Electrochemical conversion/combustion of a model organic pollutant on BDD anode: Role of sp3/sp2 ratio

• Ratio of sp3/sp2 content on BDD surface decides the electro-oxidation pathway.
• High diamond content favors electrochemical combustion to CO2.
• High graphite content promotes electrochemical conversion of the pollutant.

In this work, critical evidence about the influence of sp3/sp2 ratio on the performance of electrochemical oxidation (combustion or conversion) of Rhodamine B (RhB), used as a model organic pollutant is presented. Results demonstrate that the higher the content in diamond-carbon, the greater are the TOC and COD decay rates and hence the oxidation of organic to CO2. The evidence of chromatographic analysis also indicates that the oxidation carried out by the diamonds with a lower content of sp3-carbon is softer, favoring electrochemical conversion of RhB instead of mineralization. This degradation pathway is followed because higher graphite content on BDD anode leads to a higher direct electrochemical activity. These results are of a paramount significance for the choice of electrodes that could guarantee high efficiencies in wastewater remediation processes; because they clearly indicate that the sp3-sp2 carbon ratio should be kept as higher as possible in order to completely deplete pollutants and intermediates from the waste.