Degradation of azo dyes in water by Electro-Fenton process

Abstract

The degradation of the azo dyes azobenzene, pmethyl red and methyl orange in aqueous solution at room temperature has been studied by an advanced electrochemical oxidation process (AEOPs) under potentialcontrolled electrolysis conditions, using a Pt anode and a carbon felt cathode. The electrochemical production of Fenton's reagent (H 2 O 2 , Fe 2+ ) allows a controlled in situ generation of hydroxyl radicals ( · OH) by simultaneous reduction of dioxygen and ferrous ions on the carbon felt electrode. In turn, hydroxyl radicals react with azo dyes, thus leading to their mineralization into CO 2 and H 2 O. The chemical composition of the azo dyes and their degradation products during electrolysis were monitored by high performance liquid chromatography (HPLC). The following degradation products were identified: hydroquinone, 1,4-benzoquinone, pyrocatechol, 4-nitrocatechol, 1,3,5-trihydroxynitrobenzene and p-nitrophenol. Degradation of the initial azo dyes was assessed by the measurement of the chemical oxygen demand (COD). Kinetic analysis of these data showed a pseudo-first order degradation reaction for all azo dyes. A pathway of degradation of azo dyes is proposed. Specifically, the degradation of dyes and intermediates proceeds by oxidation of azo bonds and aromatic ring by hydroxyl radicals. The results display the efficiency of the ElectroFenton process to degrade organic matter.

Heterogeneous Photocatalytic Degradation of Dairy Wastewater Using Immobilized ZnO

“…Some AOPs have been studied recently including combinative applications of complementary technologies for organic compounds degradation in effluents such as ozonation, Fenton and Photo-Fenton, electro-Fenton, UV/photoelectroFenton, electro-Fenton and peroxicoagulation, UV/ozone (O 3 ), UV/hydrogen peroxide (H 2 O 2 ), UV/titanium dioxide (TiO 2 ), and UV/ZnO [5][6][7][8][9]. TiO 2 and ZnO are effective semiconductors, relatively cheap and nontoxic, both of which are being evaluated for respective photocatalytic efficiency [10][11][12].…”

Industrial Wastewater Treatment: A Challenging Task in the Industrial Waste Management

“…Photocatalytic mechanism occurring at the surface of the semiconductors is the other way of obtaining free radicals.. Titanium dioxide in the anatase form has reasonable photoactivity and is the most commonly used photo catalyst. It also has the advantages of being insoluble, relatively inexpensive, non-toxic, as well as having resistance to photocorrosion and biological immunity [61,62]. The photocatalytic process can be performed by simply using the slurry of fine catalyst particles dispersed in liquid phase in a reactor or by using supported/immobilized catalysts.…”

Green Synthesis of Iron Nanoparticles by Aqueous Extract of Eriobotrya japonica Leaves as a Heterogeneous Fenton-like Catalyst: Degradation of Basic Red 46

“…The world wide annual production of dyes is over 7x10 5 tons and 10 -15% of them are discharged the water sources through industrial pollutants [2], [4]. Discharge of dye-stuffs into the natural streams not only may be toxic to the aquatic lives due to the the presence of various metals and chlorides in them, but also; the presence of very small amounts (less than 1 ppm for some dyes) of dyes in water is highly visible and undesirable for any use.…”

“…Color also, reduces photosynthetic activity as it can inhibit the sunlight penetration into the streams. In addition; the most of the dye effluents are assessed as toxic, mutagenic, and carcinogenic as well as they are recalcitrant, non-biodegradable, resistant to aerobic digestion; and stable to light, heat and oxidizing agents due to the complex chemical structure of them [4]- [6].…”

“…In recent years, advanced oxidation processes (AOPs) such as Fenton's reagent (H 2 O 2 , Fe 2+ ) photocatalytic oxidation, photo-Fenton, electro-Fenton, UV/H 2 O 2 , and ozonation processes which are based on the production and the oxidative action of hydroxyl radicals have gained great attention in order to degrade various toxic organic compounds like azo dyes [4], [5].…”