Efficient removal of cationic and anionic dyes by surfactant modified Fe3O4 nanoparticles

Magnetic nanoparticle adsorbents overcome the difficulty of solid-liquid separation in adsorption technology systems. However, their extremely large specific surface energy results in high levels of nanoparticle agglomeration and reduces their adsorption efficiency. To solve this problem, this study modified Fe3O4 particles with sodium dodecyl sulfate (SDS) and Cetyl Pyridine Chloride (CPC). Compared with pure Fe3O4 particles, the size distributions of SDS@Fe3O4 and CPC@Fe3O4 were more uniform, with a high level of magnetism and the capacity to achieve rapid separation (56.49 emu/g for SDS@Fe3O4 and 55.89 emu/g for CPC@Fe3O4). The results of dye adsorption tests showed that the adsorption effect was improved after modification, resulting in adsorption capacities of 62.43 mg/g for methylene blue (MB) by SDS@Fe3O4 and 176.98 mg/g for Congo red (CR) by CPC@Fe3O4. XRD results showed that the structure did not change, while FTIR results showed that no new functional groups were formed after adsorption. Adsorption followed pseudo-second-order reaction models, indicating that adsorption occurs via chemical adsorption processes. The adsorption process occurred mostly in accordance with the Langmuir model, which illustrates that monolayer adsorption was the dominant process. Thermodynamic data indicates that the adsorption process was endothermic and spontaneous. The adsorption mechanism for MB by SDS@Fe3O4 may be electrostatic adsorption and hydrophobic interaction, while for CR by CPC@Fe3O4 the mechanism may be electrostatic adsorption and hydrogen bonding. In addition, after five cycles of regeneration, the removal rate of MB was >77.0% and the removal rate of CR was >91.9%, confirming the excellent regeneration performance of Fe3O4. The simple and environmentally friendly manufacturing method, efficient adsorption process, rapid magnetic separation, indicate that surfactant modification of magnetic nanoparticles is an effective method for dye adsorption and removal.