Correlating Chemical Reaction and Mass Transport in Hydrogen-based Direct Reduction of Iron Oxide

Steelmaking contributes 8% to the total CO2 emissions globally, primarily due to coal-based iron ore reduction. Clean hydrogen-based ironmaking has variable performance because the dominant gas-solid reduction mechanism is set by the defects and pores inside the mm-nm sized oxide particles that change significantly as the reaction progresses. While these governing dynamics are essential to establish continuous flow of iron and its ores through reactors, the direct link between agglomeration and chemistry is still contested due to missing measurements. In this work, we directly measure the connection between chemistry and agglomeration in the smallest iron oxides relevant to magnetite ores. Using synthesized spherical 10-nm magnetite particles reacting in H2, we resolve the formation and consumption of w\"ustite (FeO) - the step most commonly attributed to agglomeration. Using X-ray scattering and microscopy, we resolve crystallographic anisotropy in the rate of the initial reaction, which becomes isotropic as the material sinters. Complementing with imaging, we demonstrate how the particles self-assemble, subsequently react and sinter into ~100x oblong grains. Our insights into how morphologically uniform iron oxide particles react and agglomerate H2 reduction enable future size-dependent models to effectively describe the multiscale iron ore reduction

Magnetic Assembly of Plasmonic Nanoparticles Into Functional Superstructures

Plasmonic nanoparticles are known for their unique optical properties originating from the localized surface plasmon resonance. Assembling plasmonic nanoparticles into secondary superstructures induces plasmonic coupling, producing tunable optical properties. However, current assembly strategies lack dynamic control over the assembly, limiting real-time applications. Magnetic assembly has proven to be an effective strategy to manipulate the interaction between magneto-plasmonic nanoparticles, generating dynamically tunable optical properties featuring fast response, full reversibility, and remote control. This dissertation focuses on developing optically functional nanostructures by magnetically assembling plasmonic nanoparticles into secondary superstructures. In the first part, one-dimensional (1D) plasmonic photonic crystals with angular-dependent structural colors are fabricated by assembling magneto-plasmonic nanoparticles under an external magnetic field. Different from conventional 1D photonic crystals, the assembled 1D nanochains show angular-dependent colors from the selective activation of photonic diffraction and plasmonic scattering. In the second part, we develop magnetically tunable plasmonic chiral nanostructures by assembling magneto-plasmonic nanoparticles under a helical magnetic field from a cubic permanent magnet. The handedness and magnitude and position of the resulting circular dichroism (CD) spectra can be dynamically tuned by the orientation and strength of the helical magnetic field. In addition, we find that the chiral nanostructures are not formed from the helical alignment of magneto-plasmonic nanoparticles, but instead, the nanoparticles align along the magnetic field direction to form 1D linear periodic nanochains, which further assemble into chiral superstructures under the helical magnetic field. This assembly incorporates plasmonic coupling, photonic diffraction, and chirality into a single system, allowing multi-mode colors with selective activation and dynamic tunability. Furthermore, this helical magnetic assembly method is developed to fabricate chiral luminescent nanostructures by assembling magneto-luminescent hybrid clusters under the helical magnetic field, realizing magnetically tunable circularly polarized luminescence. In the last part, we develop a general strategy for fabricating plasmonic chiral nanostructures by stacking polymer films containing magnetically assembled linear plasmonic nanochains and further demonstrate dynamic control over the chiral optical properties by controlling the stacking angle. Overall, the magnetic assembly of plasmonic nanoparticles generates novel optical properties with dynamic tunability, promising for color displays, sensors, and optical devices

Magnetically Induced Anisotropic Interaction in Colloidal Assembly.

The wide accessibility to nanostructures with high uniformity and controllable sizes and morphologies provides great opportunities for creating complex superstructures with unique functionalities. Employing anisotropic nanostructures as the building blocks significantly enriches the superstructural phases, while their orientational control for obtaining long-range orders has remained a significant challenge. One solution is to introduce magnetic components into the anisotropic nanostructures to enable precise control of their orientations and positions in the superstructures by manipulating magnetic interactions. Recognizing the importance of magnetic anisotropy in colloidal assembly, we provide here an overview of magnetic field-guided self-assembly of magnetic nanoparticles with typical anisotropic shapes, including rods, cubes, plates, and peanuts. The Review starts with discussing the magnetic energy of nanoparticles, appreciating the vital roles of magneto-crystalline and shape anisotropies in determining the easy magnetization direction of the anisotropic nanostructures. It then introduces superstructures assembled from various magnetic building blocks and summarizes their unique properties and intriguing applications. It concludes with a discussion of remaining challenges and an outlook of future research opportunities that the magnetic assembly strategy may offer for colloidal assembly

A polymer lithium-oxygen battery based on semi-polymeric conducting ionomer as polymer electrolyte

status: publishe

Core-shell nano-structured carbon composites based on tannic acid for lithium-ion batteries

Core-shell nano-structured carbon composites have been used as electrode materials in lithium-ion batteries (LIBs) with increasing attention. The large volume swing during lithiation/delithiation processes and poor electronic conductivity are two key issues in the newly-proposed electrode materials, which severely limit their practical applications in LIBs. In order to solve these problems, we report a facile and versatile method to prepare core-shell nano-structured carbon composites using low cost and widely available tannic acid as the carbon source. The carbon layers with controlled thicknesses of 6-12 nm and 1-3 nm were coated on the surface of Si and TiO2 nanoparticles, respectively. Due to the carbon layers, both the Si@C and TiO2@C nanocomposites used as anode materials in LIBs showed excellent electrochemical performances including good cycling stability and high rate capability. We believe that this method may be applicable to various carbon-coating nanocomposites.</p

Core-shell nano-structured carbon composites based on tannic acid for lithium-ion batteries

status: publishe

Correlating chemistry and mass transport in sustainable iron production.

Steelmaking contributes 8% to the total CO2 emissions globally, primarily due to coal-based iron ore reduction. Clean hydrogen-based ironmaking has variable performance because the dominant gas-solid reduction mechanism is set by the defects and pores inside the mm- to nm-sized oxide particles that change significantly as the reaction progresses. While these governing dynamics are essential to establish continuous flow of iron and its ores through reactors, the direct link between agglomeration and chemistry is still contested due to missing measurements. In this work, we directly measure the connection between chemistry and agglomeration in the smallest iron oxides relevant to magnetite ores. Using synthesized spherical 10-nm magnetite particles reacting in H2, we resolve the formation and consumption of wüstite (Fe1-xO)-the step most commonly attributed to whiskering. Using X-ray diffraction, we resolve crystallographic anisotropy in the rate of the initial reaction. Complementary imaging demonstrated how the particles self-assemble, subsequently react, and grow into elongated whisker structures. Our insights into how morphologically uniform iron oxide particles react and agglomerate in H2 reduction enable future size-dependent models to effectively describe the multiscale aspects of iron ore reduction