Use of Sub-stoichiometric Titanium Oxide as a Ceramic Electrode in Anodic Oxidation and Electro-Fenton Degradation of the Beta-blocker Propranolol: Degradation Kinetics and Mineralization Pathway

•Excellent degradation and mineralization of Propranolol by both EF and AO-H2O2.•Efficient mineralization of propranolol with Ti4O7 compared to DSA anode.•Increase in applied current enhanced both degradation and mineralization rate.•Final end products of propranolol oxidation was carboxylic acids and inorganic ions.•Ti4O7 is a suitable and efficient anode for AO and EF oxidation of Propranolol.

Oxidative degradation of aqueous acidic solutions of the beta-blocker propranolol (PPN) has been studied by anodic oxidation (AO) and for the first time by electro-Fenton (EF) process using sub-stoichiometric titanium oxide (Ti4O7) anode elaborated by plasma deposition. The oxidative degradation of the PPN by Ti4O7(OH) formed at the surface of the Ti4O7 anode and OH generated via electrochemically assisted Fenton's reaction was investigated. Decay of PPN concentration followed pseudo-first order reaction kinetics with degradation rates influenced by both applied current and initial PPN concentration. The absolute rate constant of the reaction between PPN and OH/Ti4O7(OH) was determined by competition kinetics and found to be (2.99 ± 0.02) × 109 L mol−1 s−1. Relatively high mineralization efficiency of PPN solution (82% TOC removal) was achieved by AO with Ti4O7 anode at 120 mA after 480 min of treatment, whereas almost complete mineralization (96% TOC removal) was reached at similar conditions in EF process. Analogous EF treatment with DSA anode showed lower mineralization (89% TOC removal) compared to Ti4O7 anode. The initial N content of PPN was mainly released as NH4+, with smaller proportion of NO3−. Aromatic intermediates such as 1-naphtol; hydroxylated 1-naphtol and phthalic acid were identified by both reversed-phase HPLC and GC-MS analyses. Oxalic, oxamic, maleic and glycoxylic acids were the main short-chain carboxylic acid detected. Based on the identified intermediates, carboxylic acids and inorganic end-products as well as TOC removal results, a plausible reaction sequence for mineralization of PPN by electrogenerated hydroxyl radicals is proposed.