Facile batch synthesis of porous vaterite microspheres for high efficient and fast removal of toxic heavy metal ions

The contamination of water by heavy metals has become one of the greatest threats to global ecological systems. Vaterite, in spite of the excellent performance to remove toxic metal ions, is difficult to be prepared with a large scale production, which limits its further industrial application. To this end, we developed a green and rapid approach to prepare in batch uniform porous vaterite/chitosan oligosaccharide (COS) hybrid microspheres (VCOS) at room temperature. Especially in the presence of 5 g L-1 COS, high vaterite content (nearly 100%) and large scale production of CaCO3 microspheres were obtained within only 2 min without any other organic solvent. SEM images showed that an individual hybrid microsphere was composed of many nanoparticles, and TEM results demonstrated that these nanoparticles consisted of multiple nanocrystals. It was found that the concentration of COS and high shearing stirring were the key issues for the high production of V-COS. Based on the results the formation mechanism of V-COS was proposed. Their application for removal of lead and cadmium ions from aqueous solutions was investigated. The high and fast adsorption capacity for Pb2+ and Cd2+ ions were achieved with the adsorption amount up to 1884 and 156 mg/g within 6 min, respectively, which were much higher than that of rhombohedron CaCO3 obtained without stirring (R-COS). The porous vaterite hybrid microspheres obtained with such large scale production has never been reported before, and this will lay foundation for its further wide applications.