Effective adsorption of malachite green with silica gel supported iron-zinc bimetallic nanoparticles

Abstract

In the present study, a composite material consisting of silica gel 60 supported iron-zinc bimetallic nanoparticles (Si/Fe-ZnNPs) was prepared and characterized by SEM, EDX, FTIR, and XRD analysis. The adsorbent properties of the synthesized composite material were evaluated with the removal of Malachite Green (MG). According to characterization results, the cubic structures and agglomerated nano-sized spherical particles (≈30 nm) were formed. The FT-IR spectrum confirms the formation of Fe-Zn NPs through the observation of the Fe-O stretches and metal-metal stretching vibrations of (Zn2+ – O2ˉ) adsorption bands. Additionally, the FT-IR revealed the presence of Si-O-Si, Si-O-H stretching, and O-Si-O bending vibrations attributed to silica gel 60. The optimal environmental conditions for adsorption were determined to be a natural pH of 3.3, an adsorption temperature of 50°C, and an adsorbent concentration of 1.0 g/L. An increase in equilibrium uptakes of MG was observed with a linear correlation to initial dye concentrations. Thermodynamic studies indicated that the adsorption process was endothermic, non-spontaneous, and increasing disorder at the solid-solution interface during adsorption with positive ΔH, ΔG, and ΔS values, respectively. The experimental results revealed that the Langmuir isotherm model provided the best fit for the equilibrium data. The maximum monolayer coverage capacity of Si/Fe-ZnNPs was 666.67 mg/g at an optimum temperature of 50°C. Further analysis displayed that the kinetic adsorption data adhere to the pseudo-second-order kinetic model. Additionally, Weber-Morris model results revealed the effectiveness of both the film and intra-particle diffusion in the adsorption.