Enhanced Absorption Performance Research Articles

Self-Reactive Carbon Dioxide Absorbent with Sodium Carbonate-Based Hydrogel.

Sodium carbonate is an abundant, low-cost, and low-hazard raw material widely used as a food additive and CO2 absorbent in the food industry. However, its application in food packaging is limited because it is used in solid form, either in sachets or as a compounding ingredient in plastics. Solid sodium carbonate requires an external moisture supply for CO2 absorption, with its performance dependent on moisture availability. This limitation hinders its commercialization in food packaging applications. We developed a sodium carbonate-based, self-reactive CO2 absorbent hydrogel incorporating polyacrylic acid sodium salt (PAAS). This sodium carbonate hydrogel (SCH-PAAS) exhibits self-reactivity, eliminating the need for external moisture, and demonstrates a high CO2 absorption capacity. PAAS incorporation facilitates the formation of a porous structure during gel solidification through reactions with CO2. Increased PAAS content accelerates CO2 absorption rates, particularly under low-temperature conditions (10 °C and 25 °C). Notably, absorption was faster at 10 °C than at 25 °C. The proposed SCH-PAAS exhibits a significantly enhanced absorption performance at low temperatures compared to conventional sodium carbonate-based materials, which exhibit reduced efficiency under such conditions. The increased gas-liquid contact area in SCH-PAAS makes it highly suitable for fresh food packaging applications, particularly under low temperatures.

Piperazine induced enhancement of absorption performance and degradation resistance in biphasic CO2 capture system

Piperazine induced enhancement of absorption performance and degradation resistance in biphasic CO2 capture system

An ultra-broadband multi-layer dielectric gradient honeycomb microwave absorber enhanced by the double layer metasurface

A novel, 12 mm multilayer dielectric gradient honeycomb absorber (MGHA) was designed, fabricated and analyzed with a double layer metasurface consisting of a resistive film and an artificial magnetic conductor (AMC) checkerboard. Despite its thin profile, the MGHA demonstrates significantly enhanced absorption performance across a wide frequency range due to the impedance of the composite structure. Furthermore, two distinct metasurfaces are integrated into the dielectric gradient multilayer honeycomb absorber to further enhance its low-frequency properties without increasing thickness. This structure exhibits wideband absorption from 2.8 GHz to 18 GHz, featuring three absorption peaks at 3 GHz, 11 GHz and 16 GHz. The relative bandwidth can reach nearly 136.6 % of that achieved by a common honeycomb absorber with the same thickness, while maintaining an absorption peak reflection of about −22dB. The great attenuation of incident waves is attributed to Ohmic loss on the resistive film, electric resonance effect on the checkerboard, and magnetic resonance near 17 GHz on the checkerboard metasurface. The proposed MGHA structure holds significant potential for applications in aerospace and military.

Investigating Enhanced Microwave Absorption of CNTs@Nd0.15-BaM/PE Plate via Low-Temperature Sintering and High-Energy Ball Milling.

Composite plates comprising a blend of rare earth neodymium-(Nd) doped M-type barium ferrite (BaM) with CNTs (carbon nanotubes) and polyethylene WERE synthesized through a self-propagating reaction and hot-pressing treatment. The plates' microscopic characteristics were analyzed utilizing X-ray diffraction (XRD), Fourier transform infrared spectrophotometry (FTIR), thermo-gravimetric analysis (TGA), Raman, and scanning electron microscopy (SEM) analytical techniques. Their microwave absorption performance within the frequency range of 8.2 to 18 GHz was assessed using a vector network analyzer. It showed that CNTs formed a conductive network on the surface of the Nd-BaM absorber, significantly enhancing absorption performance and widening the absorption bandwidth. Furthermore, dielectric polarization relaxation was investigated using the Debye theory, analyzing the Cole-Cole semicircle. It was observed that the sample exhibiting the best absorbing performance displayed the most semicircles, indicating that the dielectric polarization relaxation phenomenon can increase the dielectric relaxation loss of the sample. These findings provide valuable data support for the lightweight preparation of BaM-based absorbing materials.

Research and simulation of electromagnetic wave absorbing performance for lightweight cement-based materials containing expanded polystyrene with different particle sizes and carbon black

The electromagnetic wave (EMW) absorbing performance of cement-based materials incorporating expanded polystyrene (EPS) with varying particle sizes is comprehensively studied through a combination of experimental and simulation methods. The addition of conductive carbon black (CB) to the cement matrix significantly increases the conductivity and dielectric constant, thereby improving the loss capacity. The frequency shift behavior of single and three-layer absorbing materials adheres to the effective medium theory and interference cancellation principle. The enhancement in overall EM parameters leads to a shift of the reflection loss (RL) peak towards lower frequencies. For three-layer materials, an increase in the thickness of absorbent layer proves beneficial for enhancing absorption performance. Simulations can effectively model cement-based materials by employing uniform material settings, with the size of EPS particles serving as the primary variable. The simulation results reveal that an increase in EPS particle size, in both single-layer and multi-layer materials, causes a shift of the RL peak towards lower frequencies. Additionally, analysis of electric field mode distribution and EM power loss density distribution indicates that scattering at the curved EPS interface alters the propagation direction of EMWs, increasing opportunities for loss inside the cement-based material. Moreover, the three-layer absorbing material, with a density ranging from 850 to 900 kg/m3 and compressive strength exceeding 4 MPa, is suitable for EMW absorption in building envelope structures. In conclusion, an increase in EPS particle size and CB content leads to a low-frequency shift of the RL absorption peak. This discovery not only provides an empirical foundation for the development of absorption materials tailored to specific frequency bands but also offers an efficient approach for repurposing waste EPS of diverse sizes. Furthermore, the grading of EPS with different particle sizes has important practical significance for increasing the content of EPS and preparing lightweight cement-based materials.

Ultra-wideband microwave absorber based on multilayer patterned resistive film

In this work, two ultra-wideband microwave absorbers are proposed. The absorptivity of the proposed original absorber can achieve 90% in a wide bandwidth from 2.41 GHz to 18 GHz at normal incidence. This design has been extended to enhance absorption performance and angular stability by respectively incorporating a high-dielectric substrate and adding metal vias. As a result, the absorptivity of over 90% can be achieved from 0.6 to 18 GHz in transverse magnetic (TM)-incident cases even if the incident angle goes up to 60°, which realizes a relative bandwidth of 153%. While in the transverse electrical (TE) polarization, the absorption of the new absorber performs better than the original one in the entire operational bandwidth. A prototype of the proposed absorber is fabricated and measured, good agreement is obtained between measured and simulated results, indicating the usability of our design in practical electromagnetic wave absorbing scenes.

Preparation of MOFs-derived Ni/NPC materials and absorption properties

In order to solve the problems of electromagnetic pollution, it is urgent to prepare excellent microwave absorbing materials. A solvent-thermal method is employed to synthesize the precursor Ni-MOF-74, followed by carbonization treatment at different temperatures to prepare Ni/NPC material with a porous carbon encapsulation structure. The results indicate that, with the variation of carbonization temperature, the absorption performance of Ni/NPC composite material reaches its optimum at 700 ℃. At a frequency of 17.36 GHz, the minimum reflection loss is −38.4 dB, and the effective absorption bandwidth is 2.61 GHz (15.39–18 GHz). Studies on the absorption mechanism reveal that multiple reflections of electromagnetic waves, interface polarization losses, and resonance are the main contributing factors to the enhancement of absorption performance.

Tailoring Microwave Absorption Performance Using Tunable Core–Shell CoNi Alloy Nanospheres

In contemporary research endeavors, we have successfully synthesized a composite material endowed with extraordinary microwave absorption properties through a meticulously designed process involving the encapsulation of transition metal nanoparticles with a phenolic resin layer. This innovative material, centered around a core–shell architecture, boasts the incorporation of transition metals Co and Ni, presenting a systematic exploration of their compositional influence on the material’s wave absorption characteristics. Our investigation unravels a sophisticated interplay between alloy composition and microwave absorption performance. Noteworthy observations reveal a non-linear correlation between nickel content and absorption efficiency, where an initial decline precedes a subsequent augmentation. Intriguingly, this dynamic behavior is accompanied by a gradual shift in the absorption peak towards lower frequencies, elucidating the tunable nature of the material’s performance. Crucially, the pinnacle of absorption efficiency is attained at a precisely tuned Co:Ni ratio of 2:1, underscoring the significance of alloy composition in tailoring the material’s electromagnetic response. At an absorber thickness of 2.1 mm, our engineered material achieves a remarkable minimum reflection loss (RL) of −46.1 dB at a frequency of 13.5 GHz. This achievement is coupled with an impressive effective absorption bandwidth spanning 5.5 GHz, indicative of the material’s versatility and applicability across a wide frequency range. The results not only highlight the efficacy of the core–shell CoNi alloy composites but also emphasize the importance of meticulous composition control in achieving optimal microwave absorption performance. The work reported here presents a notable advancement in the synthesis of tunable microwave-absorbing materials, showcasing the potential for tailored electromagnetic responses. The intricate relationship between alloy composition and absorption characteristics elucidated in this study opens avenues for the development of radar-absorbing materials that meet the evolving demands of reduced thickness, light weight, and enhanced absorption performance across diverse frequency ranges.

Facile fabrication of biomass chitosan-derived magnetic carbon aerogels as multifunctional and high-efficiency electromagnetic wave absorption materials

Biomass chitosan-derived porous carbon-based materials take the advantage of light weight, adjustable intrinsic conductivity, and environmental friendliness, attracting more attention in the field of electromagnetic compatibility. However, exploring a facile fabrication method to achieve rational structure design and electrical-magnetic coupling for electromagnetic absorption performance enhancement still remains challenging. Here, a unique honeycomb-like porous cobalt/carbon aerogel is fabricated through the directional freezing-drying and carbonization process, and abundant and even-distributed cobalt particles in-situ grow on the carbon skeletons. The aerogel exhibits an impressive electromagnetic wave absorption performance of a −75.8-dB absorption intensity and a −256.9-dB mm−1 specific reflection loss at a low filling content (10%), as well as an 8.53-GHz effective absorption bandwidth. Besides, the aerogel also demonstrates classy radar stealth and thermal insulation performance. The eco-friendly, easily fabricated, and high-performance cobalt/carbon aerogel suggests broad application prospects for electromagnetic compatibility and protection, thermal management, and multifarious electron devices.

Fabrication of a large scale metasurface with high resolution and enhanced absorption

Plasmonic metasurface nanostructures have the potential to enable nonlinear optical functionality in metasurfaces by reducing power operating thresholds and enabling ultra-thin subwavelength devices. However, low absorption caused by resistive losses of unwanted metallic appearance and irregular corners in the fabrication process significantly reduces this promise, leading the metasurface community toward the new approaches to fabricate large area metasurfaces with Electron Beam lithography (EBL). In this article, with controlled proximity effect and high dose exposure rate in EBL setup, large area (2 cm2) metasurfaces are fabricated with high resolution of structure. The effect of absorption resonance in Infrared (LWIR) is experimentally studied through Fourier Transform Infrared Spectroscopy (FTIR). The results signify that the metasurface with high resolution and fine metallic corners outperforms the fabricated prototype with metal residue and non-uniform corners. When compared to conventional EBL, our nanofabrication approach speeds the patterning time by three times. The experimental measurements reveal enhanced absorption performance at 8 µm wavelength. Whereas, the developed metasurface is numerically studied to explain the absorption performance with plasmonic field distributions. This approach could be used in optoelectronic devices involving plasmonic applications, such as biosensing and infrared imaging.

Microwave absorption performance enhancement of NiFe2O4/GNs composite with hollow hexagonal-like structure

It is a major aspect in the field of absorbing materials to obtain composite absorbing materials with prominent absorbing properties through shape design. In this paper, a hollow hexagonal NiFe2O4/GNs composite absorbing material was prepared by a simple hydrothermal method. The test results show that the minimum reflection loss of the composite can reach −57.4 dB at the low frequency of 6.08 GHz, and the corresponding thickness is 2.9 mm; When the hydrothermal reaction temperature is 200 ℃, the maximum effective absorption bandwidth is 3.12 GHz, and the thickness is as thin as 1.1 mm. With the increase of hydrothermal reaction temperature, the morphology of nickel ferrite gradually changed from round rod to hollow hexagonal prism, and the microwave absorption characteristics of the composite also varied and adjusted. This paper provides the preparation process of NiFe2O4/GNs composites with controllable morphology, and possesses a certain reference for the study of the interaction mechanism of ferrite and graphite nanosheets composite microwave absorbing materials. In addition, the sample has excellent microwave absorption performance in the low-frequency band, while the current wave absorption band of ferrite composites is mainly in the high-frequency band, so the sample has great research and development potential in the field of low-frequency microwave absorbing materials.

Broadband-absorption mechanism in a water-based metamaterial absorber

Bulky water has been used to construct broadband metamaterial absorbers (MAs). Herein, a broadband MA using sheet of water instead of bulky water is proposed for terahertz domain. The proposed structure has excellent stability to wide incident angles. Most important, the proposed structure surpasses those based on bulky water in terms of absorption performance. The distributions of field and power loss are investigated, which reveal that power loss is mostly contributed by magnetic resonance occurring at the borders of water and PDMS and thus broadband absorption is dependent on the contact area of water and its surrounding dielectric. Therefore, the designed absorber based on sheet of water is superior due to larger contact area. This provides an enlightenment that maximizing contact area between water and its surrounding dielectric such as using sheet of water can enhance absorption performance in the design of water-based MAs, which can facilitate the design. The results of this work may be directive and helpful for designing water-based broadband absorbers.

Enhanced Absorption Performance of Dye-Sensitized Solar Cell with Composite Materials and Bilayer Structure of Nanorods and Nanospheres

The concept of localized surface plasmon resonance has been applied to increase the absorption efficiency of dye-sensitive solar cells (DSSCs) by using various photoanode structures. A three-dimensional model for a photoanode of the DSSC based on composite materials was developed using COMSOL Multiphysics. Spherical-, rod- and triangular-shaped aluminum nanoparticles were employed in the core of SiO2 to examine the influence of morphology on the performance of DSSCs in the 350–750 nm wavelength range. The UV-Vis absorption results indicated that aluminum nanoparticles with spherical, rod and triangle morphologies had 39.5%, 36.1% and 34.6% greater absorption capability than aluminum-free nanoparticles. In addition, we investigated the effect of plasmonic absorption in DSSCs for photoanodes made of TiO2, SiO2 and bilayer TiO2/SiO2 with and without covering aluminum nanoparticles. The TiO2 and SiO2 nanoparticles had fixed diameters of 90 nm each. The UV-Vis absorption and Tauc curves indicated that the TiO2/SiO2 bilayer structure (with and without aluminum nanoparticles) had greater absorption and lower bandgap energies than individual TiO2 and SiO2 nanoparticles. Furthermore, bilayer photoanode nanostructures were investigated based on nanospheres and nanorods for core–shell Al@SiO2 nanoparticles. The results indicated that a photoanode with nanorod/nanosphere structure had a 12% better absorption capability than a nanosphere/nanorod configuration. This improvement in absorption is attributed to the high surface area, which boosts dye loading capacity and long-term light capture, resulting in greater interaction between the dye and the photon. Our study develops core–shell nanoparticles with optimized shape and materials for bilayer photoanode structures in photovoltaic technology.

Study on Microwave Absorption Performance Enhancement of Metamaterial/Honeycomb Sandwich Composites in the Low Frequency Band.

With the rapid development of electronic technology and modern radar detection system, there is increasingly urgent demand for microwave absorbing composites working efficiently in the low frequency range (e.g., 1–2 GHz). In this work, a type of metamaterial/honeycomb sandwich composite (MHSC) was proposed and fabricated, which exhibited a light weight structure and excellent wave-absorbing performance in the low frequency band. The relationship between the wave-absorbing properties and the design parameters of the composite, such as the thickness of the wave-transmitting skin, the thickness and dielectric properties of the wave-absorbing honeycomb, was systematically investigated. The electromagnetic coupling interference between the honeycomb absorber and metamaterial resonator proved to be a crucial factor that affects synergistic wave-absorbing performance in the low-frequency band. Under the rational design, the incorporation of subwavelength-sized phase-gradient metamaterial units in the composite can significantly improve low-frequency wave-absorbing performance for greater than 5 dB (an increment larger than 100%); and the obtained MHSC exhibits averaged reflectivity (Ra) less than −10 dB in the low frequency band of 1–2 GHz as well as outstanding performance (Ra < −14.6 dB) over an extremely wide frequency range (1–18 GHz). The MHSC reported in this study could be a promising candidate for the key material in high-performance radar stealth and other related applications.

Absorption properties of a multilayer composite nanoparticle for solar thermal utilization

As the primary way of solar thermal utilization, direct absorption solar collector (DASC) is attracting widespread attention. Nanofluids have good development prospects in DASC due to their excellent absorption and heat transfer properties. In this study, a three-layer cylindrical Ag-SiO2-Ag composite nanoparticle is proposed. The advantages of Ag-SiO2-Ag nanoparticle are proved by comparing the absorption performance with other materials and the same structure of sterling silver. The maximum absorption peak of the nanoparticle is 2.28 times that of the silver nanoparticle. At the same time, the influence of the size parameters of composite nanoparticle on the absorption performance is also discussed, which has an important reference value for the sensitive tuning of composite nanoparticle in different scenarios. Finally, the reasons for the enhanced absorption performance of the composite nanoparticle are revealed by analyzing the electromagnetic field distribution around the nanoparticle. The composite nanoparticle makes full use of various electrical and magnetic resonance modes to excite the three absorption peaks in 390 nm, 470 nm and 780 nm, thus improving the absorption performance of the nanoparticle. The composite nanoparticle proposed has positive significance for promoting the development of high-performance DASC.

Construction of Co/C@MoS2 core–shell nanocubes with enhanced electromagnetic-wave absorption performance

This investigation is aimed at obtaining superior electromagnetic wave (EMW) absorbers and we successfully prepared the core–shell-structured Co/C@MoS2 nanocubes comprising Co/C nanocubes tightly coated with uniform MoS2 nanosheets for the first time. The MoS2 nanoshells of the Co/C@MoS2 enabled the optimization of the impedance matching and generation of dipolar polarizations. The Co/C cores also increased the conductivity of the resultant Co/C@MoS2 composites, thus promoting the attenuation ability of the EMW. The synergetic contributions of improved impedance matching and multiple loss mechanisms led to excellent EMW absorption of the Co/C@MoS2. In particular, the reflection loss of the Co/C@MoS2 reached − 52.76 dB at 8.88 GHz for a 2.5-mm-thick absorber while the effective attenuation bandwidth under − 10 dB was 3.84 GHz for a 1.5-mm-thick absorber. Accordingly, the prepared Co/C@MoS2 with enhanced absorption performance is a promising absorber and we also proposed a facile design and synthesis strategy for new EMW absorbers in this paper.

Ultralight and Low-Cost Structural Absorbers With Enhanced Microwave Absorption Performance Based on Sustainable Waste Biomass

As a practical microwave absorber, besides satisfying the basic broadband absorption performance, the density, cost, and process complexity are considerable factors in radar stealth and electromagnetic protection fields as well. Here, a simple and economical structural absorber (SA) is proposed to remarkably broaden the absorption bandwidth of biochar from banana peel. By optimizing the size parameters of the unit cell, the optimal SA shows more than 90&#x0025; absorption in the frequency range from 3.4 to 18 GHz by employing a lightweight porous carbon derived from sustainable biomass. The lightweight porous biochar provides the SA low-density properties with a surface density of only 0.574 <inline-formula> <tex-math notation="LaTeX">$\text{g}\cdot $ </tex-math></inline-formula>cm<inline-formula> <tex-math notation="LaTeX">$^{-2}$ </tex-math></inline-formula>. In such a SA, the greatly enhanced absorption performance mainly originates from the synergistic effect of microscopic and macroscopic scales. By optimizing the pattern design of the SA, the effective impedance is matched with free space in a wide frequency range, thus dissipating more electromagnetic waves through multiple resonances and edge scattering effects. In addition, whether transverse electric or transverse magnetic polarizations, stable broadband absorption can be maintained in a wide incidence angle. Thus, this work provides a new prospect for waste utilization of banana peel and a facile low-cost route to greatly extend the microwave absorption bandwidth.

Enhancing Absorption Performance of CO2 by Amine Solution through the Spiral Wired Channel in Concentric Circular Membrane Contactors.

The CO2 absorption rate by using a Monoethanolamide (MEA) solution through the spiral wired channel in concentric circular membrane contactors under both concurrent-flow and countercurrent-flow operations was investigated experimentally and theoretically. The one-dimensional mathematical modeling equation developed for predicting the absorption rate and concentration distributions was solved numerically using the fourth Runge–Kutta method under various absorbent flow rate, CO2 feed flow rate and inlet CO2 concentration in the gas feed. An economical viewpoint of the spiral wired module was examined by assessing both absorption flux improvement and power consumption increment. Meanwhile, the correlated average Sherwood number to predict the mass-transfer coefficient of the CO2 absorption mechanisms in a concentric circular membrane contactor with the spiral wired annulus channel is also obtained in a generalized and simplified expression. The theoretical predictions of absorption flux improvement were validated by experimental results in good agreements. The amine solution flowing through the annulus of a concentric circular tube, which was inserted in a tight-fitting spiral wire in a small annular spacing, could enhance the CO2 absorption flux improvement due to reduction of the concentration polarization effect. A larger concentration polarization coefficient (CPC) was achieved in the countercurrent-flow operations than that in concurrent-flow operations for various operations conditions and spiral-wire pitches. The absorption flux improvement for inserting spiral wire in the concentric circular module could provide the maximum relative increment up to 46.45%.

Recent Progress of Sub-Nanometric Materials in Photothermal Energy Conversion.

Sub‐nanometric materials (SNMs) are an attractive scope in recent years due to their atomic‐level size and unique properties. Among various performances of SNMs, photothermal energy conversion is one of the most important ones because it can efficiently utilize the light energy. Herein, the SNMs with photothermal energy conversion behaviors and their applications are reviewed. First, a hydrothermal/solvothermal method for the synthesis of SNMs is systematically discussed, including the LaMer pathway and the cluster–nuclei coassembly pathway. Based on this synthetic strategy, many kinds of SNMs with different morphologies are successfully prepared, such as nanorings, nanowires, nanosheets, and nanobelts. These SNMs exhibit excellent photothermal performance under the laser or solar irradiation according to their different light absorption ranges. These enhanced absorption performances of SNMs are induced by the mechanism of plasmonic localized heating or nonradiative relaxation. Finally, the applications of the photothermal SNMs are illustrated. The SNMs with photothermal behaviors can be widely applied in the fields of solar vapor generation, biomedicine, and light‐responsive composites construction. It is hoped that this review can provide new viewpoints and profound understanding to the SNMs in photothermal energy conversion.

Acoustic performance optimization of a cementitious composite with a porous medium

This paper presents an optimization algorithm for band-gap maximization aimed at designing the porosity of a cementitious composite. Numerical analysis revealed the relationship between the composite porosity and band structure. With the utilization of gravels as the main aggregate, microbeads and a vesicant were also mixed to produce the porous cementitious composite, where correlative experiments were conducted on the mixture proportion. Digital microscope images were applied to evaluate the micro-construction details of the composite. The acoustic performance of the porous concrete was tested by an impedance tube. The results show that the maximum sound absorption coefficient of the phononic crystal composed of 4 mm gravels and surrounding microbeads can reach 90%. The frequency corresponding to the peak value is 1490 Hz, which is consistent with the frequency range of the band gap from theoretical derivation and simulation analysis. This developed methodology is expected to be applied to the design of cementitious structures to achieve sound absorption performance enhancement.