Visible light photocatalytic degradation of MB using UiO-66/g-C₃N₄ heterojunction nanocatalyst

A unique hybrid of Zr-based metal-organic framework (UiO-66) with graphitic carbon nitride (g-C₃N₄) nanosheets was synthesized by a facile annealing method. Photocatalytic effect was measured by the photodegradation of methylene blue (MB) under visible light irradiation. The morphology, structure, and porous properties of the as-synthesized composites were characterized by using transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), the thermogravimetric and differential scanning calorimetry analysis (TG-DSC), diffuse reflectance UV-vis spectroscopy (UV-vis DRS), photoluminescence (PL), and N₂ sorption-desorption isotherms (BET). The results showed that about 100% of MB (200 mL of 10 mg L^-1) photodegradation was achieved by the UiO-66/g-C₃N₄ hybrids (UC 10:10) in 240 min under visible light. The enhanced photocatalytic activity could be attributed to the heterojunction between UiO-66 and g-C₃N₄ therefore the photoelectron transfers efficiently from the conduction band (CB) of g-C₃N₄ to the CB of UiO-66 through the inner electric field generated by the heterojunction resulting the decreasing of recombination of electron/hole and the porous structures which enhance adsorption of the dye molecules on the catalyst surface thereby facilitates the electron/hole transfer within the framework. The trapping experiment and electron spin resonance (ESR) results showed that superoxide radicals (•O₂^-) was the main oxidative species in the photodegradation of MB and the enhanced photocatalytic mechanism of UiO-66/g-C₃N₄ heterojunction hybrids was also proposed.