Steering Electron Density of Zr Sites Using Ligand Effect in Bio‐Beads for Efficient Defluoridation

Abstract

Because of spontaneous agglomeration effect and undesirable electronic state of Zr sites on the surface, zirconium (hydro)oxides generally exhibit suboptimal defluoridation capacity. Herein, a template confinement‐ligand anchoring strategy is developed by utilizing confined growth of zirconium hydroxide (ZH) inside chitosan hydrogel beads (CHB) and subsequent anchoring of fumaric acid (fm) on its surface Zr sites in a monodentate mononuclear coordination mode. This technique leads to uniform dispersion of ultrafine fmZH (≈3.4 nm) and tunable electron density at the Zr sites. Due to the electron‐withdrawing ability of fm, electron‐delocalized Zr sites increase the orbital energy level matching and vacate Zr 4d orbitals to promote hybridization with the F 2p orbitals. Ultimately, robust ZrF bond can be formed as a result of reduced the adsorption energy toward fluoride ions. The defluoridation capacity shows positive linear relationship with the electron extraction ability of ligands. The saturation adsorption capacity and dynamic treatment capacity of CHB@fmZH are 10.8 and 45.9 times higher than that of CHB@ZH, respectively, owing to high electron extraction (0.098 e−) of fm. This study offers a novel insight into the design and synthesis of high‐efficiency metal oxide adsorbents by steering its surface metal sites’ electronic state through ligand effect.

Tailoring the Coordination Environment of Fe/Zn-BDC to Boost Peroxidase-like Activity for Highly Selective Detection of PFOS

“…To sum up, the FTIR and XPS analysis proved the strong interactions between the metal center of Fe/Zn-BDC-F 4 and the S atoms of the polar headgroup (Fe–S interactions), as well as the fluorinated nonpolar tails (Fe–F bonds) in PFOS. The experiment results were similar to those reported in the literature. , …”

“…The peaks had lower binding energies than pure PFOS at 689.3 eV, suggesting an increase of electron density around the F atoms . This implied a concerted redox process, where the F atoms interacted with Fe centers in Fe/Zn-BDC-F 4 through Fe–F bonds, and then F atoms pulled electrons away from the Fe center; thus the F atoms were reduced with lower binding energies. , It was noteworthy that the S 2p spectrum showed a similar shift as the F 1s spectrum. S 2p shifted from 169.5 eV in the pure PFOS spectrum to 168.48 eV in the PFOS-adsorbed Fe/Zn-BDC-F 4 (Figure d).…”

“…The experiment results were similar to those reported in the literature. 22,38 Finally, halogen bonding referred to noncovalent bonding interactions formed between electrophilic regions associated with halogen atoms and nucleophilic regions in the same or another molecule. 23 Since PFOS was enriched with the most electronegative F atoms, the F-functionalized nanomaterial Fe/ Zn-BDC-F 4 also contained F atoms.…”

“…For example, Zhang et al tuned the electron density of zirconium hydroxide by anchoring an organic ligand small molecule (e.g., fumaric acid) at the Zr site in the domain-limited state on its surface, which optimized the bonding ability of the Zr−F bond, and achieved efficient and selective removal of fluoride. 22 Zheng et al reported that the fluorine-functionalized spherical covalent organic frameworks was used as innovative stationary phases for the effective separation of organic halides. 23 Zhang's team used F-functionalized MOF as a stationary phase to selectively enrich PFOA, which was detected by gas chromatography− mass spectrometry with a limit of detection as low as 2.6 ng/ L. 24 Chen et al developed ion-selective electrodes with fluorinated anion-exchange membranes for potentiometric detection of PFOA and PFOS.…”

“…Due to the enrichment of highly electronegative F atoms in PFOS, materials functionalized with fluorine were demonstrated to selectively recognize, detect, and remove PFOS. For example, Zhang et al tuned the electron density of zirconium hydroxide by anchoring an organic ligand small molecule (e.g., fumaric acid) at the Zr site in the domain-limited state on its surface, which optimized the bonding ability of the Zr–F bond, and achieved efficient and selective removal of fluoride . Zheng et al reported that the fluorine-functionalized spherical covalent organic frameworks was used as innovative stationary phases for the effective separation of organic halides .…”