Abstract
Electrochemical decolorization of an azo dye Reactive Black 5 (RB5) was studied in an undivided cell using Ti and graphite, and polypyrrole (PPy) coated Ti (PPy-SLS-Ti) and graphite (PPy-SLS-G) anodes in the presence of sodium chloride as an electrolyte to investigate the effect of polypyrrol coating. The colour removal efficiencies were 52.6%, 96.3%, 51.6%, and 41.0% respectively, at the end of 90 minutes of electrolysis at current density of 5 mA/cm 2 . The presence of PPy coating resulted in lower decolorization than that in the absence of coating. No specific peak emerged in UV-Vis spectra obtained at various time points during electrolysis using uncoated Ti and Graphite anodes which indicated non-selective nature of oxidation process. In case of PPy-SLS/Ti and PPy-SLS/Graphite anodes, a peak at 254 nm emerged distinctly which was determined to be vinylsulfone (VS), an amine. Generation and accumulation of VS suggested that oxidation was suppressed and electrochemical reduction rather than oxidation, was a predominant mechanism responsible for RB5 decolourization in case of polypyrrole coated anodes. Normally, in an undivided cell, reactions on anode predominates (i.e. oxidation). The results obtained here may lead to development of anodes for undivided cells on which the extent of oxidation may be controlled by a suitable coating such as PPy.
Highlights
Dye wastewater is an environmental concern due to its huge quantity, variable nature, low biodegradability, chemical composition, and toxicity to aquatic life [1]
Of the dyes used are azo dyes, in which the azo (–N=N–) group is connected to an aromatic compounds forming a chromophoric group responsible to impart a characteristic colour to the dye
The main aim of the present study was to compare the performance of Ti, Graphite, and PPy coated Ti (PPy-SLS-Ti) and graphite (PPy-SLS-G) as anodes for electrochemical decolourization of Reactive Black 5 (RB5) in an undivided cell to investigate the influence of PPy film on the extent and mode of decolourization
Summary
Dye wastewater is an environmental concern due to its huge quantity, variable nature, low biodegradability, chemical composition, and toxicity to aquatic life [1]. The electrochemical technologies (electrochemical oxidation (EO), electrochemical reduction (ER), electrocoagulation (EC), indirect electrooxidation with strong oxidants, and emerging photoassisted electrochemical treatments for treating dye wastewaters have been proposed [4]. The application of these technologies is benefiting from advantages such as versatility, environmental compatibility, and potential cost effectiveness. In a direct EO process, pollutants are first absorbed on the anode surface and destroyed by the electron transfer reaction Different anode materials, such as dimensionally stable anodes, noble metals, carbon-based anodes, metal oxides, and boron-doped diamond electrodes have been explored for degradation of dyes. All of the oxidants are generated in situ and are utilized immediately [5,6,7]
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