The Removal of Methylene Blue from Aqueous Solutions by Using Microwave Heating and Pre-boiling Treated Onion Skins as a New Adsorbent

Varying the parameters, such as dye concentration, adsorbent dose, and pH, carried out the potential feasibility of microwave heating treated and pre-boiling treated onion skins for removal of methylene blue. The amount of dye uptake (mg g(-1)) was found to increase with an increase in contact time, adsorbent dosage, and in initial dye concentration. Lagergren first-order and second-order were used to fit the experimental data. Equilibrium isotherms were analyzed by Langmuir and Freundlich. Based on regression coefficient, the equilibrium data found fitted well to the Langmuir equilibrium model than other models. The adsorption capacities were found to be 142.67 and 55.55 mg g(-1) for microwave heating treated onion skins and pre-boiling treated onion skins by Langmuir isotherm. The equilibrium time was found to be 150 min for 50 mg L-1 dye concentrations. The maximum removals for microwave heating treated onion skins and pre-boiling treated onion skins were obtained 86.34 and 94.13% at natural pH 10.0 for adsorbent doses of 0.15 g/200 mL.