The research of zinc oxide tetrapods is a promising direction in the nano- and micro-materials field due to their unique properties. Firstly, the shape of tetrapods prevents their aggregation which is shortcomings of spherical and rod nanostructures. Secondly, zinc oxide is a non-toxic and biocompatible material. It makes zinc oxide structures are well suited for environmental, energy, and biomedical applications. Photocatalysis is one of zinc oxide’s key applications because of the high efficiency of reactive oxygen species (ROS) generation, i.e. superoxide radicals and hydroxyl radicals. Surface passivation of zinc oxide tetrapods with magnetic nanoparticles can increase their photoactivity due to effective charge separation which is useful in photocatalysis. Moreover, induced magnetic properties can be used for magnetic separation. In this work, magnetite nanoparticles were chosen as the magnetic component since they have high magnetic susceptibility, demonstrate biocompatibility and low toxicity. Various approaches to a simple formation method of such structures are considered. The composites are obtained by mixing components in water in combination with: (i) ultrasound, (ii) magnetic stirring, (iii) vortex. The samples are studied using scanning electron microscopy, absorption and luminescence spectroscopy. The results confirm that magnetite nanoparticles bind to the zinc oxide tetrapods surface in all three approaches. The photocatalytic activity of the composites is investigated using methylene blue and methyl orange as ROS indicators under light irradiation and is compared with one of the pure zinc oxide tetrapods.
The impact of prolonged irradiation of SPIONs/CdSe/ZnS nanocomposites by visible light on nanocomposite luminescence has been studied. It has been shown that prolonged irradiation of the nanocomposites with 405 nm laser can triple their photoluminescence quantum yield. It has been demonstrated that the efficiency of photoinduced processes on the nanocomposite surface correlates very well with the concentration of the nanocomposite surface ligand in our samples. We have also found that the quantum sized CdSe shell of SPIONs/CdSe/ZnS nanocomposites demonstrates the QD-like dependence of photoluminescence quantum yield on visible light dose and this nanocomposite property can be efficiently used to brighten their photoluminescence.
Magneto-luminescent materials that do not exist in nature, can find a wide application in biomedical and environmental fields. Here we describe magneto-optical properties of core-shell-shell nanocomposites consisting of a Fe3O4 superparamagnetic iron oxide nanoparticle (SPION) covered with quantum-sized brightly luminescent CdSe layer surrounded by ZnS passivating shell. The synthesized nanocomposites demonstrate excitonic bands in their absorption and photoluminescent (PL) spectra centered at 585 nm and 603 nm, respectively. The PL quantum yield of nanocomposites has been increased by 5 times due to their passivation with ZnS shell. The analysis of magneto-optical properties of the synthesized Fe3O4/CdSe/ZnS nanocomposites has shown that their magnetic circular dichroism (MCD) spectrum is characterized with the bands centered at 430 nm, 350 nm and 303 nm corresponding to 6A1 → 4E, 4A1(4G); 6A1 → 4E(4D) and 6A1 → 4T1(4P) electronic transitions, respectively. It has been found that the synthesized core-shell SPIONs demonstrate excellent colloidal stability, magneto-optical properties typical for SPIONs and bright photoluminescence
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