Chemical spray deposited SnO₂:MoO₃ composite thin films for visible light photocatalytic dye degradation application

In this work, tin oxide (SnO₂), molybdenum trioxide (MoO₃) and SnO₂: MoO₃ composite thin films were prepared using the chemical spray pyrolysis technique. X-ray diffraction (XRD) studies indicate the formation of a tetragonal phase for SnO₂, an orthorhombic phase for MoO₃ and a blend phase of SnO₂ and MoO₃ composites. The prepared SnO₂, MoO₃ and SnO₂: MoO₃ composite thin films possess a crystallite size ranging from 29.42 to 27.04 nm. Fourier transform infrared spectroscopy (FTIR) studies reveal the presence of basic vibrational modes of Sn–O and Mo–O. X-ray photoelectron spectroscopy (XPS) analysis declares that tin and molybdenum ions exist in the Sn⁴⁺ and Mo⁶⁺ electronic states, respectively. Field emission-scanning electron microscopy (FESEM) investigation demonstrates enhanced SnO₂, MoO₃, and the SnO₂:MoO₃ composite morphology. Energy dispersive X-ray spectroscopy (EDX) studies were employed to perform elemental composition analysis of Sn, Mo and O in the composite thin films. The average transmittance varies between 35 and 80% in the wavelength range of 300—1100 nm. The prepared films revealed a red shift of the absorption edge and a remarkable improvement in visible light absorption at a wavelength region of 400 to 500 nm. For visible light photocatalytic performance, the band edge potential calculation for SnO₂ (3.35 eV), MoO₃ (2.21 eV) and SnO₂: MoO₃ (3.25 eV) composite thin films was performed, which shows the presence of a defect energy level. A photoluminescence (PL) study reveals the electron–hole pair recombination and oxygen vacancy defects. The SnO₂: MoO₃ composite thin films exhibit a better photocatalytic efficiency of 92% for methylene blue dye (MB) using visible light illumination. The obtained results indicate that composite photocatalyst is a promising material (i.e., band edge potential, reduced electron pair recombination, vacancy defects) to remove organic contaminants from wastewater in the environment.