An EPR investigation of acetonitrile reactivity with superoxide radicals on polycrystalline TiO2

The interaction of acetonitrile with superoxide radicals over a polycrystalline TiO2 (Degussa P25) surface was investigated using continuous-wave electron paramagnetic resonance (cw-EPR) spectroscopy. For the first time, a thermally unstable radical intermediate has been observed following the low-temperature exposure of acetonitrile to surface-adsorbed O-2(-) radicals. The radical intermediate has been identified as an [O-2(-)center dot center dot center dot CH3CN] type surface complex characterised by the g values of g(1) = 2.031, g(2) = 2.010 and g(3) = 2.003. This surface complex is thermally unstable and decomposes at temperatures of T > 240 K. A second oxygen-centred species was also observed following acetonitrile adsorption, characterised by the spin Hamiltonian parameters of g(1) = 2.028, g(2) = 2.010, g(3) = 2.004, A(1) = 1.2 mT, A(2) = 1.0 mT and A(3) = 1.0 mT, and was assigned to a hydroperoxy radical (HO2 center dot).