Complete Destruction of p-Nitrophenol in Aqueous Medium by Electro-Fenton Method

Abstract

An indirect electrochemical method, which is very efficient for the degradation of organic pollutants in water, is described. The method, named electro-Fenton, is based on electrocatalytical generation of Fenton's reagent to produce hydroxyl radicals, which are very active toward organic compounds. An industrial pollutant, p-nitrophenol (PNP), was chosen for this study and was eventually mineralized. The major intermediary degradation products such as hydroquinone, benzoquinone, 4-nitrocatechol, 1,2,4-trihydroxybenzene and 3,4,5-trihydroxy- nitrobenzene were unequivocally identified by HPLC and GC-MS methods. The rate constants of the hydroxylation reactions were determined. The mineralization of the initial pollutant and the intermediates formed during electro-Fenton treatment was followed by total organic carbon (TOC) analyses. Dependence of mineralization on the amount of electrical energy consumed is shown by the relative decrease of TOC values. A mineralization reaction mechanism is proposed.

New insights into the origin of the visible light photocatalytic activity of Fe(iii) porphyrin surface anchored TiO2

“…This radical may further take up different reaction pathways according to the nature of the reaction medium. [35][36][37] In the oxidative medium this radical can undergo hydroxylation reactions. The identification of intermediates during the degradation process by HPLC analysis shows that degradation proceeds through the elimination of the nitro group followed by hydroxylation.…”

“…40 The possibility of hydroquinone formation also occurs by an ipso attack of the hydroxyl radical with simultaneous elimination of the nitro group, since the nitro group in nitro aromatics is always a very good leaving group. 37,38,41 Furthermore, the degradation reaction proceeds with the attack of hydroxyl radicals on the intermediate products, mainly leading to cleavage of the benzene ring and also ends in the formation of oxygenated aliphatic compounds. Successive oxidation of aliphatic products ends in the formation of CO 2 and H 2 O as shown in Scheme 2.…”

Mineralization of an azo dye Acid Red 14 by photoelectro-Fenton process using an activated carbon fiber cathode

“…In recent years indirect electrooxidation methods with hydrogen peroxide electrogeneration, such as electro-Fenton (EF) and photoelectro-Fenton (PEF) reactions, are being developed for the treatment of toxic and refractory organic pollutants in acid waters . In these environmentally friendly electrochemical techniques, hydrogen peroxide is continuously generated in an acidic contaminated solution from the two-electron reduction of O 2 which takes place on graphite [3][4][5], reticulated vitreous carbon [6][7][8][9], mercury pool [10][11][12], carbon-felt [13][14][15][16][17][18] O 2 -diffusion [19][20][21][22][23][24][25][26][27][28][29] and activated carbon fiber (ACF) [30] cathodes. In acidic aqueous medium the oxidation power will be enhanced by addition of ferrous ions to the solution that allows the production of a very reactive one-electron oxidizing agent hydroxyl radical ( OH) (E8 = 2.8 V/NHE) from the well-known Fenton reaction between both species with a secondorder rate constant k 2 = 53 M À1 s À1 [11].…”

Determination of hydroxyl radicals in advanced oxidation processes with dimethyl sulfoxide trapping and liquid chromatography

“…In these processes, the hydroxyl radicals, generated from ozonation [1], UV/H 2 O 2 [2], UV/Fe 3+ /H 2 O 2 [3], UV/TiO 2 [4], Fenton reaction [5], Fenton-like reaction [6] and other systems [7], play an important role in degradation of organic substances in water. It is of continuous interest to find new efficient chemical or physical systems to generate hydroxyl radicals for water treatment.…”