**4. Titania as active component for multifunctional coatings**

Crystalline TiO<sup>2</sup> (titanium dioxide), anatase, is widely known as material having excellent photocatalytic properties. Anatase coatings have also been prepared by a number of deposition techniques, such as sputtering, spray pyrolysis [37], and sol–gel processing [38]. The film formations are aimed at finding more flexible application in electronic devices, optical coatings, instrument hard coatings, and decorative parts. They are also generating different functionalities by engineering the surface, saving the energy consumption in production, and minimalizing the use of toxic materials since the quantity used is limited only to the surface and/or thin film layer. Thus, the film formation is an environmentally benign material technology and fits well to the current global trend of sustainable chemistry concept. However, sol–gel methods usually require a heating process at relatively high temperatures above 400°C to obtain sufficient crystallinity [39]. Thus, anatase coatings on organic substrates and incorporation of organic molecules into the coatings were not directly achieved using these techniques. TiO<sup>2</sup> layers on organic substrates are mostly amorphous, while the photoactivity of amorphous phase of TiO<sup>2</sup> has been less studied and explored. In this section, self-cleaning titania coating on textile will be discussed, as well as antibacterial functional. Recent results on coating of titania on wood as antifouling agent will also be explored.

**Self-cleaning and antibacterial coatings on textile**. This study aims at preparing amorphous and crystalline TiO<sup>2</sup> coating on cotton fabrics and examining the discoloration of organic materials modeled by turmeric extract stain on the cotton textile coated with those TiO<sup>2</sup> . Turmeric extract obtained from rhizomes of *Curcuma longa* is one of the main pigments produced in Brazil [10]. Besides the yellow pigment for food, this plant is widely used as a seasoning for Asian food including Indonesian food. Mature rhizomes are ground to give an aromatic yellow powder, employed as the coloring ingredient in curry powder. With the growing demand for natural colors, the use of turmeric is likely to increase. Therefore, turmeric extract stain is used as the model stain for self-cleaning action. It is also reported that amorphous TiO<sup>2</sup> coating on cotton fabrics has self-cleaning action similar to the crystalline TiO<sup>2</sup> coating but lower activity. The use of TiO<sup>2</sup> -loaded flexible substrates will possibly allow their application for the photodegradation of micelles, oils, solvents, sooth, and aromatic and aliphatic hydrocarbons under daylight.

have absorption spectra indicating reasonable composition of red-shift absorption maxima and blueshift absorption edges, while *tingi* dye has slightly low red-shift and blueshift contri-

**(mV)**

\*\* 70 0.80 21.00 0.05

\*\* 100 1.60 31.00 0.19

Neutral route meso-Ti-sputtered Pt counter electrode\* 688 7.60 68.14 3.56 Neutral route meso-Ti-thermal platinized counter electrode\* 717 12.12 58.11 5.05

Tegeran (*Maclura cochinensis*)\*\* 100 1.60 38.00 0.24

60 min stirring

Bixin extract *(Bixa orellana* L.*)* and commercial titania electrode\*\*\* 749 8.50 28.29 0.42 *Sargassum mclurei* Setchell\*\* 60 0.30 25.00 0.09 *Hypnea esperi* Bory\*\*` 55 1.30 31.00 0.44

Testing done at photovoltaic testing facility in Physics Department, University of Queensland, Brisbane, Australia,

**JSC (mA/cm2**

666 11.24 62.40 4.67

310 3.10 44.08 1.48

, Au counter electrode, testing done in Physics Department,

**) Fill factor (FF, %)**

*η* **(%)**

*Batik* dyes are all broadened forward to red side compared with their respective spectra in

The small red-shift of the absorption maxima suggests the absence of the formation of *J*-like aggregates which was predicted to lower the photocurrent efficiency in DSSC [36]. Thus, the natural *Batik* dyes used are predicted mostly in the monomer form. However, the absorption edges were shifted with the large blueshift of 85–165 nm, which may be induced by the formation of *H*-aggregates. In contrast with *J*-aggregates, the formation of *H*-aggregates supports efficient ability of the dyes for sensitization [36]. Low sensitization effect may occur owing to

Results on Bixin extract of achiote (*Bixa orellana* L*.*) seed as sensitizer has shown relatively higher efficiency sensitizer than the *Batik* dyes. It also confirms that nanotube titania performs better than commercial titania which has nanoparticle structure. Whereas algae's dyes (the latter two) have comparable performance as *Batik* dyes and bixin of around 0.1-0.5%. Large difference in photocurrent density of the two cells rather than in photovoltage suggests that the solar cell performance of the cells is influenced by the efficiency of the electron injection from

[1]. High photocurrent resulted from efficient electron injection of the

owing to the effective attachment of the pigment

ethanol solution. These indicate sensitizing effect of natural *Batik* dyes on TiO<sup>2</sup>

active area DSSC under illumination of 100 mW/cm<sup>2</sup>

; Pinput = 25.6 mW/cm<sup>2</sup>

**Table 4.** Solar cell parameters of various titania photoanodes and natural dyes as sensitizers.

layer, the absorption spectra of the three

power source equal to AM1.5 Direct Sun,

films [34, 35].

bution (data not shown). Upon adsorption on a TiO<sup>2</sup>

\*\*\*Testing done in Universitas Negeri Sebelas Maret, Surakarta, Indonesia.

**Sample VOC**

Acid treated-acid route meso-Ti-thermal platinized counter

458 Titanium Dioxide - Material for a Sustainable Environment

Joho (*Terminalia bellirica(gaertn)roxb*)

Bixin extract *(Bixa orellana* L.*)* and nanotube TiO<sup>2</sup>

Universitas Gadjah Mada, Yogyakarta, Indonesia.

electrode\*

\*

Tingi (*Ceriops tagal*)

prior hydrothermal\*\*\*

across a 0.025 cm2

sensitizer ruthenium N3 dye. \*\*Active area TiO = P25 0.25 cm<sup>2</sup>

self-quenching of the dyes in the *J*-like aggregate form.

the sensitizers into TiO<sup>2</sup>

molecules on the TiO<sup>2</sup>

pigments into the conduction band of TiO<sup>2</sup>

surface.

The white cotton textiles were purchased from local market after examining the burning characteristic of cotton fibers. Pure cotton fibers gave only black gray ash after burning. Turmeric powders were also obtained from local market. All the reagents are of analytical grade and used without further purification. Titanium (IV) tetraisopropoxide (TTIP 97%, Aldrich) and TiO<sup>2</sup> powder of P25 (Degussa) were used as titanium sources. TiO<sup>2</sup> P25 was a gift from Degussa Germany. The pre-cleaned cotton fabrics were dipped into the Ti suspension and withdrawn vertically at the rate of 20 cm/min. The coating was repeated one, five, and fifteen times before dried naturally and cured at 100°C for 15 min. The cured coated cotton fabrics were then rinsed with distilled water in ultrasonic washer to wash out the unbonded TiO<sup>2</sup> for 5 min and dried at room temperature [40]. **Figure 11** displays the XRD patterns of amorphous and crystalline TiO<sup>2</sup> -coated cotton fabrics.

From **Figure 11** (left), it is evident that coating by employing hydrolyzed TTIP sols results in no observable crystalline TiO<sup>2</sup> diffraction peaks. The observed peaks were corresponding to the cellulose fibers of the cotton fabrics [41]. XRD pattern of xerogels obtained from drying the sol precursor used for coating displays very broad peaks around 2θ of ~25<sup>o</sup> , suggesting that TiO<sup>2</sup> layers on the surface of cotton fabrics predominantly consisted of amorphous titania. After curing, the diffraction peaks of the coated cotton fabrics have decreased. It is presumably due to the sintering of both cellulose fibers and TiO<sup>2</sup> layers. The XRD patterns in **Figure 11** (right) shows that TiO<sup>2</sup> P25 coating resulted in crystalline peaks of anatase (A) TiO<sup>2</sup> at diffraction angle ~25<sup>o</sup> and rutile (R) TiO<sup>2</sup> at ~27<sup>o</sup> . This is in accordance with the fact known that TiO<sup>2</sup> P25 powder consists of 80% anatase and 20% rutile crystalline phases [42]. Similar to **Figure 11** (left), the bulk of the XRD peaks originated from cotton, as cotton is the underlying substrate. As the thickness of the coating layers increased, which resulted from multiple coatings, both anatase and rutile peaks are getting more intense. These results are comparable to the work of Qi et al. [41], who has observed that anatase peaks are intensifying due to increased crystalline nature of the corresponding sol precursors. It is also observed that the thicker the TiO<sup>2</sup> coating, the weaker the cotton. This may be attributed to titania coatings on cotton which shield the X-ray beam, therefore weakening the intensities of the peaks of cotton coated with titania [41, 43]. The structure and morphology of TiO<sup>2</sup> layers on cotton fabrics were investigated by using scanning electron microscopy (SEM) as depicted in Figure 4.

of the pristine cotton fibers (**Figure 12a**) has shown no such uniform layers on the surface.

tiles [44, 45]. However, the formation of interconnected layers over the fibers as observed for

bigger particle size of the coating materials. It is supposed that smaller particles have more

sition of turmeric extract stains in ethanolic solution under UV light irradiation. **Figure 13** displays the self-cleaning performance of amorphous (a)- and crystalline (b)-coated cotton

demonstrate higher photoactivity than the amorphous. The mechanism of decomposition of colorant molecules on titania under UV irradiation is widely known suggesting the generation

**Figure 12.** The SEM images of (a) pristine cotton fabrics, (b) cotton fabrics coated by amorphous TiO<sup>2</sup>

P25-coated cotton fabrics which have crystalline nature of TiO<sup>2</sup>

from 0.2 M Ti precursor.

layers covering the surface of cotton fibers. This

Nanostructured Titanium Dioxide for Functional Coatings


and for chitosan coating on tex-

http://dx.doi.org/10.5772/intechopen.74555

coating suggesting

layers

461

from 0.1 M Ti


**Figure 12b and c** has also confirmed TiO<sup>2</sup>

The self-cleaning effect of TiO<sup>2</sup>

It is clear that the TiO<sup>2</sup>

TiO<sup>2</sup>


type of coating is similar as obtained by Qi et al. [41] for TiO<sup>2</sup>

fabrics under (light) and without (dark) UV illumination.

precursor, and (c) cotton fabrics coated by amorphous TiO<sup>2</sup>

**Figure 13.** Self-cleaning action at alternated Ti loading of (a) amorphous TiO<sup>2</sup>

thicker coating of chitosan on textiles [45] was not observed for this TiO<sup>2</sup>

tendencies to form polymeric-like network due to smaller solvation spheres.

SEM images (**Figure 12**) of the coatings on cotton fabrics show that the surface structures of the two titania-coated cotton fabrics look similar. The surface structure of these titania-coated cotton fibers shows that a thick uniform layer has been formed. The low-resolution image

**Figure 11.** The XRD patterns of samples (left): (a) pristine cotton fabrics, (b) cotton fabrics coated with amorphous TiO<sup>2</sup> from 0.2 M Ti precursor, and (c) cotton fabrics coated with amorphous TiO<sup>2</sup> from 0.2 M Ti sol precursor after curing at 120°C for 1 h. P25-coated (right): (a) 1×, (b) 5×, and (c) 15× coatings with curing.

of the pristine cotton fibers (**Figure 12a**) has shown no such uniform layers on the surface. **Figure 12b and c** has also confirmed TiO<sup>2</sup> layers covering the surface of cotton fibers. This type of coating is similar as obtained by Qi et al. [41] for TiO<sup>2</sup> and for chitosan coating on textiles [44, 45]. However, the formation of interconnected layers over the fibers as observed for thicker coating of chitosan on textiles [45] was not observed for this TiO<sup>2</sup> coating suggesting bigger particle size of the coating materials. It is supposed that smaller particles have more tendencies to form polymeric-like network due to smaller solvation spheres.

From **Figure 11** (left), it is evident that coating by employing hydrolyzed TTIP sols results in

the cellulose fibers of the cotton fabrics [41]. XRD pattern of xerogels obtained from drying

titania. After curing, the diffraction peaks of the coated cotton fabrics have decreased. It is

Similar to **Figure 11** (left), the bulk of the XRD peaks originated from cotton, as cotton is the underlying substrate. As the thickness of the coating layers increased, which resulted from multiple coatings, both anatase and rutile peaks are getting more intense. These results are comparable to the work of Qi et al. [41], who has observed that anatase peaks are intensifying due to increased crystalline nature of the corresponding sol precursors. It is also

titania coatings on cotton which shield the X-ray beam, therefore weakening the intensities of the peaks of cotton coated with titania [41, 43]. The structure and morphology of TiO<sup>2</sup> layers on cotton fabrics were investigated by using scanning electron microscopy (SEM) as

SEM images (**Figure 12**) of the coatings on cotton fabrics show that the surface structures of the two titania-coated cotton fabrics look similar. The surface structure of these titania-coated cotton fibers shows that a thick uniform layer has been formed. The low-resolution image

**Figure 11.** The XRD patterns of samples (left): (a) pristine cotton fabrics, (b) cotton fabrics coated with amorphous TiO<sup>2</sup>

from 0.2 M Ti precursor, and (c) cotton fabrics coated with amorphous TiO<sup>2</sup>

120°C for 1 h. P25-coated (right): (a) 1×, (b) 5×, and (c) 15× coatings with curing.

layers on the surface of cotton fabrics predominantly consisted of amorphous

at ~27<sup>o</sup>

P25 powder consists of 80% anatase and 20% rutile crystalline phases [42].

the sol precursor used for coating displays very broad peaks around 2θ of ~25<sup>o</sup>

and rutile (R) TiO<sup>2</sup>

presumably due to the sintering of both cellulose fibers and TiO<sup>2</sup>

diffraction peaks. The observed peaks were corresponding to

P25 coating resulted in crystalline peaks of anatase (A)

coating, the weaker the cotton. This may be attributed to

, suggest-

layers. The XRD patterns

. This is in accordance with the fact

from 0.2 M Ti sol precursor after curing at

no observable crystalline TiO<sup>2</sup>

460 Titanium Dioxide - Material for a Sustainable Environment

in **Figure 11** (right) shows that TiO<sup>2</sup>

at diffraction angle ~25<sup>o</sup>

observed that the thicker the TiO<sup>2</sup>

ing that TiO<sup>2</sup>

known that TiO<sup>2</sup>

depicted in Figure 4.

TiO<sup>2</sup>

The self-cleaning effect of TiO<sup>2</sup> -coated white cotton fabrics was evaluated by the decomposition of turmeric extract stains in ethanolic solution under UV light irradiation. **Figure 13** displays the self-cleaning performance of amorphous (a)- and crystalline (b)-coated cotton fabrics under (light) and without (dark) UV illumination.

It is clear that the TiO<sup>2</sup> P25-coated cotton fabrics which have crystalline nature of TiO<sup>2</sup> layers demonstrate higher photoactivity than the amorphous. The mechanism of decomposition of colorant molecules on titania under UV irradiation is widely known suggesting the generation

**Figure 12.** The SEM images of (a) pristine cotton fabrics, (b) cotton fabrics coated by amorphous TiO<sup>2</sup> from 0.1 M Ti precursor, and (c) cotton fabrics coated by amorphous TiO<sup>2</sup> from 0.2 M Ti precursor.

**Figure 13.** Self-cleaning action at alternated Ti loading of (a) amorphous TiO<sup>2</sup> -coated cotton fabrics and (b) crystalline TiO<sup>2</sup> -coated cotton fabrics.

of highly oxidative radicals on the TiO<sup>2</sup> surface when light below 400 nm is applied on the TiO<sup>2</sup> photocatalyst surface [42, 46]. **Figure 14** shows the color difference of the self-cleaning action on the coated and uncoated cotton.

coating of nanorod-TiO<sup>2</sup>

vapor.

SiO<sup>2</sup>


and SiO<sup>2</sup>

quantitative data and elaboration on mechanism are on progress [49].

wood was achieved for the coated wood, both by TiO<sup>2</sup>

**Figure 16.** Antifouling test in the sea water: (a) uncoated wood, (b) TiO<sup>2</sup>

expected from combined effect of surface hydrophobicity and photocatalysis. Nanorod morphology is expected to build the surface roughness as well as photoactive agent [48]. The silica will provide sturdy coating formulation in the acrylic-based paints. **Figure 16** shows our prompt results on antifouling test of the coated woods in the sea water. Clean surface of

**Figure 15.** (a) XRD patterns of cotton fabrics coated by Ti:Si (A) 0:1, (B) 1:0, and (C) 2:1; (b) antibacterial test of commercial antibacterial cloth and cotton fabrics coated with silica-titania with Ti:Si 3:1 which are exposed and not exposed to water

on wood is proposed. The antifouling mechanism is

Nanostructured Titanium Dioxide for Functional Coatings

http://dx.doi.org/10.5772/intechopen.74555





. More

463

The 15 times coating of TiO<sup>2</sup> P25-coated cotton fabrics have the highest self-cleaning action which is considered to be attributed to the highest anatase crystallinity as demonstrated by its sharpest anatase peaks with greatest intensities from the XRD studies in **Figure 12**. From these self-cleaning testing, it is worth noting that the amorphous coating has demonstrated significant photocatalytic activity toward turmeric stain discoloration reaching almost 80% discoloration. The mechanism behind this is still unclear and needed further investigation.

**Antibacterial coatings on textile**. To enhance crystallization of amorphous titania coating on textiles, exposure of the coated cotton to water vapor for certain times was performed. Introduction of silica on titania coating was also done to enhance the mechanical strength of the coated titania on fabrics [47]. This section will discuss antibacterial properties of the coated cotton with TiO<sup>2</sup> -SiO<sup>2</sup> against bacteria *E. coli* by counting the bacteria before and after testing using colony counter technique. The XRD patterns of the vapor treated coated cotton are shown in **Figure 15a**, and the antibacterial test results are in **Figure 15b**.

Based on the XRD patterns (**Figure 15a**), diffraction peaks of crystalline cellulose as the major component of the cotton fabrics are prominent, with the highest at 2θ ~23 of d002 [4]. It can be seen that the higher the amount of Ti, the peak intensity tends to decrease. A very small hump was observed at sample with Ti:Si 3:1, indicating the presence of anatase titania. It also appears that the peak intensity decreases as increasing the Ti content showing the thick coating of Si-Ti on the cotton fiber. The antibacterial activities of the coated cottons are comparable to the commercial antibacterial cloth, which is Ag-coated. It is worth to note that the coated cotton without exposure to water vapor has almost similar inhibition compared to the ones that have been exposed. This supports the photoactivity of amorphous titania and the fact that the antibacterial coating is active even without UV irradiation.

**Antifouling coatings on wood**. Fouling has been a big problem for infrastructure in the sea. Algae, mollusks including zebra mussels and barnacles, wood boring worms, and also critters like to make the hull their home and can seriously affect the performance of a boat. The current antifouling agents are mostly based on organo-tin, which is highly toxic; therefore

**Figure 14.** Discoloration of coated cotton before UV illumination: (a) amorphous titania, (c) 1 time coating, and (e) 15 times coating of P25 titania; and after UV illumination: (b) amorphous titania, (d) 1 time coating, and (f) 15 times coating of P25 titania.

coating of nanorod-TiO<sup>2</sup> and SiO<sup>2</sup> on wood is proposed. The antifouling mechanism is expected from combined effect of surface hydrophobicity and photocatalysis. Nanorod morphology is expected to build the surface roughness as well as photoactive agent [48]. The silica will provide sturdy coating formulation in the acrylic-based paints. **Figure 16** shows our prompt results on antifouling test of the coated woods in the sea water. Clean surface of wood was achieved for the coated wood, both by TiO<sup>2</sup> -nanorod and TiO<sup>2</sup> -nanorod-SiO<sup>2</sup> . More quantitative data and elaboration on mechanism are on progress [49].

of highly oxidative radicals on the TiO<sup>2</sup>

462 Titanium Dioxide - Material for a Sustainable Environment

action on the coated and uncoated cotton.


The 15 times coating of TiO<sup>2</sup>

TiO<sup>2</sup>

investigation.

of P25 titania.

coated cotton with TiO<sup>2</sup>

surface when light below 400 nm is applied on the

P25-coated cotton fabrics have the highest self-cleaning action

against bacteria *E. coli* by counting the bacteria before and after

photocatalyst surface [42, 46]. **Figure 14** shows the color difference of the self-cleaning

which is considered to be attributed to the highest anatase crystallinity as demonstrated by its sharpest anatase peaks with greatest intensities from the XRD studies in **Figure 12**. From these self-cleaning testing, it is worth noting that the amorphous coating has demonstrated significant photocatalytic activity toward turmeric stain discoloration reaching almost 80% discoloration. The mechanism behind this is still unclear and needed further

**Antibacterial coatings on textile**. To enhance crystallization of amorphous titania coating on textiles, exposure of the coated cotton to water vapor for certain times was performed. Introduction of silica on titania coating was also done to enhance the mechanical strength of the coated titania on fabrics [47]. This section will discuss antibacterial properties of the

testing using colony counter technique. The XRD patterns of the vapor treated coated cotton

Based on the XRD patterns (**Figure 15a**), diffraction peaks of crystalline cellulose as the major component of the cotton fabrics are prominent, with the highest at 2θ ~23 of d002 [4]. It can be seen that the higher the amount of Ti, the peak intensity tends to decrease. A very small hump was observed at sample with Ti:Si 3:1, indicating the presence of anatase titania. It also appears that the peak intensity decreases as increasing the Ti content showing the thick coating of Si-Ti on the cotton fiber. The antibacterial activities of the coated cottons are comparable to the commercial antibacterial cloth, which is Ag-coated. It is worth to note that the coated cotton without exposure to water vapor has almost similar inhibition compared to the ones that have been exposed. This supports the photoactivity of amorphous titania and the fact

**Antifouling coatings on wood**. Fouling has been a big problem for infrastructure in the sea. Algae, mollusks including zebra mussels and barnacles, wood boring worms, and also critters like to make the hull their home and can seriously affect the performance of a boat. The current antifouling agents are mostly based on organo-tin, which is highly toxic; therefore

**Figure 14.** Discoloration of coated cotton before UV illumination: (a) amorphous titania, (c) 1 time coating, and (e) 15 times coating of P25 titania; and after UV illumination: (b) amorphous titania, (d) 1 time coating, and (f) 15 times coating

are shown in **Figure 15a**, and the antibacterial test results are in **Figure 15b**.

that the antibacterial coating is active even without UV irradiation.

**Figure 15.** (a) XRD patterns of cotton fabrics coated by Ti:Si (A) 0:1, (B) 1:0, and (C) 2:1; (b) antibacterial test of commercial antibacterial cloth and cotton fabrics coated with silica-titania with Ti:Si 3:1 which are exposed and not exposed to water vapor.

**Figure 16.** Antifouling test in the sea water: (a) uncoated wood, (b) TiO<sup>2</sup> -nanorod-coated wood, and (c) TiO<sup>2</sup> -nanorod/ SiO<sup>2</sup> -coated wood.
