Oxidation and Reduction of Polycrystalline Cerium Oxide Thin Films in Hydrogen.

This study investigates the oxidation state of ceria thin films' surface and subsurface under 100 mTorr hydrogen using ambient pressure X-ray photoelectron spectroscopy. We examine the influence of the initial oxidation state and sample temperature (25-450 °C) on the interaction with hydrogen. Our findings reveal that the oxidation state during hydrogen interaction involves a complex interplay between oxidizing hydride formation, reducing thermal reduction, and reducing formation of hydroxyls followed by water desorption. In all studied conditions, the subsurface exhibits a higher degree of oxidation compared to the surface, with a more subtle difference for the reduced sample. The reduced samples are significantly hydroxylated and covered with molecular water at 25 °C. We also investigate the impact of water vapor impurities in hydrogen. We find that although 1 × 10-6 Torr water vapor oxidizes ceria, it is probably not the primary driver behind the oxidation of reduced ceria in the presence of hydrogen.

Hydrogen Exchange through Hydrogen Bonding between Methanol and Water in the Adsorbed State on Cu(111).

The interaction between submonolayers of methanol and water on Cu(111) is studied at 95-160 K temperature range with surface-sensitive infrared spectroscopy using isotopically labeled molecules. The initial interaction of methanol with the preadsorbed amorphous solid water at 95 K is through hydrogen-bonding with the dangling hydroxyl groups of water. Upon increasing the temperature up to 140 K, methanol and deuterated water form H-bonded structures which allow hydrogen-deuterium exchange between the hydroxyl group of methanol and the deuterated water. The evolution of the O-D and O-H stretching bands indicate that the hydrogen transfer is dominant at around 120-130 K, slightly below the desorption temperature of methanol. Above 140 K, methanol desorbs and a mixture of hydrogen-related water isotopologues remains on the surface. The isotopic composition of this mixture versus the initial D2O:CH3OH ratio supports a potential exchange mechanism via hydrogen hopping between alternating methanol and water molecules in a hydrogen-bonded network.

Measuring the water content in freshly-deposited fingermarks.

The literature view regarding the composition of deposited fingermarks has long been that the average water content is in the range of 98-99wt.%. This value has recently been challenged by Kent, claiming that it should be 20wt.% at most. Herein we have measured the weight percentage of water content in freshly-deposited fingermarks, with and without hand pre-washing. Two complementary techniques were utilized for the measurements, namely quartz crystal microbalance (QCM) for determining the relative mass-loss and its rate at ca. 37°C, and temperature-programmed desorption-mass spectrometry (TPD-MS) for establishing that the mass loss arises solely from the complete evaporation of all the water content in the fingermarks (done with hand pre-washing only). Unlike the traditional narrow-range values of 98-99% and the limiting value of 20wt.% suggested by Kent, our measurements indicate the occurrence of a broad 20-70% water content. Higher contents of water in fingermarks were found post hand pre-washing, most probably due to removal of the sebum from the fingertips, but none of the results exceeded 90%.