The photocatalytic activity of anatase TiO₂ decorated with metal clusters has been widely documented, but the nature of the metal–metal oxide interface and reaction intermediates in catalytic processes are still not well understood. This in part is due to the fact that use of photoelectron spectroscopy to deduce the surface chemistry of catalytic systems has long been hampered by the huge pressure difference between real-world operation and the requirement of high vacuum for electron detection. Here, the in situ growth of silver nanoparticles on a model metal-oxide catalyst support and their reactivity with a CO/H₂O gas mixture has been investigated in detail. Using synchrotron X-ray photoelectron spectroscopy, near-ambient pressure X-ray photoelectron spectroscopy, and scanning tunneling microscopy, the interaction of Ag with the anatase TiO₂ surface leads to metal-surface charge transfer and low mobility of Ag on the surface. Upon exposure to a 1.5 mbar CO/1.5 mbar H₂O gas mixture, partial oxidation of the Ag clusters is observed. There is also evidence suggesting that a Ag–carbonyl species is formed during exposure of the Ag/TiO₂ surface to a CO/H₂O gas mixture.

Ionic liquids (ILs) supported on oxide surfaces are being investigated for numerous applications including catalysis, batteries, capacitors, transistors, lubricants, solar cells, corrosion inhibitors, nanoparticle synthesis and biomedical applications. The study of ILs with oxide surfaces presents challenges both experimentally and computationally. The interaction between ILs and oxide surfaces can be rather complex, with defects in the oxide surface playing a key role in the adsorption behaviour and resulting electronic properties. The choice of the cation/anion pair is also important and can influence molecular ordering and electronic properties at the interface. These controllable interfacial behaviours make ionic liquid/oxide systems desirable for a number of different technological applications as well as being utilised for nanoparticle synthesis. This topical review aims to bring together recent experimental and theoretical work on the interaction of ILs with oxide surfaces, including TiO₂, ZnO, Al₂O₃, SnO₂ and transition metal oxides. It focusses on the behaviour of ILs at model single crystal surfaces, the interaction between ILs and nanoparticulate oxides, and their performance in prototype devices.

Water-induced reordering in ultrathin ionic liquid films has been observed using in situ x-ray photoelectron spectroscopy. An ultrathin layer of 1-butyl-3-methylimidazolium tetrafluoroborate ([C ₄ C ₁ Im][BF ₄ ]) was deposited on a rutile TiO ₂ (1 1 0) single crystal and exposed to water vapour at a relative humidity of ~70% in an in situ cell. Water was found to adsorb onto the ionic liquid surface, causing a reordering of the ions at the interface. Water initially remained trapped on the ionic liquid surface as the in situ cell was evacuated. This could have negative implications for supported ionic liquid phase catalysis, where reactants and products move in and out of an ionic liquid containing the catalyst. This insight into the behaviour at the water/ionic liquid interface provides a basis for understanding interfacial behaviour in more complex gas/ionic liquid systems.

Superbasic ionic liquids (SBILs) are being investigated as potential carbon dioxide (CO₂) gas capture agents, however, the presence of H₂O in the flue stream can inhibit the uptake of CO₂. In this study a thin film of the SBIL trihexyltetradecylphosphonium 1,2,4-triazolide ([P₆₆₆₁₄][124Triz]) was deposited onto rutile TiO₂ (110) using in situ electrospray deposition and studied upon exposure to CO₂ and H₂O using in situ near-ambient pressure x-ray photoelectron spectroscopy (NAP-XPS). The molar uptake ratio of gas in the electrosprayed SBIL (n _gas :n _IL) was calculated to be 0.3:1 for CO₂, 0.7:1 for H₂O, and 0.9:1 for a CO₂/H₂O mixture. NAP-XPS taken at two different depths reveals that the competitive absorption of CO₂ and H₂O in [P₆₆₆₁₄][124Triz] varies with sampling depth. A greater concentration of CO₂ absorbs in the bulk layers, while more H₂O adsorbs/absorbs at the surface. The presence of H₂O in the gas mixture does not inhibit the absorption of CO₂. Measurements taken during exposure and after the removal of gas indicate that CO₂ absorbed in the bulk does so reversibly, whilst CO₂ adsorbed/absorbed at the surface does so irreversibly. This is contrary to the fully reversible CO₂ reaction shown for bulk ionic liquids (ILs) in literature and suggests that irreversible absorption of CO₂ in our highly-structured thin films is largely attributed to reactions at the surface. This has potential implications on IL gas capture and thin film IL catalysis applications.