Solvent-polarity-induced hematite (α-Fe2O3) nanostructures for lithium-ion battery and photoelectrochemical applications

Complex permittivity and power loss characteristics of α-Fe2O3/polycaprolactone (PCL) nanocomposites: effect of recycled α-Fe2O3 nanofiller

The development of microwave absorbing materials based on recycled hematite (α-Fe₂O₃) nanoparticles and polycaprolactone (PCL) was the main focus of this study. α-Fe₂O₃ was recycled from mill scale and reduced to nanoparticles through high energy ball milling in order to improve its complex permittivity properties. Different compositions (5% wt., 10% wt., 15% wt. and 20% wt.) of the recycled α-Fe₂O₃ nanoparticles were melt-blended with PCL using a twin screw extruder to fabricate recycled α-Fe₂O₃/PCL nanocomposites. The samples were characterized for their microstructural properties through X - ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). The complex permittivity and microwave absorption properties were respectively measured using the open ended coaxial (OEC) probe and a microstrip in connection with a vector network analyzer in the 1–4 GHz frequency range. An average α-Fe₂O₃ nanoparticle size of 16.2 nm was obtained with a maximum imaginary (ε") part of permittivity value of 0.54 at 4 GHz. The complex permittivity and power loss values of the nanocomposites increased with recycled α-Fe₂O₃ nanofiller content. At 2.4 GHz, the power loss (dB) values obtained for all the nanocomposites were between 13.3 dB and 14.4 dB and at 3.4 GHz, a maximum value of 16.37 dB was achieved for the 20 % wt. nanocomposite. The recycled α-Fe₂O₃/PCL nanocomposites have the potential for use in noise reduction applications in the 1–4 GHz range.

Effects of sono-assisted modified precipitation on the crystallinity, size, morphology, and catalytic applications of hematite (α-Fe2O3) nanoparticles: A comparative study

The present study reports a new approach to improve the adsorption and catalytic properties of hematite nanoparticles (HNPs) synthesized via the chemical precipitation technique as one of the most applicable and preferable synthesis methods. This could be performed through controlling the particles' crystallinity where a facile ultrasonic pathway (UP) modification was introduced as a hybrid replacement for the conventionally-used magnetic stirring pathway (MP) using different precursor concentrations. The X-ray diffraction and Raman spectra define the pristine phase of α-Fe₂O₃ crystal with lower crystallinity and higher degrees of structural disorder for UP products. UP also shows smaller nanosized particles with lower bundles of aggregations and lumps formation in addition to lesser values of polydispersity index compared to the MP products. The catalytic performance supported by the reaction kinetics for the degradation of hazardous Rose Bengal and Congo Red dyes in light and dark, respectively, were examined. It revealed superior efficiencies for all of the UP products within a short span against the conventional MP and previous studies. Moreover, it was confirmed that UP products could catalyze the biodegradation reactions of green algae (Enteromorpha) and induced higher rates of biogas production. In addition to this, decreasing the precursor concentrations was found to be another key factor reducing the produced particles' crystallinity, size, and lumps formation as well as affecting the morphology development. Thus, the synergetic effects of applying the UP at low precursor concentrations could show a practical pathway for the synthesis of low-crystalline HNPs with enhanced properties for green applications over the conventional MP products. Hence, the obtained findings are of vital importance to show the improved catalytic efficiency of HNPs by shedding new light on controlling the crystallinity and developing the surface features in the conventional precipitation process via the proposed modification.

Complex Permittivity and Microwave Absorption Properties of OPEFB Fiber-Polycaprolactone Composites Filled with Recycled Hematite (α-Fe2O3) Nanoparticles

Recycled hematite (α-Fe₂O₃) nanoparticles with enhanced complex permittivity properties have been incorporated as a filler in a polycaprolactone (PCL) matrix reinforced with oil palm empty fruit bunch (OPEFB) fiber for microwave absorption applications. The complex permittivity values were improved by reducing the particle sizes to the nano scale via high-energy ball milling for 12 h. A total of 5–20 wt.% recycled α-Fe₂O₃/OPEFB/PCL nanocomposites were examined for their complex permittivity and microwave absorption properties via the open ended coaxial (OEC) technique and the transmission/reflection line measurement using a microstrip connected to a two-port vector network analyzer. The microstructural analysis of the samples included X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and Fourier transform infrared spectroscopy (FTIR). At 1 GHz, the real (ε′) and imaginary (ε″) parts of complex permittivity of recycled α-Fe₂O₃ particles, respectively, increased from 7.88 to 12.75 and 0.14 to 0.40 when the particle size was reduced from 1.73 μm to 16.2 nm. A minimum reflection loss of −24.2 dB was achieved by the 20 wt.% nanocomposite at 2.4 GHz. Recycled α-Fe₂O₃ nanoparticles are effective fillers for microwave absorbing polymer-based composites in 1–4 GHz range applications.

Biomimetic Straw-Like Bundle Cobalt-Doped Fe2 O3 Electrodes towards Superior Lithium-Ion Storage

Biomimetic straw-like bundles of Co-doped Fe₂ O₃ (SCF), with Co²⁺ incorporated into the lattice of α-Fe₂ O₃ , was fabricated through a cost-effective hydrothermal process and used as the anode material for lithium-ion batteries (LIBs). The SCF exhibited ultrahigh initial discharge specific capacity (1760.7 mA h^-1  g^-1 at 200 mA g^-1 ) and cycling stability (with the capacity retention of 1268.3 mA h^-1  g^-1 after 350 cycles at 200 mA g^-1 ). In addition, a superior rate capacity of 376.1 mA h^-1  g^-1 was obtained at a high current density of 4000 mA g^-1 . The remarkable electrochemical lithium storage of SCF is attributed to the Co-doping, which increases the unit cell volume and affects the whole structure. It makes the Li⁺ insertion-extraction process more flexible. Meanwhile, the distinctive straw-like bundle structure can accelerate Li ion diffusion and alleviate the huge volume expansion upon cycling.

Biogenic Hematite from Bacteria: Facile Synthesis of Secondary Nanoclusters for Lithium Storage Capacity

Ferrihydrite, or iron(III) (oxyhydr)oxide (Fe(OH)₃), a representative scavenger of environmentally relevant toxic elements, has been repurposed as a low-cost and scalable precursor of well-developed hematite (α-Fe₂O₃) secondary nanoclusters with a hierarchically structured morphology for lithium-ion anode materials. Here, we report that the bacteria Clostridium sp. C8, isolated from a methane-gas-producing consortium, can synthesize self-assembled secondary hematite nanoclusters (∼150 nm) composed of small nanoparticles (∼15 nm) through the molecular structural rearrangement of amorphous ferrihydrite under mild conditions. The biogenic hematite particles, wrapped with graphene oxide reduced in situ by the reducing bacteria Shewanella sp. HN-41 via one-pot synthesis, deliver an excellent reversible capacity of ∼1000 mA h g^-1 after 100 cycles at a current density of 1 A g^-1. Furthermore, the heat-treated hematite/rGO exhibits a capacity of 820 mA h g^-1 at a high current density of 5 A g^-1 and a reversible capacity of up to 1635 mA h g^-1 at a current density of 100 mA g^-1. This study provides an easy, eco-efficient, and scalable microbiological synthetic route to produce hierarchical hematite/rGO secondary nanoclusters with potential as high-performance Li-ion anode materials.

Single-Layered Two-Dimensional Metal-Organic Framework Nanosheets as an in Situ Visual Test Paper for Solvents

Through a facile-operating ultrasonic force-assisted liquid exfoliation technology, the single-layered two-dimensional (2D) [Co(CNS)₂(pyz)₂] _n (pyz = pyrazine) nanosheets, with a thickness of sub-1.0 nm, have been prepared from the bulk precursors. The atomically thickness and the presence of abundant sulfur atoms with high electronegativity arrayed on the double surfaces of the sheets are making this kind of 2D MOF (metal-organic framework) nanosheets highly sensitive to intermolecular interactions. As a result, it can be well dispersed in all kinds of solvents to give a stable colloidal suspension that can be maintained for at least one month, accompanied by significant solvatochromic behavior and various optical properties, which thus have shown the potential to be practically applicated as in situ visual test paper for solvent identification and solvent polarity measurements. More importantly, combined with a smartphone, this kind of 2D-MOF nanosheets can be developed into in situ visual test paper to identify isomers and determine the polarity of mixed solvents quantitatively and qualitatively, suggesting the promising application of a portable, economical, and in situ visual test strategy in real world.