Removal of Mercury Ions from Ethanol Solution Using Silica Gel Functionalized with Amino-Terminated Dendrimer-Like Polyamidoamine Polymers: Kinetics and Equilibrium Studies

The potential use of silica gel functionalized with dendrimer-like, amino-terminated polyamidoamine polymers (PAMAM) as adsorbents for the removal of mercury ions from ethanol solution was evaluated. The adsorption isotherm and adsorption kinetics were investigated by using the batch method. The adsorption capacity was found to depend on the generation number of PAMAM loaded, contact time, initial concentration, and temperature. The experimental data were fitted to pseudofirst-order and pseudosecond-order kinetic models. The results indicated that all of the adsorption data fitted well with the second-order kinetic model. A stepped fitting method was adopted to determine whether intraparticle diffusion or external diffusion was the rate-limiting step. The adsorption isotherms were fitted by the Langmuir model, Freundlich model, and Dubinin–Radushkevich (D-R) model. The results showed that the Langmuir model defined the equilibrium data better than the Freundlich model. From the D-R isotherm model, the calculated mean free energy E showed that the adsorptions occurred via chemical processes. The thermodynamic parameters of ΔG0, ΔH0, and ΔS0 indicated that the Hg2+ adsorption was endothermic and spontaneous with decreased randomness at the solid–solution interface.