Linzhi Zhai,Xin Zheng,Mengqi Liu,Xinru Wang,Wenli Li,Xiufang Zhu,Aihua Yuan,Yusong Xu,Peng Song
Zr-based metal–organic frameworks (MOFs), especially the UiO-66 family, present a huge application potential for the sorptive eliminations of heavy metal ions, still most of the studies often focus on only one type of adsorbent, thus lacking in some in-depth comparisons on the microstructure produced by the organic ligands. Herein, three kinds of Zr-based MOFs (UiO-66, UiO-66-(OH) 2 , and UiO-66-NH 2 ) are prepared, and their adsorption capacities for Ni 2+ , Fe 3+ and Cr 6+ are systematically investigated and compared. Results suggest that, due to a higher specific surface area of 1569.2 m 2 /g and a larger pore volume of 0.61 cm 3 g −1 , the UiO-66 depicts a better adsorption performance for Ni 2+ and Fe 3+ with larger capacities of 6.8 and 14.1 mg g −1 , respectively. The UiO-66-(OH) 2 presents a specific surface area of 785.5 m 2 /g, which is a little lower than UiO-66 and UiO-66-NH 2 , but shows the maximum adsorption capacity of 39.0 mg g −1 for Cr 6+ , obviously surpassing two other counterparts. In addition, for a multi-ion aqueous solution, UiO-66-(OH) 2 still has an excellent Cr 6+ /Ni 2+ adsorption selectivity of 21.7. The adsorption isotherm of Cr 6+ belongs to monomolecular layer Langmuir model, further verifying –OH 2 + of the UiO-66-(OH) 2 surface acted as the chemical adsorption sites and attracted electronegative Cr 6+ -containing ions. This study dramatically highlights the importance of the organic ligands for MOFs sorbents, which may facilitate achieving their large-scale applications in wastewater treatment.
The development of new adsorbent materials to improve adsorption capacity and selectivity constitutes a significant research direction for removing toxic ions from water. In this study, a series of Zr-based metal–organic framework hierarchical porous nanofibre membranes (MOFs@PIM-W) was designed and successfully synthesised, and their adsorption properties and mechanism for fluoride ions in water were investigated. The formation of Zr–F bonds in Zr-based MOFs is a primary reason for the rapid, effective, and stable removal of fluoride ions from water. Moreover, in contrast to common powder adsorbents and the conventional static adsorption process, the obtained hierarchical porous nanofibre membranes improve the removal rate of fluoride ions, which may be attributed to the formation of hierarchical porous structures. Specifically, by modifying the types of MOFs, the obtained nanofibre membranes can effectively remove Hg(II) ions from water under a wide range of pH environments (pH = 2–10) with a removal rate of up to 99 %. This indicates that the hierarchical porous design of nanofibre membranes incorporated with their specific adsorption provides a viable option for rapidly and efficiently removing toxic ions from water.
Zr-based metal-organic frameworks (MOFs) have been developed in recent years to treat heavy metals, e.g. hexavalent chromium Cr 6+ pollution, which damages the surrounding ecosystem and threaten human health. This kind of MOF is stable and convenient to prepare, but has the disadvantage of low adsorption capacity, limiting its wide application. To this end, a novel formic acid and amino modified MOFs were prepared, referred to as Form-UiO-66-NH 2 . Due to the modification of formic acid, its specific surface area, pore size, and crystal size were effectively expanded, and the adsorption capacity of Cr 6+ was significantly enhanced. Under optimal conditions, Form-UiO-66-NH 2 exhibited an excellent adsorption capacity (338.98 mg/g), ∼10 times higher than that reported for unmodified Zr-based MOFs and most other adsorbents. An in-depth study on the photoelectronic properties and pH confirmed that the adsorption mechanism of Form-UiO-66-NH 2 to Cr 6+ was electrostatic adsorption. After modification, the improvement of Cr 6+ adsorption capacity by Form-UiO-66-NH 2 was attributed to the expansion of its specific surface area and the increase in its surface charge. The present study revealed an important finding that Form-UiO-66-NH 2 elucidated selective adsorption to Cr 6+ in mixed wastewater containing toxic heavy metal ions and common nonmetallic water quality factors . This research provided a new acid and amino functionalization perspective for improving the adsorption capacity of Zr-based MOF adsorbents while simultaneously demonstrating their pertinence to target contaminant adsorption.
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