Abstract:

Objective Toxic and persistent organic pollutants (e.g., methylene blue, MB) in water pose a severe threat to ecological safety and human health, and the efficient degradation of such pollutants has long been a tough challenge. To address this issue as well as the drawbacks of poor stability and low recyclability associated with single-phase catalysts, this study aims to fabricate polystyrene(PS)/ZIF-67 nanofiber composites. The catalytic performance of these composites in degrading MB through a peroxymonosulfate-based advanced oxidation system will be systematically evaluated, thereby providing a novel and practical material strategy for organic water pollution control.

Method Using PS powder and ZIF-67 precursor as raw materials, PS/ZIF-67 composite nanofibers were prepared via two steps, i.e., electrospinning of PS fiber (18 kV, 15 cm collector distance, 1.0 mL/h injection rate) and PS fiber post-treatment for in-situ ZIF-67 growth. The fabricated materials were comprehensively characterized by SEM, FT-IR, TG, XRD, and N₂ adsorption-desorption (morphology, structure, thermal stability), and their dye-degradation performance (e.g., methylene blue) in PMS system was tested under varied conditions (catalyst/PMS dosage, pH, temperature).

Results ZIF-67 cubic crystals were uniformly loaded onto the surface of polystyrene fibers via in-situ growth, successfully forming PS/ZIF-67 composite materials with a well-defined core-shell structure. Comprehensive characterizations, including N₂ adsorption-desorption, XRD, and TG, revealed that the composite possessed a specific surface area of 7.53 m²/g and an average pore diameter of 28.07 nm, presenting a typical mesoporous structure. This porous feature facilitates the diffusion of reactants (e.g., methylene blue, MB) and the exposure of active sites, laying a structural foundation for efficient catalysis. Compared with pure PS fibers, PS/ZIF-67 fibers exhibited significantly enhanced thermal stability with a weight loss rate reduced by about 30% at 400 - 600 ℃, as determined by TG analysis, which prevents structural collapse during catalytic reactions and ensures long-term operational reliability. Under the optimized reaction conditions (0.03 g catalyst dosage, 0.05 g peroxymonosulfate (PMS) dosage, neutral pH=7, and ambient temperature of 25 ℃), the degradation rate constant of 50 mg/L MB reached 0.189 min^-1, and the degradation efficiency exceeded 89% within 30 min, outperforming many reported MOF-based composites in similar systems. The composite also exhibited broad potential applicability. It could effectively degrade other typical pollutants, such as methyl orange (a cationic dye, about 76% degradation in 30 min) and tetracycline (an antibiotic, about 68% degradation in 30 min), demonstrating its potential for multi-pollutant water treatment. The composite maintained good cyclic stability, where after 5 consecutive catalytic cycles (each involving centrifugation, washing with deionized water, and drying at 60 ℃), its MB degradation efficiency still remained over 80%, indicating minimal loss of active sites. Kinetic analysis further confirmed that the MB degradation process followed pseudo-first-order kinetics (R² > 0.99), suggesting a consistent reaction pathway dominated by either radical oxidation or electron transfer. Additional parameter-dependent studies showed that lower initial MB concentrations (≤50 mg/L), appropriate PMS dosage (0.05 g, to avoid excessive radical quenching), and neutral pH (pH=7, optimizing catalyst surface charge) were more conducive to improving the catalytic efficiency of PS/ZIF-67.

Conclusion In this study, PS/ZIF-67 nanofiber composites, integrating PS's fibrous framework and ZIF-67's cubic phase, exhibit typical mesoporous structure (specific surface area= 7.53 m²/g, pore diameter = 28.07 nm), enhanced thermal stability, excellent MB degradation (0.189 min^-1, >89% in 30 min under optimal conditions), broad applicability to other pollutants, and good cyclic stability (>80% after 5 cycles) due to improved structural stability and retained active sites. This study supports MOFs-based composites for water decontamination, though coexisting ions in real water limit performance. Future research should explore interference mechanisms and optimize the material to boost anti-interference ability, promoting practical application.

Key words: metal-organic framework, polystyrene, ZIF-67, catalysis, methylene blue, peroxymonosulfate, advanced oxidation processes, wasterwater treatment