**1. Introduction**

Dyeing and finishing processes are the two important steps in textile industries. Large number of synthetic dyes are used extensively in the textile dyeing process and these industries produce large quantities of waste water containing carcinogenic dyes. When ground water mixes with such waste water it gets polluted and cause allergy, damage of eye, brain, liver and reproductive organs and deformities in babies during pregnant period. Thus, water pollution is a major concern in the developing nations. Though dyes are aesthetic pollutants by nature of their colour,

they may interfere with light penetration in the receiving water bodies thereby disturbing the biological processes.

Among the various types of dyes, reactive dyes are extensively used for dyeing cotton fabrics and hence they add a lot to water pollution. The volume of textile effluent discharged from dyeing industries mainly using reactive dyes are approximately calculated to be 3,00,000–4,00,000 L ton<sup>−</sup><sup>1</sup> fabric materials in a year [1].

The increased public concern and the stringent international environmental standards have prompted the need to develop novel treatment methods for converting dye effluents to harmless compounds. Although some conventional treatment technologies such as filtration, coagulation, flocculation etc. have been tried in the past they are not viable and green technologies. Zero generation of sludge and complete mineralisation of dyes are the two important criteria for the technology to be economically attractive and environmentally benign. In this context the present study of dye treatment by using photocatalysts which mineralises the carcinogens into CO2, H2O and mineral salts assumes great significance.

The ideal photocatalyst should be stable, inexpensive, non-toxic and highly photoactive. Another primary criteria for the degradation of organic compounds is that the redox potential of the H2O/OH˙ couple lies within the band gap of the semiconductor [2]. Several semiconductors have band gap energies sufficient for catalysing wide range of chemical reactions. These include TiO2, WO3, SrTiO3, ZnO, ZnS, etc. Binary metal sulphide semiconductors such as CdS, CdSe and PbS are not sufficiently stable catalysts in aqueous media as they readily undergo photoanodic corrosion [3]. These materials are also known to be toxic. The iron oxides are not suitable semiconductors as they readily undergo photocathodic corrosion [4]. ZnO is unstable in water as Zn(OH)2 being formed on the particle surface. This results in catalyst deactivation [5]. However, the anatase form of TiO2 seems to be the best. The photoactivity of TiO2 is known for approximately 60 years and investigated extensively. Although TiO2 absorbs only approximately 5% of the solar light reaching the surface of the earth, it is the best-investigated semiconductor in the field of chemical conversion and storage of solar energy. Accordingly, many efforts have been made to sensitise titania for visible light induced photocatalytic reactions. Such sensitization techniques include (i) Doping with altervalent ions, (ii) heterojunctioning with other semiconductors, (iii) dye sensitization (iv), deposition of noble metals over semiconductors etc.

Herein we report the deposition of noble metals such as Au, Pt and Pd over synthesised titania. Noble metal is important because of their own catalytic activity and they actually modify the photocatalytic properties of the semiconductor by changing the distribution of electrons. Further, it can enhance the yield of a particular product or the rate of the photocatalytic reaction. The addition of a metal to a semiconductor surface also changes the reaction products. On the other hand, the loading level is important in governing the net effect of metallation as heavy metal loading induces faster electron-hole recombination [6]. One of the main reasons for the numerous studies of titaniasupported metal catalysts is the so-called strong metal-support interaction (SMSI). The platinised titania exhibits a much higher activity in a series of photocatalytic reactions than pure anatase. Combined Pt-RuO2/TiO2 catalysts are the most promising ones for photocatalytic water cleavage [7]. The Au, Ag and Pd impregnated titania catalysts were synthesised, characterised by various instrumental techniques and evaluated towards the decolourisation of one azo dye tartrazine (TAZ) and two reactive dyes Reactive Yellow and Reactive Black (RY-17 and RB-5) (**Table 1**).

**77**

*Detoxification of Carcinogenic Dyes by Noble Metal (Ag, Au, Pt) Impregnated Titania…*

**Name of the dye Molecular Formula Structure**

C16H9N4Na3O9S2

C21H17N4K2O10S3

C26H21N5Na4O19S6

Textile dyes namely Tartrazine (TAZ), Reactive Yellow-17 (RY-17) and Reactive Black (RB-5) were procured from Bagmul Sons, India and was used without any

The anatase form of TiO2 (P-25 Degussa) with particle size 30 nm and surface

titanium isopropoxide (Lancaster >99% pure), Silver nitrate (Merck >99% pure), Chloroauric acid (Merck >99% pure) and tetraammineplatinum (II) chloride

All other chemicals namely NaCl, C2H5OH, Na2CO3, H2O2, K2S2O8, NH4OH, H2SO4, isopropanol and acetic acid were obtained from Merck (purity >98%) and were used as received. The water employed for the studies was doubly distilled.

The catalytic materials used in the present study were synthesised as described

Sol gel process was adopted for the synthesis of TiO2. Titanium isopropoxide, isopropanol, water and acetic acid were used as starting materials. Solution A contained 17 mL titanium isopropoxide and 40 mL of isopropanol and Solution B contained 60 mL of isopropanol, 15 mL acetic acid and 5 mL water. Solutions A and B were mixed and stirred for 2 h. The formed TiO2 sol was aged to get the gel of TiO2. The obtained gel was dried, ground with mortar and pestle and finally calcined at 500°C for 3 h [8].

The M/TiO2 (M = Ag, Au and Pt) catalysts were prepared by photoreduction method [9]. Calculated amounts of noble metal precursors (0.14 g of AgNO3 for

was used as such. The precursors for titania, Ag, Au and Pt were

*DOI: http://dx.doi.org/10.5772/intechopen.80467*

Tartrazine (TAZ) Molecular Weight-534.3 λ max(nm)- 455 Dye Type- Azo C I No- C.I.19140

ReactiveYellow-17(RY-17) Molecular Weight-691.1 λ max(nm)- 420 Dye Type- Reactive C.I No18852

Reactive Black-5 (RB-5) Molecular Weight-927.4 λ max(nm)- 597 Dye Type-Reactive C.I.20502

**2. Materials and methods**

*Physicochemical properties of various dyes under study.*

**2.1 Materials**

**Table 1.**

area 50 m<sup>2</sup>

below:

further purification.

g<sup>−</sup><sup>1</sup>

(Merck >99% pure) were used as received.

*2.2.2 Synthesis of M/TiO2 (M = Ag, Au and Pt)*

**2.2 Synthesis of photocatalysts**

*2.2.1 Synthesis of TiO2*

*Detoxification of Carcinogenic Dyes by Noble Metal (Ag, Au, Pt) Impregnated Titania… DOI: http://dx.doi.org/10.5772/intechopen.80467*


#### **Table 1.**

*Gold Nanoparticles - Reaching New Heights*

disturbing the biological processes.

year [1].

they may interfere with light penetration in the receiving water bodies thereby

Among the various types of dyes, reactive dyes are extensively used for dyeing cotton fabrics and hence they add a lot to water pollution. The volume of textile effluent discharged from dyeing industries mainly using reactive dyes are

The increased public concern and the stringent international environmental standards have prompted the need to develop novel treatment methods for converting dye effluents to harmless compounds. Although some conventional treatment technologies such as filtration, coagulation, flocculation etc. have been tried in the past they are not viable and green technologies. Zero generation of sludge and complete mineralisation of dyes are the two important criteria for the technology to be economically attractive and environmentally benign. In this context the present study of dye treatment by using photocatalysts which mineralises the carcinogens

The ideal photocatalyst should be stable, inexpensive, non-toxic and highly photoactive. Another primary criteria for the degradation of organic compounds is that the redox potential of the H2O/OH˙ couple lies within the band gap of the semiconductor [2]. Several semiconductors have band gap energies sufficient for catalysing wide range of chemical reactions. These include TiO2, WO3, SrTiO3, ZnO, ZnS, etc. Binary metal sulphide semiconductors such as CdS, CdSe and PbS are not sufficiently stable catalysts in aqueous media as they readily undergo photoanodic corrosion [3]. These materials are also known to be toxic. The iron oxides are not suitable semiconductors as they readily undergo photocathodic corrosion [4]. ZnO is unstable in water as Zn(OH)2 being formed on the particle surface. This results in catalyst deactivation [5]. However, the anatase form of TiO2 seems to be the best. The photoactivity of TiO2 is known for approximately 60 years and investigated extensively. Although TiO2 absorbs only approximately 5% of the solar light reaching the surface of the earth, it is the best-investigated semiconductor in the field of chemical conversion and storage of solar energy. Accordingly, many efforts have been made to sensitise titania for visible light induced photocatalytic reactions. Such sensitization techniques include (i) Doping with altervalent ions, (ii) heterojunctioning with other semiconductors, (iii) dye sensitization (iv), deposition of noble metals

Herein we report the deposition of noble metals such as Au, Pt and Pd over synthesised titania. Noble metal is important because of their own catalytic activity and they actually modify the photocatalytic properties of the semiconductor by changing the distribution of electrons. Further, it can enhance the yield of a particular product or the rate of the photocatalytic reaction. The addition of a metal to a semiconductor surface also changes the reaction products. On the other hand, the loading level is important in governing the net effect of metallation as heavy metal loading induces faster electron-hole recombination [6]. One of the main reasons for the numerous studies of titaniasupported metal catalysts is the so-called strong metal-support interaction (SMSI). The platinised titania exhibits a much higher activity in a series of photocatalytic reactions than pure anatase. Combined Pt-RuO2/TiO2 catalysts are the most promising ones for photocatalytic water cleavage [7]. The Au, Ag and Pd impregnated titania catalysts were synthesised, characterised by various instrumental techniques and evaluated towards the decolourisation of one azo dye tartrazine (TAZ) and two reactive dyes Reactive Yellow and Reactive Black

fabric materials in a

approximately calculated to be 3,00,000–4,00,000 L ton<sup>−</sup><sup>1</sup>

into CO2, H2O and mineral salts assumes great significance.

**76**

over semiconductors etc.

(RY-17 and RB-5) (**Table 1**).

*Physicochemical properties of various dyes under study.*
