Seeded preparation of ultrathin FeS2 nanosheets from Fe3O4 nanoparticles

Facile one-pot synthesis of polyethyleneimine functionalized α-FeOOH nanoraft consisted of single-layer parallel-aligned ultrathin nanowires for efficient removal of Cr (VI): Synergy of reduction and adsorption

Two-dimensional (2D) iron oxide-hydroxide (FeOOH) nanomaterials as low-cost and environmental-friendly composites are promising materials for application in heavy metal elimination. However, developing 2D FeOOH adsorbents with high adsorption capacity and excellent durability toward Cr (VI) removal is still a challenge due to the intrinsically non-layered structure. Here, a novel polyethyleneimine (PEI) functionalized 2D single-layer nano-raft-like α-FeOOH (α-FeOOH NF) consisted of parallel-aligned ultrathin nanowires was obtained via a facile one-pot hydrothermal approach. It was found that the 2D α-FeOOH NF nanostructure was formed by an in-plane iterative self-assembly mechanism, where α-FeOOH nanoparticles acted as intermediates and iterative seeds with anisotropic growth. The as-prepared 2D α-FeOOH NF possessed porous structure and high surface area, which provided a strong ability to capture the Cr (VI) ions in water. Benefiting from the unique structure and PEI modification, it exhibited fast adsorption kinetic rate, high reusability, and high adsorption capacity toward Cr(VI) removal. The removal mechanism involved adsorption and reduction process. Besides, the molecular dynamic simulations disclosed a facet-dependent Cr(VI) adsorption behavior of α-FeOOH. The maximum adsorption capacity was 67.1 mg/g and the removal efficiency still maintained 83.9 % in the fifth cycle. This work demonstrated that 2D α-FeOOH NF could be a promising adsorbent for Cr(VI) removal.

Highly efficient removal of Cr(VI) by hexapod-like pyrite nanosheet clusters

Pyrite nanomaterials show an excellent performance in remediating Cr(VI) contaminated wastewater. However, the high surface reactivity makes them easy to agglomerate to reduce their removal efficiency for Cr(VI). In this study, a novel hexapod-like pyrite nanosheet clusters material was successfully synthesized via a facile hydrothermal method with the assistance of fluorides. The products were pyrite microspherulites without fluoride ion. The hexapod-like pyrite nanosheet clusters had dramatically higher Cr(VI) removal efficiencies than microspherulites due to more dissolved Fe(II) and S(-II) into the suspension released for nanosheet clusters should be responsible for the enhanced removal rate of Cr(VI). The XPS analysis revealed that the rapid adsorption on the surface of pyrite nanosheet clusters followed by reduction of Cr(VI) to Cr(III) by FeS₂ and subsequent precipitation of Cr(III) hydroxides/oxyhydroxides are responsible for the high removal capacity of Cr(VI). The hexapod-like pyrite nanosheet clusters material had high stability and longevity, and did not aggregate during the Cr(VI) removal process. The removal efficiency of Cr(VI) was still 100% after 5 cycles. Our study shows that the hexapod-like pyrite nanosheet clusters material could be acted as a recyclable and promising mineral material with high activity, stability, feasibility for remediating Cr(VI) contaminated environment.

High-Performance Bifunctional Ni-Fe-S Catalyst in situ Synthesized within Graphite Intergranular Nanopores for Overall Water Splitting

Low-cost and efficient bifunctional catalysts are urgently needed for overall water splitting used in large-scale energy storage. In this study, we develop a nickel and iron (di)sulfide (Ni-Fe-S) composite catalyst that is in situ synthesized and fixed within the intergranular nanopores inside high pure polycrystalline graphite. Two precursor solutions (reactants) may permeate the graphite intergranular pores to a depth of more than 3.5 mm. The nanoscale pores serve as an array of nanoreactors for the synthesis of the Ni-Fe-S nanoparticles under conditions much milder than usual. The prepared catalyst efficiently catalyzes both the hydrogen and oxygen evolution reactions (HER and OER) in 1.0 M KOH. It delivers a current density of 400 mA cm^-2 at a full cell voltage of around 2.3 V without considerable activity decay over 24 h electrolysis. The active species of the catalyst are different for the HER and OER and discussed accordingly. The synthesis strategy based on the nanopores in a monolithic conductive substrate proves to be a simple, efficient, and promising way to prepare electrocatalysts that are cheap, abundant, and industrially attractive.

Nanoarchitectonics for Transition-Metal-Sulfide-Based Electrocatalysts for Water Splitting

Heterogenous electrocatalysts based on transition metal sulfides (TMS) are being actively explored in renewable energy research because nanostructured forms support high intrinsic activities for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, it is described how researchers are working to improve the performance of TMS-based materials by manipulating their internal and external nanoarchitectures. A general introduction to the water-splitting reaction is initially provided to explain the most important parameters in accessing the catalytic performance of nanomaterials catalysts. Later, the general synthetic methods used to prepare TMS-based materials are explained in order to delve into the various strategies being used to achieve higher electrocatalytic performance in the HER. Complementary strategies can be used to increase the OER performance of TMS, resulting in bifunctional water-splitting electrocatalysts for both the HER and the OER. Finally, the current challenges and future opportunities of TMS materials in the context of water splitting are summarized. The aim herein is to provide insights gathered in the process of studying TMS, and describe valuable guidelines for engineering other kinds of nanomaterial catalysts for energy conversion and storage technologies.

Robust Pitaya-Structured Pyrite as High Energy Density Cathode for High-Rate Lithium Batteries

To solve the serious problems (the agglomeration of nano-Fe⁰, dissolution of polysulfide, and low electronic conductivity of Li₂S) of earth-abundant pyrite (FeS₂) cathodes for lithium batteries, a simple in situ encapsulation and transformation route has been successfully developed to synthesis pitaya-structured porous carbon embedded with FeS₂ nanoparticles. Due to such a hierarchical architecture design, this cathode of pitaya-structured FeS₂@C can effectively avoid the serious agglomeration and coarsening of small Fe nanoparticles, reduce the dissolution of polysulfide, and provide superior kinetics toward lithium storage, resulting in enhanced reversibility and rate capability. Cycling in the voltage region of 1.0-3.0 V at 0.3 A g^-1, the current conversion-based FeS₂@C cathode displays a high and stable energy density (about 1100 Wh kg^-1), ultrahigh rate capability (a reversible capability of 660, 609, 554, 499, 449, and 400 mA h g^-1 at 0.2, 0.5, 1.0, 2.0, 5.0, and 10 A g^-1, respectively), and stable cycling performance.

Metastable Marcasite-FeS2 as a New Anode Material for Lithium Ion Batteries: CNFs-Improved Lithiation/Delithiation Reversibility and Li-Storage Properties

Marcasite (m-FeS₂) exhibits higher electronic conductivity than that of pyrite (p-FeS₂) because of its lower semiconducting gap (0.4 vs 0.7 eV). Meanwhile, as demonstrates stronger Fe-S bonds and less S-S interactions, the m-FeS₂ seems to be a better choice for electrode materials compared to p-FeS₂. However, the m-FeS₂ has been seldom studied due to its sophisticated synthetic methods until now. Herein, a hierarchical m-FeS₂ and carbon nanofibers composite (m-FeS₂/CNFs) with grape-cluster structure was designed and successfully prepared by a straightforward hydrothermal method. When evaluated as an electrode material for lithium ion batteries, the m-FeS₂/CNFs exhibited superior lithium storage properties with a high reversible capacity of 1399.5 mAh g^-1 after 100 cycles at 100 mA g^-1 and good rate capability of 782.2 mAh g^-1 up to 10 A g^-1. The Li-storage mechanism for the lithiation/delithiation processes of m-FeS₂/CNFs was systematically investigated by ex situ powder X-ray diffraction patterns and scanning electron microscopy. Interestingly, the hierarchical m-FeS₂ microspheres assembled by small FeS₂ nanoparticles in the m-FeS₂/CNFs composite converted into a mimosa with leaves open shape during Li⁺ insertion process and vice versa. Accordingly, a "CNFs accelerated decrystallization-recrystallization" mechanism was proposed to explain such morphology variations and the decent electrochemical performance of m-FeS₂/CNFs.

Novel nanofiber yarns synchronously endued with tri-functional performance of superparamagnetism, electrical conductivity and enhanced fluorescence prepared by conjugate electrospinning

[Fe₃O₄/PANI/PAN]//[Eu(BA)₃phen/PAN] heterogeneous nanofiber yarns were fabricated via electrospinning, and the yarns synchronously possess trifunctionality of superparamagnetism, electrical conductivity and enhanced fluorescence.

Novel Electrospun Dual-Layered Composite Nanofibrous Membrane Endowed with Electricity-Magnetism Bifunctionality at One Layer and Photoluminescence at the Other Layer

Dual-layered composite nanofibrous membrane equipped with electrical conduction, magnetism and photoluminescence trifunctionality is constructed via electrospinning. The composite membrane consists of a polyaniline (PANI)/Fe₃O₄ nanoparticles (NPs)/polyacrylonitrile (PAN) tuned electrical-magnetic bifunctional nanofibrous layer at one side and a Eu(TTA)₃(TPPO)₂/polyvinylpyrrolidone (PVP) photoluminescent nanofibrous layer at the other side, and the two layers are tightly combined face-to-face together into the novel dual-layered composite membrane with trifunctionality. The electric conductivity and magnetism of electrical-magnetic bifunctionality can be respectively tunable via modulating the respective PANI and Fe₃O₄ NPs contents, and the highest electric conductivity approaches the order of 1 × 10^-2 S cm^-1. Predominant red emission at 615 nm can be obviously observed in the photoluminescent layer under 366 nm excitation. Moreover, the luminescent intensity of photoluminescent layer is almost unaffected by the electrical-magnetic bifunctional layer because of the fact that the photoluminescent materials have been successfully isolated from dark-colored PANI and Fe₃O₄ NPs. The novel dual-layered composite nanofibrous membrane with trifunctionality has potentials in many fields. Furthermore, the design philosophy and fabrication method for the dual-layered multifunctional membrane provide a new and facile strategy toward other membranes with multifunctionality.