Synthetic dyes in wastewater pose persistent environmental risks due to their toxicity and resistance to conventional treatment, motivating the development of high-performance filtration membranes. In this work, a niobium pentoxide-modified polyacrylonitrile/polyvinyl pyrrolidone (PAN/PVP) nanofiber membrane (t-PAN/PVP/Nb2O5) was fabricated by electrospinning followed by a water-based post-treatment. Morphological and structural characterization (scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM/EDS), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD)) confirmed the formation of uniform nanofibers, physical incorporation of Nb2O5, and preservation of the amorphous PAN/PVP matrix. Filtration tests using a 5 ppm methylene blue (MB) solution showed that the t-PAN/PVP/Nb2O5 membrane achieved an MB rejection of 87 ± 5% with a dye flux of (26 ± 7) × 103 Lm–2 h–1 bar–1, representing approximately 235% higher rejection (about 3.3-fold improvement) compared with a commercial nylon membrane (26 ± 11% rejection; (11 ± 1) × 103 Lm–2 h–1 bar–1 flux). Batch adsorption experiments and kinetic modeling further revealed that MB uptake is best described by the pseudo-second-order (PSO) model, indicating specific interactions consistent with Nb2O5-assisted cation-exchange–type adsorption rather than simple physisorption. The membrane also displayed preferential removal of the cationic dye MB over the anionic dye Congo red, indicating a combination of charge-driven interactions and size exclusion. Overall, the results demonstrate that Nb2O5-functionalized PAN/PVP nanofibers obtained via a simple post-treatment route offer a promising platform for efficient dye removal in advanced wastewater treatment. © The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2025.