A co-relation study of efficient photocatalytic reduction of aromatic nitriles and band energies of Cu loaded elongated TiO2 nanocatalysts

Abstract Photoreduction of nitroaromatics into amines with TiO 2 (P25) via greener method has attracted a great deal of interest. Generally, this reaction is feasible as the reduction potential of nitro groups (-0.5 eV) lies below the conduction band (-0.85 eV vs. NHE) of TiO 2 . However, functional groups such as nitrile (-CN), azido (-N 3 ), aceto (-CH 3 CO), etc. are generally not photoreduced by conventional P25 due to their unfavorable reduction potential relative to titania. This report demonstrates efficient photocatalytic reduction of aromatic nitriles by tuning the band energies of Cu-TiO 2 nanostructures of different morphologies. The band energetics were determined by optical and electrochemical studies which revealed that Cu loaded titania nanotubes (Cu-TNT) possess more negative conduction band gap (-2.7 eV vs. vacuum) energy as compared to LUMO level of benzonitrile (-2.82 eV). This factor has probably facilitated better reduction efficiency of benzonitrile (> 90%) and its derivatives with Cu-TNT in comparison to almost no reactivity with Cu-P25 under similar conditions. In addition to suitable conduction band position of Cu-TNT, presence of anatase phase and higher surface area (204 m 2 /g) might have enhanced the reaction rate.