Effective adsorptive removal of anionic dyes from aqueous solution

Abstract

Congo Red (CR) and Reactive Black 5 (RB5) anionic dyes were removed from aqueous solution using Porous Magnetite Fe₃O₄ nanospheres (PMNs) as a high‐performance adsorbent. Various methods, such as Fourier transform infrared spectroscopy and X‐ray diffraction, were used to classify the synthesized PMNs. The Brunauer Emmett‐Teller (BET) method was used to calculate the sample's high specific surface area of 143.65 m².g^‐1, as well as its pore volume and pore size. The PMNs have a very uniform spherical morphology, with an average particle size of 25.84 nm, as revealed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) image analysis. Variables such as initial pH, adsorbent dosage, contact time, and temperature were investigated to determine optimal adsorption conditions for the extraction of Congo Red (CR) and Reactive Black 5 (RB5) from aqueous solutions. The optimal pH for extracting the anionic dyes tested from water solutions was 3 and 4 for CR and RB5, respectively. The maximum adsorption potential of the CR and RB5 dyes, respectively, was 1621.59 and 1070 mg.g^‐1. pH, temperature, initial concentration, contact time, salinity, and PMNs dosing were all studied in depth. Since the PMNs Zero‐charge point (pH_PZC) equals 4.3, these dyes were ideal for adsorption at an acid pH. The Langmuir, Freundlich, Dubinin ‐ Radushkevich, and Temkin adsorption isotherms were used to determine adsorption results. For both dyes, the adsorption isotherm was fitted to the Langmuir model. The mean adsorption energy (E_a) for CR and RB5, respectively, is 20.2 and 24.8 kJ.mol^‐1, suggesting a chemisorption mechanism. The kinetics of adsorption was discovered to adopt a pseudo‐second‐order kinetic model. Thermodynamic experiments confirmed that the adsorption mechanism is endothermic and spontaneous. They experimented with ethanol as a solvent for desorption of adsorbed anionic dyes.