Efficient removal of lead from highly acidic wastewater by periodic ion imprinted mesoporous SBA-15 organosilica combining metal coordination and co-condensation

Abstract

In order to develop a highly efficient method for direct removal of lead from acidic wastewater (pH 2.0), we introduce a novel highly ordered Pb²⁺ imprinted mesoporous silica (PbIMS) SBA-15 combining co-condensation and functionalized iminodiacetic acid (IDA). Fourier transform infrared spectroscopy (FTIR) and energy-dispersive X-ray (EDX) analysis provided the components of PbIMS. The solid-state ¹³C NMR spectra demonstrated the successful embedment of IDA in the mesoporous silica. Furthermore, X-ray photoelectron spectroscopy (XPS) analysis confirmed that Pb²⁺ was coordinated by the N atom and carboxyl O atom of IDA. The results of transmission electron microscopy (TEM), small angle X-ray diffraction (XRD) and N₂ adsorption–desorption measurement confirmed that the PbIMS preserved a highly ordered hexagonal P6mm mesostructure. The Brunauer–Emmett–Teller (BET) surface area was 762 m² g⁻¹. The saturated adsorption capacity of PbIMS toward lead reached up to 103 mg g⁻¹ at pH 2.0, which was greater even than that of the simply modified SBA-15 by IDA at pH 4.5. The values of selectivity coefficients of PbIMS for six competing metal ions ranged from 67.3 to 12.7. The adsorption of Pb²⁺ reached equilibrium within 7 min. The adsorption efficiency of PbIMS was above 93% after six extraction–stripping cycles. The investigation conducted with real samples of strongly acidic wastewater demonstrated the ability of PbIMS to efficiently remove lead below the current China regulatory standard.