Research on the chiral magneto-optical
properties of inorganic
nanomaterials has enabled novel applications in advanced optical and
electronic devices. However, the corresponding chiral magneto-optical
responses have only been studied under strong magnetic fields of ≥1
T, which limits the wider application of these novel materials. In
this paper, we report on the enhanced chiral magneto-optical activity
of supra-assembled Fe3O4 magnetite nanoparticles
in the visible range at weak magnetic fields of 1.5 mT. The spherical
supra-assembled particles with a diameter of ∼90 nm prepared
by solvothermal synthesis had single-crystal-like structures, which
resulted from the oriented attachment of nanograins. They exhibited
superparamagnetic behavior even with a relatively large supraparticle
diameter that exceeded the size limit for superparamagnetism. This
can be attributed to the small size of nanograins with a diameter
of ∼12 nm that constitute the suprastructured particles. Magnetic
circular dichroism (MCD) measurements at magnetic fields of 1.5 mT
showed distinct chiral magneto-optical activity from charge transfer
transitions of magnetite in the visible range. For the supraparticles
with lower crystallinity, the MCD peaks in the 250–550 nm range
assigned as the ligand-to-metal charge transfer (LMCT) and the inter-sublattice
charge transfer (ISCT) show increased intensities in comparison to
those with higher crystallinity samples. On the contrary, the higher
crystallinity sample shows higher MCD intensities near 600–700
nm for the intervalence charge transfer (IVCT) transition. The differences
in MCD responses can be attributed to the crystallinity determined
by the reaction time, lattice distortion near grain boundaries of
the constituent nanocrystals, and dipolar interactions in the supra-assembled
structures.
Coloured TiO is coveted for its ability to extract energy from the visible region of electromagnetic spectrum. Here a facile synthesis of black anatase titania microspheres (B-TiO ) through a two-step process is reported. In the first step, amorphous white TiO microspheres (W-TiO ) are obtained by hydrolysing titanium tetraisopropoxide by ammonia vapours in ethanol. In the second step, the W-TiO is thermally annealed at 500 °C to obtain B-TiO . The diffuse reflectance analysis showed that B-TiO absorbs across visible spectrum with absorption extending well into NIR region. Raman scattering together with EPR analysis showed compelling evidence of the existence of oxygen deficiency within the crystal in B-TiO that induces black colouration in the sample. The defects present in the black anatase sample were confirmed to be single-electron-trapped (or paramagnetic) oxygen vacancies (V ⋅) by XPS and EPR studies. The magnetic susceptibility studies showed existence of antiferromagnetic interactions between these unpaired electron spins.
Manganese dioxide nanomaterials with "Koosh-ball"-like morphology (MnO -KBs) as well as worm-like nanotubes (MnO -NWs) are obtained by employing Tween 20 as the reducing and structure-directing agent, and KMnO as a MnO precursor. Whereas the MnO -KBs are interconnected through tubular extensions, the MnO -NWs are largely disconnected. Both MnO -KBs and MnO -NWs have large BET surface areas (>200 m g ), and are thermally robust up to 300 °C. Electrochemical studies reveal that the highest specific capacitance (C ) obtained for MnO -KBs (272 F g ) is significantly higher than that of MnO -NWs (129 F g ). The C values correlate well with the electroactive surface areas of the materials: MnO -KBs have a significantly higher electrolyte-accessible surface area. Electrochemical impedance spectroscopy (EIS) reveals a higher electron-transfer rate at the electrode/electrolyte interface for MnO -KBs than for MnO -NWs. The multiple tubular interconnections between individual MnO -KBs allow improved ion penetration and act as conduits for their propagation, shortening the diffusion distances of the ions from external electrolytes to the interior of the MnO framework. Thus, this work exemplifies the importance of interconnections for enhancing the electrochemical performance of nanomaterials employed for energy storage.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.