Nanoconfinement boosts affinity of hydrated zirconium oxides to arsenate: Surface complexation modeling study

Pengfei Shen; Siyuan Pan; Xianfeng Huang; Xiaolin Zhang

doi:10.1016/j.chemosphere.2023.140912

Nanoconfinement boosts affinity of hydrated zirconium oxides to arsenate: Surface complexation modeling study

Chemosphere. 2024 Feb:349:140912. doi: 10.1016/j.chemosphere.2023.140912. Epub 2023 Dec 7.

Authors

Pengfei Shen¹, Siyuan Pan¹, Xianfeng Huang², Xiaolin Zhang³

Affiliations

¹ State Key Laboratory of Pollution Control and Resource Reuse, School of Environment, Nanjing University, Nanjing, 210023, China.
² National and Local Joint Engineering Research Center for Ecological Treatment Technology of Urban Water Pollution, School of Life and Environmental Science, Wenzhou University, Wenzhou, 325035, China. Electronic address: xianfeng_huang@wzu.edu.cn.
³ State Key Laboratory of Pollution Control and Resource Reuse, School of Environment, Nanjing University, Nanjing, 210023, China; Research Center for Environmental Nanotechnology (ReCENT), Nanjing University, Nanjing, 210023, China. Electronic address: XLZhang@nju.edu.cn.

PMID: 38065259
DOI: 10.1016/j.chemosphere.2023.140912

Abstract

Nanoscale hydrated zirconium oxide (HZO) holds great potential in groundwater purification due to its ability to form inner-sphere coordination with arsenate. Despite being frequently used, especially as encapsulations in host materials for practical application in water treatment, the adsorption mechanisms of solutes on HZO are not appropriately explored, in particular for arsenate adsorption. In this study, we investigated the Zr-As coordination configuration and identified the most credible Zr-As configuration using surface complexation modeling (SCM), XPS and FT-IR analysis. The corresponding intrinsic coordination constants (K^intr) values was calculated by SCM, and the nanoconfinement effects were distinguished by comparing bare HZO with the HZO nanoparticles (NPs) encapsulated inside the strongly basic anion exchanger D201. Potentiometric titration suggests that the surface Zirconium hydroxyl groups (≡ZrOH) mainly exist in protonated form (≡ZrOH₂⁺). Batch adsorption experiments demonstrate that the D201 hosts could adsorb As(V) through ion exchange by the quaternary ammonium groups under the low ionic strength (≤0.01 M NaNO₃) and at pH > 6. The nanocomposite (HZO@D201) exhibits a higher adsorption capacity in a wide range of pH (3-10) and ionic strength (0.001-0.1 M NaNO₃) than bare HZO. SCM simulations reveal that the coordination configuration of diprotonated monodentate mononuclear (MM-H2) dominates at pH 3-6, while deprotonated bidentate binuclear (BB-H0) dominates at pH > 7. For each configuration, the intrinsic coordination constants (K^intr) of HZO@D201 (10^-0.66 and 10^-16.10, respectively) are significantly higher than those of bare HZO (10^-12.24 and 10^-44.42, respectively), indicating a superior chemical bonding affinity caused by nanoconfinement. The obtained K^intr values are used to predict arsenate adsorption isotherms in pH 3 and 9, and the results align with the SCM simulation outcomes. This study may offer a feasible method for investigating the nanoconfinement effect of emerging nanocomposite adsorbents from a thermodynamic perspective, and provide reference coordination equilibrium constants of HZO for research and practical application.

Keywords: Chemical bonding affinity; Coordination constant; Electrostatic attraction; Nanocomposite; Surface inner-sphere coordination.

MeSH terms

Adsorption
Arsenates*
Hydrogen-Ion Concentration
Oxides
Spectroscopy, Fourier Transform Infrared
Water Pollutants, Chemical* / analysis
Zirconium

Substances

arsenic acid
Arsenates
zirconium oxide
Zirconium
Water Pollutants, Chemical
Oxides