Photoelectrocatalytic degradation of glyphosate on titanium dioxide synthesized by sol-gel/spin-coating on boron doped diamond (TiO₂/BDD) as a photoanode

The construction of a photoanode with several layers of titanium oxysulfate as a precursor to form titanium dioxide-TiO₂ on boron doped diamond-BDD (TiO₂/BDD), and its application for the photoelectro-degradation of glyphosate in aqueous medium are presented. The study was divided into three stages: i) optimization of the number of layers of the TiO₂ precursor to modify BDD using a novel method combining Sol-gel/Spin-Coating; ii) characterization of the TiO₂/BDD electrodes, by scanning electron microscopy-SEM, dispersive energy spectroscopy-EDX, Ray diffraction-XRD, contact angle, and electrochemical response by cyclic voltammetry using [Fe(CN)₆]^3-/4- system; iii) degradation of glyphosate (50 mg L^-1) by electrochemical oxidation on BDD and photoelectrocatalysis on TiO₂/BDD in dark and UV-light conditions, at different current densities, for 5 h. The glyphosate degradation and mineralization were evaluated by High-Performance Liquid Chromatography, Total Organic Carbon, Chemical Oxygen Demand and inorganic-ions concentration (NO₃^-, PO₄^3-, and NH₄⁺). Also, the aminomethylphosphonic acid-AMPA was quantified by HPLC, as a degradation intermediate. Using five layers of the TiO₂ precursor, in the construction of TiO₂/BDD photoanode, and a lower contact angle, greater photoelectrocatalysis against the [Fe(CN)₆]^3-/4- redox system and better degradation of glyphosate compared to BDD without modification were achieved. The formation of TiO₂ nanoparticles (14.79 ± 3.43 nm) in anatase phase on BDD was verified by SEM and XRD. Additionally, glyphosate degradation and mineralization were 2.3 times faster by photoelectrocatalysis on TiO₂/BDD, relative to BDD, at 3 mA cm^-2 and UV-light. Thus, the presence of TiO₂ on BDD increases the rate and efficiency of glyphosate degradation with respect to electrochemical oxidation on BDD.