Synthesis, characterization and application of cyclam-modified magnetic SBA-15 as a novel sorbent and its optimization by central composite design for adsorption and determination of trace amounts of lead ions

Abstract

A novel adsorbent based on 1,4,8,11-tetraazacyclotetradecane (cyclam) loaded in mesoporous silica (cyclam-SBA-15) was synthesised and modified by Fe₃O₄ magnetic nanoparticles (Fe₃O₄@cyclam-SBA-15). Characterization was performed by scanning electron microscopy (SEM), Fourier transform infra-red spectroscopy (FT-IR) and X-ray powder diffraction (XRD). The application of this sorbent was analyzed in magnetic solid phase extraction (MSPE) and adsorption of trace amounts of lead ions (Pb²⁺). The effects of various factors, such as adsorbent dosage, initial concentration of the lead ion, contact time and pH of the solution, on the removal efficiency were simultaneously evaluated by central composite design (CCD) under response surface methodology (RSM). The optimized conditions were found to be 0.004 g, 20 mg L⁻¹, 40 min and 4.8, for adsorbent dosage, initial Pb concentration, contact time and pH, respectively. For the extraction experiments, the nature and volume of the eluent were also investigated to obtain the optimum conditions for the enrichment factor. Due to the high stability of the magnetic adsorbent, it can be used several times with only a slight decrease in the recovery of Pb(II) ions. The effects of matrix ions on the retention of the Pb²⁺ ions were also studied in order to examine the selectivity of this sorbent toward Pb(II) ions. Under the optimal conditions, the proposed method exhibited a high adsorption capacity of 625 mg g⁻¹, a detection limit of 2.02 μg L⁻¹ and an enrichment factor of 200 with a relative standard deviation (RSD%) of 4.14%. Finally, the application of the synthesized material was evaluated for adsorption and preconcentration of lead ions from foods and environmental water samples.