Selective adsorption of dyes on TiO 2 -modified hydroxyapatite photocatalysts morphologically controlled by solvothermal synthesis

Many industries use purification technologies to employ environmentally sustainable processes, and hydroxyapatite (HAp) is an excellent candidate as a catalyst support for the removal of organic pollutants. The adsorption and catalytic efficiency of HAp are considered to tune by changing the crystallographic properties of HAp. Needle-shaped HAp crystals were synthesized with TiO 2 nanoparticles by solvothermal treatment using isopropanol at 150 °C. The concentration of isopropanol in the solvent ranged from 10% to 75%. The photocatalytic and adsorption properties of the samples were investigated using 5–100 ppm solutions of acidic acid fuchsin (AF) and basic methylene blue (MB) dyes. The aspect ratio of the HAp changed from 19.5 to 16.5 as the isopropanol concentration increased. In contrast to MB, the amount of AF adsorbed on the samples decreased as the aspect ratio increased, and the initial photocatalytic decolouration rate increased slightly. Although the zeta potential significantly decreased with the addition of TiO 2, the change from 6.5 mV to −6.5 mV derived from the HAp aspect ratio clearly affected the adsorption of the dyes. These findings indicate the adsorption characteristics of HAp can be controlled by changing its aspect ratio, which will contribute to the design of HAp-based remediation materials.