Model prediction of the point of zero net charge of layered double hydroxides and clay minerals

Many models such as electrostatic, crystallographic, and electronegativity models have been developed to predict the point of zero net charge (PZNC) of (hydr)oxides without structural charge. Nevertheless, there is still a lack of feasible models to predict the PZNC of structurally charged amphoteric solids, such as positively charged layered double hydroxides (LDHs) and negatively charged clay minerals, using easily available characteristic physical constants. Herein, a new model, called general "electrostatic-electronegativity" (ESEN) model, was proposed based on the classical electrostatic and electronegativity models by taking into account the structural charge (sigma(st)). The new model correlates the PZNC of amphoteric solids with sigma(st) and easily available characteristic physical constants (ionic valence, ionic radius, and electronegativity). The empirical parameters in the model were simulated using the PZNC data of 22 (hydr)oxides previously reported. The so-obtained ESEN model equations can predict the PZNC of (hydr)oxides, LDHs, and silicate clay minerals with acceptable feasibility and accuracy. To the best of our knowledge, this is the first feasible model to predict the PZNC of both LDHs and silicate clay minerals using easily available characteristic physical constants, which is important for the design synthesis and application of new materials.