CTAB modified large surface area nanoporous geopolymer with high adsorption capacity for copper ion removal

Nanoporous geopolymer was synthesized with and without using Cetyl trimethylammonium bromide (CTAB) by condensing the mixture of metakaolin and alkali solution at a fixed ratio at room temperature. The surface area of CTAB-geopolymer was found to be more (216 m²/g) as compared to without CTAB added geopolymer (137 m²/g). The experimental results verified that the geopolymer could adsorb copper ions completely at lower concentrations and partially at higher concentrations. Pseudo second order model fits well at all the concentration from 55 to 1700 ppm as the values of the correlation coefficient lies between 0.96 and 0.99. Intraparticle diffusion model at the concentration 55 ppm explains that there is only boundary layer diffusion (instantaneous) and after this step, all the Cu ions are exchanged by the nanoporous geopolymer. At 120 ppm, intraparticle diffusion model shows multilinearity. Different adsorption models - Langmuir, Freundlich and Tempkin were also tested to evaluate the most appropriate model and it was found that adsorption follows Langmuir model. The adsorption capacity and pseudo second order rate constant is estimated to be 1.65 meq/g which is significantly higher than the fly ash based nonporous geopolymer.