Identification of by-products in the degradation process of diclofenac in water using solar photo-Fenton process

• Twenty-three by-products identified using high-resolution LC-qTOF/MS. • Proposed pathways involved dechlorination, hydroxylation, decarboxylation, and ring opening. • Intermediates were tentatively assigned with MS/MS support at 45 min of treatment. • Findings provide mechanistic anchors and monitoring targets for safer scale-up. In the last two decades, pharmaceuticals have become an environmental problem due to their presence in wastewater, surface water and even drinking water sources. Many medications are used daily, leaving residual waste in wastewater since the elimination processes by water treatment plants are not efficient in removing these compounds. A drug that is more commonly detected in the aquatic environment is the analgesic diclofenac (DCF). In the present work, several degradation by-products of 1 mg l -1 of DCF under optimal operating conditions previously optimized (0.20 mg l -1 of Fe 2+ and 1 mg l -1 of H 2 O 2 ) at a simulated solar irradiance of 425 W m -2 were identified. Due to its complex structure and the non-selective nature of the hydroxyl radical (OH•), several degradation routes were proposed for DCF. It can be observed that hydroxylated diclofenac has been identified through the degradation of DCF by the photo-Fenton process under the experimental domain tested. This structure undergoes additional hydroxylation in the benzene ring containing the chlorine atoms, causing their loss and subsequent hydroxylation and, finally, resulting in the cleavage of the C N bond. The dechlorination, hydroxylation and decarboxylation processes of the DCF emerging compound allow the formation of degradation by-products that are less toxic than the parent compound to be elucidated. In this regard, the possible application of the solar photo-Fenton process under the operating conditions tested here at a larger scale could be inferred.