Protolytic behavior of hydroxylated Pyrex glass surfaces in NaCl media

Adsorption of hydrogen ions from aqueous NaCl solutions at the Pyrex glass–water interface was investigated by acid–base titration (glass electrode) at 25 °C and at the ionic strengths 0.010, 0.030, 0.10, 1.0, and 3.0 mol dm−3. The pH values ranged from 2 to 7. The Pyrex samples had a specific surface area of 19.2×103 m2kg−1 and a porous structure (pores 2.4 nm thick, 280 nm long). The reactions were found to be extremely slow but showed good reversibility. The potentiometric data, due to the small effect of ionic strength on the equilibria, were fitted with a simple nonelectrostatic model based on strong specific interactions of medium ions with deprotonated silanol, >SiO−, and boranol, >BO−, as well as with protonated sites. The acid–base properties are described by the reactions and equilibrium constants at the infinite dilution reference state: >SiONa + H+ ⇄ >SiOHNa+, logβ110Si=3.1±0.2; >SiONa + 2H+ + Cl− ⇄ >SiOH2Cl + Na+, logβ201Si=6.75±0.15; >SiONa + H+ ⇄ >SiOH + Na+, logβ100Si=1.8±0.2, >BONa + H+ ⇄ >BOH + Na+, logβ100B=6.4±0.2; >BONa + H+ ⇄ >BOHNa+, logβ110B=6.6±0.2; >BONa + 2H+ ⇄ >BOH+2 + Na+, logβ200B=11.56±0.15.

Graphical abstractAdsorption of hydrogen ions from aqueous NaCl solutions at the Pyrex glass–water interface was investigated by acid–base titrations.The acid–base properties are described by equilibrium constants.Figure optionsDownload full-size imageDownload as PowerPoint slide