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.
The
adsorption of rhodamine B (RhB) from aqueous solution on a
functionalized metal–organic framework UiO-66-(COOH)2 was studied systematically in view of the adsorption isotherm, kinetics,
thermodynamics, effect of pH and co-existing salts, and regeneration
of the material. The adsorption behavior of RhB on UiO-66-(COOH)2 followed the Langmuir isotherm model and pseudo-second-order
model. The thermodynamics study indicates that the adsorption of RhB
is mainly controlled by the entropy effect rather than the enthalpy
change. The strong electrostatic interaction as well as H-bond interaction
contributes to the capture of RhB on the nanoscale UiO-66-(COOH)2 via the surface adsorption manner. UiO-66-(COOH)2 exhibited an ultra-high adsorption capacity of 2200 mg g–1 and excellent continuous removal ability. The high adsorption capacity,
strong anti-interference ability, and easy regeneration make UiO-66-(COOH)2 as an ideal adsorbent for RhB removal from aqueous solution.
The adsorption of humic acid (HA) onto an Al 3+ -based metal− organic framework (MIL-68(Al)) was investigated. MIL-68(Al) was synthesized and characterized using powder X-ray diffraction pattern, Fourier transform infrared spectroscopy, N 2 adsorption−desorption, scanning electronic microscopy, and X-ray photoelectron spectroscopy. Adsorption of HA onto MIL-68(Al) was investigated systematically under various conditions. Experimental results indicate that the adsorption kinetics follow a pseudo-second-order model and adsorption can reach equilibrium at ∼15 min. The adsorption isotherm can be well-fitted with Freundlich model, and the adsorption capacity (115.5 mg g −1 ) is much higher than those of chitosan, fly ash, activated carbon, etc. Thermodynamic study indicates that the adsorption of HA can be enhanced under lower temperature based on the negative value of adsorption enthalpy (−10.52 kJ mol −1 ). Besides, MIL-68(Al) can exhibit a high adsorption capacity of 28.53 mg g −1 in a real water sample from Fenhe River. The adsorption mechanism can be wellexplained by electrostatic interaction and the H-bond interaction. Therefore, this work may provide a guideline to construct MOF-based adsorbents for the high-efficiency capture of HA.
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