Abstract:

Objective With the progression of the global textile industry, a substantial quantity of wastewater containing toxic and non-biodegradable synthetic dyes may impose considerable threats to public health and the environment. Peroxymonosulfate (PMS)-based advanced oxidation processes have garnered significant attention in the remediation of organic dye wastewater because of their high degradation efficiency and non-selective oxidation. As promising catalysts for PMS activation, metal-organic frameworks (MOFs) often face limitations because of particle agglomeration and challenges in recovery during liquid-phase reactions, attributed to their powdery nature. Therefore, constructing macroscopic structures from powdered MOFs is highly significant for expanding their practical applications.

Method FeCo-benzenedicarboxylate/rice husk (FeCo-BDC/RH) composite material was fabricated via solvothermal in-situ growth strategy. The morphology and structure of FeCo-BDC/RH were analyzed by scanning electron microscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). The decolorization performance of the composite material for activating PMS on Rhodamine B (RhB) was evaluated, and the key active species in the decolorization process were revealed through quenching experiments and electron paramagnetic resonance (EPR) spectroscopy.

Results The scanning electron microscopy images confirmed that the FeCo-BDC, which was grown in-situ on the surface of RH, exhibited a highly dispersed state. This is significantly different from the spindle-shaped morphology of pure FeCo-BDC, thereby highlighting the importance of the carrier. Moreover, the composite material FeCo-BDC/RH was of centimeter-scale size and easily recovered from the liquid phase after the reaction. The analytical results of FT-IR, XPS, and XRD further confirmed the successful preparation of the FeCo-BDC/RH composite material. FeCo-BDC/RH was capable of efficiently activating PMS and facilitating rapid decolorization of RhB. The decolorization rate of RhB by the FeCo-BDC/RH+PMS system reached as high as 99% within 5 min. The FeCo-BDC/RH+PMS system demonstrated stable decolorization effects under various solution pH volues and natural water quality conditions and possesses universality for the decolorization of multiple dyes. In a fixed-bed reactor with a continuous reaction for 300 min, the decolorization rate of RhB by the FeCo-BDC/RH composite material remained nearly 100%, indicating the potential for large-scale continuous treatment of organic dye wastewater. The results of quenching experiments and EPR technology indicated that the degradation of RhB included both radical (S${O}_{4}^{-}$O4-·) and non-radical (¹O₂) pathways, with ¹O₂ being the dominant one. In addition, the results of the EPR spectra confirmed the existence of these key reactive oxygen species. The variable valence state of iron and cobalt metal sites plays an indispensable role in the process of activating PMS to generate these key species. The interaction between the bimetals accelerates the redox process of Fe(Ⅲ)/Fe(Ⅱ) and Co(Ⅲ)/Co(Ⅱ) through electron transfer between metals, thereby promoting the generation of reactive oxygen species.

Conclusion The FeCo-BDC/RH composite catalyst was successfully prepared through the in-situ growth of FeCo-BDC on waste RH. This composite material demonstrated outstanding performance in activating PMS. The decolorization rate of the RhB dye reached 99% within just 5 min. Additionally, the FeCo-BDC/RH composite catalyst showed good recoverability and remarkable anti-interference ability in the face of different pH values and natural water matrices. The composite material demonstrated versatility in degrading a range of organic dyes and achieved continuous and efficient dye decolorization in a fixed-bed reactor. This study offers a low-cost waste biomass carrier for the construction of three-dimensional macroscopic structures of MOFs, thereby helping to lower the economic cost of wastewater treatment. The fabricated composite material significantly expands the potential for large-scale continuous treatment of organic dye wastewater.

Key words: metal-organic framework, waste biomass, rice husk, advanced oxidation, dye decolorization, dyeing wastewater, wastewater treatment