2 research outputs found
Cyclodextrin-Functionalized Fe<sub>3</sub>O<sub>4</sub>@TiO<sub>2</sub>: Reusable, Magnetic Nanoparticles for Photocatalytic Degradation of Endocrine-Disrupting Chemicals in Water Supplies
Water-dispersible, photocatalytic Fe<sub>3</sub>O<sub>4</sub>@TiO<sub>2</sub> coreâshell magnetic nanoparticles have been prepared by anchoring cyclodextrin cavities to the TiO<sub>2</sub> shell, and their ability to capture and photocatalytically destroy endocrine-disrupting chemicals, bisphenol A and dibutyl phthalate, present in water, has been demonstrated. The functionalized nanoparticles can be magnetically separated from the dispersion after photocatalysis and hence reused. Each component of the cyclodextrin-functionalized Fe<sub>3</sub>O<sub>4</sub>@TiO<sub>2</sub> coreâshell nanoparticle has a crucial role in its functioning. The tethered cyclodextrins are responsible for the aqueous dispersibility of the nanoparticles and their hydrophobic cavities for the capture of the organic pollutants that may be present in water samples. The amorphous TiO<sub>2</sub> shell is the photocatalyst for the degradation and mineralization of the organics, bisphenol A and dibutyl phthalate, under UV illumination, and the magnetism associated with the 9 nm crystalline Fe<sub>3</sub>O<sub>4</sub> core allows for the magnetic separation from the dispersion once photocatalytic degradation is complete. An attractive feature of these âcapture and destroyâ nanomaterials is that they may be completely removed from the dispersion and reused with little or no loss of catalytic activity
Mapping Charge Distribution in Single PbS Core â CdS Arm Nano-Multipod Heterostructures by Off-Axis Electron Holography
We
synthesized PbS coreâCdS arm nanomultipod heterostructures
(NMHs) that exhibit PbS{111}/CdS{0002} epitaxial relations. The PbSâCdS
interface is chemically sharp as determined by aberration corrected
transmission electron microscopy (TEM) and compared to density functional
theory (DFT) calculations. Ensemble fluorescence measurements show
quenching of the optical signal from the CdS arms indicating charge
separation due to the heterojunction with PbS. A finite-element three-dimensional
(3D) calculation of the Poisson equation shows a type-I heterojunction,
which would prevent recombination in the CdS arm after optical excitation.
To examine charge redistribution, we used off-axis electron holography
(OAEH) in the TEM to map the electrostatic potential across an <i>individual</i> heterojunction. Indeed, a built-in potential
of 500 mV is estimated across the junction, though as opposed to the
thermal equilibrium calculations significant accumulation of positive
charge at the CdS side of the interface is detected. We conclude that
the NMH multipod geometry prevents efficient removal of generated
charge carriers by the high energy electrons of the TEM. Simulations
of generated electronâhole pairs in the insulated CdS arm of
the NMH indeed show charge accumulation in agreement with the experimental
measurements. Thus, we show that OAEH can be used as a complementary
methodology to ensemble measurements by mapping the charge distribution
in single NMHs with complex geometries