Comparative study of 2,4,6-trichlorophenol adsorption by montmorillonites functionalized with surfactants differing in the number of head group and alkyl chain

Understanding the structures and characteristics of surfactants used to modify montmorillonites is crucial to predict the adsorption capacity of the resultant organo-montmorillonites in the aquatic environment. Herein, organo-montmorillonites modified by surfactants containing various amounts of head groups and hexadecyl chains were prepared. A general comparison was conducted of organo-montmorillonites modified by methyl hexadecyl bis[3-(dimethylhexadecylammonio)ethyl] ammonium tribromide (16-2-16-2-16), dimeric surfactants (1, 2-bis (hexadecyldimethylammonio) ethane dibromide, 16-2-16) and cetyl trimethyl ammonium bromide (CTAB) for their adsorption performance on 2,4,6-trichlorophenol (2,4,6-TCP) from aqueous solution. The resultant organo-montmorillonites were characterized by XRD, TGA and FT-IR spectroscopy. Batch studies were performed to evaluate the influences of various parameters like the amount of modifiers, the number of alkyl chain, contact time and solution pH on the removal of 2,4,6-TCP. Results indicated that the removal efficiency follows the order of CTAB-Mt <16-2-16 -Mt <16-2-16-2-16-Mt from 0.4 CEC to 1.2 CEC, which may be due to increasing hydrophobicity with the increase in hexadecyl chain number. However, the adsorption capacity is on the rise in the order 16-2-16 -Mt > 16-2-16-2-16-Mt > CTAB-Mt beyond 1.2 CEC. This might be interpreted in terms of the combined contribution of packing density of hexadecyl chains in the interlayer of montmorillonites and ion dipole interaction between the head group of intercalated surfactants and 2,4,6-TCP. Full kinetics, equilibrium and thermodynamics were also undertaken. Moreover, the maximum adsorption capacities of 2,4,6-TCP were 328.9 mg/g at 1.6 CEC for CTAB-Mt and 306.7 mg/g at 0.8 CEC for 16-2-16-Mt, respectively, whereas as high as 322.6 mg/g for 16-2-16-2-16-Mt even at the modifier amount as low as 0.6 CEC. This study suggests that 16-2-16-2-16-Mt with three head groups and hexadecyl chains can serve as a more high-efficiency and cost-effective adsorbent for removal of 2,4,6-TCP from aqueous solution. (C) 2017 Elsevier B.V. All rights reserved.