*2.4.3 Photocatalytic reaction*

250 mL of the desired dye sample was taken in a photocatalytic reactor. Calculated amount of TiO2 (P-25 Degussa) or synthesised TiO2 or M/TiO2 was added to the photocatalytic reactor and the reaction mixture was magnetically stirred before and during illumination. After specific time interval of irradiation, suitable aliquots of the sample was withdrawn and analysed to find out the extent of decolourisation and degradation.

## *2.4.4 UV-vis analysis of the decolourised products*

The extent of photocatalytic decolourisation of dyes was studied by UV-visible spectrophotometer (Hitachi U-2000) from the decrease in the respective λmax values.

The colour intensity of the dyes was measured in terms of absorbance. Decolourisation was determined by using the calibration curve.

$$\text{Decolourisation (\%)} = \frac{C\_0 - C}{C} \times 100\tag{3}$$

where C0, initial concentration of the dye; C, concentration of dye at time 't'.

#### **2.5 Photodegradation studies**

The photocatalytic degradation of dyes was evaluated in terms of total organic carbon (TOC). The total organic carbon of the pollutant was determined by using a TOC analyser (Shimadzu TOC V series).
