*2.4.5 Reflectance spectrophotocolorimetry*

With the series of samples of model solutions of 50 mg/L of concentration at which the cycles of contamination with dye and subsequent ozonation were carried out up to five times, dyeing tests were made with reactive and direct dyes applied on samples of cotton, for determining the feasibility of reusing water pretreated with ozone in dyeing processes of cellulosic materials. The dyes were made on cloth prepared for this purpose. A dyeing was made with each water sample, and the difference in color kept by the samples of cloth dyed with the pretreated water was determined in relation to a reference standard, that is, a sample of the same type dyed using distilled water and maintaining the other constant conditions. The test was carried out according to the AATCC method 173-2005 of the American Association of Textile Chemists and Colorists (AATCC) called Calculation of Small Color Differences for Acceptability, which is of extended application in the textile industry [9].

A Color Eye 7000-A spectrophotometer (Gretag-Macbeth) with color integration sphere and colorimetry software was used. This equipment simulates the color appreciation by the human eye and translates it into a value or coefficient of color difference (ΔE) that, according to the method used, should not be greater than unity, that is, ΔE < 1.0. This value less than 1.0 represents a color difference that a common observer could not perceive, while ΔE > 1.0 is a color difference that any person can detect and, therefore, implies that the result of a dye is not acceptable [9].

**41**

is almost identical.

**3. Results**

**Figure 3.**

*Chemical and Tinctorial Aspects Related to the Reuse of Effluents Treated by Ozonation…*

The principle on which the method of determination is based is of a psychophysiological nature and is known as Young's Theory. It refers to the fact that the human eye perceives color through three types of receptors and considers the sensory response as inscribed in a Cartesian space, where the axis L corresponds to the opposite pair black-white (−L corresponds to the color black and +L corresponds to the color white), the axis a corresponds to the pair green-red (−a corresponds to green and +a to red color), and the b axis corresponds to the yellow-blue pair

It is considered that each color tonality constitutes a point in the color space, and the color difference between two samples is calculated as the distance between the two points that represent the tonalities of the two samples compared, considering one of them as the standard. In this way, the color difference translates into a single numerical value that allows us to easily handle it. **Figure 3** illustrates a color differ-

In all cases, the discoloration was carried out during the first hour, despite the low concentration of ozone used. The addition of inorganic auxiliaries accelerates the reaction of ozone with textile dyes. **Figure 4** presents the variation of the UV-Vis spectra for the RR141 during 60 min of ozonation. From the variation of the spectra of the RR141 dye during ozonation, it can be concluded that this compound is rapidly destroyed under the action of ozone. The tendency to discoloration during the ozonation process is very similar for both dyes. The studied compounds are rapidly destroyed under the action of ozone. **Figure 5** shows the discoloration of

The influence of the by-products of the degradation of the dyes on the dyes made with the treated water depends not only on the accumulation of these through the cycles of ozonation contamination but also of the dyeing class of the dye used in the dyeing with the treated water, as well as the chemical constitution of the latter. The results obtained in this study showed that for both dyes studied, analyzed at

**Figure 6** shows the discoloration for the studied dyes at 50 ppm. Based on the preliminary analysis, it can be stated that the discoloration of the RR141 and RB160

*DOI: http://dx.doi.org/10.5772/intechopen.81468*

(−b corresponds to blue and +b to yellow).

*Graphic representation of color difference, ΔE.*

ence between two samples (ΔE) within the color space.

RB160 for three different concentrations at 615 nm.

50 mg/L, the color disappears after 30 min of ozonation.

*Chemical and Tinctorial Aspects Related to the Reuse of Effluents Treated by Ozonation… DOI: http://dx.doi.org/10.5772/intechopen.81468*

**Figure 3.** *Graphic representation of color difference, ΔE.*

The principle on which the method of determination is based is of a psychophysiological nature and is known as Young's Theory. It refers to the fact that the human eye perceives color through three types of receptors and considers the sensory response as inscribed in a Cartesian space, where the axis L corresponds to the opposite pair black-white (−L corresponds to the color black and +L corresponds to the color white), the axis a corresponds to the pair green-red (−a corresponds to green and +a to red color), and the b axis corresponds to the yellow-blue pair (−b corresponds to blue and +b to yellow).

It is considered that each color tonality constitutes a point in the color space, and the color difference between two samples is calculated as the distance between the two points that represent the tonalities of the two samples compared, considering one of them as the standard. In this way, the color difference translates into a single numerical value that allows us to easily handle it. **Figure 3** illustrates a color difference between two samples (ΔE) within the color space.
