Sodium dodecyl sulfate assisted synthesis hydroxyapatite for effective adsorption of methylene blue

Plate-shaped, hollow flower-shaped, and flower-clustered hydroxyapatite (HAP) were prepared with CaCl2 and (NH4)2HPO4 as raw materials and with sodium dodecyl sulfate (SDS) as additives. XRD, SEM, BET, and FT-IR were used to characterize the prepared HAP. The adsorption performance of methylene blue (MB) on HAP was investigated. The results showed that adding SDS to an appropriate amount increased the dispersibility and specific surface area of HAP. There is an electrostatic attraction between the surface of HAP and SDS, exposing an increasing number of negatively charged phosphate groups, making the adsorption capacity of cationic dye MB to be improved. SDS-HAP has a removal efficiency of more than 95% of MB under different pH and concentration conditions. The maximum saturated adsorption capacity reached 468.65 mg/g. After three adsorption-desorption cycles, the removal rate of methylene blue is still above 85%. The adsorption of MB by SDS-HAP is an exothermic physical process and conforms to the Langmuir model and the pseudo-second-order kinetic model.