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

Abstract

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−, PO43−, 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.