Effects of inorganic acids and divalent hydrated metal cations (Mg2+, Ca2+, Co2+, Ni2+) on γ-AlOOH sol–gel process

Abstract

In-depth understanding of the sol–gel process plays an essential role in guiding the preparation of new materials. Herein, the effects of different inorganic acids (HCl, HNO₃ and H₂SO₄) and divalent hydrated metal cations (Mg²⁺, Ca²⁺, Co²⁺, Ni²⁺) on γ-AlOOH sol–gel process were studied based on experiments and density functional theory (DFT) calculations. In these experiments, the sol originating from the γ-AlOOH suspension was formed only with the addition of HCl and HNO₃, but not with H₂SO₄. Furthermore, the DFT calculations showed that the strong adsorption of HSO₄⁻ on the surface of the γ-AlOOH particles, and the hydrogen in HSO₄⁻ pointing towards the solvent lead to an unstable configuration of electric double layer (EDL). In the experiment, the gelation time sequence of γ-AlOOH sol obtained by adding metal ions changed when the ionic strength was equal to or greater than 0.198 mol kg⁻¹. The DFT calculations demonstrated that the adsorption energy of hydrated metal ions on the γ-AlOOH surface can actually make a difference in the sol–gel process.