Antimony selenide has many potential applications in thermoelectric, photovoltaic, and phase-change memory devices. A novel method is described for the rapid and scalable preparation of antimony selenide (Sb2Se3) nanorods in the presence of hydrazine hydrate and/or permanganate at 40°C. Crystalline nanorods are obtained by the addition of hydrazine hydrate in a reaction mixture of antimony acetate and/or chloride and sodium selenite in neutral and basic media, while amorphous nanoparticles are formed by the addition of KMnO4 in a reaction mixture of antimony acetate/chloride and sodium selenite. The powder X-ray diffraction pattern confirms orthorhombic phase crystalline Sb2Se3 for the first and second reactions with lattice parameters
Structure, morphology, and composition of nanorods and nanoparticles are important parameters that give rise to their properties and thus applications. Morphological and structural changes associated with semiconducting V2VI3 compounds such as Sb2Se3 are not well understood.
The semiconducting V2VI3 compounds (Sb2S3 and Sb2Se3) are highly anisotropic semiconductors with a layered structure parallel to the growth direction with orthorhombic phase crystal structure, which is known to adopt a number of packing structures resulting in either trigonal prismatic or octahedral coordination of the metals within a layered matrix of chalcogens [
All chemicals were of analytical grade and were used as received. All glassware were acid-cleaned, and the ultrapure water was devoid of any trace of organics. The synthesis of Sb2Se3 is performed by a new redox method using antimony acetate and/or chloride salts, sodium selenite, hydrazine hydrate (N2H4
For the second reaction, the above process was repeated, except that SbCl3 was used in place of Sb(CH3COO)3 with no NaOH, to study the effect of salt type and pH on the reaction. In this case, the solids produced are black:
For the third reaction, the above process (reaction 1) is also repeated with minor changes; SbCl3 is used in place of Sb(CH3COO)3; KMnO4 is used together with hydrazine and NH3 in place of NaOH. The pH of this mixture was around 10. The solids produced are a mixture of reddish brown and black in color:
The Sb2Se3 solids produced were characterized by X-ray powder diffraction (XRD) using a PANalytical X’Pert PRO X-ray diffractometer with a Cu-K
Surface structure and morphology of the sample were obtained with the aid of a Field Emission Scanning Electron Microscope (FESEM, Hitachi S-4200, Japan). The samples for FESEM analysis were prepared by suspending about 3 mg of the solid Sb2Se3 oxide in 1 mL of isopropanol. After the isopropanol was evaporated, the dry solid was placed on a double-sided black tape and then coated with sputtered platinum thin film prior to FESEM imaging.
Transmission electron microscopy (TEM) images were obtained with a Tecnai G2 F20 S-Twin TEM instrument. The TEM operates at 200 KV using a field emission gun in Schottky mode as an electron source. The samples for TEM analysis were prepared by placing 3 mg of the air-dried solid Sb2Se3 in 10 mL of 2-propanol and sonication for 5 min for homogeneity. The holey carbon copper grid is dipped into the sonicated solution for a few seconds and then air-dried in the dark before analysis. UV-vis absorptions were carried out using a Shimadzu 160A (Japan) spectrophotometer. Photocatalytic performance of the Sb2Se3(s) rods and Sb2Se3(s) particles was evaluated by monitoring the decolorization of Rhodamine B in aqueous solution. The catalytic reaction is carried out in a 20 mL glass vial, which contained 10 mL of the Rh B (0.05 mM) dye solution and 15 mg of Sb2Se3 rods and/or Sb2-xSe3 particles. The mixture was allowed to react at 25°C under stirring. After reaction, the suspension was centrifuged and filtered and the supernatant analyzed using a UV-vis spectrometer (Shimadzu 160A UV, Japan). The efficiency of the catalysts is determined by difference in concentration of RhB between the initial and final readings at
The synthesis of Sb2Se3 nanorods consists of the reaction between N2H4
The temperature of 40°C was chosen because at this temperature a balance is maintained between minimum input of energy (more cost-effective) and a good product yield.
The phases formed by the new method described above are characterized by XRD. Figure
XRD patterns of ((a) and (b)) crystalline Sb2Se3 nanorods (reactions (
The element composition and purity of these nanomaterials were analyzed using EDXS. Figure
EDX and XPS spectra of the Sb2Se3 nanorods synthesized in the presence of hydrazine hydrate (reactions (
The nanostructures of both crystalline and poorly crystalline Sb2Se3 are studied using SEM, TEM, and HRTEM imaging. Figure
SEM images of ((a) and (b)) large crystalline Sb2Se3 nanorods (reaction (
The TEM images shown in Figures
((a), (b), and (c)) TEM and HRTEM images of the large crystalline Sb2Se3 nanorods (at three different magnifications); ((d), (e), and (f)) TEM and HRTEM images of the small crystalline Sb2Se3 nanorods; ((g), (h), and (i)) TEM and HRTEM image of the poorly crystalline Sb2Se3 nanoparticles. The insets in (c), (f), and (i) correspond to the FFT’s and SAED patterns of a single Sb2Se3 nanorod and nanoparticle.
The TEM and HRTEM images of the poorly crystalline Sb2Se3 are shown in Figures
The XRD patterns and the TEM images confirm the structures of Sb2Se3 nanorods and suggest that the preferred ratio of Sb to Se is the one from the second reaction in which hydrazine hydrate was used in near neutral solution (cf. Figure
The UV-vis absorption spectrum of the crystalline and amorphous Sb2Se3 samples is shown in Figure
UV absorption patterns of the crystalline ((a) red and (b) green lines) Sb2Se3 nanorods and poorly crystalline ((c) blue line) Sb2Se3 nanoparticles.
The efficiency of the semiconductor nanoparticles and nanorods with different band gap to function as photocatalyst was measured using RhB as a model organic pollutant in the presence of natural light. Figure
UV-vis absorbance spectra of RhB in solution after exposure to Sb2Se3 nanoparticles, in the presence of natural light, for 0, 2, and 4 h, respectively.
A new method using hydrazine hydrate and permanganate was developed to prepare Sb2Se3 nanorods and nanoparticles with uniform size and morphology. The use of hydrazine hydrate in basic solution (in the presence of selenite and antimony acetate) channels the reaction towards the production of large rod-like Sb2Se3 nanocrystals, while the use of hydrazine hydrate in near neutral solution (in the presence of selenite and antimony chloride) channels the reaction in the direction of producing small rod-like Sb2Se3 nanocrystals. The use of permanganate, hydrazine, Sb(CH3COO)3, and selenite produces Sb2Se3 nanocrystals with Mn as an impurity. One attractive feature for our system is that it is simple, cost-effective, and reproducible. Large scale production would depend on what is desired. For large nanorods, the first reaction is recommended, while for fine nanorods, the second reaction is best. The photocatalytic study demonstrated that semiconductor nanoparticles are more effective in the decolorization of RhB via possibly free radical formation. Antimony selenide nanoparticles may find potential application not only in thermoelectric, photovoltaic, and phase-change memory devices but also as catalyst for the transformation of organic pollutants.
The authors declare that they have no conflicts of interest.
This work was supported by the National Research Foundation of Korea (Grant NRF-2015-002423).