Ampholytic microspheres constructed from chitosan and carrageenan in alkali/urea aqueous solution for purification of various wastewater

Natural polymers as abundant resource are excellent candidates of adsorbents for wastewater purification due to their inherent advantages such as strong affinity, biodegradability, and non-toxic. In this work, ampholytic polyelectrolyte microspheres were fabricated successfully via emulsification procedure from the homogeneous chitosan/carrageenan solution in LiOH/KOH/urea aqueous system, showing good compatibility and homogeneous network structure. In the chitosan/carrageenan blend solution, chitosan displayed the neutral feature, as a result of the dissolution caused by destruction of the native intermolecular hydrogen bonds rather than protonation of the amino groups, thus no flocculation occurred here. The experimental results demonstrated that the ampholytic microspheres were composed of positively charged chitosan and negatively charged carrageenan, and the magnetic Fe3O4 nanoparticles with a mean diameter of 180 nm were embedded in the composite matrix, showing a sensitive magnetic responsiveness. The ampholytic microspheres exhibited highly efficient adsorption capacity towards both cationic and anionic dyes and heavy metal ions in wastewater, as a result of their strong electrostatic and chelating affinity. The ampholytic chitosan/carrageenan composite matrix in microspheres played a dominant role in the adsorption of pollutants, and the Fe3O4 nanoparticles were mainly contributed to magnetic separation. The effects of ionic strength and pH value on adsorption behaviors indicated that the microspheres were available to be used in a harsh environment. The ampholytic microspheres could also be used as column packing for rapid and efficient dye wastewater purification. Furthermore, the microspheres could be recycled, reused, and biodegraded in soil, showing great potentials in the field of the water decontamination.