Walnut bloom powder as a waste-based sorbent for cationic dyes removal: equilibrium, kinetic, and thermodynamic studies

Abstract

In the present study, for the first time, walnut bloom (WB) powder was used as a natural and economic sorbent for the removal of methylene blue (MB) from an aqueous solution. This new biosorbent was characterized using the following techniques: scanning electron microscopy (SEM), X-ray diffraction (XRD), COHNS, BET (Brunauer-Emmett-Teller) analysis and Fourier transform infrared (FTIR) spectroscopy. MB removal efficiency and its adsorption onto WB powder were tested in a batch system by varying parameters such as initial dye concentration, contact time, pH, temperature, and dosage of biosorbent in which the removal percentages of ∼92% was achieved under the optimum conditions. Equilibrium data and adsorption isotherms fitted well with the Langmuir model (R2= 0.999, 0˂RL˂1) with a maximum monolayer adsorption capacity of 46 mg g-1. The chemical kinetics of MB adsorption followed the pseudo-second-order model. Also, the magnitude of thermodynamic functions identified the removal of MB. ΔH° of -7.32 kJ mol-1 and ΔS° of -4.32 kJ mol-1 indicated the spontaneity, exothermicity, and favorability of the adsorption process at room temperature.