Adsorption of PAEs from aqueous solution by modified zeolites

Natural zeolites (NZ), zeolites modified with hexadecyl trimethylammonium bromide (CTMZ), and zeolites modified with hexadecyl trimethyl ammonium bromide/sodium dodecyl sulfate (CSMZ) were prepared and used for the adsorption of phthalate esters (PAEs). The adsorbents were characterized using scanning election microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and thermogravimetric, Brunauer-Emmett-Teller, and organic carbon analyses. Adsorption characteristics, such as kinetics, isotherms, thermodynamics, and renewability, were also evaluated. The amount of PAEs adsorbed followed the order of CSMZ>CTMZ>NZ at all adsorption times. The kinetic data were fitted into three kinetic models, namely, pseudo-first-order, pseudo-second-order, and intra-particle diffusion. The pseudo-second-order model was the most suitable in describing the experimental process. The adsorption isotherms were also correlated using four different models. The equilibrium adsorption data of PAEs fitted better with the linear isotherm model for CTMZ and CSMZ and with the non-linear isotherm model for NZ. Hence, partition primarily contributes to PAEs adsorption onto CTMZ and CSMZ. PAEs adsorption onto NZ, CTMZ, and CSMZ was spontaneous and exothermic in nature, and was not affected by pH. The regeneration experiment results showed that CTMZ and CSMZ are potential adsorbents because of their low cost and reusability.