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.
Chromium(VI) is known for its severe threat to humans and the environment. Herein, a valid strategy has been developed to effectively remove this pollutant. Based on the short organic linker of fumaric acid, MOF-801 (or Zr-fum) is the smallest Zr-MOF with fcu topology up to date. Accordingly, this Zr-MOF possesses much higher density of μ-OH sites than other fcu-Zr-MOFs. Based on the H-bond interaction between Cr(VI) and these μ-OH sites, MOF-801 shows a high maximum adsorption capacity of 156.2 mg g −1 , superior to other two fcu-Zr-MOFs and most of the reported adsorbents. Besides, the adsorption equilibrium can be achieved at ∼60 min and most of co-existing salts have only slight influences on Cr(VI) adsorption in MOF-801; more importantly, MOF-801 can be well regenerated with the eluent of methanol−acetic acid. The adsorption mechanism as well as the important role of μ-OH was reasonably explained through Fourier transform infrared spectra, XPS pattern, theoretical calculation, and zeta potential measurement.
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