Insight into efficient photocatalytic elimination of tetracycline over SrTiO3 (La,Cr) under visible-light irradiation: The relationship of doping and performance

Antibiotic has become an important organic contaminant in surface water, which poses a huge threat to human health and ecosystem. SrTiO3 is an attractive perovskite structured semiconductor material and shows promising applications in photocatalysis. Herein, a series of lanthanum and chromium codoped SrTiO3 (denoted as SrTiO3(La,Cr)-x) with different dopant amount of La and Cr have been successfully fabricated via a facile sol-gel hydrothermal method and employed as efficient photocatalysts for the elimination of tetracycline (TC) from aqueous solution under visible-light irradiation. It indicates that the photocatalytic performance is highly dependent on the La and Cr content in the samples. Among the catalysts, the porous SrTiO3(La,Cr)-6 spheres with a moderate dopant amount exhibit the best photocatalytic activity for TC removal, which is approximately 4.4 and 2.3 times as superior as SrTiO3(La,Cr)-2 with the least dopants and SrTiO3(La,Cr)-8 with the most dopants, respectively. Detailed characterizations reveal that the significant improvement of photocatalytic activity is attributed to the increasing molar ratio of Cr3+/Cr6+, which can be facilely adjusted by tuning the doping amount of La and Cr during the synthesis process. In addition, the catalyst shows excellent photocatalytic stability and can be recycled over ten times with negligible activity decline. Active species trapping experiments demonstrate that superoxide radicals, holes and hydroxyl radicals are responsible for TC degradation. On the basis of the intermediate products identified using HPLC-MS, four possible reaction pathways and TC degradation mechanism have been put forward. This study offers an effective strategy to modulate the photocatalytic properties of SrTiO3 by simple tuning the dopant content for environment and energy applications, which can be facilely extended to the modification of other semiconductors.