The effect of microtube formation with walls, containing Fe$_3$O$_4$ nanoparticles, via gas-solution interface technique by hydrolysis of the FeCl$_2$ and FeCl$_3$ mixed solution with gaseous ammonia

In this work, microtubes with walls, containing Fe$_3$O$_4$ nanoparticles, obtained by “rolling up” of the interfacial films, were synthesized by the gas-solution interface technique (GSIT), using a mixture of aqueous solutions of FeCl$_2$ and FeCl$_3$ and gaseous ammonia. The synthesized microtubes were characterized by Scanning Electronic Microscopy (SEM), Energy-Dispersive X-ray spectroscopy (EDX), X-Ray Diffraction analysis (XRD) and magnetization measurements. It was established that under optimal synthetic conditions the microtube diameter ranged from 5 to 10 $\mu$m, the length was up to 120 $\mu$m and the thickness of walls was about 0.6 m, the walls themselves being formed by nanoparticles with a size of about 10 nm. The reversible hysteresis behavior, the low coercive force, the low remanence magnetization and the approaching of M$_r$/M$_s$ to zero, confirmed the superparamagnetic nature of the synthesized microtubes. A hypothesis on the formation of microtubes by the gas-solution interface technique was proposed.