Electrochemical oxidation of 4-chlorophenol and its by-products using Ti/Ru0.3M0.7O2 (M = Ti or Sn) anodes: preparation route versus degradation efficiency

Abstract

The electrochemical degradation of 4-chlorophenol and its main by-products was investigated in acid medium using binary oxides electrodes of nominal composition Ti/Ru 0.3 Ti 0.7 O 2 and Ti/Ru 0.3 Sn 0.7 O 2 prepared by thermal decomposition through two different routes: inorganic precursors dissolved in isopropanol and polymeric precursors (PPM). The aim of this study was to investigate the influence of both the composition and preparation methodology of these electrodes in the electrooxidation of the organic pollutants 4-chlorophenol and its by-products. Electrolyses were carried out using a filter press-type flow cell and monitored by high performance liquid chromatography (HPLC), total organic carbon (TOC), and chloride analyses. Besides CO 2 , the by-products formed in the reactions were 1,4-benzoquinone, 4-chlorocatechol, and hydroquinone, as well as oxalic, maleic, malic, malonic, and succinic acids. The electrocatalytic efficiency with respect to the degradation of by-products was evaluated through the electrooxidation of 1,4-benzoquinone and oxalic acid (OA).The anodes investigated in this work are very promising for the degradation of pollutants because of their excellent efficiency concerning the consumption of 4-chlorophenol and its by-products, although the mineralization of the starting material is not complete. The cleavage of the aromatic ring occurs preferentially in the case of electrodes prepared by decomposition of inorganic precursors due to their larger electrochemically active area and electrocatalytic activity for oxygen evolution reaction (OER). However, OA oxidation is favored on Ti/Ru 0.3 Sn 0.7 O 2 prepared through decomposition of PPM.

Electrooxidation of Phenol on a Ti/RuO2 anode: effect of some electrolysis parameters

“…For the lower NaCl concentration, the low chlorophenols formation rate did not favor the buildup of adsorbed products, which block the anode surface. 6,[30][31][32] Several researchers 5,12,24,25,[33][34][35][36] observed that the decrease of the electrode efficiency due to organic matter adsorption depends on the electrolysis conditions, such as phenol concentration, supporting electrolyte type, electrode material, electrode potential and time. According to Zareie et al, 30 although high NaCl concentrations favor the formation of adsorbed intermediate products on the anode surface, the hypochlorite and chlorine ions act on the destruction of this blocking layer under longer times.…”

“…[1][2][3][4] They are refractory to conventional treatment process and, in the presence of chlorine, they may produce chlorophenols, which are carcinogenic and even more refractory to degradation than the phenols themselves. [4][5][6] There are several available processes to treat effluents containing phenols, such as biological treatment, advanced oxidation processes, oxidation in supercritical water and electrochemical oxidation. [6][7][8] Furthermore, some of those processes, for instance photocatalytic oxidation process, presents high operational costs and operational issues due to catalyst deactivation.…”

“…[4][5][6] There are several available processes to treat effluents containing phenols, such as biological treatment, advanced oxidation processes, oxidation in supercritical water and electrochemical oxidation. [6][7][8] Furthermore, some of those processes, for instance photocatalytic oxidation process, presents high operational costs and operational issues due to catalyst deactivation. 9 The electrolytic process has shown to be an efficient low cost, an alternative to the treatment of several aqueous effluents containing organic and inorganic pollutants.…”

“…9 The electrolytic process has shown to be an efficient low cost, an alternative to the treatment of several aqueous effluents containing organic and inorganic pollutants. 3,4,6,[10][11][12][13][14][15] In this process, different electrode materials, such as Ti/RuO 2 , Ti/IrO 2 , Pt, Ti/PbO 2 , borondoped diamond (BDD) and Ti/SnO 2 -Sb have been tested. Some authors [16][17][18] reported that the "active" electrodes such as Ti/RuO 2 and Ti/IrO 2 are not very effective for phenols degradation.…”

Electro-oxidation of chlorophenols on powdered carbon electrodes of different porosity

“…In addition, the electro-polymerization behavior of CPs during voltammetric measurements (electrode fouling) has been reported, as has the fact that the tars formed display a low rate of oxidation, low permeability and strong adhesion to the electrode [14][15][16][17]. Electrode fouling is more likely to occur in the potential range of water stability, but fouling is less of a problem in the oxygen evolution region, probably due to oxygen bubbles attacking the polymeric films and to the oxidative destruction of these films [18]. Many new modified electrode materials [4,13] have been developed to minimize the fouling effect.…”