Synergistic adsorption-photocatalytic degradation of different antibiotics in seawater by a porous g-C3N4/calcined-LDH and its application in synthetic mariculture wastewater.

In this work, a modified g-C3N4/MgZnAl-calcined layered double hydroxide composite (M-CN/cLDH) was successfully fabricated via a template method. The composite material is a hierarchical porous flower-like nanostructure self-assembled from stacked hybrid flakes. The 3D M-CN/cLDH architectures exhibit a synergistic effect of adsorption and photocatalysis for eliminating typical tetracycline antibiotics in seawater, i.e., oxytetracycline (OTC), tetracycline (TC), chlortetracycline (CTC), and doxycycline (DXC). The synergistic removal rate of OTC in seawater of M-CN/cLDH is 2.73 times higher than that of g-C3N4 after 120 min of visible-light illumination, and M-CN/cLDH also performs better adsorption-photocatalytic degradation on OTC in the continuous flow reaction process. The superior adsorption capability of the M-CN/cLDH is attributed to the open porous structures of cLDH, and its excellent photocatalytic degradation activity is ascribed to the closely bonded heterojunctions between g-C3N4 (CN) and cLDH double layers. The mass spectra reveals the degradation pathways of OTC, and its byproducts are less toxic after degradation for 120 min. The exploration of the M-CN/cLDH in synthetic mariculture wastewater suggested a huge potential for its practical application. With the assistance of magnesium ammonium phosphate (MAP) precipitation pretreatment, the material can effectively retain the high OTC removal rate in the synthetic mariculture wastewater circumstance.