Decolourisation of Metanil Yellow by visible-light photocatalysis with N-doped TiO2 nanoparticles: influence of system parameters and kinetic study

A nitrogen-doped photocatalyst (N-TiO2) is prepared from 15% TiCl3 and 25% aqueous NH3 solution as precursor. The synthesised material is characterised by XRD, BET, TEM, DRS and XPS and is used for photocatalytic decolourisation of Metanil Yellow under visible-light illumination. The experimental parameters, viz, photocatalyst dose, initial dye concentration and solution pH influence the decolourisation process. At pH 3.5, N-TiO2 can decolourise almost 89% of the dye at equilibrium within 240 min. COD study reveals similar to 92% mineralisation of the dye in 360 min of irradiation. The photocatalytic reaction is allowed to proceed only after the attainment of adsorption equilibrium between N-TiO2-Metanil Yellow. The adsorption is carried out by batch process under different experimental conditions, namely, N-TiO2 dose, initial dye concentration and solution pH. The adsorption process attains equilibrium within 60 min and follows Lagergren first-order kinetics. On the other hand, the photocatalytic decolourisation of Metanil Yellow is suitably fitted with the modified Langmuir-Hinselwood model. Modification of TiO2 improved the decolourisation of the dye by similar to 8 times compared to TiO2 P25.