Development of SnO2-SnSe composites for the efficient photocatalytic degradation of methylene blue

Abstract

The discharge of toxic industrial effluents into freshwater has a significant impact on both humans and aquatic lives, which needs to be addressed on an urgent basis. SnO₂, a wide bandgap material possesses good photocatalytic properties, which can be exploited to degrade organic pollutants. However, there is a need to develop an appropriate strategy to decrease its bandgap and minimize the recombination of charge carriers. For this purpose, we are reporting the synthesis of SnO₂/SnSe composites by wet chemical process in various ratios. The as-synthesized samples were analyzed through various characterization techniques. The X-ray diffraction (XRD) patterns confirmed the successful synthesis of tetragonal rutile SnO₂ and orthorhombic structure of SnSe. The average crystallite size varied between 25 and 35 nm. UV–visible spectroscopy (UV–vis) confirmed that the bandgap of SnO₂ and SnSe was 3.63 eV and 1.21 eV, respectively, whereas the bandgap of composites ranged from 3.47 to 3.03 eV. The FTIR spectrum exhibited absorption peaks at 745 cm⁻¹, 1113 cm⁻¹, and 1381 cm⁻¹ due to the Sn–O–Sn bond and Sn–OH bond vibrations. Whereas the absorption observed at 665 cm⁻¹ is associated with Se–O bond vibration. Raman spectroscopy revealed the bands at 629 cm⁻¹ and 767 cm⁻¹ for the rutile structure of SnO₂ and bands at 75 cm⁻¹, and 152 cm⁻¹ are characteristic of SnSe. Scanning electron microscopy (SEM) illustrated the formation of irregular-shaped agglomerated nanoparticles of the prepared materials. Photodegradation of methylene blue (MB) revealed that the composite containing 78% SnO₂ and 32% SnSe (denoted as SS-4) was highly an highly effective catalyst and degraded 97.1% of MB in 120 min. The reaction kinetics of the prepared photocatalysts satisfied the Langmuir–Hinshelwood model.