Adsorption of reactive dyes on lignocellulosic waste; characterization, equilibrium, kinetic and thermodynamic studies

Abstract

This study researched the use of the easily obtainable and economic agricultural waste of corn silk (CS) for removal of Reactive Blue 19 (RB19) and Reactive Red 218 (RR218) dyes with the adsorption process. Lignin, holocellulose, α-cellulose, thermogravimetric analysis (TGA), fourier transform infrared (FTIR) and scanning electron microscopy (SEM) analyses were completed with the aim of determining the physical and chemical characteristics of the lignocellulosic adsorbent and ash content was determined. Additionally, the contact duration of adsorption, concentration of dye, temperature and pH parameters were investigated with equilibrium, kinetic and thermodynamic parameters determined to research the mechanism of adsorption. For both reactive dyes the removal efficiency is linked to the effective pH. With initial dye concentration of 200 mg/L, temperature of 25 °C, and adsorbent concentration of 0.25 g/50 mL fixed, maximum removal efficiency was 99% obtained at pH 2.0. The study calculated 6 different two-parameter isotherms and according to the best R2 value, the Temkin and Freundlich isotherm models were selected. The maximum capacity of CS for adsorption of RB19 and RR218 was 71.6 mg/g and 63.3 mg/g at adsorbent dose of 0.25 g/50 mL for initial dye concentration of 500 mg/L, pH 2.0 and 25 °C. According to the kinetic model results calculated with the aid of experimental data, a good adsorption process occurred. Thermodynamic parameters like enthalpy variation (ΔH0), entropy variation (ΔS0) and free Gibbs energy variation (ΔG0) were calculated with the aid of data obtained at different temperatures. As temperature increased dye adsorption was observed to increase confirming this event is endothermic.