Abstract
Tweezer-like adsorbents with enhanced surface area were synthesized by grafting aniline onto the amine sites of a chitosan biopolymer scaffold. The chemical structure and textural properties of the adsorbents were characterized by thermogravimetric analysis (TGA) and spectral methods, including Fourier transform infrared (FT-IR), nuclear magnetic resonance (1H- and, 13C-NMR) and scanning electron microscopy (SEM). Equilibrium solvent swelling results for the adsorbent materials provided evidence of a more apolar biopolymer surface upon grafting. Equilibrium uptake studies with fluorescein at ambient pH in aqueous media reveal a high monolayer adsorption capacity (Qm) of 61.8 mg·g−1, according to the Langmuir isotherm model. The kinetic adsorption profiles are described by the pseudo-first order kinetic model. 1D NMR and 2D-NOESY NMR spectra were used to confirm the role of π-π interactions between the adsorbent and adsorbate. Surface modification of the adsorbent using monomeric and dimeric cationic surfactants with long hydrocarbon chains altered the hydrophile-lipophile balance (HLB) of the adsorbent surface, which resulted in attenuated uptake of fluorescein by the chitosan molecular tweezers. This research contributes to a first example of the uptake properties for a tweezer-like chitosan adsorbent and the key role of weak cooperative interactions in controlled adsorption of a model anionic dye.
Highlights
Water pollution by different contaminants from industrial activities remains a topic of major environmental concern [1]
The resulting surface modification of chitosan yielded a porous adsorbent with high adsorption capacity
Complementary spectral characterization (FT-IR, 1 H/13 C-Nuclear Magnetic Resonance (NMR)) and thermogravimetric analysis (TGA) revealed covalent grafting of aniline onto chitosan
Summary
Water pollution by different contaminants from industrial activities remains a topic of major environmental concern [1]. Various techniques for the removal of contaminants include precipitation [2], ion exchange [3], filtration [4], solvent extraction [5], reverse osmosis [6], coagulation-flocculation [7,8], adsorption [9], and others. Among these approaches, adsorption-based techniques have been extensively studied as an efficient mode of contaminant removal from water, due to their low cost, process flexibility, easy handling and limited usage of secondary chemicals [10,11,12]. It is noteworthy that comparatively few studies have investigated fluorescein removal from aqueous media using adsorption techniques [23,24,25,26,27,28,29,30,31]
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