<p>The development of efficient and stable photocatalysts for nitrogen photofixation is necessary and remains challenging. Herein, sulfur doped carbon nitride was composited with cerium oxide (SCN/CeO), which was treated by oxygen vacancies (OVs) engineering to remain Ce³⁺/Ce⁴⁺ redox pairs for the improvement of photocatalytic activity. Further, SCN/CeO was loaded at wheat straw cellulose hydrogel (WSCH) to form SCN/CeO@WSCH composited photocatalysts for the enhancement of dispersity and stability. The optimized SCN/CeO-3 catalyst, treated with hydrazine hydrate, exhibited an optimal Ce³⁺/Ce⁴⁺ ratio and abundant OVs, synergistically boosting visible-light-driven conversion of nitrogen-to-ammonia. Without sacrificial agents, SCN/CeO-3 achieved a nitrogen fixation efficiency of 39.19 μmol g⁻¹ h⁻¹ within 120 min. WSCH was used as catalyst support to improve catalyst dispersion and active site accessibility, which elevated the efficiency to 75.34 μmol g⁻¹ h⁻¹ under identical conditions, and maintained an excellent stability after five cycles. In this study, S-doping effectively expanded the visible light response range. Oxygen vacancies in cerium oxide facilitated N₂ adsorption/activation, while the Ce³⁺/Ce⁴⁺ pair enhanced charge separation and electron transfer. In addition, wheat straw cellulose hydrogel (WSCH) derived from agricultural waste straw not only stabilized the catalyst, but also contributed to environmental sustainability. Therefore, the designed research system integrated redox-active metal centers, vacancy engineering, element doping and eco-friendly supports, which provides new insights into designing novel photocatalytic systems for renewable energy applications.</p>