Visible Light Induced NO₂ ⁻ Removal Over CuCrO₂ Catalyst

The delafossite CuCrO₂ is a promising candidate for the visible light driven catalysis. The NO₂ ⁻ removal by photoelectrochemical process is studied under mild conditions, close to that encountered in the natural environment. CuCrO₂ exhibits a long term chemical stability with a corrosion rate of 0.34 μmol m⁻² year⁻¹ in KCl (0.5 M). A forbidden band of 1.3 eV has been evaluated from the diffuse reflectance spectrum. The flat band potential (-0.07 V SCE) determined from the Mott-Schottky plot is close to the photocurrent onset potential (0 V SCE). Hence, the conduction band is positioned at -1.08 V SCE and thus lies below the NO₂ ⁻ level leading to a feasible reduction upon visible illumination. The conversion occurs in less than ~5 h with a quantum efficiency of ~0.5%. The possibility of identifying the reaction products via the intensity-potential characteristics was explored by using standard solutions. The decrease of the conversion rate over time is attributed to the competitive water reduction. In absence of catalyst, NO₂ ⁻ is oxidized to NO₃ ⁻ in air equilibrated solution and the reaction follows a first order kinetic with a half life of 21 h, NO₃ ⁻ has been identified by iodometry through copper titration.