Enhanced degradation of dyes by Cu-Co-Ni nanoparticles loaded on amino-modified octahedral metal–organic framework

Materials of Institut Lavoisier (MILs) are metal–organic frameworks (MOFs) that exhibit excellent porosity and high specific surface areas. In this study, trimetallic Cu-Co-Ni nanoparticles (NPs) were anchored to amino-modified MOF MIL-101(Fe) through a direct solution impregnation method to enhance the visible light photo-Fenton reaction. The structure and properties of the NH2-MIL-101(Fe)@CuCoNi composite catalyst were characterised using X-ray diffraction analysis, Fourier transform infrared spectroscopy, transmission electron microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller measurements, diffuse reflectance spectroscopy, zeta potential measurements, and inductively coupled plasma spectroscopy. The results showed that the Cu-Co-Ni NPs were evenly distributed on the surface and within the cavities of the composite. Further, compared with pure MIL-101(Fe) and NH2-MIL-101(Fe), NH2-MIL-101(Fe)@CuCoNi exhibited a higher light-utilisation rate and better catalytic performance. The 2-h removal rates of the anionic dye methyl blue (MB) and cationic dye crystal violet (CV) under continuous visible light irradiation in the presence of NH2-MIL-101(Fe)@CuCoNi and a trace amount of H2O2 were 99% and 93%, respectively. An analysis of the degradation kinetics indicated that the photocatalytic process followed a pseudo-first-order kinetics model. After five cycles, the composite continued to exhibit a degradation efficiency of approximately 80%; this confirmed its stability. In addition, the results of trapping experiments and electron paramagnetic resonance spectroscopy indicated that the reactive species involved in the degradation of the MB and CV dyes at different pH levels were not the same. While •OH active free radicals were responsible for the removal of MB, •O2− free radicals were responsible for the degradation of CV.