Synthesis of cross-linked cationic surfactant nanoparticles for removing anions from water

Abstract

A new quaternary ammonium hydroxypropyl conjugated linoleic acid ester (QACLE, a mixture of 2-hydroxy-N,N,N-trimethyl-3-(9,11-octadeca-dienoyloxy)propyl-1-aminium chloride and 2-hydroxy-N,N,N-trimethyl-3-(10,12-octadeca-dienoyloxy)propyl-1-aminium chloride) cationic surfactant has been synthesized via reaction between conjugated linoleic acid (CLA) and (2,3-epoxypropyl)-trimethylammonium chloride (ETAC). The QACLE surfactant was identified by measuring the molecular weight by electrospray mass spectroscopy (ESI-MS), and Fourier transform infrared spectrum (FTIR) absorbance bands were consistent with known functional group characteristics. Several chemical properties were determined, including the critical micelle concentration (CMC) and the size distribution of the micelles. For this surfactant, these and other property values were compared to those of two commercially available cationic surfactants, cetyltrimethylammonium bromide (CTAB) and cetylpyridinium chloride (CPC). When present in aqueous micellar form, QACLE was cross-linked by UV-light in the presence of a photo-initiator, forming stable nanoparticles with high anion exchange capacity. Because the cross-linking reaction destroys the conjugated double bonds, the nanoparticle product contains cross-linked monomers of a (propyl) quaternary amine stearic (acid) ester (QASE). The cationic QASE nanoparticles were separated from non-cross-linked monomers by dialysis, and the stability of the nanoparticles was studied and confirmed by dialysis and solvency. Results of chromate removal by the cationic nanoparticles across an ultrafiltration membrane are presented as an initial study of potential applications.