Evaluation of removal efficiency of fluoride from aqueous solutions using synthesis of nano-scale alumina on multi walled carbon nanotube (MWCNTs): equilibrium and kinetic studies

Fluoride is an essential compound in drinking water for preventing the dental caries, however excess intake of fluoride leads to various diseases. If amount of fluoride in drinking water exceeds the permissive limit, it is essential to remove fluoride from water. The aim of this study was to investigate the removal of fluoride from drinking water by nano- alumina coated on multi-walled carbon nanotubes (MWCNTs). The impact of various parameters, such as, pH, contact time, adsorbent dose, and initial fluoride concentration was investigated in the solution. The results of this research showed that, with decreasing pH from 9 to 3, removal efficiency increased, meanwhile the time for fluoride ion adsorption to reach equilibrium was 60 min. Also, increasing the adsorbent dosage from 0.5 to 1.5 g/L with fluoride concentration of 4 mg/L, resulted in increasing the removal from 70.5 to 97.1. The results for the adsorption were fitted to the model of the Freundlich with value (R-2 = 0.997 at 25 degrees C). Therefore, the combined nano- alumina/MWCNTs process was shown to be an excellent option for the removal of fluoride from drinking water.