College of Materials Science and Engineering, Nanjing Tech University, Nanjing 210009, China.
Nanoscale. 2017 Jun 8;9(22):7408-7418. doi: 10.1039/c7nr02628e.
Lightweight microwave absorbing materials have drawn tremendous attention. Herein, nano-porous biomass carbon materials have been prepared by carbonization with a subsequent potassium hydroxide activation of walnut shells and the microwave absorption properties have also been investigated. The obtained samples have large specific surface areas with numerous micropores and nanopores. The sample activated at 600 °C with a specific surface area of 736.2 m g exhibits the most enhanced microwave absorption performance. It has the maximum reflection loss of -42.4 dB at 8.88 GHz and the effective absorption bandwidth (reflection loss below -10 dB) is 1.76 GHz (from 8.08 GHz to 9.84 GHz), corresponding to a thickness of 2 mm. Additionally, the effective absorption bandwidth can reach 2.24 GHz (from 10.48 GHz to 12.72 GHz) when the absorber thickness is 1.5 mm. Three-dimensional porous architecture, interfacial polarization relaxation loss, and the dipolar relaxation loss make a great contribution to the excellent microwave absorption performance. In contrast, the non-activated sample with lower specific surface area (435.3 m g) has poor microwave absorption performance due to a poor dielectric loss capacity. This comparison highlights the role of micropores and nanopores in improving the dielectric loss property of porous carbon materials. To sum up, porous biomass carbon has great potential to become lightweight microwave absorbers. Moreover, KOH is an efficient activation agent in the fabrication of carbonaceous materials.
轻质微波吸收材料引起了极大的关注。本文通过碳化和随后的氢氧化钾对核桃壳进行活化，制备了纳米多孔生物质碳材料，并研究了其微波吸收性能。所得样品具有大的比表面积和大量的微孔和纳米孔。在 600°C 下活化、比表面积为 736.2 m²/g 的样品表现出最增强的微波吸收性能。在 8.88 GHz 时，它具有最大的反射损耗-42.4 dB，有效吸收带宽（反射损耗低于-10 dB）为 1.76 GHz（从 8.08 GHz 到 9.84 GHz），对应于 2 mm 的厚度。此外，当吸收体厚度为 1.5mm 时，有效吸收带宽可达到 2.24 GHz（从 10.48 GHz 到 12.72 GHz）。三维多孔结构、界面极化弛豫损耗和偶极弛豫损耗对优异的微波吸收性能做出了巨大贡献。相比之下，比表面积较低（435.3 m²/g）的未活化样品由于介电损耗能力差，微波吸收性能较差。这种对比突出了微孔和纳米孔在提高多孔碳材料介电损耗性能中的作用。总之，多孔生物质碳在成为轻质微波吸收体方面具有巨大的潜力。此外，KOH 是制备碳质材料的有效活化剂。
