Adsorption capacity of single and twin-tailed cationic and anionic surfactant-modified chitosan hydrogel beads for PAH removal from aqueous solutions

This study presents a thorough investigation into the use of single and twin-tailed cationic and anionic surfactant-modified chitosan (SMCS) hydrogel beads as effective adsorbents for the elimination of hazardous polycyclic aromatic hydrocarbons (PAHs) from aqueous solutions. The Chitosan (CS) hydrogel beads were modified with single/twin-tailed anionic surfactants, sodium dodecyl sulfate (SDS) and sodium bis(2-ethylhexyl) sulfosuccinate (AOT), and cationic surfactants, dodecyltrimethylammonium bromide (DTAB) and didodecyldimethylammonium bromide (DDAB), to enhance their adsorption capacity of PAHs. The CS and SMCS beads were evaluated for their structural, mechanical, and adsorption properties using a range of techniques, including infrared spectroscopy (IR), energy-dispersive X-ray spectroscopy (EDX), rheometry, and field emission scanning electron microscopy (FESEM). Adsorption experiments of naphthalene (Nap), acenaphthene (Ace), and phenanthrene (Phe) on SMCS beads demonstrate that they have significantly higher adsorption capacities than CS beads, due to increase in hydrophobic interactions. Adsorption capacity followed the trend, Phen > Ace > Nap for all the beads revealing that twin-tailed SMCS bead possess much higher adsorption capacities (Q_max) compared to single-tailed SMCS beads. For twin tailed surfactants, the maximum adsorption capacities for Nap, Ace and Phe varied as CS-AOT (CS-DDAB): 430.0 (323.8) 611.60 (538.18) 633.39 (536.99) mg/g respectively, outperforming other reported hydrogel beads. The study highlights the simplicity, eco-friendliness, and enhanced performance of surfactant modification for developing high-efficiency adsorbents, paving the way for cost-effective solutions in water remediation.