Green synthesis of SiO₂/CuO binary nanocomposites by a modified sol–gel method based on rice husk ash for lead extraction in water samples

In this study, silica nanoparticles were prepared from rice husk ash (RHA), a sustainable agricultural waste, and used to synthesize SiO₂/CuO nanocomposites via a sol-gel technique for the removal of Pb(II) ions from aqueous water samples. First, 0.2 g of the SiO₂/CuO nanocomposite was added to 10 mL of standard or environmental water samples adjusted to pH 5.5. The mixture was ultrasonicated to enhance adsorption and facilitate the extraction of Pb(II) ions via surface complexation at the Si–O–Pb and Cu–O–Pb active sites. After adsorption, the nanocomposite was separated by filtration, and the retained Pb(II) ions were desorbed under acidic conditions. Finally, the concentration of lead was determined by electrothermal atomic absorption spectrometry (ET-AAS). Nanocomposites with molar ratios of SiO2 to CuO (1:1, 1:2, and 2:1) were prepared and calcined at temperatures ranging from 200 to 600 °C. Fourier-transform infrared spectroscopy (FTIR) confirmed the presence of typical Si–O–Si bands (~1065 and 800 cm−1) and CuO vibrations (~492 and 449 cm−1). Also, energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), and atomic force microscopy (AFM) were performed. Brunauer-Emmett-Teller (BET) analysis revealed that the surface area ranged from 0.96 to 71.06 m2 g-1, with a pore diameter of 5.7–42.09 nm, and that both parameters were significantly dependent on the calcination temperature. The proposed method exhibited an enrichment factor of 9.68, a linear range of 0.3–10.5 µg L⁻¹, an LOD of 0.068 µg L⁻¹, and RSD values below 5% for Pb (II) determination in water samples (n=5).