Surface modified exfoliated graphite as a novel adsorbent for de-fluoridation of drinking water

Abstract

Excessive fluoride concentration (>1 mg l−1) is responsible for dental and skeletal fluorosis. Out of the several fluoride removal methodologies available for de-fluoridation of drinking water, the present studies focused on the adsorption technique. The surface modification of exfoliated graphite was achieved by impregnating it with alumina by wet-chemical method. It was further subjected to physico-chemical characterizations such as Raman spectroscopy, SEM, TGA, XRD, point of zero charge etc. The batch adsorption studies of the adsorbent were conducted while varying the pH, adsorbent doses, contact time and initial fluoride concentrations. It followed the second order kinetics model and Langmuir model fitted well during the adsorption process shows the monolayer adsorption at lower fluoride concentration. However, the D-R model reveals that the adsorption of fluoride is due to the physical adsorption at higher fluoride concentration. The alumina impregnated exfoliated graphite could effectively remove fluoride to less than 0.01 ppm when the initial fluoride concentration in water was 10 ppm. Moreover the equilibrium pH achieved with the present adsorbent is favorable for drinking purpose.