Comparison of Different Photocatalytic Systems for Acetonitrile Degradation in Gas–solid Regime

Photocatalytic degradation of acetonitrile was carried out in gas–solid regime by using two commercial TiO₂ samples (Merck and Degussa P25) irradiated in two continuous annular photoreactors. The inlet gas flow consisted of oxygen, nitrogen, acetonitrile and water vapours. The influence on the photodegradation rate of gas flow rate, acetonitrile, oxygen and water concentrations and photon flux was investigated. The degradation products of acetonitrile were carbon dioxide and hydrogen cyanide. The photocatalysts performance was not affected by the presence or absence of water vapour in the reacting mixture. The Langmuir–Hinshelwood model describes adequately the photoreactivity results and provides the values of kinetic and equilibrium adsorption constants. FT-IR spectroscopy was used to investigate the adsorption patterns and photo-oxidation intermediates of acetonitrile on fully hydrated surface of TiO₂ powders. Acetonitrile was adsorbed on Ti⁴⁺ surface ions and hydroxyl groups for both types of TiO₂. In the absence of UV light this interaction was completely reversible for Merck catalyst whereas for Degussa P25 part of adsorbed acetonitrile molecules reacted to form acetamide-like species.