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The modified-solvothermal method has been used to synthesize pure anatase and anatase-rutile mixed-phase TiO2nanomaterials using titanium isopropoxide, sodium hydroxide, and triethylamine as primary sources with different calcination temperatures (500 °C and 700 °C). The effect of the precipitating agent, capping agent, and calcination temperatures on the properties, such as structural, morphological, and optical of the resultant nanomaterials has been investigated through several techniques including X-ray diffraction (XRD), Raman spectroscopy, Transmission electron microscopy (TEM), UV–Vis absorption spectroscopy, Scanning electron microscopy (SEM), selected area electron diffraction (SAED), and high-resolution transmission electron microscopy (HRTEM). XRD and Raman spectra confirmed the pure anatase and anatase-rutile mixed structures of the prepared nanomaterials at 500 °C and 700 °C. Furthermore, the Raman active modes confirmed the formation of TiO2. It is noticed that the crystallite size of the nanomaterials increased with increasing calcination temperature of the XRD pattern. The morphologies of the prepared samples were displayed using SEM and TEM micrographs, which are almost the same in shape (cubic and cubic rod mixed). The particle size increased with an increase in calcination temperature and was found to be between 10 and 20 nm, which is similar to the crystallite size. The lattice fringes (d) from HRTEM images are assigned to the XRD plane (101) and (110) plane of anatase and anatase-rutile TiO2, respectively. The SAED exhibited well crystalline nature and confirmed the polycrystalline nature of the prepared nanomaterials by the bright points and the ring patterns. The optical band gap decreased with an increase in temperature and the optical properties are affected by calcination temperature and triethylamine.