Ti3+ and oxygen defects controlled colored TiO2 nanoparticles by continuous spray pyrolysis

Different coloured TiO2 nanoparticles were fabricated by continuous spray pyrolysis (CoSP) technique due to the controlled manner of defects formation in large scale synthesis of black, green and white TiO2 with the creation of selective Ti3+ defects as well as defects correlated to oxygen vacancies. The enhancement in the zone temperatures in CoSP furnace is resulted changed in the color of TiO2 nanoparticles. The change in colour is also affected by the subsequent annealing of nanoparticles. The changes occur due to a controlled and selective growth of TiO2 nanostructures inside the CoSP furnace. Ti3+ defects creation in the nanoparticles/hollow microspheres seems to occur because of a high pressure created during the synthesis. XPS analysis revealed that the black colour of as-prepared TiO2 is due to the formation of high concentration of Ti3+ defect (peak at 456.84 eV), which is also confirmed by the electron paramagnetic resonance analysis.