The Role of Cellulosic and Noncellulosic Functional Groups in the Biosorption of Lead Ions by Waste Flax Fibers

In this study, waste flax fibers with different levels of cellulosic and noncellulosic components were obtained by oxidative and alkali treatments and used to assess the influence of the fiber’s structural and chemical properties on the biosorption of lead ions. Scanning electron microscopy was used for the characterization of the flax fibers’ surface morphology, while the physicochemical properties of the fibers’ surface were determined by the streaming potential method, and Fourier transform infrared spectroscopy. Alkaline treatment decreased, while oxidative increased the crystallinity index of flax fibers by approximately 10%, due to the changes in the content of cellulosic components. Adsorption of lead ions was studied in detail, including kinetics, isotherms, and thermodynamic parameters analysis. It was shown that the amount and distribution of oxygen-containing groups, originating from cellulosic components, have the highest influence on the adsorption capacity of flax fibers, increasing Langmuir adsorption capacity from 12.76 mg g−1 for untreated to 21.9 and 79.9 mg g−1 for alkali-treated and oxidized fibers, respectively. Obtained negative values of ∆GӨ (−4.874 to −0.807 kJ mol−1) and ∆HӨ (−42.81 to −13.65 kJ mol−1) indicated that the adsorption of lead ions onto flax fibers is a spontaneous and endothermic process, which occurs through electrostatic attraction and ion-exchange. The results presented in this work demonstrate that the waste flax fibers of suitable chemical composition may be used as sustainable and renewable low-cost biosorbents