*3.1.5 Transmission electron microscopy*

TEM images and particle size histograms of synthesised TiO2, Ag, Au and Pt deposited TiO2 catalysts are shown in **Figure 3**. Almost uniform dispersion was obtained

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

with all the catalysts. The average size of the particles was calculated by averaging particle sizes of 20–30 particles. The plot of particle size distribution is also shown. The average particle size of TiO2, Ag/TiO2, Au/TiO2 and Pt/TiO2 catalyst was

*Transmission electron micrograph and particle size histograms of (A) synthesised TiO2, (B) Ag/TiO2,*

The effect of initial concentration of dye on the rate of decolourisation was studied by taking 250 mL of dye solutions and varying the concentrations between 8 × l0<sup>−</sup><sup>5</sup>

ried out for 6 h by using 125 W low pressure mercury arc lamp (wave length 254 nm) and 85 W tungsten lamp (wave length 365 nm) as UV and visible light sources, respectively. **Figure 4** shows that percentage decolourisation decreases as the initial concentration of the dye increases under both UV and visible light illumination.

Similar results in the photocatalytic degradation of phenol were reported in the literature [18, 19]. The decolourisation rate relates to the probability of formation of hydroxyl radicals (OH˙) on the catalyst surface and the probability of hydroxyl radicals reacting with dye molecules. Hence the rate constant depends on the prob-

k̕=k0 <sup>x</sup> POH x Pdye molecules (6)

where k' is the overall rate constant and k0 is the reaction rate constant. POH˙ and Pdye molecules refer to the probabilities of generation of OH˙ radicals and OH˙ radicals reacting with dye molecules. We all know that the reaction rate constant k0 is independent of initial dye concentration but POH˙ and Pdye molecules will be affected by the dye concentration. Literature suggests that photocatalytic degradation of aromatic compounds mainly occurs by hydroxyl radicals [20]. The rate determining step of the reaction may be the formation of OH˙ radicals that are formed through

and 1.6 × l0<sup>−</sup><sup>5</sup>

for RB-5 with constant catalyst weight (1.5 g). The irradiation was car-

M for RY-17 and 6 × l0<sup>−</sup><sup>6</sup>

found to be 27 nm, 11 nm, 10 nm and 19 nm respectively.

M for Tartrazine (TAZ), 8 × l0<sup>−</sup><sup>6</sup>

abilities of the formation of these two. Hence k' can be expressed as

the reaction of holes with adsorbed OH<sup>−</sup> and H2O [21, 22].

**3.2 Photocatalytic studies on TiO2 (P-25 DEGUSSA)**

*3.2.1 Effect of initial concentration of dye*

and 1.3 × l0<sup>−</sup><sup>4</sup>

**Figure 3.**

*(C)Au/TiO2 and (D) Pt/TiO2.*

and 1.6 × l0<sup>−</sup><sup>5</sup>

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

**Figure 2.** *X-ray diffraction patterns of (A). synthesised TiO2, (B). Ag/TiO2, (C) Au/TiO2 and (D). Pt/TiO2.*

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

#### **Figure 3.**

*Gold Nanoparticles - Reaching New Heights*

Β = full width at half maximum in radians.

*3.1.5 Transmission electron microscopy*

be in the nanometre range as shown in **Table 2**.

*Physicochemical characteristics of bare and M/TiO2 catalysts.*

where d, diameter of the metal particle; λ, wavelength of the X-ray radiation (λ = 0.15418 nm), K = 0.98 (constant); θ, characteristic X-ray diffraction peak;

The average particle diameter of the synthesised TiO2 and M/TiO2 was found to

TEM images and particle size histograms of synthesised TiO2, Ag, Au and Pt deposited TiO2 catalysts are shown in **Figure 3**. Almost uniform dispersion was obtained

*X-ray diffraction patterns of (A). synthesised TiO2, (B). Ag/TiO2, (C) Au/TiO2 and (D). Pt/TiO2.*

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**Figure 2.**

**Table 2.**

*Transmission electron micrograph and particle size histograms of (A) synthesised TiO2, (B) Ag/TiO2, (C)Au/TiO2 and (D) Pt/TiO2.*

with all the catalysts. The average size of the particles was calculated by averaging particle sizes of 20–30 particles. The plot of particle size distribution is also shown.

The average particle size of TiO2, Ag/TiO2, Au/TiO2 and Pt/TiO2 catalyst was found to be 27 nm, 11 nm, 10 nm and 19 nm respectively.
