Synthesis and characterization of samarium-doped ZnS nanoparticles: A novel visible light responsive photocatalyst

doi:10.1016/j.materresbull.2015.12.035

Materials Research Bulletin

Volume 76, April 2016, Pages 411-421

https://doi.org/10.1016/j.materresbull.2015.12.035 Get rights and content

Highlights

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Sm-doped ZnS Nanomaterials were synthesized by hydrothermal method.
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The as-prepared compounds were characterized by XRD, TEM, XPS, SEM and UV techniques.
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The photocatalytic effect of compounds was determined by Reactive Red 43 degradation.
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The degradation of RRed 43 followed the Langmuir–Hinshelwood kinetic model.

Abstract

We prepared pure and samarium-doped ZnS (Sm_xZn_1−xS_1+0.5x) nanoparticles via hydrothermal process at 160 °C for 24 h. XRD analysis shows that the particles were well crystallized and corresponds to a cubic sphalerite phase. SEM and TEM images indicate that the sizes of the particles were in the range of 20–60 nm. The photocatalytic activity of Sm-doped ZnS nanoparticles was evaluated by monitoring the decolorization of Reactive Red 43 in aqueous solution under visible light irradiation. The color removal efficiency of Sm_0.04Zn_0.96S and pure ZnS was 95.1% and 28.7% after 120 min of treatment, respectively. Among the different amounts of dopant agent used, 4% Sm-doped ZnS nanoparticles indicated the highest decolorization. We found that the presence of inorganic ions such as Cl⁻, CO₃²⁻ and other radical scavengers such as buthanol and isopropyl alcohol reduced the decolorization efficiency.

Graphical abstract

Introduction

Recently, nanocrystalline semiconductor photocatalysis systems have been broadly studied as the most promising photocatalyst for environmental remediation processes such as air purification, water purification, heavy metal removal, and hazardous waste remediation because of their high functionality and non-secondary pollution [1], [2], [3], [4]. Due to the adverse effects of organic dyes on human health, several treatment technologies have been applied to treating colored effluents including coagulation/flocculation, biological treatment, electrochemical treatment, membrane filtration, ion exchange, adsorption, chemical oxidation and advanced oxidation processes (AOPs) [5], [6], [7], [8]. Studies of the effects of impurity and doping agents on the physical properties of semiconductors are interesting both for basic and applied research [9], [10]. Rare earth metals that have incompletely occupied 4f and empty 5d orbitals are often used as a catalyst or they promote catalysis. Furthermore, doping with lanthanide ions with 4f electron configurations could significantly improve the separation rate of photo-induced charge carriers in semiconductor photocatalysts and greatly enhance the photocatalytic activity [11], [12], [13].

Zinc sulfide (ZnS) is an important II–VI semiconductor material with a wide direct band gap Eg = 3.68 eV (bulk) [14]. ZnS has been studied due to its wide applications as phosphors and catalysts [15]. ZnS is a promising material for electro-luminescent devices, solar cells, and many other optoelectronic devices due to its extremely low bulk losses, high resistance to thermal shock, and stability in virtually all environments [16]. As some researchers have reported, ZnS is a promising and effective catalyst for photocatalytic degradation of organic pollutants [17], [18]. However, to the best of our knowledge, no studies have been reported on the doping of ZnS by other metals, especially lanthanides, to improve its photocatalytic efficiency. In this study, a simple hydrothermal route has been introduced for the synthesis of pure and Samarium-doped ZnS (Sm_xZn_1−xS_1+0.5x) nanoparticles. The photocatalytic activity of undoped and Sm-doped ZnS nanoparticles was investigated with regard to Reactive Red 43 (RR43) (as a model organic dye) decolorization under visible light irradiation (see Table 1). Moreover, the performance of as-prepared samples in terms of decolorization efficiency and kinetic rate constant were studied and compared. To the best of our knowledge, there is no literature report on the use of ZnS and Sm_xZn_1−xS_1+0.5x nanoparticles for the removal of RR43. We also investigated the effect of inorganic ions on the decolorization efficiency of RR43, and modeled the kinetics of the process using nonlinear regression analysis.

Section snippets

Chemicals

All chemicals used in this study were of analytical grade and were used without further purification. ZnSO₄·6H₂O (99.5%), N₂H₄·H₂O (99%), S (99%) and NaOH were obtained from Merck. Sm (NO₃)₃·6H₂O and ethanol (99%) were obtained from Sigma–Aldrich. RR43 was purchased from the Zhejiang Yide Chemical Company (China).

Synthesis of Sm-doped ZnS samples

Sm-doped ZnS nanoparticles with variable Sm contents (0–4% mol) were prepared by a hydrothermal method using hydrazine hydrate (N₂H₄·H₂O) as the reducing agent. In a typical synthesis,

Characteristics and physical properties of synthesized nanoparticles

Fig. 1 shows the powder X-ray diffraction (P-XRD) patterns of the pure and Sm-doped ZnS samples. All the diffraction peaks of the samples can be readily indexed to the pure typical well-crystallized cubic sphalerite ZnS (JCPDS No. 05-0566) [19]. No peaks indicating impurities were detected, confirming that the hydrothermal method applied in this study was successful in synthesizing the desired samples. Moreover, the sharp diffraction peaks in the XRD spectra of the synthesized samples show that

Conclusion

Pure and samarium-doped ZnS were synthesized by a facile hydrothermal method and were used as photocatalyst for degradation of RR43 under visible light irradiation. XRD analysis shows the crystalized nature of ZnS with a cubic sphalerite structure. The incorporation of Sm ions into the ZnS lattice was confirmed by the results of the XPS analysis. By doping the Sm³⁺ ions into the structure of ZnS, the surface morphology and size of the samples have no obvious changes. Our results indicate that

Acknowledgment

This work is funded by the grant NRF-2015-002423 of the National Research Foundation of Korea.

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View full text

Synthesis and characterization of samarium-doped ZnS nanoparticles: A novel visible light responsive photocatalyst

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Chemicals

Synthesis of Sm-doped ZnS samples

Characteristics and physical properties of synthesized nanoparticles

Conclusion

Acknowledgment

Electrochim. Acta.

Surf. Sci. Rep.

J. Alloy. Compd.

Eng. Asp.

J. Hazard. Mater.

Mater. Lett.

Ceram. Int.

Mater. Lett.

J. Photochem. Photobiol. A

J. Alloys Compd.

Appl. Surf. Sci.

J. Colloid. Interface Sci.

Ultrason. Sonochem.

Chemosphere

Mater. Chem. Phys.

J. Colloid. Interf. Sci.

J. Lumin.

J. Hazard. Mater.

J. Hazard. Mater.

Appl. Surf. Sci.

Ceram. Int.

Appl. Catal. B Environ.

Mater. Res. Bull.

Ultrason. Sonochem.

J. Hazard. Mater.

J. Hazard. Mater.