**2.4 Photodecolourisation studies**

*Gold Nanoparticles - Reaching New Heights*

**2.3 Characterisation of the catalysts**

*2.3.2 Transmission electron microscopy*

*2.3.3 BET surface area analysis*

*2.3.1 X-ray diffraction analysis*

product for Au/TiO2.

Scherrer equation,

1% Ag/TiO2, 0.15 g of AuCl3 for 1% Au/TiO2, 0.14 g of [Pt(NH3)4]Cl2 for 1% Pt/TiO2) taken in minimum amount of water was added to 10 g of synthesised TiO2 and was stirred at 70°C till the evaporation of the solvent. The colloidal solution was then irradiated with 125 W halogen lamp until complete reduction was observed visually by the formation of black precipitate for Ag/TiO2, Pt/TiO2 and purple coloured

Synthesised TiO2 and M/TiO2 photocatalyst were subjected to powder X-ray diffraction to confirm the crystalline size and the presence of the metal ion. The powder X-ray diffractograms were recorded using a X-ray diffractometer (PANalytical X'Pert Pro) with Cu Kα source having wavelength of 1.54 Å operating at 20 mA and 50 kV. The samples were scanned from 0.5–80° (2*θ*) for the confirmation of phase and presence of metal particles. The diameter of the metal particles was calculated from the (111) reflection of metal atom using Debye

d = Kλ/β Cos θ (1)

where d, diameter of the metal particle; K, constant; λ, wavelength of the X-ray

Particle size of the noble metals deposited on TiO2 was determined from electron micrographs taken by using transmission electron microscope (JEOL JEM-2010F) operating at 200 kV. A drop of alcoholic solution of the catalysts was placed on Cu grid and kept aside for about 45 s. Then transmission electron micrographs were recorded for the particles present on the grid. From the TEM images, average particle size of the catalysts was determined be taking minimum of 30 particles.

BET surface area analyser (Nova-Quantachrome 4200 e) was used to measure the surface area of all the catalysts. The measurement was done by using N2 as probe molecule at liquid nitrogen temperature (−190°C). Before the measurement, all the

Torr for 6 h. Linear portion

(1.54 Å); β, full width at half maximum; θ, angle of diffraction.

catalysts were degassed at 300°C at the pressure of 10<sup>−</sup><sup>5</sup>

*2.3.4 Atomic absorption spectroscopic studies*

*2.3.5 UV-visible spectrophotometry*

of the BET plots was used for the determination of BET surface area.

The actual amount of metal content present in the synthesised catalysts (M/TiO2, M = Ag, Au and Pt) was determined using atomic absorption spectrophotometer (Perkin Elmer 2380) after digesting the photocatalysts in aqua regia.

UV-visible spectra of all the samples were recorded using UV-Vis double beam spectrophotometer (Hitachi U-2000) in the range 200–800 nm. The course of

**78**
