Sensitivity of micro-Raman spectrum to crystallite size of electrospray-deposited and post-annealed films of iron-oxide nanoparticle suspensions

Structural characterization of self-assembled chain like Fe-FeOx Core shell nanostructure

One of the big challenge of studying the core-shell iron nanostructures is to know the nature of oxide shell, i.e., whether it is γ-Fe₂O₃ (Maghemite), Fe₃O₄ (Magnetite), α-Fe₂O₃ (Hematite), or FeO (Wustite). By knowing the nature of iron oxide shell with zero valent iron core, one can determine the chemical or physical behavior of core-shell nanostructures. Fe core-shell nanochains (NCs) were prepared through the reduction of Fe³⁺ ions by sodium boro-hydride in aqueous solution at room atmosphere, and Fe NCs were further aged in water up to 240 min. XRD was used to study the structure of Fe NCs. Further analysis of core-shell nature of Fe NCs was done by TEM, results showed increase in thickness of oxide shell (from 2.5, 4, 6 to 10 nm) as water aging time increases (from 0 min, 120 min, 240 min to 360 min). The Raman spectroscopy was employed to study the oxide nature of Fe NCs. To further confirm the magnetite phase in Fe NCs, the Mössbauer spectroscopy was done on Fe NCs-0 and Fe NCs-6. Result shows the presence of magnetite in the sample before aging in water, and the sample after prolonged aging contains pure Hematite phase. It shows that prolonged water oxidation transforms the structure of shell of Fe NCs from mixture of Hematite and Magnetite in to pure hematite shell. The Magnetic properties of the Fe NCs were measured by VSM at 320 K. Because of high saturation magnetization (Ms) values, Fe NCs could be used as r₂ contrasts agents for magnetic resonance imaging (MRI) in near future.

Compact hematite buffer layer as a promoter of nanorod photoanode performances

The effect of a thin α-Fe₂O₃ compact buffer layer (BL) on the photoelectrochemical performances of a bare α-Fe₂O₃ nanorods photoanode is investigated. The BL is prepared through a simple spray deposition onto a fluorine-doped tin oxide (FTO) conducting glass substrate before the growth of a α-Fe₂O₃ nanorods via a hydrothermal process. Insertion of the hematite BL between the FTO and the nanorods markedly enhances the generated photocurrent, by limiting undesired losses of photogenerated charges at the FTO||electrolyte interface. The proposed approach warrants a marked improvement of material performances, with no additional thermal treatment and no use/dispersion of rare or toxic species, in agreement with the principles of green chemistry.

Water chemistry impacts on arsenic mobilization from arsenopyrite dissolution and secondary mineral precipitation: implications for managed aquifer recharge

Managed aquifer recharge (MAR) is a water reuse technique with the potential to meet growing water demands. However, MAR sites have encountered arsenic mobilization resulting from recharge operations. To combat this challenge, it is imperative to identify the mechanisms of arsenic mobilization during MAR. In this bench-scale study, arsenic mobilization from arsenopyrite (FeAsS) was characterized for conditions relevant to MAR operations. Experimentally determined activation energies for arsenic mobilization from FeAsS under aerobic conditions were 36.9 ± 2.3 kJ/mol for 10 mM sodium chloride, 40.8 ± 3.5 kJ/mol for 10 mM sodium nitrate, and 43.6 ± 5.0 kJ/mol for secondary effluent from a wastewater treatment plant. Interestingly, the sodium chloride system showed higher arsenic mobilization under aerobic conditions. In addition, secondary mineral precipitation varied among systems and further affected arsenic mobilization. For example, the wastewater system inhibited precipitation, while in the sodium chloride system, faster phase transformation of iron(III) (hydr)oxide precipitates was observed, resulting in hematite formation after 7 days. The phase transformation to hematite will result in less available surface area for arsenic attenuation. These new observations and activation energies can be useful to develop improved reactive transport models for the fate of arsenic during MAR, and develop strategies to minimize arsenic release.

Phase discrimination through oxidant selection in low-temperature atomic layer deposition of crystalline iron oxides

Control over the oxidation state and crystalline phase of thin-film iron oxides was achieved by low-temperature atomic layer deposition (ALD), utilizing a novel iron precursor, bis(2,4-methylpentadienyl)iron. This low-temperature (T = 120 °C) route to conformal deposition of crystalline Fe3O4 or α-Fe2O3 thin films is determined by the choice of oxygen source selected for the second surface half-reaction. The approach employs ozone to produce fully oxidized α-Fe2O3 or a milder oxidant, H2O2, to generate the Fe(2+)/Fe(3+) spinel, Fe3O4. Both processes show self-limiting surface reactions and deposition rates of at least 0.6 Å/cycle, a significantly high growth rate at such mild conditions. We utilized this process to prepare conformal iron oxide thin films on a porous framework, for which α-Fe2O3 is active for photocatalytic water splitting.

Characterization and deposition of various light-harvesting antenna complexes by electrospray atomization

Photosynthetic organisms have light-harvesting complexes that absorb and transfer energy efficiently to reaction centers. Light-harvesting complexes (LHCs) have received increased attention in order to understand the natural photosynthetic process and also to utilize their unique properties in fabricating efficient artificial and bio-hybrid devices to capture solar energy. In this work, LHCs with different architectures, sizes, and absorption spectra, such as chlorosomes, Fenna-Matthews-Olson (FMO) protein, LH2 complex, and phycobilisome have been characterized by an electrospray-scanning mobility particle-sizer system (ES-SMPS). The size measured by ES-SMPS for FMO, chlorosomes, LH2, and phycobilisome were 6.4, 23.3, 9.5, and 33.4 nm, respectively. These size measurements were compared with values measured by dynamic light scattering and those reported in the literature. These complexes were deposited onto a transparent substrate by electrospray deposition. Absorption and fluorescence spectra of the deposited LHCs were measured. It was observed that the LHCs have light absorption and fluorescence spectra similar to that in solution, demonstrating the viability of the process.