Interaction of Zinc Oxide Nanoparticles with Water: Implications for Catalytic Activity

Takat B. Rawal; Ali Ozcan; Shih Hsien Liu; Sai Venkatesh Pingali; Oguz Akbilgic; Laurene Tetard; Hugh O'Neill; Swadeshmukul Santra; Loukas Petridis

doi:10.1021/acsanm.9b00714

Interaction of Zinc Oxide Nanoparticles with Water: Implications for Catalytic Activity

Takat B. Rawal, Ali Ozcan, Shih Hsien Liu, Sai Venkatesh Pingali, Oguz Akbilgic, Laurene Tetard, Hugh O'Neill, Swadeshmukul Santra, Loukas Petridis

Biological Labeling and Scattering

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

35 Scopus citations

Abstract

Novel technological applications in catalysis and bactericidal formulation have emerged for zinc oxide (ZnO) nanoparticles owing to their ability to generate reactive oxygen species by fostering H₂O dissociation. Rational improvement of those properties requires a mechanistic understanding of ZnO nanoparticle reactivity, which is currently lacking. Here, we determine the structural and electronic properties of nanometer-sized ZnO, determine the binding energetics of H₂O adsorption, and compare to an extended macroscopic surface. We show that the electronic density of states of ZnO nanoparticles is size-dependent, exhibiting a decreasing bandgap with the increase of nanoparticle diameter. The electronic states near the Fermi energy dominantly arise from O 2p states, which are spatially localized on "reactive" surface O atoms on the nanoparticle edges that are doubly coordinated. The frontier electronic states localized at the low coordinated atoms induce a spontaneous dissociation of H₂O at the nanoparticle edges. The surface Zn and O atoms have inhomogeneous electronic and geometrical/topological properties, thus providing nonequivalent sites for dissociative and molecular H₂O adsorption. The free energy of H₂O binding is dominated by the electronic DFT interaction energy, which is site-dependent and correlated with the Bader charge of surface Zn atom. Entropy is found to stabilize the bound form, because the increase in the vibrational contribution is greater than the decrease in the translational and rotational contribution, whereas solvation stabilizes the unbound state. The absence of rough edges on an extended, macroscopic ZnO surface prevents spontaneous dissociation of a single H₂O. This study underlies the importance of coupling geometrical and electronic degrees of freedom in determining the reactivity of nanoparticles and provides a simple elucidation of the superior catalytic activity of ZnO nanoparticles compared to ZnO in macroscopic forms.

Original language	English
Pages (from-to)	4257-4266
Number of pages	10
Journal	ACS Applied Nano Materials
Volume	2
Issue number	12
DOIs	https://doi.org/10.1021/acsanm.9b00714
State	Published - Jul 26 2019

Funding

This work is supported by U.S. Department of Agriculture (USDA) National Institute of Food and Agriculture (NIFA) under grant FLAW-2014-10120. Small-angle neutron scattering experiments were performed on the Bio-SANS (CG-3) instrument, operated by the Center for Structural Molecular Biology (CSMB) under Contract FWP ERKP291, supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, using the Oak Ridge High Flux Isotope Reactor that is sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. AO, LT, and SS acknowledge technical support from the UCF Materials Innovation for Sustainable Agriculture (MISA) center.

Funders	Funder number
Center for Structural Molecular Biology	FWP ERKP291
MISA
Office of Basic Energy Sciences
Office of Biological and Environmental Research
Scientific User Facilities Division
UCF Materials Innovation for Sustainable Agriculture
U.S. Department of Energy
U.S. Department of Agriculture
National Institute of Food and Agriculture	CG-3, FLAW-2014-10120
Office of Science

Keywords

ZnO
catalysis
zinc oxide

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10.1021/acsanm.9b00714

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title = "Interaction of Zinc Oxide Nanoparticles with Water: Implications for Catalytic Activity",

abstract = "Novel technological applications in catalysis and bactericidal formulation have emerged for zinc oxide (ZnO) nanoparticles owing to their ability to generate reactive oxygen species by fostering H2O dissociation. Rational improvement of those properties requires a mechanistic understanding of ZnO nanoparticle reactivity, which is currently lacking. Here, we determine the structural and electronic properties of nanometer-sized ZnO, determine the binding energetics of H2O adsorption, and compare to an extended macroscopic surface. We show that the electronic density of states of ZnO nanoparticles is size-dependent, exhibiting a decreasing bandgap with the increase of nanoparticle diameter. The electronic states near the Fermi energy dominantly arise from O 2p states, which are spatially localized on {"}reactive{"} surface O atoms on the nanoparticle edges that are doubly coordinated. The frontier electronic states localized at the low coordinated atoms induce a spontaneous dissociation of H2O at the nanoparticle edges. The surface Zn and O atoms have inhomogeneous electronic and geometrical/topological properties, thus providing nonequivalent sites for dissociative and molecular H2O adsorption. The free energy of H2O binding is dominated by the electronic DFT interaction energy, which is site-dependent and correlated with the Bader charge of surface Zn atom. Entropy is found to stabilize the bound form, because the increase in the vibrational contribution is greater than the decrease in the translational and rotational contribution, whereas solvation stabilizes the unbound state. The absence of rough edges on an extended, macroscopic ZnO surface prevents spontaneous dissociation of a single H2O. This study underlies the importance of coupling geometrical and electronic degrees of freedom in determining the reactivity of nanoparticles and provides a simple elucidation of the superior catalytic activity of ZnO nanoparticles compared to ZnO in macroscopic forms.",

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T2 - Implications for Catalytic Activity

AU - Rawal, Takat B.

AU - Ozcan, Ali

AU - Liu, Shih Hsien

AU - Pingali, Sai Venkatesh

AU - Akbilgic, Oguz

AU - Tetard, Laurene

AU - O'Neill, Hugh

AU - Santra, Swadeshmukul

AU - Petridis, Loukas

PY - 2019/7/26

Y1 - 2019/7/26

N2 - Novel technological applications in catalysis and bactericidal formulation have emerged for zinc oxide (ZnO) nanoparticles owing to their ability to generate reactive oxygen species by fostering H2O dissociation. Rational improvement of those properties requires a mechanistic understanding of ZnO nanoparticle reactivity, which is currently lacking. Here, we determine the structural and electronic properties of nanometer-sized ZnO, determine the binding energetics of H2O adsorption, and compare to an extended macroscopic surface. We show that the electronic density of states of ZnO nanoparticles is size-dependent, exhibiting a decreasing bandgap with the increase of nanoparticle diameter. The electronic states near the Fermi energy dominantly arise from O 2p states, which are spatially localized on "reactive" surface O atoms on the nanoparticle edges that are doubly coordinated. The frontier electronic states localized at the low coordinated atoms induce a spontaneous dissociation of H2O at the nanoparticle edges. The surface Zn and O atoms have inhomogeneous electronic and geometrical/topological properties, thus providing nonequivalent sites for dissociative and molecular H2O adsorption. The free energy of H2O binding is dominated by the electronic DFT interaction energy, which is site-dependent and correlated with the Bader charge of surface Zn atom. Entropy is found to stabilize the bound form, because the increase in the vibrational contribution is greater than the decrease in the translational and rotational contribution, whereas solvation stabilizes the unbound state. The absence of rough edges on an extended, macroscopic ZnO surface prevents spontaneous dissociation of a single H2O. This study underlies the importance of coupling geometrical and electronic degrees of freedom in determining the reactivity of nanoparticles and provides a simple elucidation of the superior catalytic activity of ZnO nanoparticles compared to ZnO in macroscopic forms.

AB - Novel technological applications in catalysis and bactericidal formulation have emerged for zinc oxide (ZnO) nanoparticles owing to their ability to generate reactive oxygen species by fostering H2O dissociation. Rational improvement of those properties requires a mechanistic understanding of ZnO nanoparticle reactivity, which is currently lacking. Here, we determine the structural and electronic properties of nanometer-sized ZnO, determine the binding energetics of H2O adsorption, and compare to an extended macroscopic surface. We show that the electronic density of states of ZnO nanoparticles is size-dependent, exhibiting a decreasing bandgap with the increase of nanoparticle diameter. The electronic states near the Fermi energy dominantly arise from O 2p states, which are spatially localized on "reactive" surface O atoms on the nanoparticle edges that are doubly coordinated. The frontier electronic states localized at the low coordinated atoms induce a spontaneous dissociation of H2O at the nanoparticle edges. The surface Zn and O atoms have inhomogeneous electronic and geometrical/topological properties, thus providing nonequivalent sites for dissociative and molecular H2O adsorption. The free energy of H2O binding is dominated by the electronic DFT interaction energy, which is site-dependent and correlated with the Bader charge of surface Zn atom. Entropy is found to stabilize the bound form, because the increase in the vibrational contribution is greater than the decrease in the translational and rotational contribution, whereas solvation stabilizes the unbound state. The absence of rough edges on an extended, macroscopic ZnO surface prevents spontaneous dissociation of a single H2O. This study underlies the importance of coupling geometrical and electronic degrees of freedom in determining the reactivity of nanoparticles and provides a simple elucidation of the superior catalytic activity of ZnO nanoparticles compared to ZnO in macroscopic forms.

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EP - 4266

JO - ACS Applied Nano Materials

JF - ACS Applied Nano Materials

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ER -

Interaction of Zinc Oxide Nanoparticles with Water: Implications for Catalytic Activity

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