Phase transformation induced structural, optical and photocatalytic investigations of TiO2 nanoparticles

Titanium dioxide (TiO2) nanoparticles were synthesised by the modified sol–gel method at different calcination temperatures. Samples were characterized using X-ray diffraction (XRD), high-resolution transmission microscopy, scanning electron microscopy, energy dispersive X-ray analysis (EDAX), Fourier transform infrared (FTIR) spectroscopy, Brunauer, Emmett and Teller surface area analyzer (BET) and diffuse reflectance spectroscopy (DRS). Phase transformation of TiO2 nanoparticles from anatase to rutile phase with an increase in calcination temperature from 573 to 1173 K was observed from XRD analysis. Detailed structural analysis using size–strain plot and Halder–Wagner method was done for all samples. The formation of TiO2 nanoparticles was confirmed from FTIR and EDAX spectra. The TEM image of the sample calcined at 673 K showed non-spherical shaped particles having particle sizes 13.16 ± 3.35 nm. The bandgap energy calculated from DRS decreases with an increase in calcination temperature, which supports phase transformation observed in XRD analysis. The photocatalytic degradation efficiency was evaluated by monitoring the degradation of Congo red (CR) azo dye under UV light and natural sunlight. The degradation of CR dye was confirmed by analysing the FTIR spectrum of the degraded sample. The sample calcined at 673 K, in the pure anatase phase, exhibited the highest photocatalytic activity.