Hydroxyl Identification on ZnO by Infrared Spectroscopies: Theory and Experiments

Herein, we present a thorough density functional study combining experiments on ZnO nanostructures aimed at the identification, by means of infrared (IR) spectroscopies, of hydroxyl and hydride species formed on the most stable low-index Miller surfaces of wurtzite ZnO, namely, the Zn- and O-terminated (0001) and (000 (1) over bar) polar surfaces and the nonpolar (10 (1) over bar0) and (11 (2) over bar0) surfaces. The Perdew-Burke-Ernzerhof functional was employed in periodic slab calculations, all possible H and OH adsorption modes were studied at medium and full coverages, and IR spectra were simulated for the most favorable situations. This information was used to model the most likely surface arrangements upon exposure to either H-2 or H2O. IR experiments on ZnO surfaces and nanoparticles are discussed based on the calculated adsorption energy values and simulated IR spectra. This study emphasizes the detailed assignment of OH moieties with the help of IR spectra and their interpretation as fingerprints of surface morphology, allowing for a consistent interpretation of the stability of water adlayers and their corresponding vibrational fingerprints as a function of coverage, low-index Miller surface, and hydrogen source.