As cutting-edge emerging electromagnetic (EM) wave-absorbing materials, the Achilles’ heel of graphenes is vulnerable to oxidation under high temperature and oxygen atmosphere, particularly at temperatures more than 600 °C. Herein, a graphene@Fe3O4/siliconboron carbonitride (SiBCN) nanocomplex with a hierarchical A/B/C structure, in which SiBCN serves as a “shield” to protect graphene@Fe3O4 from undergoing high-temperature oxidation, was designed and tuned by polymer-derived ceramic route. The nanocomplexes are stable even at 1100–1400 °C in either argon or air atmosphere. Their minimum reflection coefficient (RCmin) and effective absorption bandwidth (EAB) are −43.78 dB and 3.4 GHz at ambient temperature, respectively. After oxidation at 600 °C, they exhibit much better EM wave absorption, where the RCmin decreases to −66.21 dB and EAB increases to 3.69 GHz in X-band. At a high temperature of 600 °C, they also possess excellent and promising EW wave absorption, for which EAB is 3.93 GHz, covering 93.6% range of X-band. In comparison to previous works on graphenes, either the EAB or the RCmin of these nanocomplexes is excellent at high-temperature oxidation. This novel nanomaterial technology may shed light on the downstream applications of graphenes in EM-wave-absorbing devices and smart structures worked in harsh environments.

The hierarchically macro/micro-porous silicon–carbon–nitrogen (Si–C–N) hybrid material was presented with novel functionalities of totally selective and highly efficient adsorption for organic dyes. The hybrid material was conveniently generated by the pyrolysis of commercial polysilazane precursors using polydivinylbenzene microspheres as sacrificial templates. Owing to the Van der Waals force between sp2-hybridized carbon domains and triphenyl structure of dyes, and electrostatic interaction between dyes and Si-C-N matrix, it exhibites high adsorption capacity and good regeneration and recycling ability for the dyes with triphenyl structure, such as methyl blue (MB), acid fuchsin (AF), basic fuchsin and malachite green. The adsorption process is determined by both surface adsorption and intraparticle diffusion. According to the Langmuir model, the adsorption capacity is 1327.7 mg·g−1 and 1084.5 mg·g−1 for MB and AF, respectively, which is much higher than that of many other adsorbents. On the contrary, the hybrid materials do not adsorb the dyes with azo benzene structures, such as methyl orange, methyl red and congro red. Thus, the hierarchically porous Si–C–N hybrid material from a facile and low cost polymer-derived strategy provides a new perspective and possesses a significant potential in the treatment of wastewater with complex organic pollutants.

No abstract

No abstract

High-temperature stable and metal-free siliconboron carbonitride ceramics with high electromagnetic (EM) wave-absorbing efficiency were achieved through the structural design and pyrolysis of carbon-rich hyperbranched polyborosilazane precursors with pendent phenyl groups. The introduction of benzene rings into the precursors dramatically changes the microstructure and the EM wave-absorbing property of ceramics. It reveals that the ceramics pyrolyzed from the benzene ring-containing preceramic precursors have a higher carbon content and a larger number of sp carbons and generate crystalline carbons (graphitic carbons and tubular carbons) in situ, which lead to excellent EM wave-absorbing properties. The EM wave absorption efficiency and effective absorption bandwidth (EAB, reflection coefficient (RC) below -10 dB) can be tuned via annealing of the ceramics. The ceramics stable at 1320 °C exhibit their optimized EM wave-absorbing performance with a minimum RC (RC) of -71.80 dB and an EAB of 3.65 GHz (8.2-11.85 GHz). We believe that the research extends the design strategy of advanced EM wave-absorbing functional materials, which have great potential as promising absorbers in commercial or military applications.

No abstract

The enhancement of electromagnetic wave absorption at high-temperature as well as oxidation is cutting-edge issue in current electromagnetic functional materials due to the strong demand of stealth aircrafts or aero-engines working in harsh environments. In this contribution, the excellent electromagnetic wave absorption at 1158 K (885 C) with a minimum reflection coefficient (RC min ) of À12.62 dB and a wide effective absorption bandwidth (RC min < -10 dB) of 3.2 GHz was achieved on iron-containing siliconboron carbonitride (SiBCN) monolithic ceramics by using polymer-derived ceramics (PDC) route, setting a new record for EM wave absorption materials at high-temperature. In addition, these materials exhibited desirable mechanical properties and excellent hightemperature resistance until 1400 C in argon atmosphere and 885 C in air atmosphere, respectively. This ingenious strategy is generally benefiting the promotion of EM wave absorption materials with great potential in antenna housings, radomes, areo-engines, and stealth aircrafts in harsh environments.With rapid development of electronic equipments in wireless communication, medical and aerospace fields, electromagnetic (EM) wave transparency, absorption, and shielding are important issues. [1][2][3][4] EM wave absorbing materials are mainly deployed in high-power electronic instruments, satellite communication, radar, stealth ships, and aircrafts, which can eliminate adverse EM waves by converting into thermal energy. However, the stealth aircrafts or aero-engines are working in harsh environments such as high temperature and oxidation, the enhancement of electromagnetic wave absorption and stealth performance at high temperature more than 600 C (873 K) is cutting-edge issue in current electromagnetic functional materials.In this field, metamaterials, ferrites, carbon family materials (carbon black, carbon fibers (CFs), carbon nanotubes (CNTs), graphite flakes, graphene foams, or graphenes), metal-carbon nano-hybrids (Fe 3 O 4 /CNTs/CFs, Fe 3 O 4 /graphene capsules, Co-carbon nanotubes-graphene, Co-Carbon metal-organic framework), core/shell hierarchical nanostructures and dielectronic ceramics, 2D transition metal carbides (MXenes) show favorable EM absorbing performance in ambient environment. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] However, at high temperature more than 873 K (600 C), most of ferrites are limited by low Curie temperature (T c ), for example, 360-440 C for Ba 3 Me 2-Fe 24 O 41 (Me ¼ Co, Cu, Ni) and 570 C for Ni-Zn ferrites. [5] Above T c , the ferrite will be converted to paramagnetic and lose EM wave absorption functionality. For metamaterials, MXenes, and carbon family materials, they always suffer from the thermolysis and oxidation at high temperature more than 600 C (873 K).With resistance to both high temperature and oxidation, silicon carbide (SiC) or silicon nitride (Si 3 N 4 )-based ceramics are important dielectronic type EM wave absorbing materials in harsh environments. The SiC-based materials, including SiC ...

The highly efficient electromagnetic (EM) wave absorbing metal-free and carbon-rich ceramics derived from hyperbranched polycarbosilazanes are presented in this contribution. The novel metal-free hyperbranched polycarbosilazanes with pendant cyano groups (hb-PCSZ-cyano) were synthesized through aminolysis reaction and subsequent Michael addition reaction, i.e., cyanoethylation reaction. As metal-free preceramic precursors, the pyrolysis of hb-PCSZ-cyano under high temperature and argon atmosphere generated carbon-rich Si−C−N multiphase ceramics. The ceramics reserve amorphous structure even at high temperature. The introduction of cyano groups in precursors leads to numerous sp 2 carbons and interface polarization in ceramics and favors the EM wave absorption performance. The minimum reflection coefficient (RC) value of Si−C−N multiphase ceramic is −59.59 dB at 12.23 GHz when the sample thickness is 2.30 mm, which means >99.99% electromagnetic waves can be absorbed. The effective absorption bandwidth (RC below −10 dB) is 4.2 GHz, covering the whole X-band (8.2−12.4 GHz). The EM wave absorption property is very excellent in comparison to current electromagnetic wave absorbing materials including transition metal-induced nanocrystals-containing ceramics. The carbon-rich Si−C−N ceramic derived from metal-free precursors provides a new strategy for highly efficient EM wave absorbing functional materials with great potential in electronic devices, antenna housings, and radomes in harsh environments.