Qinghong Kong

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.

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.

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.

Flame-retardant effect of montmorillonite intercalation iron compounds in polypropylene/aluminum hydroxide composites system

Abstract Montmorillonite possesses nanometer size effect and layer blocking effect, and iron compounds have significant catalytic carbonization performance. Based on these above, the new montmorillonite intercalation iron compounds (MIICs) are designed and synthesized. The MIIC is a typical lamellar compound that holds the homogeneity crystal structure and the adjustable component. The MIIC was modified by cetyltrimethylammonium bromide and obtained organic MIIC (OMIIC). Polypropylene (PP)/aluminum hydroxide (ATH)/OMIIC nanocomposites were prepared via melting intercalation. The structures of PP/ATH/OMIIC nanocomposites were studied by XRD and transmission electron microscope, which indicate that OMIIC disperses well in PP composites, and PP/ATH/OMIIC nanocomposites have the exfoliated and intercalated structures. The combustion tests show that the small amount of OMIIC in PP/ATH composites can apparently favor UL94 test and suppress dripping phenomenon. The cone calorimeter tests indicate that the heat release rate is significantly reduced by the formation of nanocomposites, and the THR of the PP/ATH/OMIIC nanocomposites was decreased in comparison with that of the PP/ATH nanocomposites, which should be attributed to the formation of compact protective char layer.

Simultaneously improving the fire safety and mechanical properties of epoxy resin with Fe-CNTs via large-scale preparation

To further improve the catalytic carbonization efficiency of polymer composites for the formation of compact protective layers in the combustion process, a novel type of Fe-CNTs was prepared in large scale. The Fe-CNTs were used as nanofillers to efficiently improve catalytic carbonization, flame retardancy, and mechanical performances of epoxy resin (EP). With the incorporation of 6 wt% Fe-CNTs, the LOI value of the EP/Fe-CNTs nanocomposites was improved to 35.0 and the UL-94 V-1 rating was passed with an average (t1 + t2) value of 13.3. As compared to pure EP, the PHRR, THR, and TSP of EP/6 wt% Fe-CNTs nanocomposites decreased by 30.7%, 39.1%, and 48.6%, respectively. The significantly improved flame retardancy could be attributed to the compact carbonaceous ceramic layers, which significantly retarded the transfer of heat and combustible gas between the EP nanocomposites and the flame zone. Moreover, the EP/Fe-CNTs nanocomposites exhibited excellent impact and tensile strength performances due to the formation of a strong three-dimensional network structure in the EP matrix.

Improving flame retardancy of PP/MH/RP composites through synergistic effect of organic CoAl-layered double hydroxide

To improve the flame retardant efficiency of polypropylene/magnesium hydroxide/red phosphorus (PP/MH/RP) composites, organic CoAl-layered double hydroxide (CoAl-OLDH) was designed and prepared. And PP/MH/RP/CoAl-OLDH nanocomposites were fabricated via melt blending method. The results indicated that CoAl-OLDH was dispersed uniformly in PP matrix to form exfoliated–intercalated structures. The combustion results showed that the limiting oxygen index (LOI) value and UL-94 vertical burning rating of PP/MH/RP/CoAl-OLDH nanocomposites were increased comparing with pure PP, PP/MH/RP and PP/MH/RP/CoAl-LDH. When 3 mass% CoAl-OLDH replaced MH/RP, PP/MH/RP/CoAl-OLDH nanocomposites passed UL-94 V-0 rating and the LOI value was high to 27.8%. The cone calorimeter test results indicated that the peak heat release rate, total heat release and total smoke release of PP/MH/RP/CoAl-LDH nanocomposites with 3 mass% CoAl-OLDH were decreased by 36.9, 14.4, 18.4%, respectively. The improved flame retardant and smoke suppression properties were attributed the excellent sheet barrier effect and good catalytic carbonization performances of CoAl-OLDH due to the well dispersion.

General fabrication and enhanced VOC gas-sensing properties of hierarchically porous metal oxides

A facile and general route to synthesize hierarchically porous metal oxide nanostructures was reported here. The results indicate that the hierarchically porous metal oxides show high sensitivity to toxic or dangerous gases. The signal sensitivity of the gas sensors exhibits a good linear relation with the VOC gas concentration. As one of the as-synthesized hierarchically porous metal oxides, ZnO exhibits the lowest detection limit of 15 ppb for formaldehyde, which is much lower than the limit value of indoor formaldehyde (60 ppb). Furthermore, the sensitivity of the ZnO porous nanosheets decorated with Au nanoparticles is 10 ppb for formaldehyde, which is about 1.5 times higher than that of the unmodified ZnO porous nanosheets.

Simultaneously improving flame retardancy and dynamic mechanical properties of epoxy resin nanocomposites through synergistic effect of zirconium phenylphosphate and POSS

To simultaneously improve flame retardancy and dynamic mechanical properties of epoxy resin (EP) nanocomposites, layered zirconium phenylphosphate (ZrPP) was successfully synthesized through mixed solvothermal technique and added with polyhedral oligomeric silsesquioxane (POSS) to EP to prepare ZrPP/POSS/EP nanocomposites. The results indicated that molecular formula of ZrPP was Zr(O3PC6H5)2·H2O with suitable thermal stability as flame retardant for EP. Based on the synergism of ZrPP and POSS, ZrPP/POSS/EP nanocomposites exhibit higher thermal stability, better flame retardancy, and more residue than pure EP. More importantly, addition of low content of ZrPP optimized dynamic mechanical properties of ZrPP/POSS/EP nanocomposites. Compared with those of 5 mass% POSS/EP, the storage modulus of 1 mass% ZrPP/4 mass% POSS/EP increased by 9% and the glass transition temperature scarcely changed, which was speculated that there were some of three-dimensional POSS molecules intercalating into interlayers of ZrPP and led to excellent dispersion state and increased nanoreinforcing effect in EP nanocomposites.