The increasing demand for sustainable and environmentally friendly nanomaterials has driven the development of green synthesis approaches in nanotechnology. In this study, zinc oxide (ZnO), silver (Ag), and titanium dioxide (TiO2) nanoparticles were synthesized using a green synthesis approach with extracts of Viburnum opulus L., a plant known for its high phenolic content. The synthesized nanoparticles were subsequently incorporated into nanofibrous structures produced from recycled polystyrene (PS) via the electrospinning technique, resulting in environmentally friendly and multifunctional nanocomposite materials. Following fabrication, structural and morphological characterizations were conducted; X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) analyses confirmed the successful integration and homogeneous distribution of metal oxide nanoparticles within the PS nanofiber matrix. The photocatalytic performance of the nanocomposites was evaluated, and both ZnO/PS and Ag/PS nanofibers exhibited high degradation efficiency. In vitro anticancer assays conducted on HT-29, Caco-2, MDA-MB-231, and DU-145 cancer cell lines demonstrated significant cytotoxicity for the ZnO/PS nanofiber, with an IC50 value of 6.13 µg/mL against HT-29 cells. Furthermore, ZnO/PS nanofiber showed minimal toxicity toward healthy HEK-293 and HUVEC cells, with 87.38% cell viability, indicating high selectivity. In antibacterial activity tests carried out against K. pneumoniae, P. aeruginosa, and S. aureus, Ag nanoparticles produced the largest inhibition zone. In addition to disk diffusion tests, minimum inhibitory concentration (MIC) tests were also performed using the same bacteria and the same materials. Among the tested materials, ZnO nanoparticles exhibited the strongest antibacterial effect, with MIC values of 1.56 µg/mL against P. aeruginosa and 3.12 µg/mL against both E. coli and S. aureus. All other inhibition zone values were close to this result, indicating that the synthesized nanoparticles are suitable candidates for antibacterial applications. When all these results are evaluated, it is observed that, along with all the materials, ZnO/PS nanofibers in particular possess significant potential.