Development of Novel Nanoadsorbent from Azadirachta indica (Neem) Dead Bark for Removal of Organic Contaminants from Polluted Water: Kinetic, Isotherm and Thermodynamic Study

Abstract

Abstract In this study, the adsorption of cationic organic dye methylene blue (MB) from an aqueous solution was investigated using a nano-adsorbent (active carbon) made from the dead bark of Azadirachta indica (neem) by using FTIR, zeta-potential analysis, X-ray diffraction, ultraviolet-visible spectroscopy, FESEM, BET, and TEM analytical tools, the synthesized nano adsorbent was evaluated for its characteristics. N2 sorption study confirms that the prepared adsorbent depicted a type IV isotherm with H3 type of hysteresis loop, which reveals the subsistence of the development of mesoporous material with a pore diameter in the 2–50 nm range. In the batch approach, the experimentations were run to equilibrium isotherm study. For the removal of the dye, the effects of variables, including contact time, pH, temperature, initial dye concentration, and adsorption dose, were investigated. In 80 min. of equilibrium time, 99.49% of MB dye at 30 mg/L of initial concentration was withdrawn at pH 11 with 30 mg of adsorbent. However, the % removal of dye was found to be declined to 90.62% on a rising initial concentration of 60 mg/L under similar conditions. The adsorption data was found to be appropriate to the Langmuir isotherm model, as confirmed by the correlation coefficient (R2) value (0.997), and the utmost adsorption competence was estimated to be 106.92 mg/g at 303 K. In addition, it was found that the removal process followed a pseudo-second-order kinetics and intra-particle diffusion of MB dye molecules process is the controlling process but not a sole directing factor. The negative ΔG° and positive ΔH° decided the spontaneity and endothermic nature of adsorption practice, while the positive value entropy (ΔS°) reflected that adsorption of MB molecules favored an increment of disorderliness at the adsorbate-adsorbent interface.