Comparative assessment of the decolorization of aqueous bromophenol blue using Fe nanoparticles and Fe-Ni bimetallic nanoparticles

Iron nanoparticles (Fe NPs) and bimetallic iron-nickel nanoparticles (Fe-Ni NPs) were synthesized by liquid phase reduction method, and were characterized using XRD, XPS, SEM and TEM techniques. A comparative study was performed to assess the efficiency of Fe and Fe-Ni NPs in the removal of bromophenol blue (BPB) dye from aqueous media. The effects of pH, time, initial dye concentration, and temperature on the removal process were investigated. The results showed that the highest dye removal is obtained at pH of 4.0. The removal of BPB follows a pseudo second order rate kinetics, with the dye removal by Fe NPs being faster than that achieved using Fe-Ni NPs, and the maximum sorption capacities being 1667 and 213 mg/g, respectively. Equilibrium constant (K) values were calculated using a modified form of the linear isotherm, and the K values at 298 K were 64416 and 11901 mL/g for Fe and Fe-Ni NPs, respectively. The removal of BPB by Fe NPs and Fe-Ni NPs was exothermic with ∆H° values being –35.8 and –51.9 kJ/mol, respectively. Entropy of the system decreased in both cases, and the corresponding values were –28.2 and –96.3 J/mol·K for Fe and Fe-Ni NPs, respectively.