The effects of temperature and pH on the shape, size, and color of the synthesized nano-plate shape hematite by hydrothermal method

By controlling the synthesis conditions, hematite particles with different geometric shapes and different optical and magnetic properties can be obtained. In this study, due to its high potential for the synthesis of a wide range of particles with different shapes and sizes, the hydrothermal method was used for the synthesis of hematite. Iron (III) hexahydrate, ethanol, sodium acetate, and polyethylene glycol were used as raw materials. In this study, without using common organic solvents and in contrast with most previous researches that focused on the magnetic properties of hematite, Samples were synthesized at 180 and 250 °C and pHs 5, 7, and 11. The phase composition, particle shape, and optical properties of the particles were investigated by XRD, SEM, FTIR, and DRS methods. Hematite particles synthesized at the temperature of 180 °C at pHs 5, 7, and 11 had particle dimensions 293.47, 95.41, and 83.95 nm and at the temperature of 250 °C at pHs 5, 7, and 11 had particle dimensions 88.29, 73.79, and 59.33 nm respectively. As the pH increased, due to the smaller particle size and thus more light absorption, the color of the hematite powder darkened. By using XRD analysis and Scherer equation, it was found that the pH of the process did not affect the size of the unit cells, and the average size of the unit cells at both synthesis temperatures was 27.8 nm. However, the SEM images showed that by increasing pH the hematite particles became more spherical and smaller.