ZnS nanoparticles for high-sensitive fluorescent detection of pyridine compounds

https://doi.org/10.1016/j.jallcom.2013.01.076Get rights and content

Abstract

Water-soluble ZnS nanoparticles (NPs) capped with alpha-thioglycerol (TGO) have been synthesized through a chemical precipitation method. The nanoparticles were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), UV–Vis absorption spectroscopy, fluorescence spectroscopy, and fluorescence decay spectroscopy. Results showed that the TGO-capped ZnS NPs exhibited the cubic zinc blende structure, and the average size was found to be ∼2.94 nm. Compared with the bulk ZnS, the band-gap energy of the nanoparticles (4.40 eV) rose significantly due to the strong quantum confinement. The TGO-capped ZnS NPs showed a characteristic blue luminescence corresponding to two emission peaks at 419 nm and 460 nm associated with the defect states of the nanoparticles. Such functionalized nanoparticles can be used as fluorescent sensor for the determination of pyridine compounds because they quenched the fluorescence of the nanoparticles effectively. The detection limit was 6.76 × 10−5 M for pyridine. The quenching mechanism was studied in detail, and the results demonstrated the existence of dynamic quenching processes. The proposed sensing method is not only sensitive, simple, fast and low cost, but also meaningful for practical applications.

Highlights

► The synthesis of ZnS nanoparticles (NPs) is simple and low cost. ► The nanoparticles are water-soluble, which could expand their applying areas. ► The fluorescence intensity of ZnS NPs can be quenched by pyridine compounds. ► ZnS NPs can act as a novel fluorescent sensor for pyridine compounds. ► The sensor exhibits high sensitivity, fast response and low detection limit.

Introduction

Nowadays, nanostructure materials are not only at the very frontier of fundamental materials research, but they have also entered into people’s daily life step by step [1], [2], [3]. With the deteriorating trend of environmental pollution and the rising awareness of the public vulnerability to the chemical and biological threats, the detection techniques with both high sensitivity and reliability are demanded urgently. The application of nanostructure materials to the design of chemical sensors has attracted considerable attention due to their tremendous specific surface, high activity, excellent anti-photobleaching and tunable emission [4], [5], [6]. As a developing semiconductor material star, ZnS nanoparticles (NPs) are low toxicity materials with a wide band gap [7] of ∼3.72 eV (cubic zinc blende structure) and ∼3.78 eV (hexagonal wurtzite structure), exhibiting remarkable optical and electrical properties [8], [9], [10], [11], which suggest that they may be particularly well-suited for the manufacture of novel sensor. At present, ZnS NPs can be used to detect the DNA molecular [12], [13], protein [14], organic molecule [15], [16], [17], pH value [18], [19], metal ion [20], [21], [22], [23], etc.

Pyridine and its derivatives are important chemical raw materials, which are mainly used as solvent and intermediate in the production of agricultural chemicals, dyestuffs, additives, drugs, and others. However, this foul-smelling and toxic substance could intrude into the human living environment through the discharge of various industrial effluents and exhaust gases. Besides, pyridine and its derivatives are frequently found in the cigarette smoke [24], and also generated during the putrefaction processes of certain foodstuffs [25]. If inhaled, ingested or absorbed through skin, these chemicals can cause many potentially harmful effects on human body, which include nausea, vomiting, headaches, coughing, asthmatic breathing, laryngitis and even cancers [26]. Consequently, the detection of pyridine has become a heightened need for the health of human and the development of environment-friendly society. Various approaches have been established for the detection of pyridine, such as barbituric acid spectrophotometry [27], high-performance liquid chromatography [28], [29], gas chromatography [30], [31], [32], liquid chromatography–mass spectrometry (LC–MS) [24], gas chromatography–mass spectrometry (GC–MS) [33], [34], optical fiber sensing method [35], but the method based on the fluorescent of nanomaterials has not been reported so far.

Herein, we report a very simple method for the synthesis of TGO-capped ZnS NPs with a narrow size distribution and good optical properties. Compared with other traditional methods, the preparation is a one-step approach using non-toxic and low cost raw materials, and the obtained nanoparticles are water-soluble, which could expand their applying areas particularly in chemical and biological fields. When the pyridine is added to TGO-capped ZnS NPs aqueous solution, it could attach to the surface of ZnS NPs, and result in a significant fluorescence quenching. Based on this phenomenon, a novel fluorescent sensor for the determination of pyridine compounds is proposed, and the performance of this ZnS NPs sensor exhibits high sensitivity, simple, fast and low detection limit. The possible mechanism of fluorescence quenching is also discussed.

Section snippets

Experimental

The TGO-capped ZnS NPs were synthesized by chemical precipitation method as follows: 1.00 g Zn (CH3COO)2·2H2O (Tianjin Bodi Chemical Holding Co., Ltd.) and 1.20 g alpha-thioglycerol (TGO, Shanghai TCI Development Co., Ltd.) were dissolved in 285 mL secondary distilled water (homemade). The TGO acts as a capping agent to prevent the agglomeration of particles and stabilize the ZnS NPs. The pH value of the mixed solution was adjusted to 11.20 by 2 M NaOH solution. After about 30 min of bubbling

Results and discussion

FT-IR spectra of TGO and TGO-capped ZnS NPs are shown in Fig. 1. A broad absorption band in the 3000–3696 cm−1region is associated with the stretching vibrations of hydroxyl groups in bound water and TGO. The peaks at 2930 and 2879 cm−1 are assigned to the stretching vibrations of C–H groups of TGO on the surface of ZnS NPs. The deformation vibrations of the methine and methylene groups in TGO located at 1633 and 1417 cm−1 are also found. The characteristic vibrations at 1064 and 1035 cm−1 belong

Conclusions

In summary, water-soluble ZnS NPs were successfully fabricated through a simple chemical precipitation method. Formation of TGO-capped ZnS NPs was confirmed by FT-IR measurement. TGO-capped ZnS NPs exhibited the cubic zinc blende structure with an average diameter of ∼2.94 nm. The band-gap energy of TGO-capped ZnS NPs was estimated to be 4.40 eV, showing the influence of strong quantum confinement. The fluorescence properties of TGO-capped ZnS NPs were investigated in depth, the peaks located at

Acknowledgments

This work was supported by the Key Technologies R&D Program for the 12th Five-Year Plan (2012BAJ24B04-3) of the Ministry of Science and Technology of the Peoples Republic of China and by the Fundamental Research Funds for the Central Universities, China.

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