Preparation of superhydrophobic nanocalcite crystals using Box–Behnken design

Superhydrophobic nanocalcite crystals were prepared via an adjusted aqueous reaction of CaO, CO₂ gas and sodium oleate. Box–Behnken design was used to optimize the preparation parameters such as CaO concentration, CO₂ gas flow rate and surfactant concentration. The results revealed that the produced CaCO₃ is indexed to the calcite phase. The crystallite size, particle size, morphology, hydrophobicity and surface charge of CaCO₃ are significantly affected by changing the preparation parameters. The addition of sodium oleate helps in reducing the crystallite size from 101 nm to 48 nm, reducing the particle size from 1.5 μm length scalenohedral particles to 40 nm rhombohedral particles and modifying the properties of pure CaCO₃ from highly hydrophilic to superhydrophobic.