Mercury sorption by silica/carbon nanotubes and silica/activated carbon: a comparison study

Nanocomposites of silica incorporated with carbon nanotubes (silica/CNT) and activated carbon (silica/AC) were synthesized and characterized by scanning electron microscopy (SEM), element mapping, energy dispersive X-ray spectroscopy (EDX), thermogravimetric analyzer (TGA) and Fourier transform infrared spectroscopy (FTIR). Silica/CNT and silica/AC were investigated for efficient removal of mercury ions from aqueous solutions. The adsorbents have been analyzed on the basis of adsorption capacity, reusability, and their application in packed columns. The effects of experimental parameters, like pH, contact time and initial concentrations on the adsorption of mercury ions, were optimized. The kinetic data for the adsorption process obeyed a pseudo-second-order kinetic model with R² of 0.999. Fitting the data to an intraparticle diffusion model indicated that surface adsorption and intraparticle diffusion were concurrently operating. In addition, this study used the Langmuir, Freundlich and Temkin isotherms to describe the behaviour of equilibrium adsorption. The equilibrium adsorption of the studied mercury ions is best fitted using the Freundlich isotherm, with silica/CNT of higher capacity than silica/AC. The silica/CNT showed better performance than silica/AC indicating silica/CNT has better efficiency.