Abstract:

Objective Aiming at problems in the field of photodegradation, such as low mass transfer efficiency of a single catalyst, easy recombination of photogenerated carriers, limited light absorption performance and reaction active site, and poor reusability, a self-assembly method was used to construct a g-C₃N₄/MXene/Ag₃PO₄ S-type heterojunction catalyst structure, attempting to dope catalyst into polyacrylonitrile (PAN) spinning solution. The g-C₃N₄/MXene/Ag₃PO₄/PAN composite nanofiber membranes were successfully prepared using electrospinning technology.
Method In order to further characterize the morphology and structure of the composite nanofiber membrane, we used scanning electron microscopy, transmission electron microscope, infrared spectroscopy, and X-ray diffraction to characterize the size and morphology of the nanofiber membrane and its photocatalytic degradation performance for specific dyes. We also investigated its photocatalytic degradation performance for dye wastewater such as Reactive Red 195 in order to further explore its practical application potential. SEM and TEM characterization analysis showed that when photocatalysts were added, the nanofibers changed from a uniform long straight fibrous structure to a curved network structure.
Results The morphology of the nanofibers in the PAN composite nanofiber membrane was better, and g-C₃N₄/MXene/Ag₃PO₄ could be loaded onto the PAN through electrospinning technology. The g-C₃N₄/MXene/Ag₃PO₄ could be uniformly distributed on the surface of the composite nanofiber membrane. The diameter before and after loading g-C₃N₄/MXene/Ag₃PO₄ on the fibers showed a uniform state, with a size of approximately 200-400 nm. To investigate the specific impact effects, a composite nanofiber membrane was used for photocatalytic degradation of 50 mL of Reactive Red 195 (0.05 mmol/L) solution. The experimental results showed that the degradation rate of g-C₃N₄/MXene/Ag₃PO₄ gradually increased with time, and the dye was almost completely degraded after 60 min. This fully demonstrated the very important role of g-C₃N₄/MXene/Ag₃PO₄ in the degradation of Reactive Red 195 dye. In addition, although the degradation rate of dyes by g-C₃N₄/MXene/Ag₃PO₄/PAN was slow in the early stage of the reaction, the dyes were almost completely degraded at 180 min, indicating that the composite nanofiber membrane showed the same degradation effect as g-C₃N₄/MXene/Ag₃PO₄ and still had good photocatalytic degradation performance for dyes. After 180 min, the photocatalytic activity of g-C₃N₄/MXene/Ag₃PO₄/PAN composite nanofiber membrane was still high, with a degradation rate of 91.23%, exhibiting good recyclability. The g-C₃N₄/MXene/Ag₃PO₄/PAN still had a high decolorization rate for Reactive Red 195 after 5 cycles of used. The degradation rates of Reactive Red 195 were 91.23%, 82.54%, 81.40%, 79.30%, and 77.11% after 5 cycles of reaction for 180 min, respectively, indicating that g-C₃N₄/MXene/Ag₃PO₄/PAN had good reusability and stability. Exploring the photocatalytic mechanism of g-C₃N₄/MXene/Ag₃PO₄ catalyst, it was found through radical quenching experiments that superoxide radicals ·$\mathrm{O}_{2}^{-}$ and hole h⁺ were the main active species in the oxidative degradation reaction of dyes. After adding tert-butanol, disodium ethylenediaminetetraacetic acid, and p-benzoquinone to the reaction system, the degradation rates of Reactive Red 195 were 86.15%, 42.31%, and 10.82% at 180 min, respectively. This indicated that in the g-C₃N₄/MXene/Ag₃PO₄/PAN system, the contributions of ·OH, h⁺ and ·$\mathrm{O}_{2}^{-}$ to the decolorization and degradation reactions of dyes were 5.05%, 48.89%, and 80.38%, respectively. The ·$\mathrm{O}_{2}^{-}$ and h⁺ were the main active species in the oxidative degradation reactions of dyes.
Conclusion It was proposed that the mechanism of photocatalytic oxidation degradation of dyes may be the formation of a reasonable S-type heterojunction in g-C₃N₄/MXene/Ag₃PO₄. The introduction of MXene with high conductivity as a solid-state electron mediator leads to faster electron transfer from Ag₃PO₄ to the surface of g-C₃N₄, resulting in higher catalytic performance of the catalyst. This S-type heterostructure provides stronger reduction/oxidation ability to generate more active free radicals and higher catalytic activity to degrade pollutants, thereby decomposing Reactive Red 195 into small molecules under the synergistic effect of ·$\mathrm{O}_{2}^{-}$ and h⁺.

Key words: photocatalytic degradation, g-C₃N₄, electrostatic spinning, recycling performance, nanofiber membrane, polyacrylonitrile