LAUSR

Abstract A simple process to synthesize H-octosilicate that is coated with a biocompatible natural surfactant lecithin has been developed, where the hydrothermal synthesis of Na-octosilicate, ion exchange of sodium ions in Na-octosilicate with protons, and surface modification with hydrogenated soy lecithin are sequentially performed in an identical reactor vessel. In the hydrothermal process, the solution pH was appropriately controlled according to a specific pH adjustment procedure, which successfully achieved a high yield (91% in 72 h) of Na-octosilicate. This high yield enabled the conversion of Na-octosilicate to H-octosilicate in the slurry through an acid treatment with no additional operations to remove the unreacted silicate species, such as washing and solid-liquid separation. Subsequently, the addition of a lecithin solution to the H-octosilicate slurry resulted in the formation of lecithin-coated H-octosilicate in situ. The final product (organo-octosilicate) was characterized through XRD, FT-IR, TG-DTA and SEM analyses, which confirmed that it maintained original shapes after the treatments, and lecithin was adsorbed on the surface of H-octosilicate with a mass ratio of approximately 0.24 g-lecithin/g-H-octosilicate. An aqueous suspension of lecithin-coated H-octosilicate showed good dispersion under neutral conditions according to the pH dependence of the zeta potential. In addition, the surface modification inhibited their aggregation even under dry conditions. The results suggest that the developed process contributes to an industrial production of surfactant-coated H-octosilicate.