Bicrystalline Titania Photocatalyst for Reduction of CO2 to Solar Fuels
Second Year SeminarUCSC Chemistry and Biochemistry
November 16, 2016A’Lester Allen
Walton Lighthouse in Santa Cruz
Agenda Motivating Questions Introduction
Overview of Photocatalysis History and Popularization Photocatalytic Redox
Paper of Interest Summary and Critiques
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Questions to Answer Major Question:
What benefit does a bicrystalline mixture (Anatase-Rutile or Anatase-Brookite) have over pure anatase TiO2 photocatalyst?
Related Questions: How does the position of the band gap of
polymorphous TiO2 affect photocatalytic activity?
What reactive species are formed during CO2 reduction?
How is photo-induced charge transfer affected by the interface between crystalline phases? 4
Three Phases Rutile Anatase BrookiteMixed Phases Degussa P25 most
widely used photocatalyst
Other mixtures have not been heavily researched
The relationship between phase and photocatalytic activity is unclear.
Overview of Titania (TiO2)
Rutile Anatase Brookite
(112) (100)(001) (110) (010)(011) (001)
(312) (110)(111) (101)
(101) (210)
Table 1. Structurally Similar active phases of TiO2 polymorphs.
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Overview of Titania (TiO2)Natural and Synthetic Photocatalysis
Novel application mixed phase anatase-brookite to CO2 reduction.
A photocatalyst absorbs light from UV, IR, or visible radiation and is involved in the transformation of reaction partners affecting the change in rate of a chemical reaction or its initiation.
http://www.abolinco.comZhao, H.; Liu, L.; Andino, J. M.; Li, Y. Journal of Materials Chemistry A 2013, 1 (28), 8209.
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First successful photoelectrochemical decomposition of water reported by Fujishima and Honda in 1972 They found when TiO2 was illuminated:
Hydrogen was evolved at the cathode
A. Fujishima and K. Honda, Nature, 238, 37 (1972).
Overview of Titania (TiO2)History
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New Materials for CO2 Photoreduction Yong Zhou*a,b, Wenguang Tua,b, and Zhigang Zou*b aKey Laboratory
CO2 + 8H+ + 8e- CH4 + 2H2O Eoreduction = -
0.24VH2O ½ O2 + 2H+ + 2e- Eooxidation =
0.82V
Theory of TiO2 PhotocatalysisSchematic, Standard Reduction Potentials, Band Gap
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Mixed phase TiO2 exhibits band bending
Paper of Interest
Zhao, H.; Liu, L.; Andino, J. M.; Li, Y. Journal of Materials Chemistry A 2013, 1 (28), 8209.
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Overview 1.Targeted enhancing base TiO2 with a
polymorphous mixture. 2.Demonstrated a hydrothermal method to
control brookite composition3.Characterized the success of their synthesis.
1. X-Ray Diffraction and Raman Spectroscopy (phase and chemical content)
2. Scanning Electron Microscopy (SEM) (surface morphology)
4.Analyzed the effect of mixed phase on:1. Band Gap using Ultraviolet/Visible Spectroscopy
(UV/Vis)2. Photocatalytic Activity using a photoreactor3. Reaction Intermediates using Diffuse Reflectance
Infrared Fourier Transform Spectroscopy (DRIFTS)Zhao, H.; Liu, L.; Andino, J. M.; Li, Y. Journal of Materials Chemistry A 2013, 1 (28), 8209. 10
Kandiel, T. A. et al. Chemistry of Materials Chem. Mater. 2010, 22 (6), 2050–2060.Zhao, H.; Liu, L.; Andino, J. M.; Li, Y. Journal of Materials Chemistry A 2013, 1 (28), 8209.http://www.kprblog.in/cse/sem1/hydrothermal/
Hydrothermal method
Titanium bis(ammonium lactate) dihydroxide precursor
Synthesis
Catalyst
Urea conc. (M)
Anatase (%)
Brookite (%)
A100 0.1 100 0A96B4 0.25 96 4A75B25 0.5 75 25A50B50 1 50 50A37B63 1.5 37 63B100 7 0 100
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Zhao, H.; Liu, L.; Andino, J. M.; Li, Y. Journal of Materials Chemistry A 2013, 1 (28), 8209.
What were the Phases present and their compositions?X-Ray Diffraction and Raman Spectroscopy
Urea conc. related to phase content
Rietveld refinement of A50B50
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Zhao, H.; Liu, L.; Andino, J. M.; Li, Y. Journal of Materials Chemistry A 2013, 1 (28), 8209.
Chemical IdentificationRaman Spectroscopy
A A
A
B BB B B
BB
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a) Pure anataseb) Anatase96Brookite4
c) Anatase75Brookite25
d) Anatase50Brookite50
e) Anatase63Brookite37
f) Pure brookite
Zhao, H.; Liu, L.; Andino, J. M.; Li, Y. Journal of Materials Chemistry A 2013, 1 (28), 8209.
How does the surface change?Scanning Electron Microscopy
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Zhao, H.; Liu, L.; Andino, J. M.; Li, Y. Journal of Materials Chemistry A 2013, 1 (28), 8209.
What happens at the interface?Transmission Electron Microscopy
TEM displayed the interface between anatase and brookite in an Anatase75Brookite25 sample.
Spacing of lattice fringe can be used to determine the lattice plane
a) Anatase – spherical particles
(5-10 nm across) brookite – rod like structure
(20nm wide, 60nm long)b) Region 1 shows overlap of phases
resulting in fuzzy lattice fringe Region 2 shows the planes present in each phasec) Lattice spacing of anatase at the interface with brookite matched
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Critique of Surface Interface Analysis
Compared results to ab initio study which found that: Brookite (210) [Fig. b] and anatase
(101) [Fig. c] have a similar shape
Zhao, H.; Liu, L.; Andino, J. M.; Li, Y. Journal of Materials Chemistry A 2013, 1 (28), 8209.Gong, X.-Q.; Selloni, A. Phys. Rev. B Physical Review B 2007, 76 (23).
Rutile Anatase Brookite (112) (100)
(001) (110) (010)(011) (001)
(312) (110)(111) (101)
(101) (210)structurally similar planes
Table 1. Structurally similar active phases of TiO2 polymorphs.
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Zhao, H.; Liu, L.; Andino, J. M.; Li, Y. Journal of Materials Chemistry A 2013, 1 (28), 8209.
Wang, B.; et al. T. Physical Chemistry Chemical Physics 2013, 15 (24), 9891.
How is the Band Gap affected?Ultraviolet/Visible Spectroscopy
SampleAbsorption Edge
(nm)
Li et al. Band Gap (eV)
Literature Band
Gap (eV)
A100 402 3.08 3.29A96B4 398 3.12A75B25 394 3.15A50B50 394 3.15A37B63 388 3.20B100 386 3.22 ~3.5
Commercial P25 - - ~3.05Rutile - - 3.05
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Reaction chamber
Y. Izumi / Coordination Chemistry Reviews 257 (2013) 171– 186
What is the photocatalytic activity?Photocatalytic Activity
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Zhao, H.; Liu, L.; Andino, J. M.; Li, Y. Journal of Materials Chemistry A 2013, 1 (28), 8209.
What is the photocatalytic activity?Photocatalytic Activity
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Zhao, H.; Liu, L.; Andino, J. M.; Li, Y. Journal of Materials Chemistry A 2013, 1 (28), 8209.
What is the photocatalytic activity?Photocatalytic Activity
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Why is CO produced over CH4?Reaction Intermediates measured by Diffuse Reflectance IR-FT Spectroscopy
Zhao, H.; Liu, L.; Andino, J. M.; Li, Y. Journal of Materials Chemistry A 2013, 1 (28), 8209.
Present in the dark: HCO3
- at 1220 and 1420cm-1
CO2- at 1250 and
1673cm-1
bidentate carbonate (b-CO3
2-) at 1570cm-1
Present when Irradiated: H2O at 1639cm-1
monodentate carbonate (m-CO3
2-at 1300 and 1540 cm-1
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Kumar, B.; et al. Annual Review of Physical Chemistry Annu. Rev. Phys. Chem. 2012, 63 (1), 541–569.Mino, L., et al. J. Phys. Chem. C The Journal of Physical Chemistry C 2014, 118 (43), 25016–25026.
Why is CO produced over CH4?Proposed Mechanisms
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Summary
Critique
Pros Demonstrate mixed
Anatase75 Brookite25 has superior photocatalytic activity
Verify theoretical brookite (210) - anatase (101) interface
Cons Begin a mechanistic
conversation but fail to make significant conclusions
No discussion why CO is the major product.
No discussion mention given to urea affecting results
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ConclusionQuestions Answered√ Was there any
enhancement from brookite?
√ Is anatase-brookite mixture better than anatase-rutile?
√ How does the band gap shift?
√ Which reactive intermediates are formed?
Questions Remaining? Which reactive
intermediates decrease photoactivity?
? What mechanism of CO2 reduction occurs?
? Do synergistic effects remain with doping, co-catalysts, different nanostructures?
Acknowledgements
Committee Members
Prof. David Kliger (chair)
Prof. Jin Z. Zhang (P.I.) Prof. Ilan Benjamin
Big Thanks Mauricio Rojas-
Andrade Gabriella Chan Longbo Li Rene Mercado Bin Yao Jeff Chern (for making
the unit cells) Zhanglab
Questions?
Supplemental Slides
MotivationCarbon Dioxide vs WaterWhy not Hydrogen instead of Methane?
Industrial H2 Synthesis In comparison
Formation of 3 mol H2 from water splitting
Combustion of Methane
Currently it’s still best to use methane as it integrates with current engines
Also The atmospheric CO2 rose125 ppm in the past 100 years.
Naturally rose 180-330 ppm over the past millions of years
Atkins, Peter, and Julio De Paula. "Atkins’ physical chemistry." New York(2006): 776-780.Ma, Yi, et al. "Titanium dioxide-based nanomaterials for photocatalytic fuel generations." Chemical reviews 114.19 (2014): 9987-10043.
“This plot is courtesy of the National Renewable Energy Laboratory, Golden, CO.”
Context - NREL
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Different of TiO2 Phases All four types of TiO2 consist
of TiO6 octahedra, but differ in the distortion of the octahedron units and share edges and corners in different manners
For anatase, octahedra. arranging in zigzag chains along {221} share four edges; in rutile, octahedra share only two edges and connect in linear chains parallel to {001};32 while in brookite both corners and edges are connected.
Figure 2. Crystalline structures of TiO2 in different phases: (a) anatase, (b) rutile, (c) brookite, and (d) TiO2(B).
Ma, Y.; Wang, X.; Jia, Y.; Chen, X.; Han, H.; Li, C. Chemical Reviews Chem. Rev.2014, 114 (19), 9987–10043.31
Methods of improving TiO2 photocatalyst Doping
Cation & anion Surface (Dye) sensitization Co-catalysts Band Gap engineering
Nanostructure Particle Size
Ma, Y.; Wang, X.; Jia, Y.; Chen, X.; Han, H.; Li, C. Chemical Reviews Chem. Rev.2014, 114 (19), 9987–10043.
Crystal Lattice Defects
By Gabe rosser at the English language Wikipedia, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=1466963
Defect Free Crystal Lattice
Schottky Defect
Frenkel Defect
Photoreactor Set-up
Catal. Sci. Technol., 2012, 2, 2558–2568
Other CO2 Reduction Products
New Materials for CO2 Photoreduction Yong Zhou*a,b, Wenguang Tua,b, and Zhigang Zou*b aKey Laboratory
N2 adsorption–desorption was used to find the surface area, pore size, and pore area.
Results showed a mesoporous structure.
Zhao, H.; Liu, L.; Andino, J. M.; Li, Y. Journal of Materials Chemistry A 2013, 1 (28), 8209.
CharacterizationSurface Properties
Adsorption Isotherm
Hysteresis loop a
dynamic lag between the input and an output.
The shape of the loop is path dependent.
Type IV Isotherm Explained
Type I saturate when a complete monolayer forms Type IV do not exhibit a saturation limit for a
monolayer but have a finite multi-layer formation corresponding to complete filling of the capillaries.
The adsorption terminates near to a relative pressure of unity.http://www.separationprocesses.com/Adsorption/AD_Chp01c.htm
CharacterizationOxygen Generation
Photoreactor was purged of O2. Background O2 and N2 still remain
Thus ratio is better measurement Results for Anatase 75Brookite25
sample Initial drop is due to the
reduction of O2
Steady is from the production of O2
Significance Confirms that O2 competes with
CO2 but O2 concentration is negligible
Confirms that reduction of CO2 occurs because counter redox reaction occurs
Urea Sprectra Raman
Surmacki, J.; Wroński, P.; Szadkowska-Nicze, M.; Abramczyk, H. Chemical Physics Letters 2013, 566, 54–59.
Applications of TiO2Solar Cells
Typical Layers of a Solar Cell
Plexcore OS 2100 . Product of Plextronics, Inc. U.S. Patent 6,166,172
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