Detection of Ag+ using graphite carbon nitride nanosheets based on fluorescence quenching

https://doi.org/10.1016/j.saa.2016.06.024Get rights and content

Highlights

  • A fluorescence probe with graphite carbon nitride nanosheets for Ag+ is fabricated.

  • The proposed method exhibits high sensitivity, short analysis time and wide linear range.

  • The quenching mechanism is briefly discussed.

Abstract

The graphite carbon nitride (g-C3N4) nanosheets were synthesized and applied for the detection of Ag+ ion in aqueous solutions. Transmission electron microscopy, Fourier infrared spectroscopy, x-ray diffraction, ultraviolet/visible and photoluminescence spectroscopy were used for characterization of g-C3N4 nanosheets. The fluorescence intensity of g-C3N4 nanosheets decreases with the increase in the concentration of Ag+. The fluorescence probe can be applied for detection of Ag+. The results show that it has high selectivity to Ag+ and exhibits a good linearity over the concentration range 0.020–2.0 μM with a detection limit of 27 nM. Most cations do not have any interference on the detection of Ag+. The quenching process is assessed and discussed. Finally, the g-C3N4 nanosheets have been successfully used for the detection of Ag+ in real water samples. The recoveries of spiked water samples are > 97%.

Graphical abstract

Graphite carbon nitride nanosheets (g-C3N4 nanosheets) were successfully synthesized by an ultrasonic exfoliation method from bulk g-C3N4 in aqueous medium. The g-C3N4 nanosheets is seriously quenched by Ag+. The fluorescence probe can be applied for detection of Ag+.

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Introduction

With the development of the industry, heavy metal ions have already become a kind of common toxic pollutants [1], [2], which cause serious harm to the ecological environment and human beings [3], [4], [5], [6]. More seriously, water, soil and biology are difficult to be completely refreshed once polluted by heavy metal ions. Silver is one of the metals and is widely used in cosmetic, medicine and other industries with good antibacterial properties [7], [8], [9]. Traces of silver is harmless to the human body; however, accumulation of too much silver ion in the body will inhibit the activity of protein in the body, resulting in various health problems [10], [11], [12]. As such, the determination of silver ion in water is very important and necessary.

Up to now, the main methods for detection of silver ions are atomic absorption spectrometry [13], inductively coupled plasma-atomic emission spectrometry [14] and inductively coupled plasma-mass spectrometry [15]. However, the sample pre-treatment of these methods are complex and the instruments required are costly. Thus, they are not suitable for cost-effective detection of silver ion (Ag+). With the recent synthesis of nano-materials, a lot of methods have been developed for detection of Ag+. For instances, Butwong et al. [16] used mercaptoacetic acid capped CdS quantum dots for fluorescence analysis of Ag+. Ingole et al. [17] applied citrate-capped CdSe quantum dots as a luminescent probe for detection of Ag+. Chen et al. [18] prepared aluminum oxide supported fluorescent gold nanodots for detection of Ag+ in aqueous solutions. Although these probes possess the characteristics of rapid and high sensitivity and are low cost, their toxicity and relatively complicated synthesis process restrict their potential applications. As such, an economic, non-toxic, sensitive and stable fluorescent probe synthesized from the green synthesis method is urgently needed for detection of Ag+.

As a semiconductor material, graphite carbon nitride (g-C3N4) with a special structure have drawn much attention in many fields in recent years [19], [20], [21], [22], [23], [24]. Compared with other materials, g-C3N4 possesses various advantages such as low-cost, good biocompatibility, high quantum yield, excellent stability and nontoxicity. It has been brought into some brilliant applications [25], [26], [27], [28], [29], [30]. For examples, Tian et al. [26] synthesized ultrathin g-C3N4 nanosheets as a rapid and ultrasensitive fluorescence sensor for detecting Cu2 +. Zhang et al. [27] developed a fluorescence sensor for Fe3 + and Cu2 + based on the fluorescence quenching of g-C3N4. Hu et al. [28] demonstrated that g-C3N4 as a fluorescent nanoprobe can detect DNA in solution. Chen et al. [29] successfully synthesized g-C3N4 nanosheets and applied for the detection of nitro-aromatic explosives. Tang et al. [30] prepared a turn-on luminescence probe based on metal-free g-C3N4 for detecting biothiols.

Herein, g-C3N4 nanosheets were successfully synthesized by exfoliating bulk g-C3N4 under ultrasonic sound and were subsequently characterized by transmission electron microscopy (TEM), x-ray diffraction (XRD), Fourier transmission infrared spectroscopy (FTIR) and ultraviolet–visible (UV–vis) spectroscopy. The fluorescence of g-C3N4 nanosheets is quenched in the presence of Ag+. The fluorescence intensity decreases with the increase in the concentration of g-C3N4. The g-C3N4 nanosheets were utilized as a fluorescent probe to detect Ag+ in aqueous solution with high sensitivity, short analysis time and wide linear range. Finally, the quenching process was briefly studied and the fluorescent probe was successfully for determination of Ag+ in real water samples.

Section snippets

Materials

Melamine was purchased from Aladin (Shanghai, China). All other reagents of analytical reagent grades were used as received without further purification. Double deionized water (≥ 18.25 MΩ·cm) was obtained from a Milli-Q-RO4 water purification system (Millipore, Bedford, MA, USA) and used for the preparation of all solutions.

Apparatus

Fluorescence spectra of g-C3N4 nanosheets were recorded on a Hitachi F-4500 fluorescence spectrophotometer (Tokyo, Japan). UV–vis absorption spectra were acquired on a

Characterization

Fig. 1 displays the TEM image of the g-C3N4 nanosheets. The as-prepared g-C3N4 nanosheets with an average diameter of ca. 12 nm has a laminar morphology. Moreover, the different transparency of nanosheets suggests that they have an ultrathin thickness. Fig. 2 shows the UV–vis absorption, photoluminescence excitation and emission spectra of g-C3N4 nanosheets. The UV–vis absorption spectrum possesses an absorption peak at 313 nm which can be attributed to the n–π* transitions of the unsaturated

Conclusion

In summary, g-C3N4 nanosheets have been successfully synthesized from bulk g-C3N4 in aqueous solution by an ultrasonic exfoliation method. The fluorescence of g-C3N4 nanosheets is heavily quenched by Ag+. The fluorescence probe based on g-C3N4 nanosheets shows high selectivity and sensitivity to Ag+ with a low detection limit of 27 nM. The interaction between g-C3N4 nanosheets and Ag+ is based on the static quenching process. Finally, g-C3N4 nanosheets have been successfully applied for

Acknowledgements

This work is supported by the National Natural Science Foundation of China (21175086), Local Colleges in 2015 National College Students' Innovative Entrepreneurial Training Program (201510114006), Natural Science Foundation of Shanxi Province of China (2016011018), Shanxi College Students' Innovative Entrepreneurial Training Project (2015128), Shanxi Medical University of Science and Technology Innovation Fund (01201312), and 331 Early Career Research Grant of Basic Medical College in Shanxi

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