Synthesis of poly(ethyleneimine)-functionalized mesoporous silica gel with dual loading of host ion and crosslinking for enhanced heavy metal removal in multinary solutions

Polyethyleneimine (PEI)-functionalized mesoporous silica gel (SG) was synthesized through dual loading (d-PEI-SG) of copper (Cu) as a host ion for Cu(II)-PEI complex and crosslinking with glutaraldehyde in the synthesis pathway to enhance deposition of PEI on the SG. For comparison, the PEI-functionalized SG was also prepared through single loading (s-PEI-SG) of the host ion and crosslinking with glutaraldehyde. In thermogravimetric analysis, the weight loss of d-PEI-SG at 110–500 °C (7.8%) was greater than that of s-PEI-SG (2.8%), indicating the enhanced deposition of PEI on the silica gel surface of d-PEI-SG. The elemental composition from X-ray photoelectron spectroscopy analysis demonstrated that relative quantities of carbon and nitrogen in d-PEI-SG were larger than those of s-PEI-SG. In batch tests, the maximum Cu(II) adsorption capacity of d-PEI-SG was determined to 170.4 μmol g−1, which was four times larger than that (41.8 μmol g−1) of s-PEI-SG. In a multinary solution of divalent metal ions (Cu(II), Pb(II), Zn(II), Ni(II), and Co(II)) and trivalent/tetravalent metal ions (Cu(II), Al(III), Cr(III), and Zr(IV)), d-PEI-SG had a higher Cu(II) adsorption capacity and selectivity than s-PEI-SG. Column experiments were also conducted in the multinary solution of Cu(II), Pb(II), Zn(II), Ni(II), and Co(II), demonstrating that d-PEI-SG could remove more Cu(II) than s-PEI-SG in flow-through conditions.