Preparation of Cu₄SnS₄/CuCo₂S₄ Nanoparticles Using Combustion Reaction Accelerated by Organic Driving Agents under Microwave Irradiation ^†

Abstract

Copper-based sulfide-rich nanomaterials have recently attracted attention in various applications due to the lack of expense, abundance, and non-toxicity of their constituent elements. As the members of this family, Cu₄SnS₄ and CuCo₂S₄ have exhibited good capability in a stable manner in solar cells, energy storage electrodes, batteries, etc. In this work, through a facile and rapid combustion reaction accelerated by microwave irradiation, Cu₄SnS₄/CuCo₂S₄ nanoparticles were prepared. Thiourea was used as a sulphur source and also organic driving agent. The features of the synthesized product were studied using FT-IR, XRD, SEM, and EDX techniques. The FT-IR and XRD results showed the formation of a multi-components structure containing orthorhombic crystalline phase of Cu₄SnS₄ alongside carrollite CuCo₂S₄ phase.

1. Introduction

In recent years, copper-based sulfide rich nanomaterials have attracted lots of attention because of having more abundant, low-cost, easily available, and non-toxic constituents compared to cadmium and lead-based compounds [1]. Usually, sulfide-rich materials have a higher activity and conductivity, as well as a lower electronegativity and band gap, than metal oxides. These compounds have significant features such as layered structures and suitable band gaps for light absorption, which enable them to be semiconductor materials in various applications [2].

Copper-based ternary sulfides, such as Cu₄SnS₄ and CuCo₂S₄ (as the members of this large family), have been studied in variety of photovoltaic, energy storage, solar cells, and catalytic applications, among others [3,4,5]. The synthesis of hetero-structured building blocks consisting of these compounds to improve multifunctional features and create highly efficient products is notable. Amongst reported synthesis methods, such as the solvothermal/hydrothermal, hot-injection, and sol–gel approaches, microwave-assisted technique can be introduced as a simple and rapid method to prepare nanomaterials [6,7,8]. As a matter of fact, the synthesis of Cu₄SnS₄/CuCo₂S₄ heterostructure nanoparticles using a solvent-free microwave-assisted procedure has not been yet reported.

2. Experimental Section

2.1. Materials

All initial reactants were provided from valid Co. and used without further purification.

2.2. Synthesis Method

The proper stoichiometric amounts of metal sources in the presence of thiourea as a sulphur source and driving agent were mixed with each other, put into a microwave oven, and treated with microwave irradiation at a power of 900 W for 20 minutes. The resulting black powder was washed, dried overnight, and characterized by FT-IR, XRD, and SEM analyses.

2.3. Characterizations

XRD patterns were recorded by a DRON-8 powder diffractometer using Cu Kα radiation (λ = 1.54060 Å). FT-IR spectra were obtained by a Shimadzu-8400S spectrometer in the range of 400–4000 cm⁻¹ using KBr pellets. SEM and energy-dispersive X-ray images were taken on a VEGA\\TESCAN S360 with gold coating.

3. Results and Discussion

Figure 1 indicates the FT-IR spectrum of the prepared sample. The observed strong peaks at 522, 569, and 664 cm⁻¹ could be assigned to vibration frequencies of the Co-O, Sn-S, CoS, and Cu-S bands from the prepared heterostructure molecule [9,10]. The peaks at 2361 and 3403 cm⁻¹ could have been related to the vibrational frequencies of the H-O and C-O-C functional groups from the adsorbed H₂O and CO₂ molecules on the product surface.

The recorded XRD pattern of Cu₄SnS₄/CuCo₂S₄ nanoparticles is shown in Figure 2. Based on this pattern, it can be said that the diffractions peaks were related to the formation of orthorhombic phase of Cu₄SnS₄ structure (JCPDS card No. 27-0196). In addition, the diffraction peaks at 26.59°, 31.26°, 32.70°, 38.88°, 44.88°, 48.84°, 51.89°, 54.73°, 58.29°, 61.74°, 64.79°, 66.11°, 68.14°, 71.39°, 75.36°, and 78.91°—in close accordance with the 220; 311,222; 400; 331; 422; 333,440; 531; 620; 533; 622,444; 711; 642; and 731 crystal planes—were attributed to the cubic phase of the carrollite CuCo₂S₄ structure (JCPDS card No. 75-1570). The slight shift at the 2 theta positions could have been a result of being the sandwich and crystallization of the carrollite CuCo₂S₄ phase between the Cu₄SnS₄ layers.

The elemental EDX analysis (Figure 3) revealed the presence of Cu, Sn, Co, and S elements, thus confirming the mentioned structural data of FT-IR and XRD analyses.

The recorded SEM images of the prepared product depicted aggregations of crystalline flake-like morphology with an average thickness of 40 nm and a width of 210 nm (Figure 4). This morphology could have originated from the role of thiourea as a driving agent, alongside being sulfide source. A particulate morphology with an average particle size of 60 nm was also observed.

4. Conclusions

Cu₄SnS₄/CuCo₂S₄ nanoparticles were well-synthesized by a microwave-assisted method. Amongst various chemical methods, the advantages of this synthesis technique include its simplicity, high speed, low energy consumption, and solvent-free reaction. In an effort to decrease the growth time, microwave heating treatment can be introduced as a capable technique to produce nanomaterials in the short reaction time compared to the conventional procedures with a long reaction time.