**3.3 Comparison of photocatalytic activities of synthesised TiO2 with TiO2 (P-25 Degussa)**

The photocatalytic decolourisation of the dyes TAZ, RY-17 and RB-5 were carried out with the synthesised TiO2 catalyst under the conditions optimised for the best decolourisation with TiO2 (P-25 Degussa). The optimised conditions for the complete decolourisation of various dyes are given in **Table 4** and the time taken for complete decolourisation of the dyes over the synthesised titania is given in **Table 5**.

Among the three dyes, RY-17 reached complete decolourisation at a shorter irradiation time under both the light sources. RB-5 took longer irradiation time for complete decolourisation. This may be due to its chemical nature (i.e.) RB-5 being diazo dye. Diazo dyes are less degradable than mono azo dye during ozonation [43]. Similar trend of decolourisation was observed with visible light irradiation.


**91**

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

**Catalyst Time taken for complete decolourisation (h)**

However, the times at which complete decolourisation took place were different and

TiO2 (P-25 Degussa) 5½ 6½ 5 6 6 7 Synthesised TiO2 4 3 3½ 4 4½ 5

*Time taken for complete decolourisation (100%) of various dyes using TiO2 (P-25 Degussa) and synthesised* 

/g)

M) and 1.5 g of

/g). Similar type of results was

**TAZ RY-17 RB-5 UV Visible UV Visible UV Visible**

The higher efficiency of the synthesised catalyst when compared to P-25 Degussa may be due to the larger surface area of the synthesised TiO2 (90.5 m2

also observed by [44]. Because of the increase in the surface area of synthesised

From the above discussions, it is clear that both degradation and decolourisation of the dyes are highly effective with synthesised TiO2 compared to TiO2 (P-25 Degussa) under both the light sources. To further the photocatalytic activity further in the visible region, the modification in the synthesised catalyst has to be carried out by noble metal deposition. Noble metals such as Ag, Au and Pt have been deposited on the synthesised catalyst and they were evaluated for their photocatalytic activity.

**3.4 Photodecolourisation studies of metal impregnated titania photocatalysts**

M/TiO2 catalyst at neutral pH. The irradiation was carried out 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. The results obtained in the decolourisation of various dyes with M/TiO2 under UV and visible irradiations

From the above photocatalytic decolourisation studies the following observations were made: Photocatalytic efficiency of the different catalysts for the deco-

Au/TiO2 > Ag/TiO2~Pt/TiO2 > synthesised TiO2 > TiO2 (P − 25 Degussa)

The time at which the complete decolourisation occurred for the different

decolourise RY-17 to the maximum extent followed by TAZ and RB-5.

The percentage decolourisation of different dyes obtained with the different catalysts were determined at the time at which the Au/TiO2 catalyst showed 100% decolourisation of the respective dyes (TAZ, RY-17 and RB-5) using different

• As far as the decolourisation of the dyes are concerned, all the catalysts found to

lourisation of different dyes were found to be in the following order:

To evaluate the photocatalytic activity of noble metal deposited titania catalyst, the decolourisation of dyes (TAZ, RY-17 and RB-5) was carried out under visible and UV light irradiations. The reaction was carried out with 250 mL of dyes of

M, RY-17 and RB-5 = 1 × 10<sup>−</sup><sup>5</sup>

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

**Table 5.**

*TiO2.*

higher for visible light when compared with UV.

when compared with TiO2 (P-25 Degussa) (50 m2

various concentration (TAZ =1 × 10<sup>−</sup><sup>4</sup>

are shown in **Figures 10** and **11**.

catalysts is given in **Table 6**.

catalysts are given in **Table 7**.

TiO2 there may be increase in the adsorption of the three dyes.

#### **Table 4.**

*The optimised conditions for the complete decolourisation of different dyes using TiO2 (P-25 Degussa).*

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


**Table 5.**

*Gold Nanoparticles - Reaching New Heights*

**90**

**Table 4.**

**Dye Initial** 

**TiO2 (P-25 Degussa)**

*(reaction conditions: Dye concentration: TAZ = 2 × 10<sup>−</sup><sup>4</sup>*

**Figure 9.**

**concentration [M]**

**pH Time taken for complete** 

**UV irradiation**

TAZ 1 × 10<sup>−</sup><sup>4</sup> 7 5 ½ 6 ½ 1.5 RY-17 1 × 10<sup>−</sup><sup>5</sup> 7 5 6 1.5 RB-5 1 × 10<sup>−</sup><sup>5</sup> 7 6 7 1.5

**3.3 Comparison of photocatalytic activities of synthesised TiO2 with** 

The photocatalytic decolourisation of the dyes TAZ, RY-17 and RB-5 were carried out with the synthesised TiO2 catalyst under the conditions optimised for the best decolourisation with TiO2 (P-25 Degussa). The optimised conditions for the complete decolourisation of various dyes are given in **Table 4** and the time taken for complete decolourisation of the dyes over the synthesised titania is given in **Table 5**. Among the three dyes, RY-17 reached complete decolourisation at a shorter irradiation time under both the light sources. RB-5 took longer irradiation time for complete decolourisation. This may be due to its chemical nature (i.e.) RB-5 being diazo dye. Diazo dyes are less degradable than mono azo dye during ozonation [43]. Similar trend of decolourisation was observed with visible light irradiation.

*Effect of (A) H2O2 and (B) K2S2O8 on decolourisation of dyes under visible and (C and D) UV irradiations.* 

*catalyst (P-25 Degussa) = 1.5 g, volume of dye solution =250 mL, pH = neutral and irradiation time = 7 h).*

 *M, RY-17 = 2 × 10<sup>−</sup><sup>5</sup>*

 *M, RB-5 = 2 × 10<sup>−</sup><sup>5</sup>*

*The optimised conditions for the complete decolourisation of different dyes using TiO2 (P-25 Degussa).*

**Decolourisation (h)**

**Visible irradiation** **Weight of catalyst (g) TiO2 (P-25 Degussa)**

 *M, weight of* 

*Time taken for complete decolourisation (100%) of various dyes using TiO2 (P-25 Degussa) and synthesised TiO2.*

However, the times at which complete decolourisation took place were different and higher for visible light when compared with UV.

The higher efficiency of the synthesised catalyst when compared to P-25 Degussa may be due to the larger surface area of the synthesised TiO2 (90.5 m2 /g) when compared with TiO2 (P-25 Degussa) (50 m2 /g). Similar type of results was also observed by [44]. Because of the increase in the surface area of synthesised TiO2 there may be increase in the adsorption of the three dyes.

From the above discussions, it is clear that both degradation and decolourisation of the dyes are highly effective with synthesised TiO2 compared to TiO2 (P-25 Degussa) under both the light sources. To further the photocatalytic activity further in the visible region, the modification in the synthesised catalyst has to be carried out by noble metal deposition. Noble metals such as Ag, Au and Pt have been deposited on the synthesised catalyst and they were evaluated for their photocatalytic activity.

### **3.4 Photodecolourisation studies of metal impregnated titania photocatalysts**

To evaluate the photocatalytic activity of noble metal deposited titania catalyst, the decolourisation of dyes (TAZ, RY-17 and RB-5) was carried out under visible and UV light irradiations. The reaction was carried out with 250 mL of dyes of various concentration (TAZ =1 × 10<sup>−</sup><sup>4</sup> M, RY-17 and RB-5 = 1 × 10<sup>−</sup><sup>5</sup> M) and 1.5 g of M/TiO2 catalyst at neutral pH. The irradiation was carried out 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. The results obtained in the decolourisation of various dyes with M/TiO2 under UV and visible irradiations are shown in **Figures 10** and **11**.

From the above photocatalytic decolourisation studies the following observations were made: Photocatalytic efficiency of the different catalysts for the decolourisation of different dyes were found to be in the following order:

Au/TiO2 > Ag/TiO2~Pt/TiO2 > synthesised TiO2 > TiO2 (P − 25 Degussa)

The time at which the complete decolourisation occurred for the different catalysts is given in **Table 6**.

• As far as the decolourisation of the dyes are concerned, all the catalysts found to decolourise RY-17 to the maximum extent followed by TAZ and RB-5.

The percentage decolourisation of different dyes obtained with the different catalysts were determined at the time at which the Au/TiO2 catalyst showed 100% decolourisation of the respective dyes (TAZ, RY-17 and RB-5) using different catalysts are given in **Table 7**.

#### **Figure 10.**

*Decolourisation of (A)TAZ, (B) RY-17 and (C) RB-5 using different TiO2 catalysts under UV irradiation. (reaction conditions: Dye concentration: TAZ = 1 × 10<sup>−</sup><sup>4</sup> M, both RY-17 & RB-5 = 1 × 10<sup>−</sup><sup>5</sup> M, weight of catalyst = 1.5 g, volume of dye solution = 250 mL and pH = neutral).*

#### **Figure 11.**

*Decolourisation of (A)TAZ, (B) RY-17 and (C) RB-5 using different TiO2 catalysts under visible irradiation. (reaction conditions: Dye concentration: TAZ = 1 × 10<sup>−</sup><sup>4</sup> M, both RY-17 & RB-5 = 1 × 10<sup>−</sup><sup>5</sup> M, weight of catalyst = 1.5 g, volume of dye solution = 250 mL and pH = neutral).*

Among all the catalysts, M/TiO2 catalysts show the higher photocatalytic activity towards the decolourisation of all the three dyes. The higher catalytic activity of M/TiO2 catalysts may be due to the smaller band gap values when compared to TiO2 (P-25 Degussa) and the ability of the noble metals trap the electrons, thus preventing the recombination. The rate constant values obtained with different M/TiO2 catalysts in the photocatalytic decolourisation of all the three dyes were found to be highest for Au/TiO2 followed by Ag/TiO2 and Pt/TiO2. The higher photocatalytic activity of the Au/TiO2 catalyst when compared to the other metals is due to the lowered band gap values [45, 46], which leads to the effective absorption of visible light by the catalyst resulting in higher decolourisation.

### **3.5 Photodegradation studies**

The photodegradation studies was carried out with 250 mL of dyes of various concentration (TAZ = 1 × 10<sup>−</sup><sup>4</sup> M, RY-17 and RB-5 = 1 × 10<sup>−</sup><sup>5</sup> M) and 1.5 g of M/TiO2 catalyst at neutral pH. The irradiation was carried out 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. The degradation was monitored by a TOC analyser and the results are shown in **Figure 12**.

All the above photodegradation experiments show that like photodecolourisation that photodegradation efficiency of all the synthesised catalyst follow similar trend as mentioned below:


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

**UV Visible UV Visible UV Visible UV Visible UV Visible**

**UV Visible UV Visible UV Visible UV Visible UV Visible**

TAZ 5 ½ 6 ½ 4 4 ½ 3 2 2 ½ 2 2 1 ½ RY-17 5 6 3 ½ 4 2 ½ 2 2 1 ½ 1 ½ 1 RB-5 6 7 4 ½ 5 3 ½ 2 ½ 3 2 ½ 2 ½ 1 ½

*Time taken for the 100% decolourisation of the dyes (TAZ, RY-17 and RB-5) using different catalysts.*

**Pt/TiO2 Ag/TiO2 Au/TiO2**

**Pt/TiO2 Ag/TiO2 Au/TiO2**

**Dye Time taken for complete Decolourisation (h)**

**Synthesised TiO2**

**Dye Decolourisation (%)**

**Synthesised TiO2**

The degradation percentage of the dyes (TAZ, RY-17 and RB-5) using different

*Percentage decolourisation of the different dyes (TAZ, RY-17 and RB-5) using different catalysts.*

TAZ 26 16 79 75 79 75 85 83 100 100 RY-17 28 17 83 80 83 80 90 88 100 100 RB-5 24 11 70 72 70 72 88 76 100 100

The photocatalytic studies carried out under UV and visible irradiations leads to

• The photocatalytic activity of the synthesised catalyst in the decolourisation and degradation of all the dyes was found to be better than TiO2 (P-25

• Higher percentage of decolourisation and degradation occurred for both TiO2 (P-25 Degussa) and the synthesised catalyst under UV irradiation when

both UV and visible irradiations than the synthesised TiO2.

Schottky barriers are formed leading to electron hole pair [45].

oxygen present in the solution to form the highly oxidative O2˙

the electron transfer from the semiconductor to O2 [48].

light irradiation when compared to the UV irradiation.

• The photocatalytic activities of M/TiO2 catalysts were found to be higher under

• The photocatalytic efficiency of the M/TiO2 was remarkable even under visible

The higher activity of M/TiO2 catalysts under visible region is explained below:

• The activity of noble metals may be attributed to the electronic interaction between the impregnated noble metal and TiO2. Due to this interaction,

• The metal deposits traps the electrons and quickly transfers the electrons to

• The trapping rate of electrons by noble metals is faster rate when compared to

<sup>−</sup> radical [47].

catalysts at the time period of 8 h are given in **Table 8**.

Degussa) under both UV and visible irradiations.

compared to visible irradiation.

the following observations:

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

**TiO2 (P-25 Degussa)**

**TiO2 (P-25 Degussa)**

**Table 6.**

**Table 7.**

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


**Table 6.**

*Gold Nanoparticles - Reaching New Heights*

Among all the catalysts, M/TiO2 catalysts show the higher photocatalytic activity towards the decolourisation of all the three dyes. The higher catalytic activity of M/TiO2 catalysts may be due to the smaller band gap values when compared to TiO2 (P-25 Degussa) and the ability of the noble metals trap the electrons, thus preventing the recombination. The rate constant values obtained with different M/TiO2 catalysts in the photocatalytic decolourisation of all the three dyes were found to be highest for Au/TiO2 followed by Ag/TiO2 and Pt/TiO2. The higher photocatalytic activity of the Au/TiO2 catalyst when compared to the other metals is due to the lowered band gap values [45, 46], which leads to the effective absorption of visible

*Decolourisation of (A)TAZ, (B) RY-17 and (C) RB-5 using different TiO2 catalysts under visible irradiation.* 

*Decolourisation of (A)TAZ, (B) RY-17 and (C) RB-5 using different TiO2 catalysts under UV irradiation.* 

 *M, both RY-17 & RB-5 = 1 × 10<sup>−</sup><sup>5</sup>*

 *M, both RY-17 & RB-5 = 1 × 10<sup>−</sup><sup>5</sup>*

The photodegradation studies was carried out with 250 mL of dyes of various

catalyst at neutral pH. The irradiation was carried out 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. The degradation was moni-

All the above photodegradation experiments show that like photodecolourisation that photodegradation efficiency of all the synthesised catalyst follow similar

• Au/TiO2 > Ag/TiO2 ≈ Pt/TiO2 > Synthesised TiO2 > TiO2 (P-25 Degussa)

• As far as the dyes are concerned, all the catalysts found to degrade RY-17 to the

M, RY-17 and RB-5 = 1 × 10<sup>−</sup><sup>5</sup>

M) and 1.5 g of M/TiO2

 *M, weight of* 

 *M, weight of* 

light by the catalyst resulting in higher decolourisation.

*(reaction conditions: Dye concentration: TAZ = 1 × 10<sup>−</sup><sup>4</sup>*

*(reaction conditions: Dye concentration: TAZ = 1 × 10<sup>−</sup><sup>4</sup>*

*catalyst = 1.5 g, volume of dye solution = 250 mL and pH = neutral).*

*catalyst = 1.5 g, volume of dye solution = 250 mL and pH = neutral).*

tored by a TOC analyser and the results are shown in **Figure 12**.

maximum extent followed by TAZ and RB-5.

**3.5 Photodegradation studies**

**Figure 11.**

**Figure 10.**

concentration (TAZ = 1 × 10<sup>−</sup><sup>4</sup>

trend as mentioned below:

**92**

*Time taken for the 100% decolourisation of the dyes (TAZ, RY-17 and RB-5) using different catalysts.*

