Comparative photocatalytic degradation of monoazo and diazo dyes under simulated visible light using Fe3+/C/S doped-TiO2 nanoparticles

Abstract

This research work delved into the photocatalytic degradation of monoazo dye (methyl orange) and diazo dye (congo red) in aqueous solution using Fe³⁺/C/S-doped TiO₂ nanocomposites. The nanocomposites were synthesised through sol-gel method and characterized using XRD, FTIR, SEM, TEM, EDX, BET and UV-Vis. Photocatalytic degradation of the dyes was monitored under simulated visible light using pristine TiO₂, C/S/doped-TiO₂ and Fe³⁺/C/S doped-TiO₂ with varying concentrations of Fe³⁺. The influence of catalyst doping, solution pH, and light intensity were also examined.  Doping TiO₂ with Fe³⁺/C/S caused reduction in its band gap value with the resultant improvement in its visible light activity. The photocatalytic efficiency of the catalysts are given as follows: TiO₂ < C/S/TiO₂ < Fe³⁺/C/S-TiO₂ with Fe³⁺/C/S-TiO₂ (0.3 % Fe³⁺) as the best performing photocatalyst. The monoazo dye experienced higher degradation efficiency than the diazo dye. Degradation of the azo dyes was observed to decrease with increasing pH from 3 to 12. Increased visible light intensity enhanced the photodegradation efficiency of the dye. Dye decolourization was observed to be faster than its mineralization.