Functional Materials

Photocatalytic Titanium Dioxide, ST/STS Series

Titanium Dioxide exhibits strong oxidizing photoactivity when irradiated by UV ray.

The surface of pigmental titanium dioxide used for paints and plastics is usually treated with inorganic compounds (partially with organic compound) to restrain the photoactivity. Photocatalytic titanium dioxide utilizes the photoactivity at the most.

With the light energy, photocatalyst decomposes pollutants and malodors mainly made of organic compounds into carbon dioxide and water. By super-hydrophilicity induced by light energy, affinity to water increases and anti-fogging effect, anti-stain effect and self-cleaning effect can be imparted. In addition, this photoactive reactions can last by its regenerating property.

ISK's photocatalytic titanium dioxide ST, STS products are manufactured in ISK's original technology to further enhance photoactivity.

(Visible light photocatalyst)

ISK has newly developed visible light photocatalytic powder (preliminary sample:MPT-623). Due to excellent sensitivity to visible light, photoactivity can be obtained by not only sun light but also by fluorescent light. With the sensitivity, this photocatalyst is expected to be used for more versatile applications.

Click the flame below (in the flame below with→)

Figure: Variety of TiO2 photocatalysis in practical use

Photocatalytic powder

Photocatalytic sol

Figure: Application areas of TiO2 photocatalysis

TiO2 + UV light / photocatalytic reaction

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Photocatalytic Powder ST Series

1. Characteristics of ST series

Various grades with different particle size and adsorption properties are available.

grades X-ray diameter(nm) SSA(m²/g) photoactivity characteristics
ST-01 7 300 highest photoactivity
ST-21 20 50 high activity and dispersibility
ST-31 7 250 excellent gas absorption
ST-41 200 10 excellent dispersibility

2. Electron Micrographs of ST series

ST-01 (*400,000)

Photo: ST-01 (*400,000)

ST-21 (*400,000)

Photo: ST-21 (*400,000)

ST-41 (*100,000)

Photo: ST-41 (*100,000)

3. Photocatalytic properties of ST series

in gas (acetaldehyde)

Graph 1

Graph 1

amount of TiO2: 0.1g
light source intensity: black light 0.5mW/cm²
irradiation area: 24cm²
reaction volume: 2.8L

in liquid (2-propanol)

Graph 2

amount of TiO2: 4g/L
light source intensity: black light 2mW/cm²
irradiation area: 24cm²
reaction volume: 80mL

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Photocatalytic Hydrosol STS Series

Acidic and neutral sols are available.

grade TiO2content (wt%) X-ray particle size (nm) pH characteristics
STS-01 30 7 1.5 acidic with nitric acid, excellent dispersibility
STS-02 30 7 1.5 acidic with hydrochloric acid, excellent dispersibility
STS-21 40 20 8.5 slightly basic

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The mechanism of photocatalysis and Characteristics of photocatalytic TiO2 and photo-hydrophilic function

1. Photocatalysis

A typical semiconductor, TiO2, creates holes and electrons by irradiating light with higher energy than TiO2's band gap energy (wave length < 380nm). The holes and electrons react with oxygen and hydroxyl ions, producing hydroxyl radicals and superoxide anions. Oxidation power of the chemicals are so strong that the chemicals decompose and eliminate organic compounds and NOx.

Figure: Reaction mechanism of TiO2 photocatalysis

2. Characteristics of TiO2 photocatalyst.

  1. High oxidizing ability
    As oxidative OH radicals produced by TiO2 photocatalysis have high oxidation potential shown in Table.1, TiO2 photocatalyst exhibits high oxidizing ability.
  2. Chemical stability
    TiO2 is chemically stable and not dissolved in water, although some other semiconductive photocatalytic compounds are dissolved when irradiated in water. TiO2 is so chemically stable that it is not dissolved in almost all acidic, basic and organic solvent.
  3. Safety
    TiO2 is regarded as a safe and inert material in general.

Graph: Energy diagram for typical semiconductors

Table 1 Comparison of oxidation potential of various oxidizing agents.
Oxidizing agent Reaction Oxidation potential (V)
Fluorine F2+2e=2F- 2.87
OH radical OH・+H++e=H2O 2.80
Ozone O3+2H++2e=H2O+O2 2.07
Hydrogen peroxide H2O2+2H++2e=2H2O 1.77
Manganese peroxide MnO4-+8H++5e=Mn2++4H2O 1.51
hypochlorous acid HClO+H++2e=Cl-+H2O 1.50
Chlorine Cl2+2e=2Cl- 1.36
Oxygen O2+4H++2e=2H2O 1.23

3. Photo-induced super-hydrophilicity

The surface coated with photocatalytic TiO2 shows super-hydrophilicity by UV irradiation. On the super-hydrophilic surface, adsorbed water does not create dew but become thin layer. Thus, the surface exhibits anti-fogging effect and gets uneasy to be attached by stain itself. Furthermore, the surface becomes easy to wash away attached stain by water.

Figure: Mechanism of Superhydrophilicity

Figure: Applications ~Superhydrophilicity~