Fabrication of S-scheme ZnO/Zn3(PO4)2 heterojunction photocatalyst toward photodegradation of tetracycline antibiotic and photocatalytic mechanism insight

In this work, a S-scheme ZnO/Zn3(PO4)2 heterojunction photocatalyst was fabricated by a simple co-precipitation manner under reflux condition. The ZnO/Zn3(PO4)2 heterostructured nanocomposite was employed for the degradation of tetracycline antibiotic under UV and visible light irradiation. The structure, composition, morphology, and optical properties of the as-synthesized ZnO/Zn3(PO4)2 products were characterized by XRD, EDS, FESEM, TEM, UV–Vis DRS, and PL measurements. The hybrid ZnO/Zn3(PO4)2 nanoparticles exhibited the highest photocatalytic efficiency in the degradation of tetracycline under ultraviolet (97%) and visible (82%) light irradiation, which was ∼1.5 times more than sole Zn3(PO4)2 nanostructures. The promoted light harvesting and generated heterojunction interfaces between ZnO and Zn3(PO4)2 can obviously reduce the recombination rate of charge carriers in the ZnO/Zn3(PO4)2 heterostructure. Moreover, a reasonable photocatalytic mechanism of the UV and visible light-induced degradation of antibiotic over ZnO/Zn3(PO4)2 nanocomposites is suggested. The results indicated that under UV, the mechanism follows from the S-scheme in the presence of •O2− and •OH as predominant species, while upon visible, the type-II heterojunction utilizing •O2− as prevailing radical is possible.