Microfluidic preparation of magnetic chitosan microsphere and its adsorption towards Congo red

Facile separation from feed liquid is practically important for application of adsorbents, especially for powdery adsorbents. To this challenge, a co-flow microfluidic device was set up in this work to prepare a magnetic chitosan microsphere without using any surfactant or cross-linking agent. In the microfluidic preparation, a chitosan solution containing Fe2+ and Fe3+ was cut by the shear force of the flow of the continuous phase of isopentanol to form monodispersed droplets, which were introduced into an ammonia aqueous solution bath to obtain the magnetic microspheres. The microstructure of the magnetic chitosan microsphere was carefully characterized, and was compared with that of the neat chitosan microsphere. Our results indicate that the co-precipitated Fe2+ and Fe3+ form in situ magnetite Fe3O4 nanoparticles of 4.6 ± 1.7 nm in the matrix of chitosan, endowing the magnetic chitosan microsphere with superparamagnetic property and with 41.3 emu/g saturation magnetization. In addition, the magnetic chitosan microsphere displays only slight decrease in equilibrium adsorption capacity towards Congo red, but reveals much faster adsorption, when compared with the neat chitosan microsphere. We attribute those to the walnut-like wrinkle surface and high zeta potential of the magnetic chitosan microsphere. Therefore, our work provides a method of preparing even-sized magnetic chitosan microsphere, which can adsorb anionic dye quickly and can be facilely removed from liquid phase after adsorption, implying an excellent adsorbent candidate with great potential.