Electrochemical decolorization of Reactive Black 5 in an undivided cell using Ti and graphite anodes: Effect of polypyrrole coating on anodes

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/cm2. 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.