Facile preparation of polyethylenimine-tannins coated SiO2 hybrid materials for Cu2+ removal

Polyethylenimine-tannins coated SiO 2 (SiO 2 @PEI-TA) hybrid materials have been prepared via a single-step multifunctional coating with polyethylenimine (PEI) and tannins (TA), and characterized by transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). The as-prepared SiO 2 @PEI-TA composites were examined as adsorbents to remove the Cu 2+ from aqueous solution. The effects of contact time, initial Cu 2+ concentration, solution pH and temperature, on Cu 2+ adsorption have been investigated. The results show that the adsorption of Cu 2+ onto SiO 2 @PEI-TA is dependent on the contact time, Cu 2+ concentration, pH and temperature. The SiO 2 @PEI-TA composites show a 2.4-fold increase in adsorption capacity, implying that the introduction of PEI-TA coating is in favor of the Cu 2+ adsorption. Based on the analysis of kinetic data, the kinetics of Cu 2+ adsorption is more accurately described by the pseudo-second-order model. The equilibrium data are analyzed by Langmuir and Freundlich isotherms. Results of isotherms show that the better agreement is Freundlich isotherm model with correlation coefficient of 0.9914, which suggests that the adsorption of Cu 2+ onto SiO 2 @PEI-TA is mainly a heterogeneous adsorption process. Thermodynamic analyses show that the adsorption interaction is actually a spontaneous and endothermic chemical process, which might involve the chemical chelation between Cu 2+ and functional groups (amine and carboxyl groups) on the surface of SiO 2 @PEI-TA. In addition, the Cu 2+ ions could desorb from SiO 2 @PEI-TA by using acid solution and the adsorption efficiency remains at high level after five adsorption-desorption recycles. These results provide potential applications of these novel adsorbents for the removal of heavy metal Cu 2+ from aqueous solution and also provide strong evidence to support the adsorption mechanism proposed in the study.