Chitosan functionalized with N,N-(2-aminoethyl)pyridinedicarboxamide for selective adsorption of gold ions from wastewater

doi:10.1016/j.ijbiomac.2021.11.125

International Journal of Biological Macromolecules

Volume 194, 1 January 2022, Pages 781-789

https://doi.org/10.1016/j.ijbiomac.2021.11.125 Get rights and content

Highlights

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A novel chitosan adsorbent was synthesized.
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The adsorbent has a maximum adsorption capacity of 659.02 mg/g at 318 K.
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The adsorbent is suitable for a wide range of pH values.
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The adsorbent has excellent selectivity and reusability.
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The adsorption mechanism is electrostatic, chelation and reduction.

Abstract

The recovery of gold from wastewater has always been a research hotspot. Here, a novel chitosan-based adsorbent (CS-DPDM) was successfully synthesized by functionalizing chitosan with (N, N-(2-aminoethyl))-2,6-pyridinedicarboxamide. The adsorbent was analyzed by fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy (¹H NMR), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and zeta potential method (Zeta). To investigate the adsorption performance of CS-DPDM for Au(III), the effects of pH, temperature, adsorption time and initial concentration were discussed. The maximum adsorption capacity of CS-DPDM for Au(III) at pH 5.0 is 659.02 mg/g at 318 K. The adsorption is a spontaneous endothermic behavior, and the adsorption process follows the quasi-second-order kinetic and Langmuir isotherm models, indicating that a single layer of chemical adsorption may have occurred on the surface of the adsorbent. The competitive adsorption and repetitive experiments show that CS-DPDM has considerable selectivity and reusability for Au(III). X-ray photoelectron spectroscopy (XPS) results show that N and O functional groups adsorb Au(III) on the surface of CS-DPDM through electrostatic, chelation and reduction. These results indicate that CS-DPDM has broad application prospects in recovering gold ions from aqueous solutions.

Graphical abstract

Introduction

For a long time, gold has been sought after by people as a precious metal. Due to its good ductility and chemical inertness, it is widely used in the electronics, aviation industries, jewelry and commodity currency [1]. However, the content of gold is very scarce, the average concentration in the biosphere is only 0.005 ppm [2]. Due to the scarcity and wide application of gold, the value of gold is very expensive. Therefore, the recovery of gold from wastewater is of great significance for reducing environmental pressure and improving the reuse of secondary resources.

At present, several methods such as chemical precipitation [3], solution extraction [4], ion exchange [5] and adsorption [6] have been widely used to recover gold from aqueous solutions. Among them, the adsorption technology is highly efficient, environmentally friendly, convenient and economical, and is expected to become one of the most effective methods for recovering gold ions from wastewater in the future [7], [8]. Currently, many kinds of adsorbents are widely used, such as activated carbon [9], [10], [11], nanomaterials [12], organometallic framework compounds [13], polymers and biological macromolecules [14]. In recent years, chitosan has attracted attention as a kind of biosorbent.

Chitosan (CS), a derivative of chitin, is composed of 2-amino-2-deoxy-d-glucose repeating units of polymers [7], [15]. Its structure is rich in hydroxyl and amino groups, which contribute to the metal absorption by providing chelating and ion exchange properties, resulting in stable complexes [16], [17]. However, chitosan has swelling properties, dissolves at low pH due to its poor acid resistance, small surface area and other shortcomings, which limit its adsorption performance. It is usually modified with appropriate crosslinking agent to improve its physical/mechanical properties and become a new type of adsorption material [18], [19], [20]. The crosslinking can improve the durability of chitosan. However, due to the reduction of active groups in the crosslinking reaction, the absorption capacity of chitosan will reduce [7], [21], [22]. Therefore, it is necessary to further chemically modify the cross-linked chitosan for the increase of primary amine groups and functional groups that can be used to adsorb metal ions to improve the adsorption capacity.

According to the theory of soft, hard acid and base (SHAB), the organic ligand with a certain number of N atoms is effective for adsorption of soft metal ions (Au) [23], [24], [25]. (N, N-(2-aminoethyl))-2,6-pyridinedicarboxamide with C double bond O and NH₂ functional groups is capable of forming highly stable chelates with soft metal ions (Au). Here, we modified CS with (N, N-(2-aminoethyl))-2,6-pyridinedicarboxamide by formaldehyde crosslinking to develop an adsorbent for gold ions. The effects of pH, temperature, adsorption time, initial concentration, coexisting ion and number of cycles on the adsorption of gold ions were discussed. Finally, the kinetics, isotherm, and thermodynamics of the adsorption mechanism of gold ions by the modified CS were examined.

Section snippets

Material

All reagents are used as received. Chitosan powder (CAS#9012-76-4 BR, degree of deacetylation(90%) was purchased from Shanghai Yuanye Biotechnology Co., Ltd. 2,6-pyridinedicarboxylic acid(99%) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Ethylenediamine(99%) was purchased from Tianjin Fuchen Chemical Reagent Co., Ltd. Glacial acetic acid(99.5%) was purchased from Tianjin Kemei Chemical Reagent Co., Ltd. Sodium hydroxide(96%) was provided by Tianjin Fengchuan Chemical

Characterization of CS-DPDM

The surface shapes of chitosan and CS-DPDM were observed by scanning electron microscope (SEM) in Fig. 2a-b. The SEM image of chitosan showed a dense and smooth surface, and CS-DPDM has an irregular surface structure. This morphological change indicated that a modification reaction had occurred.

Additionally, the element distribution of CS and CS-DPDM was also studied by EDS. The results were shown in Fig. 2c-d. CS and CS-DPDM are composed of C, N and O elements. Compared with CS, the percentage

Conclusions

A new chitosan adsorbent (CS-DPDM) was designed by modified CS to recover Au(III) in wastewater. A series of characterizations including SEM, XRD, FT-IR and NMR showed that the adsorbent was successfully synthesized. At 318 K and pH = 5, the maximum adsorption capacity of CS-DPDM for Au(III) reached 659.02 mg/g. Through adsorption isotherms and kinetic studies, the adsorption of Au(III) on CS-DPDM is more consistent with Langmuir and quasi-second-order models, indicating that the rate

CRediT authorship contribution statement

Shuai Wang: Investigation, Formal analysis, Writing-original draft. Hao Wang: Investigation, Formal analysis, Writing-original draft. Jiali Tang: Investigation, Formal analysis, Writing-original draft. Investigation, Yingbi Chen: Formal analysis, Writing-original draft. Shixing Wang: Conceptualization, Methodology. Libo Zhang: Conceptualization, Methodology.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared in influence the work reported in this paper.

Acknowledgments

The authors are grateful to the National Natural Science Foundation of China (No. U1702252).

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Citation Excerpt :
Compared to the other methods, adsorption has been widely used because of its technical simplicity and economic viability [7]. Traditional adsorbents include activated carbon, chitosan, cellulose and resin [8–11]. Limitations, however, exit for these adsorbents with respect to their adsorption capacity, selectivity, and reusability [12,13].
A novel sulfhydryl-modified MOF (UiO-66-MSA) was prepared by externally optimizing UiO-66-NH₂ with mercaptomalic acid (MSA) and its capacity in selective recovering of Au(III) from solution was examined. Tests indicated that external modification of UiO-66-NH₂ by MSA increased its theoretical maximal adsorption capacity at pH 5 by 24.57% from 578.0 to 720.0 mg/g. Simulation of the kinetics data revealed that Au(III) binding on both UiO-66-MSA and UiO-66-NH₂ followed the pseudo-second-order model, with the former material having significantly higher kinetics. In the existence of competing ions, Au(III) recovery by sulfydryl-modified UiO-66-NH₂ (UiO-66-MSA) was increased from 72.06% to 98.59% at an initial Au(III) concentration of 56.9 mg/L. This material also had a fairly good reusability. At 5 times of regeneration, it was still able to capture 99.42% Au(III) from solution. Analysis of the changes in XPS patterns and the electrokinetic properties of UiO-66-MSA suggested that Au(III) binding on this MSA-modified MOF was complex. The electrostatic interaction, reduction and chelation may have all actively participated in the adsorption process. DFT calculation revealed that Au(III) binding was attributed to the -SH, -NH and C=O functional groups residing on the repeating unit of UiO-66-MSA, with its sulfhydryl functional group being the strongest binding site.

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Chitosan functionalized with N,N-(2-aminoethyl)pyridinedicarboxamide for selective adsorption of gold ions from wastewater

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Material

Characterization of CS-DPDM

Conclusions

CRediT authorship contribution statement

Declaration of competing interest

Acknowledgments

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