Electrochemical synthesis of peroxomonophosphate using boron-doped diamond anodes

A new method for the synthesis of peroxomonophosphate, based on the use of boron-doped diamond electrodes, is described. The amount of oxidant electrogenerated depends on the characteristics of the supporting media (pH and solute concentration) and on the operating conditions (temperature and current density). Results show that the pH, between values of 1 and 5, does not influence either the electrosynthesis of peroxomonophosphate or the chemical stability of the oxidant generated. Conversely, low temperatures are required during the electrosynthesis process to minimize the thermal decomposition of peroxomonophosphate and to guarantee significant oxidant concentration. In addition, a marked influence of both the current density and the initial substrate is observed. This observation can be explained in terms of the contribution of hydroxyl radicals in the oxidation mechanisms that occur on diamond surfaces. In the assays carried out below the water oxidation potential, the generation of hydroxyl radicals did not take place. In these cases, peroxomonophosphate generation occurs through a direct electron transfer and, therefore, at these low current densities lower concentrations are obtained. On the other hand, at higher potentials both direct and hydroxyl radical-mediated mechanisms contribute to the oxidant generation and the process is more efficient. In the same way, the contribution of hydroxyl radicals may also help to explain the significant influence of the substrate concentration. Thus, the coexistence of both phosphate and hydroxyl radicals is required to ensure the generation of significant amounts of peroxomonophosphoric acid

A comparison of electrochemical degradation of phenol on boron doped diamond and lead dioxide anodes

This work compares two electrode materials used to mineralize phenol contained in waste waters. Two disks covered with either boron doped diamond (BDD) or PbO2 were used as anodes in a one compartment flow cell under the same hydrodynamic conditions. Efficiencies of galvanostatic electrolyses are compared on the basis of measurements of Total Organic Carbon (TOC) and Chemical Oxygen Demand (COD). Galvanostatic electrolyses were monitored by analysis of phenol and of its oxidation derivatives to evaluate the operating time needed for complete elimination of toxic aromatics. The experimental current efficiency is close to the theoretical value for the BDD electrode. Other parameters being equal, phenol species disappeared at the same rate using the two electrode materials but the BDD anode showed better efficiency to eliminate TOC and COD. Moreover, during the electrolysis less intermediates are formed with BDD compared to PbO2 whatever the current density. A comparison of energy consumption is given based on the criterion of 99% removal of aromatic compounds

Performance of Ti/Pt and Nb/BDD anodes for dechlorination of nitric acid and regeneration of silver(II) in a tubular reactor for the treatment of solid wastes in nuclear industry

One of the problems frequently encountered in the processing of nuclear fuels is the recovery of plutonium contained in various solid wastes. The difficulty is to make soluble the plutonium present as the refractory oxide PuO2. The dissolution of this oxide in nitric acid solutions is easily performed by means of silver(II) a strong oxidizing agent which is usually electrochemically generated on a platinum anode. However, certain solid residues that must be treated to separate actinides contain important quantities of chloride ions that require after dissolution in nitric acid a preliminary electrochemical step to be removed before introducing Ag(I) for Ag(II) electrogeneration. Research is conducted to find electrocatalytic materials being able to replace massive platinum in view to limit capital costs. In the present work a set-up including a two-compartment tubular reactor with recirculation of electrolytes was tested with anodes made of boron doped diamond coated niobium (Nb/BDD) and platinum coated titanium (Ti/Pt) grids for the removal of chlorides (up to 0.1 M) and for silver(II) regeneration. The study showed that these two anodes are effective for the removal of chlorides contained in 6 M HNO3 solution as gaseous chlorine, without producing the unwanted oxyanions of chlorine. Furthermore, the regeneration rate of silver(II) on Nb/BDD anode is approximately equal to that obtained on Ti/Pt anode for the same hydrodynamic conditions in the tubular reactor. Accordingly, dechlorination as well as silver(II) regeneration can be performed in the same reactor equipped either with a Nb/BDD or a Ti/Pt anode. Besides, the service life of Nb/BDD anodes estimated by accelerated life tests conducted in 6 M HNO3 can be considered as very satisfactory compared to that observed with Ti/Pt anodes

On the performance of Ti/SnO2 and Ti/PbO2 anodes in electrochemical degradation of 2-chlorophenol for waste water treatment

Electrochemical oxidation of 2-chlorophenol was studied at Ti/PbO2 and Ti/SnO2 anodes. The performance of the electrodes was evaluated in terms of faradaic yield and fraction of toxic intermediates removed during the electrolysis. Results showed that, although similar average faradaic yields were obtained using Ti/PbO2 or Ti/SnO2 anodes, the latter material is preferred because of its ;better ability to oxidise toxic compounds. An effective electrochemical treatment (eta(F) congruent to 50%) may be accomplished, in which electrolysis at Ti/SnO2 can be stopped when, in spite of a relatively high COD, only a small amount of easily biodegradable oxalic acid is present in the effluent