Zr-Based Metal–Organic Framework Nanocrystals for Water Remediation

Abstract

A series of derivatives of the Zr-based MOF UiO-66 were synthesized, fully characterized, and tested for their efficiency in the adsorption and removal of the highly toxic elements lead (Pb­(II)), cadmium (Cd­(II)), arsenate As­(V), and selenite Se­(IV). Different structural engineering techniques were employed to alter the properties of the Zr-MOFs, such as linker functionalization and defect creation to increase the density of adsorption sites. The functionalization of the UiO-66-based structures with carboxylate groups increased the removal efficiency of Pb­(II) cations by more than 70% and that of Cd­(II) cations by more than 60% to reach 125.2 and 69.1 mg/g, respectively. Moreover, the induced cluster defects were found to be the preferred adsorption sites of the anion pollutants. The adsorption of As­(V) and Se­(IV) by the high-defect UiO-66-200FA was 132.5 and 30.8 mg/g, respectively, which was higher than that of the less defect UiO-66, while almost no adsorption was achieved by UiO-66­(COOH)2. Furthermore, a multivariate (MTV-MOF) approach was employed to investigate the effect of the functional groups on the diffusion of the adsorbates within the porous networks. Interestingly, adsorption equilibrium was reached within minutes for the best-performing MOFs, highlighting their potential to be used in practical water treatment applications. Finally, chemical adsorption seemed to be dominant among binding mechanisms for all the pollutants, which were analyzed in detail to determine the characteristics that govern the adsorption efficiency of UiO-66-based adsorbents. The conclusions provided by this comprehensive study help serve as a guideline for future researchers aiming to employ UiO-66-based adsorbents by providing them with a deep understanding of the design strategies required to maximize the performance of this robust MOF.

Critical Role of Defects in UiO-66 Nanocrystals for Catalysis and Water Remediation

“…Highly defective UiO-66−200FA yielded a maximum adsorption capacity of 132.5 mg/g, while the carboxylated structure UiO-66(COOH) 2 did not show almost any As v adsorption. 23 4.1.2. Selenium.…”

“…Recently, our group investigated the efficiency of As v removal using UiO-66 and a series of its derivatives. Highly defective UiO-66–200FA yielded a maximum adsorption capacity of 132.5 mg/g, while the carboxylated structure UiO-66­(COOH) 2 did not show almost any As v adsorption …”

“…The strong affinity between Zr­(IV) and carboxylate O atoms, caused by the high charge density and polarization of bonds, resulted in unparalleled stability of these Zr-MOFs nanocrystals compared to other structures. , Consequently, most Zr-MOFs remain stable in water, inorganic solvents, and even acidic aqueous solutions . This contributed to their successful use in various applications such as heterogeneous catalysis, , gas separation and storage, , water purification, , drug delivery, , and electrochemistry. , …”

“…18,19 Consequently, most Zr-MOFs remain stable in water, inorganic solvents, and even acidic aqueous solutions. 18 contributed to their successful use in various applications such as heterogeneous catalysis, 11,20 gas separation and storage, 21,22 water purification, 12,23 drug delivery, 24,25 and electrochemistry. 26,27 Like other crystalline materials formed by, theoretically, a perfect periodic repetition of identical groups, MOFs' structures deviate from "ideal" crystallinity and present structural irregularities that are mostly referred to as "defects".…”

Diatomite-Based Adsorbent Decorated with Fe3O4 Nanoparticles for the Removal of Hazardous Metal Ions

“…With the increasing generation of metals from technological activities, the treatment of wastewater containing hazardous metal ions has become extremely important for environmentally sustainable development. − Adsorption is one of the most important water treatment methods due to its simple operation, high efficiency, and wide applicability, inspiring researchers to develop new adsorbent materials, such as activated carbon synthesized from waste materials, carbon nanomaterials prepared from herbaceous biomass, diatom stalks, hydrogels, and metal–organic frameworks. − Among them, diatomite, as a class of common biogenic siliceous sedimentary rock, owning microscale morphology and an intrinsic hierarchical pore structure, is widely considered a green candidate adsorbent. , However, most raw diatomite (RD) is covered by a variety of impurities (e.g., metal oxides and organic substances), limiting its adsorption capacity and further functionalization. , Therefore, it remains a challenge to develop a high-performance diatomite-based adsorbent meeting realistic demands.…”