A nano-titanium dioxide (nano-TiO2) powder, with Zr (0.5–1 %) and Nb (0.5–1 %) impurities, is fabricated using a modified hydrothermal method, with low-grade mineral precursors. Samples were then sintered at 600, 800, and 1,000 °C, then analysed using XRD (crystallite size and phase conversion temperature) scanning electron microscope (SEM) (morphology), N2 adsorption–desorption isotherms (surface area), and UV–vis–NIR (absorbance and optical transmission) to study the effects of sintering on the structural and optical properties of the synthesized nanopowders. It was discovered that sintering to 1,000 °C reduces the surface area by 99 %, and increases the crystallite size by almost 2,000 %. Meanwhile, the phase conversion temperature of this sample is 33.3 % higher than that reported in the literature for 600 °C. SEM shows an extensive agglomeration and uneven distribution of nano-TiO2 particles before sintering. However, the sintered sample shows uniformity in particle size and distribution, and even though it is reduced significantly, agglomeration is still present. The absorbance of the samples is red-shifted towards the visible region (i.e., 380–700 nm), with the optical band-gap reduced by 10 %, when sintered to 1,000 °C. The optical transmission of nano-TiO2 is also reduced by 10 % when sintered to 1,000 °C, due to changes in its microstructure. It is therefore concluded that sintering nano-TiO2 improves its structural and optical properties, and paves the way for a multitude of novel applications.