Intrinsic Surface Reaction Constant in 1‐pK Model of Mg‐Fe Hydrotalcite‐like Compounds

The relationship among intrinsic surface reaction constant ( K ) in 1‐pK model, point of zero net charge (PZNC) and structural charge density (σ st ) for amphoteric solid with structural charges was established in order to investigate the effect of σ st on pK . The theoretical analysis based on 1‐pK model indicates that the independent PZNC of electrolyte concenmtion (c) exists for amphoteric solid with structural charges. A common intersection point (CIP) should appear on the acid‐base titration curves at different c. and the pH at the CIP is pH PZNC . The pK can be expressed as pK=‐pH PZNC +log[(l+2α PZNC )/(1–2α PZNC )], where α‐ PZNC σ/e N A N s , in which e is the elementary charge, N a the Avogadro's constant and N S the total density of surface sites. For solids without structural charges, pK=‐ pH PZNC . The pK values of hydrotalcite‐like compounds (HTlc) with general formula of [Mg 1‐x Fe x (OH) 2 ](Cl, OH) x were evaluated. With increasing x . the pK increases, which can be explained based on the affinity of metal cations for H − or OH − and the electrostatic interaction between charging surface and H − or OH − .