**3.1 Characterisation of synthesised TiO2 and M/TiO2 photocatalysts**

## *3.1.1 UV-visible spectrophotometry*

The absorption spectra of synthesised TiO2 (gel form) was recorded using UV-visible spectrophotometer and given in **Figure 1**. An absorption maxima observed around 320 nm is due to the charge transfer from the VB of 2p orbitals of the oxide ions to the CB of 3dt2g orbitals of the titania cations [12].

The optical absorption evolution spectra of solutions of noble metal precursors (2 × 10<sup>−</sup><sup>3</sup> M AgNO3, 2 × 10<sup>−</sup><sup>4</sup> M HAuCl4 and 1 × 10<sup>−</sup><sup>5</sup> M [Pt(NH3)4]Cl2) in the presence of TiO2 colloid during visible irradiation are shown in **Figure 1**.

This figure shows that on visible irradiation, appearance of new bands centred on 370 nm for Ag, 520 nm for Au and 502 nm for Pt were observed. The reason for

#### **Figure 1.**

*(a) UV-visible spectrum of synthesised TiO2 and optical absorption evolution spectra of (b) Ag/TiO2 (c) Au/TiO2 and (d) Pt/TiO2 at different time intervals.*

**81**

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

equation. The values were consistent with the values reported already [16].

appearance of these peaks is due to the surface plasmon excitation of the respective

The band gap values of all the synthesised catalysts (TiO2 and M/TiO2) were calculated from the corresponding λ values obtained by extrapolating the rising portion of the spectrum to the × axis at zero absorbance and by using the following

Eg = hc/λ (4)

where Eg, band gap energy; h, Planck's constant in eV (4.135 × 10<sup>−</sup>15 eV); c, velocity

The band gap values for the synthesised TiO2 and metal loaded TiO2 are given in **Table 2**. The band gap values were found to be lower for the metal loaded catalyst

Although lowering of band gap is not good for better catalytic activity under UV irradiation due to easy recombination, the presence of metals act as electrons traps and prevents the recombination process and also making the photocatalyst active in

To determine the actual metal content of all the synthesised M/TiO2 catalysts, they were subjected to AAS analysis after dissolving them. The metal content in each catalyst determined is given in **Table 2**. The results show that the experimentally determined metal content value is close to that of the theoretical value (1% w/w).

The surface area of all the synthesised catalysts viz., TiO2 (P-25 Degussa), TiO2 and M/TiO2 catalysts were determined and given in **Table 2**. **Table 2** clearly shows that the synthesised catalysts show higher surface than commercial TiO2 (P-25 Degussa). It is to be noted that impregnation of noble metals (Pt, Pd and Au) over TiO2 did not alter the surface area values significantly. A very small reduction in the surface area observed may be due to the blocking of fine capillaries present on TiO2 surface by metal thin islands. These islands prevent the entry of the probe molecule

To obtain information regarding the phase formation and crystallite size, X-ray diffraction measurements were performed for the synthesised TiO2 and M/TiO2 (M = Ag, Au and Pt) photocatalysts and the XRD patterns are shown in **Figure 2**. The synthesised TiO2 has both anatase and rutile phases but not the brookite phase. Anatase and rutile phases are confirmed by the appearance of major peaks at 2θ = 25.4 and 48° respectively. The corresponding d (111) reflections of the noble metal atoms were found at 2θ = 38.1, 38.8 and 40° for Ag, Au and Pt, which confirms the impregnation of metal particles on TiO2 lattice. From the X-ray diffraction patterns the average particle size of the synthesised TiO2 and M/TiO2 was calculated

d=Kλ/β Cos θ (5)

m/s); λ, wavelength of corresponding M/TiO2 catalysts 370 nm for Ag,

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

metal colloids [13–15].

of light (3 × 108

the visible range.

520 nm for Au and 502 nm for Pt.

*3.1.3 BET surface area measurements*

*3.1.4 X-ray diffraction analysis*

using Debye-Scherrer equation.

when compared to the synthesised TiO2 catalyst.

*3.1.2 Atomic absorption spectrophotometric analysis*

(nitrogen gas) into the pores during BET measurement [17].

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

appearance of these peaks is due to the surface plasmon excitation of the respective metal colloids [13–15].

The band gap values of all the synthesised catalysts (TiO2 and M/TiO2) were calculated from the corresponding λ values obtained by extrapolating the rising portion of the spectrum to the × axis at zero absorbance and by using the following equation. The values were consistent with the values reported already [16].

$$\mathbf{E}\_{\mathfrak{g}} = \mathbf{h}\mathbf{c}/\lambda\tag{4}$$

where Eg, band gap energy; h, Planck's constant in eV (4.135 × 10<sup>−</sup>15 eV); c, velocity of light (3 × 108 m/s); λ, wavelength of corresponding M/TiO2 catalysts 370 nm for Ag, 520 nm for Au and 502 nm for Pt.

The band gap values for the synthesised TiO2 and metal loaded TiO2 are given in **Table 2**. The band gap values were found to be lower for the metal loaded catalyst when compared to the synthesised TiO2 catalyst.

Although lowering of band gap is not good for better catalytic activity under UV irradiation due to easy recombination, the presence of metals act as electrons traps and prevents the recombination process and also making the photocatalyst active in the visible range.

## *3.1.2 Atomic absorption spectrophotometric analysis*

To determine the actual metal content of all the synthesised M/TiO2 catalysts, they were subjected to AAS analysis after dissolving them. The metal content in each catalyst determined is given in **Table 2**. The results show that the experimentally determined metal content value is close to that of the theoretical value (1% w/w).

### *3.1.3 BET surface area measurements*

The surface area of all the synthesised catalysts viz., TiO2 (P-25 Degussa), TiO2 and M/TiO2 catalysts were determined and given in **Table 2**. **Table 2** clearly shows that the synthesised catalysts show higher surface than commercial TiO2 (P-25 Degussa). It is to be noted that impregnation of noble metals (Pt, Pd and Au) over TiO2 did not alter the surface area values significantly. A very small reduction in the surface area observed may be due to the blocking of fine capillaries present on TiO2 surface by metal thin islands. These islands prevent the entry of the probe molecule (nitrogen gas) into the pores during BET measurement [17].

## *3.1.4 X-ray diffraction analysis*

To obtain information regarding the phase formation and crystallite size, X-ray diffraction measurements were performed for the synthesised TiO2 and M/TiO2 (M = Ag, Au and Pt) photocatalysts and the XRD patterns are shown in **Figure 2**.

The synthesised TiO2 has both anatase and rutile phases but not the brookite phase. Anatase and rutile phases are confirmed by the appearance of major peaks at 2θ = 25.4 and 48° respectively. The corresponding d (111) reflections of the noble metal atoms were found at 2θ = 38.1, 38.8 and 40° for Ag, Au and Pt, which confirms the impregnation of metal particles on TiO2 lattice. From the X-ray diffraction patterns the average particle size of the synthesised TiO2 and M/TiO2 was calculated using Debye-Scherrer equation.

*Gold Nanoparticles - Reaching New Heights*

To check the photocatalytic activity of M/TiO2 catalyst for the photocatalytic degradation of actual textile effluent, the samples were collected from M/s Ramkay & Co, Erode, Tamil Nadu, India, filtered and diluted. Since the effluent contains number of unknown dyes it gave a broad peak in the wavelength range of 500–600 nm. Since the absorbance is additive, the effluent simply shows a broad peak in this range. To the diluted effluent (250 mL), 6 g of M/TiO2 (M = Ag, Au and Pt) catalyst was added and

Chemical oxygen demand (COD) of the samples collected at different intervals was determined by dichromate method in the presence of a catalyst Ag2SO4 [10, 11].

the photocatalytic study was performed in the photocatalytic reactor.

**3.1 Characterisation of synthesised TiO2 and M/TiO2 photocatalysts**

the oxide ions to the CB of 3dt2g orbitals of the titania cations [12].

ence of TiO2 colloid during visible irradiation are shown in **Figure 1**.

The absorption spectra of synthesised TiO2 (gel form) was recorded using UV-visible spectrophotometer and given in **Figure 1**. An absorption maxima observed around 320 nm is due to the charge transfer from the VB of 2p orbitals of

M HAuCl4 and 1 × 10<sup>−</sup><sup>5</sup>

*(a) UV-visible spectrum of synthesised TiO2 and optical absorption evolution spectra of (b) Ag/TiO2*

*(c) Au/TiO2 and (d) Pt/TiO2 at different time intervals.*

The optical absorption evolution spectra of solutions of noble metal precursors

This figure shows that on visible irradiation, appearance of new bands centred on 370 nm for Ag, 520 nm for Au and 502 nm for Pt were observed. The reason for

M [Pt(NH3)4]Cl2) in the pres-

**2.6 Textile effluent study**

*2.6.1 COD experiment*

(2 × 10<sup>−</sup><sup>3</sup>

**3. Results and discussion**

*3.1.1 UV-visible spectrophotometry*

M AgNO3, 2 × 10<sup>−</sup><sup>4</sup>

**80**

**Figure 1.**


#### **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; Β = full width at half maximum in radians.

The average particle diameter of the synthesised TiO2 and M/TiO2 was found to be in the nanometre range as shown in **Table 2**.
