Stabilized fabrication of anatase-TiO2/FeS2 (pyrite) semiconductor composite nanocrystals for enhanced solar light-mediated photocatalytic degradation of methylene blue

Abstract

A novel visible light active TiO₂/FeS₂ semiconductor photocatalyst was synthesized by a simple wet chemical process. X-ray diffraction (XRD) was used to analyze the anatase TiO₂ and pyrite structures in FeS₂/TiO₂ nanocrystals. Scanning electron microscopy (SEM) confirmed the spherical morphology of composite nanocrystals. X-ray photoelectron spectroscopy (XPS) identified the Fe²⁺, S¹⁻, Ti⁴⁺, and O²⁻ oxidation states of relevant species. Energy dispersive X-ray (EDX) analysis was performed for compositional analysis. The measured band gap of the TiO₂/FeS₂ nanocomposite system was 2.67 eV, which is smaller than un-doped TiO₂ (3.10 eV) and larger than FeS₂ (1.94 eV). The photocatalytic activity of TiO₂/FeS₂ was significantly higher than pure FeS₂ for degrading methylene blue (MB) under solar light irradiation due to the increase in visible light absorption, reduction in band gap energy, and better election–hole pair separation. The photocatalytic degradation of MB was investigated under the influence of solution pH, dye concentrations, and varied catalyst dosage. The optimum degradation (100%) of MB was observed in 180 min and the photocatalysis of MB reduced as the dye concentrations in the solution increased from 15 to 75 mg L⁻¹. These results prove that the TiO₂/FeS₂ nanocomposite has the stability, recycling, and adaptability for its practical application as a visible light photocatalyst for wastewater treatment. TiO₂/FeS₂ showed increased degradation of the organic pollutant; which is confirmed by the increased rate of chemical reaction following pseudo first-order reaction kinetics with the highest rate constant value of 0.0408 m⁻¹ having highest R² value of 0.9981.