Surface functionalization of reed beads with pentaethylenehexamine for improved dual contaminant removal

A multitude of pollutants, spanning from plastic contamination to light intrusion, exerts an impact on the marine ecosystem. Nevertheless, substantial endeavors have been undertaken to advance low-carbon footprint technologies, including the utilization of lignocellulosic materials in wastewater treatment. This research aimed to formulate a fresh, uncomplicated, and environmentally benign sorbent, derived from reed indigenous to Tunisia and functionalized with pentaethylenehexamine (PEHA), for the efficient treatment of wastewater. The synthesis was effectively executed by affixing PEHA onto reed-based beads (RB) through the application of epichlorohydrin (ECH) as a crosslinking agent, resulting in the creation of what we will refer to as "GRB." This innovative biosorbent was deployed for the concurrent adsorption of Congo Red (CR) and hexavalent chromium Cr(VI) in an aqueous solution. Central Composite Design for Response Surface Methodology (CCD-RSM) was employed to assess and fine-tune various biosorption parameters. The optimal adsorption conditions were as follows: pH 4.5, 30 mg L⁻¹ of Cr(VI), 40 mg L⁻¹ of CR, and a contact time of 120 min with a constant adsorbent mass of 1 g L⁻¹ at 25 °C. Under these conditions, the highest adsorption rates were achieved for both CR (98%) and Cr(VI) (84%). The GRB characterization was carried out using Fourier-Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), and Atomic Force Microscopy (AFM) before and after the grafting and adsorption processes. The isotherm analysis results indicated that the Sips model provided the most accurate fit for the concurrent adsorption of CR and Cr(VI). Thermodynamic analysis revealed that the adsorption process was spontaneous, physical, endothermic, and led to an increase in randomness at the solid/liquid interface. Kinetic investigations showed that the nonlinear pseudo-second-order model offered the best mathematical representation of the experimental data. Furthermore, the GRB was found to be easily reusable and capable of regeneration for up to ten cycles.