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

Abstract

The detection and removal of heavy metal species in aquatic environments is of continued interest to address ongoing efforts in water security. This study was focused on the preparation and characterization of aniline grafted chitosan (CS-Ac-An), and evaluation of its adsorption properties with Cu(II) under variable conditions. Materials characterization provides support for the grafting of aniline onto chitosan, where the kinetic and thermodynamic adsorption properties reveal a notably greater uptake (>20-fold) of Cu(II) relative to chitosan, where the adsorption capacity (Qm) of CS-Ac-An was 106.6 mg/g. Adsorbent regeneration was demonstrated over multiple adsorption-desorption cycles with good uptake efficiency. CS-Ac-An has a strong fluorescence emission that undergoes prominent quenching at part per billion levels in aqueous solution. The quenching process displays a linear response over variable Cu(II) concentration (0.05–5 mM) that affords reliable detection of low level Cu(II) levels by an in situ “turn-off” process. The tweezer-like chelation properties of CS-Ac-An with Cu(II) was characterized by complementary spectroscopic methods: IR, NMR, X-ray photoelectron (XPS), and scanning electron microscopy (SEM). The role of synergistic effects are inferred among two types of active adsorption sites: electron rich arene rings and amine groups of chitosan with Cu(II) species to afford a tweezer-like binding modality.

Design of Sustainable Biomaterial Composite Adsorbents for Point-of-Use Removal of Lead Ions From Water

“…The lamp current was set to 5 mA while using an air-acetylene flame. The wavelength was 283.3 nm with a 0.5 nm slit width and optimum working range from 0.5 to 50 µg/mL similar to that reported elsewhere (Vafakish and Wilson, 2020). The calibration results for the PbNO 3 analytical standards covered a linear range (R 2 = 0.9915) between 5 and 100 ppm.…”

Shaping MOF oxime oxidation catalysts as three-dimensional porous aerogels through structure-directing growth inside chitosan microspheres

“…This further corroborates the intimate interaction of Cu species with nitrogen. 69 A close look at the XPS spectra of Cu 2p3/2 in the three materials ( HKUST-1 , Cu@CS and HKUST-1@CS ) shown in Fig. S10† reveals intense broad lines at 934.7 eV for Cu@CS and at 934.5 eV for HKUST-1@CS accompanied by satellites centered around at 939–945 eV corresponding to the Cu 2+ state.…”

The Application of Chitosan-Based Adsorbents for the Removal of Hazardous Pollutants from Aqueous Solutions—A Review

“…Research relating to the possibility of using crosslinked and/or grafted chitosan was mainly related to the possibility of obtaining efficient, selective, and resistant (e.g., to pH changes) adsorption materials with suitable mechanical strength, which are also economical and safe for the environment. In order to obtain novel crosslinked/grafted CS-based materials, various chemical compounds can be used, both those with simple structures (e.g., alanine) and more complex ones (e.g., poly(N-vinylimidazole) [70,73]. However, the possibility of using non-toxic substances of natural origin (e.g., tannins) [79] is increasingly being explored to create adsorptive materials that will not pose a threat to the aquatic environment if they are used on a larger scale.…”

“…In the last five years, there has also been an increasing interest in CS-based materials that are characterized by additional, useful properties (apart from the ability to efficiently adsorb metal/metalloid ions), e.g., fluorescence emission, and such materials may potentially be utilized in solutions as new sensing materials. For example, Vafakish and Wilson [70] reported that aniline-grafted chitosan (A-CS) adsorbent has a strong fluorescence emission that undergoes quenching in aqueous solution in the presence of copper(II) ions (linear relation). They found that such properties of A-CS enable quick detection of Cu(II) ions in aqueous solutions, even in small amounts.…”