Iron–Manganese Double Oxide Nanomaterial for Efficient Removal of Methylene Blue and Cr(VI) from Aqueous Systems

Abstract

In this study, an iron−manganese double oxide containing wood fiber-based nanomaterial was synthesised for enhanced removal of organic dyes and toxic metals from contaminated water using a modified hydrothermal technique. This adsorbent was formed in situ within the porous structure of wood fibers after a portion of the lignin was removed. Analytical methods, in particular: scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), derivative thermogravimetric (DTG) and energy-dispersive X-ray spectroscopy (EDX) were used to characterise the synthesised nanomaterial. UV-visible spectroscopy and atomic absorption spectroscopy (AAS) were utilised for the investigation of the kinetics of adsorption and adsorption isotherms of organic dye Methylene Blue (MB) and metal pollutant Cr(VI). From the analysis of kinetics data, it is observed that in both cases the adsorption exhibited a superior fit to the pseudo-second-order kinetics model of non-linear form. The Langmuir adsorption isotherm model demonstrated a better fit for the adsorption of MB, displaying a maximum adsorption capacity of approximately 92% over the synthesised material. On the other hand, the Freundlich adsorption isotherm model showed a notably improved fit for Cr(VI) adsorption, displaying very high adsorption capacity. Thus, the specifically designed binary metal oxide was found to be a potential material for applications in environmental remediation initiatives.