This research offers a bio-template synthesis for NiZrO3 and Ag-NiZrO3. On the other hand, it introduces simple and rapid preparation of carbon-based nano-photocatalyst including g-C3N4 and g-C3N5. The main objective was to obtain photocatalysts with improved efficiency while maintaining a sustainable synthesis strategy for overall water splitting. The obtained materials were examined using PXRD, DRS, FT-IR, FESEM, and BET techniques. These analyses verified the successful formation of crystalline phases and also revealed changes in the surface properties of the prepared samples. The photocatalytic performance of the prepared samples was evaluated under simulated solar light. Among them, the Ag–NiZrO₃/g-C₃N₅ nanocomposite exhibited the highest oxygen evolution activity, producing 6.9 μmol of O₂. Other nanocomposites showed lower oxygen evolution values, with oxygen production ranging from 5.3 to 5.9 μmol. This behavior may be attributed to the narrower band gap of the composite (1.8 eV) together with its larger specific surface area. These features can increase the number of available active sites and help to promote the separation of photogenerated charge carriers. The presence of Ag nanoparticles in the NiZrO₃/g-C₃N₅ composite is likely associated with the observed enhancement in photocatalytic activity. This effect may arise from changes in the electronic structure including a reduction in band gap energy and more efficient charge transport across the heterostructure. Based on these results, Ag–NiZrO₃/g-C₃N₅ appears to be a suitable candidate for solar-driven water splitting, particularly when environmentally friendly photocatalytic systems are desired.