Assessment of Ti, Ir, Ta and Ru influence on mixed metal oxide electrodes for photoelectrochemical generation of persulfate: Impact on sulfamethoxazole degradation

The presence of persulfate (S₂O₈^2-) in decontamination processes favors the oxidation of organic pollutants due to its strong oxidation power. In this research we study the photoelectrochemical generation of persulfate using five mixed metal oxides electrodes (MMO) with different compositions and its effect on the degradation of sulfamethoxazole antibiotic (SMX) by photoelectrocatalysis (PEC) and electro-oxidation (EO). By PEC, all anodes generated a higher concentration of S₂O₈^2- than those not exposed to light. The high S₂O₈^2-concentration obtained by PEC was 0.150 mM using MMO_[Ti/Ir/Ta] in a solution with Na₂SO₄ 100 mM applying a current density of 2 mA/cm². On the other hand, the maximum concentration obtained was 0.250 mM at 30 min of electrolysis for MMO_[Ti/Ir/Ta] using Na₂SO₄ 50 mM and applying current density of 5 mA/cm². S₂O₈^2-production by EO was between 0.005 and 0.089 mM. It is observed that MMO based in Ta₂O₅ showed the best S₂O₈^2- production. The effect of S₂O₈^2- electro-generation (using the anode with the highest and the anode with the lowest S₂O₈^2- production) on the degradation of sulfamethoxazole by PEC and EO was studied using the experimental conditions with the best production of this oxidant. MMO_[Ti/Ir/Ta] and MMO_[Ti/Ru] were used as anodes, and it was observed that by PEC, 100% of SMX was degraded after 30 min of electrolysis using MMO_[Ti/Ir/Ta] and 60 min using MMO_[Ti/Ru]. By EO, the degradation of SMX was partial, demonstrating that the electrophotocatalytic effect favors the generation of S₂O₈^2-, enhancing the degradation of SMX at short electrolysis times.