Treatment of crystal violet and acid green 25 using Fenton process

The objective of this research was to investigate the application of the Fenton process for the degradation of cationic and anionic dyes, namely crystal violet (CV) and acid green 25 (AG 25), respectively. The operational parameters investigated were the effect of initial concentration of dye, effect of Fe²⁺ concentration, effect of H₂O₂ concentration, effect of solution pH and effect of solution matrix such as methanol (CH₃OH), ethanol (C₂H₅OH), oxalate (C₂O₄ ^2-), chloride (Cl^-), nitrate (NO₃ ^-), sulfate (SO₄ ^2-) and combined inorganic anion species. The mechanism for dyes removal was due to the generation of hydroxyl radicals (•OH) which are produced by the reaction of ferrous ion (Fe²⁺) and hydrogen peroxide (H₂O₂). The optimum conditions which achieved the highest degradation efficiency of 5 mg/L CV and 5 mg/L AG 25 were 5 mg/L Fe²⁺, 50 mg/L H₂O₂, initial solution pH 3 and room temperature. At 20 min of Fenton oxidative treatment, the degradation efficiencies of CV and AG 25 were 99.67% and 97.17%, respectively. Presence of CH₃OH, C₂H₅OH and C₂O₄ ^2- significantly decreased the degradation efficiency of CV as compared to presence of other solution matrix and combined species. Interestingly, the addition of organic solvent namely CH3OH had resulted in increased degradation efficiency of AG 25 instead of inhibiting the degradation reaction. Kinetic rate constant of reaction (k) and coefficient of determination (R²) for the optimum experimental conditions for the degradation of CV and AG 25 were 0.1415 min^-1 and 0.9819 (first-order reaction) and 0.3517 Lmg^-1min^-1 and 0.9756 (second-order reaction), respectively.