Use of curcumin as a sensitizer with ZnO nanoparticles for the visible light photocatalytic degradation of methylene blue

This work aims to examine the application of ZnO/Curcumin nanocomposite materials, in which curcumin (natural dye) is used as a photosensitizer in the photocatalytic degradation of methylene blue (MB) under visible light irradiation. The ZnO/x% curcumin nanocomposite materials (with x = 3, 5, 7, 10 and 20) are prepared by the wet impregnation method. These nanocomposite materials are characterized using various techniques; including Fourier transform infrared spectroscopy, X-ray diffraction, ultraviolet–visible spectroscopy and scanning electron microscopy. Optimal MB degradation of ~ 99% was obtained with a concentration of 0.5 g L⁻¹ of 5% curcumin/ZnO nanocomposite catalyst material, at natural pH and initial MB concentration of 10 mg L⁻¹ for 90 min exposure to visible light irradiation. The kinetic indicates that the Langmuir–Hinshelwood (L–H) model is well adapted to the experimental data. Pseudo-first order kinetics were obtained with a rate constant (k) and half-life time ( \({t}_{1/2}\) $t_{1/2}$ ) of 0.0423 min⁻¹ and 16 min. The significant improvement in the photocatalytic properties of ZnO under visible light irradiation induced by the addition of curcumin as a photosensitizer could be due to the increase in the concentration of reactive radical species in the solution, such as superoxide ( \({\text{O}}_{2}^{ \cdot - }\) ${\text{O}}_2^{·-}$ ) and hydroxyles ( \({\text{OH}}^{ \cdot }\) ${\text{OH}}^{·}$ ).