Photocatalytic activity of N, Fe and Cu co-doped TiO2 nanoparticles under sunlight

Photocatalytic activity of N doped with one transition metal is well known. This article reports the synthesis of TiO2 nanoparticles doped with only N, N co-doped with Fe, N co-doped with Cu and N co-doped with both Fe and Cu by sol-gel method. Their photocatalytic activity was evaluated for the degradation of methylene blue under sunlight. Nanoparticles were characterized by X-ray diffractometry (XRD), Raman spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and diffuse reflectance UV–visible spectroscopy (DRS). XRD analysis revealed the presence of anatase phase TiO2 nanoparticles which was confirmed by Raman spectroscopic and TEM analysis. The crystal structure has not been disturbed by doping with N, Fe and Cu as shown by both XRD and Raman analysis. TEM and SEM images exhibit the nanoparticles which are interconnected due to sintering. XPS analysis revealed the presence of the only Ti4+ in undoped TiO2 but both Ti4+ and Ti3+ are present in doped TiO2 nanoparticles. According to the DRS analysis, the band gap of all doped TiO2 is lower than that of the undoped TiO2, where N, Fe and Cu co-doped TiO2 showed the lowest band gap (2.51 ​eV) proving that the visible light sensitivity of TiO2 increase with metal and non-metal doping. The rate of photodegradation of methylene blue in the presence of undoped TiO2 (0.016 min−1) is higher than all the doped TiO2 nanoparticles. N doped TiO2 show the highest activity among the doped TiO2 nanoparticles (0.006 min−1). Doped TiO2 nanoparticles showed a lower photocatalytic activity due to the electron hole pair recombination and the shielding effect of the dopants.