Mesoscale Transformation of Amorphous Calcium Carbonate to Porous Vaterite Microparticles with Morphology Control

The morphology controlled synthesis of porous vaterite microparticles from amorphous calcium carbonate (ACC) nanoparticles via mesoscale transformation and self-assembly is presented. The morphology of vaterite microparticles ranging from ellipsoidal to spherical can be controlled by adjusting the amount of adipic acid (AA) additive during synthesis. Electron microscopy and electron diffraction reveal that the vaterite microparticles are formed by the oriented self-assembly of vaterite nanocrystals. The Brunauer–Emmett–Teller (BET) surface area of the vaterite microparticle varies between ∼30 and ∼80 m2/g. The coverage of AA on the surface of the ACC nanoparticle plays the pivotal role in the morphology controlled synthesis of vaterite microparticles. 6-Aminocaproic acid (6A), benzoic acid (BA), citric acid (CA), and poly(acrylic acid) (PAA) are also tested as additives and their effect on the morphology of vaterite microparticles is presented. Morphology control of functional materials can be beneficial for application where the morphology and porosity are critical, such as drug delivery. This work demonstrates a possible method to finely adjust the morphology of vaterite microparticles with the assistance of additives through mesoscale transformation and self-assembly using amorphous nanoparticles as precursors.