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⁺, S^1-, Ti⁴⁺, and O^2- 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 <i>R</i> ² value of 0.9981.