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Bicrystalline Titania Photocatalyst for Reduction of CO2 to Solar Fuels
- 1. Bicrystalline Titania Photocatalyst for Reduction of CO2 to Solar Fuels Second Year Seminar UCSC Chemistry and Biochemistry November 16, 2016 A’Lester Allen
- 2. Walton Lighthouse in Santa Cruz
- 3. Agenda Motivating Questions Introduction Overview of Photocatalysis History and Popularization Photocatalytic Redox Paper of Interest Summary and Critiques 3
- 4. 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
- 5. Three Phases Rutile Anatase Brookite Mixed 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. 5 5
- 6. 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.com Zhao, H.; Liu, L.; Andino, J. M.; Li, Y. Journal of Materials Chemistry A 2013, 1 (28), 8209. 6 6
- 7. 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 7
- 8. New Materials for CO2 Photoreduction Yong Zhou*a,b, Wenguang Tua,b, and Zhigang Zou*b aKey Laboratory CO2 + 8H+ + 8e- CH4 + 2H2O Eo reduction = -0.24V H2O ½ O2 + 2H+ + 2e- Eo oxidation = 0.82V Theory of TiO2 Photocatalysis Schematic, Standard Reduction Potentials, Band Gap 8 Mixed phase TiO2 exhibits band bending
- 9. Paper of Interest Zhao, H.; Liu, L.; Andino, J. M.; Li, Y. Journal of Materials Chemistry A 2013, 1 (28), 8209. 9
- 10. Overview 1. Targeted enhancing base TiO2 with a polymorphous mixture. 2. Demonstrated a hydrothermal method to control brookite composition 3. 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 photoreactor 3. 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
- 11. 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 0 A96B4 0.25 96 4 A75B25 0.5 75 25 A50B50 1 50 50 A37B63 1.5 37 63 B100 7 0 100 12
- 12. 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 13
- 13. Zhao, H.; Liu, L.; Andino, J. M.; Li, Y. Journal of Materials Chemistry A 2013, 1 (28), 8209. Chemical Identification Raman Spectroscopy A A A B B B B B B B 14
- 14. a) Pure anatase b) 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 15
- 15. 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 phase c) Lattice spacing of anatase at the interface with brookite matched 16
- 16. 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. 17
- 17. 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 Sample Absorption Edge (nm) Li et al. Band Gap (eV) Literature Band Gap (eV) A100 402 3.08 3.29 A96B4 398 3.12 A75B25 394 3.15 A50B50 394 3.15 A37B63 388 3.20 B100 386 3.22 ~3.5 Commercial P25 - - ~3.05 Rutile - - 3.05 18
- 18. Reaction chamber Y. Izumi / Coordination Chemistry Reviews 257 (2013) 171– 186 What is the photocatalytic activity? Photocatalytic Activity 19
- 19. 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 20
- 20. 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 21
- 21. 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 22
- 22. 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 23
- 23. Summary
- 24. 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 25
- 25. Conclusion Questions 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?
- 26. 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
- 27. Questions?
- 29. Motivation Carbon Dioxide vs Water Why not Hydrogen instead of Methane? 𝐻2 𝑔 + 1 2 𝑂2 𝑔 → 𝐻2 𝑂 𝑙 Δ𝐻 𝑜 = −286kJ Industrial H2 Synthesis 𝐶𝐻4 𝑔 + 𝐻2 𝑂 𝑔 → 3𝐻2 𝑔 + 𝐶𝑂 𝑔 Δ𝐻 𝑜 = 206kJ In comparison Formation of 3 mol H2 from water splitting Δ𝐻 𝑜 = 858kJ Combustion of Methane 𝐶𝐻4 𝑔 + 𝑂2 𝑔 → 𝐶𝑂2 𝑔 + 2𝐻2 𝑂 𝑙 Δ𝐻 𝑜 = −891kJ 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.
- 30. “This plot is courtesy of the National Renewable Energy Laboratory, Golden, CO.” Context - NREL 30
- 31. 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
- 32. 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.
- 33. 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
- 34. Photoreactor Set-up Catal. Sci. Technol., 2012, 2, 2558–2568
- 35. Other CO2 Reduction Products New Materials for CO2 Photoreduction Yong Zhou*a,b, Wenguang Tua,b, and Zhigang Zou*b aKey Laboratory
- 36. 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. Characterization Surface Properties
- 37. 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
- 38. Characterization Oxygen 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
- 39. Urea Sprectra Raman Surmacki, J.; Wroński, P.; Szadkowska-Nicze, M.; Abramczyk, H. Chemical Physics Letters 2013, 566, 54–59.
- 40. Applications of TiO2 Solar Cells Typical Layers of a Solar Cell Plexcore OS 2100 . Product of Plextronics, Inc. U.S. Patent 6,166,172
Editor's Notes
- The motivation for this talk is presenting work that progresses technology to world where we could utilize more solar energy. There is enough energy hitting the surface of the earth to power the world. Also industrialization has added carbon dioxide to the environment at a rate that is over 4 billion times the natural rate. much sunlight hits the earth each day. In fact The energy from the sun that reaches the Earth in 1 h is 9000 times (4.3×1020 J h−1) the energy consumed on the Earth in 1 h in 2001 (4.7×1016 J h−1). Enough to power the earth for a year. Sun Liu Yang JACS 2011, 133, 19306–19309 Give details Solar energy is, among various renewable energy sources, the largest energy source that would ultimately solve the terawatt energy challenge.1 Because of its intermittency and daily and seasonal variation, solar energy must be captured, converted, and stored for use upon demand. Storing solar energy directly in highenergy chemical bonds, such as solarwater splitting to hydrogen and oxygen, is one of the most attractive approaches.2 A single semiconductormay be used to achieve overall solar water splitting.However, because of the large overpotentials associated with the sluggish multielectron-transfer kinetics at semiconductorelectrolyte interfaces, this generally requires semiconductors having large band gaps that poorly match the solar spectrum, resulting in low efficiency.3 This problem may be overcome by using two small-band-gap semiconductors having a Z-scheme configuration (i.e., one as the photocathode for hydrogen evolution and the other as the photoanode for oxygen evolution), which closely mimics nature’s photosynthesis.4
- What are the steps needed to accomplish the goal of society eating all the ice cream in the world without gaining weight (analogy for harvesting solar energy – using so much power without damaging the environment)
- TiO2 is cheap, durable and easily modified. There are 3 Phases Anatase is the most active photocatalyst, rutile is the least active because fast recombination of electron and holes, brookite is least researched because it has historically been hard to synthesize. But brookite has been heavily theorized to have a higher photocatalytic activity than both anatase and rutile Each plane has different surface activity. P25 is commercially available and the benchmark. Whenever a paper reports using TiO2, the majority of time, they start with P25 Other mixtures haven’t been researched, thus The relationship between phase and photocatalytic activity is unclear.
- Another aspect of this talk is the novel application of mixedphase TiO2 to CO2 reduction. Chlorophyll of plants is a type of photocatalyst. Photocatalysis compared to photosynthesis, in which chlorophyll captures sunlight to turn water and carbon dioxide into oxygen and glucose, photocatalysis creates strong oxidation agent to breakdown any organic matter to carbon dioxide and water in the presence of photocatalyst, light and water
- Discovery took place at University of Tokyo N-type TiO2 (anode) was irradiated with a platinum catalyst (cathode) Honda and Fujishima used n-type TiO2 as the anode and Pt as the cathode. When the TiO2 photocatlyst was illuminated under short circuit conditions, hydrogen was evolved at the Pt electrode Todai aka University of Tokyo has a really good track record with catalysis, but there were published attempts working with
- From a thermodynamic point of view, an efficient photocatalyst should have a more negative Conduction Band Energy compared to the reduction potentials of CO2
- Reduction of CO2 is much more difficult than reduction of protons because:
- Proposed using a mixture of phases of TiO2 as the photocatalyst Novel method of controlling brookite composition Revisit Questions
- Varied Urea Concentration to control brookite composition
- Differeing ratios of brooite confirmed by XRD. Fig a shows XRD data where the the brookite phase composition is demonstrated to grow while the anatase peaks disappear Fig. 1b shows the Rietveld refinement used to result of A50B50 as an example. It can be observed that all the black solid fitting lines of the Rietveld refinement match the experimental XRD data (blue dots) very well. The low fluctuation of the goodness of fitting (GOF) curve at the bottom indicates a high reliability of the Rietveld refinement method.
- Three spectra demonstrated the success of the synthesis. The pure phase compounds had characteristic peaks Anatase: 399, 519, 640cm-1 Brookite: 245, 320, 366, 637cm-1 The mixed phase material contained the peaks from its two components. (N-TiO2 (anatase) )peaks at 144 cm-1 Urea (NH2)2CO) peak at 1010cm
- Synthesis used urea to control the formation of brookite (add a slide about the formation of brookite) SEM shows the results where anatase are more spherical particles while brookite forms an n-orthotope (a 3D rectangle/ brick) structure. Brookite composition is dependent upon urea concentration There is a change in the surface morphology
- READ: The lattice fringe is a periodic fringe in a TEM image, which is formed by two waves; a transmitted wave exiting from a crystal and a diffracted wave from one lattice plane of the crystal. The spacing of the fringe corresponds to that of this lattice plane. Begin to explain interface using TEM and lattice planes. Found that B (210) and A (101) have the same lattice spacing which followed first principle calculations of that found that these two phases were the most identical and thus most probable interface for electron transfer for the mixed phase structure
- Zhao et al. compared their TEM data to a DFT calculation that found the equilibrium crystal structure of brookite. In short, Anatase 101 plane and Brookite 210 plane were found to be structurally similar meaning their lattice spacings are the same. The hypothesis is that since they are similar, they will have a good contact at the interface. Details of DFT: Electron-ion interactions were described by ultrasoft pseudopotentials,28 with electrons from O 2s, 2p and Ti 3s, 3p, 3d, 4s shells explicitly included in the calculations. Plane-wave basis set cutoffs for the smooth part of the wave functions and the augmented density were 25 and 200 Ry, respectively. For calculations on bulk brookite, a 233 k-point mesh was used to sample the Brillouin zone corresponding to the primitive unit cell, which contains eight TiO2 units. The optimized a, b, and c bulk lattice parameters are 9.140 9.166, 5.407 5.436, and 5.176 5.135 Å, respectively,
- An absorption edge, absorption discontinuity or absorption limit is a sharp discontinuity in the absorption spectrum of a substance. These discontinuities occur at wavelengths where the energy of an absorbed photon corresponds to an electronic transition or ionization potential. When the quantum energy of the incident radiation becomes smaller than the work required to eject an electron from one or other quantum states in the constituent absorbing atom the incident radiation ceases to be absorbed by that state. For example, incident radiation on an atom of a wavelength that has a corresponding energy just below the binding energy of the K shell electron in that atom cannot eject the K shell electron.[1]
- Photocatalytic activity measured in terms of CO2 reduction to CO Efficiency evaluated by measuring the production of products. The measure products of CO2 reduction are: CO (major) CH4 (minor) longer chain hydrocarbons (very minor) Used 100mg in a photoreactor Increased photocatalytic behavior typically achieved from co-dopants to increase the charge separation Here the two phase system increases this behavior
- A75B25 data The photocatalytic activity lasts for ~ 3 hrs
- DRIFTS is a sampling technique We see carbon dioxide, bidentate carbonate, and bicarbonate at the surface in the dark showing that titanium reacts with CO2 in the reaction chamber. When irradiated, we see mostly water at the surface. Sadly this paper ends the story on a cliffhanger. Had they shown the drifts data from another sample and there were different production rates of these intermediates, we could comment on the reaction mechanism. As of right now we can only speculate the mechanism.
- Methane production occurs at a less negative reduction potential but carbond monoxide production is a kinetically easier reaction. CH4 involves 8 electrons, various energetically uphill conformations, and 8 protons. Both (a The Sav´eant-proposed mechanism and) In Figure(b) the Hori-proposed mechanism for CO production that starts with a CO2-. The hori mechanism occurs at the surface and could be what we are seeing
- Zhao et al. concede to the existing point of view that mixtures of brookite anatase have higher photocatalytic efficiency by qualifying the CO and CO2 reduction efficiency of a two phase Titania. They hypothesize that anataase-brooktite heterojunctions enhance charge separation and state that the CB and VB are close and demonstrating through TEM and further showing the two phases have crystallographic phases that overlap allow for a good interface. Li et al. 1 exemplify their point by showing photocatalytic activity results 2 do a lot of theorizing using DFT calc to explain the empirical observation Li et al. thoroughly prove (using SEM , TEM, DFT, CO evolution) that mixed phase AB is better than A and B alone, but they just compare P25 to A25B75. There is no reason given why the photocatalyic activity of A75B25 is better than P25.
- Dhof H2O (l) = -286kJ; Dhof H2O (g) = -242kJ; Dhof CH4 (g) = -75kJ; Dhof CO (g) = -110.5kJ
- 13 TiO2(B) is mainly derived from the layered titanates. Therefore, the structure of TiO2(B) is similar to that of the layered precursor, which is composed of corrugated sheets consisting of both edges and corners shared TiO6 octahedra.33 These differences in lattice structures cause different mass densities and electronic band structures in different phase forms of TiO2. Thermodynamically, rutile is the most stable phase, while anatase, brookite, and TiO2(B) are the metastable ones. Rutile can be normally obtained after annealing the other three polymorphs at elevated temperatures.
- B100 and A37B63(not shown) were similar. A100, A96B4, A75B25 were similar Mesoporous means material containing pores with diameters between 2 and 50 nm Hysteresis - can be a dynamic lag between an input and an output that is state dependent. Explain Type IV isotherm and meaning and use to calculate pore size and SA based on BET theory Mass Flow Controller is the typical experimental apparatus.
- Reduction of CO2 is much more difficult than reduction of protons because: