Direct Z-scheme CoTiO3/g-C3N4 nanoparticles: fabrication and application as a photocatalyst for degradation of tetracycline hydrochloride assisted by peroxydisulfate or peroxymonosulfate under simulated sunlight

In this work, with ultrasound and thermal treatment, direct Z-scheme CoTiO 3 /g-C 3 N 4 heterojunctions were constructed from pristine CoTiO 3 and g-C 3 N 4 prepared separately by solgel, and thermal polycondensation methods, respectively. The photocatalytic activities of CoTiO 3 /g-C 3 N 4 composites were evaluated in degrading tetracycline hydrochloride (TCH) with an initial concentration of 10 mg L −1 under simulated solar irradiation exposed from a low-power light bulb (26 W). The XRD and SEM results of CTO-1/CN sample (CoTiO 3 /g-C 3 N 4 = 1.0 wt%) showed the simultaneous presence of both CoTiO 3 and g-C 3 N 4 phases as the structure of uniform heterojunction, where CoTiO 3 nanoparticles were evenly distributed on the surface of g-C 3 N 4 . A decrease in PL intensity of CTO-1/CN compared to that of the pristine materials suggested that the existence of CoTiO 3 promoted separation and suppressed the recombination of charge carriers in the composites. In the scope of this research, CTO-1/CN composite exhibited the best photocatalytic activity with TCH-degradation efficiency up to 79.60% after 60-min irradiation, where the rate constant of TCH-degradation reaction was 3.18 × 10 –2 min –1 , 1.5 times higher than that of pristine g-C 3 N 4 . Superoxide radicals (O 2 •− ) were proved as a main oxidative specie. Peroxydisulfate (PDS, 3 mM) or peroxymonosulfate (PMS, 200 mg L –1 ) greatly assisted CTO-1/CN in exhibiting higher degradation efficiencies of 84.7% after 60 min or 100% after only 20-min treatment, respectively. Intermediate products of TCH degradation were determined by UHPLC-MS test, and the possible degradation pathways of the CoTiO 3 /g-C 3 N 4 photocatalytic system were also proposed. The findings demonstrated the potential of the Z-scheme CoTiO 3 /g-C 3 N 4 system with high effective for TCH degradation in particular and for actual wastewater treatment in general. Graphical abstract