The preparation of core-shell Fe3O4@SiO2 magnetic nanoparticles with different surface carboxyl densities and their application in the removal of methylene blue

The removal of methylene blue (MB) with the magnetic separation in water treatment is of increasing attentions due to its high solubility and chemical stability, which poses a great challenge on the ecological environment and human health. Herein, with assistance of simplified modification strategies, multi-carboxyl functionalized Fe3O4@SiO2 magnetic nanoparticles (mCMNPs) have been developed with a novel insight into the grafting densities effects on the adsorption process. The results of UV-Vis spectrometry obviously showed that the increased carboxyl content on the surface of CMNPs resulted in the significant improvement in the removal process of MB. Among different types of CMNPs, mCMNPs were chosen for the separation of MB owing to possessing the highest surface carboxyl densities 0.2363 mmol/g and exhibiting the highest removal efficiency of 96.18%. Several important factors including solution pH, initial MB concentration and sorption time were optimized to achieve the best removal efficiency. Desired adsorption capacity for MB (34.75 mg/g) was achieved using mCMNPs with the pH 10, sorption time of 100 min and initial MB concentration of 50 mg/L. The sorption isotherms and sorption kinetics can be well in agreement with the Langmuir model and pseudo-second-order kinetic model, respectively. Most importantly, the synthesized mCMNPs still exhibited high removal efficiency (63%) after 5 cycle numbers. As adsorbents, it is noted that the prepared mCMNPs possessed the excellent regeneration ability and recyclability and could be a promising adsorbent for the removal of MB in water treatment.