Characteristics and toxic dye adsorption of magnetic activated carbon prepared from biomass waste by modified one-step synthesis

Abstract

Magnetic activated carbons (MACs) were synthesized by modified one-step method under CO2 atmosphere for the purification of toxic dye, using the mixture of FeCl3·6H2O and peanut shells as precursor. Textural characterization showed that the CO2-MACs synthesized were high surface area carbons and micro-mesoporous structure accounted for a large proportion in the MAC samples as a result of the etching effect of iron oxides and drastic C-CO2 reaction. XRD analysis indicated that magnetite nanoparticles were formed and the presence of CO2 promoted the formation of thermodynamically stable Fe3O4. SEM images showed that the nanoparticles were well-dispersed on the surface MACs, which occupied some of the void spaces and led to the decrease in adsorption potential and surface area if excessive FeCl3 was impregnated. Superparamagnetic behavior derived from the magnetically active magnetite enabled easy removal of the spent MAC with malachite green (MG) dye from solutions by a simple bar magnet. The best fit of PSO kinetic model and Freundlich isotherm model suggested that the adsorption on the heterogeneous surface was influenced by physisorption and chemisorption might be the rate-limiting step, and the diffusion process was mainly controlled by film diffusion and intraparticle diffusion. Spontaneous (ΔGo<0) and exothermic (ΔHo<0) nature was obtained in the entropy-controlled adsorption process through thermodynamic study. FT-IR investigation on the fresh and spent MAC coupled with pH experiments showed that interactions between CO2-MAC10 and MG could be electrostatic attraction and π-π stacking.