Surface modification of silica-coated magnetic nanoparticles for effective removal of methylene blue from water samples

Abstract

Magnetic nanoparticles were successfully modified with a thin layer of molecularly imprinted polymers (MIPs) via the admicellar polymerization technique for the selective removal of methylene blue (MB) from real water samples. The chemical and morphological properties of the synthesized materials were comprehensively characterized using Fourier Transform Infrared Spectroscopy–Attenuated Total Reflectance (FTIR–ATR), X-ray Photoelectron Spectroscopy (XPS), and Transmission Electron Microscopy (TEM). The adsorption kinetics were better described by the pseudo-second-order kinetic model (R² > 0.99), indicating that the adsorption process was mainly governed by chemical interactions. The maximum binding capacity of the MB-imprinted polymer-modified magnetic nanoparticles was determined to be 5.64 mg g⁻¹ (95% CI: 6.76–4.52 mg g⁻¹). Equilibrium adsorption data showed a better fit to the Freundlich isotherm model (R² > 0.99), suggesting heterogeneous adsorption behaviour, which is characteristic of molecularly imprinted systems. The prepared adsorbent exhibited excellent reusability and maintained its adsorption performance over seven consecutive adsorption–desorption cycles without significant efficiency loss. The imprinting factor for MB was calculated as 7.18, while lower values were obtained for methylene violet (3.11) and indigo carmine (1.97), demonstrating the high selectivity of the imprinted cavities toward the template molecule. Moreover, the selectivity coefficients (k) for methylene violet (2.41) and indigo carmine (3.18) confirmed the preferential recognition of MB over competing dye molecules. The optimum adsorption conditions were determined as pH 7 and an incubation time of 35 min. The applicability of the developed MIP-based magnetic adsorbent was further validated using real water samples collected from different natural sources. The findings highlight the novelty and potential of the proposed system as a selective, reusable, and efficient adsorbent for wastewater treatment applications.