Synergy Effect of Pore Structure and Amount of Carboxyl Site for Effective Removal of Pb2+ in Metal–Organic Frameworks

Herein, we report a series of carboxyl-grafted metal–organic frameworks (UiO-66-(COOH)n, n = 0,1,2,4) for Pb2+ removal and the important role of carboxyl groups in capture of Pb2+. Among these materials, UiO-66-(COOH)2 exhibits a large adsorption capacity of 420.2 mg g–1, superior to that of other metal–organic frameworks and most of reported adsorbents. Besides, 99.99% of Pb2+ can be removed from water in the concentration range of <100 ppm with the UiO-66-(COOH)2 dosage of 0.5 mg mL–1. Furthermore, UiO-66-(COOH)2 can be easily regenerated through a simple method. Mechanism analysis (Fourier transform infrared, X-ray photoelectron spectroscopy, and density functional theory calculation) indicates that the synergy effect of rich carboxyl groups and proper pore structure plays a critical role in the capture of Pb2+. This work may provide a guideline to design high-efficiency adsorbents for Pb2+ from water.