Natural Dyes: From Cotton Fabrics to Solar Cells

*Indriana Kartini and Adhi Dwi Hatmanto*

#### **Abstract**

This article will discuss natural dyes' role, from colouring the cotton fabrics with some functionality to harvesting sunlight in the dye-sensitized solar cells. Natural dye colourants are identical to the low light- and wash-fastness. Therefore, an approach to improving the colourant's physical properties is necessary. Colouring steps employing silica nanosol and chitosan will be presented. The first part will be these multifunctional natural dye coatings on cotton fabrics. Then, functionality such as hydrophobic surfaces natural dyed cotton fabrics will be discussed. Natural dyes are also potential for electronic application, such as solar cells. So, the second part will present natural dyes as the photosensitizers for solar cells. The dyes are adsorbed on a semiconductor oxide surface, such as TiO2 as the photoanode. Electrochemical study to explore natural dyes' potential as sensitizer will be discussed, for example, natural dyes for *Batik*. Ideas in improving solar cell efficiency will be discussed by altering the photoanode's morphology. The ideas to couple the natural dyes with an organic–inorganic hybrid of perovskite and carbon dots are then envisaged.

**Keywords:** natural dyes, cotton fabrics, hydrophobic, multifunctional textiles, dye-sensitized solar cells

#### **1. Introduction**

Technology is a means to achieve enhanced goals towards advancing human civilization, as is textile dyeing technology. Dyeing is an integral part of the wet textile processing process, which involves massive amounts of chemicals, both in type and quantity. Recently, the development of the concept of eco-fashion or sustainable textiles has led to the development of dyeing technology using natural dyes that care about aspects of water pollution, the sustainability of raw materials and processed products, biodegradability and other environmentally friendly attributes [1]. Human awareness of a healthy environment has revived interest in products that use natural dyes.

Eco-fashion or Sustainable Fashion as a trend against fast fashion is part of a developing design philosophy to create a system that can support and counteract the impact of human activities on the environment. The focus of eco-fashion is not only on the aspects of the materials used and the environment affected by it but also on the wearer's health and the durability of the clothes. An example is the use of natural pesticide-free materials, the use of materials that can be recycled, clothes that are made to last longer and are not easily damaged, to cover the welfare

guarantee for fashion workers. Conventional clothing production is known to involve many resources and produce hazardous waste for the environment. Three criteria attached to environmentally friendly textile creation products include less toxic chemicals, less land or water, and reduction of greenhouse gases. The advantages of nano-sized materials promise exploration opportunities for new technologies with achievements beyond those achieved in computers and biotechnology in recent decades.

natural dyes used for production, mostly are rich of tannins. Potential of this natural dyes will be explored in the fourth section. Finally, some ideas to improve the performance of the natural dyes solar cell will be envisaged in the concluding

**2. Improving the wash-fastness of the natural dyed cotton fabrics**

as a dye for *Batik* and tanners because of its high tannin content. According to Kasmudjiastuti [4] the tannin content in the bark reaches as high as 26%. The *tingi* bark gives a reddish brown colour with a large enough tannin content. The availability of *tingi* bark as a raw material is very abundant in Indonesia. According to Nazir [5] tannins from *Tingi* dyes fall into the category of condensation tannins, with 26% more tannins than other woody plants such as Avaram, Hemlock, Oak, and Chestnut. Kasmudjiastuti [4] characterised the extract of *tingi* tree wood, resulting in that *tingi* wood contains 70.91% of tannins which are included in procyadinin condensation tannins. However, natural dyes derived from plant extraction have a weakness in their fastness resistance to washing processes and exposure to light. Modification of

Dipping the dyed cotton into silica nanosols using the sol–gel method can improve the fastness resistance of a synthetic dye of malachite green b (MG) on cotton fabrics [7, 8]. The hydrogen interaction that occurs between the hydroxyl groups on the cellulose fibers and the hydroxyl groups from the silica sol probably made the silica-MG nanosols to be firmly coated on cotton fabrics. The thin silicon dioxide layer forms a layer that is resistant to heat, light, chemical processes and microbial attack. The oxide thin layer can improve the properties of mechanical

The silica nanosol was prepared using the sol gel method with tetraethylortosilicate

.

(TEOS) as a precursor for Si. This process was carried out in an acidic solution of pH 3-4 using HCl as the catalyst and pH regulator [8]. **Figure 2** showed UV–Vis spectra of the *Tingi* extract in water and the mixture of silica nanosol and *Tingi* extract in volume ratio of 1:4 and 1:40. The maximum absorbance of the natural dye is at 473 nm and did not show any shifting after mixing with nanosol silica indicating no structure changes in the dye and the sols. The infrared spectra of the corresponding dried-powder of the mixture dye sols confirmed this, as implied in **Figure 3**. The more the dyes in the mixture sols, the weaker the peaks for Si-O-Si, at around 1080 cm<sup>1</sup>

The dyeing process on the fabric was done by using the dip coating method, which is the direct immersion of the cloth in a solution mixture of silica sol and the

*The* Tingi *tree (left) and its corresponding bark for the natural dye's resource (right).*

the dye composition can increase the dye fastness [6].

*Natural Dyes: From Cotton Fabrics to Solar Cells DOI: http://dx.doi.org/10.5772/intechopen.97487*

strength and resistance to abrasion [7].

The wood of the *tingi* tree (**Figure 1**) is usually used as firewood. The bark is used

remarks.

**Figure 1.**

**61**

The advantage of using natural dyes lies in the smoothness and softness of the colour. This product is highly valued and maintained because it reflects the beauty, prestige, and cultural structures whose existence cannot be replaced by synthetic dyes. However, despite the advantages of natural dyes, several shortcomings of natural dyes have made *Batik* (tradisitional Indonesia fabrics) craftsmen still reluctant to change their *Batik* dyes from synthetic dyes to natural dyes. Among them are the high price, limited availability, long manufacturing process, and low colour resistant to light or washing.

Natural dyes that are currently often used for *Batik* production besides indigo blue are *Tingi* (*Ceriops tagal*) natural dyes. This dye is obtained from the extraction of the bark of the *Tingi* tree, a type of mangrove plant, which has a high tannin content and is used as a dye for *Batik* and tanners. This dye gives the distinctive brown colour of *Batik*. Like most other natural dyes,*Tingi* natural dyes also have a low degree of fastness to washing. So it requires treatment to increase its fastness to washing. Efforts to increase the colour resistance to washing of cotton fabrics coloured by *Tingi* natural dyes will be discussed in the next section. Afterward, works to attach hydrophobic functionality to result in a multifunctional textiles will be described.

Nanotechnology is a technology related to materials or systems at the nanometer scale (1 nm = 10<sup>9</sup> m). Unusual changes, which cannot be predicted using classical mechanical models, will be obtained at the nanometer scale, such as changes to electronic properties, mechanical properties, magnetic properties, optical properties and chemical reactivity. The potential for a revival of natural dyes can occur through treaties with nanotechnology.

One of the breakthroughs in photovoltaic technology was the photovoltaic cell's invention based on the photoelectrochemical concept employing nanomaterial by a group of Swiss researchers [2], which became popular as dye-sensitized solar cells (DSSC). The solar cell is composed of a thin layer of semiconductor material, such as titanium dioxide or titania (TiO2), which has a porous structure, a complex ruthenium (Ru) compound as a sensitizer, and an electrolyte system for the redox pair of iodine compounds. The ruthenium dye complex has a role in absorbing solar radiation, which will generate the dye's electron system so that it flows into the semiconductor material and is connected to a circuit to generate an electric current. The excited electrons from the dye are immediately replaced by the electrons produced from the electrolyte redox pair system, I/I3 . The natural mechanisms of photosynthesis inspire technology to harvest and use continuous sunlight as a source of energy for all life on earth. Harvesting sunlight ultimately requires the sensitizer to have an absorption character like a black body. So far, ruthenium complex dye as a DSSC photosensitizer has produced a conversion efficiency of 10% [2]. However, ruthenium is not environmentally friendly. Therefore environmentally friendly sensitizers need to be sought. This environmental demand raises the potential of natural dyes as solar cell sensitizers.

Natural sources of natural dyes for sensitizers are directed to plants that have no potential as a food source and have a large percentage of active colouring agents. Several natural dyes that can be used as solar cell sensitizers have been identified to contain tannins, anthocyanins, betalains, flavonoids, and carotenoids [3]. *Batik*'s

guarantee for fashion workers. Conventional clothing production is known to involve many resources and produce hazardous waste for the environment. Three criteria attached to environmentally friendly textile creation products include less toxic chemicals, less land or water, and reduction of greenhouse gases. The advantages of nano-sized materials promise exploration opportunities for new technologies with achievements beyond those achieved in computers and biotechnology in

*Dyes and Pigments - Novel Applications and Waste Treatment*

The advantage of using natural dyes lies in the smoothness and softness of the colour. This product is highly valued and maintained because it reflects the beauty, prestige, and cultural structures whose existence cannot be replaced by synthetic dyes. However, despite the advantages of natural dyes, several shortcomings of natural dyes have made *Batik* (tradisitional Indonesia fabrics) craftsmen still reluctant to change their *Batik* dyes from synthetic dyes to natural dyes. Among them are the high price, limited availability, long manufacturing process, and low colour

Natural dyes that are currently often used for *Batik* production besides indigo blue are *Tingi* (*Ceriops tagal*) natural dyes. This dye is obtained from the extraction of the bark of the *Tingi* tree, a type of mangrove plant, which has a high tannin content and is used as a dye for *Batik* and tanners. This dye gives the distinctive brown colour of *Batik*. Like most other natural dyes,*Tingi* natural dyes also have a low degree of fastness to washing. So it requires treatment to increase its fastness to washing. Efforts to increase the colour resistance to washing of cotton fabrics coloured by *Tingi* natural dyes will be discussed in the next section. Afterward, works to attach hydrophobic functionality to result in a multifunctional textiles will

Nanotechnology is a technology related to materials or systems at the nanometer scale (1 nm = 10<sup>9</sup> m). Unusual changes, which cannot be predicted using classical mechanical models, will be obtained at the nanometer scale, such as changes to electronic properties, mechanical properties, magnetic properties, optical properties and chemical reactivity. The potential for a revival of natural dyes can occur

One of the breakthroughs in photovoltaic technology was the photovoltaic cell's invention based on the photoelectrochemical concept employing nanomaterial by a group of Swiss researchers [2], which became popular as dye-sensitized solar cells (DSSC). The solar cell is composed of a thin layer of semiconductor material, such as titanium dioxide or titania (TiO2), which has a porous structure, a complex ruthenium (Ru) compound as a sensitizer, and an electrolyte system for the redox pair of iodine compounds. The ruthenium dye complex has a role in absorbing solar radiation, which will generate the dye's electron system so that it flows into the semiconductor material and is connected to a circuit to generate an electric current. The excited electrons from the dye are immediately replaced by the electrons

photosynthesis inspire technology to harvest and use continuous sunlight as a source of energy for all life on earth. Harvesting sunlight ultimately requires the sensitizer to have an absorption character like a black body. So far, ruthenium complex dye as a DSSC photosensitizer has produced a conversion efficiency of 10% [2]. However, ruthenium is not environmentally friendly. Therefore environmentally friendly sensitizers need to be sought. This environmental demand

Natural sources of natural dyes for sensitizers are directed to plants that have no potential as a food source and have a large percentage of active colouring agents. Several natural dyes that can be used as solar cell sensitizers have been identified to contain tannins, anthocyanins, betalains, flavonoids, and carotenoids [3]. *Batik*'s

. The natural mechanisms of

recent decades.

be described.

**60**

resistant to light or washing.

through treaties with nanotechnology.

produced from the electrolyte redox pair system, I/I3

raises the potential of natural dyes as solar cell sensitizers.

natural dyes used for production, mostly are rich of tannins. Potential of this natural dyes will be explored in the fourth section. Finally, some ideas to improve the performance of the natural dyes solar cell will be envisaged in the concluding remarks.
