Removal of methylene blue dye from aqueous solutions onto Morus nigra L. (mulberry tree) leaves powder and its biochar— equilibrium, kinetic and thermodynamic study

Abstract

ABSTRACT The present study was conducted to remove methylene blue (MB) dye from aqueous solution as this dye is also present in the waste water; using untreated, cheap and non- toxic mulberry leaves powder (MLP) and mulberry leaves biochar (MLB) prepared from Morus nigra L. (mulberry tree) leaves. The mulberry leaves powder and its biochar were characterised by Fourier transform infrared spectroscopy (FTIR). Batch mode experiments were conducted to investigate the effect of various variables like contact time, absorbent dosage, initial dye concentration, salt treatment, temperature and pH. The adsorption isotherm models used in this search were Langmuir, Freundlich and Temkin. Langmuir and Freundlich equations were found to have the correlation coefficient value in good agreement with MLP; however MLB for methylene blue dye shows good agreement with Langmuir only. Adsorption of methylene blue dye by the mentioned adsorbents (MLP and MLB) followed pseudo second order kinetic model. The calculated values of ΔGo, ΔHo and ΔSo were found to be −3.7 to −1.7 kJ mol−1 (MLP) and −0.8 to −3.1 KJ mol−1 (MLB), −13.92 (MLP) and 12.45 J mol−1 K (MLB) and −0.035 (MLP) and 0.046 kJ mol−1 (MLB), respectively. The calculated values indicated that adsorption process of methylene blue dye onto MLP and MLB adsorbents was spontaneous, exothermic (MLP) and endothermic (MLB).