Photochemistry and Gas-Phase FTIR Spectroscopy of Formic Acid Interaction with Anatase Ti¹⁸O₂ Nanoparticles

The photoinduced isotope exchange between 18 O atoms in the lattice of vacuum-calcinated solid Ti 18 O 2 and 16 O atoms of formic acid and its photoproducts was studied with gas-phase high-resolution Fourier transform infrared absorption spectroscopy. The rotation–vibration absorption spectra of all products from the photochemical reactions of formic acid were measured over a broad infrared spectral range and used to quantify the time-dependent isotope exchange between the oxygen atoms on solid Ti 18 O 2 and the oxygen atoms in gaseous HC 16 O 16 OH and the isotopologues of CO 2, CO, and H 2 O. It was found that formic acid did not exchange oxygen with titania during adsorption and decomposition processes; strongly bonded formate species blocked active sites and thereby inhibited the exchange between CO 2 and Ti 18 O 2 . Similar blocking was observed by adsorbed water. The isotopologues C 16 O 18 O and C 18 O 2 are the products of the spontaneous exchange of oxygen atoms in C 16 O 2 and the active sites on Ti 18 O 2 that are unblocked during the irradiation of the surface by UV photons. The C 18 O molecules are a product of the UV decomposition of C 16 O 18 O or C 18 O 2 that is formed during the spontaneous exchange process.