Schematic, synthesis and characterization of MnCO3@Te. (a) Synthetic scheme including TeNDs, MnCO3 and MnCO3@Te. TEM images of MnCO3 (b) and MnCO3@Te (c) nanosystems under different scales. (d) SEM image of MnCO3@Te. (e) Elemental mapping analysis of MnCO3@Te. (f) TEM images of MnCO3@Te obtained at different reaction times to show the reaction progress. (g–h) Hydrodynamic diameters and zeta potentials of MnCO3, TeNDs and MnCO3@Te. (i) Digital photograph of MnCO3, TeNDs and MnCO3@Te in water solution. (j) XRD analysis of MnCO3, TeNDs and MnCO3@Te. (k) Whole XPS spectrum of MnCO3, TeNDs and MnCO3@Te. (l–n) High-resolution XPS spectrum of Mn3s, Mn 2p and Te3d in MnCO3 and MnCO3@Te nanomaterials.