Degradation of Amaranth Dye Using Zero Valent Iron Nanoparticles: Optimal Conditions and Mechanism

Reductive and oxidative degradation of amaranth dye using zero valent iron nanoparticles (ZVINP) has been investigated. Effect of various reaction parameters such as the iron dosage, stirring speed, and influence of pH were studied, and an optimum condition deduced. The ideal operational conditions were 1.5-2.5 g/L of ZVINP, 15-30 min of reaction time, stirring speed of 150-200 rpm and pH of 3-9 for an initial dye concentration of 5070 mg/L. Different mechanisms are suggested for the reactions at lower and higher pHs. At low pH, direct reduction followed by protonation and Fenton reaction is responsible for decoloration and degradation. But at higher pH, in addition to reduction, reactions of superoxide radical and ferryl ions also play a role in the degradation and decoloration. On the other hand, there is no contribution from Fenton reaction at higher pH. With these optimized conditions when applied to a coir factory effluent, a complete decolorization and 34% total organic carbon (TOC) reductions were observed within 30 min of treatment. Both oxidative and reductive mechanisms are explained based on the product profile determined by LC-Q-ToF-MS (liquid chromatography connected with quadrupole time of flight mass spectrometry) analysis.