Catalytic effect of Fe²⁺, Cu²⁺and UVA light on the electrochemical degradation of nitrobenzene using an oxygen-diffusion cathode

Abstract

The electrochemical treatment of 100 mg L À1 nitrobenzene solutions in 0.05 M Na 2 SO 4 in the pH range 2.0-4.0 at 25 C has been comparatively studied in the presence of Fe 2þ , Cu 2þ and/or UVA light as catalysts using an undivided cell with a Pt anode and an O 2 -diffusion cathode able to electrogenerate H 2 O 2 . A quite slow degradation is found for the solution with 1 mM Cu 2þ due to the low production of oxidizing hydroxyl radical (OH ) from anodic oxidation of water and the action of the Cu 2þ /Cu þ system. Electro-Fenton treatment with 1 mM Fe 2þ leads to a high concentration of OH in the medium from Fenton's reaction, but less than 70% of the nitrobenzene is mineralized since stable complexes of Fe 3þ with products are formed. These complexes are quickly photodecomposed in the photoelectro-Fenton treatment of the same solution under UVA irradiation, leading to overall depollution at low currents. Complete degradation is also feasible using 1 mM Cu 2þ and 1 mM Fe 2þ at high current because OH can slowly destroy the complexes between Cu 2þ and intermediates. The positive synergetic effect of all catalysts allows the quickest nitrobenzene mineralization using 1 mM Cu 2þ and 1 mM Fe 2þ under UVA irradiation. The nitrobenzene decay always follows a pseudo-first-order reaction. Aromatic products such as o-nitrophenol, m-nitrophenol, p-nitrophenol and 4-nitrocatechol have been followed by reverse-phase chromatography. Nitrate ions are formed from oxidation of nitroaromatic products. Generated carboxylic acids such as maleic, fumaric and oxalic have been detected by ion-exclusion chromatography. The different evolution of complexes of oxalic with Cu 2þ and Fe 3þ explains the influence of the catalysts on nitrobenzene degradation.

Oxidation of herbicides by in situ synthesized hydrogen peroxide and fenton’s reagent in an electrochemical flow reactor: study of the degradation of 2,4-dichlorophenoxyacetic acid

“…In the last two decades, electrosynthesis of hydrogen peroxide has received considerable attention, and several papers have demonstrated that in situ electrogenerated H 2 O 2 may also be successfully used for the treatment of aqueous effluents containing organic pollutants [1][2][3][4][5][6][7][8][9][10][11][12][13]. Hydrogen peroxide is a popular non-selective oxidizing reactant for the oxidation of organic pollutants to carbon dioxide.…”

“…H 2 O 2 electrosynthesis is also of interest because of the cost and risks associated with transportation, storage and handling of concentrated hydrogen peroxide. Graphite flat plates [1,2] and three-dimensional electrodes made from reticulated vitreous carbon (RVC) [3][4][5][6], and gas diffusion electrodes (GDE) [7][8][9][10][11][12][13] have been used to reduce oxygen to hydrogen peroxide. This paper reports an investigation of the performance of an electrochemical flow reactor, using a RVC cathode for H 2 O 2 electrosynthesis and the simultaneous oxidation of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D).…”

Catalytic Degradation of Nitrobenzene and Aniline in Presence of Ozone by Magnesia from Natural Mineral

“…Recently, considerable attention has been focused on the treatment of nitrobenzene and aniline in wastewater. Different methods have been proposed such as photo-catalytic process [4][5][6][7], wet air oxidation [1,8,9], catalytic electrochemical treatments [10][11][12] and ozonation [13][14][15][16][17][18][19].…”

Electrochemical Treatment of Dye Solution by Oxalate Catalyzed Photoelectro‐Fenton Process Using a Carbon Nanotube‐PTFE Cathode: Optimization by Central Composite Design

“…(2)) and 1e À reduction of ferric ions which are initially introduced at a catalytic concentration (Eq. (3)) [13][14][15][16].Electrogeneration of hydrogen peroxide (Eq. (2)) usually occurs at carbon-felt [17][18][19][20][21][22] and carbon-polytetrafluoroethylene (PTFE) O 2 -diffusion [23,24] cathodes.…”