New optimization approach for successive cationic and anionic dyes uptake using reed-based beads

摘要

The search for new and operative biosorbents to remove environmental pollutants has always attracted much attention. The invasive common reed plant, Phragmites australis, has long been mistakenly considered an environmental issue, and consequently, the first objective of this study was to discredit this idea and show its immense value as a depolluting material. A new biosorbent material made of this natural herb in the form of millimetric beads has been developed. This innovative natural composite has displayed the ability to adsorb numerous polluting chemical products consecutively. Tests have been performed on model dyes such as Methylene Blue (MB), then Congo Red (CR), and a mixture of both using the central composite design (CCD) of response surface methodology (RSM). The optimal adsorption conditions were found with a desirability function (Df). The highest adsorption yield with an MB equal to 120 mg L-1 demanded a pH of 9.3 and a contact time of 230 min. However, an adsorption yield of 170 mg L-1 for CR necessitated a pH of 4.3 and a contact time of 180 min. And attaining 145 mg L-1 for the mixture of MB + CR required a pH of 4.3 and a contact time of 180. Finally, reed beads were characterized by Fourier transform infrared (FTIR) spectroscopy, X-Ray Photoelectron Spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscope (AFM), and their behavior modeled before and after adsorption. We observed that the maximum adsorption capacity increased from 56.8 mg g(-1) to 165 mg g(-1) for CR according to Sips model and reached 42 mg g(-1) for MB, according to Toth model. These models also demonstrated that the adsorbent surface was heterogeneous and that pseudo-second-order adsorption kinetics could fit the MB, CR, and MB + CR adsorption phenomenon for those natural materials. The thermodynamic study showed that the dye adsorption was spontaneous, physical, and endothermic for MB and MB + CR but exothermic for CR. These findings may have an eminent impact on implementing those biomaterials as potential filters for anionic and cationic dyes, due to their adequate adsorption capacity, regeneration ability after six cycles, and affordability. (C) 2021 Elsevier Ltd. All rights reserved.