Study on the degradation of methyl orange by UV-acetylacetone advanced oxidation system

Abstract

In recent years, Acetylacetone (abbreviated as AA) has garnered considerable scientific interest, particularly in the field of dye wastewater treatment due to its distinctive enol-keto structures. In this work,degradation of methyl orange(MO) by UV/AA process was explored. Effects of AA dosage, MO concentration, initial pH value and water matrices were investigated.Experimental results showed that under conditions of 298 K, a pH of approximately 5.73, a stirring speed of 1150 rpm, an initial MO concentration of 15 mg/L and an AA dosage of 0.5 mM, the decolorization rate reached nearly 98.4 % after 12 min of photolysis. The decolorization process fitted well with the pseudo-zero-order reaction model in the UV/AA system with an R2 value greater than 0.990. The reaction rate increases as the pH decreases; at approximately pH 2.0, the decolorization rate is 99.3 % after 6 min, while at approximately pH 9.0, it is only 41.2 %. 10 mM HCO3⁻significantly inhibit the system, 0.1 mM Cl⁻has a slight promoting effect at low concentrations but inhibits at high concentrations and NO3⁻inhibits the reaction while SO42- has minimal impact at a concentration of 0.1–10 mM .0.1 mM iron ions accelerated the reaction.The sodium citrate, a printing and dyeing auxiliary, has negative impacts on the MO degradation. Free radical capture experiments and Electron Paramagnetic Resonance (EPR) tests reveal that singlet oxygen (¹O2) is the primary active species in the UV/AA system. UV-Vis absorption spectroscopy indicates that azo bonds are largely destroyed after 12 min, with a decrease in AA concentration as the reaction proceeds. Liquid chromatography-mass spectrometry (LC-MS) results suggest a possible conversion pathway for MO during the UV/AA advanced oxidation process.