Synthesis of SiO₂@NiO magnetic core–shell nanoparticles and their use as adsorbents for the removal of methylene blue

SiO₂@NiO core–shell nanoparticles with variable NiO shell thickness have been prepared via homogeneous precipitation. The as prepared and calcined core–shell nanoparticles have been characterized using powder X-ray diffraction, thermal gravimetric analysis, FT-IR spectroscopy, scanning electron microscopy, transmission electron microscopy, and surface area measurements. The shell thickness and the particle size of NiO in the core–shell nanoparticles have been controlled using different concentrations of the nickel salt. The NiO shell thickness, as observed by the TEM, varies from about 46 to 144 nm. The SiO₂@NiO core–shell nanoparticles show higher remanent magnetization, saturation magnetization, and lower coercivity compared to pure NiO nanoparticles. The SiO₂@NiO core–shell nanoparticles have been tested as adsorbents for the removal of methylene blue from an aqueous solution and the core–shell nanoparticles possess good adsorption efficiency for the cationic dye compared to pure NiO and SiO₂.