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In recent years, organic pollutants such as antibiotics and dyes in wastewater have posed a serious threat to the ecological environment. Take Norfloxacin (NFX) as an example. It is used to treat various bacterial infections. However, due to its low absorption rate in humans and animals, NFX remains in water bodies, which may contribute to the emergence of drug-resistant microbial pathogens. To address this issue, advanced oxidation technologies based on •SO₄⁻ have received much attention. This technology can efficiently oxidize organic pollutants into harmless products. The peroxy bond in peroxymonosulfate (PMS) can be activated by heat, ultrasound, and light to generate highly oxidizing •OH and •SO₄⁻. Among them, photoactivation has significant advantages. It can enhance the activation efficiency of PMS and inhibit the recombination of photogenerated carriers, thus synergistically promoting the removal of pollutants.
Cellulose - based electrospun nonwoven membranes, due to their renewability, rich functional groups, and simple operation and preparation processes, perform well in loading and fixing metal - organic framework (MOF) nanoparticles and have great potential in PMS - assisted photocatalysis. In this study, an electrospinning machine was employed to prepare a novel cellulose@g - C₃N₄@ZIF - 67 nonwoven membrane via a one - step electrospinning process. This electrospinning machine - assisted process not only enhanced the light absorption and photocatalytic degradation performance of ZIF - 67 but also avoided the aggregation and detachment of ZIF - 67 during use through an in - situ growth strategy. The leaching concentration of cobalt after use was only 0.093 mg/L. The membrane exhibited high and non - selective PMS photocatalytic degradation capabilities for Norfloxacin, Tetracycline, and Congo Red. •SO₄⁻ was found to be the main reactive species in the photocatalytic degradation process. Moreover, the membrane had excellent stability and recyclability, showing great potential in future wastewater treatment.
The cellulose@g - C₃N₄@ZIF - 67 composite membrane was fabricated using an electrospinning device. In this one - step electrospinning method, a cellulose solution containing g - C₃N₄ and Co(NO₃)₂·6H₂O was used as the spinning dope, and an aqueous solution of 2 - methylimidazole was used as the coagulation bath to achieve the in - situ growth of ZIF - 67 on the fiber surface. As can be seen from Figure 1, the composite membrane has a three - dimensional microstructure with numerous pores inside. This structure has obvious advantages, facilitating full contact between active sites and wastewater, enhancing the adsorption capacity, and promoting light propagation within the membrane, providing a good foundation for subsequent photocatalytic reactions.
The heterojunction formed between g - C₃N₄ and ZIF - 67 is a key factor in enhancing photocatalytic performance. According to the UV - vis DRS spectra in Figure 2, the absorption edge of the composite membrane is red - shifted and the range is broadened, significantly improving the light absorption ability. Its band gap becomes narrower, and the separation efficiency of photogenerated carriers is increased. In the PL spectrum, the composite membrane has the lowest fluorescence intensity, indicating that the heterojunction effectively inhibits the recombination of photogenerated electrons and holes, allowing more carriers to participate in the photocatalytic reaction and thus enhancing the degradation performance.
The composite membrane shows high photocatalytic degradation capabilities for organic pollutants such as Norfloxacin, Tetracycline, and Congo Red. Taking the Norfloxacin degradation experiment as an example, Figure 3 demonstrates its excellent performance. In the presence of PMS and light, the degradation efficiency can reach as high as 99.7% within 60 minutes, much higher than 53.6% of cellulose@ZIF - 67. Moreover, the kinetic rate constant is 1.6 times that of cellulose@ZIF - 67. The degradation efficiency for Tetracycline and Congo Red exceeds 80% within 30 minutes, reflecting the high - efficiency and non - selective degradation characteristics of the composite membrane for different organic pollutants.
The main active species in the photocatalytic degradation process were determined through radical trapping experiments and EPR tests. The EPR spectra in Figure 3 show that active species such as •SO₄⁻, •O₂⁻, and •OH were generated in the system, and •SO₄⁻ is the key species dominating the photocatalytic degradation process. The degradation mechanism is that NFX and PMS are adsorbed onto the surface due to the strong hydrophilicity of the composite membrane. ZIF - 67 and g - C₃N₄ act as active sites to generate photogenerated electrons and holes, and then generate •O₂⁻, etc. These active species react with PMS to produce •SO₄⁻ and •OH, which oxidize and decompose NFX into harmless products.
The cellulose@g - C₃N₄@ZIF - 67 composite membrane has good stability and recycling performance. After 7 cycles of use, the degradation efficiency for Norfloxacin can still remain at 89.8%. The FTIR spectra and XRD patterns show that the structure of the composite membrane remains basically stable before and after use. Although some characteristic peaks of ZIF - 67 change, the overall stability is good, providing strong support for its long - term application in actual wastewater treatment.
In this study, a cellulose@g - C₃N₄@ZIF - 67 electrospun nonwoven membrane was constructed by a one - step method, and its photocatalytic performance in the presence of PMS was investigated. The heterojunction formed between g - C₃N₄ and ZIF - 67 broadens the light absorption wavelength range of ZIF - 67, generating more photogenerated carriers and thus improving the photocatalytic degradation performance. At the same time, the electrospun membrane with a three - dimensional microstructure and numerous hierarchical pores can enrich PMS to the active sites more quickly, accelerating the redox reaction and promoting the degradation of Norfloxacin through •SO₄⁻. In addition, the large number of - OH groups on cellulose are conducive to fixing g - C₃N₄ through hydrogen bonds and promoting the in - situ growth of ZIF - 67, reducing the leakage risk of nanoparticles. The leaching concentration of cobalt after use is only 0.093 mg/L.
The prepared cellulose@g - C₃N₄@ZIF - 67 nonwoven membrane exhibits high and non - selective PMS photocatalytic degradation efficiency for Norfloxacin, Tetracycline, and Congo Red. It was found that •SO₄⁻ is the main reactive species in the photocatalytic degradation process. In addition, the membrane also shows excellent stability and recycling performance, indicating high application potential in future wastewater treatment.
Electrospinning Nanofibers Article Source: https://doi.org/10.1016/j.carbpol.2025.123508
