Calcination‐Free Hydrothermal Synthesis of Nitrogen‐Doped TiO ₂ : Integrating Photocatalytic Performance and Life Cycle Assessment for Sustainable Water Treatment

Abstract A sustainable, calcination‐free hydrothermal synthesis of nitrogen‐doped TiO 2 (N─TiO 2 ) nanoparticles is reported, offering a low‐energy route to visible‐light‐active photocatalysts. By eliminating the conventional high‐temperature calcination step and employing urea as a benign nitrogen dopant, the synthesis achieves a 40% reduction in energy input. The resulting nanomaterials exhibit enhanced photocatalytic degradation of methylene blue (MB, 5 mg L −1 ) under visible light, with N─TiO 2 –6 h achieving 97.6% removal within 180 min and a rate constant of 0.0243 min −1 . Beyond performance, a life cycle assessment (LCA) was conducted to quantify the environmental impacts, including global warming potential (GWP), freshwater use, human toxicity, and ecotoxicity. A positive correlation between photocatalytic efficiency and environmental burden highlights the trade‐offs inherent in materials optimization. To address this, an environmental efficiency (EE) metric integrating photocatalytic activity with GWP was applied, identifying N─TiO 2 –6 h as the top‐performing candidate, while N─TiO 2 –4 h offered a more sustainable balance. These findings demonstrate how merging green synthetic chemistry with life cycle thinking can guide the rational design of next‐generation photocatalysts. The scalable, calcination‐free method and decision‐support framework presented herein advance the development of environmentally responsible materials for decentralized water treatment aligned with global sustainability goals.