TiO 2 particles - Fundamentals and Applications as photocatalyst

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Paula Kerrie Summers
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1 TiO 2 particles - Fundamentals and Applications as photocatalyst Most information taken from TiO2 photocatalysis Fundamentals and Applications by Akira Fujishima, Dr. Kazuhito Hashimoto, and Dr. Toshiya Watanabe TiO 2 particles Used in paints and cosmetics Consumption exceeds 3 million tons a semiconductor can be chemically activated by light energy Paint chalking stabilisers or/and additives are added to solve the problems 1

2 17.5 cm Synthesis and Functionalisation Nanomagnetite WO3 TiO2 Pt/WO3 WO3 Linkers Protective Layer Magnetic Core Fluorescent Signaling Environment Energy Health Care Antigen Detection Biocompatibility Shape Recognition TiO2 Fresh Air Clean Water Self cleaning super - surface Harnessing Solar Energy through Photocatalysis Renewable Energy 2

3 Photocatalyst light sun Decomposition by powerful oxidising action Self cleaning Self sterilising TiO2 Solar Induced Photocatalysis Need for ecologically clean chemical processes and technology - solar induced photocatalysis Low quantum efficiency- less than 1% of the input electrical energy is effectively utilised by UV-photocatalytic systems. 3

4 Two requirements: Substance to be degraded need to be brought into contact with TiO 2 Light needs to reach the surface TiO 2 Semiconductor Photocatalyst UV Light less than 380nm CB VB Electron e - + O 2 O 2- O 2- OH Hole Organic matter oxidation Org + h + Org + OH h + + H 2 O H + + OH h + + OH - OH Intermediates CO 2 + H 2 O Intermediates CO 2 + H 2 O 4

5 Electrons and holes are generated For metals, these two are immediately recombined On semiconductors, they survive for longer periods of time Holes have greater oxidising power than the reducing power of the excited electrons. Destructive power is stronger than chlorine, ozone, hydrogen peroxide so in theory it can decompose almost all hydrocarbon organic compounds to C, H, O Energy has been quantised - it means regardless of the intensity level energy of each photon is the same Energy of photons of light equivalent to greater than 30,000 o C in thermal energy 5

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7 Germ Killer E.Coli Methicilin-resistant Staphylococcus aureus (MRSA) resistant to most commonly used antibiotics Pseudomonas aeruginosa 1 hour illumination at 1000 lux 99% of the three bacteria are killed 7

8 Antimicrobial Tiles TiO 2 was applied onto the tiles by spray coating The tile is then heated at 800 o C. For tiles where the light is harder to reach could deposit metal such as Ag (antimicrobial metal particles) onto the tiles. Ag metals could be deposited onto the TiO2 by illumination. 8

9 After installing photocatalytic tiles numbers of bacteria on the wall surfaces and number of airborne bacteria dropped. Could be used to reduce the unpleasant odour from public toilet facilities (pets and rats) In addition to its antibacterial properties, it has the ability to combat viruses, molds and algae. Decomposing Endotoxin as well as killing the bacteria Endotoxin toxin released when E.coli cells die can cause more problems than E.coli itself 9

10 E.Coli Survival (%) Dark (P25) UV P25 HPC MPC Time (min) Self cleaning transparent glass Development: Coating a transparent TiO 2 thin film on glass When coated onto a common sheet glass (soda-lime glass) activity drops WHY????? 10

11 The one that works TiO2 Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ SiO2 Sodium lime glass Other examples Ventilation fan - 0.1mg/cm 2 /day the use of black-light UV could decompose the grease to CO 2. Tunnel light Exterior materials 11

12 Antifogging Typical contact angle between water and inorganic materials, such as glass (20 o to 30 o ) On a plastic 70 o to 90 o On silicone resin and fluororesins angle is higher than 90 o Some water absorbing surfaces or activated with surfactants or detergents could show contact angle lower than 10 o Superhydrophilicity completely non water repellent A thin film of titanium dioxide combined with suitable additives initial contact angle of water several tens of degrees UV illumination water droplet spread out flat giving contact angle approaching zero superhydrophilicity When light is off, still retain contact angle of a few degrees for water for a few days and eventually contact angle increases hydrophobic again Superhydrophilicity properties can be recovered by exposing it with UV light. 12

13 Bare Glass 13

14 TiO 2 coated glass Anti Fogging 14

15 How does it work? - Postulation not exact answer When TiO 2 is illuminated with light have oxygen defects on the surface of TiO 2 Enabling water molecules to be attached on to the Ti structure 15

16 Superhydrophilicity vs Photocatalytic technology Photocatalytic technology decompose the dirt, odourous compounds by oxiding the compounds Superhydrophilicity altering the properties of the surface by photocatalytic action Both need light Air purification Decomposition of malodorous pollutant (of low concentration ppm levels) Indoor air cleaners Oxidation of SOx and NOx Limited to 0.01 ppm to 10 ppm levels Can be integrated with other process such as adsorption 16

17 Water Purification Treating recalcitrant organic matters in low concentrations Not suitable to treat high concentration of organic matters Suitable as a polishing method Application is still limited due to recovery of the photocatalyst Magnetic TiO 2 Photocatalyst P P P P MAGNET 17

Magnetic Photocatalyst Synthesis Magnetite in

Magnetic Photocatalyst (TSM) Transmission

18 Magnetic Photocatalyst Synthesis Magnetite in TMAOH Sodium Silicate 80 C Silica Coated Magnetite (SM) Titanium Tetrachloride 6 h hydrothermal at 90 C 1 h calcination at 450 C Magnetic Photocatalyst (TSM) Transmission Electron Microscopy Magnetite Titania Silica SiO2 coated Fe3O4 40 mm TiCl4 18

19 Water splitting Electrolysis (High School Chemistry experiments) two electrodes (cathodes and anodes) A little salt, acid Apply a direct current What did you see? Honda and Fujishima did experiments which water splitting can be carried out without the need of electricity Problems : low H 2 generation requires artificial light to be effective ie extra energy 19

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21 Another application of TiO2 is Dye sensitised solar cells (DSC) More applications out there perhaps you will be the engineer to put them into reality 21

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