Coconut-Shell-Derived Carbon/Carbon Nanotube Composite for Fluoride Adsorption from Aqueous Solution

Devastating effect of fluoride in drinking water on human health is a great concern and defluoridation is essential to make groundwater suitable for drinking. The aim of this study is to evaluate the dissolved fluoride removal efficiency of a novel and low-cost carbon/carbon nanotube (CNT) composite under batch conditions. CNTs are coated on the coconut-shell charcoal surface at 450 degrees C by using plasma-enhanced chemical vapor deposition. Thereafter, processed charcoal samples are ball milled and used for the fluoride removal from aqueous medium. The amount of fluoride removal is found to be approximate to 65% of the initial concentration of 4.4mgL(-1) in 3h contact time at the adsorbent dose of 10gL(-1). The linear forms of three isotherm models (Langmuir, Freundlich, and Temkin) and two kinetic models (pseudo-first order and pseudo-second order) are applied to the adsorption data to determine the best fit for equilibrium expression. Isotherm data fit the Langmuir model while the adsorption kinetics is represented by the pseudo-second-order kinetic model. The fluoride adsorption process onto prepared carbon/CNT composite occurred spontaneously (Delta G degrees=-1.656kJmol(-1)) in an endothermic nature (Delta H degrees=11.07kJmol(-1)) with increased randomness (Delta S degrees=41.69Jmol(-1)K(-1)). To validate the performance further, the as-prepared adsorbent is successfully used to treat groundwater samples with excess fluoride concentration collected from Nalgonda district, Telangana, India.