Element Directed Aqueous Solution Synthesis of Copper Telluride Nanoparticles, Characterization, and Optical Properties Pushpendra Kumar and Kedar Singh*,† Department of Physics, Faculty of Science, Banaras Hindu UniVersity, Varanasi 221005 India
CRYSTAL GROWTH & DESIGN 2009 VOL. 9, NO. 7 3089–3094
ReceiVed July 31, 2008; ReVised Manuscript ReceiVed March 3, 2009
ABSTRACT: The present study describes large-scale synthesis of transition metal chalcogenide in its nanoregime by an elementdirected, less hazardous, template-free, inexpensive aqueous solution method. Nearly homogeneous green luminescent copper telluride (Cu2Te) nanoparticles (NPs) have been synthesized in a single reaction at 70 °C within 9 h by a wet chemical method. The method ensures almost complete utilization of the precursors with a very high productive yield. The product was well characterized by X-ray diffraction (XRD), UV-visible spectroscopy (UV-vis), Fourier transform infrared spectroscopy (FTIR), photoluminescence spectroscopy (PL), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), energy dispersive X-ray diffraction (EDX), and atomic force microscopy (AFM) techniques. XRD, TEM, and HRTEM analysis revealed that the diameters of the particles are in the range of 25-30 nm. The described protocol allows a precise control and a synchronized isolation of aliquots of Cu2Te nanoparticles with defined sizes, avoiding disturbance of the growth of nanocrystals (existing in the reaction mixture) to the isolation of the next aliquot.
1. Introduction Transition-metal chalcogenides in nanocrystalline form exhibit numerous interesting and useful characteristic properties different from their bulk counterpart. As a consequence of the quantum confinement effect, binary chalcogenide semiconductors have received attention due to their size-dependent optical, physical, and chemical properties. In this context, the impetus for considerable research into the synthesis of coinage metal chalcogenide nanostructures emanates from their potential application in various fields.1-5 Among these chalcogenides, copper chalcogenides have been widely used as optical recording material,6 solar cells,7 super ionic material,8 thermoelectric cooling material,9,10 and optical filters.11 Among them, copper telluride p-type semiconductor is attractive for thermoelectric application and ionic conductivity, owing to its very high thermo power values.12 Previous studies were mainly on thin films and on bulk copper tellurides.13-15 However, there are fewer reports about the nanostructures, especially one-dimensional (1D) nanostructures, of copper tellurides, although their preparation is strongly desired. During the past few years, a variety of synthetic strategies for coinage metal semiconductor nanostructured materials, for example, the solid-state reaction of metals, solid state metathesis, self-propagating high-temperature synthesis, vacuum deposition, sonochemical methods, ultrasonic irradiation, laser abolition, template synthesis, hydrothermal process etc., had been described.16-20 Recently, we have developed a general low temperature, facile aqueous solutionphase strategy to grow nanostructured metal chalcogenides through an electromagnetic stirring refluxing technique which is low cost and less hazardous.17,21 Herein we report a simple, straightforward, single step, less hazardous, element-directed, wet chemical technique for synthesis of Cu2Te nanoparticles in the presence of ethylene glycol and hydrazine hydrate. The synthesis was accompanied at relatively low temperature and in a closed system which could be easily controlled. It has to guarantee of the production of * Author to whom any correspondence should be addressed. E-mail:
[email protected]. † Present address: Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306, USA.
nanoparticles with a narrow size distribution and high productive yield. Simple precursors elemental copper and tellurium have been utilized for synthesis of the final product. The present study tries to satisfy all of these requirements to the large-scale production of Cu2Te nanoparticles. The results showed that hexagonal structured Cu2Te nanoparticles can be obtained, and the formation mechanism is also discussed. To the best of our knowledge, copper telluride nanoparticles has not been synthesized yet by this method.
2. Experimental Procedures 2.1. Materials Preparation. In the typical synthesis of Cu2Te nanoparticles, highly pure Cu (99.999%) and tellurium (99.999%) purchased from Alfa were used without further purification. Ethylene glycol and hydrazine hydrate (analytical grade) purchased from Merck, Germany, were used as received. In the synthesis (0.8 g) copper and (0.406 g) tellurium (in powder form) were taken with deionized water, ethylene glycol, and hydrazine hydrate in a volume ratio of 7:3:1 respectively in a 200 mL capacity conical flask. Then the solution was refluxed under vigorous stirring at 70 °C for 9 h. Finally, the black precipitates were collected and washed with anhydrous ethanol and hot distilled water several times, and then dried in a vacuum at 50 °C for 5 h. 2.2. Characterization Techniques. The X-ray diffraction pattern of as-synthesized, freshly dried Cu2Te was recorded by Rigaku Rotoflux rotating anode diffractometer (operating at 40 kV, 100 mA) with Cu KR radiation. FTIR spectrum was measured by using a Varian-3100 (USA) Fourier transform infrared spectrometer at room temperature with sample milled in KBr. UV-visible spectra were recorded by a UV-vis160 spectrophotometer (Shimadzu, Japan) in the spectral range between 300 and 900 nm using a spectral bandwidth of 1 nm, and absorption experiments were preformed at room temperature. Global photoluminescence spectra of the as-prepared sample were recorded by a computer controlled rationing luminescence spectrometer (LS55Perkin-Elmer Instruments, UK) with an accuracy of (1.0 nm and reproducibility of (0.5 nm. A tunable 2 kW pulse
