Innovative photoelectrocatalytic water remediation system for ammonia abatement.

Ammonia, produced by human and animal activities, contributes to water and soil pollution because it is toxic for aquatic flora and fauna, and responsible for eutrophication. In this work, the photoelectrocatalytic (PEC) oxidation of ammonia is investigated employing a stainless-steel PEC reactor, consisting of a central UV Hg-vapor lamp surrounded by a metallic Ti mesh coated with a photoactive TiO 2 film, directly grown by Plasma Electrolytic Oxidation (PEO). The so prepared TiO 2 film is characterized by XRD, SEM, UV–vis DRS and IPCE. The PEC reactor operates at 4 V potential drop between the TiO 2 coated mesh (photoanode) and the body of the reactor (cathode). The effect of the operating parameters (recirculation flowrate and air bubbling) and type of electrolyte solution (KCl or K 2 SO 4) on the PEC performance are investigated in terms of ammonia conversion and selectivity to nitrite, nitrate and molecular nitrogen. Full ammonia conversion (X NH3) with a selectivity to molecular nitrogen up to 67 % are attained after 12 h in 5 mM KCl electrolyte solution. Nitrite is produced within the first 6 h irradiation and then fully converted into nitrate. By contrast, only a slight X NH3 (ca. 10 %) is observed in K 2 SO 4 electrolyte solution. These results suggest that chlorine has a crucial role in the ammonia PEC oxidation process: photo-generated holes on the photoanode surface can oxidize Cl− to Cl• (electro-induced process), which is a reactive radical able to oxidase ammonia. [Display omitted] • TiO 2 coated mesh prepared with PEO has excellent photoelectrochemical properties. • PEC exploits UV/electro-chloride process to oxidize NH 3 with high selectivity to N 2. • NH 3 removal follows a pseudo zero order kinetics under this PEC conditions. • No photocurrent decays after 160 h, proving the stability of the TiO 2 coated mesh. [ABSTRACT FROM AUTHOR]