Bimetallic zeolitic imidazolate framework (Ni/Co‐ZIF) on coffee husk hydrochar to activate peroxymonosulfate for organic pollutant degradation

Abstract In this study, the Ni/Co‐ZIF@HC catalyst was prepared by a green solvothermal method under ambient conditions by modifying hydrochar from coffee husks with the bimetallic zeolitic imidazolate framework of Ni/Co in water to activate peroxymonosulfate (PMS) for the decomposition of para‐nitrophenol (PNP). The material properties were studied by scanning electron microscopy, X‐ray diffraction, Fourier transform infrared spectroscopy, energy‐dispersive X‐ray spectroscopy, and Brunauer–Emmett–Teller analyses. The synergistic effect between single materials in Ni/Co‐ZIF@HC demonstrated high efficiency of PMS activation and extremely fast PNP removal (99.4% within 15 min). The PNP degradation rate constant of the Ni/Co‐ZIF@HC/PMS system was 58.03, 4.48, and 2.44 times higher than that of the PMS, HC/PMS, and Ni/Co‐ZIF/PMS systems, respectively. The optimal conditions were determined to be pH 7, Ni/Co‐ZIF@HC dosage of 60 mg/L, PMS concentration of 0.814 mM, and temperature of 30 °C. In addition, 2,4,6‐trinitrophenol (TNP), 2,4,6‐trinitroresorcinol, ciprofloxacin, metronidazole, and methylene blue were also tested with a removal efficiency of 91–98% in this oxidation system. Both radical and non‐radical pathways were involved in the degradation of PNP. Besides, the Ni/Co‐ZIF@HC composite demonstrated good reusability, maintaining a degradation efficiency of ≈78% after three cycles. Moreover, the degradation pathway of PNP in the Ni/Co‐ZIF@HC/PMS system was proposed based on the mass spectrometry results. This study proposes a method to utilize potential resources from agricultural waste to produce effective catalysts for water treatment.