PH regulated rapid photocatalytic degradation of methylene blue dye via niobium-nitrogen co-doped titanium dioxide nanostructures under sunlight

Abstract

Niobium and nitrogen co-doped titanium dioxide (Nb-N-TiO2) semiconductor nanostructures were synthesized through a facile sol-gel protocol using titanium tetra iso-propoxide (TTIP), urea and niobium pentoxide as precursors followed by calcination at 450 °C for 4 h. The synthesized nanomaterial (Nb-N-TiO2) was characterized via Fourier Transform Infrared (FTIR) and Raman spectroscopy, UV-Visible (UV-Vis) Spectroscopy, Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), Brunauer-Emmett-Teller (BET) technique, Dynamic Light Scattering (DLS) technique and ZETA Potential analysis. The band gap of Nb-N-TiO2 was reduced as compared to TiO2 due to reduced space between valance and conduction band which also reduced the electron-hole (e-, h+) recombination and led to better photocatalytic activity of the Nb-N-TiO2 as confirmed by TAUC plot. Photocatalytic activity of Nb-N-TiO2 was investigated for degradation of methylene blue (MB) dye under sunlight as cheaper light source. Factors like dye concentration, dosage of catalyst, volume of solution time and pH were studied and optimized for MB degradation. Under finally optimized conditions, 97% of 25 ppm MB was degraded just in one minute using 45 mg of photocatalyst. The co-doped nanocatalyst, was re-used for MB degradation upto 4th cycle with its efficiency reduced to 75% which shows a better catalytic role by the catalyst. Degradation products of MB were recognized through electrospray ionization coupled mass spectroscopy (ESI-MS) and liquid chromatography coupled mass spectroscopy (LC-MS) techniques. The catalyst was also applied for MB degradation in tap water sample.