Extracting lignin from sugarcane bagasse for methylene blue and hexavalent chromium adsorption in textile wastewater: a facile, green, and sustainable approach

Abstract

This study presents the process of extracting lignin from sugarcane bagasse collected in the Mekong Delta, Vietnam by the alkali method. NaOH has been used as an effective, environmentally friendly chemical to enhance the extraction process. The obtained lignin was applied for methylene blue (MB) and hexavalent chromium (Cr(VI)) removal. Factors influencing lignin extraction and adsorption processes of MB and Cr(VI) were investigated, showcasing the sustainable reusability of lignin extracted from sugarcane bagasse. Lignin characterization was also carried out by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA) techniques. The results showed that the extracted lignin content reached 38.61% under optimal conditions (NaOH concentration of 10%, reaction temperature of 90 °C and reaction time of 90 min). The adsorption efficiency and capacity of lignin reached 90.90% and 9.09 mg g⁻¹ for MB and 80.10% and 28.04 mg g⁻¹ for Cr(VI), respectively, under optimum adsorption conditions (pH, adsorption time, initial methylene blue concentration, and used lignin content). The adsorption process obeyed Langmuir adsorption and was principally physical adsorption. These findings prove sugarcane bagasse based lignin as a cheap and efficient adsorbent for MB and Cr(VI) removal, which contributes to the utilization of the abundant agricultural by-product for wastewater treatment.