Self-assembled Fe₃O₄-layered double hydroxide colloidal nanohybrids with excellent performance for treatment of organic dyes in water

We report a remarkably simple and efficient method for the preparation of colloidal nanohybrids consisting of Fe₃O₄ nanoparticles and nitrate-containing MgAl-layered double hydroxide (LDH) nanocrystals. The electrostatic interaction between the negatively charged magnetite nanoparticles and the positively charged LDH nanocrystals is sufficient to induce the formation of stable self-assembly of the two components. At a mass ratio of 1:0.3 (LDH:Fe₃O₄), all Fe₃O₄ nanoparticles are attached on the LDH nanocrystals. The resulting nanohybrids maintained an overall positive zeta potential of +42 mV and can form a stable colloidal suspension in water. Separation/re-dispersion of the nanohybrids in the aqueous phase can be easily achieved in the presence/absence of an external magnetic field. The combination of these unique properties allows the nanohybrids to exhibit superior performance in the treatment of organic dyes in wastewater. The colloidal suspension of the nanohybrids leads to fast adsorption kinetics and high adsorption capacity of the acid organic dyes via quick surface adsorption. In addition, the spent nanohybrids can be easily recycled after catalytic regeneration by advanced oxidation technology.