Gallic acid influence on azo dyes oxidation by Fenton processes

ABSTRACT

The present work consisted in evaluating the effect of a natural plant reducer, gallic acid (GA), on the discolouration/oxidation of two azo dyes by Fenton processes (Fe³⁺/H₂O₂ and Fe²⁺/H₂O₂). A kinetic study was performed to better interpret the discolouration data at different temperatures. The 1st-order kinetic model presented the best fit for the experimental data of methyl orange discolouration, while the 2nd-order was better for chromotrope 2R. Due to the addition of GA and the temperature rise, there were increases in discolouration and in the reaction rate constant values. As a highlight, it was possible to verify the reduction of the apparent activation energy (Ea) due to the presence of GA. For example, Ea for discolouring methyl orange corresponded to 81.5 and 53.6 kJ.mol⁻¹ by Fe²⁺/H₂O₂ and Fe²⁺/H₂O₂/GA, respectively. Thus, it can be inferred that the GA reduces the energy barrier to increase the oxidation of dyes by Fenton processes.

GRAPHICAL ABSTRACT

KEYWORDS:

• Fenton reaction
• dyes
• gallic acid
• kinetics
• hydroxyl radical

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by Fundação de Amparo à Pesquisa do Estado de Minas Gerais [grant number APQ-01898-17] and CNPq for the scientific initiation grants (processes 124592/2019-8 and 124642/2019-5).