Adsorption and substitution effects of Mg on the growth of calcium sulfate hemihydrate: An ab initio DFT study

• Published in: Applied surface science 2015-12, Vol.357, p.1552-1557
• Main Authors: Xin, Yan, Hou, S.C., Xiang, Lan, Yu, Yang-Xin
• Format: Article
• Language: English
• Subjects: Adsorption; Calcium sulfate; Calcium sulfate hemihydrate; Charging; Density functional theory; Electrostatics; First principle; Growth of nanocrystal; Mathematical analysis; Planes; Substitution; Surface chemistry
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2015.09.223

•Adsorption/substitution of Mg on CaSO4·0.5H2O was studied theoretically.•The (200)1 plane shows significant interaction with Mg than the other planes.•Weak adsorption of Ca on Mg-doped (200)1 plane and strong on (002) plane.•Mg2+ is proved to be the best additive compared with other metal ions. Calcium sulfate hemihydrate (CaSO4·0.5H2O, CSH) whiskers with high aspect ratio are promising reinforce materials which have drawn much attention. In order to obtain high quality CSH materials, effect of Mg2+ ions on properties of the (002), (200)1 and (200)2 planes of CSH is investigated using an ab initio density functional theory (DFT) with a van der Waals (vdW) dispersion-correction. The computed results show that strong adsorption and substitution effects take place between Mg2+ ion and (200)1 plane. The adsorption energies of an Mg2+ ion on the (002), (200)1 and (200)2 planes are −0.066, −0.571 and −0.047eV, respectively. An insight into the electrostatic potential of pristine CSH planes has demonstrated that the (200)1 plane is much more negatively charged than the (002) and (200)2 planes. The energies of the substitution of a Ca atom with an Mg atom on the CSH (002), (200)1 and (200)2 planes are 1.572, 0.063 and 1.349eV, respectively. It is found that Ca atoms on the (200)1 plane are relatively easy to be substituted by Mg atoms. The calculation results of a Ca2+ ion adsorption on the Mg-doped (200)1 plane indicate that the adsorption energies increase apparently as the doping ratio varies from 0 to 1.0. Compared with K+, Na+ and Al3+ ions, Mg2+ ion is the most promising additive to promote the growth of CSH along c axis.