Chemical extraction of cellulose from Ligno-cellulosic Astragalus armatus pods: Characterization, and application to the biosorption of methylene blue

The most widely available substrate, cellulose biopolymer, was shown to be used for several interesting applications such as pharmaceutical, composites, water treatment, textiles, etc. In this study, cellulose was chemically extracted from abundant Astragalus armatus pods through alkali and bleaching processes. The untreated biomass and the extracted polymer were characterized using FT-IR, XRD, SEM, and TGA-DTA analyses. FT-IR spectrum of the extracted cellulose confirmed that lignin and hemicellulose constituents were removed during alkali and bleaching treatments. The crystallinity index calculated for the extracted cellulose and the untreated Astragalus armatus pods were 38.2% and 25%, respectively. These small values proved the existence of the amorphous constituents in the composition of Astragalus armatus. The high crystallinity index calculated for the extracted cellulose confirmed the elimination of the amorphous constituents present in the untreated biomaterial. The change in the thermal decomposition indicated that the extracted cellulose was more thermally stable than the untreated biomass. At optimum conditions (T = 20 °C, pH = 6, and t = 60 min), the adsorption quantities were 165 mg/g and 148 mg/g of for untreated Astragalus armatus pods, and extracted cellulose, respectively. The adsorption mechanism was non spontaneous and the interaction between the studied biomaterials and methylene blue was exothermic. Overall, the adsorption results demonstrated that the untreated Astragalus armatus pods and the extracted cellulose were excellent candidates for color uptake from water.