Fig. 3.

Binding energy of the modifiers on the COM surface and Ca²⁺. a The optimized structures of COM, taurine, suberic acid, succinic, salicyluric and gentisic acids. b, c Optimized structures of the molecules on the COM (100) and COM (021) surface, with the light-pink, light-blue, brown, blue, yellow and red balls denoting the H, Ca, C, N, S and O atoms, respectively. d X-ray photoelectron spectra (XPS) of taurine, suberic acid, succinic, salicyluric and gentisic acids adsorbed to Ca²⁺. The fitted peaks in blue, pink and red correspond to the C1s peaks of C = O, C–O and C–C, respectively