Synthesis of Silica@Ni-Co Mixed Metal Oxide Core-Shell Nanorattles and Their Potential Use as Effective Adsorbents for Waste Water Treatment

SiO2@Ni-Co mixed metal oxide core-shell nanorattles with different Ni2+/Co2+ molar ratios have been successfully synthesized through a facile, inexpensive self-template route by the calcination of SiO2@Ni-Co layered double hydroxides at 500 degrees C. The formation of SiO2@Ni-Co mixed metal oxide core-shell nanorattles has been confirmed by an array of characterization techniques. Field-emission scanning electron microscopy (FE-SEM) analysis indicates a hierarchical flowerlike morphology for the SiO2@Ni-Co mixed metal oxide core-shell nanorattles, and transmission electron microscopy (TEM) analysis confirms the formation of core-shell nanorattles. The diffuse reflectance spectra of the SiO2@Ni-Co mixed metal oxide core-shell nanorattles show two bandgap absorptions attributed to metal-to-ligand charge-transfer transitions (Mn+ -> O2-). The SiO2@Ni-Co mixed metal oxide core-shell nanorattles have been explored as effective adsorbents for the removal of rhodamine B, methylene blue, and their mixture from aqueous solutions. The adsorption of the single dye systems follows Langmuir and Freundlich isotherms, whereas a binary Langmuir model has been applied for the binary dye systems. The SiO2@Ni-Co mixed metal oxide core-shell nanorattles possess higher adsorption capacity for the individual dyes than for the mixture of dyes. Kinetic studies indicate that the adsorptions of rhodamine B, methylene blue, and their mixture follow pseudo-second-order kinetics.