Fabrication of BaCO3 sheaves tailored by carboxymethyl cellulose under compressed CO2

► Sheaf-like BaCO3 crystals with rods branched off are obtained under compressed CO2. ► BaCO3 sheaves are concentration-dependent on the added CMC. ► Molecular dynamic simulation reveals the selective attachment of CMC onto witherite unit. ► BaCO3 sheaves are formed by twinning and spherulitic growth.