Superparamagnetic NiO-doped mesoporous silica flower-like microspheres with high nickel content

Morphology oriented synthesis of metal oxide doped silica structures have fascinating properties which needed to be explored extensively. In this work, NiO doped silica microsphere with beautiful flower-like morphology has been achieved by adopting a facile surfactant-assisted synthetic route using CTAB-ammonia in H₂O–ethanol mixed solvent media. The sol–gel synthesis with effective variations of Ni/Si ratios up to 7.0, followed by a simple hydrothermal treatment and subsequent calcination leads to the formation of NiO–silica mesostructures with high nickel content. Detailed structural and elemental characterizations by using powder X-ray analysis (XRD), scanning electron (SEM) and transmission electron microscopy (TEM), N₂ adsorption–desorption, X-ray photoelectron spectroscopy (XPS) revealed that single cubic phase NiO doped mesoporous silica microspheres (for Ni/Si = 5:1 and 7:1) with good surface area (169 and 205 m² g⁻¹ for sample with Ni/Si = 7:1 and 5:1, respectively) and pore width 3–5 nm, have been formed with 3D flower-like shape and 500–600 nm particle size. These NiO–silica microspheres containing high Ni content up to 76 wt% have shown excellent paramagnetic properties at room temperature.