Aqueous interfaces play a central role in transport and reactive processes such as photo-electrochemistry for fuel production and environmental recovery, water treatment for electrochemical desalination, and self-cleaning for antimicrobial surfaces. Of particular relevance is the water interface with TiO2, one of the most widely used materials in photocatalysis. In this talk I will discuss recent applications of first principles simulations to characterize the water interfaces with pristine and chemically-modified TiO2 surfaces. For example, ab-initio molecular dynamics (AIMD) simulations of formic and acetic acid covered anatase TiO2 in contact with water provide insight into the role of the competitive interactions of carboxylic acid and water on functionalized TiO2as well as the observed hydrophobic behavior of TiO2 surfaces under ambient conditions. However, the time and length scales sampled by AIMD are often insufficient to fully characterize the structure of interfacial water on solid materials, in particular the extent of water dissociation at the TiO2-water interface. To address this issue, we simulated the TiO2–water interface using molecular dynamics with an ab initio-based deep neural network potential. These simulations provide a new picture of this interface, revealing a dynamical equilibrium of molecular and dissociated water on the oxide surface. Due to the relevance of surface hydroxyl groups to the surface chemistry of TiO2, these results might be key to understanding phenomena ranging from surface functionalization to photocatalytic mechanisms.

First principles simulations of water: Titania interfaces

ACS Spring 2022

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