Temperature effects on the surface acidity properties of zirconium diphosphate

As part of the temperature effects study on the sorption of metallic cations onto zirconium diphosphate, we have first investigated the intrinsic surface properties of this synthetic compound for different temperatures (25, 50, 75 and 90 °C). A physico-chemical study (IR, XRD) assessed its purity, and the measured N2-BET specific area was 13.4±0.2 m2g−1. Mass and potentiometric titrations showed that the experimental point of zero charge (pHpzc=2.6±0.2pHpzc=2.6±0.2) and the surface site density remained constant between 25 and 90 °C. The potentiometric titration data were simulated with the constant capacitance model, considering two reactive surface sites, with a total surface site density equal to 7.2 sitesnm−2. The intrinsic protonation and deprotonation constants were found to increase with the temperature, as well as the calculated apparent constants. The simulation results showed that the capacitance increased with the temperature. The proportions of the neutral, protonated and deprotonated forms for each site type were quantified thermodynamically by application of the Van't Hoff relation.

The variation of the surface acidity constants of ZrP2O7 have been calculated from the simulation of the potentiometric data, using a surface complexation model (CCM). The endothermic character is clearly evidenced as the plotted constants increase with temperature.Figure optionsDownload as PowerPoint slide