Elucidating the Bimodal Acid-base Behavior of the Water-silica Interface from First Principles

Abstract

Understanding the acid-base behavior of silica surfaces is critical for many nanoscience and bio-nano interface applications. Silanol groups (SiOH) on silica surfaces exhibit two acidity constants--one as acidic as vinegar--but their structural basis remains controversial. The atomic details of the more acidic silanol site govern not just the overall surface charge density at near neutral solution pH, but also how ions and bio-molecules interacts with and bind to silica immersed in water. Using initio molecular dynamics simulations and multiple representative crystalline silica surfaces, we determine the deprotonation free energies of silanol groups with different structural motifs. We show that previously proposed motifs related to chemical connectivity or inter-silanol hydrogen bonds do not yield high acidity. Instead, a plausible candiate for pKa=4.5 silanol groups may be found in locally strained or defected regions with sparse silanol coverage. In the process, irreversible ring-opening reactions of strained silica trimer rings in contact with liquid water are observed.

10 pages, 7 figures

Cited by in corpus (6)

• Using atomic layer deposition to hinder solvent decomposition in lithium ion batteries: first principles modeling and experimental studies
• Electronic Structure Modeling of Electrochemical Reactions at Electrode/Electrolyte Interfaces in Lithium Ion Batteries
• Cobalt-Porphyrin Catalyzed Electrochemical Reduction of Carbon Dioxide in Water II: Mechanism from First Principles
• Optical Imaging of Surface Chemistry and Dynamics in Confinement
• Influence of interface dipole layers on the performance of graphene field effect transistors
• Interplay of Physically Different Properties Leading to Challenges in Separating Lanthanide Cations -- an Ab Initio Molecular Dynamics and Experimental Study