skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


  • NSF Public Access
  • Search Results
  • Mechanistic Insights into the Selectivity for Arsenic over Phosphate Adsorption by Fe 3+ -Cross-Linked Chitosan Using DFT
Title: Mechanistic Insights into the Selectivity for Arsenic over Phosphate Adsorption by Fe 3+ -Cross-Linked Chitosan Using DFT
Fe3+-cross-linked chitosan exhibits the potential for selectively adsorbing arsenic (As) over competing species, such as phosphate, for water remediation. However, the effective binding mechanisms, bond nature, and controlling factor(s) of the selectivity are poorly understood. This study employs ab initio calculations to examine the competitive binding of As(V), P(V), and As(III) to neat chitosan and Fe3+-chitosan. Neat chitosan fails to selectively bind As oxyanions, as all three oxyanions bind similarly via weak hydrogen bonds with preferences of P(V) = As(V) > As(III). Conversely, Fe3+-chitosan selectively binds As(V) over As(III) and P(V) with binding energies of −1.9, −1, and −1.8 eV for As(V), As(III), and P(V), respectively. The preferences are due to varying Fe3+–oxyanion donor–acceptor characteristics, forming covalent bonds with distinct strengths (Fe–O bond ICOHP values: – 4.9 eV/bond for As(V), – 4.7 eV/bond for P(V), and −3.5 eV/bond for As(III)). Differences in pKa between As(V)/P(V) and As(III) preclude any preference for As(III) under typical environmental pH conditions. Furthermore, our calculations suggest that the binding selectivity of Fe3+-chitosan exhibits a pH dependence. These findings enhance our understanding of the Fe3+–oxyanion interaction crucial for preferential oxyanion binding using Fe3+-chitosan and provide a lens for further exploration into alternative transition-metal–chitosan combinations and coordination chemistries for applications in selective separations.  more » « less
Award ID(s):
2019435
PAR ID:
10519847
Author(s) / Creator(s):
;
Publisher / Repository:
ACS Publications
Date Published:
Journal Name:
The Journal of Physical Chemistry B
Volume:
128
Issue:
7
ISSN:
1520-6106
Page Range / eLocation ID:
1689 to 1699
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; (, The Journal of Physical Chemistry A)
    Ferrocene (Fc)/ferrocenium (Fc+)-decorated carbon nanotube electrode materials have shown promise for selectively adsorbing arsenic (As) over dissimilar anions like Cl– and ClO4–, and isostructural transition-metal oxyanions for water remediation; however, the competition between same-group oxyanions (such as arsenate vs phosphate) is underexplored and poorly understood. We use ab initio calculations to examine the competitive binding of As(V), P(V), and As(III) to Fc/Fc+ with and without functional substitutions (OH, SH, NH2, COOH, CH3, C2H5, NO2, and Cl). This work aims to understand factors that induce the selective binding of toxic arsenic over phosphate. We find that neat Fc cannot distinguish the three oxyanions because physical forces (electrostatics and dispersion) dominate the Fc-oxyanion interactions. However, combined oxidation and substitution effects enable selectivity for As(V) over P(V). Oxidation of Fc to Fc+ allows the formation of Fc+-oxyanion covalent bonds with varying donor–acceptor character depending on the oxyanion. Additionally, NH2 and SH groups that donate charge to the base Fc+ molecule and H-bond to oxyanion induce an energetic preference for As(V) over P(V) by −0.23 and −0.13 eV, respectively. Differences in pKa between As(V)/P(V) and As(III) preclude any preference for As(III) over the other anions. Using the calculated energetics, we predict the pH-dependent binding selectivity of functionalized ferrocenium. These findings demonstrate the challenges of Fc/Fc+-oxyanion interaction for selective binding and provide a path for identifying other molecules and substituents for efficient metallocene adsorbent design. 
    more » « less
  2. ; (, Chemical Communications)
    We report the activation of nitrogen-containing oxyanions using an oxygen-deficient polyoxovanadate–alkoxide cluster. Reduction of NO 2 1− and NO 3 1− results in near-quantitative oxygen atom transfer to the coordinatively unsaturated V III ion, and selective formation of NO. These results provide insight into possible mechanisms of oxyanion reduction by polyoxometalates. 
    more » « less
  3. ; ; ; ; ; (, Angewandte Chemie International Edition)
    Abstract Undirected C(sp3)−H functionalization reactions often follow site‐selectivity patterns that mirror the corresponding C−H bond dissociation energies (BDEs). This often results in the functionalization of weaker tertiary C−H bonds in the presence of stronger secondary and primary bonds. An important, contemporary challenge is the development of catalyst systems capable of selectively functionalizing stronger primary and secondary C−H bonds over tertiary and benzylic C−H sites. Herein, we report a Cu catalyst that exhibits a high degree of primary and secondary over tertiary C−H bond selectivity in the amidation of linear and cyclic hydrocarbons with aroyl azides ArC(O)N3. Mechanistic and DFT studies indicate that C−H amidation involves H‐atom abstraction from R‐H substrates by nitrene intermediates [Cu](κ2‐N,O‐NC(O)Ar) to provide carbon‐based radicals R.and copper(II)amide intermediates [CuII]‐NHC(O)Ar that subsequently capture radicals R.to form products R‐NHC(O)Ar. These studies reveal important catalyst features required to achieve primary and secondary C−H amidation selectivity in the absence of directing groups. 
    more » « less
  4. ; ; (, Water Environment Research)
    Abstract There is a strong impetus to establish a circular phosphorus economy by securing internally renewable phosphate (Pi) resources for use as agricultural fertilizers. Reversible Piadsorption technologies such as ion exchange can remove and recover Pifrom water/wastewater for reuse. However, existing reversible adsorbents cannot effectively discriminate against arsenate (As(V)) due to the similarity between As(V) and Pichemical structure. If As(V) is co‐recovered with Pi, the value of the recovered products for agricultural reuse is low. The objective of this study was to construct an immobilized phosphate‐binding protein (PBP)‐based Piremoval and recovery system and analyze its selectivity for Piadsorption in the presence of As(V). A range of conditions was tested, including independent, sequential, and simultaneous exposure of the two oxyanions to immobilized PBP (PBP resin). The purity of the recovered Piproduct was assessed after inducing controlled desorption of the adsorbed oxyanions at high pH (pH 12.5). Piconstituted more than 97% of the adsorbed oxyanions in the recovered product, even when As(V) was initially present at twofold higher concentrations than Pi. Therefore, PBP resin has potential to selectively remove Pi, as well as release high‐purity Pifree of As(V) contamination suitable for subsequent agricultural reuse. Practitioner pointsExisting reversible phosphate (Pi) adsorbents cannot effectively discriminate against arsenate (As(V)) due to the similarity in their chemical structure.Co‐recovery of As(V) with Pican reduce the recovered product's reuse as a fertilizer.An immobilized phosphate‐binding protein (PBP)‐based system can be highly selective for Pieven in the presence of As(V).Piconstituted more than 97% of the recovered product, even when As(V) was present at 2‐fold higher concentrations than Pi.Immobilized PBP offers advantages over existing Piadsorbents by providing high‐purity Piproducts free of As(V) contamination for reuse. 
    more » « less
  5. ; (, The Journal of Physical Chemistry A)
    The vibrational structure and binding motifs of vanadium cation-ethane clusters, V(+)(C2H6)n, for n = 1 – 4 are probed using infrared photodissociation spectroscopy in the C-H stretching region (2550 – 3100 cm-1). Comparison of spectra to scaled harmonic frequency spectra obtained using density functional theory suggest that ethane exhibits two primary binding motifs when interacting with the vanadium cation, an end-on 𝜂2 configuration and a side-on configuration. The lower-energy side-on configuration predominates in smaller clusters, but the end-on configuration becomes important for larger clusters as it helps to maintain a roughly square planar geometry about the central vanadium. Proximate C-H bonds exhibit elongation and large red-shifts when compared to bare ethane, particularly in the case of the side-on isomer, which are underestimated by scaled harmonic frequency calculations, demonstrating initial effects of C-H bond activation. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email