Adsorption and photocatalytic degradation of eriochrome Black-T by TiO2 of different shapes

Abstract

Titania based nanocatalysts of different morphologies having superior surface properties such as high surface area and pore volume are getting wide importance in adsorption and photocatalysis research for the degradation of textile dyes. Hence, present work demonstrates the influence of BET surface area, surface charge, pore volume and Fe+3 and Pt+4 ions impregnation onto asprepared TiO2 nanostructure for the dark adsorption and photocatalytic degradation of Eriochrome Black-T dye. Inspite of the least surface area of P25-TiO2 among titania nanotubes and nanorods, highest dark adsorption for anionic Eriochrome black T has been found it, whichcan be accredited to its cationic surface responsible for better adsorption of oppositely charged dye molecules. Fe+3 and Pt+4 loading have been done to enhance the rate of adsorption and photocatalytic rate. Fe+3 loaded P25-TiO2 is found to show the highest adsorption rate, 8.6 ~10-2 min-1 as compared to P25-TiO2 , 8.06 ~10-2 min-1 followed by nanotubes, 2.0 ~10-2 min-1 and nanorods, 3.24 ~10-2 min-1. The dark adsorption behaviour is investigated by varying the catalyst and dye concentration that follows the Freundlich adsorption isotherm with adsorption constant (K) varies from 4.0 ~10-2 . 5.4 ~10-2 ƒÊmol/ml and the value of n lies between 0.4.1, indicating pseudo-first order kinetic for the adsorption of present dye. Moreover, the photocatalytic degradation of dye also follows pseudo first-order decay kinetics. The kobs values for photocatalytic degradation indicated an inverse dependence on the initial dye concentration and were fitted to the Langmuir-Hinshelwood equation. Photodegradation and adsorption rate increased with titania nanocatalysts dosage, but overdoses did not increase the photocatalytic efficiency. The photoinduced dissipation of Eriochrome Black-T results into formation of a number of intermediate photoproducts among them few has been identified by GC-MS analysis as: 2-diazenylnaphthalen-1-ol, 7-nitro-1,8a-dihydronaphthalene-1,3-diol,3-hydroxy-7-nitroso- f51,8a-dihydronaphthalene-1sulfonoperoxoic acid, and 3-hydroxy-7-nitro 1,8adihydronaphthalene- 1-carboxylic acid etc.