Study on ultralight and flexible Fe3O4/melamine derived carbon foam composites for high-efficiency microwave absorption

Enhanced electromagnetic wave absorption of bacterial cellulose/ reduced graphene oxide aerogel by eco-friendly in-situ construction

Electromagnetic wave absorption materials (EWAMs) have become an effective means to address electromagnetic (EM) radiation and enhance stealth technology, among which aerogels are valued for their lightweight nature and excellent designability. This study utilized environmentally friendly preparation and in-situ reduction techniques to fabricate bacterial cellulose (BC) / reduced graphene oxide (RGO) aerogels, achieving tailored EM wave loss capabilities by controlling the reduction time of ascorbic acid. Benefitting from the effects of freeze-casting, BC winding, hydrogen bond, and RGO layers coupling, the aerogel maintains their original structure after reduction and exhibits satisfactory EM wave absorption. The minimum reflection loss (RLmin) is -38.52 dB, with an effective absorption bandwidth (EAB) of 6.68 GHz and a maximum radar cross section (RCS) reduction of 44.69 dBsm. Additionally, the aerogel's lightweight (a low density of 9.03 mg/cm3) and outstanding thermal insulation properties enable it to adapt to complex conditions. Thus, the study provides a novel approach for the construction of industrialized and sustainable RGO-based EWAMs.

Ultra-flexible silver/iron nanowire decorated melamine composite foams for high-efficiency electromagnetic wave absorption and thermal management

Nowadays, functional electronic devices with excellent flexibility and thermal management capability for effective electromagnetic wave absorption are urgently in demand. Herein, a novel and highly flexible silver nanowire (AgNW)/iron nanowire (FeNW) decorated melamine composite foam (AgFe-MF) was prepared via simple dip-coating process. Owing to optimal impedance matching, synergistic dielectric and magnetic losses as well as three-dimensional porous structure, the AgFe-MF with an ultra-low filler content (0.22 vol%) exhibited an outstanding minimum reflection loss of -69.61 dB, and the best effective absorption bandwidth (EAB) could reach up to 6.37 GHz. Importantly, the EAB of long-time working AgFe-MF was enhanced to 7.01 GHz after 1000 compress-release cycles under 40 % strain. Besides, it also featured considerate Joule heating capacity and achieved a saturation temperature of over 85.7 ℃ under 2.6 V voltage. The impressive thermal isolation and long-term stability ensured the safety used as portable heater. Therefore, this work will provide a vital slight for fabricating smart wearable electronic devices with integrated anti-electromagnetic radiation and personalized thermal management performances towards potential thermal and health threats.

Synthesis of NiCo-BNSA/RGO/MDCF with three-dimensional porous network structure as an excellent microwave absorber

Melamine-derived carbon foam (MDCF) and nickel-cobalt bimetallic nanosheet arrays (NiCo-BNSA) possess unique porous structures and excellent microwave absorption (MA) properties, making them potentially useful in MA applications. In this investigation, we fabricated NiCo-BNSA/reduced graphene oxide/MDCF (NiCo-BNSA/RGO/MDCF) composites utilizing a two-stage synthesis protocol. This process incorporated melamine foam (MF) pretreatment, carbonization, and a subsequent in-situ growth stage, resulting in the creation of a three-dimensional porous network structure. By adjusting the RGO volume, we were able to manipulate the structure and composition of the NiCo-BNSA/RGO/MDCF composites, leading to an enhancement in their MA performance. It was also observed that the NiCo-BNSA was evenly distributed on the surface of both the RGO and MDCF. The composites exhibited an optimal reflection loss (RLmin) of -67.8 dB at a thickness of 2.50 mm, and by varying their thickness, the effective absorption bandwidth (EAB, RL ≤ -10 dB) extended to 9.80 GHz, encompassing the entire C and X bands. This study presents a novel approach for fabricating lightweight and efficient carbon-based MA composites.

Hydroxyl-modified zirconia/porous carbon nanocomposite used as a highly efficient and renewable adsorbent for removal of carbamazepine from water

Metal-organic frameworks (MOFs) derived metal oxides/porous carbon nanocomposites were used as adsorbents to remove pollutants from wastewater. The adsorption performance of the metal oxides/porous carbon nanocomposites could be improved by introducing functional groups. In this study, hydroxyl-modified zirconia/porous carbon nanocomposite (C-UiO-66-OH) was prepared and tested, choosing carbamazepine as a typical pollutant. The results showed that the adsorption capacity (186.21 mg g^-1) of C-UiO-66-OH was 6.96 times to that of normal UiO-66. The Langmuir isotherm model and pseudo-first-order kinetic model was well fit the adsorption process. The thermodynamic parameters indicated that the adsorption process was spontaneous and endothermic. The adsorbent regeneration could be accomplished by washing C-UiO-66-OH with ethanol and DI water. The good adsorption/desorption performance comes from the synergistic effect of (EDA) interaction and hydrogen bond between C-UiO-66-OH and CBZ molecule. A membrane prepared by immobilizing C-UiO-66-OH into melamine foam (MF) with sodium alginate (SA) was also investigated for CBZ adsorption. The results indicated the excellent removal efficiency (86.0%) and good regeneration of the prepared membrane. Therefore, this paper provides an efficient and applicable way to remove CBZ from water.

Synthesis of Lightweight Renewable Microwave-Absorbing Bio-Polyurethane/Fe3O4 Composite Foam: Structure Analysis and Absorption Mechanism

Sustainable renewable polymer foam used as a lightweight porous skeleton for microwave absorption is a novel strategy that can effectively solve the problems of the large surface density, high additive amount, and narrow absorbing band of absorbing materials. In this article, novel renewable microwave-absorbing foams were prepared using Sapiumse biferum kernel oil-based polyurethane foam (BPUF) as porous matrix and Fe₃O₄-nanoparticles as magnetic absorbents. The microstructure and the microwave absorption performance, the structural effects on the properties, and electromagnetic mechanism of the magnetic BPUF (mBPUF) were systematically characterized and analyzed. The results show that the mBPUF displayed a porous hierarchical structure and was multi-interfacial, which provided a skeleton and matching layer for the Fe₃O₄ nanoparticles. The effective reflection loss (RL ≤ −10 dB) frequency of the mBPUF was from 4.16 GHz to 18 GHz with only 9 wt% content of Fe₃O₄ nanoparticles at a thickness of 1.5~5 mm. The surface density of the mBPUF coatings was less than 0.5 kg/cm² at a thickness of 1.8 mm. The lightweight characteristics and broadband absorption were attributed to the porous hierarchical structures and the dielectric combined with the magnetic loss effect. It indicates that the mBPUF is a prospective broadband-absorbing material in the field of lightweight stealth materials.

Controllable graphitization degree of carbon foam bulk toward electromagnetic wave attenuation loss behavior

The graphitization degree is of great importance for determining the electromagnetic (EM) wave attenuation loss behavior. The conductive loss is considered to be the mechanism resulting from tailoring the graphitization degree. There is a lack of in-depth research on the dipole polarization caused by defects and functional groups and the interface polarization caused by graphite/amorphous carbon. Herein, lightweight carbon foam (CF) bulk derived from mesophase pitch was prepared to clarify the effect of the graphitization degree systematically. The results demonstrate that with an increase graphitization degree, the interfacial polarization improves and dipole polarization decreases. The synergistic effect of conduction loss and dipole and interfacial polarization dominates the impedance matching and further changes the EM loss behavior of CFs. Particularly, the minimum reflection loss is - 16.69 dB and effective absorption bandwidth is 3.63 GHz, the EM interference shielding effectiveness attains 35.13 dB and the compressive strength is up to 11.73 MPa when the optimal graphitization degree is achieved. Therefore, this work elucidates the effect of the interface polarization of graphite/amorphous carbon, thus providing a valuable insight into the design of advanced carbon-based materials for EM wave absorption and shielding.