the introduction of dahlia nano-tio2 coated functional...
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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.