Microwave-assisted synthesis of nanostructured tin sulfide as a highly efficient visible-light active photocatalyst: Characterization, applications, and theoretical studies

Abstract

In this study, nanostructured tin sulfide was synthesized using a facile microwave-assisted method. The as-prepared sample was further characterized via X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDS), UV–Visible Diffuse Reflectance Spectroscopy (DRS), Brunauer-Emmett-Teller (BET), Barrett-Joyner-Halenda (BJH) and Mott-Schottky analyses. Based on the results, the synthesized SnS is an n-type semiconductor and has a direct band gap of 1.32 eV. Photocatalytic activity of nanostructured SnS was then evaluated through degrading methylene blue (MB) under visible light in a cylindrical batch reactor. The results show that this highly efficient photocatalyst can degrade almost up to 83.06% of 14 mg/L pollutant within 10 min, which can be attributed to its relatively high specific surface area of 52.819 m2/g. In addition, the photocatalyst performance was studied from the isothermic, thermodynamic, and kinetic points of view. The results suggest that Fritz-Schlunder along with Baudu are the most appropriate models to describe the adsorption process (the first step of photochemical reactions), as they have the lowest error functions and highest correlation coefficients. Based on kinetic studies results, there is a good agreement between the pseudo-second-order adsorption kinetic model and our experimental data. Additionally, the corresponding structural parameters of SnS were compared by size-strain plot (SSP), and Williamson-Hall methods. Furthermore, a density functional theory (DFT) approach was conducted to get more insight into the electronic and structural properties of the SnS. In terms of the band structure, 1.35 eV of band gap energy (Eg) is obtained, which perfectly matches with the results of characterization tests (1.32 eV). Finally, the partial density of states curves indicate that the valence band maximum (VBM) is mainly generated from 3pS, 5sSn, and 5pSn states while the conduction band minimum (CBM) is made of 5pSn states. Consequently, the spin-up and spin-down curves are found to be highly symmetric, indicating the non-magnetic property of tin sulfide.