Compact and uniform TiO₂@g-C₃N₄ core-shell quantum heterojunction for photocatalytic degradation of tetracycline antibiotics

Optimizing the heterojunction structure of semiconductor photocatalysts is significant for taking full advantage of their abilities for organic molecules degradation. Here, we demonstrate a feasible strategy of polymerizing the quantum-thick graphitic carbon nitride (g-C₃N₄) on to the surface of anatase titanium dioxide (TiO₂) nanosheets with exposed {001} facets to form the TiO₂@g-C₃N₄ (TCN) core-shell quantum heterojunction for improving photocatalytic tetracycline degradation activity. 100 mg of TCN photocatalyst shows the highest tetracycline degradation rate of 2.2 mg/min, which is 36% higher than that of the TiO₂/g-C₃N₄ random mixture (TCN(mix)), 2 times higher than that of TiO₂, and 2.3 times higher than that of bulk g-C₃N₄. Results also indicate that h⁺ and ·O₂⁻ are the main oxidant species for the efficient photocatalytic reaction. The decisive factors in improving the photocatalytic activity of TCN is the unique structural advantages of quantum-thick g-C₃N₄ shell, compact and uniform contact interface, richly available reaction sites, more surface adsorbed hydroxyl (OH) groups. Efficient electron transfer between TiO₂ and g-C₃N₄ is also demonstrated by the significant enhancement of photocurrent response of TCN electrodes and decrement of fluorescence emission spectra. This work demonstrates new sights for synthesizing high-efficient and environment-stable photocatalysts by engineering the surface heterojunction.