Bicrystalline Titania Photocatalyst for Reduction of CO2 to Solar Fuels

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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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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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


How does the surface change?Scanning Electron Microscopy

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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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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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Why is CO produced over CH4?Reaction Intermediates measured by Diffuse Reflectance IR-FT Spectroscopy


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.


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

Bicrystalline Titania Photocatalyst for Reduction of CO2 to Solar Fuels

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