Highly efficient organic dye removal from waters by magnetically recoverable La₂O₂CO₃/ZnFe₂O₄-reduced graphene oxide nanohybrid

Organic dyes released in the form of textile effluent have caused serious pollution of aqueous environments. Here, we report a reduced graphene oxide (rGO) loaded with La₂O₂CO₃ and ZnFe₂O₄ (ZF) nanoparticles (LGZF) as a highly efficient adsorbent, which was synthesized through a simple precipitation-hydrothermal method. The LGZF nanohybrids were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, transmission and scanning electron microscopy, magnetic property, zeta potential, and surface area measurements. The effectiveness of cationic dye sorption on the adsorbent was examined under several experimental variables such as contact time, initial dyes concentrations, solution pH, and solution temperature. A novel magnetic nanohybrid with interlayer crystal structures exhibited an enhanced sorption capacities for methylene blue (MB) and rhodamine B (RhB) from contaminated water in comparison to bare rGO and ZF, in which LGZF with a mass ratio of La to Fe of 1:1 showed the highest adsorption activity. The Langmuir and pseudo-second-order model fully explained experimental adsorption and kinetics data. LGZF displayed maximum adsorption capacity of 201 and 98.4 mg/g for MB and RhB, respectively. The MB and RhB adsorption onto LGZF involved a spontaneous and an endothermic chemisorption through a combination of π–π interaction, electrostatic interaction, surface complexation, and hydrogen bonding. Furthermore, feasibility on the removal of organic dyes and antibiotic in surface water was also evaluated. The enhanced adsorption performance of the LGZF nanohybrid can be attributed to the incorporation of the characteristic La and Zn elements on rGO, which promotes the synergistic effects between rGO, La₂O₂CO₃, and ZF.