An overview on the use of adsorption and reactions of NO to probe (photocatalytic) TiO2

[Display omitted] •Surface probing potentialities of NO must not be overlooked.•Surface probing potentialities of NO essentially arise from the unpaired π*electron 83.•N18O isotopic exchange informs on O lability of semiconductor oxides 68.•NO isotopic exchange and reduction inform on charge transfer capacity under irradiation 87.•NO reduction can inform on the environment of photo-sensitive oxides in materials 82. Studies of the adsorption and reactions of appropriate molecules are a valuable means to probe active surfaces. This overview deals with the use of nitrogen monoxide – a molecule that has less been utilized than some others as a surface probe – to investigate TiO2 and TiO2-containing materials, with or without photo-excitation. It shows that diverse information can be derived from: (1) the infrared spectra of adsorbed NO; (2) the isotopic exchange of N18O; (3) the formation of N2O and N2; (4) the use of NO (or N18O) in oxidation reactions in place of O2; and (5) the evaluation of the electron transfer to NO through density functional theory calculations, ultraviolet photoemission spectroscopy, and photoconductance measurements. Valuable knowledge may thus be potentially acquired on: the accessibility and reactivity of surface OH groups, the lability of surface O atoms, the self-cleaning efficacy, the environment and dispersion of TiO2 in composite materials, the existence of bandgap electronic states, and the electron transfer capacity, depending on the investigation technique employed, the conditions and the type of TiO2 sample.