Zr(IV) functionalized graphene oxide anchored sand as potential and economic adsorbent for fluoride removal from water

Excessive fluoride (F) in drinking water is a major problem affecting human health in many parts of the world. Cost-effective adsorbents are required for the defluoridation of drinking water. A carbon-based adsorbent, graphene oxide coated sand was produced from very inexpensive materials, sugar and river sand and impregnated with zirconium (Zr) for defluoridation of water. F adsorption by Zr impregnated graphene oxide coated sand (ZIGCS) at pH 4.0 satisfactorily fitted to Langmuir and Freundlich adsorption models with a Langmuir maximum adsorption capacity of 6.12 mg/g which is one of the highest values among the other carbon-based economic adsorbents reported for defluoridation. The adsorption of F on to ZIGCS (point of zero charge of pH 4.5) increased from pH 2 to 4 and then decreased up to 12. However, considerable adsorption capacity was observed throughout this pH range. Pseudo-second order model successfully described the adsorption reaction kinetics. Fluoride adsorbed on to ZIGCS was effectively desorbed using 0.1 M NaOH and the regenerated adsorbent maintained approximately 75% of the original F adsorption capacity even after five regeneration cycles. Thermodynamic data revealed that the adsorption process was endothermic and spontaneous with increase in randomness at the solid/solution interface.