Acidity constants and redox potentials of uranyl ions in hydrothermal solutions

Xiandong Liu*, Jun Cheng, Mengjia He, Xiancai Lu, Rucheng Wang

*Corresponding author for this work

Research output: Contribution to journalArticle

4 Citations (Scopus)
6 Downloads (Pure)

Abstract

We report a first principles molecular dynamics (FPMD) study of the structures, acidity constants (pK(a)) and redox potentials (E-0) of uranyl (UO22+) from ambient conditions to 573 K. It is found that UO22+ keeps five coordination up to 573 K whereas UO2+ transforms from 5 to 4-coordinate as temperature increases to 573 K. The FPMD-based vertical energy gap method is used to derive pK(a)s and E(0)s. The method is validated by comparing with available experimental data (for E0 under the ambient conditions and for pKas from ambient conditions to 367 K), with an uncertainty of 1-2 pKa units and 0.2 V for pK(a) and E-0. The encouraging results demonstrate that the method may be used to predict the pH-Eh diagrams of f-block elements under the conditions of hydrothermal solutions. The results show that the acidity constants of uranyl decrease with temperature and are lower than 3.0 when the temperature is above 473 K, indicating that hydrolytic forms are dominant for U(VI) in the near neutral pH range. The reduction potential increases with temperature, indicating that the reduced state is more significant at higher temperatures.

Original languageEnglish
Pages (from-to)26040-26048
Number of pages9
JournalPhysical Chemistry Chemical Physics
Volume18
Issue number37
Early online date24 Aug 2016
DOIs
Publication statusPublished - 7 Oct 2016

Keywords

  • DENSITY-FUNCTIONAL THEORY
  • 1ST-PRINCIPLES MOLECULAR-DYNAMICS
  • TRANSITION-METAL CATIONS
  • AQUEOUS-SOLUTION
  • FREE-ENERGY
  • COMPUTATIONAL ELECTROCHEMISTRY
  • THERMODYNAMIC PROPERTIES
  • HYDROLYSIS CONSTANTS
  • ELECTRONIC-STRUCTURE
  • CHLORO COMPLEXES

Cite this

Acidity constants and redox potentials of uranyl ions in hydrothermal solutions. / Liu, Xiandong; Cheng, Jun; He, Mengjia; Lu, Xiancai; Wang, Rucheng.

In: Physical Chemistry Chemical Physics, Vol. 18, No. 37, 07.10.2016, p. 26040-26048.

Research output: Contribution to journalArticle

Liu, Xiandong ; Cheng, Jun ; He, Mengjia ; Lu, Xiancai ; Wang, Rucheng. / Acidity constants and redox potentials of uranyl ions in hydrothermal solutions. In: Physical Chemistry Chemical Physics. 2016 ; Vol. 18, No. 37. pp. 26040-26048.
@article{109db1c22af7454eb1dd88de8dde0781,
title = "Acidity constants and redox potentials of uranyl ions in hydrothermal solutions",
abstract = "We report a first principles molecular dynamics (FPMD) study of the structures, acidity constants (pK(a)) and redox potentials (E-0) of uranyl (UO22+) from ambient conditions to 573 K. It is found that UO22+ keeps five coordination up to 573 K whereas UO2+ transforms from 5 to 4-coordinate as temperature increases to 573 K. The FPMD-based vertical energy gap method is used to derive pK(a)s and E(0)s. The method is validated by comparing with available experimental data (for E0 under the ambient conditions and for pKas from ambient conditions to 367 K), with an uncertainty of 1-2 pKa units and 0.2 V for pK(a) and E-0. The encouraging results demonstrate that the method may be used to predict the pH-Eh diagrams of f-block elements under the conditions of hydrothermal solutions. The results show that the acidity constants of uranyl decrease with temperature and are lower than 3.0 when the temperature is above 473 K, indicating that hydrolytic forms are dominant for U(VI) in the near neutral pH range. The reduction potential increases with temperature, indicating that the reduced state is more significant at higher temperatures.",
keywords = "DENSITY-FUNCTIONAL THEORY, 1ST-PRINCIPLES MOLECULAR-DYNAMICS, TRANSITION-METAL CATIONS, AQUEOUS-SOLUTION, FREE-ENERGY, COMPUTATIONAL ELECTROCHEMISTRY, THERMODYNAMIC PROPERTIES, HYDROLYSIS CONSTANTS, ELECTRONIC-STRUCTURE, CHLORO COMPLEXES",
author = "Xiandong Liu and Jun Cheng and Mengjia He and Xiancai Lu and Rucheng Wang",
note = "Acknowledgements We thank Matthias Krack for supplying us with the pseudopotential and basis sets for U. We acknowledge the National Science Foundation of China (No. 41222015, 41273074, 41572027 and 21373166), Special Program for Applied Research on Super Computation of the NSFC-Guangdong Joint Fund (the second phase), the Foundation for the Author of National Excellent Doctoral Dissertation of PR China (No. 201228), Newton International Fellowship Program and the financial support from the State Key Laboratory at Nanjing University. We are grateful to the High Performance Computing Center of Nanjing University for allowing us to use the IBM Blade cluster system. Open access via RSC Gold 4 Gold.",
year = "2016",
month = "10",
day = "7",
doi = "10.1039/c6cp03469a",
language = "English",
volume = "18",
pages = "26040--26048",
journal = "Physical Chemistry Chemical Physics",
issn = "1463-9076",
publisher = "ROYAL SOC CHEMISTRY",
number = "37",

}

TY - JOUR

T1 - Acidity constants and redox potentials of uranyl ions in hydrothermal solutions

AU - Liu, Xiandong

AU - Cheng, Jun

AU - He, Mengjia

AU - Lu, Xiancai

AU - Wang, Rucheng

N1 - Acknowledgements We thank Matthias Krack for supplying us with the pseudopotential and basis sets for U. We acknowledge the National Science Foundation of China (No. 41222015, 41273074, 41572027 and 21373166), Special Program for Applied Research on Super Computation of the NSFC-Guangdong Joint Fund (the second phase), the Foundation for the Author of National Excellent Doctoral Dissertation of PR China (No. 201228), Newton International Fellowship Program and the financial support from the State Key Laboratory at Nanjing University. We are grateful to the High Performance Computing Center of Nanjing University for allowing us to use the IBM Blade cluster system. Open access via RSC Gold 4 Gold.

PY - 2016/10/7

Y1 - 2016/10/7

N2 - We report a first principles molecular dynamics (FPMD) study of the structures, acidity constants (pK(a)) and redox potentials (E-0) of uranyl (UO22+) from ambient conditions to 573 K. It is found that UO22+ keeps five coordination up to 573 K whereas UO2+ transforms from 5 to 4-coordinate as temperature increases to 573 K. The FPMD-based vertical energy gap method is used to derive pK(a)s and E(0)s. The method is validated by comparing with available experimental data (for E0 under the ambient conditions and for pKas from ambient conditions to 367 K), with an uncertainty of 1-2 pKa units and 0.2 V for pK(a) and E-0. The encouraging results demonstrate that the method may be used to predict the pH-Eh diagrams of f-block elements under the conditions of hydrothermal solutions. The results show that the acidity constants of uranyl decrease with temperature and are lower than 3.0 when the temperature is above 473 K, indicating that hydrolytic forms are dominant for U(VI) in the near neutral pH range. The reduction potential increases with temperature, indicating that the reduced state is more significant at higher temperatures.

AB - We report a first principles molecular dynamics (FPMD) study of the structures, acidity constants (pK(a)) and redox potentials (E-0) of uranyl (UO22+) from ambient conditions to 573 K. It is found that UO22+ keeps five coordination up to 573 K whereas UO2+ transforms from 5 to 4-coordinate as temperature increases to 573 K. The FPMD-based vertical energy gap method is used to derive pK(a)s and E(0)s. The method is validated by comparing with available experimental data (for E0 under the ambient conditions and for pKas from ambient conditions to 367 K), with an uncertainty of 1-2 pKa units and 0.2 V for pK(a) and E-0. The encouraging results demonstrate that the method may be used to predict the pH-Eh diagrams of f-block elements under the conditions of hydrothermal solutions. The results show that the acidity constants of uranyl decrease with temperature and are lower than 3.0 when the temperature is above 473 K, indicating that hydrolytic forms are dominant for U(VI) in the near neutral pH range. The reduction potential increases with temperature, indicating that the reduced state is more significant at higher temperatures.

KW - DENSITY-FUNCTIONAL THEORY

KW - 1ST-PRINCIPLES MOLECULAR-DYNAMICS

KW - TRANSITION-METAL CATIONS

KW - AQUEOUS-SOLUTION

KW - FREE-ENERGY

KW - COMPUTATIONAL ELECTROCHEMISTRY

KW - THERMODYNAMIC PROPERTIES

KW - HYDROLYSIS CONSTANTS

KW - ELECTRONIC-STRUCTURE

KW - CHLORO COMPLEXES

U2 - 10.1039/c6cp03469a

DO - 10.1039/c6cp03469a

M3 - Article

VL - 18

SP - 26040

EP - 26048

JO - Physical Chemistry Chemical Physics

JF - Physical Chemistry Chemical Physics

SN - 1463-9076

IS - 37

ER -