The effect of ZnCl2 activation on microwave absorbing performance in walnut shell-derived nano-porous carbon

Synthesis and applications of biomass-derived porous carbon materials in energy utilization and environmental remediation

Renewable biomass and its waste are considered among the most promising applications materials owing to the depletion of fossil fuel and concerns about environmental pollution. Notably, advanced porous carbon materials derived from carbon-rich biomass precursors exhibit controllable pore structures, large surface areas, natural microstructures, and abundant functional groups. In addition, these three-dimensional structures provide sufficient reaction sites and fascinating physicochemical properties that are conducive to heteroatom doping and functional modification. This review systematically summarizes the design methods and related mechanisms of biomass-derived porous carbon materials (BDPCMs), discusses how the synthesis conditions influence the structure and performance of the carbon material, and emphasizes the importance of its use in energy utilization and environmental remediation applications. Current BDPCMs challenges and future development strategies are finally discussed to provide systematic information for further synthesis and performance optimization, which are expected to lead to novel ideas for the future development of bio-based carbon materials.

Facile One-Step Pyrolysis of ZnO/Biochar Nanocomposite for Highly Efficient Removal of Methylene Blue Dye from Aqueous Solution

In this work, we developed a facile one-step pyrolysis method for preparing porous ZnO/biochar nanocomposites (ZBCs) with a large surface area to enhance the removal efficiency of dye from aqueous solution. Peanut shells were pyrolyzed under oxygen-limited conditions with a molten salt ZnCl2, which played the roles of the activating agent and precursor for the formation of nanoparticles. The effects of the mass ratio between the molten salt ZnCl2 and peanut shells as well as pyrolysis temperature on the formation of ZBCs were investigated. Characterization results revealed that the as-synthesized ZBCs exhibited a highly porous structure with a specific surface area of 832.12 m2/g, suggesting a good adsorbent for efficient removal of methylene blue (MB). The maximum adsorption capacity of ZBCs on MB was 826.44 mg/g, which surpassed recently reported adsorbents. The formation mechanism of ZnO nanoparticles on the biochar surface was due to ZnCl2 vaporization and reaction with water molecules extracted from the lignocellulosic structures. This study provides a basis for developing a simple and large-scale synthesis method for wastewater with a high adsorption capacity.

High-performance multifunctional porous iron Acetylacetonate/N, O-doped carbon nanospheres for electromagnetic wave absorption at 2-18 GHz and methyl orange absorption

Nowadays, multifunction is regarded as an advanced development direction of new-generation electromagnetic wave absorption (EMWA) materials to fulfill the ever-growing demands in complex environment and situation. Environmental pollution and electromagnetic pollution are all difficult problems for human beings all the time. Now, there is no multifunctional materials for collaborative treatment of environmental and electromagnetic pollution. Herein, We synthesized nanospheres with divinyl benzene (DVB) and N-[3-(dimethylamino)propyl]methacrylamide (DMAPMA), using a simple one-pot method. After calcination at 800 ℃ in N₂, porous N, O-doped porous carbon materials were prepared. By regulating the mole ratio of DVB and DMAPMA, the ratio was 5:1 reached excellent EMWA property. Remarkably, the introduction of iron acetylacetonate into the reaction of DVB and DMAPMA was effective in enhancing the absorption bandwidth to 8.00 GHz at a 3.74 mm thickness, which depended on the synergistic effects from dielectric and magnetic losses. Simultaneously, the Fe-doped carbon materials had a methyl orange adsorption capacity. The adsorption isotherm conformed to the Freundlich model. After methyl orange absorption, the EMWA property did not greatly change. Thus, this research paves the way for the creation of multifunctional materials to solve environmental pollution and electromagnetic pollution together.

Recent progress in biomass-derived carbonaceous composites for enhanced microwave absorption

Carbonaceous microwave absorbing materials are in vital demand due to the extensive electromagnetic pollution in 5G network era and urgent requirements for stealth technology in national defense domain. Rather than the complicated vapor deposition method, a simple biomass-derived approach sheds light on the mass production of carbon materials for its ubiquitous, environmental-friendly, cost-off, and sustainable advantages. Herein, a concise review of recent advances in designing carbonaceous materials for EM attention is provided with particular stress on the biomass categories and the synthetic method. The three dimensional (3D) interconnected network of carbon materials are highlighted in analysis regarding the biomass selection, functional process, pore-forming strategy and the microwave absorption performance of the corresponding composites. Nature fiber-derived carbon materials, possessing high-aspect ratio fiber structure, are also discussed due to their potential in weaving manufacture and diverse application for flexible cloaking fabric. In the end, the current challenge and the directional perspective for utilizing biomass-derived carbon absorbing materials with effective EM properties are outlined.

MoS2 nanoparticle/activated carbon composite as a dual-band material for absorbing microwaves

In the search for novel high-performance microwave (MW) absorbers, MoS2 has shown promise as a MW-absorbing material, but its poor impedance matching limits its applications. Herein, a facile hydrothermal method was used to produce a composite consisting of activated carbon (AC) derived from waste biomass and in situ-grown MoS2 nanoparticles. Its microwave absorption properties were examined in the 2-18 GHz frequency range, and FESEM and HRTEM images confirmed the formation of MoS2 nanoparticles on the AC. The maximum reflection loss (RLmax) for the MoS2/AC composite was -31.8 dB (@16.72 GHz) at 20 wt% filler loading. At 50 wt% filler loading, the MoS2/AC (MAC50) composite exhibited unique dual-band absorption characteristics in the C and Ku bands. An effective absorption bandwidth (RL < -10 dB) of 10.4 GHz (3-5.2 GHz, 9.8-18 GHz) was achieved at various thicknesses that covered the entire Ku band. Therefore, a sole dielectric absorber can easily be tuned to absorb MWs at multiple frequency ranges. The large surface area and conduction losses of AC combined with the superior dielectric loss properties of MoS2 resulted in improved impedance matching and attenuation ability of the MoS2/AC composite. Thus, MoS2/AC is a promising low-cost dielectric absorber for MW absorption applications.

Natural iron embedded hierarchically porous carbon with thin-thickness and high-efficiency microwave absorption properties

The traditional strategy for fabricating transition metal/carbon composite microwave absorbing materials (MAMs) is to combine different metallic salts and carbon precursors via various techniques, in which raw material waste and environmental pollution are inevitable. In this work, without addition of any metallic salts, natural iron embedded hierarchically porous carbon (HPC) composites are synthesized for the first time via facile pyrolysis and subsequent “reductive activation” with KOH. Using KOH to react with carbon to generate H₂ can not only generate abundant nanoscale structures in the composites, but also in situ reduce the natural iron present in the bio-precursor to Fe nanoparticles, which facilitates the interfacial polarization and conductive loss of samples considerably. In turn, the modulation of graphitization degree could be realized by simply adjusting the ingredient ratio. Due to the synergistic effect between porosity and graphitization degree, the impedance matching of composites can be well regulated. The reflection loss of HPC-1 achieves −53.6 dB and the effective absorption bandwidth can cover the whole X and Ku bands with a thickness of only 1.4–2.4 mm. This study may pave a way to research on using bio-precursors rich in iron to synthesize high-efficiency and thin–thickness microwave absorbers and promote the diversified development of bio-derived materials in a gentle and facile way.

Natural iron embedded HPCs are prepared using “reductive activation” with KOH for the first time, and exhibit excellent microwave absorption.

Multifunctional Bulk Hybrid Foam for Infrared Stealth, Thermal Insulation, and Microwave Absorption

Taking serious microwave pollution issues and the complex application environment into consideration, it is quite urgent to integrate several functions into one material. Electromagnetic (EM) absorbing materials with multiple functions are highly attractive to next-generation wireless techniques and portable electronic devices. Herein, melamine foam provides a decent platform for the uniform growth of Co-based metal-organic frameworks (MOFs), which bring the as-obtained hybrid foam with three-dimensional porous network structure and combination of dielectric along with magnetic attenuation abilities as advanced materials in multifunctional fields. Remarkably, the relevant microwave absorption (MA) performance of the hybrid foam can reach an extremely high reflection loss value of -59.82 dB. Furthermore, the hybrid foam exhibits excellent infrared stealth and optimiztic heat insulation function, demonstrating the potential in plenty of practical applications. These results may arouse interests and inspirations of the elaborately design and facilely synthesis of high-performance foamlike microwave absorbers with multiple functions.

Silica-Modified Ordered Mesoporous Carbon for Optimized Impedance-Matching Characteristic Enabling Lightweight and Effective Microwave Absorbers

Ordered mesoporous carbon (OMC) is considered to be a prospective carbon-based material for microwave absorption because of its abundant well-ordered mesoporous structures, high specific surface area, numerous active sites, and facile preparation process. However, its development has been seriously hindered by its poor impedance-matching characteristic. Herein, silica-modified OMC composites with a designable impedance-matching transition layer are successfully fabricated via a self-assembly method and succeeding calcination treatment. In addition, the silica in OMC@SiO₂ composites can maintain the mesoporous structure, which facilitates the scattering and reflection of microwaves in the tunnel structure. The as-prepared sample OMC-5@SiO₂ exhibits a minimum reflection loss (RL) value of -40.7 dB at 10.8 GHz with 2 mm and an effective absorption bandwidth (RL ≤ -10 dB) of 4.8 GHz with a thinner absorber thickness of 1.5 mm. We believe that the as-prepared OMC@SiO₂ composites can be prospective candidates as high-efficiency and lightweight microwave absorbers.

Broadband microwave absorber constructed by reduced graphene oxide/La0.7Sr0.3MnO3 composites

High-performance microwave absorbing materials require optimized impedance matching and high attenuation ability. Here we meet the challenge by incorporating electric loss with magnetic loss materials to prepare carbon-based/magnetic hybrids. The reduced graphene oxide (rGO)/La0.7Sr0.3MnO3 (LSMO) composites were prepared by dispersing the LSMO powders into 4.25, 6.25, 8.16, and 10 wt% of the graphene oxide aqueous solution, then the rGO/LSMO composites were formed by hydrothermal method. The pure rGO, LSMO, and rGO/LSMO composites were studied using X-ray diffraction and SEM. Microwave absorption properties were investigated by using coin method. Simulation studies show that 6.25 wt% of rGO/LSMO in a wax matrix exhibits the strongest reflection loss of -47.9 dB @ 10.7 GHz at a thickness of 2.5 mm. Moreover, the effective absorption bandwidth with the reflection loss below -10 dB is up to 14.5 GHz, ranged from 3.5 to 18 GHz for the composites with a thickness of 1.5-5.5 mm, due to a synergism between dielectric loss of rGO and magnetic loss of magnetic LSMO, which is an interesting exploration in the applications of rGO and LSMO. This method can be extended to design and fabricate hybrid absorbers with effective microwave absorption.

Porous carbon material derived from fungal hyphae and its application for the removal of dye

A highly porous carbon material based on fungal hyphae was prepared using mixed alkali and its application for removal of dye investigated.