Xiaosi Qi

Large-Scale Synthesis of Carbon Nanomaterials by Catalytic Chemical Vapor Deposition: A Review of the Effects of Synthesis Parameters and Magnetic Properties

The large-scale production of carbon nanomaterials by catalytic chemical vapor deposition is reviewed in context with their microwave absorbing ability. Factors that influence the growth as well as the magnetic properties of the carbon nanomaterials are discussed.

The effect of nitrogen incorporation on the magnetic properties of carbon-doped ZnO

Samples of carbon-doped ZnO powders were prepared by the standard solid-state reaction method and sintered separately in argon and nitrogen atmospheres. According to the results of Raman spectroscopic investigation, the samples sintered in nitrogen showed lower D-bond (disordered) and G-bond (graphitic) concentrations, plausibly a result of nitrogen incorporation into the carbon-doped ZnO sample. All the samples are ferromagnetic at room temperature, and compared with those sintered in argon, those sintered in nitrogen have a lower magnetic moment. We found that the electrons-mediated mechanism is more suitable than the holes-mediated one for the explanation of ferromagnetism of carbon-doped ZnO materials.

Heteronanostructured Co@carbon nanotubes-graphene ternary hybrids: synthesis, electromagnetic and excellent microwave absorption properties

In order to explore high efficiency microwave absorption materials, heteronanostructured Co@carbon nanotubes-graphene (Co@CNTs-G) ternary hybrids were designed and produced through catalytic decomposition of acetylene at the designed temperature (400, 450, 500 and 550 °C) over Co3O4/reduced graphene oxide (Co3O4/RGO). By regulating the reaction temperatures, different CNT contents of Co@CNTs-G ternary hybrids could be synthesized. The investigations indicated that the as-prepared heteronanostructured Co@CNTs-G ternary hybrids exhibited excellent microwave absorption properties, and their electromagnetic and microwave absorption properties could be tuned by the CNT content. The minimum reflection loss (RL) value reached approximately −65.6, −58.1, −41.1 and −47.5 dB for the ternary hybrids synthesized at 400, 450, 500 and 550 °C, respectively. And RL values below −20 dB (99% of electromagnetic wave attenuation) could be obtained over the as-prepared Co@CNTs-G ternary hybrids in the large frequency range. Moreover, based on the obtained results, the possible enhanced microwave absorption mechanisms were discussed in details. Therefore, a simple approach was proposed to explore the high performance microwave absorbing materials as well as to expand the application field of graphene-based materials.

Metal-free carbon nanotubes: synthesis, and enhanced intrinsic microwave absorption properties.

In order to clearly understand the intrinsic microwave absorption properties of carbon nanomaterials, we proposed an efficient strategy to synthesize high purity metal-free carbon nanotubes (CNTs) over water-soluble K2CO3 particles through chemical vapor decomposition and water-washing process. The comparison results indicated the leftover catalyst caused negative effects in intrinsic microwave absorption properties of CNTs, while an enhanced microwave absorption performance could be observed over the metal-free CNT sample. Moreover, the results indicated that the microwave absorption properties could be tuned by the CNT content. Therefore, we provided a simple route to investigate the intrinsic properties of CNTs and a possible enhanced microwave absorbing mechanism.

The synthesis and excellent electromagnetic radiation absorption properties of core/shell-structured Co/carbon nanotube–graphene nanocomposites

Through the reduction process involving Co3O4/reduced graphene oxide and acetylene, core/shell structured Co/carbon nanotube–graphene nanocomposites were synthesized on a large scale. Because of their special structure, high attenuation constant and good complementarity between magnetic loss material and dielectric loss material, the obtained Co/carbon nanotube–graphene nanocomposites exhibited very attractive microwave absorption. An optimal reflection loss (RL) of up to −65.6 dB at 12.4 GHz was observed with a thickness of 2.19 mm, and RL values below −20 dB were obtained in almost the entire frequency range. Therefore, a simple approach was proposed to explore the high-performance microwave-absorbing materials as well as expand the fields of application of graphene-based materials.

Large-scale and controllable synthesis of metal-free nitrogen-doped carbon nanofibers and nanocoils over water-soluble Na2CO3

Using acetylene as carbon source, ammonia as nitrogen source, and Na2CO3 powder as catalyst, we synthesized nitrogen-doped carbon nanofibers (N-CNFs) and carbon nanocoils (N-CNCs) selectively at 450°C and 500°C, respectively. The water-soluble Na2CO3 is removed through simple washing with water and the nitrogen-doped carbon nanomaterials can be collected in high purity. The approach is simple, inexpensive, and environment-benign; it can be used for controlled production of N-CNFs or N-CNCs. We report the role of catalyst, the effect of pyrolysis temperature, and the photoluminescence properties of the as-harvested N-CNFs and N-CNCs.

Preparation of porous Fe 2 O 3 nanorods-reduced graphene oxide nanohybrids and their excellent microwave absorption properties

In this paper, α-Fe2O3 nanoparticles (NPs)-reduced graphene oxide (RGO), α-FeOOH nanorods (NRs)-RGO and porous α-Fe2O3 NRs-RGO could be selectively synthesized by hydrothermal method. The investigations indicated that the obtained α-Fe2O3 NPs, α-FeOOH NRs and porous α-Fe2O3 NRs were either attached on the surface of RGO sheets or coated uniformly by the RGO sheets. And the as-prepared nanohybrids exhibited excellent microwave absorption performance, which was proved to be ascribed to the quarter-wavelength matching model. The optimum reflection loss (RL) values for α-Fe2O3 NPs-RGO, α-FeOOH NRs-RGO and porous α-Fe2O3 NRs-RGO were ca. −32.3, −37.4 and −71.4 dB, respectively. Moreover, compared to the obtained α-Fe2O3 NPs-RGO and α-FeOOH NRs-RGO, the as-prepared porous α-Fe2O3 NRs-RGO nanohybrids exhibited enhanced microwave absorption properties because of their special structure and synergetic effect. The possible enhanced microwave absorption mechanisms were discussed in details. Our results confirmed that the geometrical morphology had a great influence on their microwave absorption properties, which provided a promising approach to exploit high performance microwave absorbing materials.

Synthesis of high purity chain-like carbon nanospheres in ultrahigh yield, and their microwave absorption properties

Over Fe/SnO2 nanoparticles generated by a combined sol–gel/reduction method, high purity chain-like carbon nanospheres (CNSs) could be synthesized in large quantities through the catalytic decomposition of acetylene at 700 °C. The effect of SnO2 content on the yield, microstructure and microwave absorbing properties of the obtained CNSs were studied in detail. The results demonstrate that the content of SnO2 has a great impact on the yield and dimensions of the obtained CNSs, and an ultrahigh yield of 309 was reported. Moreover, the smaller size of chain-like CNSs, which can be obtained over the catalysts with higher SnO2 content, exhibit enhanced microwave absorption properties due to their better complementarities between the dielectric and magnetic tangent loss. Based on the results, we also discuss the possible formation mechanism of CNSs. Therefore, we propose a simple and environmentally-friendly route for the mass production of chain-like CNSs with high purity, and the as-synthesized chain-like CNSs exhibit good microwave absorbing abilities.

Water-assisted and controllable synthesis of core/shell/shell structured carbon-based nanohybrids, and their magnetic and microwave absorption properties

By controlling the pyrolysis temperature, core/shell/shell structured Fe/Fe5C2/carbon nanotube bundles (Fe/Fe5C2/CNTBs), Fe/Fe3C/helical carbon nanotubes (Fe/Fe3C/HCNTs) and Fe/Fe3C/chain-like carbon nanospheres (Fe/Fe3C/CCNSs) with high encapsulation efficiency could be selectively synthesized in large-scale by water-assisted chemical vapor deposition method. Water vapor was proved to play an important role in the growth process. Because of α-Fe nanoparticles tightly wrapped by two layers, the obtained core/shell/shell structured nanohybrids showed high stabilities and good magnetic properties. The minimum reflection loss values of the as-prepared nanohybrids reached approximately −15.0, −46.3 and −37.1 dB, respectively. The excellent microwave absorption properties of the as-prepared core/shell/shell structured nanohybrids were considered to the quarter-wavelength matching model. Moreover, the possible enhanced microwave absorption mechanism of the as-prepared Fe/Fe3C/HCNTs and Fe/Fe3C/CCNSs were discussed in details. Therefore, we proposed a simple, inexpensive and environment-benign strategy for the synthesis of core/shell/shell structured carbon-based nanohybrids, exhibiting a promising prospect as high performance microwave absorbing materials.

Morphology-controllable synthesis of carbon nanomaterials directly on Al2O3 substrates, and their photoluminescence

By controlling the growth temperature, different categories of carbon nanomaterials (CNMs) such as carbon nanocoils (CNCs) and chain-like carbon nanospheres (CNSs) can be synthesized directly over Al2O3 substrate without using any transition-metal catalysts. It is proposed that the Al2O3 particles play a key role in the CNM growth, and the reaction temperature has a great impact on the morphology of the obtained CNMs. Furthermore, the photoluminescence studies indicate that the obtained CNCs and chain-like CNSs show different optical properties, which suggest that the optical properties of the obtained CNMs may be tuned by controlling their structures.