Exploring Zn-based Compounds for Visible Light Induced ...€¦ · through synthesis of new...
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Exploring Zn-based Compounds for Visible Light Induced Photocatalysts Emily Nishiwaki, 1,2,3 Daichi Kato, 4 and Hiroshi Kageyama 4 1 College of Arts and Sciences, Cornell University, Ithaca, NY, USA 2 Department of Materials Science and Engineering, Case Western Reserve University, Cleveland, OH, USA 3 Nakatani RIES: Research and International Experience for Students Fellowship in Japan, Rice University, Houston, Texas, USA 4 Department of Energy and Hydrocarbon Chemistry, Kyoto University, Kyoto, Japan The implications of climate change urge the need for efficient alternative energy sources such as H 2 gas. H 2 gas can be produced by reducing and oxidizing (splitting) of water; however, this process is thermodynamically unfavorable. Many catalysts already exist that can utilize UV light to assist in the splitting of water, but compounds that can utilize visible light, which have a band gap of less than 3.0eV, are still being developed. Mixed anion compounds, which often have small band gaps, have great potential to split water with visible light. A variety of oxynitrides with perovskite structure and their derivatives, which have octahedral coordination, have proved to be successful visible light induced photocatalysts. However, one of the most efficient visible light induced photocatalysts is ZnO-GaN, which has a wurzite crystal structure, with tetrahedral coordination. It is thought that Zn-based mixed anion compounds are promising catalysts due to the Zn-N bonds that raise the energy of the valence band. Unfortunately, it is harder to derive new materials from this solid solution due to the inflexibility in the wurzite structure for chemical substitutions. This research project focuses on the advancement of the knowledge surrounding visible light induced photocatalysts with tetrahedral coordination through synthesis of new Zn-based compounds. Inspired by SrZnO 2 , synthesis of the new compound Sr(Zn (1-x) Ga x )O (1-x) N x was used as a route to understand tetrahedral photocatalysts and mixed anion compounds as a whole.
Transcript of Exploring Zn-based Compounds for Visible Light Induced ...€¦ · through synthesis of new...
Exploring Zn-based Compounds for Visible Light Induced Photocatalysts
Emily Nishiwaki,1,2,3 Daichi Kato,4 and Hiroshi Kageyama4 1College of Arts and Sciences, Cornell University, Ithaca, NY, USA
2Department of Materials Science and Engineering, Case Western Reserve University, Cleveland, OH, USA
3Nakatani RIES: Research and International Experience for Students Fellowship in Japan, Rice University, Houston, Texas, USA
4Department of Energy and Hydrocarbon Chemistry, Kyoto University, Kyoto, Japan
The implications of climate change urge the need for efficient alternative energy sources such as H2 gas. H2 gas can be produced by reducing and oxidizing (splitting) of water; however, this process is thermodynamically unfavorable. Many catalysts already exist that can utilize UV light to assist in the splitting of water, but compounds that can utilize visible light, which have a band gap of less than 3.0eV, are still being developed. Mixed anion compounds, which often have small band gaps, have great potential to split water with visible light. A variety of oxynitrides with perovskite structure and their derivatives, which have octahedral coordination, have proved to be successful visible light induced photocatalysts. However, one of the most efficient visible light induced photocatalysts is ZnO-GaN, which has a wurzite crystal structure, with tetrahedral coordination. It is thought that Zn-based mixed anion compounds are promising catalysts due to the Zn-N bonds that raise the energy of the valence band. Unfortunately, it is harder to derive new materials from this solid solution due to the inflexibility in the wurzite structure for chemical substitutions. This research project focuses on the advancement of the knowledge surrounding visible light induced photocatalysts with tetrahedral coordination through synthesis of new Zn-based compounds. Inspired by SrZnO2, synthesis of the new compound Sr(Zn(1-x)Gax)O(1-x)Nx was used as a route to understand tetrahedral photocatalysts and mixed anion compounds as a whole.
ExploringZn-BasedVisibleLightInducedPhotocatalystsEmilyNishiwaki,1,2,3 Daichi Kato,4 andHiroshiKageyama4
1CollegeofArtsandSciences,CornellUniversity,Ithaca,NY,USA2DepartmentofMaterialsScienceandEngineering,CaseWesternReserveUniversity,Cleveland,OH,USA
3NakataniRIES: ResearchandInternationalExperiencesforStudents Fellowship,RiceUniversity,Houston,Texas,USA4DepartmentofEnergyandHydrocarbonChemistry,KyotoUniversity,Kyoto,Japan
Contact:[email protected]
ObjectiveUnderstandhowoxynitride compounds with
tetrahedralcoordinationcanbeutilizedasvisiblelightinducedphotocatalysts.
TheoryandSynthesisMethodology
VisibleLightPhotocatalysts
ResultsandDiscussion
Acknowledgements
H2O+hvà H2 +½O2
• Catalyststhatcanutilizevisiblelight(b.g <3.0eV)areessentialforefficientH2production
• Mixedoxyanioncompoundshavesmallbandgaps
• Currentresearchfocusesonperovskite structureoxynitrides (octahedralcoordination)
Climatechangewillnotwaitforsciencetocatchup;efficientalternativeenergysourcesneedto
bedeveloped.
• ZnO-GaN hasasuitablebandgapandexhibitsefficientphotocatalyticactivity
• Zn-Nbondsraiseenergyofvalenceband
• Wurzite structure(tetrahedralcoordination)
Sr(Zn(1-x)Gax)O(2-x)Nx and LaZnONwereinvestigatedaspotentialvisiblelightinduced
photocatalysts.
SrO +(1-x)ZnO +xGaN x=0.1
(x/3)Sr3Ga2O6 +(1-x)SrZnO2+(x/6)Ga2O3 x=0.2
SpecialthankstoKato-san,Kageyama-sensei,andeverymemberoftheKageyama Laboratoryforan
amazingresearchexperience.
Thisresearchprojectwasconductedaspartofthe2017Nakatani RIESFellowshipfor(U.S./Japanese)StudentswithfundingfromtheNakatani Foundation.Formoreinformationsee http://nakatani-ries.rice.edu/.
• Investigatethechangeinbandgap• AnalyzetheSr phasepresent inthesample• Understandreasonbehinddrasticcolorchange
Sr(Zn(1-x)Gax)O(2-x)Nx
½La2O3 +ZnO x=0.1
LaZnON
ThoughtProcessforConstructingNewMixedOxyanions
• Basestructure
• ChargeNeutrality
• Radiusofsubstitutedcation
SrZnO(2-x)Nx
+2+2-2-3
Sr(Zn(1-x)Gax)O(2-x)Nx
+2+2+3-2-3SrZnO2
+2-2-2
NC=0 NC=- x NC=0
Maeda,Ketal.JACS,2005, 1278289-8287
• AmbiguouswhetherSr4Ga2O7 orSrZnO2 wasproduced• Latticeparametersdidnotchangeà nosubstitution
AttemptedsynthesiswithNH3 gasflow;unclearpeaksformed.
SrO +(1-x)ZnO +½xGa2O3 x=0.1
Sr(OH)2 isformed
Highpressuresynthesis;peaksdidnotshift.
Latticeparametersdidnotchangeà nosubstitution
(1-x)ZnO +xGaNà (ZnO)(1-x)(GaN)x x=0.25SrO +(ZnO)(1-x)(GaN)x
MixedphasesofZnOGaN andSrZnO2.NoSrO peaks.
NH3 synthesisattwodifferenttemperatures;reactiondidnotoccur.
• RoughcrystalshigherSrcontent,smoothcrystalslowerSr content
• SrO isnotpresent,butlatticeparametersdidnotchange
• Darkgreentorosepink
cellgoeshere
Graphite
Sample
Pyrophyllite
BNorNaCl Sleeve
BNorNaCl cap
Mosheet
PyrocapwithSUSring
HighPressureCell
元素 質量濃度 原子数[%] 濃度[%]
NK 2.20 5.48OK 27.56 60.06ZnL 43.22 23.05GaL 6.49 3.25Sr L 20.52 8.16ﾄｰﾀﾙ 100.00
元素 質量濃度 原子数
[%] 濃度[%]NK 1.51 3.51OK 35.31 71.62ZnL 10.23 5.08GaL 1.90 0.88Sr L 51.05 18.91ﾄｰﾀﾙ 100.00
Sampleafterreaction(4.5GPa,1000°C).
HighPressuresynthesisofZnOGaN andSrOrequiresfurtherinvestigation.
FutureWork
a (Å) c (Å)ZnO-GaN 3.2411 5.2112
3GPa, 900°C 3.2393 5.21284.5GPa,1000°C 3.2404 5.2125
ComparingLatticeParameters
BandgapofsampleissmallerthanZnOGaN!
