Optical and magnetic behavior of Ag encapsulated β-Fe2O3 core–shell hollow nanotubes

This paper reports the synthesis of silver encapsulated β-Fe2O3 core–shell hollow nanotubes soluble in aqueous medium. Colloidal β-Fe2O3 nanoparticles produced by the hydrolysis of FeCl3 are grown on Ag nanoparticles in N2 environment to produce core–shell hollow tubular structure. A variation in the amount of silver (0.23 × 10−4 mol dm−3 – 0.76 × 10−4 mol dm−3) regularly blue shifts the excitonic band due to β-Fe2O3, and reduces the thickness of β-Fe2O3 in the shell besides changing the morphology of the nanostructures. A typical amount of silver (0.58 × 10−4 mol dm−3) leads to the development of core–shell hollow tubes (SC) in which the core consists of Ag nanoparticles with an average diameter of 3.5 nm and the shell is made of β-Fe2O3 hollow nanotubes consisting of Cl− and NO3− ions with an average thickness and the inner diameter of 3 nm and 9 nm, respectively. Unlike pure β-Fe2O3 nanorods, SC at 7 T exhibits superparamagnetic behavior at a relatively higher temperature (100 K), whereas β-Fe2O3 under these conditions depicted paramagnetic behavior. However, at 7 T and 5 K both of the samples exhibited superparamagnetic behavior, but the magnetization for SC (0.4 emu cm−2) was about 5.6 times higher compared to that of pure β-Fe2O3. The presence of specific amount of Ag in SC possibly results in the observed change in morphology, decrease in dimension and the orientation of β-Fe2O3 nanorods in a particular direction, which contributes to the transformation in magnetic behavior associated with enhanced saturation magnetization.