Enhanced Photocatalytic Activity of Anatase/Rutile‐Mixed Phase Titanium Dioxide Nanoparticles Annealed with Polyethylene Glycol at Low Temperatures in Aluminum Foil‐Covered Combustion Boats

A facile carbon‐doping process is proposed to enhance the photocatalytic activity of anatase/rutile‐mixed phase TiO₂ nanoparticles using polyethylene glycol (PEG). The TiO₂‐PEG composite is loaded into a boat and covered tightly with Al foil to increase the pressure inside that boat during annealing. The boat is annealed for 1 h at different temperatures and PEG ratios. The annealing with 30% PEG at 300 °C enhances the decomposition of organic pollutants and bacterial inactivation under 405 nm light compared to the annealing without Al films. This annealing causes 2.5–3% carbon doping, introduces more oxygen vacancies, and converts PEG into organic compounds rich in CC bond components. These modifications of TiO₂ can be attributed to carbon‐centered radicals produced from PEG during annealing. The modifications change the band structure to enhance the photogenerated carrier concentration responsible for the photocatalytic activity. The carbon doping narrows the anatase and rutile bandgaps, allowing the anatase phase to absorb 405 nm light. The introduced oxygen vacancies increase the electron‐trapping sites and raise the adsorbed oxygen groups enhancing the upward band bending and the depletion layer depth at the surface. The PEG‐converted compounds can transfer photogenerated electrons within the compounds to the TiO₂ conduction band.