Fluorescence modulation and photodegradation characteristics of safranin O dye in the presence of ZnS nanoparticles

https://doi.org/10.1016/j.jphotochem.2009.04.021Get rights and content

Abstract

ZnS nanoparticles were synthesized using a chemical precipitation method and were characterized with FTIR, transmission electron microscope (TEM), X-ray diffraction analysis (XRD) and UV–vis absorption. XRD analysis shows that the diameter of the particles is 1.6 nm. The interaction between ZnS nanoparticles and safranin O (SO) dye was studied with UV–vis absorption as well as fluorescence emission and excitation spectra. The results show fluorescence enhancement from dye molecules with nanoparticles upon excitation at 325 nm. In contrast, the fluorescence of the dye monitored at 520 nm is quenched by ZnS nanoparticles. ZnS nanoparticles were used as a photocatalyst in order to degrade SO dye. A maximum degradation efficiency of 51% of the dye has been achieved in the presence of ZnS as a nanophotocatalyst at pH 7. Photodegradation of the dye follows second-order kinetics.

Introduction

Semiconductor nanoparticles have attracted considerable attention due to their size-dependent photophysical and photochemical properties [1], [2]. Such materials are promising for the production of optical sensitizers and photocatalysis [3], [4], [5]. Further, they can be used for optoelectronic devices [6], [7], electroluminescent applications [8], quantum devices [9], and in novel biomolecular applications, such as DNA detection [10], [11]. Zinc sulphide (ZnS) is one of the semiconductor nanomaterials that show promise for the production of optical sensitizers, photocatalysis, electroluminescent materials, optical sensors [12], [13] and for solar energy conversion [14]. Some dyes are also used as photosensitizers for solar energy conversion, or as photosensitizers for wide band-gap semiconductors, extending the wavelength absorbed by the system to the visible range [15], [16].

Safranin-O (3,7-diamino-2,8-dimethyl-5 phenylphenazinium chloride (SO), Scheme 1) is a phenazine dye, that has been used as a photosensitizer in electron- and energy-transfer reactions [17]. Also, it is used as a sensitizer in visible light photopolymerization [18]. Phenazine dyes are used in the textile industry and are photodegraded under UV light using a semiconductor as a catalyst [19]. We have examined the fluorescence quenching of safranin T by thiones in micelles and homogeneous media [20]. Youqiu et al. reported the decrease in the absorbance and fluorescence quenching for safranine T by gold nanoparticles [21]. Recently, Hamity et al. have investigated the effect of CdS nanoparticles on the photodegradation of SO [22].

In the present work, we describe the synthesis and characterization of ZnS nanoparticles. Also, we report the interaction between ZnS nanoparticles and SO dye and the possible roles of the nanoparticles as a catalyst for photodegradation of the dye.

Section snippets

Materials

Safranin O (Sigma), zinc acetate (Aldrich), thiourea (Aldrich) and ammonia (Aldrich) were of analytical grade and were used without further purification. Deionized water was used to prepare the buffer solution.

Equipment

The morphology of ZnS nanoparticles was observed by a transmission electron microscope (TEM, JEM-200CX). UV–vis absorption spectra were measured on a Shimadzu UV-2450 spectrophotometer. Fluorescence spectra were recorded on a Shimadzu RF-5301PC spectrofluorometer. The FT-IR analysis was

Structure and characterization

Fig. 1(a) shows a typical TEM image of ZnS nanoparticles. It can be seen that ZnS nanoparticles are polydispersed and almost spherically shaped. The XRD spectra of ZnS are shown in Fig. 1(b). We observe three reflection peaks at 2θ values of 28·978°, 48·519°, and 57·927° corresponding to the (1 1 1), (2 2 0), and (3 1 1) diffraction planes, respectively, of the cubic crystalline structure of ZnS. These values are close to those reported by Pant et al. [23]. The mean particle diameter d (1.6 nm) was

Conclusion

ZnS nanoparticles with extremely small size (1.6 nm) were synthesized via a chemical precipitation method. It is found that luminescence properties of dye molecules are modulated by adding small quantities of colloidal ZnS nanoparticles. Coupling of dye molecules with ZnS nanoparticles leads to many interesting optical and electronic properties which may be relevant for a variety of applications such as biological sensing, light emitting diodes, etc. The photodegradation of the dye molecules in

Acknowledgements

A Kafrelsheikh University grant is gratefully acknowledged. We thank Professor S. Buckner, Saint Louis University, for his useful discussions.

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