Electro-oxidation of nitrophenol by ruthenium oxide coated titanium electrode: Parametric, kinetic and mechanistic study

• Electrochemical oxidative degradation of p-nitrophenol by Ti/RuO2 electrode.
• Study of effect of parameters such as initial pH, current density, NaCl concentration and initial concentration.
• Identification of intermediates and mineralization products by GC/MS.
• Proposal of degradation mechanism.
• Kinetic modeling by heterogeneous kinetics.

Present study investigates mechanism of electrochemical (EC) oxidative degradation of p-nitrophenol (PNP) by ruthenium oxide coated titanium (Ti/RuO2) electrode. First, the process proficiency was determined in terms of chemical oxygen demand (COD), total organic carbon (TOC), current efficiency (CE) and specific energy consumption (SEC) under different experiment conditions of initial pH (pHo), current density (j), electrolyte concentration (m) and initial PNP concentration (Co). Maximum COD and TOC removal efficiencies of 98.9% and 81.9%, respectively, were obtained at j = 168.9 A/m2, pHo = 5.5, Co = 100 mg/L and m = 300 mg/L with SEC of 535.7 kW h/kg COD. PNP degradation mechanism has also been proposed on the basis of identification of intermediates by gas chromatograph coupled with mass spectrometry (GC/MS). Various intermediates such as quinine, benzoquinone, organic acids and small mineralization products were obtained during the EC treatment of PNP. PNP was found to be oxidized by both direct (hydroxyl radical generated via water electrolysis on anode surface) and indirect (via mediators, hypochlorous acid and active chlorine generated during chlorine oxidation in solution) EC oxidation. Kinetics of EC oxidation was represented by pseudo-first order kinetic model.