Removal of Methylene Blue from Aqueous Solution by Adsorption onto Crofton Weed Stalk

Abstract

Crofton weed stalk (CWS) was used as an adsorbent to remove methylene blue (MB) from aqueous solution. The adsorbent was analyzed by FT-IR and observed by SEM. The porosity and pHzpc were measured. The effects of adsorbent dose, initial dye concentration, solution pH, and solution temperature were investigated. Models of the adsorption kinetics and isotherms were analyzed, and thermodynamic parameters were calculated at different temperatures. The results showed that the adsorption capacity of MB on CWS increased with increasing initial concentration from 10 to 40 mg/L and pH from 2 to 7. The amount of MB removed increased as the adsorbent dosage was increased from 0.2 to 1.2 g/L. The maximum dye adsorption capacity of 28 mg/g was reached at around 120 min in a solution of 40 mg/L. A pseudo-second-order kinetic model described the kinetics well, and the experimental data followed the Freundlich model. The calculated values of standard free energy (ΔGo) and standard enthalpy (ΔHo) were negative, which indicates the adsorption process is spontaneous and exothermic. The values of both free energy and ΔGo indicate that the adsorption is a physical process. This work shows CWS could be utilized as an effective adsorbent for treating dye wastewater.