Enhanced removal of Cr(III), Mn(II), Cd(II), Pb(II) and Cu(II) from aqueous solution by N-functionalized ordered silica

Abstract

Chelating and ion-exchange N-functionalized mesoporous silicas (SBA-15) as selective adsorbents for removal of heavy metals were synthesized using template method. Fourier transform infrared spectroscopy, TEM analysis, N2 adsorption/desorption isotherms and titration analysis confirmed successful functionalisation of the tri-sodium salt of N-(triethoxysilylpropyl)ethylenediaminetriacetic acid (EDTA), protonated primary amine (NH3+Cl−) and its combinations onto the mesoporous silica (SBA-EDTA/NH2). The obtained materials featured beneficial properties of mesoporous silica SBA-15 with its high surface area and were successfully fictionalized with N-containing groups. The synthesized series of silicas were investigated for removal of Cr(III), Mn(III), Pb(II), Cd(II) and Cu(II) from model water solutions. The adsorption of target ions increased with the increase pH and its concentration in solution. The adsorption equilibrium data were well fitted to Langmuir isotherm model and maximum monolayer adsorption capacities for cations Pb(II), Cd(II), Cr(III) and Mn(II) were 185.6\xa0mg\xa0g−1, 111.2\xa0mg\xa0g−1, 57.7\xa0mg\xa0g−1 and 49.4\xa0mg\xa0g−1, respectively. The chelating interaction was considered as the main adsorption mechanism for metal ions (Cr(III), Mn(II), Pb(II), Cd(II), and Cu(II)). The adsorption capacities of SBA-EDTA and SBA-EDTA/NH2 samples toward studied metal ions were consistent with the Lewis ‘hard and soft acids and bases’ theory. The metal removal efficiency of adsorbents was near 96–92% during three regeneration cycles. All these results indicated that the produced N-functionalized silica were promising for applications in environmental and analytical separation fields.