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 CoTiO3/g-C3N4 heterojunctions were constructed from pristine CoTiO3 and g-C3N4 prepared separately by solgel, and thermal polycondensation methods, respectively. The photocatalytic activities of CoTiO3/g-C3N4 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 (CoTiO3/g-C3N4 = 1.0 wt%) showed the simultaneous presence of both CoTiO3 and g-C3N4 phases as the structure of uniform heterojunction, where CoTiO3 nanoparticles were evenly distributed on the surface of g-C3N4. A decrease in PL intensity of CTO-1/CN compared to that of the pristine materials suggested that the existence of CoTiO3 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-C3N4. Superoxide radicals (O2•−) 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 CoTiO3/g-C3N4 photocatalytic system were also proposed. The findings demonstrated the potential of the Z-scheme CoTiO3/g-C3N4 system with high effective for TCH degradation in particular and for actual wastewater treatment in general. Graphical abstract: [Figure not available: see fulltext.] © 2023, The Author(s), under exclusive licence to Springer Nature Switzerland AG.