Facile ligand-regulated synthesis of defective Fe-MOF nanosheets for efficient tetracycline degradation via photoassisted enhanced activation of persulfate

In this work, defective Fe-based metal organic framework (Fe-MOF) were synthesized by a simple and eco-friendly method, in which the benzenetricarboxylic acid (BTC) ligand was partially replaced by cheap terephthalic acid (TPA) to regulate the crystalline morphology, pore structure and ligand defects. At BTC/TPA = 5/3, 4/4 and 3/5 (molar ratio), lamellar crystal (1-Fe-MOF), a mixture of lamellar crystal and nanosheets (2-Fe-MOF), and nanosheets (3-Fe-MOF) were obtained, respectively, which were distinctly different from the octahedral Fe-MOF. In the visible-light-driven persulfate (PS) activation coupled system, 3-Fe-MOF exhibited highest catalytic activity for tetracycline hydrochloride (TCH). 96.5% of TCH was removal within 20 min and the degradation kinetics rate of 0.144 min−1 was 3.5 times higher than that over the intact Fe-MOF. The enhancement in degradation activity was mainly attributed to the emergence of mesoporous structure, exposure of more metal active sites, and accelerated Fe2+/Fe3+ cycling due to more efficient charge separation and electron transfer efficiency, which favored the generation and dominant role of ∙SO4− in TCH degradation. Furthermore, demethylation, deamidation, double-bond oxidation and ring-opening reactions were inferred as the two possible degradation pathways of TCH in 3-Fe-MOF/PS/Vis system. This study provides useful guidance for the design of novel and sustainable MOFs with good application performance and industrialization potential.