Crystal violet dye removal from aqueous solution by nanohydroxyapatite

In the present study, the crystal violet dye adsorption on the nanocrystalline hydroxyapatite was investigated. The nanohydroxyapatite was prepared by wet coprecipitation method and investigated using scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX), X-ray diffraction (XRD) and Brunauer-Emmett-Teller (BET) methods. The hydroxyapatite has a high specific surface area (BET) of 81 m 2 /g and crystal sizes smaller than 50 nm. The pH at the point of zero charge (pH pzc ) of hydroxyapatite sample was 7.9. The batch adsorption experiments were performed by monitoring the pH, adsorbent dosage, dye solution concentration and contact time. High removal rate (R%) of crystal violet dye of about 90.71% was obtained at pH 10 and ambient temperature. The adsorption capacity (q) was high at low adsorbent dosages and reduced at high dosages. The crystal violet dye adsorption on hydroxyapatite may be explained to proceed via the electrostatic attraction between the negatively charged surface of the hydroxyapatite and the positively charged group of the dye. The results obtained indicated that the nanohydroxyapatite possessed good adsorption ability towards crystal violet dye.