Ni²⁺-doped magnesium aluminosilicate nanoceramics: structural, optical, dielectric, and antimicrobial properties

Herein, nanospheres of Ni²⁺-doped magnesium aluminosilicate (MAS) glass-ceramics were produced utilizing a sol-gel processing technique in order to examine the impact of the incorporation of different levels of Ni (0, 1, 2, 3, 4, or 5 mol%) on their structural, optical, electrical and antimicrobial characteristics. X-ray diffraction analysis revealed that the samples predominantly consist of two polycrystalline phases: hexagonal Mg₂Al₄Si₅O₁₈ and orthorhombic Mg₂SiO₄; as the level of Ni²⁺ incorporation increased, more and more prominent orthorhombic reflections became apparent. It was found from the examination of electron micrographs that the average crystallite diameter was approximately 23 nm and that the particles were nearly spherical with diameters between 20 and 30 nm, exhibiting a uniform dispersion of Ni throughout the MAS matrix. Optical diffuse reflectance (DR) spectra demonstrated that all of the studied samples contained the characteristic absorption features associated with Ni²⁺ ions coordinated to six oxygen atoms and that the optical band gap of Ni(doped)-MAS varied non-linearly with respect to the increasing amounts of Ni, which can be explained by the existence of the defect states that are created by dopant incorporation and/or changes that occur in the electronic structure. At temperatures of 30 °C, 60 °C, and 100 °C, dielectric measurements exhibited stable high-frequency permittivity values (≈15-20) for all sample compositions measured, indicating significant dependence on Ni. At low frequencies and temperatures, dielectric measurements indicate that the MAS-1Ni sample has an extraordinarily high permittivity value of 5.12 × 10⁴ at 0.1 Hz and 100 °C. The antimicrobial assessment of Gram-positive and Gram-negative bacteria and fungi samples demonstrated visible clear inhibition zones (max 18 mm) as a result of the continuous release of Ni²⁺ ions and the alteration of the cell wall structure in microbial organisms. These findings demonstrate that MAS glass-ceramic nanospheres modified with Ni have the ability to offer tunable multifunctional properties, making them promising candidates for biomedical, antimicrobial and functional ceramic applications.