Chemical extraction of lignin from Micropus erectus L. fibers, functionalization with polyethyleneimine, characterization, and application in acid dyes adsorption
摘要
In this work, Micropus erectus L fibers were used as a source of lignin and the extracted lignin was chemically functionalized with polyethyleneimine (PEI). The resulting materials were analyzed using Fourier Transform Infrared (FT-IR), Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), Thermogravimetric (TGA), and, Differential thermogravimetric analyses (DTG). The resulting materials were further used for the elimination of Acid red 183 (AR183) and Acid blue 25(AB25) from a synthetic aqueous medium. SEM micrographs showed that the functionalized lignin was rough and presented several hollows. FT-IR data of the functionalized lignin displayed new absorption peak at 1651–1670 cm-1 confirming amino groups grafting. XRD diffractograms indicated the amorphous structure of lignin. Lignin displayed three stages of degradation; the first event occurred at 59.4 °C, the second event happened at 267.6 °C, and the last one occurred at 543.1 °C. Compared to the raw material, the functionalized lignin samples exhibited four main decomposition stages. This change in thermal behavior evidenced the chemical modification of lignin. The adsorption process depended on several studied experimental factors (pH, time, initial dye concentration, and temperature). The maximum adsorption amounts were attained using lignin-PEI (5%) and they were equal to 173 mg/g and 119 mg/g for AB25 and AR183, respectively, at optimum adsorption conditions (time = 60 min, pH = 5, and T = 21 °C), The adsorption process fitted well to the pseudo second order kinetic equation and Freundlich isotherm. The negative values of the enthalpy indicated that the adsorption process was exothermic. However, the negative values of the entropy suggested the decrease in the disorder during the adsorption phenomenon.