Preparation of Nanocrystalline Bismuth-Containing Powders through Solution-Phase Reductions
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not been explored, and several recent publications have suggested34 that quantum confined bismuth may exhibit enhanced thermoelectric properties. In spite of these results, we are aware of only one report in the literature of nanocrystalline bismuth being prepared through wet chemical methods5 , and the product was prepared only at very low reaction concentrations. Recently, in an attempt to synthesize such materials and understand the fundamental chemistry behind their formation, we have begun to examine the preparation of nanocrystalline bismuth through straightforward solution reductions. By reducing BiC13 in the presence of strongly coordinating ligands and solvents, we have obtained nanocrystalline bismuth powders. In addition, carrying out these reductions in the presence of HAuCl 4 has led to the isolation of Au 2Bi of similar dimensions. Herein we report the details of the synthesis and characterization of these materials using XRD and TEM. EXPERIMENTAL General Considerations: The reductions were carried out using commercially available reagents and standard Schlenk techniques, when necessary. The compounds BiCl3, NaBH,, LiBEt 3H (1 M in THF), HAuCl, (C8 H,,) 4NBr, and C8HSH were purchased from Aldrich and used as received. In general, rigorous drying of solvents was found not to be necessary, and was not performed unless otherwise indicated. XRD measurements were obtained on a Phillips XRG 53 Mat. Res. Soc. Symp. Proc. Vol. 581 © 2000 Materials Research Society
2500 X-ray instrument using Cu Kat radiation, from powder samples attached to a glass slide using hydrocarbon grease. TEM measurements were performed on a Zeiss EM-10C instrument, operating at 60 kV. The samples were prepared by sonicating the appropriate powder for 1 to 2 minutes in MeOH and placing a drop on a carbon coated copper grid, which was wicked off after 10 seconds. 'H NMR measurements were obtained on a Bruker AC-300 spectrometer, using 5mm tubes which were septum sealed under argon. Peaks were referenced to the residual protons of deuterated-benzene at 6 7.15. IR measurements were obtained on a Nicolet Magna 750 FTIR using KBr pellets. Preparation of Nanocrystalline Bi: A typical reaction was carried out as follows: BiCl3 (0.027 g; 0.09 mmol) was added to a flask in a He filled dry-box, the flask was removed, and approximately 25 mL of ethylenediamine added under an Ar purge. The resulting hazy white mixture was stirred for several minutes at room temperature while the reducing agent, NaBH 4 (0.0102 g; 0.27 mmol) was dissolved in 10 mL of warm ethylenediamine.
Once the NaBH 4
solution had cooled to room temperature, it was added to the BiCl 3 mixture via pipet, once again under Ar. This resulted in a gradual darkening in color to black while the mixture was stirred overnight at room temperature. The black solid was isolated by centrifuge, washed twice with EtOH, and dried yielding a black powder (0.272 g; 145% yield). The extra weight present in the final product can be attributed to reaction byproducts not removed by the EtOH. This
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