In situ synthesis of g-C 3 N 4 /TiO 2 heterojunction by a concentrated absorption process for efficient photocatalytic degradation of tetracycline hydrochloride.

The construction of heterojunctions between semiconductors is a preferred route to improve overall photocatalytic activity. In this work, a facile and feasible method was innovatively developed to one-step prepare g-C 3 N 4 /TiO 2 heterojunctions via an absorption-calcination process using nitrogen and titanium precursors directly. This method can effectively avoid interfacial defects and establish a tight interfacial connection between g-C 3 N 4 and TiO 2 . The resultant g-C 3 N 4 /TiO 2 composites exhibited prominent photodegradation efficiency for tetracycline hydrochloride (TC-HCl) under visible light and simulated-sunlight irradiation. The optimal g-C 3 N 4 /TiO 2 composite (urea content of 4 g) showed the highest photocatalytic efficiency, which can degrade 90.1% TC-HCl under simulated-sunlight irradiation within 30 min, achieving 3.9 and 2 times increases compared to pure g-C 3 N 4 and TiO 2 , respectively. Besides, photodegradation pathways based on the role of active species ·O 2 - and ·OH were identified, indicating that a direct Z-scheme heterojunction was formed over the g-C 3 N 4 /TiO 2 photocatalyst. The enhanced photocatalytic performance can be attributed to the close-knit interface contact and the formation of Z-scheme heterojunction between g-C 3 N 4 and TiO 2 , which can accelerate the photo-induced charge carrier separation, broaden the spectra absorption range, and retain a higher redox potential. This one-step synthesis method may provide a new strategy for the construction of Z-scheme heterojunction photocatalysts consisting of g-C 3 N 4 and TiO 2 for environmental remediation and solar energy utilization.