Loading carbonaceous materials with silver for the treatment of chloro-organic compounds in aqueous phase

Abstract

Many electrochemical technologies, either based on novel concepts (such as microbial fuel cells), experimental setups (such as photoelectrochemical or solar photoelectro-Fenton reactors) or materials (mainly focused on the use of large O2-overpotential anodes like BDD) have been devised in recent years for water remediation. Special attention has been paid to highly toxic, biorefractory organic pollutants such as the chlorinated hydrocarbons, which conjugate toxicity with chemical stability, bioaccumulation and long-range diffusivity [1]. Electroreduction at silver cathodes becomes an interesting alternative to degrade chloro-organic compounds, but it may lead to the accumulation of reaction by-products, even upon coupling with electro-oxidation at BDD [2]. On the other hand, some Fenton-based processes have proven very effective for the destruction of organic matter due to the action of •OH formed when cathodically electrogenerated H2O2 reacts with added Fe2+ [3]. Based on this, we have envisaged a potential strategy for the enhanced removal of chloro-organic pollutants and their by-products: electro-Fenton process in the bulk upon H2O2 electrogeneration at a carbonaceous cathode, which can simultaneously act as the substrate for electroreduction at loaded Ag nanoparticles. To achieve this goal, a highly efficient material for H2O2 production, i.e., a gas diffusion electrode (GDE), has been chosen for Ag-loading experiments. Several authors have reported the preparation of Ag-loaded carbonaceous materials based on a simple electroless deposition (ELD) process from Ag+ solutions. Some of them have addressed the full preparation of GDEs with Ag catalysts [4,5]. Here, we report the use of a commercial GDE as a suitable substrate to obtain conveniently dispersed Ag nanoparticles. The effect of several ELD parameters (e.g., nature of reductant, mode of application and deposition time) on the surface morphology has been mainly studied by SEM-EDX. Bulk electrolyses in 50 mM Na2SO4 at various pH were subsequently performed with the best materials to assess their ability to electrogenerate H2O2. For comparison, carbon paper was used as an alternative substrate. An important objective of the research was to find the optimum conditions to load the substrate so as to keep the balance between covered and uncovered area, in order to favor both H2O2 production and pollutant electroreduction. The performances of these electrodes for the electrogeneration of H2O2 and the abatement of chloro-organic pollutants is currently being investigated. [1] S. Rondinini, A. Vertova, in Electrochemistry for the environment, 2010, pp. 279–306. [2] O. Scialdone, A. Galia, L. Gurreri, S. Randazzo, Electrochim. Acta 55 (2010) 701–708. [3] E. Brillas, I. Sirés, M.A. Oturan, Chem. Rev. 109 (2009) 6570–6631. [4] E. Gülzow, N. Wagner, M. Schulze, Fuel Cells 3 (2003) 67–72. [5] S. Rondinini, G. Aricci, Z. Krpetic, C. Locatelli, A. Minguzzi, F. Porta, A. Vertova, Fuel Cells 3 (2009) 253–263.