Surface-dependent cytotoxicity on bacteria as a model for environmental stress of halloysite nanotubes

Nanoparticles of CoDy_0.1Fe_1.9O₄ were synthesized by sol–gel auto-combustion method. Four samples were synthesized from precursor solutions having different pH values in the range of 2.5–10. X-ray diffraction patterns were analyzed to determine the crystal phase of CoDy_0.1Fe_1.9O₄ nanoparticles synthesized at different pH. The XRD patterns confirm the formation of cubic spinel structure for CoDy_0.1Fe_1.9O₄ nanoparticles synthesized at different pH values. However the single phase is obtained only at pH 7.5, while γ and α-Fe₂O₃ phases appeared at pH 2.5, 5.0, and 10.0. Transmission electron microscopy shows that the structural morphology of the nanoparticles is highly dependent on the pH concentration. Particle size varies in between 24 and 36 nm with respect to change in pH concentration of the sample. Particle size increases to 36 nm with increase in pH up to 7.5 followed by a decrease in particle size for further increase in pH value. Magnetic properties were explored by vibrating sample magnetometry. The variation in pH during the synthesis process changes the size and structural morphology of the nanoparticles, which ultimately causes the variation in the values of the magnetic parameters such as saturation magnetization and coercivity. Infrared spectroscopy is employed to determine the local symmetry in the crystalline solids and to shed light on the ordering phenomenon under the influence of different pH values.