Acid washed black cumin seed powder preparation for adsorption of methylene blue dye from aqueous solution: Thermodynamic, kinetic and isotherm studies

Abstract

The present study deals with the preparation, characterization of a green natural product-based adsorbent, acid washed black cumin seeds (AWBC), and its application for adsorption of Methylene blue (MB) dye from aqueous solution. AWBC was prepared by washing black cumin (BC) seed powder with hydrochloric acid which was characterized using Fourier transform infrared (FT-IR), X-ray diffraction (XRD), scanning electron microscopy equipped with Energy-dispersive X-ray spectroscopy (SEM-EDAX) and transmission electron microscopy (TEM) techniques. Batch experiments were performed with varying adsorbent dose (1–5 g L−1), pH of the solutions (2−10), contact time (15–120 min), concentration (10–60 mgL−1), temperature (27, 35 and 45 °C) and agitation at 215 rpm. Langmuir, Freundlich, Temkin, and D-R isotherm models were used to determine the adsorption capacity, mechanism and other various parameters related to temperature effects. Results of the study indicated that the AWBC adsorption data fitted well with the Langmuir and Freundlich isotherms. The maximum Langmuir adsorption capacity of acid washed BC seeds for methylene blue was found to be 73.529 mg g−1 at 27 °C which decreased slightly with the rise of solution temperature. The pseudo-first-order, pseudo-second-order and Elovich kinetic models were used to demonstrate the reaction kinetics. Adsorption reaction followed the pseudo-second order kinetics. Overall, hydrochloric acid washed BC seeds offered low-cost adsorbent for MB removal from water.