Enhanced radical formation and water purification via lanthanide-nitrogen co-doped strontium titanate

Traditional water treatment methods including physical, chemical, and biological approaches often fall short of achieving the required purification standards. Photocatalysis has emerged as a promising alternative due to its efficiency, sustainability, and cost-effectiveness. Among the various photocatalysts investigated, strontium titanate (SrTiO3) has attracted considerable attention for its high stability and photocatalytic potential. However, its wide bandgap (3.2 eV) limits its activity to the ultraviolet region, thereby restricting its ability to utilize the broader solar spectrum. To address this limitation, doping strategies have been employed to extend light absorption into the visible range. In particular, co-doping with lanthanide and nitrogen ions has demonstrated the potential to enhance photocatalytic performance by altering the material's electronic structure and suppressing charge carrier recombination. This study evaluates the photocatalytic activity of SrTiO3 co-doped with various lanthanide and nitrogen ions, offering a comparative analysis across the lanthanide series. Among the tested materials, the La/N co-doped SrTiO3 exhibited the highest efficiency in the degradation of phenol, which was used as a model pollutant. The degradation mechanism and the reactive species involved were investigated using electron paramagnetic resonance (EPR) spectroscopy combined with the spin-trapping technique. The analysis of photogenerated species in solution revealed that photogenerated holes, in synergy with superoxide radicals, play the most significant role in phenol degradation.