Fe(III)–oxalate complexes mediated photolysis of aqueous alkylphenol ethoxylates under simulated sunlight conditions

Photolysis of octylphenol ethoxylates Triton X-100 (TX) in water under simulated sunlight conditions was investigated in the presence of Fe(III)–oxalate complexes. The results showed that Fe(III)–oxalate complexes mediated TX degradation followed the first-order kinetics and the photolysis efficiency was dependent on the pH, Fe(III) concentration, Fe(III)/oxalate ratio and initial TX concentration. The active oxygen species generated by photolysis of Fe(III)–oxalate complexes were monitored by electron paramagnetic resonance (EPR) method using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as the spin-trapping reagent. The steady-state concentration of OH radicals was 8.33 × 10−14 M and the rate constant of TX reaction with OH radical was 1.29 × 109 M−1 s−1 under our experimental conditions. The degradation products were analyzed by the high-performance liquid chromatography–electrospray ionisation-mass spectrometry and the degradation mechanisms of TX in the presence of Fe(III)–oxalate complexes was proposed. The OH radical can react with the alkyl chain, ethoxy (EO) chain and the aromatic ring of TX molecule during TX photolysis process. The main degradation pathway of TX involves the OH radical addition to the aromatic ring and the cleavage of the alkyl chain followed by combination with OH radical. The OH radical also attacks the polyethoxylated chain to generate short polyethoxylated chains or formyl ethoxylates.