Improvement of the degradation of Methyl Orange Using a TiO2/BDD composite electrode to promote electrochemical and photoelectro-oxidation processes

Abstract

Electrophoretic deposit of titanium dioxide (TiO2) was carried out over a boron doped diamond plate of 2 cm2, annealing at 350 °C to produce binary TiO2/BDD composite electrode. The composite was characterized by scanning electron microscopy (SEM) and linear sweep voltammetry (LSV) response. N,N-dimethyl-p-nitrosoaniline (RNO) was used as a probe molecule for the detection of free radicals (•OH) during the oxidation of water in phosphate buffer (pH 4) solution; at the TiO2/BDD/hv composite, an apparent first-rate kinetic constant of kobs = 0.1314 min-1 was observed. Afterwards, the composite electrode was applied to degrade 40 and 100 mg L-1 of a typical azo dye methyl orange (MO) via electrochemical process, such as: electro-oxidation (EO) and photoelectro-oxidation (PEO) under 25, 75 and 125 mA cm-2 current density (j); the PEO tests were performed using a UVA lamp at 365 nm. Results showed that the discoloration in the PEO process was larger than in the EO process, 96 and 100 %, respectively. Chemical Oxygen Demand (COD) was tested to evaluate the degradation. Hydroxylated derivatives were identified by means of mass spectroscopy during the PEO of MO in a TiO2/BDD/hv composite electrode.