Microporous nano-activated carbon type I derived from orange peel and its application for Cr(VI) removal from aquatic environment

Abstract

In this work, microporous nano-activated carbon (MNAC) was prepared from orange peel by chemical activation with zinc chloride (ZnCl2). MNAC has been characterized by FTIR, BET, TGA, TEM, SEM, and EDAX analyses. The fabricated MNAC has 1228.2 m2/g-specific surface area and was considered microporous nano-material. The MNAC has been tested for the adsorption of hexavalent chromium from its aqueous solution. MNAC showed good adsorption behavior towards Cr(VI) ions from aqueous environment. To achieve the optimum condition for the adsorption process, solution pH, time of reaction, adsorbent dose, initial concentration of Cr(VI) ions, and solution temperature have been investigated. The maximum monolayer capacity (133.33 mg/g) of MNAC was achieved at pH 1, 100-min reaction time, and 1.0 g/L adsorbent dosage. The pseudo-second-order model described the kinetics of Cr(VI) ions adsorption (R2 > 0.9972). Isotherm results showed that both Langmuir and Freundlich isotherm models are applicable to the batch experimental data, with the Langmuir model considered as the most applicable model. Thermodynamic parameters explained that the process of adsorption is appropriate in nature, endothermic, and spontaneous. The thermodynamic parameters, such as Gibb’s free energy (∆G°), standard entropy (∆S°), and standard enthalpy changes (∆H°), were estimated. The value of ∆G° was found to be negative for the adsorption of Cr(VI) ions, which confirmed the feasibility and spontaneous probability of the adsorption process.