In situ synthesis of g-C3N4/TiO2 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-C3N4/TiO2 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-C3N4 and TiO2. The resultant g-C3N4/TiO2 composites exhibited prominent photodegradation efficiency for tetracycline hydrochloride (TC-HCl) under visible light and simulated-sunlight irradiation. The optimal g-C3N4/TiO2 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-C3N4 and TiO2, respectively. Besides, photodegradation pathways based on the role of active species ·O2- and ·OH were identified, indicating that a direct Z-scheme heterojunction was formed over the g-C3N4/TiO2 photocatalyst. The enhanced photocatalytic performance can be attributed to the close-knit interface contact and the formation of Z-scheme heterojunction between g-C3N4 and TiO2, 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-C3N4 and TiO2 for environmental remediation and solar energy utilization.

Ag-enhanced CeF3-O: highly enhanced photocatalytic performance under NIR light irradiation.

CeF3-O with intermediate band showed improved synergic photodegradation activity toward HCl-TC and RhB under NIR light irradiation when enhanced by Ag as a cocatalyst. Ag+ ions take electrons from the second transition in CeF3-O's intermediate band, which are then reduced to Ag as cocatalyst. The photodegradation efficiencies of HCl-TC by various Ag/CeF3-O nanoparticles in 180-min increase from 26.5 to 73.1%. The optimal Ag/CeF3-O-100 is about 2.76 times that of pure CeF3-O. Ag/CeF3-O-100 has an apparent rate constant of 4.5 × 10-3 min-1, which is 3.0 times that of pure CeF3-O. Similarly, Ag/CeF3-O-10 achieves a superior photodegradation efficiency of RhB at 96.7% under NIR light within 120 min. Its apparent rate constant of 27.7 × 10-3 min-1 is 12.0 times that of pure CeF3-O (2.3 × 10-3 min-1). Further, the turnover frequencies of Ag/CeF3-O nanoparticles are greatly higher than that of the corresponding pure CeF3-O nanoparticles. Ag-enhanced CeF3-O has a unique metal-semiconductor interface where Ag acts as a bridge for facilitating charge transfer and the separation efficiency of photogenerated carries. The synergic effect between CeF3-O and Ag provides a practical technique for enhancing the wastewater treatment with NIR light irradiation.