Structure‐Property Relationship in Lightly and Heavily Gas‐Phase N‐Doped TiO₂ Nanoparticles for Solar‐Driven Photocatalysis

Lightly and heavily nitrogen (N)‐doped TiO 2 systems (LD‐TO and HD‐TO) were synthesized via ammonia (NH 3 ) gas‐assisted annealing at 450 and 750 °C. XRD patterns showed low‐ and high‐angle shifts for LD‐TO and HD‐TO, indicating lattice expansion (LD‐TO) and contraction in HD‐TO, with a Ti‐oxynitride (TiON) peak in HD‐TO indicating secondary phase segregation. FESEM analysis shows spherical particles (∼30 nm for TO) growing to ∼40–50 nm with a layered structure in doped samples. BET surface areas were 37.8, 41.8, and 27.1 m 2 /g for TO, LD‐TO, and HD‐TO, respectively. XPS confirmed Ti 4+ , O 2‐ , and N doping of ∼5.7% (LD‐TO) and 10.4% (HD‐TO). Optical analysis showed reduced band gaps (3.12 eV for LD‐TO, 3.02 eV for HD‐TO versus 3.21 eV for TO) and improved light absorption. Urbach energies (0.603 meV for LD‐TO; 0.926 meV for HD‐TO) reflected moderate defect density in LD‐TO. Electrochemical measurements indicated enhanced charge transfer, with LD‐TO outperforming HD‐TO in photocurrent response. LD‐TO degraded ∼98% rhodamine B in 150 min and produced H 2 at 935.2 µmol g −1 h −1 under sunlight, compared to 86% degradation and 765.4 µmol g −1 h −1 for HD‐TO. These results highlight that optimal N doping enhances TiO 2 ’s electronic, structural, and photocatalytic properties, while excessive doping leads to secondary phase formation and reduced performance.