Comparison investigation of the effects of ionic surfactants on the crystallization behavior of calcium oxalate: From cationic to anionic surfactant

Calcium oxalate particles with different morphologies and phase structures were prepared by a facile precipitation reaction of sodium oxalate with calcium chloride in the presence of sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) at different temperatures. The as-prepared products were characterized with scanning electron microscopy (SEM) and X-ray diffraction (XRD). It was found that the variations in the concentration of surfactants and temperatures significantly influenced the crystal structure, morphology, and particle size of the products. Cationic surfactant CTAB did not affect the crystal phase: calcium oxalate monohydrate (COM) was the only hydrate formed. Anionic surfactant SDS, however, not only changed the crystal shape, but also induced the formation of metastable calcium oxalate dihydrate (COD) with increasing surfactant concentration. High temperature favored the formation of COM. This work may provide new insights into the morphological control of calcium oxalate particles.