Junhao Zhang

MOF-derived bi-metal embedded N-doped carbon polyhedral nanocages with enhanced lithium storage

To tackle the issue of the low specific capacity (372 mA h g−1) of graphite as the anode material for lithium-ion batteries (LIBs), an effective and controllable strategy was developed to construct porous bimetallic Co/Zn embedded N-doped carbon (Co–Zn/N–C) polyhedral nanocages via annealing a ZIF-8@ZIF-67 precursor at 800 °C under Ar atmosphere. The results clearly displayed that metallic Co and Zn particles are uniformly dispersed in the carbon matrix. Porous Co–Zn/N–C polyhedral nanocages have a large specific surface area of 349.12 m2 g−1 and contain plenty of micropores and mesopores, which benefit from the carbonization of organic ligands and the catalytic effect of cobalt in the calcination process. As anodes for LIBs, the porous Co–Zn/N–C polyhedral nanocages showed an initial discharge capacity of 809 mA h g−1 and a capacity retention of 702 mA h g−1 after 400 cycles at a current density of 0.2 A g−1. Furthermore, a reversible capacity of 444 mA h g−1 was obtained at a much higher current density of 2 A g−1. The improved electrochemical performance was attributed to the synergistic effect of Zn and Co, the unique porous hollow structure as well as N doping, which relieved the impact of volume changes, maintained perfect electrical conductivity throughout the electrode and enhanced the electrochemical activities of lithium storage.

Few layered Co(OH)2 ultrathin nanosheet-based polyurethane nanocomposites with reduced fire hazard: from eco-friendly flame retardance to sustainable recycling

Huge consumption of thermoplastic polyurethane (TPU) results in two serious challenges for our society: fire hazards and environment pollution. To address these challenges, on the one hand, ultrathin β-Co(OH)2 nanosheets were devised and synthesized by a surfactant self-assembly technique and their application in TPU reduced the fire hazard; on the other hand, a green method was developed to sustainably recycle TPU nanocomposites into high value-added carbon materials. The structural characterizations demonstrate that the ultrathin β-Co(OH)2 nanosheets showed a typical two-dimensional lamellar morphology, possessing a lateral dimension of ca. 2 μm and a low thickness of ca. 2.6 nm, corresponding to the two layers of β-Co(OH)2. The incorporation of ultrathin β-Co(OH)2 nanosheets into the TPU matrix effectively reduced the heat release and restrained the toxicity of the volatiles, which was attributed to the ultrathin β-Co(OH)2 nanosheets in the TPU matrix offering an enhanced barrier effect and catalytic charring capability and Co3O4 decomposed from β-Co(OH)2 possessing superior catalytic oxidation of CO. Moreover, a green autocatalytic process in a sealed autoclave was developed to convert TPU/Co(OH)2 nanocomposites into high value-added Co/CNTs nanocomposites with more than 85% yield. This innovative idea may be expanded to other polymer systems and opens a new door to developing high performance polymer nanocomposites via green approaches and in particular, the sustainable recycling of the polymer-based materials.

Ultrasmall SnS2 nanoparticles anchored on well-distributed nitrogen-doped graphene sheets for Li-ion and Na-ion batteries

Well-distributed graphene sheets doped with nitrogen (NGSs) were prepared via a thermal annealing strategy with the use of cyanamide. The cyanamide can efficiently restrain the conglomeration of the resultant graphene sheets and simultaneously ensure the doping of nitrogen. Followed by the next-step of the low-temperature solvothermal route, uniform ultrasmall tin sulfide (SnS2) nanocrystals were readily grown on the preformed NGS (denoted as SnS2–NGS). Benefiting from the synergistic function between NGSs and SnS2, the resultant composites exhibit excellent electrochemical performance. When evaluated as anode materials for lithium-ion batteries (LIBs), SnS2–NGS with a moderate weight ratio of SnS2 delivers outstanding electrochemical performance giving a high reversible capacity of 1407 mA h g−1 at 200 mA g−1 after 120 cycles. The composites can also maintain a reversible capacity of about 200 mA h g−1 at a high current density of 10 A g−1. The lithium-ion storage ability of the prepared SnS2–NGS electrode is at the top rank in comparison with those of other studies. The obtained composites also achieved good sodium storage ability.

Synthesis of carbon-coated Fe3O4 composites with pine-tree-leaf structures from catalytic pyrolysis of polyethylene

A simple one-step method to synthesize carbon-coated Fe3O4 composites with complex pine-tree-leaf structures has been developed. As revealed in FESEM and TEM analysis, the Fe3O4 nanoparticles were self-assembled to chains-like structures, which were coated by carbon shells with a thickness of about 150 nm, and the needle-like pine-tree-leaf organization grown perpendicular to the central stems are carbon nanorods. Some important preparative parameters related to the synthesis have been identified and investigated with some designed experiments. Ferromagnetic properties of the carbon-coated Fe3O4 composites with pine-tree-leaf structures have been further differentiated for the different structures, and the results show that the saturation magnetization value (18.4 emu g−1) is lower than that of bulk Fe3O4, and the coercivity value (142.3 Oe) is much higher than that of the bulk Fe3O4.

Rationally Incorporated MoS2/SnS2 Nanoparticles on Graphene Sheets for Lithium-Ion and Sodium-Ion Batteries

Herein, we have designed and first synthesized a unique ternary hybrid structure by simultaneously growing SnS2 and MoS2 particles on graphene sheets (denoted as MoS2/SnS2-GS) via one-pot hydrothermal route. The charge incompatibility between MoO42- and graphene oxide with negative charged functional groups on surface can be compromised with the aid of Sn4+ cations, which renders the final formation of SnS2 and MoS2 on GS surface. This is the first report of the cohybridization of MoS2 and SnS2 with GS matrix from anionic and cationic precursors in the absence of premedication of graphene surface. When MoS2/SnS2-GS acts as anodes for lithium-ion batteries, the hybrids exhibit much better cycling stability than MoS2-GS and SnS2-GS counterparts. The compact adhesion of MoS2/SnS2 nanoparticles helps offset the undesired result of destruction of electrode materials resulting from volume expansion during repeated cycles. Furthermore, by combination with their synergetic effect on interface and the presence of discrepant asynchronous electrochemical reactions for SnS2 and MoS2, MoS2/SnS2-GS hybrids are endowed with improvement of electrochemical capabilities. Besides, they also showed outstanding Na-storage ability.

Synergistic effect of organophilic Fe-montmorillonite on flammability in polypropylene/intumescent flame retardant system

Polypropylene/intumescent flame retardant/organophilic Fe-montmorillonite (PP/IFR/Fe-OMT) nanocomposites were prepared by melting intercalation. In order to investigate the effect of structural Fe3+ in the PP/IFR system, the corresponding PP/IFR and PP/IFR/Na-OMT composites were prepared under the same conditions. The thermo-gravimetric analysis data show that the PP/IFR/Fe-OMT nanocomposites have higher thermal stability than the PP/IFR and PP/IFR/Na-OMT composites. The flame retardant results indicate that the limiting oxygen index values of the nanocomposites with Fe-OMT are basically higher than those of the pure PP and the composites containing IFR or Na-OMT/IFR. And the addition of a suitable amount of Fe-OMT in PP/IFR composites can apparently favor UL94 test, and no dripping phenomenon was found. The cone calorimeter test indicates that the heat release rate (HRR) is significantly reduced by the formation of the nanocomposites, and the HRR of the PP/IFR/Fe-OMT nanocomposites are decreased in comparison with those of the PP/IFR/Na-OMT nanocomposites. It is noteworthy that Fe-OMT is helpful to smoke suppression by smoke density test.

Sustainable processing of waste polypropylene to produce high yield valuable Fe/carbon nanotube nanocomposites

With the increasingly serious environmental contamination and energy crisis, it is highly necessary that polyolefin-based waste plastics are converted into valuable materials by innovative upcycling processes. This study presents an environmentally benign and solvent-free autogenic process to produce sponge-like Fe/carbon nanotube nanocomposites by catalytic pyrolysis of waste polypropylene (PP) at 600 °C. The composition and morphology of the products were characterized by powder X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). The results show that the products are Fe/carbon nanotube nanocomposites with sponge-like structures, and the diameter of the carbon nanotubes is about 30 nm while the diameter of the Fe nanoparticles in the carbon nanotubes is also about 30 nm, which illustrates that the size of the Fe nanoparticles determines the diameter of the carbon nanotubes. Nitrogen adsorption–desorption measurements indicate that the Brunauer–Emmett–Teller (BET) surface area is calculated to be 197.6 m2 g−1, and the Barrett–Joyner–Halenda (BJH) adsorption cumulative volume of pores is up to 0.2860 cm3 g−1. Magnetic measurements at room temperature indicate that the values of saturation magnetization (62.7 emu g−1) and coercivity (187.3 Oe) of the sponge-like Fe/carbon nanotube nanocomposites are different from those of bulk Fe due to the broad distribution of carbon nanotubes and the small size of the Fe nanoparticles.

Large-scale controllable preparation and performance of hierarchical nickel microstructures by a seed-mediated solution hydrogen reduction route

As a part of the persistent efforts to accomplish a sustainable society, solution-hydrogen reduction was developed for preparing metal materials. Large-scale hierarchical nickel microstructures with controllable sizes and pores were constructed by adjusting the reaction conditions and the cycles of repeated reduction using nickel nanoparticles of about 700 nm as seeds and H2 as the reductant. The investigation results of the reaction conditions indicated that ammonia and nickel seeds played crucial roles in the reduction reaction. The possible formation process of self-assembled hierarchical nickel microstructures was proposed based on the results of experiments and analysis. The magnetic hysteresis loops show that the magnetic properties of nickel microstructures were also controllable by controlling the cycles. The hydrogen storage indicates that the hierarchical nickel microstructures have better hydrogen storage performance at 298 K, which may be ascribed reasonably to the H2 molecules that were adsorbed onto the surface of nickel particles and formed activated hydrogen (Ni–H). Such a cost-effective and environmentally friendly procedure is a versatile approach that may be extended to the mass production of some metals and the fabrication of some other hierarchical microstructures.

Self-assembled synthesis of carbon-coated Fe3O4 composites with firecracker-like structures from catalytic pyrolysis of polyamide

Carbon-coated Fe3O4 composites with firecracker-like structures have been fabricated by catalytic pyrolysis of polyamide (PA) in a sealed reaction system. As revealed in field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) analysis, the diameter of the one-dimensional firecracker-like structures is about 4 μm and the diameter of the secondary nanorods is about 620 nm. The diameter of Fe3O4 nanorods inside the carbon shells is about 82 nm, and the thickness of the carbon shells is about 265 nm. Some important preparative parameters related to the synthesis have been identified and investigated by some designed experiments. The magnetic measurement at room temperature indicates that the values of saturation magnetization (19.2 emu g−1) and coercivity (270.1 Oe) of the carbon-coated Fe3O4 composites with firecracker-like structures are different from those of Fe3O4 nanoparticles and bulk Fe3O4 due to the different carbon content, dipolar interaction, size and morphology of the products. The results also indicate that the one-dimensional Fe3O4@C core–shell structures possess good acid resistance.

Characterization and mechanism analysis of AgBr mixed cuboid WO3 rods with enhanced photocatalytic activity

Cuboid rods of monoclinic WO3 (m-WO3) were successfully prepared by employing preoxo-polytungstic acid as the precursor via a hydrothermal method. AgBr/m-WO3 photocatalysts with varying loadings of AgBr were synthesized and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM). Photocatalytic degradation of rhodamine B (rhB), methyl orange (MO) and methyl blue (MB) were carried out to evaluate the photocatalytic activity of AgBr/m-WO3 under visible-light irradiation (λ ≥ 420 nm). Among such catalysts, the AgBr (30 wt%)/m-WO3 exhibits the highest visible-light-responsible photoactivity. However, these AgBr/m-WO3 materials gradually lost their photoactivity in the cycling photocatalytic tests. Possible mechanisms for both the enhance photocatalytic activity and deactivation of the AgBr/m-WO3 were proposed on basis of theoretical speculation and experimental observations.