Effect of Pore Morphology on the Dielectric Properties of Porous Carbons for Microwave Absorption Applications

Abstract

The porous carbons (PCs) with tunable morphologies and pore sizes were prepared by the sol–gel process via a freeze-drying technique for microwave absorption applications. The results of Raman spectroscopy and nitrogen sorption analysis showed that the graphitization degree was barely influenced as the ratio of tert-butanol (T) to resorcinol (R) decreased, while the pore morphologies changed from the disordered slit-shaped pores to the uniform cage-like pores. Dielectric properties of the as-prepared carbon samples were determined by a vector network analyzer in the frequency range of 8.2–12.4 GHz. Results showed that the effect of pore morphology on the dielectric loss of PCs was dominant in the case of similar graphitization. When the T/R ratio was 7.5, the sample with cage-like pores revealed the maximum values in the real part ε′ and the imaginary part ε″ of complex permittivity, which were 13.2–6.5 and 15.6–10.1, respectively, suggesting a better capacity of dielectric loss in the 8.2–12.4 GHz range. The proposed mechanism for the effect of the pore morphologies on microwave absorption performance was discussed.

Carbon-Supported Copper-Based Nitrogen-Containing Supramolecule as an Efficient Oxygen Reduction Reaction Catalyst in Neutral Medium

“…The presence of two types of nitrogen elements was consistent with the structure of Cu-SOCBP. The binding energies of pyridinic-N found in this study were higher than those usually reported for pyridinic-N, and this is an apparent indication of complexation between copper ions and The surface areas and pore volumes of the samples including Vulcan XC-72 carbon and Cu-SOCBP/C were determined by nitrogen sorption analysis [28]. The sorption isotherms of samples are shown in Figure 2.…”

“…This favorable structure may play a pivotal function in improving the ORR activity of materials. The surface areas and pore volumes of the samples including Vulcan XC-72 carbon and Cu-SOCBP/C were determined by nitrogen sorption analysis [28]. The sorption isotherms of samples are shown in Figure 2.…”

Electromagnetic and microwave absorption characteristics of PMMA composites filled with a nanoporous resorcinol formaldehyde based carbon aerogel

“…Structural properties, chemical functionality as well as particle size distribution (PSD) are some special intrinsic characteristics having the dominant effect on the electromagnetic properties of these types of absorbents. 4,8,[18][19][20][21] For example, Huang et al 22 investigated the effect of pore texture of sol-gel derived resorcinol-furfural on EM characteristics of the mesoporous carbons. It was concluded that the synthesized porous carbons with a cage-like structure exhibited interesting electromagnetic properties in terms of the real and imaginary parts of the permittivity.…”

“…The two broad peaks positioned at 2q ¼ 24 and 42 correspond to the reections of (002) and (100) planes of graphite, respectively. 22,29,35 Since the peak intensity of d 002 plane in CAs is weak, it is concluded that the CAs structure consists of low degree of crystallinity.…”

“…3,8,24 Moreover, in addition to general absorption mechanisms, multiple reections of microwaves in CAs composites also lead to an additional loss mechanism of EM energy, which is based on the interference of reected waves inside CAs particles. 8,18,22,48,52 In comparison with the typical carbon-based absorbers, depends on synthesis procedure CAs possess pores with different sizes and shapes within their structure, which could provide additional pathway for the absorption of EM waves. 22 Hence, under the above circumstances, preparation of CAs composites with larger particle sizes results in better impedance matching condition under which the EM waves are retract and attenuate when penetrate through the carbon particles.…”