The Introduction of Dahlia Nano-TiO2 coated Functional Tiles

1. Introduction

With the improvement of living standards, the living environment becomes

more important. People want to live in a comfortable, clean and healthy

environment. However, modern living environment cannot fulfil this

requirement. Luxurious decoration and sumptuous furniture are invisible

pollution sources. They continuously release toxic organic substances into the

air, such as formaldehyde, toluene and so on. At the same time, with the

increase of these aerial pollutants and dust, the dust-stains which adhere to

the external walls and glass of buildings, not only affect the city's cleanliness,

but also are difficult to clean. If people live in such environment, the harm to

the human body is self-evident.

Modern scientific researches have proven that nano-titanium dioxide

(TiO2) in its anatase form has very beneficial photo-catalytic properties under

the irradiation of ultraviolet light (from the sunlight); the majority of organic

pollutants will be decomposed into harmless carbon dioxide and water.

The surfaces of Dahlia Nano-TiO2 functional tiles are coated with nano-

titanium dioxide films, and under the sunlight (UV) irradiation the tiles have

the following proven functions:

Ⅰ.Self-Cleaning

Under the irradiation of light, TiO2 will play the role of self-cleaning by

decomposing the oil and organic substances that come in contact with the

surface of the tiles. The tiles are also super-hydrophilic. That means that with

just the rinsing of water, the oil attached to the tiles surface will be washed

away. Hence, the pollutants are easily removed.

Ⅱ.Self-Sterilising

Now, most of the anti-bacterial products are either organic or inorganic. If

bacteria absorbs the ingredients of these anti-bacterial products, the

bactecidal effect is limited and slow in reaction. Comparatively, the nano-TiO2

on the tile surface will destroy the cell membrane in a very short time with

the irradiation of ultraviolet light (sunlight); and further decompose them into

carbon dioxide and water.

Ⅲ. Air Purification

There are a variety of air pollutants and irritants around us, such as nitrogen

oxides, aldehydes and other harmful gases; the stench of substances, such as

rotten food, animal and poultry’s excretion, etc. Under the irradiation of

ultraviolet light, Dahlia Nano-TiO2 tile can decompose organic pollutants in the

air (such as toluene, formaldehyde produced during home decoration process;

fumes produced by cooking; nicotine, tar produced by smoking), and improve

the air quality and protect people from air pollution, without resorting to

expensive electrical and mechanical devices.

2. The Function and Principle of TiO2

The Nano-TiO2 coatings on the surface of the Dahlia Nano-TiO2 tiles ensure

that the functions mentioned above are possible. In the photocatalytic

reaction, TiO2 acts as the photocatalyst. During the whole reaction, the

catalyst itself does not change, but it can effectively promote the chemical

reaction. Thus, under the irradiation of light, all material which possess the

function of catalysis are term photocatalysts.

In fact, the most common photocatalyst is the chlorophyll. In

photosynthesis, chlorophyll absorbs sunlight to produce carbohydrates and

oxygen, and the chlorophyll does not change during the entire reaction. The

photosynthesis cannot be carried out without the sunlight being absorbed by

the chlorophyll. In this case, "Chlorophyll" can appropriately be referred to as

a "photocatalyst”. In the photocatalytic reaction with TiO2, TiO2 is equivalent

to the chlorophyll in the photosynthesis, and it is the photocatalyst in the

reaction.

Figure 1 There is basically resemblance between plant’s photosynthesis and TiO2 photocatalytic reaction

With the significant industrial development, convenience in life is

proportional to the increase in the consumption of fossil fuels. At the same

time, a lot of harmful pollutants are produced. In order to solve this problem,

we must consider it from the material cycle perspective on the earth. What

the world needs now is the technology that turns the pollutants into carbon

dioxide and water with the natural energy, and it seems that the

photocatalytic technology is what we should be aiming for. We should allow

the amount of the natural fuels consumed by human activities gradually

return to the original status by using natural energy through artificial

technology (photocatalysis technology).

Light Light

CO2

O2

H2O TiO2

H2

O2

H2O

Chlorophyll absorbs light

Titanium dioxide absorbs light

The decomposition reaction of water is a slow. However,if there is organic matter, the decomposition rate is increased.

Figure 2 understanding the environmental photocatalytic purification technology based on the view of natural material cycle

Titanium dioxide and light are two key factors in the photocatalytic reaction. It

will require a lot of effort to achieve the maximum efficacy, regardless of the change

of the way, the basic mechanism of the technology will be invariable: the two

phenomena on the surface of titanium dioxide after the absorption of light:

Ⅰ. Photocatalytic Oxidation and Decomposition

TiO2 is a N-type semiconductor. The band gap is 3.0eV, which belong to the

excitation scope of ultraviolet (380nm). The electron (e-) on the valence band of TiO2

can be excited to the conduction band with the effects of light; at the same time, the

corresponding hole (h+) appears on the valence band. The electrons and the holes

diffuse on the surface of the titanium dioxide. The h+ and e- react with the H2O

adsorbed on the TiO2 surface, then generate •OH and •O2- which are high-activity

groups. The active oxygen and hydroxyl groups which have strong oxidation

functions can decompose formaldehyde, methylamine and other harmful organic

compounds, effluvium of pollutants and bacteria into harmless CO2 and H2O.

Based on this characteristic, nano-TiO2 has the following capabilities:

Photosynthesis

Pollutant

Fossil fuels, chemical

Organic matter

CO2+H2O

CO2+H2O

TiO2

+O2

+O2

Consumption

TiO2 photocatalytic

reaction

(a). The Strong Ability to Decompose the Pollutants:

Bacteria, viruses are everywhere, such as in hospitals, shopping malls,

stations, homes, sanitary wares, underwear, and so on. There are a large

number of bacteria and viruses which seriously threaten people's lives and

health. Under natural light, lighting, especially UV light irradiation and if the

nano-titanium dioxide photocatalyst is placed in an appropriate manner at the

above-mentioned places, a variety of bacteria and virus will be killed

efficiently, quickly and thoroughly with the natural air flow. In addition, the

bacteria, viruses and micro-organisms which have resistance to the common

disinfectants can also be easily decomposed. In tests conducted on various

types of common bacteria, after 24 hours the bacterial kill-rate have been

recorded as more than 90% in the confined rooms whose walls have been

coated by TiO2. So that the security of people's living environment will be

enhanced greatly.

(b). The Function of Decontamination of Air

With the development of society, high-rise buildings and individual

household’s decoration has become vogue. However, the environmental

impact of decorating materials is catastrophic, releasing formaldehyde,

benzene, amine and other harmful gases into the air. These have harmed

people's lives and health. In addition, the pollution of CO, SO2, NO and other

exhaust gases have always impacted our personal life, and people's living

environment has become worse.

Nano-titanium dioxide photocatalyst has the beneficial function to

decompose the above harmful gases and other organic matter into CO2 and

H2O. The removal rate of harmful gases will be more than 90% with having

the catalyst in the just-decorated rooms. With the comprehensive applications

of photocatalyst, the air pollution will be reduced or completely removed, and

the air will be fresh.

(c). The Effect on Sewage Treatment

Nowadays, the environmental problem has attracted more and more

attention. At the same time, people have paid a heavy price on it. The Chinese

Government have committed to improve the environmental condition, the nation and

enterprises spend a great deal of manpower, material and financial resources to

control the pollution, in order to create a great environment for their citizens.

According to the features and experimental results of nano-titanium dioxide

photocatalyst, it can decompose most of the organic compounds in industrial waste-

water. The macro-molecule organic compounds in the waste-water which are

produced by paper mills, printing and dyeing mills, ethanosl producing plants and

chemical plants together with formaldehyde and other pollutants mentioned above,

are also decomposed into CO2 and H2O. This is the beneficial properties of the

titanium dioxide photocatalyst.

(d). The Use of Nano TiO2 on the Anti-Bacterial Fabric

Presently, the trend on the research, application and development of nano-

materials in the textile industry is generally divided into three ways: adding the Multi-

fiber, mixture of various powders and multi-functional complex. Through the

applications, we can develop the anti-ultraviolet type, anti-bacterial and deodorant

type, infrared reflection type, and cooling type, water-resistant type, pollution

prevention type, conductive type, flame-retardant type and other functional type of

new products. This is the principle behind the use of nano-materials in the textile

industry. At present, a variety of nano-fibers have been produced using the method

of adding nano-materials into the spinning solution. Likewise, anti-bacterial and

deodorant fibers have been made by mixing Nano-TiO2 powder into a polymer. Nano

anti-bacterial dacron products can be widely used in knitted underwear, sports

clothing, socks, carpets, medical sheets, clothing for the surgical and in-patient

services, food industry professionals’ uniforms, as well as beddings, coverings for

furniture, decorative fabrics and all kinds of underwear, clothings, non-woven fabrics,

etc. Since Japan developed the deodorant fibers in 1984, new nano products have

been increasing in the markets. The research and development of other anti-

ultraviolet radiation nano-fiber and functional infrared fibre products have made

great progress.

O2

·O2-

O2

e(电子)

δ+

OH-·OHH2O

超氧阴离子羟基离子自由羟基

被捕获空穴

Figure 3 the role of TiO2 on surface

Ⅱ. Super-Hydrophilicity

Figure 4 the self-cleaning effects of the two major characteristics of TiO2

Ti

Ti

H2

CO

CO

Lig

Ligh

（a

（b

Oxidize the slowly adsorbed oil with the effect of

d i i

Water slides between the surface and decomposed oil

i l l h f

TiO2

Ti

O O

OO

O

Ti

OH

HHH

H

Ti

O O

O

HOO

Ti

OH

HHH

(ht+)

Ti

O O

OO

O

Ti

O

HHHH

O

HH

hv(h+)

-H+

H2O

暗处

Figure 5 changes of surface structure causes the changes to TiO2 hydrophilicity

Photo-induced changes of hydrophilicity, for one thing, is due to the absorption

and the decomposition of organic matter on the surface of TiO2 under the irradiation

of the light. However, the more important reason is the change of surface structure

with the increase of the surface hydroxyl groups. The mechanism of the photo-

induced changes of hydrophilicity which is caused by the changes of surface

structure is shown in Figure 5. In the photocatalytic reaction，the light-generated

hole spreads to the surface, then captured by oxygen in the crystalline form to

generate OH free radicals or oxidize the adsorbed material. After the capture of the

hole by Lattice oxygen, Ti-O chemical bond length becomes longer. Under the

irradiation of light, the interaction between the hydroxyl in coordination with

defective oxygen and TiO2 weakens. At the time, adsorbed water and the Ti

coordinate to form new surface hydroxyl groups. The hydroxyl density on the surface

of TiO2 increases. In the dark, the surface of titanium dioxide gradually restored to

the original weak hydrophilicity with the reduction of surface hydroxyl groups, so the

light generated surface hydroxyl groups are in a thermodynamic instable

Dark

metastability. After the irradiation of light, the surface free energy of TiO2 turns

higher than that of the pre-illumination, so it will be super hydrophilic.

3. Characterization and Performance of Product

Ⅰ. Proving existence and the Effective Crystalline Form of TiO2

The spectrum analysis shows that, Dahlia Nano-TiO2 contain not only silicon,

oxygen, sodium, calcium, nitrogen, phosphorus, magnesium and other ordinary

elements, but also the element titanium which common tiles don’t have. It indicates

that there are nano-TiO2 films on the surface of Dahlia nano-TiO2 tiles.

Figure 6 the surface electron energy spectrum of Dahlia nano-TiO2 tiles

Figure 7 the XRD spectrum of Dahlia Nano-TiO2 ceramic tiles

There are two common types of crystalline forms for TiO2: rutile and anatase.

The former doesn’t have photo-catalytic properties, and is mainly used in white dope,

paint and cosmetics. The latter has high photocatalytic properties, and is also the

type we need. The XRD spectrum verifies that the crystalline form of the TiO2 film on

the surface of Dahlia Nano-TiO2 ceramic tiles is anatase.

Ⅱ. Super Hydrophilicity

At the interface between solid, liquid and gas phases, the angle between the

solid-liquid interface to the gas-liquid interface is called the contact angle, usually

expressed as θ (showed in the figure 8). We study the degree of hydrophilicity

through the measurement of the contact angle, the smaller the contact angle is, the

better the hydrophilicity will be; and the bigger the contact angle is, the worse the

hydrophilicity will be.

Figure 8 the contact angle between liquid and solid surface

We irradiated the cleaned common tiles and nano-TiO2 ceramic tiles respectively

under the ultraviolet light, then measured the contact angle at different times, as

the duration of the illumination time increases, the contact angle decreases. However,

the contact angle of TiO2 ceramic tiles decreases faster, comparing to that of the

common tiles. When the irradiation time reached 270min, the contact angle of TiO2

tiles reduced to 6°, and the contact angle of the common tiles remained at 30°. This

proves that the nano-TiO2 tiles through the irradiation of UV light will be super

hydrophilic (less than 10°).

0 50 100 150 200 250 30005

101520253035404550556065707580

Cont

act a

ngle

（

θo ）

Irradiation time（h）

blank nano TiO2 tile

Figure 9 the contact angle comparison of Dahlia Nano-TiO2 tiles and common tiles

Ⅲ. The Photodegradation of Benzene

Figure 10 the photodegradation ability comparison of Dahlia Nano-TiO2 tiles and common tiles

Ct: the concentration of benzene at t time; C0: the initial concentration of benzene

The contact angle of common tiles still stayed at 30°through the irradiation of UV

light for 270min

The contact angle of Nano-TiO2 tiles reached 6° through the irradiation of UV

light for 270min

0 1 2 3 4

0.760.780.800.820.840.860.880.900.920.940.960.981.001.02

C t/C0

irradiation time (h)

Blank Nano TiO2 tile

Under the same conditions, the speed at which Dahlia nano-TiO2 tiles degrade

benzene was faster than that of the common tiles. This indicated that Dahlia nano-

TiO2 tiles have excellent efficiency in the decomposition of organic pollutants.

Ⅳ. Anti-Bacterial Properties

The comparison on the antimicrobial tests were carried out on the common tiles and

the Dahlia nano-TiO2 tiles. The bacteria were Staphylococcus aureus and Colon

bacillus, being the 2 most common types in the environment. After the irradiation of

ultraviolet light for a certain period of time, the bacteria which had been introduced

onto the tiles were placed in nutrient-rich solutions culture, and then we monitored

the antibacterial property through observing the growth of bacteria.

Table 1 the antimicrobial test results of common tiles and Dahlia nano-TiO2 tiles

(College of Pharmacy, Suzhou University)

As Table 1 shows, with the irradiation for only 8 minutes, Dahlia nano- TiO2 tiles

have a very significant inhibitory effect on Staphylococcus aureus and Colon bacillus.

The antibacterial rate was more than 90%, while the antibacterial rate of common

tiles was only 25%. In conclusion， Dahlia nano-TiO2 tiles have good anti-bacterial

properties.

Under the same experimental conditions, in accordance with national standards

of China (GB), we studied the anti-bacterial performance of Dahlia nano-TiO2 tiles

through researching the resistance of Staphylococcus aureus on the surfaces of

Dahlia nano-TiO2 tiles respectively. (Main wavelength of UV lamp was 365nm, the

light intensity on the sample surfaces were 0.1mw/cm2 and the irradiation time was

24h).

Table 2 the anti-bacterial test results of Dahlia nano-TiO2 and common tiles

(Test Center of Antimicrobial materials, Technical Institute of Physics and Chemistry, Chinese Aacademy of Science)

As Table 2 shows, with the irradiation for 24h, Dahlia nano-TiO2 white tiles had

great inhibitory effect to Staphylococcus aureus, the antibacterial rate of Dahlia

nano-TiO2 white tiles were more than 99%, and the antibacterial rate of Dahlia nano-

TiO2 gray tiles were 95%, while the common tiles didn’t have anti-bacterial

performance. So it can be concluded that the Dahlia nano-TiO2 tiles have good anti-

bacterial properties.

Ⅴ. The Abrasion Test of Dahlia Nano-TiO2 Tiles

According to China’s National Standards GB 9266-88(the resistant determination of

coatings), the surfaces of Dahlia nano-TiO2 tiles were scrubbed with the bristle test-

brush repeatedly for a 1000 scrub cycle. After the tests, it was proven that the

quality of the coating was not affected. This shows that TiO2 nano-particles bonded

with the surfaces of ceramic tiles strongly; and the nano-TiO2 film wouldn’t break

away from the surface of tiles with standard mechanical force.

4. The Limitations of the Product

TiO2 is not photocatalytic and hydrophilic without light, so the extent of the

illuminated area is of importance. Considering the use of photocatalysis and the

illumination area, it is favorable to spread the Dahlia nano-TiO2 tiles on the external

walls of the buildings or if used indoors, the tiles must be illuminated by fluorescent

light or natural light. As we know, the pollution has been one of the biggest

problems facing the entire world, and the best way is to eliminate it from the source

of pollution. Nowadays, the technology to semi-permanent removal of pollutants

combining with the non-depleting solar energy and TiO2 is no doubt the best way.