Hydrothermal synthesis of PbSe, PbTe semiconductor nanocrystals

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Abstract

Hydrothermal reaction of selenium or tellurium with lead acetate in sodium hydroxide solution in the presence of hydrazine hydrate as a reductive was investigated to prepare lead chalcogenides, PbE (E=Se, Te). Nanocrystals with different morphology could be obtained under mild conditions. Our experiment shows that source materials and reaction temperature play important roles in forming the objective products and controlling their morphologies. The formation of lead chalcogenides in our process is based on a direct elemental combination pathway. The products were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM).

Introduction

Due to their special crystal structure, morphology and grain size, semiconductor nanocrystals have many unique properties, including electrical, optical, magnetic properties [1], [2], [3], [4], [5]. The superior properties and potential applications of II–VI and III–V semiconductor nanocrystals have been widely and thoroughly investigated and the currently available synthetic methods to them are rich. Recently, we synthesized some II–VI and III–V nanocrystals through solvothermal process [6], [7], [8], [9], [10]. To IV–VI semiconductor nanocrystals, such as PbE (E=S, Se, Te), the synthesis of PbS could be easily fulfilled for the convenient accessibility of sulfur source, such as H2S, Na2S, etc. However, the extension of this method to PbSe and PbTe seems to be inappropriate since it will use very toxic H2Se or H2Te. Recently, Unuma et al. [11] reported the synthesis of PbSe fine powders with relatively large grain size by sintering a reaction product of lead-ascorbic acid and sodium selenosulfate. Parkin et al. [15] reported a room temperature method for the synthesis of metal chalcogenides by a reaction between metal and E (E=S, Se, Te) in liquid ammonia. The elemental reactions were also investigated in n-hexylamine, ethane-1,2-diamine, cyclohexane and aqueous ammonia solution [12], [13], [14], [15].

In order to alleviate the reaction conditions and decrease the economic cost, the synthesis of this kind of materials through the hydrothermal process would be prior to solvothermal or metalorganic process if the properties of them could be retained. In this work, we reported a new pathway to synthesize PbSe, PbTe nanocrystals and PbTe nanorods by a hydrothermal reaction between lead acetate and E (E=Se, Te) in sodium hydroxide solution with the presence of hydrazine hydrate as reductive. X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and X-ray energy dispersive analysis (EDX) were used to characterize the PbSe and PbTe nanocrystalline structures, morphologies and compositions.

Section snippets

Experimental

In a typical procedure, stoichiometric element Se (99.95%) or Te (99.95%) and lead acetate (99%) were added to a Teflon-lined stainless steel autoclave with a capacity of 50 ml. Then the autoclave was filled with 30 ml NaOH aqueous solution (1.0 mol/l) and 10 ml hydrazine hydrate (>50% v/v). The solution was neither shaken nor stirred during the heating period. The autoclave was maintained at 100–160°C for 18–72 h and then allowed to cool to room temperature. Black precipitates were collected and

Results and discussion

Fig. 1(a) and (b) shows the XRD patterns of PbSe obtained under 100°C for 18 h and PbTe obtained under 160°C for 18 h through this hydrothermal process. The obtained samples are all pure cubic phase (JCPDS card file: PbSe No. 6-354, PbTe No. 4-554). The average grain sizes of samples calculated from the Scherrer equation based on the XRD line width were 23 nm for PbSe and 18 nm for PbTe, respectively. Fig. 2(a) and (b) show that the two products consist of mainly spherical particles with average

Conclusion

In conclusion, a new hydrothermal pathway to lead chalcogenides nanocrystals and nanorod by reaction of lead acetate with selenium or tellurium in sodium hydroxide solution in the presence of hydrazine hydrate as a reductive was successfully established. The reaction condition was mild. The possible mechanism, the effect of solvent alkality and temperature are discussed.

Acknowledgements

This work is supported by the National Nature Science Foundation of China (No. 29871028) and State Key Project of Fundamental Research.

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