Abstract
The surface chemistry of water on zinc oxides is an important topic in catalysis and photocatalysis. Interaction of D2O with anisotropic ZnO(101‾ 0) surfaces was studied by IR reflection absorption spectroscopy using s‐ and p‐polarized light incident along different directions. Interpretation of the experimental data is aided using isotopologues and DFT calculations. The presence of numerous species is revealed: intact monomers, a mixed 2D D2O/OD adlayer, an anisotropic bilayer, and H‐bonded 3D structures. The isolated water monomers are identified unambiguously at low temperatures. The thermally induced diffusion of water monomers occurs at elevated temperatures, forming dimers that undergo autocatalytic dissociation via proton transfer. Polarization‐ and azimuth‐resolved IR data provide information on the orientation and strength of H‐bonds within the 2D and 3D structures. Ab initio molecular dynamics simulations reveal strong anharmonic couplings within the H‐bond network.
Highlights
The interaction of water with solid substrates is a topic of pronounced fundamental interest.[1,2,3] In catalysis, photocatalysis, and corrosion, water is omnipresent, either as a reactant, product, solvent, or contamination.[4,5,6,7,8,9,10,11,12] In some cases water even takes the role of a catalyst.[13]
Previous extensive research efforts combining experiments and density functional theory (DFT) calculations revealed that the properties of water/zinc oxide (ZnO) systems vary strongly depending on preparation conditions and the surface termination of the substrate.[20,21,22,23,24,25,26,27,28,29,30,31,32]
We present a comprehensive atomic-level picture of the surface chemistry of water on the non-polar ZnO(101 ̄ 0) surface derived from experimental data obtained using infrared reflection–absorption spectroscopy (IRRAS), which are interpreted by state-of-the-art DFT calculations and ab initio molecular dynamics (AIMD) simulations
Summary
The interaction of water with solid substrates is a topic of pronounced fundamental interest.[1,2,3] In catalysis, photocatalysis, and corrosion, water is omnipresent, either as a reactant, product, solvent, or contamination.[4,5,6,7,8,9,10,11,12] In some cases water even takes the role of a catalyst.[13]. Hydration processes at ZnO surfaces are of relevance for numerous catalytic reactions, such as methanol production from synthesis gas and the water-gas shift reaction, producing hydrogen.[15,16,17,18,19] Previous extensive research efforts combining experiments and density functional theory (DFT) calculations revealed that the properties of water/ZnO systems vary strongly depending on preparation conditions and the surface termination of the substrate.[20,21,22,23,24,25,26,27,28,29,30,31,32]. Despite substantial experimental effort dedicated to water/ZnO interfaces, many important issues are still debated, including the identification of isolated water monomers, the transition from monomer species to a full monolayer, the structural evolution of bi- and multilayers, and insight into the importance of the formation of H-bonded 2D and 3D structures. The thorough polarization and azimuth- and temperature-dependent IRRAS data allow for a detailed determination of adsorbate geometry as well as of the orientation and strength of various H-bonds in 2D and 3D structures
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