Photo-anodes based on B-doped TiO2 for photoelectrocatalytic degradation of propyphenazone: Identification of intermediates, and acute toxicity evaluation

The photoelectrocatalysis (PEC) using B-doped TiO2 photo-anodes for degradation of the propyphenazone (PPZ) was investigated. For this, four different composites based on TiO2 and TiO2-x%B (x = 1, 3 or 5) were synthesized by sol-gel method and supported on titanium substrate by the dip-coating technique. The morphology, optical and electrochemical properties of photo-anodes were evaluated by SEM, TEM, XPS, TGA, DSC, XRD, FTIR, DRS, and sweep voltammetry, respectively. The influence of pH (3, 6 or 9) and electrical potential intensity (+1 V, +2 V or +3 V) used in PEC were evaluated by kinetic study. To understand the synergistic effect of the composition of the photoelectrochemical system, photolysis (PS), electrocatalysis (EC) and photocatalysis (PC) experiments were realized under comparative conditions. Doping 3% of B into TiO2 promoted a decrease in band gap energy (Ebg = 2.91 eV), thus providing better radiation absorption and greater generation of charge carriers on the surface of the photo-anode. Characterization analyzes indicate the presence of B2O3 coexisting with TiO2. The most promising results were obtained using Ti/TiO2-3%B photo-anode (vs a DSA cathode), applying + 1 V at pH 6, resulting in 91% of PPZ degradation after 60 min of PEC treatment. Toxicity tests using A. salina and L. sativa showed that the effluent generated after 2 h of PEC treatment of 30 mg L-1 of PPZ is non-toxic for the studied species. Up to 13 by-products formed during the PEC and PS treatment were detected and a proposal pathway involving possible routes of PPZ degradation were presented. [Display omitted] •Boron modification doubled the current density value relative to the TiO2 photoelectrode.•The pH did not significantly affect the PPZ degradation rates in PEC treatment.•The increase from 3% to 5%(w/w) of B content decrease PPZ degradation rate.•Tests with A. salina and L. sativa did not reveal acute toxicity after the PEC treatment.