Influence of functionalization, surface area and charge distribution of SBA15-based adsorbents on CO (II) and NI (II) removal from aqueous solutions

•Cobalt and nickel remotion by functionalized silicas from aqueous solutions was studied.•Metal removal depends on the silica surface chemistry.•From binary metal solutions, preferential nickel adsorption occurred on SBA-15-EDTA.•SBA-15-EDTA shows the highest removal efficiency for both heavy metals.•Theoretical predictions are consistent with experimental results. Amino functionalized solids were obtained by anchoring ethoxysilane and ethylenediaminetetraacetic groups onto the surface of a mesostructured silica SBA-15. The materials were characterized by nitrogen adsorption-desorption, Fourier transform infrared spectroscopy (FTIR), and potentiometric titration. The samples SBA-15, SBA-15 -NH2 and SBA-15-EDTA were tested in the simple and competitive adsorption of Co (II) and Ni (II) ions from aqueous solutions. The equilibrium data were analyzed using the Langmuir isotherm by nonlinear regression analysis. The influence of textural and chemical characteristics of the three different silicas on Co (II) and Ni (II) removal was also studied. A complementary study based on density functional theory was performed. Adsorption isotherms of Ni and Co fitted well with Langmuir model, exhibiting high adsorption capacity of 47.7 and 27.4 mg of metal/g of SBA-15, 62.9 and 59.7 mg of metal/g of SBA-15-NH2 and 74 and 67.7 mg of metal/g of SBA-15-EDTA, respectively, in simple adsorption tests. In the case of adsorption from binary solutions, both cations compete for the same active sites, a preferential Ni adsorption being shown. A detailed data analysis demonstrated that EDTA functionalization allows the best retention efficiency of both heavy metals from their corresponding aqueous solution.