Water agglomerates on Fe ₃ O ₄ (001)

Abstract

Determining the structure of water adsorbed on solid surfaces is a notoriously difficult task and pushes the limits of experimental and theoretical techniques. Here, we follow the evolution of water agglomerates on FeO(001); a complex mineral surface relevant in both modern technology and the natural environment. Strong OH-HO bonds drive the formation of partially dissociated water dimers at low coverage, but a surface reconstruction restricts the density of such species to one per unit cell. The dimers act as an anchor for further water molecules as the coverage increases, leading first to partially dissociated water trimers, and then to a ring-like, hydrogen-bonded network that covers the entire surface. Unraveling this complexity requires the concerted application of several state-of-the-art methods. Quantitative temperature-programmed desorption (TPD) reveals the coverage of stable structures, monochromatic X-ray photoelectron spectroscopy (XPS) shows the extent of partial dissociation, and noncontact atomic force microscopy (AFM) using a CO-functionalized tip provides a direct view of the agglomerate structure. Together, these data provide a stringent test of the minimum-energy configurations determined via a van der Waals density functional theory (DFT)-based genetic search.

Hydrogen production and photocatalytic activity of g‐C3N4/Co‐MOF (ZIF‐67) nanocomposite under visible light irradiation

“…The spectra of N 1 s shown in Figure d and it contains three peaks and labeled as N1, N2 and N3 and the binding energies are 398.3 eV, 399.7 eV, and 400.6 eV respectively, the N1 peak attributed to C=N‐C, N2 peak attributed to C‐NH 2 and the final N3 peak attributed to N=N respectively . The spectra of O 1 s shown in Figure e and it contains two peaks, the first peak (O1 peak) at 531.5 eV and it belongs to OH group and the second peak (O2 peak) at 534.0 eV belongs to H 2 O molecule adsorbed on g‐C 3 N 4 /ZIF‐67 surface …”

Influence of Local Defects on the Dynamics of O–H Bond Breaking and Formation on a Magnetite Surface

“…Surface hydroxyl groups result naturally from background water dissociation during the annealing process. 15 A boron nitride heater was used to heat the sample and a type K thermocouple attached to the crystal to record the temperature. The thermocouple is referenced internally to the chamber temperature.…”

“…On the magnetite Fe3O4(001) surface, however, only confined diffusion of hydrogen atoms was observed below the water desorption temperature. [13][14][15] Here, hydrogen can bind to two specific sites in the unit cell of the surface reconstruction and switch between them reversibly. 16,17 In the present work, we investigate the switching between these two adjacent sites at elevated temperaturesi.e.…”

“…Fe3O4(001) has a rich defect chemistry that has been discussed in the literature at length. 15,[22][23][24] We focus here on the so-called unreconstructed unit cells of the SCV structure, a local region on the surface where the interstitial tetrahedral Fe atom (Fetet) of the SCV reconstruction is missing and instead two additional Fe atoms are located in octahedral sites (Feoct) of the third atomic layer. 8,22 The defect is the result of a surplus Fe atom in one Feoct site (labelled +Feoct in Figure 1d) which causes the Fe atom in the tetrahedral site of the second layer to move to the other octahedral site in the third layer (indicated by the dashed arrow in Figure 1d).…”

“…These surface hydroxyl groups result from H adatoms which are formed during the crystal preparation process, where water from the residual gas atmosphere can dissociate at oxygen vacancies. 15 Here, we present the first quantitative analysis of the H adatom switching between two adjacent O atoms in the Fe3O4(001) unit cell to determine the energetics involved in this process. Our…”