Review of surface water interactions with metal oxide nanoparticles
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FOCUS ISSUE
UNDERSTANDING WATER-OXIDE INTERFACES TO HARNESS NEW PROCESSES AND TECHNOLOGIES
Review of surface water interactions with metal oxide nanoparticles Jason J. Calvin1, Peter F. Rosen1, Nancy L. Ross2, Alexandra Navrotsky3, Brian F. Woodfield1,a) 1
Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602, USA Department of Geosciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA 3 Peter A. Rock Thermochemistry Laboratory and NEAT ORU, University of California Davis, Davis, California 95616, USA a) Address all correspondence to this author. e-mail: brian_woodfi[email protected] 2
Received: 5 September 2018; accepted: 21 November 2018
Surface water can affect the properties of metal oxide nanoparticles. Investigations on several systems revealed that nanoparticles have different thermodynamic properties than their bulk counterparts due to adsorbed water on their surfaces. Some thermodynamically metastable phases of bulk metal oxides become stable when reduced to the nanoscale, partially due to interactions between high energy surfaces and surface water. Water adsorption microcalorimetry and high-temperature oxide melt solution calorimetry, low-temperature specific heat calorimetry, and inelastic neutron scattering are used to understand the interactions of surface water with metal oxide nanoparticles. Computational methods, such as molecular dynamics simulations and density functional theory calculations, have been used to study these interactions. Investigations on titania, cassiterite, and alumina illustrate the insights gained by these measurements. The energetics of water on metal oxide surfaces are different from those of either liquid water or hexagonal ice, and there is substantial variation in water interactions on different metal oxide surfaces.
Introduction Nanoparticles often have properties different from their bulk counterparts, and novel nanoparticle synthetic techniques have created unique materials for new applications. For example, nanoparticle systems, such as fluorescing quantum dots or photovoltaic semiconductors with tunable band gaps, demonstrate quantum effects on a macroscopic scale [1, 2, 3]. Other useful properties of nanoparticles include their high surfacearea-to-volume ratio, which has a wide range of applications in heterogeneous catalysis [4]. Significant progress has been made in studying the physics, chemistry, and stability of the surfaces of nanoparticles to gain more knowledge about their potential uses. Most metal oxides can be synthesized as nanoparticles, and several of these oxides exist in a variety of crystalline polymorphs, many with unique properties. For example, c-Al2O3 nanoparticles are excellent catalyst supports due to large surface area, large pore volume, and moderate to high acid site concentration [5], while the thermally stable a-Al2O3 nanoparticles with little porosity are less favorable as catalyst
ª Materials Research Society 2019
supports but have applications in the ceramics industry [
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