Binary bismuth chalcogenides have received considerable attention for their application in thermoelectric materials; however, there have been relatively fewer reports on the ternary and quarternary bismuth chalcogenides; but nevertheless, a slowly growing number of them can be found.
1Among them, NaCl-type MBiQ 2 (M = Li, Na, K; Q = S, Se) is the most elementary, and was first synthesized 70 years ago in a solid state reaction, and the structures of them have been determined merely by the powder X-ray diffraction method (XRD).2-5 Synthetic methods had been largely limited to molten salt synthesis in a sealed quartz tube for very long reaction time (~9 d)
5, until Qian et al. reported that NaBiS 2 could be isolated as a byproduct, during the synthesis of 1-D bismuth sulfide (Bi 2 S 3 ) nanoribbons, under solvothermal condition (glycerol:water = 2:1). 6,7 In that report, when higher concentration of NaOH is added to the reaction medium, NaBiS 2 is found at the bottom of the autoclave.
6The NaBiS 2 was characterized only by XRD and scanning electron microscopy (SEM), but no other characterization was performed.6 Inspired by this finding, we have tried to synthesize sodium bismuth sulfide as a sole product, in aqueous medium. Herein, we report the synthesis of NaBiS 2 as the sole product by hydrothermal reaction, for the first time. The synthesis produced NaBiS 2 nanosheets, and it was characterized by XRD, diffuse reflectance spectrophotometry, X-ray photoelectron spectroscopy (XPS), and elemental analysis by energy dispersive X-ray spectroscopy (EDX). This synthetic method might open up new opportunities to access NaBiS 2 , and is environmentally benign; it might therefore be utilized in a variety of fields, including thermoelectric materials, and light harvesting materials.
Experimental SectionAll the chemicals were of analytical grade, and were used as-received, without further purification. Distilled water was purified by a New P.nix UP 900 water purification system (Human Corporation, South Korea). IR spectra were recorded, using a MIDAC M series spectrometer. Powder X-ray diffraction (XRD) data were collected at 40 kV and 35 mA, using a Philips X'pert MPD diffractometer (Philips Analytical, Netherlands); CuK α radiation was used as the source (λ = 1.5418 Å). Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) analyses were performed, using a Bruker Quantax 200 125ev SEM spectrometer (Germany). X-ray photoelectron spectra (XPS) were recorded, using an ESCALAB 210 X-ray Photoelectron Spectroscope.Synthesis of Sodium Bismuth Sulfide. Synthesis of sodium bismuth sulfide (NaBiS 2 ) was performed by the following procedures: Bi(NO 3 ) 3 ·5H 2 O (40 mM, 4.0 mmol) and L-Cys (120 mM, 12.0 mmol) were mixed to make a 100 mL of aqueous solution, followed by adding NaOH (2.5 M, 0.25 mol). The resulting solution was transferred to a teflon-lined autoclave reactor, and stirred with magnetic stirrer for an additional 30 min. Subsequently, the autoclave reactor was placed in an electric convectio...
