The relationship among intrinsic surface reaction constant (K) in 1-pK model, point of zero net charge (PZNC) and structural charge density (st) for amphoteric solid with structural charges was established in order to...The relationship among intrinsic surface reaction constant (K) in 1-pK model, point of zero net charge (PZNC) and structural charge density (st) for amphoteric solid with structural charges was established in order to investigate the effect of st on pK. The theoretical analysis based on 1-pK model indicates that the independent PZNC of electrolyte concentration (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 pHPZNC. The pK can be expressed as pK=-pHPZNC+log[(1+2aPZNC)/(1-2aPZNC)], where aPZNC≡st/eNANs, in which e is the elementary charge, NA the Avogadro抯 constant and Ns the total density of surface sites. For solids without structural charges, pK=-pHPZNC. The pK values of hydrotalcite-like compounds (HTlc) with general formula of [Mg1-xFex(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-.展开更多
基金Project supported by the National Natural Science Foundation of China (No. 20273041) and State Education Ministry.
文摘The relationship among intrinsic surface reaction constant (K) in 1-pK model, point of zero net charge (PZNC) and structural charge density (st) for amphoteric solid with structural charges was established in order to investigate the effect of st on pK. The theoretical analysis based on 1-pK model indicates that the independent PZNC of electrolyte concentration (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 pHPZNC. The pK can be expressed as pK=-pHPZNC+log[(1+2aPZNC)/(1-2aPZNC)], where aPZNC≡st/eNANs, in which e is the elementary charge, NA the Avogadro抯 constant and Ns the total density of surface sites. For solids without structural charges, pK=-pHPZNC. The pK values of hydrotalcite-like compounds (HTlc) with general formula of [Mg1-xFex(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-.
