Coconut-shell derived carbon/carbon nanotube composite f or fluoride adsorption from aqueous solution

Araga, Ramya and Kali, SURESH and Sharma, Chandra Shekhar (2019) Coconut-shell derived carbon/carbon nanotube composite f or fluoride adsorption from aqueous solution. CLEAN - Soil, Air, Water. ISSN 1863-0650

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Abstract

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 was to evaluate the dissolved fluoride removal efficiency of a novel and low‐cost carbon/carbon nanotube (CNT) composite under batch conditions. CNTs were coated on the coconut‐shell charcoal surface at 450 °C by using plasma enhanced chemical vapor deposition. Thereafter, processed charcoal samples were ball milled and used for the fluoride removal from aqueous medium. The amount of fluoride removal was found to be approximately 65% of the initial concentration of 4.4 mg L−1 in 3 h contact time at the adsorbent dose of 10 g L−1. The linear forms of three isotherm models (Langmuir, Freundlich, and Temkin) and two kinetic models (pseudo‐first order and pseudo‐second order) were applied to the adsorption data to determine the best fit for equilibrium expression. Isotherm data fit the Langmuir model while the adsorption kinetics was represented by the pseudo‐second‐order kinetic model. The fluoride adsorption process onto prepared carbon/CNT composite occurred spontaneously (ΔG° = –1.656 kJ mol−1) in an endothermic nature (ΔH° = 11.07 kJ mol−1) with increased randomness (ΔS° = 41.69 J mol−1 K−1). To validate the performance further, the as‐prepared adsorbent was successfully used to treat groundwater samples with excess fluoride concentration collected from Nalgonda district, Telangana, India.

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