Elsevier

Materials Letters

Volume 62, Issue 1, 15 January 2008, Pages 125-127
Materials Letters

Two-step solvothermal synthesis of α-MnS spheres: Growth mechanism and characterization

https://doi.org/10.1016/j.matlet.2007.04.093Get rights and content

Abstract

Stable α-MnS spheres have been successfully synthesized by two-step solvothermal method and traditional solvothermal technique without any surfactant assistance. The XRD patterns and FE-SEM images show that the as-prepared samples are cubic α-MnS micro-spheres with different morphologies. The formation of spheres was studied under different experimental conditions. The two-step solvothermal method helps us cognize the growth mechanism in the solvothermal synthesis better. The result shows that template-direct growth and Ostwald ripening for the formation of the α-MnS spheres are approved. In addition, both mechanisms can be effective at the same time. The UV–Vis absorption spectra reveal that the samples synthesized by different methods have the maximal absorption at the same wavelength (around 365 nm).

Introduction

Materials with different architectures and sizes may have some novel physical and chemical properties. In the past years, there has been extensive interest in synthesis of material with specific morphologies [1], [2], [3]. Well-known that many research efforts have focused on sphere structure, owing to their potential applications in the drug delivery, sensor, coating and chemical catalysis [4], [5], [6], [7], [8], while there has been not a consensus on growth mechanism of spheres yet.

As a p-type semiconductor with a wide gap, manganese sulfide (MnS) has potential application in solar cells as a window/buffer material [9]. Previously, the solvothermal method has been used to prepare metastable (β and γ) and stable α-MnS. Metastable hierarchical architecture γ-MnS was achieved by solvothermal method in the presence of surfactant [9], [10], [11]. Stable α-MnS polyhedrons and spheres were synthesized with cetyltrimethylammonium bromide (CTAB) as surfactant via solvothermal method [12], [13]. But to the best of our knowledge, α-MnS spheres with special structure have not been prepared and investigated yet.

In our experiment, three α-MnS spheres were synthesized without any surfactant assistance via one- and two-step solvothermal technique. The simplified solution and two-step synthesis are useful to analyze the growth mechanism of α-MnS spheres. The results reveal that template-direct growth and Ostwald ripening mechanism can be effective in the solvothermal synthesis. For application, we also studied the optical properties of the products by UV–Vis absorption spectrophotometer.

Section snippets

Experimental

Sample A was prepared by one-step solvothermal method. With a typical procedure, 0.125 g MnCl2·4H2O (1 mM) and 0.048 g sulfur powder (1.5 mM) were added to a Teflon-lined stainless autoclave with 23 mL capacity, which was filled with 12 mL ethylenediamine (EDA, 99.0%) and 3 mL hydrazine hydrate solution (50%, v/v). The mixture was stirred for 5 min by the magnetic force stirrer, maintained at 140 °C for 8 h, and then cooled to room temperature naturally. Then the resulting precipitates were

Result and discussion

The XRD patterns of the as-prepared α-MnS sample A and sample B are shown in Fig. 1. All of the diffraction peaks on the curves can be readily indexed to the cubic unit cell of α-MnS (JCPDS, No. 06-0518), the strong and narrow peaks show good crystallinity of them. Comparing to the two curves, the peak of Fig. 1A is broader than that of Fig. 1B. As the Scherrer formula (D = /βcosθ), the samples prepared by two-step solvothermal method have smaller size than that synthesized through one-step

Conclusions

In summary, three α-MnS spheres were successfully synthesized without any surfactant assistance through two-step solvothermal method and traditional solvothermal technique. This two-step synthesis helps us cognize the growth mechanism in solvothermal synthesis better. It can be extended to design and prepare other transition metal sulfide with special structure in the future.

Acknowledgments

This work was financially supported by the National Natural Science Foundation of China (NCFC, No. 20671027), and by the Natural Science Foundation of Anhui Provinces, China (No. 050440904).

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