Acid Stability of MIV (M = Zr, Hf, Ce, Th) UiO-66 MOFs from a Solution Perspective

Makenzie T. Nord; Alyson S. Plaman; Lev N. Zakharov; Omar K. Farha; May Nyman

doi:10.1021/acsami.4c21721

Acid Stability of M^IV (M = Zr, Hf, Ce, Th) UiO-66 MOFs from a Solution Perspective

Makenzie T. Nord, Alyson S. Plaman, Lev N. Zakharov, Omar K. Farha, May Nyman^*

^*Corresponding author for this work

Chemistry

Research output: Contribution to journal › Article › peer-review

Abstract

UiO-66 is one of the most studied metal-organic frameworks (MOFs), comprised of hexamer nodes M^IV₆O₄(OH)₄ (M₆; M = Zr, Ce, Hf, Th) bridged by benzenedicarboxylate (BDC) linkers. UiO-66 is well-known for its stability, based on the characterization of solids after treatment with mineral acids or more rarely, carboxylic acids to engineer defects. Characterization of the solutions to quantify and determine the speciation of dissolved UiO-66 has been largely ignored, regardless of the acid type. However, this information could yield better control over intentional defect engineering, the design of colloidal MOFs, and assembly of new materials from MOF building blocks. We show that Zr, Hf, and Ce-UiO-66 are wholly disassembled into soluble hexamer nodes and precipitated BDC linkers in 2-10 M acetic and formic acid. In contrast, Th-UiO-66 nodes erode completely to monomers and crystallize as acetate-linked Th-monomer chains. The Zr, Hf, and Ce formate solutions crystallize hexamer compounds, affirming the presence of M₆ in solution, as initially observed by small-angle X-ray scattering (SAXS). Two new crystal structures are reported: (1) [Ce₆O₄(OH)₄(H₂O)(HCOO)₁₂]·4.8H₂O, a 1-dimensional hexamer framework and (2) [Hf₆O₄(OH)₄(H₂O)₄(HCOO)₁₂]Cl₂·8H₂O, a 2-dimensional hexamer framework. SAXS of colloids from 0.5 M formic acid-treated UiO-66 (Zr, Hf) shows that the 100-200 nm aggregates retain the long-range order of the MOF and coexist in solution with dissolved linked hexamers, providing an understanding of the dissolution process. Quantification of metal dissolved from UiO-66 into 2 M formic acid indicates ∼0.2 M Zr₆/Hf₆ solubility limit in these conditions. We also show leaching of 4-5% Hf, 16% Zr, and 57% Ce from their respective UiO-66 frameworks into two mineral acids, where the high solubility of cerium is attributed to its facile Ce^III/IV redox activity. The higher solubility of Zr compared to Hf in mineral acids is attributed to greater Zr-ligand lability, an emerging and consistent trend that defines and differentiates Zr/Hf oxocluster behavior.

Original language	English (US)
Pages (from-to)	21357-21370
Number of pages	14
Journal	ACS Applied Materials and Interfaces
Volume	17
Issue number	14
DOIs	https://doi.org/10.1021/acsami.4c21721
State	Published - Apr 9 2025

Funding

M.T.N. and M.N. acknowledge support from the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Science and Engineering under award DE SC0010802. We acknowledge the Murdock Charitable Trust (grant SR-2017297) for the acquisition of the SCXRD. We also acknowledge Dr. Jeffrey Nason at Oregon State University for his help in collecting the DLS measurements and Dr. Peter Eschbach and Rebecca Jackson for their assistance at the OSU electron microscopy facility. A.L.P. and O.K.F. acknowledge the use of the Keck-II facility (RRID: SCR_026360) of Northwestern University\u2019s NUANCE Center for XPS data collection, which has received support from the SHyNE Resource (NSF ECCS-2025633), the IIN, and Northwestern\u2019s MRSEC program (NSF DMR-2308691).

Keywords

hafnium
hexamer clusters
metal−organic frameworks
small-angle X-ray scattering
UiO-66
zirconium

ASJC Scopus subject areas

General Materials Science

Access to Document

10.1021/acsami.4c21721

Cite this

@article{c6686bbc6d504ac1b3deb03ced8550aa,

title = "Acid Stability of MIV (M = Zr, Hf, Ce, Th) UiO-66 MOFs from a Solution Perspective",

abstract = "UiO-66 is one of the most studied metal-organic frameworks (MOFs), comprised of hexamer nodes MIV6O4(OH)4 (M6; M = Zr, Ce, Hf, Th) bridged by benzenedicarboxylate (BDC) linkers. UiO-66 is well-known for its stability, based on the characterization of solids after treatment with mineral acids or more rarely, carboxylic acids to engineer defects. Characterization of the solutions to quantify and determine the speciation of dissolved UiO-66 has been largely ignored, regardless of the acid type. However, this information could yield better control over intentional defect engineering, the design of colloidal MOFs, and assembly of new materials from MOF building blocks. We show that Zr, Hf, and Ce-UiO-66 are wholly disassembled into soluble hexamer nodes and precipitated BDC linkers in 2-10 M acetic and formic acid. In contrast, Th-UiO-66 nodes erode completely to monomers and crystallize as acetate-linked Th-monomer chains. The Zr, Hf, and Ce formate solutions crystallize hexamer compounds, affirming the presence of M6 in solution, as initially observed by small-angle X-ray scattering (SAXS). Two new crystal structures are reported: (1) [Ce6O4(OH)4(H2O)(HCOO)12]·4.8H2O, a 1-dimensional hexamer framework and (2) [Hf6O4(OH)4(H2O)4(HCOO)12]Cl2·8H2O, a 2-dimensional hexamer framework. SAXS of colloids from 0.5 M formic acid-treated UiO-66 (Zr, Hf) shows that the 100-200 nm aggregates retain the long-range order of the MOF and coexist in solution with dissolved linked hexamers, providing an understanding of the dissolution process. Quantification of metal dissolved from UiO-66 into 2 M formic acid indicates ∼0.2 M Zr6/Hf6 solubility limit in these conditions. We also show leaching of 4-5% Hf, 16% Zr, and 57% Ce from their respective UiO-66 frameworks into two mineral acids, where the high solubility of cerium is attributed to its facile CeIII/IV redox activity. The higher solubility of Zr compared to Hf in mineral acids is attributed to greater Zr-ligand lability, an emerging and consistent trend that defines and differentiates Zr/Hf oxocluster behavior.",

keywords = "hafnium, hexamer clusters, metal−organic frameworks, small-angle X-ray scattering, UiO-66, zirconium",

author = "Nord, {Makenzie T.} and Plaman, {Alyson S.} and Zakharov, {Lev N.} and Farha, {Omar K.} and May Nyman",

note = "Publisher Copyright: {\textcopyright} 2025 American Chemical Society.",

year = "2025",

month = apr,

day = "9",

doi = "10.1021/acsami.4c21721",

language = "English (US)",

volume = "17",

pages = "21357--21370",

journal = "ACS Applied Materials and Interfaces",

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TY - JOUR

T1 - Acid Stability of MIV (M = Zr, Hf, Ce, Th) UiO-66 MOFs from a Solution Perspective

AU - Nord, Makenzie T.

AU - Plaman, Alyson S.

AU - Zakharov, Lev N.

AU - Farha, Omar K.

AU - Nyman, May

PY - 2025/4/9

Y1 - 2025/4/9

N2 - UiO-66 is one of the most studied metal-organic frameworks (MOFs), comprised of hexamer nodes MIV6O4(OH)4 (M6; M = Zr, Ce, Hf, Th) bridged by benzenedicarboxylate (BDC) linkers. UiO-66 is well-known for its stability, based on the characterization of solids after treatment with mineral acids or more rarely, carboxylic acids to engineer defects. Characterization of the solutions to quantify and determine the speciation of dissolved UiO-66 has been largely ignored, regardless of the acid type. However, this information could yield better control over intentional defect engineering, the design of colloidal MOFs, and assembly of new materials from MOF building blocks. We show that Zr, Hf, and Ce-UiO-66 are wholly disassembled into soluble hexamer nodes and precipitated BDC linkers in 2-10 M acetic and formic acid. In contrast, Th-UiO-66 nodes erode completely to monomers and crystallize as acetate-linked Th-monomer chains. The Zr, Hf, and Ce formate solutions crystallize hexamer compounds, affirming the presence of M6 in solution, as initially observed by small-angle X-ray scattering (SAXS). Two new crystal structures are reported: (1) [Ce6O4(OH)4(H2O)(HCOO)12]·4.8H2O, a 1-dimensional hexamer framework and (2) [Hf6O4(OH)4(H2O)4(HCOO)12]Cl2·8H2O, a 2-dimensional hexamer framework. SAXS of colloids from 0.5 M formic acid-treated UiO-66 (Zr, Hf) shows that the 100-200 nm aggregates retain the long-range order of the MOF and coexist in solution with dissolved linked hexamers, providing an understanding of the dissolution process. Quantification of metal dissolved from UiO-66 into 2 M formic acid indicates ∼0.2 M Zr6/Hf6 solubility limit in these conditions. We also show leaching of 4-5% Hf, 16% Zr, and 57% Ce from their respective UiO-66 frameworks into two mineral acids, where the high solubility of cerium is attributed to its facile CeIII/IV redox activity. The higher solubility of Zr compared to Hf in mineral acids is attributed to greater Zr-ligand lability, an emerging and consistent trend that defines and differentiates Zr/Hf oxocluster behavior.

AB - UiO-66 is one of the most studied metal-organic frameworks (MOFs), comprised of hexamer nodes MIV6O4(OH)4 (M6; M = Zr, Ce, Hf, Th) bridged by benzenedicarboxylate (BDC) linkers. UiO-66 is well-known for its stability, based on the characterization of solids after treatment with mineral acids or more rarely, carboxylic acids to engineer defects. Characterization of the solutions to quantify and determine the speciation of dissolved UiO-66 has been largely ignored, regardless of the acid type. However, this information could yield better control over intentional defect engineering, the design of colloidal MOFs, and assembly of new materials from MOF building blocks. We show that Zr, Hf, and Ce-UiO-66 are wholly disassembled into soluble hexamer nodes and precipitated BDC linkers in 2-10 M acetic and formic acid. In contrast, Th-UiO-66 nodes erode completely to monomers and crystallize as acetate-linked Th-monomer chains. The Zr, Hf, and Ce formate solutions crystallize hexamer compounds, affirming the presence of M6 in solution, as initially observed by small-angle X-ray scattering (SAXS). Two new crystal structures are reported: (1) [Ce6O4(OH)4(H2O)(HCOO)12]·4.8H2O, a 1-dimensional hexamer framework and (2) [Hf6O4(OH)4(H2O)4(HCOO)12]Cl2·8H2O, a 2-dimensional hexamer framework. SAXS of colloids from 0.5 M formic acid-treated UiO-66 (Zr, Hf) shows that the 100-200 nm aggregates retain the long-range order of the MOF and coexist in solution with dissolved linked hexamers, providing an understanding of the dissolution process. Quantification of metal dissolved from UiO-66 into 2 M formic acid indicates ∼0.2 M Zr6/Hf6 solubility limit in these conditions. We also show leaching of 4-5% Hf, 16% Zr, and 57% Ce from their respective UiO-66 frameworks into two mineral acids, where the high solubility of cerium is attributed to its facile CeIII/IV redox activity. The higher solubility of Zr compared to Hf in mineral acids is attributed to greater Zr-ligand lability, an emerging and consistent trend that defines and differentiates Zr/Hf oxocluster behavior.

KW - hafnium

KW - hexamer clusters

KW - metal−organic frameworks

KW - small-angle X-ray scattering

KW - UiO-66

KW - zirconium

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