**3. Titania as the photoanode for dye-sensitized solar cells**

The dye-sensitized solar cell consists of three main components, namely, a working electrode, a counter electrode, and an electrolyte. The current most efficient cells of 10.4% [33] used a nanostructured titanium dioxide film on a transparent conducting glass (TCO) as a working electrode, a platinized conducting glass as the counter electrode and I3 pairs as the electrolyte solution. In this section, performance of the mesoporous titania electrodes as photoanodes in DSSCs is presented. Some results using natural dyes as the photosensitizers will also be discussed.

Since the anatase crystalline phase seems to be preferred for this DSSC, attempts to incorporate the neutral route hydrothermal powder into a DSSC were carried out. A one-coat slip-cast electrode was assembled with sputtered and thermally platinized counter electrodes. **Figure 10** shows the I-V curves of these DSSCs using ruthenium "N3" as the sensitizer by using different

it produces anatase crystalline phase. Diffraction at 2θ ≈ 24° is probably due to the shifts from peak at 25° of anatase (101) and titanate (011). Peak shifts are preferred due to the formation of nanotubes, which put strains on the bonding in sample. The corresponding Raman spectra

nia were open-ended nanotubes. The nanotubes are highly distributed (separated from each other), showing that the bundles of titania did not form. Yet a few nanosheets are visible in the image, confirming that the morphological changes did not perfectly occur. High amount of

Short-time synthesis of titania nanotube was proposed by applying mechanical or sonicationassisted stirring prior hydrothermal. The effect of various stirring times and hydrothermal treatments on the crystalline phases and morphology of the resulted titania has been studied [32]. It has been shown that the nanotube titania can be obtained after 5 h hydrothermal treatment at 150°C. The XRD patterns of the resulted powders showed the existence of a mixture of anatase and titanate crystalline phases with increased intensity of [200] as the stirring time

have also confirmed the existence of both anatase and titanate crystalline phases. The high textural coefficient for [200] (TC200) has indicated oriented growth of one-dimensional anatase along [200]. All powders resulted at various stirring time were nanotubes, as confirmed by

The next section will discuss the application of titanium dioxide for photoelectrochemical

The dye-sensitized solar cell consists of three main components, namely, a working electrode, a counter electrode, and an electrolyte. The current most efficient cells of 10.4% [33] used a nanostructured titanium dioxide film on a transparent conducting glass (TCO) as a working

solution. In this section, performance of the mesoporous titania electrodes as photoanodes in DSSCs is presented. Some results using natural dyes as the photosensitizers will also be

Since the anatase crystalline phase seems to be preferred for this DSSC, attempts to incorporate the neutral route hydrothermal powder into a DSSC were carried out. A one-coat slip-cast electrode was assembled with sputtered and thermally platinized counter electrodes. **Figure 10** shows the I-V curves of these DSSCs using ruthenium "N3" as the sensitizer by using different

leads to the transformation from nanotubes into nanosheets and later to spherical struc-

) was found to be similar with Na-Ti-H, as mostly all of the morphology of tita-

as the alkaline results in the formation of spherical nanoparticle titania with


ratio to NaOH of 1:3. Alteration

(B) was observed. Raman spectra

pairs as the electrolyte

published elsewhere [31] support the formation of anatase phase after acid washing.

The morphological structure for sample 3:1 NaNH<sup>3</sup>

456 Titanium Dioxide - Material for a Sustainable Environment

tures [31]. Thus, nanotube preparation can be sought at NH3

increasing. At the longest stirring time, the existence of TiO<sup>2</sup>

solar cells (DSSC) and multifunctional coatings for textiles and woods.

**3. Titania as the photoanode for dye-sensitized solar cells**

electrode, a platinized conducting glass as the counter electrode and I3

transmission electron microscope (TEM).

(NaOH:NH<sup>3</sup>

to only using NH3

discussed.

anatase crystalline phase [31].

NH3

**Figure 10.** I-V curves of mesoporous titania derived from neutral hydrothermal route using different platinization methods for counter electrodes: (A) light current and (B) the corresponding dark current curves [1].

counter electrodes. It is observed that the thermally platinized counter electrode gave better DSSC performance with increased open-circuit voltage (VOC) and short-circuit current (ISC). The increased variables enhanced the cell efficiency to about 5%. This improvement can be attributed to the high surface area of platinum in thermally platinized counter electrode that will act as an efficient catalyst for iodine reduction [8]. The redox electrolyte shuttles the electron from the site of regeneration on the sensitized titania working electrode to the counter electrode to complete the electron cycle. During this process, the iodine must be reduced back to iodide at minimum energy loss on the counter electrode. However, the fill factor of this cell is much lower than that assembled with a sputtered Pt counter electrode. This may be caused by the loss of some scattered light, which may enhance the electron generation throughout the titania film. The possible recombination rate for this thermally platinized cell is slightly lower than that of the sputtered Pt counter electrode. Thus, it is expected to compromise the losses. In addition, this type of counter electrode produced a transparent DSSC. Illumination can be performed in both sides of the sandwiched cells that cannot be done by using sputtered Pt counter electrode.

Comparing the performance of acid treated-acid route photoanode with neutral route, a higher efficiency was achieved for the latter photoanode [1]. High open-circuit voltage and short-circuit current are responsible for this performance, which may be caused by the presence of the full anatase domain characteristic of the powder precursor as previously demonstrated (Section 1).

**Table 4** shows the solar cell parameters of various titania photoanodes and natural dyes as sensitizers. Results on natural dyes as the sensitizers are not as high as the cells using ruthenium complex. Dried fruit of *joho*, bark of *tingi*, and *tegeran* were commonly used as dyes for traditional *Batik* clothes in Indonesia. The cells with *joho* and *tegeran* dyes have shown appreciable generated photovoltage and photocurrent compared to *tingi*. Both *joho* and *tegeran* dyes


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

not directly achieved using these techniques. TiO<sup>2</sup>

amorphous, while the photoactivity of amorphous phase of TiO<sup>2</sup>

(titanium dioxide), anatase, is widely known as material having excel-

layers on organic substrates are mostly

Nanostructured Titanium Dioxide for Functional Coatings

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

459

has been less studied and

. Turmeric

coat-

coating but lower

P25 was a gift from

lent 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

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

**Self-cleaning and antibacterial coatings on textile**. This study aims at preparing amorphous

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>

photodegradation of micelles, oils, solvents, sooth, and aromatic and aliphatic hydrocarbons

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)

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

powder of P25 (Degussa) were used as titanium sources. TiO<sup>2</sup>


rials modeled by turmeric extract stain on the cotton textile coated with those TiO<sup>2</sup>

ing on cotton fabrics has self-cleaning action similar to the crystalline TiO<sup>2</sup>

coating on cotton fabrics and examining the discoloration of organic mate-


Crystalline TiO<sup>2</sup>

will also be explored.

and crystalline TiO<sup>2</sup>

activity. The use of TiO<sup>2</sup>

under daylight.

and TiO<sup>2</sup>

and crystalline TiO<sup>2</sup>

\* Testing done at photovoltaic testing facility in Physics Department, University of Queensland, Brisbane, Australia, across a 0.025 cm2 active area DSSC under illumination of 100 mW/cm<sup>2</sup> power source equal to AM1.5 Direct Sun, sensitizer ruthenium N3 dye.

\*\*Active area TiO = P25 0.25 cm<sup>2</sup> ; Pinput = 25.6 mW/cm<sup>2</sup> , Au counter electrode, testing done in Physics Department, Universitas Gadjah Mada, Yogyakarta, Indonesia.

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

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

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 contribution (data not shown). Upon adsorption on a TiO<sup>2</sup> layer, the absorption spectra of the three *Batik* dyes are all broadened forward to red side compared with their respective spectra in ethanol solution. These indicate sensitizing effect of natural *Batik* dyes on TiO<sup>2</sup> films [34, 35]. 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 self-quenching of the dyes in the *J*-like aggregate form.

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 the sensitizers into TiO<sup>2</sup> [1]. High photocurrent resulted from efficient electron injection of the pigments into the conduction band of TiO<sup>2</sup> owing to the effective attachment of the pigment molecules on the TiO<sup>2</sup> surface.
