Synthesis of a functionalized fibrous adsorbent of high uptake capacity: a study on Pb(ii) uptake and simple acidic site model development

Abstract

The breakdown of the lignin barrier by acid treatment could expose cellulosic functional groups on the surface of biomaterials. In this study, a new functionalized fibrous adsorbent (FFA) was prepared using arecanut (Areca catechu) husk in sulfuric acid media. The synthesized FFA was characterized using proximate & ultimate analyses, thermogravimetric analysis (TGA), Brunauer–Emmett–Teller (BET) surface area, scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and Fourier transform infrared (FTIR) spectroscopy. A simple dual-site proton adsorption (DSPA) model was developed and applied for equilibrium Pb(II) uptake on the basis of mass balance. The quantity of proton absorbed onto FFA, obtained from potentiometric titrations, was used to determine the acid dissociation constants (pK_a) and the concentration of functional groups. The model fitted parameters showed a great agreement to the experimental results. The FTIR spectra and also the pK_a values of 3.21 and 1.62, respectively, confirmed the presence of surface carboxylic and sulfonic groups. FFA exhibited significant Pb(II) uptake and the Pb(II) ions predominantly attached to the carboxylic group even though the concentration was about 25% lower than the sulfonic group. FFA with a dose of 1 g L⁻¹ showed around 98.3% Pb(II) removal at pH 5 from an initial concentration of 32 mg L⁻¹ (0.157 mM). It could be used for 12 cycles with the exhaustion capacity of 194.94 mg g⁻¹ of FFA which was about 3.4 times higher than the commercial activated carbon.