Phosphorus Doping Effects on the Rutile−Anatase Phase Transition, Surface Redox Properties and Visible Light Activity of Porous Titanium Dioxide

Dopants influence the anatase-rutile phase transition of titanium dioxide, primarily affecting the temperature at which this transformation occurs. The specific effect (promotion or inhibition) depends on the dopant type (metal or non-metal), its ionic radius, and its concentration. Phosphorus (P) doping, in particular, retards the formation of rutile at high annealing temperatures. However, there are no reports on P doping in predominantly rutile TiO 2 or the influence of P concentration on preferential anatase formation for a rutile-driven synthesis process. Herein, phosphorus-doped titanium dioxide (P-TiO 2 ) photocatalysts were synthesized via a modified inverse micelle sol-gel route. At 0.5-1 mol% P concentration, the materials retain a rutile composition of 97-98%, indicating a critical doping threshold where phosphorus has minimal effect on rutile inhibition. At 2 mol% P, the anatase-to-rutile ratio shifts to 55% anatase and 45% rutile, whereas 3% loading results in 99% anatase TiO 2 . The P-TiO 2 photocatalysts exhibited enhanced visible-light Methylene Blue (MB) degradation compared with commercial P25. MB dye degradation mechanistic studies were conducted through reactive oxygen species (ROS) probing and quenching experiments. Electrospray Ionization-Mass Spectrometry (ESI-MS) studies led to the proposal of MB degradation via oxidation and cleavage of the central thiazine ring. • At 0.5 and 1 mol% P doping, the materials retain a rutile composition of 97-98%. • P doping improves TiO 2 surface hydroxylation, surface area, and surface acidity. • Methylene blue degradation proceeds via oxidation and cleavage of the central thiazine ring. • ROS studies support the proposed methylene blue degradation mechanism.