Exploring the Potential of Novel ZnO-SnSe Composites for Efficient Photodegradation of Methylene Blue under Visible Light

With increasingly strict water regulations, the removal of toxic organic pollutants from industrial wastewaters has become a critical challenge. Herein, a series of novel ZnO-SnSe composite-based photocatalysts were effectively synthesized by an inexpensive, facile chemical process. The prepared composites were analyzed thoroughly by utilizing different techniques, and their physiochemical characteristics were compared with pure ZnO rods and SnSe nanoparticles. X-ray diffraction (XRD) data showed the existence of a hexagonal wurtzite phase of ZnO and an orthorhombic structure of SnSe. The average crystallite sizes of ZnO and SnSe were determined to be 37 and 16 nm, while for the composite samples, the size varied between 20 and 26 nm, respectively. The purity of the samples was confirmed through an elemental compositional study using energy-dispersive X-ray analysis (EDX). Field emission scanning electron micrographs (FESEM) showed that ZnO appeared to be rod-shaped with random orientation. Similarly, SnSe was composed of agglomerated particles. The microstructure of ZnO-SnSe composites showed the coexistence of both nanoparticles and rod-like structures. The PL spectra revealed defects associated with oxygen vacancies, which were dominant factors for the enhanced photocatalytic activities. The absorption spectra and band gap energies of ZnO-SnSe composites revealed a red shift compared to pure ZnO rods. The band gap values were reduced from 3.2 eV (pure ZnO) to 1.9 eV by increasing the concentration of SnSe in the composites. The prepared samples were tested for the visible light-mediated decomposition of methylene blue (MB) with and without H2O2. The ZnO-SnSe composites showed a significantly enhanced photocatalytic degradation of methylene blue compared to the pure ZnO and SnSe, achieving a degradation efficiency of over 98% in 300 min (without H2O2) and 97% in 160 min of exposure time (with H2O2). Furthermore, the degradation rate, determined via the Langmuir–Hinshelwood model, increased from 3.38 × 10–3 to 1.12 × 10–2 min–1 for ZnO-SnSe composites. The scavenger studies elucidated that •OH radicals and holes were primarily responsible for the enhanced photodegradation of MB.