A review on adsorptive removal of dyes from wastewater by hydroxyapatite nanocomposites

Dye removal from wastewater is of prominence due to its hostile effects on human health and the environment. The complex structure of the dye molecule is responsible for its difficulty in removal. Adsorption is found to be a promising technique to eliminate dye wastes due to its high removal capacity at low concentration. Among different adsorbents used, hydroxyapatite is a biocompatible adsorbent that is relatively efficient in both anionic and cationic dye removal. Recently, modification of hydroxyapatite by doping with other materials to increase its removal efficiency has gained much attention. This review summarizes compilation of recent literature on the removal of anionic and cationic dye by different hydroxyapatite nanocomposites, comparison of adsorption capacities of different hydroxyapatite nanocomposites, the possible adsorption mechanism of removal of dyes, the general isotherm, and kinetic and thermodynamic studies explaining the type of adsorption and the characteristics, advantages, and limitations of adsorbents.