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.

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Modifications of commercial activated carbons by chemical treatment with HNO 3 or HCl and HF and the adsorption behavior of simple aromatic compounds (aniline, pyridine, phenol, and benzene) on activated carbon and modified activated carbon were investigated. The results show that the textural properties change a little after these modifications, but the surface acidity (mainly oxygen-containing groups) of activated carbon modified with HNO 3 increases greatly. The effect of ash of activated carbon on adsorption of the organic compounds mentioned above is insignificant. However, addition of surface acidity (mainly surface oxygen-containing groups) decreases the adsorption capacity of compounds significantly. The adsorption uptake of compounds on activated carbon with oxidation of HNO 3 is low possibly due to dispersive interaction, water cluster blocking, or competition between water and compounds adsorbed on activated carbon's surface because of hydrophilic increase of the activated carbon surface. The solubility of aromatic compounds in water has an important effect on the adsorption capacity of activated carbon. q m and K L (Langmuir adsorption parameters) for the aromatic compounds vary similarly.

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