in the decrease of the solubilization extent of phenol in CPC micelle.