Pioneering the design of S-scheme SnS2/g-C3N4 nanocomposites via sonochemical and physical mixing methods for solar degradation of cationic rhodamine B dye

Abstract

Since the advent of photocatalysis, various research studies have been devoted to exploring novel high-performance photocatalysts for converting solar energy into chemical energy. However, the employment of natural solar radiation in the degradation of organic pollutants has not been attained until now. This novel research work recorded the employment of natural solar illumination in degrading rhodamine B [RhB] dye on the surface of S-scheme SnS₂/g-C₃N₄ heterojunctions. SnS₂/g-C₃N₄ heterojunctions containing different rational compositions of g-C₃N₄ and SnS₂ nanoparticles were synthesized via sonochemical and physical mixing approaches. Sonochemistry is a novel approach with multiple applications and is of significant importance since ultrasonic waves form acoustic cavitation in solutions, enhancing chemical activity with remarkable economic value. The textural, optical and nanostructural properties of the heterojunctions were investigated through diffuse reflectance spectroscopy [DRS], high-resolution transmission electron microscopy [HRTEM], photoluminescence [PL], N₂-adsorption–desorption isotherms, scanning electron microscopy [SEM], energy dispersive X-ray spectroscopy [EDX], X-ray diffraction [XRD], electrochemical impedance spectroscopy [EIS] and X-ray photoelectron spectroscopy [XPS]. The diffraction results from XRD, HRTEM and SAED analyses revealed remarkable distortion in the crystalline properties of g-C₃N₄ upon the introduction of SnS₂ nanoparticles, implying a strong chemical interaction between SnS₂ nanoparticles and g-C₃N₄ sheets, which manifested the construction of an effective heterojunction. Homogeneous deposition of SnS₂ nanoparticles on g-C₃N₄ sheets was achieved through a sonochemical route. However, SnS₂ nanoparticle agglomeration was recorded on g-C₃N₄ sheets synthesized by means of a physical mixing process. Photocatalytic experimental results revealed the degradation of 34% of RhB dye on g-C₃N₄ sheets due to the limited absorption of natural solar radiation and the fast and uncontrolled electrostatic forces between electron–hole pairs. By incorporating 5, 10, 15 and 20 wt% SnS₂ nanoparticles in the ultrasonic bath on g-C₃N₄ sheets, the amount of RhB dye discharge was raised to 51, 78, 98 and 69%, respectively, during two hours of sunlight illumination. Alternatively, only 55% of RhB dye was decomposed on the surface of CNSnS15 synthesized through the physical mixing route. Hydroxyl radicals played a crucial role in the degradation of RhB dye, as proved by the PL of terephthalic acid and scavenger trapping experiments. The charge transport mechanism followed the S-scheme mechanism, as elucidated from scavenger trapping experiments. The novel as-synthesized sonicated SnS₂/g-C₃N₄ nanocomposite is considered a promising photocatalyst in degrading organic pollutants under low-cost natural solar radiation.