Synthesis and application of surface-imprinted activated carbon sorbent for solid-phase extraction and determination of copper (II)

https://doi.org/10.1016/j.saa.2013.08.045Get rights and content

Highlights

  • Solid phase extraction combined with Cu(II)-imprinted sorbent was used for selective extraction of Cu(II).

  • The Cu(II)-imprinted sorbent had higher selectivity and adsorption capacity for Cu(II).

  • Cu(II)-imprinted sorbent showed high selectivity coefficients for Cu(II) relative Zn(II), Ni(II) and Pb(II).

  • The precision and accuracy of the method are satisfactory.

  • The adsorbent has great potential for preconcentration of Pb(II).

Abstract

A new Cu(II)-imprinted amino-functionalized activated carbon sorbent was prepared by a surface imprinting technique for selective solid-phase extraction (SPE) of Cu(II) prior to its determination by inductively coupled plasma atomic emission spectrometry (ICP-AES). Experimental conditions for effective adsorption of Cu(II) were optimized with respect to different experimental parameters using static and dynamic procedures in detail. Compared with non-imprinted sorbent, the ion-imprinted sorbent had higher selectivity and adsorption capacity for Cu(II). The maximum static adsorption capacity of the ion-imprinted and non-imprinted sorbent for Cu(II) was 26.71 and 6.86 mg g−1, respectively. The relatively selectivity factor values (αr) of Cu(II)/Zn(II), Cu(II)/Ni(II), Cu(II)/Co(II) and Cu(II)/Pb(II) were 166.16, 50.77, 72.26 and 175.77, respectively, which were greater than 1. Complete elution of the adsorbed Cu(II) from Cu(II)-imprinted sorbent was carried out using 2 mL of 0.1 mol L−1 EDTA solution. The relative standard deviation of the method was 2.4% for eleven replicate determinations. The method was validated for the analysis by two certified reference materials (GBW 08301, GBW 08303), the results obtained is in good agreement with standard values. The developed method was also successfully applied to the determination of trace copper in natural water samples with satisfactory results.

Introduction

In recent years, the toxicity and the effect of trace elements on human health and the environment are receiving increasing attention in pollution and nutritional studies. Copper is one of the most widespread heavy metal contaminants in environment. It is an important element for most life forms as a micronutrient, but is also toxic at high concentrations [1]. Therefore, sensitive, reproducible and accurate analytical methods are required for the determination of trace Cu in environmental and biological samples.

Monitoring environmental pollutants at ultra-trace level needs an effective sample preconcentration step. Solid phase extraction (SPE) is the most common technique used for preconcentration of analytes in environmental waters because of its advantages of high enrichment factor, high recovery, rapid phase separation, low cost, low consumption of organic solvents and the ability of combination with different detection techniques in the form of on-line or off-line mode [2], [3].

The choice of sorbent is therefore a key point in SPE because it can control the analytical parameters such as selectivity, affinity and capacity [4], [5]. Activated carbon, among a large variety of sorbents, is still by far the most important one in current use in the environmental pollution control due to its large surface area, high adsorption capacity, porous structure, selective adsorption and high purity standards [6]. However, without any surface treatment, activated carbon presents an adsorption capacity for metal ions from fair to as low to none, due to the fact that metal ions often exist in solution either as ions or as hydrous ionic complex [7], [8]. For this reason, modification and impregnation techniques have long been used to increase the surface adsorption to activated carbon. However, the selectivity of these functionalized sorbents is usually unremarkable because many metals have the ability to bind with the ligands without consideration of the stereo chemical interactions between the ligand and metal ion. Recently, highly selective molecularly imprinted materials have been extensively studied [9], [10], [11].

Molecular imprinting has become a powerful method for the preparation of robust materials that have the ability to recognize a specific chemical species [12]. In molecular imprinting, a molecular “memory” is imprinted on the polymer. Molecular imprinting polymers (MIPs) are capable of recognizing and binding the desired molecular target with a high affinity and selectivity [13]. Metal ion imprinted polymers (IIPs) are similar to MIPs, but they can recognize metal ions after imprinting and retain all the virtues of MIPs [14]. IIPs have been investigated as highly selective sorbents for SPE in order to concentrate and clean up samples prior to analysis. One potential application that has recently attracted widespread interest is their use for clean up and enrichment of analytes present at low concentrations in complex matrices [15], [16]. Numerous studies on IIPs and their use for selective preconcentration and separation of metal ions have been reported [17], [18]. However, to the best of our knowledge, there has been no report on using surface-imprinted activated carbon sorbent for Cu(II) enrichment.

The main aim of the present work is to synthesize a new ion-functionalized activated carbon sorbent by combining a surface molecular imprinting technique for selective separation and preconcentration of Cu(II) in natural water samples. The proposed method presented high selectivity and adsorption capacity for Cu(II), and possessed simple, convenient and accurate characteristics.

Section snippets

Apparatus

An Iris Advantage ER/S inductively coupled plasma emission spectrometer, Thermo Jarrel Ash (Franklin, MA, USA) was used for all metal ions determination. The instrumental parameters were those recommended by the manufacturer. The wavelength selected for Cu was 216.999 nm. The pH value was controlled with a pHs-3C digital pH meter (Shanghai Lei Ci Device Works, China). Infrared spectra (4000–400 cm−1) in KBr were recorded on a Nicolet NEXUS 670 FT-IR apparatus (USA). A JSM-6701F (JEOL, Japan) was

Characterization of Cu(II)-imprinted sorbent

SEM was conducted to characterize the activated carbon and Cu(II)-imprinted sorbent. The representative SEM images were shown in Fig. 2. The activated carbon was formed a dense and robust structure (see Fig. 2a). In contrast, the surface structure and physical characteristics of Cu(II)-imprinted sorbent were changed. The hole structure was more looser, and a high specific surface area was also obtained (see Fig. 2b).

The modified activated carbon was also confirmed by IR analysis (see Fig. 3).

Conclusions

Ion-imprinted sorbent have attracted widespread attention as highly selective sorbent to remove metal ions selectively in the presence of other metal ions. In this study, a surface Cu(II)-imprinted sorbent was prepared. The imprinted sorbent showed high affinity, selectivity and good accessibility for Cu(II) than non-imprinted sorbent. In addition, the adsorption capacity of Cu(II)-imprinting for Cu(II) was larger than that of non-imprinted sorbent and other methods reported. A selective and

Acknowledgments

This work was supported by the research start-up funds for introduced talents, Northwest University for Nationalities (NO. xbmuyjrc201109) and the Fundamental Research Funds for the Central Universities, Northwest University for Nationalities (NO. zyz2011065).

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