Synthesis of poly(styrene-co-methacrylic acid)-coated magnetite nanoparticles as effective adsorbents for the removal of crystal violet and Rhodamine B: a comparative study

In this work, Fe₃O₄/Poly(styrene-co-methacrylic acid) (St-co-MAA) particles with different particle sizes (20 and 255 nm) were synthesized by miniemulsion polymerization via two routes. The synthesized particles were used as adsorbents for the removal of crystal violet (CV) and Rhodamine B (RB) from water solution. The as-prepared adsorbents were characterized by Fourier transform infrared (FT-IR) spectra, transmission electron microscope (TEM), vibrating sample magnetometer (VSM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). Magnetic measurements revealed that the obtained Fe₃O₄/Poly(St-co-MAA) with small particle size (20 nm) has superparamagnetism properties. The effects of various factors on the adsorption capacity, such as contact time, pH of dyes solution, and initial dyes concentration were investigated. The studies showed that the experimental data are fitted well with Langmuir model, indicating homogeneous monolayer adsorption process. Adsorption kinetics of Fe₃O₄/Poly(St-co-MAA) were well explained by the pseudo-second-order model, suggesting a chemical adsorption process. The maximum adsorption capacities (q _m) of CV and RB onto Fe₃O₄/Poly(St-co-MAA) with small particles size were 416.66 and 69.54 mg g⁻¹, respectively, which were much higher than the adsorption capacities of adsorbent with large particle sizes (q _m of CV = 207.9 and q _m of RB = 38.91 mg g⁻¹). The dye-adsorbed magnetic Poly(St-co-MAA) could be easily desorbed and reused for at least four cycles with a little decrease in adsorption capacity.