Selective and Recyclable Congo Red Dye Adsorption by Spherical Fe ₃O ₄ Nanoparticles Functionalized with 1,2,4,5-Benzenetetracarboxylic Acid

Abstract

In this study, the new material Fe ₃O ₄@BTCA has been synthesized by immobilization of 1,2,4,5-Benzenetetracarboxylic acid (BTCA) on the surface of Fe ₃O ₄ NPs, obtained by co-precipitation of FeCl ₃.6H ₂O and FeCl ₂.4H ₂O in the basic conditions. Characterization by P-XRD, FE-SEM, and TEM confirm Fe ₃O ₄ has a spherical crystalline structure with an average diameter of 15 nm, which after functionalization with BTCA, increases to 20 nm. Functionalization also enhances the surface area and surface charge of the material, confirmed by BET and zeta potential analyses, respectively. The dye adsorption capacity of Fe ₃O ₄@BTCA has been investigated for three common dyes; Congo red (C.R), Methylene blue (M.B), and Crystal violet (C.V). The adsorption studies show that the material rapidly and selectively adsorbs C.R dye with very high adsorption capacity (630 mg/g), which is attributed to strong H-bonding ability of BTCA with C.R dye as indicated by adsorption mechanism study. The material also shows excellent recyclability without any considerable loss of adsorption capacity. Adsorption isotherm and kinetic studies suggest that the adsorption occurs by the Langmuir adsorption model following pseudo-second-order adsorption kinetics.