# Temperature Based Investigation on Structure and Optical Properties of Bi2S3 Nanoflowers by Solvothermal Approach

J Arumugam, A Dhayal Raj, A Albert Irudayaraj, T Pazhanivel

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J Arumugam, A Dhayal Raj, A Albert Irudayaraj, T Pazhanivel. Temperature Based Investigation on Structure and Optical Properties of Bi2S3 Nanoflowers by Solvothermal Approach. Mechanics, Materials Science & Engineering Journal, 2017, 9, 10.2412/mmse.73.16.231. hal-01499445

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# Temperature Based Investigation on Structure and Optical Properties of Bi₂S₃ Nanoflowers by Solvothermal Approach

J. Arumugam¹, A. Dhayal Raj¹, a, A. Albert Irudayaraj¹, T. Pazhanivel²

1. Department of Physics, Sacred Heart College, Tirupattur, Vellore Dist, Tamilnadu, India

2. Department of Physics, Periyar University, Salem, Tamilnadu, India

a. dhayalraj03@gmail.com

<figure><img src="image_2.png" /></figure>

DOI 10.2412/mmse.73.16.231 provided by [Seo4U.link](https://seotoolbox.com/)

**Keywords:** Bi₂S₃ nanostructures, XRD, SEM, UV-Vis, FTIR.

**ABSTRACT.** A solvothermal process has been employed to synthesis Bi₂S₃ nanostructures which has a wide spread applications in photodiode, hydrogen storage, high energy batteries, as well as luminescence and catalytic fields. Bismuth nitrate, thiourea and PolyVinyPyrrolidene (PVP), used as the starting materials are dissolved in ethylene glycol for different reaction times. It was found that the temperature plays a key role in determining the shape of the products. The crystalline phase and structure of the Bi₂S₃ nanostructures were investigated by power X-ray diffraction (XRD). The surface morphology has been analyzed by Scanning electron microscopy (SEM), the optical properties of the Bi₂S₃ nanoparticles were analyzed using UV-Vis spectroscopy. The functional groups present in the Bi₂S₃ nanoparticles were characterized by FT-IR spectroscopy. The novel Bi₂S₃ nanoparticles will be exploited for its application as photocatalyst.

**Introduction.** Recently, nanostructured materials have gained their importance in science and technology due to their novel optical, electric, magnetic and catalytic properties as compared to the corresponding bulk counter parts due to their large surface areas, smaller size, reduced numbers of free electrons and possible quantum confinement effects [1]. The integration of one-dimensional nanoscale building blocks into two-and three-dimensional ordered superstructures or complex functional architectures, which not only open up possibilities for advanced nanodevices but also offers opportunities to explore their novel collective properties, has recently been proposed [2]. In particular, nanostructures like nanopariticles and nanoflowers of semiconductor materials have attracted much attention due to their possible applications in nanoscale electronic and optoelectronic devices. Nanowiskers so called by reason off their appearance have become the subject of intensive study in recent years because of their remarkable characteristics [3]. However, the organization of building blocks into ordered patterns through direct manipulation receives increasing research interest in the synthesis of nanomaterials.

Bismuth sulfide (Bi₂S₃) is one of the most studied semiconductors with E_g of 1.3eV [4] owing to its wide spread applications, such as photodiode arrays, photovoltaic converters, photodetectors, thermoelectric and electrochemical hydrogen storage as an imaging agent in X-ray computed tomography, in biomolecules detection, H₂ sensing and so on. Extensive research has been focused on the synthesis of one dimensional Bi₂S₃ nanostructures in a controlled fashion by various methods [5]. Qiaofeng Han et al., have reported the Orthorhombic Bi₂S₃ nanorods with diameters in the ranging of 20-35 nm and with lengths of hundreds of nanometers by hydrothermal treatment [6]. Xuefeng Qian et al., have reported Bi₂S₃ naniwiskers through microwave method and influence of PVP and sulfur sources on the morphology of the prepared Bi₂S₃ have also been reported [3]. Yonghong Ni et al., have reported flowerlike Bi₂S₃ microspheres and have studied catalytic activity

© 2017 The Authors. Published by Magnolithe GmbH. This is an open access article under the CC BY-NC-ND license
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[7]. Anukorn Phuruangrat et al., have reported the Influence of PVP on the Morphologies of Bi₂S₃ Nanostructures synthesized by Solvothermal Method [8], K. Kavi rasu et al., have reported the structural and optical properties of PVP/Bi₂S₃ nanoparticles by chemical method [9]. Ding et al., have synthesized the 3D Hierarchical Bi₂S₃ nanostructures through PolyVinylPyrrolidone (PVP) and Chloride Ion-assisted synthesis [10]. However, most of the techniques mentioned above are of higher temperature and pressure, or the preparation procedures are complex. Therefore, it remains a challenge to develop a facile route to fabrication of Bi₂S₃ nanomaterials in order to investigate its unusual properties [11].

In this study, we report the facile route to synthesize flower-like Bi₂S₃ nanostructures via a solvothermal approach with different reaction temperature.

**Experimental Procedure:** Bismuth Nitrate, Thiourea, Polyvinylpyrrolidone (PVP) and ethylene glycol (EG) were purchased from merck without further purification. In a typical procedure required amount of bismuth nitrate, thiourea and PVP were successively mixed in 40 ml of ethylene glycol. The resulting mixtures were sonicated to obtain a clear yellow solution, which was then transferred in to 40 mL Stainless steel Teflon-lined autoclave. The autoclaved was maintained for different temperatures (60°C, 100°C, 120°C, 160°C and 200°C). Finally, the sample was collected, washed with double distilled water and ethanol for few times and then dried at 60°C in hot air oven. Further the sample was characterized by XRD, HR-SEM, EDAX, UV-Vis and FTIR.

**Result and discussion**

**Structural analysis.** Fig.1 shows the XRD pattern of the Bi₂S₃ nanostructures obtained via a one-pot Solvothermal method. All the peaks can be indexed to the orthorhombic Bi₂S₃ phase (JCPDS no. 17-0320), with lattice constants a=11.15Å, b=11.30Å and c= 3.981Å and no characteristic peaks of any other phases or impurities are observed. Furthermore, the intense and sharp peaks indicate the product is well crystallized. In another investigation, the average crystalline size was derived from Dye-Scherrer formula as shown below:

$$D = \frac{k \lambda}{\beta \cos\theta'}$$

where D is the average crystalline size, k is a constant whose value is typically 0.9 of non-spherical crystals, β is the full width at half maximum (FWHM) of the diffraction peak (in radians) that has the maximum intensity in the diffraction pattern, λ is the wavelength of incident X-ray beam (0.154184 nm) and θ is diffraction angle or Bragg angle.

From this formula, the average crystalline size of Bi₂S₃ was calculated as 17 nm, 21nm, 28 nm, 30 nm and 32nm for samples prepared at 60°C, 100°C, 120°C, 160°C and 200°C respectively. When the reaction temperature is increased up to 200°C, the diffraction peaks become stronger gradually. When reaction temperature is reached at 200°C, the diffraction peaks are narrow and strong, indicating that the improvement in crystallinity.
<figure><img src="image_3.png" /><figcaption>Fig. 1. XRD Pattern of Bi₂S₃ nanoparticles prepared for 24 hours at (a) 60°C (b) 100°C (c) 120°C (d) 160°C (e) 200°C.</figcaption></figure>

**Morphological analysis:** Fig.2 Shows the HR-SEM image of Bi₂S₃ nanoparticles obtained at different temperatures by solvothermal approach. The SEM image in Fig.2 (a) corresponding to the sample prepared at 60°C, shows numerous well-distributed flower-like nanostructures formed from the reactant Bi₂S₃ powder.

Inset the Fig.2 (a) shows a single flower-like structure. The flowers are approximately of 1µm in size and composed of tens of petals. The petals of these Bi₂S₃ nanoflowers are smooth flaks-structures and approximately 250 nm in width and 166 nm in thickness as shown in Fig.2 (a). As the reaction temperature is increased the nanoflowers turn up to nanoparticles with some agglomeration. The average particle size has been calculated as 166nm, 180 nm, 249nm and 250nm for sales prepared at 100°C, 120°C, 160°C and 200°C respectively. When the reaction temperature is increased the particle size also increased. The composition of the nanoflowers as extracted from the energy dispersive spectroscopy (EDAX) spectrum and are presented in Fig. 2 (f) which confirms the presence of Bi and S atoms. The deficiency of S with respect to stoichiometry in the nanoflowers can be attributed to the vapour pressure of S higher than that of Bi. Little evidence of O was detected in this spectrum.
<figure><img src="image_4.png" /><figcaption>Fig. 2. HR-SEM image of Bi₂S₃ nanoparticles obtained at different temperatures (a) 60°C, (b) 100°C, (c) 120°C, (d) 160°C, (e) 200°C and (f) EDAX spectrum of Bi₂S₃ nanoflowers prepared by solvothermal approach for 24 hours.</figcaption></figure>
<figure><img src="image_5.png" /><figcaption>Fig. 3. UV absorption spectra of Bi₂S₃ nanoparticles prepared for 24 hours at (a) 60°C, (b) 100°C, (c) 120°C, (d) 160°C, (e) 200°C.</figcaption></figure>

**Optical analysis.** Fig.3 shows the UV-Vis spectra of Bi₂S₃ nanoparticles obtained at different temperatures by solvothermal approach. The optical properties of Bi₂S₃ semiconducting compounds result from band structures of the materials and are very important in a large number of applications. The (αhu)² ~ hu curve are shown as inset in Fig.3. From the Fig., the band gap of Bi₂S₃ semiconductor nanoflowers and nanoarticles could be determined to be about 1.70 to 1.82 eV by extrapolating the linear portion of (αhu)² Vs hu curve. The band gap values thus obtained is higher than that of the bulk Bi₂S₃ (1.3eV). The blue shift might be ascribed to the quantum effect due to the high aspect ratio of the nanoflower and nanoparticles.

**Functional group analysis.**

<figure><img src="image_6.png" /><figcaption>Fig. 4. FTIR spectra of Bi₂S₃ nanoparticles prepared for 24 hours at (a) 60°C by solvothermal approach.</figcaption></figure>

The composition and quality of the product were analyzed by FT-IR spectroscopy. Fig.4 FTIR spectra of Bi₂S₃ nanoflowers prepared for 24 hours at 60°C by solvothermal approach. The broad absorption
band centered at 3426 cm⁻¹, must be associated with the (OH) stretching vibration. A broad band at 3300 to 3500 cm⁻¹ attributed to the stretching vibration of H₂O, while the band centered at 1623 cm⁻¹ corresponds to the bending vibrations of H₂O. The strong peaks at 1370 cm⁻¹ attributed to C-S stretching vibration [12], indicating the formation of the [Bi(Tu)₃]³⁺ complex in the porous nanoflowers, as shown in the Fig. 4. The peaks at 1207 cm⁻¹ could be attributed to the stretching of C–O–C– bonds [13]. The strong absorption band at 428 cm⁻¹ and 478 cm⁻¹ is due to Bi [14]. The peak at 618 cm⁻¹ may be attributed to stretching vibrations of sulphur indicating the formation of Bi₂S₃.

**Summary.** Well-crystallined Bi₂S₃ nanoflowers have been successfully synthesized by solvothermal approach with low reaction temperature. The structure of the Bi₂S₃ nanoparticles is confirmed to be orthorhombic from the X- ray diffraction patterns. The Vibrational peaks at 423 cm⁻¹ and 618 cm⁻¹ confirm the formation of Bi₂S₃. From the optical absorption spectra, the band gap of Bi₂S₃ nanostructures were found to be in the range 1.70 to 1.82eV, which are higher than that of bulk Bi₂S₃ materials. The as-synthesized Bi₂S₃ nanoflowers, can be potentially applied in the field of photocatalysis.

**Acknowledgments**

The authors would like to acknowledge the management, Sacred Heart College for extending support to complete this work successfully.

**References**

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Cite the paper

J. Arumugam, A. Dhayal Raj, A. Albert Irudayaraj, T. Pazhanivel (2017). *Temperature Based Investigation on Structure and Optical Properties of Bi₂S₃ Nanoflowers by Solvothermal Approach*. *Mechanics, Materials Science & Engineering*, Vol 9. doi:10.2412/mmse.73.16.231