The Role of Calcination Temperature in the Self-cleaning Functionality of Urea-Doped TiO2 Prepared through In Situ Heat-Assisted Sol–Gel Synthesis

In this study, urea-doped titanium dioxide (urea-TiO2) nanoparticles were synthesized through an in situ heat-assisted sol–gel technique using titanium (IV) isopropoxide as the precursor for titanium dioxide and urea as a nitrogen source. The nanoparticles were calcined at 300, 500, and 700 °C to study the effect of the calcination temperature on their function as self-cleaning material. The nanoparticles were characterized using a scanning electron microscope and a transmission electron microscope for morphology, X-ray diffraction, Raman spectroscopy, and Fourier transformed infrared spectroscopy for structure, UV–Vis, and photoluminescence spectroscopy for optical analysis. The self-cleaning study was carried out by letting samples degrade methylene blue and Rhodamine-B under UV irradiation. The morphological analysis reveals particle size distribution with more disparity at higher calcination temperatures. At lower calcination temperatures, the dopant caused high clustering of particles, keeping them linked together in muddy form and layers. Structural analysis showed that the particles were nanostructured with average crystallite sizes ranging from 2.35 to 16.13 nm and phase transformation from anatase to rutile after calcining at 700 °C. The nitrogen presence created a lattice disorder in the TiO2 structure, and the impact of higher calcination temperature on the nanoparticles further shifted the band toward a higher wavenumber under FTIR analysis. The optical bandgap reduced from 3.29 eV at 300 °C to 3.09 eV at 700 °C. The determined values of the rate constant from the photodegradation test showed that the highest rate was obtained at 700 °C, indicating enhanced self-cleaning functionality with an increase in calcination temperature of urea-TiO2.