Adsorption of methylene blue and rhodamine B on graphene oxide-Fe₃O₄ nanocomposite: Molecular dynamics and Monte Carlo simulations

Graphene oxide based magnetic nanocomposite (GO-Fe₃O₄) was synthesized using the coprecipitation method. Intercalation of nanoparticles has resulted in the modified interlayer spacing of GO sheets, it is increased from 0.82 to 1.11 nm. Nanocomposite was characterized using TEM, AFM, XRD, UV-Visible and Raman spectroscopy. Magnetic nanocomposite is tested for removal of industrial dyes MB and RB through the adsorption process. The adsorbent dosage, dye concentration, and adsorption time are optimized in an optimal condition in the dye removal experiments (0.1 g/L adsorbent (GO), 10 mg/L of MB and RB with 25 minutes adsorption time). Adsorption capacity of 100 and 80 mg/g was achieved for MB and RB respectively. Preferential behavior of nanocomposite towards MB over RB can be attributed to the differential electrostatic and geometrical interactions. Differential behavior towards adsorption of dyes is further studied by Monte Carlo adsorption locator and molecular dynamics simulations. Adsorption energies corresponding to MB/GO, RB/GO, MB/Fe₃O₄, and RB/Fe₃O₄ systems show that certain configurations favor adsorption on GO and Fe₃O₄ surfaces. Radial distribution function calculation shows the geometric separation of 2.23 and 5.13 Å for MB and RB respectively, which has profound effect on electrostatic and π-π interaction.