Coupled Light Capture and Lattice Boltzmann Model of TiO 2 Micropillar Array for Water Purification
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.467
Coupled Light Capture and Lattice Boltzmann Model of TiO2 Micropillar Array for Water Purification Pegah S. Mirabedini1, Agnieszka Truskowska2, Duncan Z. Ashby3, Masaru P. Rao1,3&4, and P. Alex Greaney1&3 1
Materials Science and Engineering Program, University of California, Riverside, CA 92521, USA Scientific Computation Research Center, Rensselaer Polytechnic Institute, Troy, NY, 12180, USA 3 Department of Mechanical Engineering, University of California, Riverside, CA 92521, USA 4 Department of Bioengineering, University of California, Riverside, CA 92521, USA 2
ABSTRACT
TiO2 has been widely studied as a photocatalytic material due to its nontoxicity, chemical inertness, and high photocatalytic activity. Here, we explore the operational behavior of a novel TiO2 micropillars array being developed to use solar radiation to treat recycled wastewater in long-duration space missions. A Light Capture model was developed to model light absorption. The Lattice Boltzmann method was used to simulate water flow, and the finite element method was used to model waste mass transfer. INTRODUCTION Titanium dioxide (TiO2) is the most widely used material for photocatalytic degradation of organic compounds – with the purpose of removing pollutants from water – due to its high catalytic activity, long-term stability against photocorrosion and chemical corrosion, and low cost [1-3]. The most common phases of TiO2 include rutile and anatase with tetragonal structures and brookite with an orthorhombic structure. Among these phases, anatase has been found to have the highest photocatalytic activity because of its relatively high electron mobility [2,4]. Anatase with its wide bandgap of 3.2 eV is only photocatalytically active under ultraviolet (UV) irradiation [2,5]. For terrestrial applications this is problematic and has driven much research on enhancing the light capture and quantum efficiency of anatase based photocatalysts. In space however,
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free from the shielding of the earth’s atmosphere, the abundance of solar UV makes anatase TiO2 an attractive photocatalytic material. TiO2’s mechanism for water purification is through the generation of highly reactive hydroxyl radicals at the catalyst’s surface. Absorption of UV light generates photoexcited electron-hole pairs in the TiO2 that can diffuse to the free surface where they take part in oxidation and reduction reactions. The holes can react with water to dissociate it into its components, hydrogen (H +) and hydroxyl radicals (OH•). The generated OH• radicals can be used for the degradation of organic pollutants in water [1]. As the photocatalytic reactions happen at the surface of the photocatalyst, their efficiency is controlled by the fundamental surface propertie
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