Fig. 2: Modified precursors with different silica shell thicknesses.

a HR-TEM image of an akaganeite nanorod with crystal planes analyzed by Fast Fourier Transformation (inset). b The hydrodynamic size of the particle system increases with the polymer modification (@pH = 7.0, 0.12 mg mL⁻¹, grey) of the akaganeite rods (initial @pH = 2.5, orange). In reference, an akaganeite solution at pH 7 (bright orange) is shown. The hydrodynamic radius was measured thrice for each sample, and the Z-average was calculated. c The change of the surface charge in aqueous particle solutions from positively charged iron oxide hydroxide (@pH = 2.5) to negatively charged acrylic acid end groups (@pH = 7.0, 0.12 mg mL⁻¹) is indicated by the change of the zeta potential. d The silica thicknesses d_SiO2 are depicted as a function of the molar amount of tetraethoxysilane per surface area and per volume of the reaction solution, exemplified for the aka@0.12PAA precursors. TEM images in different magnetizations and corresponding photos (inlet) of akaganeite@0.12PAA@SiO₂ particle solutions with e d_SiO2 = 2.2 nm, f d_SiO2 = 4.7 nm, and g d_SiO2 = 6.8 nm are shown, exemplarily. The precursors with silica shells with h d_SiO2 < 4 nm and j d_SiO2 > 4 nm do not show significant differences in crystallinity, as both cases are assumed to be amorphous, as indicated in the HR-TEM images and by the shape of the line profile scans. Despite the silica shells of i d_SiO2 < 4 nm and k d_SiO2 > 4 nm, the presence of akaganeite is detectable, as confirmed by nanorod areas (top) and corresponding EDX line-scan profiles (bottom).