In Situ Driven Formation of Anatase/Brookite/Rutile Heterojunction N/TiO₂ Nanocrystals as Sustainable Visible‐Light Catalysts

Abstract Visible‐light active anatase/brookite/rutile (A/B/R) ternary N‐doped titania (N/TiO 2 ) crystals are successfully prepared by a facile sol‐gel method using titanium butoxide and benign N‐dopant source, guanidinium chloride. Systematically varying the aging time (1, 4, 8, and 12 d), its influence on physicochemical properties of as‐obtained spherical heterojunction nanomaterials is studied. Detailed characterizations confirm that a substantial amount of anatase (88% to 50%) is transformed to rutile (2% to 38%) via intermediate brookite phase (9% to 25%) as the function of aging time; not only the A/B/R phase content of the samples is tuned by sol‐gel aging time of the precursors solution but also their optical‐response and methylene blue photocatalytic properties are profoundly dictated. Notably under visible‐light irradiation, the photostable rutile rich mesoporous A/B/R triphasic N/TiO 2 (50% A, 12% B, 38% R) aged for 12 d demonstrates higher degradation activity (97%) with a faster degradation rate (0.033 min −1 ) than both lesser aged N/TiO 2 and undoped titania. This enhancement is attributed to the synergistic effect of interstitial‐N‐doping and optimal A/B/R interfacial charge transfer that leads to higher light absorption, lower bandgap energy and well‐separated charge carriers. The current work provides a new perspective for designing highly active visible‐light heterostructure nanomaterials with controllable phase composition.