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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

TiO2 Photo Catalysis [Compatibility Mode]

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Page 1: TiO2 Photo Catalysis [Compatibility Mode]

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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