- Nano Express
- Open Access
Facile Synthesis of Colored and Conducting CuSCN Composite Coated with CuS Nanoparticles
© The Author(s). 2017
- Received: 14 June 2017
- Accepted: 16 August 2017
- Published: 23 August 2017
Conductivity-tunable, different colored CuS nanoparticle-coated CuSCN composites were synthesized in a single pot using a mixture of copper sulfate and sodium thiosulfate in the presence of triethyl amine hydrothiocyanate (THT) at the ambient condition. When these reagents are mixed in 1:1:1 molar ratio, white-gray-colored CuSCN was produced. In the absence of THT, microsized dark blue-colored CuS particles were produced. However, when THT is present in the solution mixture by different amounts, colored conducting CuS nanoparticle-coated CuSCN composite was produced. CuS nanoparticles are not deposited on CuSCN soon after mixing these regents, but it takes nearly overnight to see the color change (CuS production) in the white CuSCN dispersed mixture. TEM analysis shows that composite consists of hexagonal CuS nanoparticles in the range of ~ 3–10 nm in size. It is interesting to note that CuS-coated CuSCN possesses higher conductivity than neat CuS or CuSCN. Moreover, strong IR absorption was observed for CuS-coated CuSCN composite compared to neat CuS (absence of THT) or CuSCN. Lowest resistivity of 0.05 Ω cm was observed for annealed (250 °C) CuS-coated CuSCN particles (adding 10 ml of THT) under nitrogen atmosphere. Also, this simple method could be extended to be used in the synthesis of CuS-coated composites on the other nanomaterials such as metal oxides, polymers, and metal nanoparticles.
- CuS nanocoating
- Colored conducting composite
- IR absorption
Synthesis of nanostructured materials has attracted much attention due to their unique optical, electrical, mechanical, and electronic properties which cannot be obtained from macroscopic materials. Copper sulfide has drawn significant interest owing to the variations in stoichiometric composition, valence states, nanocrystal morphologies, complex structures, and their different unique properties [1–5]. The stoichiometric composition of copper sulfide varies in a wide range from Cu2S at copper-rich side to CuS2 at the copper-deficient side, such as CuS, Cu1.96S, Cu1.94S, Cu1.8S, Cu7S4, and Cu2S [6, 7]. In the copper-rich section, all the stable compounds of Cu x S are p-type semiconductor as the copper vacancies are within the lattice . As a p-type semiconductor with small bandgap and high ionic conduction, Cu x S nanocrystals are expected to be notable candidates for photovoltaics, field emission devices, and lithium-ion batteries [9–11].
CuS (covellite) shows excellent metallic conductivity, and it is possible to transform this to type 1 superconductor at 1.6 K . It has attracted utilizability in several potential applications such as in photocatalysis , photovoltaics , cathode materials , supercapacitors , and lithium ion batteries . Various morphologies of CuS such as nanowires , nanodisks , hollow spheres , and flower-like structures  have been reported by using different preparation methods, mostly by hydrothermal method.
Several studies on CuS-based composite are reported [20–30]. Yuan et al. have synthesized CuS (nanoflower)/rGo composite using ultrafast microwave-assisted hydrothermal method using Cu(NO3)2 and thiourea for lithium storage application . Yu et al. have synthesized CuS/ZnS nanocomposite hollow spheres with diameters of about 255 nm and shells composed of nanoparticles by an ion-exchange method using monodisperse ZnS solid spheres as a precursor . Hong et al. have synthesized CuS-coated ZnO rod by two-step dipping methods in the sodium sulfide and copper sulfate for piezo-photocatalytic application . Bagheri et al. have synthesized CuS-coated activated carbon by mixing of activated carbon in the mixture of copper(II) acetate and thioacetamide for the removal of ternary dyes .
In the present study, we have synthesized CuS nanoparticle-coated different colored CuSCN composites employing a mixture of copper sulfate and sodium thiosulfate in the presence of triethyl amine hydrothiocyanate (THT) at the ambient condition. This method enables us to produce different colored and conductivity-tunable CuS-coated CuSCN particles. This composite shows excellent optical and electrical properties as explained below. Here, we have selected CuSCN, p-type, high-bandgap (~ 3.6 eV), and air-stable semiconductor as the second material to match the p-type nature of two materials . Moreover, this method can be easily used to prepare CuS nanoparticle-coated composites in the presence of other nanomaterials such metal oxides. Also, this method can be used for the bulk production of CuS nanoparticle-coated composites. We have synthesized CuS nanoparticle-coated TiO2 composites, and XRD and EDX spectra of this composite are shown in Additional file 1: Figure S1. To the best of our knowledge, no reports have been found regarding this simple method to prepare CuS nanoparticle-coated composites.
Sodium thiosulfate pentahydrate (Na2S2O3·5H2O), copper(II) sulfate (CuSO4), triethyl amine, and ammonium thiocyanate were purchased from Sigma-Aldrich, and they were all used as received.
Synthesis of Nano-CuS-Coated CuSCN
Triethyl amine hydrothiocyanate (THT) was synthesized as described in our previous publication . 0.1 M copper sulfate (100 ml) was mixed with 0.1 M sodium thiosulfate pentahydrate (100 ml) in 1:1 ratio and stirred for 30 min. Then, different volumes of 0.1 M THT solution were added dropwise, and the resultant solution was kept overnight while stirring. The precipitate was then centrifuged and washed with distilled water several times prior to characterization.
The morphology of prepared NPs and nanocomposites were observed with scanning electron microscope (SEM; Hitachi SU6600) and high-resolution transmission electron microscope (HRTEM; JEOL JEM 2100). Electron energy loss spectroscopy (EELS-GATAN 963 spectrometer) was used to determine the elemental spectroscopy. Powder X-ray diffraction patterns were recorded by Bruker D-8 Focus instrument (40 kW, 40 mA) with Cu-Kα radiation with a wavelength of 0.15418 nm. UV-Vis spectra were obtained by Shimadzu UV-3600 NIR spectrometer and diffuse reflectance modes.
Figure 1 shows the morphology of CuS (a) and CuS-coated CuSCN nanoparticles (b–d). Figure 1a has significant amount of microscale spherical particles of CuS together with scattered CuS nanoparticles. Images (b) to (d) show CuS-coated CuSCN nanoparticles where CuS cannot be distinguished from the CuSCN. The notable difference in this methodology is the in situ synthesis of CuS nanoparticles on CuSCN instead of precipitation of large spherical shaped CuS.
Resistance of each thin film prepared and their calculated resistivity
Resistivity (Ω cm)
Resistance between electrodes/Ω
CuSCN only (100 ml THT)
CuS microparticles (without THT)
CuS-coated CuSCN (50 ml THT)
CuS-coated CuSCN (25 ml THT)
CuS-coated CuSCN (10 ml THT)
Conductivity-tunable, different colored CuS-coated CuSCN composites were synthesized with a mixture of copper sulfate and sodium thiosulfate in the presence of THT. It was noted that CuS-coated CuSCN materials have unique properties compared to pure CuSCN and CuS. This material has absorption in both the visible region and IR region up to 1900 nm. Minimum resistivity of 0.05 Ω cm was observed for annealed (250 °C) CuS-coated CuSCN under nitrogen atmosphere. On the other hand, this method can easily be utilized to synthesize other CuS-based nanocomposite in the presence of other nanomaterials such as metal oxide.
All of the funding for this research including design of the study and collection, analysis, interpretation of data, and writing of the manuscript is covered by the Sri Lanka Institute of Nanotechnology (SLINTEC).
EVAP contributed to the research idea, laboratory work, data analysis, and writing of the manuscript. YYK carried out the laboratory work. SPR carried out the laboratory work and contributed to the data analysis. KMNdS reviewed the manuscript. All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
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