Efficient Adsorptive Removal of Cationic Dyes from Aqueous Solution by Magnetic Silica Core-Shell Nanoparticles

The use of magnetic nanomaterials (MNPs) as adsorbents to eliminate pollution causing dyes from water has attracted substantial attention in recent years because they can be easily isolated and reused. In this work, core–shell Fe₃O₄@SiO₂ MNPs in which magnetic Fe₃O₄ NPs as a core enclosed with a thick SiO₂ shell were successfully synthesized by chemical co–precipitation followed by hydrolysis and condensation of alkoxysilanes in a mixture of ammonia, ethanol and water. The formation of core–shell Fe₃O₄@SiO₂ MNPs has been characterized by TEM, TEM-EDS, XRD, FT-IR and VSM. TEM characterization revealed that several Fe₃O₄ NPs (around 10 nm) aggregated to form a Fe₃O₄ magnetic core and surrounded by an uniform SiO₂ shell of 40-50 nm thickness to obtain Fe₃O₄@SiO₂ magnetic core–shell NPs. As synthesized core–shell NPs were employed as adsorbent for elimination of two cationic toxic dyes, crystal violet (CV) and malachite green (MG) from aqueous solutions. Further, different adsorption parameters such as pH, adsorbent dosage and contact times of the dyes were found to enhance the adsorption of cationic dyes. At neutral pH 7 the cationic dyes could be speedily removed from aqueous solution with high efficiency. It has been observed that 0.35 g of adsorbent dosage is sufficient for 95% of dye removal efficiency. The contact time is optimised for 20 min for both the dyes. The Langmuir model adsorption isotherm is best suitable which indicates that the cationic dyes adsorption behaviour of Fe₃O₄@SiO₂ is a homogeneous monolayer chemisorption process. The adsorptive binding of CV/MG with Fe₃O₄@SiO₂ was directed through electrostatic interactions. Moreover, the magnetic adsorbents could be easily reused and regenerated with almost no adsorption capability is significantly reduced up to 5 cycles. So, the Fe₃O₄@SiO₂ is an efficient and reusable adsorbent for rapid and removal of cationic dyes from the aqueous solution.