Co-doped 3D petal-like ZnIn2S4/GaN heterostructures for efficient removal of chlortetracycline residue from real pharmaceutical wastewater

A novel Co-doped 3D petal-like ZnIn 2 S 4 /GaN heterostructures highly efficient, long-term stability and strong visible-light responsive photocatalyst was prepared for removal of chlortetracycline residue from real pharmaceutical wastewater. • A new Co-doped 3D petal-like ZnIn 2 S 4 /GaN heterostructure is successfully constructed. • The catalysts show promising removal ability of tetracycline (TC) in real wastewater. • The presence of GaN significantly retarded the aggregation of ZnIn 2 S 4 to microsphere. • The formation of type-II heterostructure accelerates the interfacial charges transfer. • Possible degradation pathways for TC are deduced using UPLC-MS and DFT calculation. It is of utmost priority to remedy environmental pollution caused by antibiotics contamination through visible-light driven catalysts. However, exploring of photocatalysts simultaneous with properties of strong visible-light harvesting ability, superior efficiency and long-term stability, is still a tremendous challenge in the field of photocatalysis. Herein, using Gallium nitride (GaN) as a promising wide-band-gap support material, a new Co-doped 3D petal-like ZnIn 2 S 4 /GaN heterostructure is successfully constructed by combining hydrothermal and metal organic chemical vapour deposition (MOCVD) methods for the first time. The optimized 3Co/0.3ZnIn 2 S 4 /GaN photocatalyst demonstrates remarkably increased photocatalytic activity for chlortetracycline decomposition in various aqueous solutions with long-term stability under visible-light illumination. Its elimination rates in deionized water, tap water and real pharmaceutical wastewater are 81%, 85% and 72%, respectively. It is almost 5 times higher than that of pristine GaN in deionized water. The results of the experiments evidenced that the dramatically increased photocatalytic capability is due to the synergetic co-effects of incorporating band gap match-able ZnIn 2 S 4 and co-catalytic role of Co-doping. This facilitated photo-excited electron-hole pairs separation and transport due to the direct formation of heterojunction with type-II charge transfer mechanism. Furthermore, two possible degradation pathways are deduced from the ultra-performance liquid chromatography mass spectrometry (UPLC-MS) analysis combined with the density functional theory computation of frontier electron densities. This research gives a typical example of the rational design and fabrication of highly efficient GaN-based photocatalysts towards the practical treatment of antibiotic contaminated wastewater.