Surface-Modified Chitosan: An Adsorption Study of a “Tweezer-Like” Biopolymer with Fluorescein

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.

Preparation of Multicomponent Biocomposites and Characterization of Their Physicochemical and Mechanical Properties

“…10-fold lower Q m values versus the doped composites. By contrast, pristine chitosan has negligible adsorption, in agreement with other reports [29,35]. Regarding the adsorptive properties towards FL with pristine PANI, no relevant literature data were found, revealing a knowledge gap for such dye systems in this field of polymer adsorbents.…”

“…Q m is the Sips fitting parameter from Equation (1), expressed in mol/g adsorbent, N A is Avogadro's number (6.02 × 10 23 mol −1 ), σ is the cross-sectional molecular surface area (m 2 /molecule) where σ(MB) = 8.72 × 10 −19 and σ(FL) = 7.13 × 10 −19 , and Y is the coverage factor (non-dimensional quantity) where Y = 2.0 for MB and FL [34,35].…”

Cu(II) Ion Adsorption by Aniline Grafted Chitosan and Its Responsive Fluorescence Properties

“…The synthesis of a "tweezer-like" adsorbent was adapted from a previous report with slight modifications [30]. In brief, 0.6 g of chitosan was dissolved in 40 mL of 2% aqueous solution of acetic acid with mixing for 30 min at 23 • C. To the light-yellow solution, acetaldehyde (145 µL, 1.1 mol equivalents relative to the glucosamine monomer subunits) was added with stirring for 30 min.…”

“…To confirm the grafting of aniline onto the backbone of chitosan (CS) through the acetaldehyde linker, an IR spectrum for pristine chitosan was recorded (Figure 1a), in agreement with IR reported previously (cf. Figure 2 in [30]). The strong OH and NH 2 hydrogen band at 3000-3500 cm −1 disappeared upon grafting.…”

“…In the present study, a "tweezer-like" chitosan-based adsorbent was studied, where the grafting of aniline onto the amine groups of chitosan was reported in an earlier work [30]. Herein, the "tweezer-like" adsorbent was used as an effective turn-off sensor for the detection of low levels of Cu(II) in aqueous solution.…”