Synthesis of bimetallic Fe–Zn nanoparticles and its application towards adsorptive removal of carcinogenic dye malachite green and Congo red in water

Abstract

In this study, a novel bimetallic Fe–Zn nanoparticle was synthesized via a coprecipitation method and applied for the adsorptive removal of carcinogenic dye malachite green (MG) and Congo red (CR) in water. The synthesized bimetallic Fe–Zn nanoparticles were characterized by TEM, XRD, FTIR, and SEM with an attached EDX, a BET surface area analyzer, and by determining pHzpc. Batch adsorption experiments were conducted to evaluate the adsorption process by varying the optimization parameters such as the solution pH, time, and initial dye concentration. The process was initially very rapid, and the maximum adsorption was observed within 60min of contact time. The kinetics of removal were tested with a pseudo-first order, a pseudo-second order, and an intra-particle diffusion model and showed the best agreement with the pseudo-second order model. Adsorption data were modeled with Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich isotherms and had a good fit with the Langmuir isotherm model. The Langmuir maximum adsorption capacity for MG and CR was found to be 21.74 and 28.56mg/g, respectively. The adsorption process was endothermic with positive values of ΔH° of 62.73 and 69.65kJ/mol for MG and CR, respectively, and was spontaneous, as the ΔG° value was negative for all of the samples. A positive ΔS° value indicates increased disorder at the solid–solution interface during the adsorption of the MG and CR dyes. An attempt was made to regenerate the MG- and CR-loaded bimetallic Fe–Zn nanoparticles with suitable eluents and the regenerated bimetallic Fe–Zn nanoparticles were reused seven and six times with removal levels higher than 70% for the adsorption of MG and CR, respectively.