15th ORIENTATION COURSE ON CATALYSISNOVEMBER 29- DECEMBER 16, 2014

NATIONAL CENTRE FOR CATALYSIS RESEARCH, IIT MADRASMISCONCEPTIONS IN PHOTOCATALYSIS, 9th Dec 2014

HARIPRASAD NARAYANANRESEARCH SCHOLAR

ENVIRONMENTAL CHEMISTRY LABSCHOOL OF ENVIRONMETAL STUDIES

COCHIN UNIVERSITY OF SCIENCE AND TECHNOLOGY

© 2013 American Chemical SocietyACS Catal. 2013, 3, 1486−1503

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PHOTOCATALYSIS

ANALYTICAL CHEMISTRY

CATALYSIS

MATERIAL SCIENCE

ELECTROCHEMISTRY

PHOTOCHEMISTRY

ENVIRONMENTAL TECHNOLOGY

SURFACE SCIENCE

INORGANIC CHEMISTRY

SEMICONDUCTOR PHYSICS

RADIATION CHEMISTRY

ORGANIC CHEMISTRY

Contributions to photocatalysis from various sub-disciplines of chemistry

What is meant by photocatalysis ?

“Photocatalysis is the acceleration of a photoreaction in the presence of catalyst”

“Photocatalysis is using light as a catalyst to increase the rate of a photoreaction”

Change in the rate of a chemical reaction or its initiation under the action of ultraviolet, visible or infrared radiation in the presence of a substance- the photocatalyst- that absorbs light and is involved in the chemical transformation of the reaction partners.

PAC, 207, 79, 293 (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 384

3© IUPAC

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Catalysis and Photocatalysis© J.W. NiemantsverdrietTU/e, Eindhoven, The Netherlandswww.catalysiscourse.com

Catalysis is the acceleration of a reaction that proceeds spontaneously from the viewpoint of thermodynamics by reducing the activation energy.

Photocatalysis includes reactions that accumulate energy , e.g., water splitting, photocatalysis cannot be included in the category of catalysis and therefore a photocatalyst cannot be called a ‘‘catalyst.’’

Honda Fujishima Effect• Undoubtedly an origin of research activity of photocatalysis but not an origin of photocatalysis in

the bibliographic sense.• First article related to photocatalysis was published in 1921 by Renz

5© 1972 Nature Publishing Group

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1921 C. Renz., Helv. Chim. Acta, 4: 961-968 1924 E. Baur, A. Perret, Helv. Chim. Acta, 7: 910-9151927 E. Baur, C. Neuweiler, Helv. Chim. Acta, 10: 901-9071932 C. Renz, Helv. Chim. Acta, 1077-10841937 C. F. Goodeve, J.A. Kichener, Trans. Far. Soc., 34 : 570-5791953 M.C . Markham, K.J. Laidler, J. Phys. Chem., 57: 363-3691955 M.C. Markham, J. Chem. Edu., 540-5431962 J.C. Kuriacose, M.C. Markham, J. Catal., 1: 498-5071964 W. Doerfler, K. Hauffe, J. Catal., 3, 156

W. Doerfler, K. Hauffe, J. Catal., 3, 1561966 H.P. Boehm, Adv. Catal., 16, 1791969 A. Fujishima, K. Honda, S.Kikuchi, Kogyo Kagaku Zasshi, 72, 1081970 M. Formenti, F. Juillet, S.J. Teichner, C.R. Acad. Sci. (Paris) 270,1381972 A. Fujishima, K. Honda, Nature, 238 : 37-38

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© 1972 Nature Publishing Group

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1. N. Serpone, A. V. Emeline, S. Horikoshi, V. N. Kuznetsov and V. K. Ryabchuk, On the genesis of heterogeneousphotocatalysis: a brief historical perspective in the period 1910 to the mid-1980s, Photochem. Photobiol. Sci., 2012, 11 , 1121.

2. S. J. Teichner, The origins of photocatalysis, J. Porous Mater., 2008, 15, 311–3143. K. Hashimoto, H. Irie and A. Fujishima, TiO2 Photocatalysis: A historical overview and future prospects, Jpn. J. Appl. Phys.,

2005, 44, 8269–8285.4. A. Fujishima, X. Zhangb and D. A. Tryk, TiO2 photocatalysis and related surface phenomena, Surf. Sci. Rep., 2008, 63, 515–

582.5. K. Tokumaru, The Research on photocatalysis in the early days, Koukagaku, 2005, 36, 153–162.6. N. Serpone, A. V. Emeline, Semiconductor Photocatalysis – Past, Present, and Future Outlook, J. Phys. Chem. Lett. 2012, 3,

673-6777. B. Viswanathan, M. Aulice Scibioh, Photoelectrochemistry : Principles and Practices, Narosa Publications, New Delhi, 2014.8. Kazuhito Hashimoto, Hiroshi Irie, Akira Fujishima, TiO2 Photocatalysis : A Historical Overview and Future Prospects, Jap. J.

App. Phy., 2005, 44(12), 8269-8285.

Recommended Reading Materials

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Relationship between band structure of semiconductor and redox potentials

Charge Separation• Electron and positive holes are spatially separated from their mutual attraction in

an intermediate stage of photocatalytic reaction.• Electron hole pair not produced after photoabsorption!!• Photoabsorption and electron hole generation are the same phenomenon• Most of them are using the term “Charge Separation” term for interpretation or

speculation of results without any valid proof.

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© 1995 American Chemical SocietyChem. Rev. 1995, 95, 735-758

• Charge separation is mainly due to space charge layer at the semiconductor electrolyte (solution) interface.

• The presence of space charge layer is least expected in the case of ordinary metal oxide photocatalysts.

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Solar Irradiation

Content of UV light in solar irradiation 3-5% (http://rredc.nrel.gov/solar/spectra/am1.5/ )

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Is Oxidation Ability of a Titania Photocatalyst High ?

© 1980 ElsevierD. E. Scaife, Sol. Energy 1980, 25, 41.

Yes. Then the question is how?

Nearly all metal oxides have the same oxidation ability, i.e., the same potential of the top of the valence band, the potential of the conduction band varies depending on the kind of metal. High reduction ability of titania to inject photoexcited electrons into molecular oxygen adsorbed

on the surface of photocatalysts. Titania has sufficient ability for electron utilization to drive

oxidation by positive holes (or intermediate species produced by them) of high oxidation ability

Other metal oxides with low photocatalytic activity may have lowreduction ability even though they also have high oxidationability

improvement of reduction ability and/or modification of the reduction mechanism of metal oxides other than titania may produce a photocatalyst with higher photocatalytic activity under visible light irradiation

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Participation of Hydroxyl Radicals and Other Active Species

Hydroxyl radical Superoxide anion radical Hydroperoxy radical Hydrogen peroxide Singlet oxygen

Pierre Pichat, Photocatalysis and Water Purification : From Fundamentals to Recent Applications, Wiley 2013

© 2013 Wiley-VCH Verlag GmbH & Co.KGaA, Boschstr. 12, 69469 Weinheim,Germany

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Use of Dyes as Model compounds© Springer Verlag 2012 Environ. Sci. Pollut. Res., (2012), 19, 3655–3665

DOI 10.1007/s11356-011-0697-8

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Photocatalytic Activity

RSC Adv., 2,3165-3172 (2012)

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Synergetic EffectWhen more than two kinds of photocatalysts are used as a mixture, the overall photocatalyticactivity exceeds the sum of activities of each photocatalyst

© 2013 Macmillan Publishers LimitedScanlon et al, Nature Materials 2013, 12, 798-801© 2014 Wiley

Wooyul Kim et al., Angew. Chem., 2014, 126, 1-7

© Elsevier 2011Inorganic Photochemistry

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© Springer Verlag 2012 Environ. Sci. Pollut. Res., (2012), 19, 3655–3665

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Hydrogen Production/ Water Splitting

The reaction mechanism depicted in Figure 1b illustrates quite nicely that due to the current doubling effect, at least half of the detected H2 gas that is generated in a system containing methanol as the sacrificial reagent is formed through the action of holes and not that of electrons!

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References1. Akira Fujishima, Kenichi Honda, Electrochemical Photolysis of Water at a Semiconductor Electrode, Nature, 238 (1972), 37 –

38.2. Lorette Pruden Childs, David F. Ollis, Is photocatalalysis Catalytic?, J. Catal., 66 (1980), 383-390.3. Bunsho Ohtani, Preparing Articles on Photocatalysis- Beyond the Illusions, Misconceptions, and Speculation, Chem.Lett., 37

(2008), 217-229.4. Bunsho Ohtani, Photocatalysis A to Z- What we know and what we do not know in a scientific sence, J.Photochem. Photobiol.

C Photochem. Rev., 11 (2010), 157-178.

5. Jean-Mary Hermann, Fundamentals and misconceptions in photocatalysis, J. Photo.chem. Photobiol. A Chem., 216, (2010),85-93.

6. Jean-Mary Hermann, Photocatalysis fundamentals revisited to avoid several misconceptions, App. Catal. B, Environ. , 99(2010), 461-468.

7. Bunsho Ohtani, Chapter 10- Photocatalysis by inorganic solid materials: Revisiting its definition, concepts, and experimentalprocedures, Advances in Inorganic Chemistry, 63, (2011), 395-430.

8. Nick Serpone, Semiconductor Photocatalysis- Past, Present, and Future Outlook, J. Phys. Chem. Lett., 3 (2012), 673-677.9. B. Viswanathan and K.R. Krishnamurthy, Nitrogen Incorporation in TiO2: Does It Make a Visible Light Photo-Active

Material?, Int. J. Photoenergy, 2012 (2012), Article ID 269654. http://dx.doi.org/10.1155/2012/269654.10. Kihsuke Mori, Hiromi Yamashita and Masakazu Anpo, Photo-catalytic reduction of CO2 with water on various titanium oxide

photo-catalysts, RSC Advances, 2 (2012), 31165-3172.

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11. Jenny Schneider, Detlef W. Banhemann, Undesired Role of Sacrificial Reagents in Photocatalysis, J. Phys. Chem. Lett,4 (2013), 3479-3483.

12. Sagi Pasternak, Yaron Paz, On the Similarity and Dissimilaity between Photocatalytic Water Splitting and PhotocatalyticDegradation of Pollutants, Chem.Phys.Chem., 14 (2013), 2059-2070.

13. David O. Scanlon, Charles W. Dunnill, John Buckeridge, Stephen A. Shevlin, Andrew J. Logsdail,Scott M. Woodley, C.Richard A. Catlow, Michael. J. Powell, Robert G. Palgrave, Ivan P. Parkin, Graeme W. Watson, Thomas W. Keal, PaulSherwood, Aron Walsh and Alexey A. Sokol., Band alignment of rutile and anatase TiO2, Nat. Mater.,12 (2013), 798-801.

14. Israel E. Wachs, Somphonh P. Phivilay, and Charles A. Roberts, Reporting of Reactivity for Heterogeneous Photocatalysis,ACS Catal., 3 (2013), 2606-2611.

15. Bunsho Ohtani, Revisiting the fundamental physical chemistry in heterogeneous photocatalysis: its thermodynamics andkinetics, Phys. Chem. Chem. Phys., 16 (2014), 1788-1797.

16. Ji Bong Joo, Robert Dillon, Ilkeun Lee, Yadong Yin, Christopher J. Bardeen, Francisco Zaera, Promotion of atomic hydrogenrecombination as an alternative to electron trapping for the role of metals in the photocatalytic production of H2, Proc. Natl.Acad. Sci.,111 (2014), 7942–7947.

17. Kim W, Tachikawa T, Moon GH, Majima T, Choi W., Molecular-Level Understanding of the Photocatalytic ActivityDifference between Anatase and Rutile Nanoparticles, Angew Chem Int Ed.,. (2014), doi: 10.1002/anie.201406625.

18. B.Viswanathan, Cabon Dioxide to Chemicals and Fuels Course Material, 20-25th Lectures, (2014) 421-612.

References