Water pollution from industrial and household waste presents significant environmental challenges, particularly owing to the widespread use and toxicity of organic dyes such as rhodamine B (RhB). This study investigates the photocatalytic degradation of RhB using composite films composed of zinc oxide (ZnO) and silver nanowires (AgNWs) under ultraviolet (UV) irradiation. ZnO is well known for its strong photocatalytic activity because of its high charge-carrier mobility and ability to generate reactive oxygen species (ROS). However, its relatively large bandgap (approx. 3.3 eV) limits its light absorption primarily to the UV range, restricting its photocatalytic efficiency under visible light. The incorporation of AgNWs is expected to enhance charge separation, increase electron mobility and introduce localized surface plasmon resonance effects, which contribute to improved light absorption and photocatalytic performance. The ZnO/AgNW composite films were synthesized using a sol–gel method and characterized through scanning electron microscopy and energy-dispersive X-ray spectroscopy to analyse the morphology and elemental composition, X-ray diffraction to confirm the crystallinity structure, and UV–visible spectroscopy to determine optical properties and bandgap energy. The bandgap reduction observed in ZnO/AgNW composites, as confirmed by Tauc plot analysis, is attributed to structural modifications, oxygen vacancy formation and plasmonic interactions that enhance charge transfer and light absorption. This enhanced optical response directly contributed to the superior photocatalytic efficiency of the composite. The reduction in bandgap directly influenced the photocatalytic performance of the ZnO/AgNW composites. A lower bandgap extends light absorption into the visible range, allowing the material to use a broader spectrum of incident light. Furthermore, the enhanced charge-carrier separation and increased ROS generation contributed to superior photocatalytic efficiency. As a result, the ZnO/AgNW composite films achieved a 90% degradation efficiency of RhB within 40 min of UV exposure, demonstrating a significant improvement over conventional ZnO-based photocatalysts. These findings highlight the potential of ZnO/AgNW nanocomposites as efficient, reusable and scalable solutions for water purification and environmental remediation applications.