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TiO2 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
TiO2 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
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Synthesis and Functionalisation
EnvironmentEnergyHealth Care
17.5
cm
Nanomagnetite
Protective Layer
Magnetic Core
Antigen Detection
Shape Recognition
Biocompatibility
FluorescentSignaling
Linkers
WO3Pt/WO3
WO3
TiO2
TiO2
Clean Water
Fresh Air
Self cleaning super - surface
Renewable Energy
Harnessing Solar Energy through Photocatalysis
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Photocatalyst
Self cleaning
Self sterilising
Decomposition by powerful oxidising action
light
TiO2
sun
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
.
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• Two requirements:
Substance to be degraded need to be brought into contact with TiO2
Light needs to reach the surface
CB
VB
TiO2 Semiconductor Photocatalyst
UVOrganic matter oxidation
Org + h+ → Intermediates → CO2 + H2O
Org + OH• → Intermediates → CO2 + H2O
Hole
h+ + H2O → H+ + OH•
h+ + OH- → OH•
Electron
e- + O2→ O2-•
O2-• ⇒ OH•
Light less than 380nm
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• 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 oC in thermal energy
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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
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Antimicrobial Tiles
• TiO2 was applied onto the tiles by spray coating – The tile is then heated at 800oC.
• 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.
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• 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
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0
20
40
60
80
100
0 10 20 30 40 50 60
Time (min)
E.C
oli S
urvi
val (
%)
Dark (P25)
UV
P25
HPC
MPC
Self cleaning transparent glass
Development:
• Coating a transparent TiO2 thin film on glass
• When coated onto a common sheet glass (soda-lime glass) – activity drops
• WHY?????
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TiO2
Sodium lime glass
SiO2Na+ Na+ Na+ Na+Na+ Na+
Na+ Na+ Na+
The one that works…………
Other examples
• Ventilation fan - 0.1mg/cm2/day – the use of black-light UV could decompose the grease to CO2.
• Tunnel light
• Exterior materials
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Antifogging
Typical contact angle between water and inorganic materials, such as glass (20o to 30o)
• On a plastic – 70o to 90o
• On silicone resin and fluororesins – angle is higher than 90o
• Some water absorbing surfaces or activated with surfactants or detergents could show contact angle lower than 10o
• 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.
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Bare Glass
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TiO2 coated glass
Anti Fogging
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• How does it work? - Postulation – not exact answer
When TiO2 is illuminated with light – have “oxygen defects” on the surface of TiO2
Enabling water molecules to be attached on to the Ti structure
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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
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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 TiO2 Photocatalyst
MAGNET
P
P
P
P
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Magnetic Photocatalyst Synthesis
Magnetic Photocatalyst (TSM)
Magnetitein TMAOH
Sodium Silicate
Silica Coated Magnetite
(SM)
Titanium Tetrachloride
6 h hydrothermal at 90°C1 h calcination at 450°C
80°C
Transmission Electron Microscopy
40 mM TiCl4
Titania
SiO2 coated Fe3O4
Magnetite
Silica
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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 H2 generation
– requires artificial light to be effective – ie extra energy
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• 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