Deliberate Modification of Fe3O4 Anode Surface Chemistry: Impact on Electrochemistry

Double-Shelled Fe-Fe3C Nanoparticles Embedded on a Porous Carbon Framework for Superior Lithium-Ion Half/Full Batteries

Cost-effective and environmentally friendly Fe-based active materials offer exceptionally high energy capacity in lithium-ion batteries (LIBs) due to their multiple electron redox reactions. However, challenges, such as morphology degradation during cycling, cell pulverization, and electrochemical stability, have hindered their widespread use. Herein, we demonstrated a simple salt-assisted freeze-drying method to design a double-shelled Fe/Fe3C core tightly anchored on a porous carbon framework (FEC). The shell consists of a thin Fe3O4 layer (≈2 nm) and a carbon layer (≈10 nm) on the outermost part. Benefiting from the complex nanostructuring (porous carbon support, core-shell nanoparticles, and Fe3C incorporation), the FEC anode delivered a high discharge capacity of 947 mAh g-1 at 50 mA g-1 and a fast-rate capability of 305 mAh g-1 at 10 A g-1. Notably, the FEC cell still showed 86% reversible capacity retention (794 mAh g-1 at 50 mA g-1) at a high cycling temperature of 80 °C, indicating superior structural integrity during cycling at extreme temperatures. Furthermore, we conducted a simple solid-state fluorination technique using the as-prepared FEC sample and excess NH4F to prepare iron fluoride-carbon composites (FeF2/C) as the positive electrode. The full cell configuration, consisting of the FEC anode and FeF2/C cathode, reached a remarkable capacity of 200 mAh g-1 at a 20 mA g-1 rate or an energy density of approximately 530 Wh kg-1. Thus, the straightforward and simple experimental design holds great potential as a revolutionary Fe-based cathodic-anodic pair candidate for high-energy LIBs.

Biofabrication of Silver Nanoparticles Using Teucrium Apollinis Extract: Characterization, Stability, and Their Antibacterial Activities

Medical science has paid a great deal of attention to green synthesis silver nanoparticles (AgNPs) because of their remarkable results with multidrug-resistant bacteria. This study was conducted on the preparation of AgNPs, using the teucrium apollinis extract as a reducing agent and a capping ligand. The AgNP produced was stable in room condition up to 10 weeks. The AgNP was characterized using UV-visible absorption spectroscopy (UV-Vis), attenuated Fourier transform infrared (ATR-FTIR), transmission electron microscopy (TEM), and dynamic light scattering (DLS). The study confirms the ability of teucrium apollinis to produce AgNPs with high stability. The influence of pH was studied over a pH range of (2–12) on the stability of synthesized AgNPs. The best value of pH was 7.2, where AgNP showed a good stability with high antibacterial activity against Pseudomonas aeruginosa. AgNP synthesis is confirmed by a strong peak in the UV-Vis due to surface plasmon resonance (SPR) at 379 nm. Based on TEM findings, monodispersed AgNP has a spherical shape with a small size of 16 ± 1.8 nm. In this study, teucrium apollinis extract was used for the first time, which could be a good environmental method for synthesizing AgNP, which offers a possible alternative to chemical AgNPs.

Engineered assembly of water-dispersible nanocatalysts enables low-cost and green CO2 capture

Catalytic solvent regeneration has attracted broad interest owing to its potential to reduce energy consumption in CO₂ separation, enabling industry to achieve emission reduction targets of the Paris Climate Accord. Despite recent advances, the development of engineered acidic nanocatalysts with unique characteristics remains a challenge. Herein, we establish a strategy to tailor the physicochemical properties of metal-organic frameworks (MOFs) for the synthesis of water-dispersible core-shell nanocatalysts with ease of use. We demonstrate that functionalized nanoclusters (Fe₃O₄-COOH) effectively induce missing-linker deficiencies and fabricate mesoporosity during the self-assembly of MOFs. Superacid sites are created by introducing chelating sulfates on the uncoordinated metal clusters, providing high proton donation capability. The obtained nanomaterials drastically reduce the energy consumption of CO₂ capture by 44.7% using only 0.1 wt.% nanocatalyst, which is a ∽10-fold improvement in efficiency compared to heterogeneous catalysts. This research represents a new avenue for the next generation of advanced nanomaterials in catalytic solvent regeneration.

Catalytic solvent regeneration is of interest to reduce energy consumption in CO2 separation, however, the development of engineered nanocatalysts remains a challenge. Here, a new avenue is presented for the next generation of advanced metal-organic frameworks (MOFs) in energy-efficient CO2 capture.

Discharging Behavior of Hollandite α-MnO2 in a Hydrated Zinc-Ion Battery

Hollandite, α-MnO₂, is of interest as a prospective cathode material for hydrated zinc-ion batteries (ZIBs); however, the mechanistic understanding of the discharge process remains limited. Herein, a systematic study on the initial discharge of an α-MnO₂ cathode under a hydrated environment was reported using density functional theory (DFT) in combination with complementary experiments, where the DFT predictions well described the experimental measurements on discharge voltages and manganese oxidation states. According to the DFT calculations, both protons (H⁺) and zinc ions (Zn²⁺) contribute to the discharging potentials of α-MnO₂ observed experimentally, where the presence of water plays an essential role during the process. This study provides valuable insights into the mechanistic understanding of the discharge of α-MnO₂ in hydrated ZIBs, emphasizing the crucial interplay among the H₂O molecules, the intercalated Zn²⁺ or H⁺ ions, and the Mn⁴⁺ ions on the tunnel wall to enhance the stability of discharged states and, thus, the electrochemical performances in hydrated ZIBs.

Shaping Magnetite by Hydroxyl Group Numbers of Small Molecules

Despite numerous reports on magnetite formation with the assistance of various additives, the role of hydroxyl group (-OH) numbers in small polyol molecules has not yet been understood well. We selected small molecules containing different -OH numbers, such as ethanol, ethylene glycol, propanetriol, butanetetrol, pentitol, hexanehexol, and cyclohexanehexol, as additives in coprecipitation. By increasing the -OH number in these small polyol molecules, the formation of crystallization was slowed, and the size and shape of magnetite were regulated as well possibly due to the changed complexation strength and the stability of the precursor. The increase in temperature and the Fe²⁺/Fe³⁺ ratio can reduce the complexation strength. The nucleation and growth of magnetite proceed possibly through the aggregation of polyol-stabilized amorphous complexes and two-line ferrihydrite with low crystallinity based on the -OH numbers, suggesting a nonclassical pathway. The as-prepared magnetite showed a r₂/r₁ ratio after in vitro MRI measurement as follows: Fe₃O₄@He-6OH rod < Fe₃O₄@Pr-3OH sheet < Fe₃O₄@Pe-5OH cube. The Fe₃O₄@He-6OH rod and Fe₃O₄@Pr-3OH sheet displayed T₁-T₂ dual modal contrast ability, while the Fe₃O₄@Pe-5OH cube can be T₂-dominated. This research provides a simple but an essential approach for designing MRI contrast agents.

Self-Formed Channel Boosts Ultrafast Lithium Ion Storage in Fe3O4@Nitrogen-Doped Carbon Nanocapsule

Investigations into conversion-type materials such as transition-metal oxides have dominated in energy-storage systems, especially for lithium ion batteries in recent years. A common understanding of taking account of high energy density and high power density allows us to design reasonable electrodes. In this study, the unique Fe₃O₄@nitrogen-doped carbon (denoted as Fe₃O₄@NC) nanocapsule with self-formed channels was synthesized based on a facile hydrothermal-coating-annealing route. With respect to the effect of this rational architecture on lithium-storage performance, excellent behavior (a high reversible capacity of 480 mAh g^-1) could be maintained at 20 A g^-1 during 1000 cycles, with an average Coulombic efficiency of 99.97%. It also means that such a Fe₃O₄@NC electrode can meet a fast-charge challenge (end-of-charge within ∼2 min). By a series of investigations, we certainly considered that uniform carbon coating improved electrical conductivity and acted as a buffer layer to accommodate volume variations of Fe₃O₄ nanoparticles during cycling. It is more interesting that self-formed channels can effectively shorten the ion diffusion path and provide a necessary space to buffer volume expansion as well. Benefiting from these synergetic advantages, this Fe₃O₄@NC nanocapsule also delivered outstanding electrochemical performances in full cells.