Multifunctional Adsorption of Cationic Dyes Using Sodium 1-Hexadecanesulfonate-Modified Fe ₃ O ₄ @SiO ₂ @Polypyrrole Nanochains: Kinetics, Isotherms, and Mechanistic Elucidation

With the rapid growth of industries such as textiles and dyeing, water pollution caused by cationic dyes has become increasingly severe. To address this issue, 1D sodium 1-hexadecanesulfonate-modified Fe₃O₄@SiO₂@polypyrrole (1D FSP/S1-HS) composite was synthesized and employed for the removal of four typical cationic dyes: methylene blue (MB), malachite green (MG), crystal violet (CV), and rhodamine B (RhB). Adsorption studies under various conditions revealed that the maximum adsorption capacities for MB, MG, CV, and RhB were 135.037, 102.759, 170.744, and 160.586 mg/g, respectively, demonstrating excellent adsorption performance. This excellent performance stems from the material's advantageous physicochemical characteristics, such as its high saturation magnetization (39.596 emu/g) and stable negative surface charge (zeta potential <0 mV) over a broad pH range (2-12). The adsorption kinetics and isotherm data were best described by the pseudo-second-order and Langmuir models, respectively, indicating a chemisorption process involving monolayer coverage. Thermodynamic parameters revealed the adsorption to be a spontaneous, heat-absorbing process. After five adsorption-desorption cycles and in the presence of coexisting ions, the removal efficiency decreased by less than 3%, indicating excellent reusability and stability. Finally, density functional theory (DFT) calculations supported a multimechanism adsorption process involving electrostatic interactions, hydrogen bonding, and π-π stacking. Overall, the 1D FSP/S1-HS composite exhibits great potential for practical applications in dye-contaminated wastewater treatment.