Baoliang Lv

Fabrication of Fe3O4@C core–shell nanotubes and their application as a lightweight microwave absorbent

With the continuing growth in demand for the reduction of electromagnetic radiation, lightweight and highly efficient microwave absorbents are greatly needed. In this study, Fe3O4@C core–shell nanotubes, with Fe3O4 nanotubes as cores and carbon as shells, of about 10 nm thickness have been successfully synthesized. Coating Fe3O4 nanotubes with carbon shells effectively increased dielectric loss and improved impedance matching of the composites, resulting in enhanced microwave absorption performance. The effective absorption bandwidth, with reflection loss (RL) less than −10 dB, was up to 6 GHz when the thickness of the test sample was as little as 1.7 mm, as determined using a vector network analyzer. Possessing a very low density of 1.4 g cm−3 and good microwave absorption performance, the as-fabricated Fe3O4@C core–shell nanotubes can meet the multiple property requirements of microwave absorbents.

Hexagonal α-Fe2O3 nanorods bound by high-index facets as high-performance electrochemical sensor

Hexagonal α-Fe2O3 nanorods with high-index facets exposed were synthesized using a double ligand-assisted hydrothermal method (involving PO43− and formamide). The growth process of the synthesized particles obviously proceeded by two stages: (i) formation of capsule-shaped α-Fe2O3 nanoparticles along [001] directions and (ii) preferential grow along [112] and/or its equivalent directions to form hexagonal nanorods. The occurrence of this process can be attributed to the stepwise effect of PO43− and formamide. First, the shape of the capsule-shaped α-Fe2O3 is mainly regulated by the adsorption of PO43− on those facets parallel to the c-axis of α-Fe2O3 during the nanocrystal growth because of the special double coordinated surface hydroxyl on (001) facets, and then the hexagonal structure should result from the preferential growth along [112] and/or its equivalent directions due to the weak adsorption of formamide in the Ostwald ripening process. The as-prepared α-Fe2O3 exhibits an excellent electrochemical sensing capability towards H2O2 due to the exposed high-index facets and more active sites of low-coordinated atoms that are located on the edges.

Synthesis and properties of octahedral Co3O4 single-crystalline nanoparticles enclosed by (111) facets

Co3O4 octahedral particles, with lengths of ~70 nm and widths of ~60 nm, were hydrothermally synthesized under the assistance of triphenylphosphine (PPh3). X-ray powder diffraction (XRD) showed that the Co3O4 octahedra belong to the cubic crystal system. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) analysis indicated that these octahedral Co3O4 nanoparticles were enclosed by eight (111) facets. On the basis of crystal structure analysis and condition-dependent experiments, the unique O-terminated structure of (111) facet of Co3O4 and crystal interface restriction effect after the adsorption of [Co(OH)a(H2O)b(PPh3)x−a−b]h−a on the surface of Co3O4 nuclei were used to explain the formation of octahedral Co3O4 nanoparticles. The catalytic activity characterization showed that the as-obtained Co3O4 octahedra can catalyze the thermal decomposition of ammonium perchlorate effectively.

Fe–Fe3C/C microspheres as a lightweight microwave absorbent

As electromagnetic pollution is becoming more and more serious, novel composite microwave absorbents are gaining much attention. In this work, low-cost glucose was used as a carbon source to prepare hydrochar, and Fe–Fe3C/C microspheres for microwave absorption were successfully synthesized through the hydrothermal synthesis of Fe3O4/hydrochar and subsequent high-temperature carbonization at different temperatures. The results showed that the Fe–Fe3C nanoparticles were uniformly loaded on the carbon microspheres. Resulting from the synergistic effect of Fe–Fe3C nanoparticles and partially graphitized carbon, a wide region of microwave absorption was achieved due to dual dielectric and magnetic losses. An effective bandwidth of reflection loss less than −10 dB could reach up to 4 GHz with 1.5 mm thickness. Owing to the characteristics of the cost-effective synthetic route, low density and good microwave absorption with thin thickness, the Fe–Fe3C/C microspheres could be used as a lightweight and highly efficient microwave absorbent.

Facile synthesis of porous nitrogen-doped holey graphene as an efficient metal-free catalyst for the oxygen reduction reaction

Nitrogen-doped graphene is a promising candidate for the replacement of noble metal-based electrocatalysts for oxygen reduction reactions (ORRs). The addition of pores and holes into nitrogen-doped graphene enhances the ORR activity by introducing abundant exposed edges, accelerating mass transfer, and impeding aggregation of the graphene sheets. Herein, we present a straightforward but effective strategy for generating porous holey nitrogen-doped graphene (PHNG) via the pyrolysis of urea and magnesium acetate tetrahydrate. Due to the combined effects of the in situ generated gases and MgO nanoparticles, the synthesized PHNGs featured not only numerous out-of-plane pores among the crumpled graphene sheets, but also interpenetrated nanoscale (5–15 nm) holes in the assembled graphene. Moreover, the nitrogen doping configurations of PHNG were optimized by post-thermal treatments at different temperatures. It was found that the overall content of pyridinic and quaternary nitrogen positively correlates with the ORR activity; in particular, pyridinic nitrogen generates the most desirable characteristics for the ORR. This work reveals new routes for the synthesis of PHNG-based materials and elucidates the contributions of various nitrogen species to ORRs.

Morphology evolution of α-Fe2O3 nanoparticles: the effect of dihydrogen phosphate anions

α-Fe2O3 nanoparticles with various morphologies (including spindles, rods, tubes, disks and nanorings) were synthesized under the influence of H2PO4− ions via a simply hydrothermal method. It was found that the morphologies of the α-Fe2O3 nanoparticles were highly sensitive to the concentration of H2PO4− ions. The special all doubly coordinated surface hydroxyl configuration on (001) facets of α-Fe2O3 was the most important factor for the morphology evolution. The final morphologies of the samples mainly depend on how the H2PO4− anions oriented the growth of the (001) facet. All morphologies of the synthesized α-Fe2O3 nanoparticles could be systemically evaluated by the competition of Fe3+ and H2PO4− ions on the (001) facets.

Facile synthesis of self-assembled ultrathin α-FeOOH nanorod/ graphene oxide composites for supercapacitors

A one-pot facile, impurity-free hydrothermal method to synthesize ultrathin α-FeOOH nanorods/graphene oxide (GO) composites is reported. It is directly synthesized from GO and iron acetate in water solution without inorganic or organic additives. XRD, Raman, FT-IR, XPS and TEM are used to characterize the samples. The nanorods in composites are single crystallite with an average diameter of 6nm and an average length of 75nm, which are significantly smaller than GO-free α-FeOOH nanorods. This can be attributed to the confinement effect and special electronic influence of GO. The influences of experimental conditions including reaction time and reactant concentration on the sizes of nanorods have been investigated. It reveals that the initial Fe2+ concentration and reaction time play an important role in the synthetic process. Furthermore, a possible nucleation-growth mechanism is proposed. As electrode materials for supercapacitors, the α-FeOOH nanorods/GO composite with 20% iron loading has the largest specific capacitance (127Fg-1 at 10Ag-1), excellent rate capability (100Fg-1 at 20Ag-1) and good cyclic performance (85% capacitance retention after 2000 cycles), which is much better than GO-free α-FeOOH nanorods. This unique structure results in rapid electrolyte ions diffusion, fast electron transport and high charging-discharging rate. In virtue of the superior electrochemical performance, the α-FeOOH nanorods/GO composite material has a promising application in high-performance supercapacitors.

Facile Fabrication of BCN Nanosheet-Encapsulated Nano-Iron as Highly Stable Fischer–Tropsch Synthesis Catalyst

The few layered boron carbon nitride nanosheets (BCNNSs) have attracted widespread attention in the field of heterogeneous catalysis. Herein, we report an innovative one-pot route to prepare the catalyst of BCNNSs-encapsulated sub-10 nm highly dispersed nanoiron particles. Then the novel catalyst was used in Fischer-Tropsch synthesis for the first time and it exhibited high activity and superior stability. At a high temperature of 320 °C, CO conversion could reach 88.9%, corresponding catalytic activity per gram of iron (iron time yield, FTY) of 0.9 × 10-4 molCO gFe-1 s-1, more than 200 times higher than that of pure iron. Notably, no obvious deactivation was observed after 1000 h running. The enhanced stability of the catalyst can be ascribed to the special encapsulated structure. Furthermore, the formation mechanism of highly dispersed iron nanoparticle also was elaborated. This approach opens the way to designing metal nanoparticles with both high stability and reactivity for nanocatalysts in hydrogenation application.

Precisely tailoring dendritic α-Fe2O3 structures along [100] directions

In the present work, a significant advance has been made in precisely tailoring dendritic α-Fe2O3 structures along [100] and/or its equivalent directions. We proposed that the benzoate anions adsorb on (100) and/or its equivalent facets, leading to the slow growth of these facets. By carefully controlling the experimental conditions, the dendritic structures can be gradually tailored to nanorods and finally to dodecahedral α-Fe2O3 nanoparticles with twelve exposed (012) planes. Interestingly, with the process proceeding, the coercivity (Hc) of these particles decreases successively due to the reduction in magnetic anisotropy by lessening intensity of hierarchical hyperbranched structure. The tailoring process gives us an in-depth understanding of the formation mechanism of dendritic α-Fe2O3 structures, which is not possibly achieved by the traditional time-dependent method.

Ultrathin N-rich boron nitride nanosheets supported iron catalyst for Fischer–Tropsch synthesis

The boron nitride nanosheets (BNNSs) have attracted great interest in the field of energy storage and heterogeneous catalysis. In this paper, BNNSs supported iron (Fe/BNNSs) catalysts were prepared by one-pot solid state reaction and used in Fischer–Tropsch synthesis (FTS) for the first time. The microscopic structure, morphology and metal–support interaction of the Fe/BNNSs catalysts were investigated by TEM, FT-IR, 1H MAS NMR and H2-TPR. The average thickness of the N-rich BNNSs support was 4–8 nm, and the mean size of the iron nanoparticles was 25–40 nm. The CO conversion, CH4 and C5+ selectivity of typical Fe/BNNSs catalyst with 33 wt% Fe-loading were 47%, 13.7% and 48% at 270 °C, respectively. No obvious deactivation was observed even after 270 h running. The conversion, selectivity and the iron time yield (FTY) of Fe/BNNSs catalysts were highly related to the loading, dispersion of iron nanoparticles. The lower loading and better dispersion of the iron nanoparticles in Fe/BNNSs catalyst resulted in the better FTY and C5+ selectivity. The N-rich defects of BNNSs and porous structure of BNNSs anchored active phases to prevent them from growing larger. Therefore, the BNNSs support plays an important role in retarding the catalyst from deactivation.