The effect of pH on the physical and structural properties of TiO2 nanoparticles

•Prepared TiO2 nanoparticles using the sol–gel method with solutions of various pH values (1.5, 4.5, 7,5 and 10.5).•The structural, morphological and optical properties of the prepared TiO2 nanoparticles were analyzed.•The lattice parameters and crystal size have been calculated.•The band gaps of the prepared nanoparticles were calculated. The present study prepared TiO2 nanoparticles using the sol–gel method with solutions of various pH values (1.5, 4.5, 7.5 and 10.5). The structural, morphological and optical properties of the prepared TiO2 nanoparticles were analyzed. A mixture of anatase–rutile phase was obtained with nanoparticles prepared in an acidic medium such as pH = 1.5 and 4.5. A pure anatase phase was obtained with nanoparticles prepared in an alkaline medium such as pH = 7.5 and 10.5. The average crystallite size was calculated for the prepared nanoparticles. The crystallite sizes decreased with increased pH values. The band gaps of the prepared nanoparticles were calculated. The band gap value of the sample with a limit pH value of 4.5 for anatase–rutile phase transformation was calculated to be 3.89 eV for direct transitions and 3.68 eV for indirect transitions.