Porous Absorber Research Articles

High-performance honeycomb porous microwave absorbers: Gelatin-based carbon nanotube/nickel nanowire aerogels

Biomass-derived carbon absorbent materials have received significant attention due to their renewability, diverse sources, and ease of preparation. In this work, a honeycomb porous electromagnetic wave absorber with excellent performance was successfully prepared by blending gelatin and multi-walled carbon nanotubes (MWCNTs), followed by freeze-drying. Metallic nickel nanowires (NiNWs) were then introduced as a second phase using an in-situ growth method. The minimum reflection loss (RL) of the aerogel containing 8.06 wt% MWCNTs and 3.36 wt% NiNWs was −36.1 dB at a thickness of 3.1 mm, with the effective absorption bandwidth (EAB) covering the entire X-band. Additionally, the aerogel exhibited a very low density (36 mg/cm3) and remarkable strength, capable of supporting over 1658 times its weight for more than 24 h without deformation. These properties make it highly valuable for commercial use and provide new inspiration for the future development of biomass carbon-based electromagnetic absorbing materials.

Genipap Oil as a Natural Cross-Linker for Biodegradable and Low-Ecotoxicity Porous Absorbents via Reactive Extrusion.

Proteins derived from agroindustrial coproducts and a natural cross-linking agent (genipap oil containing genipin) were used to develop porous materials by reactive extrusion for replacing fossil-based absorbents. Incorporating genipap oil allowed the production of lightweight structures with high saline uptake (above 1000%) and competing retention capacity despite their porous nature. The mechanical response of the genipap-cross-linked materials was superior to that of the noncross-linked ones and comparable to those cross-linked using commercial genipin. The extruded products were hemocompatible and soil-biodegradable in less than 6 weeks. The compounds generated by the degradation process were not found to be toxic to the soil, showing a high bioassimilation capacity by promoting grass growth. The results demonstrate the potential of biopolymers and new green cross-linkers to produce fully renewable-based superabsorbents in hygiene products with low ecotoxicity. The study further promotes the production of these absorbents using low-cost proteins and continuous processing such as reactive extrusion.

High-Temperature Electrolysis with Superheated Steam Provided by Volumetric-Type Steam Generator

High-temperature steam is essential for operating solid oxide electrolysis cells (SOEC). This paper demonstrated a new type of high-temperature solar steam generator that uses ceramic foam as a porous absorber. Water is sprayed into the porous absorber as microdroplets by using a nozzle. Experiments show that the solar steam generator is capable of generating superheated steam beyond 800 oC. The peak thermal efficiency in the steady state can reach 60.92% under a mass flow rate of 2.359 kg/h corresponding to an outlet temperature of 877.3 oC. The superheated steam will be supplied to a SOEC system to generate hydrogen. Thus, a comprehensive model is developed in this paper to research the performance of the solar SOEC system under fluctuated solar irradiation

Towards topology optimisation of poroelastic materials using field-based heuristics

In passive noise control, it is well known that the shapes of acoustic porous material absorbers can be modified to achieve favourable resonances resulting in high sound absorption. However, finding the optimised shapes for a given sound field environment is challenging as it involves solving an inverse problem. Recently, the use of topology optimisation for designing the shapes of acoustic porous material absorbers has gained interest. Previous studies suggest that conventional gradient methods can often result in local optimal results that may be poorer in overall absorption than what can be achieved by using heuristic optimisation techniques. In this study, the use of field variables such as acoustic pressures and velocities in developing better heuristic optimisation methods are explored with the aim of avoiding cumbersome gradient computations. The acoustic shapes produced by the field-based heuristics are compared with traditional approaches to develop insights as to what patterns in the shape designs contribute to improved sound absorption in various target frequencies.

The frame around a test specimen and its influence on the measured sound absorption coefficient

For most practical cases of reverberation room measurements of sound absorption coefficient according to ISO 354:2003, the standard requires the edges of the test specimen to be covered by a reflective frame. The purpose of this requirement is to keep the edges of the test specimen from absorbing sound. While this statement is consistent with practical measurement results at medium to high frequencies, it has been shown that the low frequency performance of a high-absorbing test specimen worsens when a frame is not in place. To further investigate this phenomenon, a series of reverberation room measurements have been carried out on several variations of a porous absorber test specimen. The goal of the measurements has been to determine whether the size and dimensions of the test specimen affect the test results, and if any such affections are dependent on the presence of a frame. Additionally, the sound absorption area of the frame itself has been measured to elucidate whether the frame is likely to give a significant contribution to the total sound absorption area of a framed test specimen. The results will be presented and discussed in this paper.

Time-domain simulation of sound propagation through anisotropic porous media for room acoustic applications

Wave-based room acoustic simulations require accurate modeling of sound propagation in the presence of extended (bulk) reacting porous absorbers. The sound absorption in porous media is typically addressed by means of equivalent fluid models that provide frequency-dependent effective material parameters, such as density and bulk modulus. In the time domain, these frequency dependent properties result in the computation of convolution integrals, which is effectively handled via an auxiliary differential equations (ADE) method. In this work, we apply the time-explicit discontinuous Galerkin approach to modelling of sound propagation in anisotropic porous media (with an anisotropic equivalent fluid model) together with the ADE method. We demonstrate the importance of using the extended approach for porous media, where the sound absorption depends not only on the frequency and incident angle, but also on the travelling wave direction.

Spectral properties regulation for the performance improvement of solar-driven methane dry reforming reactor based on the photothermal synergistic catalysis

With the development of chemical industry, many chemical reactions are expected to be directly driven by solar energy. Among them, methane dry reforming (MDR) is a highly promising reaction system. Since all the energy required for MDR comes from solar energy, the temperature distribution and reaction characteristics in the reactor are determined by radiation transportation, and therefore regulating the optical properties according to the spectral distribution characteristics becomes necessary for improving the chemical conversion performance of the reactor. In this paper, aiming at the specific strengthening mechanism of different spectra in photothermal synergistic catalysis, the spectral response characteristics in the reactor were purposefully regulated, so as to achieve the improvement of reactor efficiency and reaction conversion performance. By adjusting the optical properties of compound parabolic concentrator (CPC) and porous catalytic absorber (PCA) in a cavity reactor, the CO2 conversion can be increased by 68.52%, the CH4 conversion can be increased by 54.48%, and the solar-fuel efficiency can be increased to 6.16%. This indicates that the selectivity of different bands of full spectrum can significantly affect the reactor performance. Through the above research, this paper aims to provide a new optimization idea for the photothermal reactor.

Optimization of acoustic porous material absorbers modeled as rigid multiple microducts networks: Metamaterial design using additive manufacturing

This research presents a strategy to enhancing sound absorption in porous acoustic metamaterials through the optimization of micro-duct networks. The study employs a combination of analytical and numerical methods, systematically adjusting micro-duct diameters within a 2D grid to optimize absorption coefficients at specific frequency bands. The Finite Element Transfer Method (FETM) is utilized for modeling, supported by a multi-objective function influenced by the surface impedance of the network. This approach ensures practical applicability and manufacturability of the designed metamaterial. A significant aspect of the study is the development of an analytical mobility matrix for each microduct, integrated through the Transfer Matrix Method using the visco-thermal dissipation theory. This integration results in a physically coherent model, for which a semi-analytical sensitivity analysis related to the microduct diameters can be directly performed. The optimization employs the Method of Moving Asymptotes (MMA), effectively managing the complexity associated with a large number of design variables. Subsequently, the optimized structure is adapted into a 3D grid, facilitating prototype creation using Additive Manufacturing Technology (AMT) with a specific polymer material. The research methodology is validated through four distinct test cases, each demonstrating the efficacy and adaptability of the optimization tools and techniques. Experimental validation, conducted using an impedance tube, indicates a significant shift in the first absorption maximum from 2500 Hz to 1000 Hz, achieved without altering the material thickness. Additional validation through 3D Finite Element Method (FEM) modeling, which includes visco-thermal effects, further confirms the acoustic efficiency of the final designs. While the potential for achieving lower sub-wavelength conditions is recognized, the study opts for simpler structures, considering the current limitations of 3D printing technology. This study contributes to both theoretical understanding and practical application in acoustic material design, emphasizing the potential for customizing materials to specific frequency ranges. The integration of FETM modeling with MMA provides a systematic and effective approach for optimizing acoustic materials, particularly in enhancing absorption at lower frequencies.

Silicon porous disc featured parabolic trough collector functioned with paraffin: Thermal performance study

The advancement of renewable solar energy has potential for industrial heat exchanger applications, and its performance is enhanced by using nanofluid. Besides, the losses of heat during the energy transfer from solar to heat exchanger limit thermal performance and lead to reduced thermal efficiency. The conventional solar system functioning with nanofluid needs to be upgraded with an advanced thermal management system to limit energy loss and enrich the thermal performance of the overall system. The investigation aims to enrich the thermal performance of a parabolic trough solar collector (PTC), which features silicon porous discs and phase change material (PCM-paraffin). During the investigation, the flow of fluid ranged from 100 to 200 LPH with an interval of 50 LPH. Influences of silicon porous disc and phase change material melting phase on fluid temperature, temperature, energy stored, and thermal efficiency of the present system are experimentally investigated, and its values are related to conventional absorber performance without porous material and phase change material. The output results prove the significance of silicon porous and phase change material related to conventional absorber systems. The parabolic solar collector functioned with silicon porous material with phase change material phase on 200LPH spotted superior thermal performance including fluid temperature, PCM temperature, energy stored by phase change material, and average thermal & exergy efficiency of 84.2 °C, 98.5 °C 599.7 kJ, and 73.8 % & 15.1 %. These findings underscore the promising potential of porous medium absorbers in significantly elevating the efficiency of parabolic trough collector systems.

Determination of diffuse field sound absorption of a porous absorber from Biot parameters using simulation

Porous sound absorbers are commonly assessed by their diffuse field sound absorption. In the test, a sample of the material, having a recommended surface area of 2.44 m by 2.74 m, is placed on the floor of a reverberation room. The average sound pressure level in the room is measured using a reference sound source and compared to the level in an empty room. Using room acoustic theory, the diffuse field sound absorption of the sample can be determined. This sound absorption is often much higher than the normal incidence sound absorption due to diffraction effects especially at lower frequencies. In this research, a hybrid simulation method is used to determine the diffuse field sound absorption from the Biot properties of the sound absorber. Statistical energy analysis is used to model the room and finite element analysis is used to simulate the material sample. Results from simulation are compared against measurement and agreement is acceptable.

Enhancing the absorption performance of minimal surface-based bulk absorbers via symmetry-breaking

The examination of Triply Periodic Minimal Surfaces (TPMSs) in the context of their acoustic dampening qualities has established them as viable alternatives to conventional porous absorbers. By adjusting the structure's porosity, one can significantly alter the TPMSs' acoustic absorption characteristics. Traditionally, enhancing sound absorption has involved decreasing porosity, which unfortunately increases the material's weight. In this study, we introduce a different approach to alter their absorption performance without altering their overall relative density. Our approach relies on leveraging the mathematical formulation of such structures to break their underlying geometrical symmetry. This symmetry-breaking results in altering their sound absorption characteristics while introducing an anisotropic acoustic response. In this paper, we present the mathematical design and fabricate the samples using the Fused Filament Fabrication (FFF) additive manufacturing method. The sound absorption characteristics of the printed samples are tested using a two-microphone normal incidence impedance tube setup. The presented results demonstrate that symmetry-breaking provides a viable route towards improving the low-frequency response of TPMS sound absorbers.

Comparison of modelling methodologies for large porous absorbers hanging in a volume

Porous material simulation methodologies are well established. However, most methods, like the Transfer-Matrix Method (TMM) make the assumption that there is a source side and a receiver side. In practice, this works for the majority of industrial noise control treatments. For architectural applications, this is not always the case. Hanging absorbers and curtains are common materials that add absorption to a space, but do not have a boundary condition at a wall or a well-defined source and receiver side. To evaluate the validity of existing simulation methods for this condition, a reverb room test was simulated with a large cube of melamine foam inside the volume. The effective absorption of the cube in the space was then calculated using various simulation methodologies, and compared to results from a measured reverb room absorption test.

Effect of Internal Reflectors on Daily Performance of Double Slope Solar Stills with Porous Fin Absorber Plate

Effect of Internal Reflectors on Daily Performance of Double Slope Solar Stills with Porous Fin Absorber Plate

Study of Heavy Metal Removal with Porous Nanocomposite Scaffolds based on Hybrid Inorganic/Organic Nanoparticles (MSN@COF)

aims: Synthesis of organic-inorganic hybrids as 3D adsorbents for heavy metal removal background: Synthesis of organic-inorganic hybrids objective: Study of heavy metal removal with porous nanocomposite scaffolds based on hybrid organic/inorganic nanoparticles (MSN@COF) method: Using soluthermal methods for the synthesis of organic-inorganic hybrids and studying the removal of heavy metals in them result: Precise and defect-free synthesis of organic-inorganic hybrids Removal of over 90% of heavy metals conclusion: In this research work, in order to achieve the desired product, mesoporous silica nanoparticles were first synthesized based on TEOS, and then the surface modification of these nanoparticles was done with APTES in order to achieve MSN-NH2. Next, organic covalent frameworks based on cyanuric chloride were synthesized. The main goal in this research work was the synthesis of porous nanocomposites based on MSN and COF, so that it is possible to synthesize hybrid organic/inorganic porous nanocomposites by in situ growth of COF on porous silica nanoparticles. Therefore, after synthesizing both hybrid organic/inorganic porous nanocomposites (COF and MSN) and examining their morphology and how to identify them, porous nanocomposites (MSN@COF) resulting from the growth of COF on MSN were synthesized. To achieve a proper comparison of the porosity and nature of these nanocomposites, once this nanocomposite was synthesized using MSNs whose surfactant was not removed, the CTAB surfactant was removed after COF growth on it. In another synthesis, the nanocomposite was synthesized from the growth of COF on MSN-NH2 whose surfactant was removed. This nanocomposite, due to the open pores of the MSNs, the growth of COF started by connecting to the amino groups obtained from APTES from within the MSN-NH2 themselves. The nanocomposite had less porosity than the other composite due to the growth of COF inside it. But the remarkable thing was the growth and presence of COF with its constituent atoms inside the MSN cavities. Due to the fact that porous nanomaterials have their own unique morphology, nature, function, and application according to their constituents and porosity category, both porous nanoparticles used in the preparation of these nanocomposites are well-known and widely used porous nanomaterials. They are in industry and medicine, so we decided to synthesize porous nanocomposites that have the special characteristics, behavior, and ability of both MSN and COF. Relevant analyses confirmed the synthesis of these porous nano absorbents. The growth of COF on MSNs, according to the data obtained from BET, has reduced the surface area and volume of pores in porous nanocomposites, but on the other hand, the presence of COF with its constituent atoms definitely gives a special characteristic and ability to nanocomposites. Porous materials will give in exchange for a decrease in the surface area and volume of the initial MSN cavities. The results of this study demonstrated that MSN@COF(WC) absorbs a higher percentage of zinc and cadmium metal ions than other adsorbents at various levels of adsorbent consumption, demonstrating that hybrid adsorbents are more effective than COF and MSN in removing these heavy metals from the primary solution. Also, the evaluation of the equilibrium time showed that the adsorption of heavy metals zinc and cadmium by MSN, COF adsorbents has a greater speed, while the MSN@COF(NC) hybrid adsorbent needs the greatest time to reach equilibrium conditions. When hybrid absorbents and two other absorbents were compared at various pollution levels, it became clear that hybrid absorbents at low pollution levels and other absorbents at high pollution levels are more effective in removing metals heavier than the original solution. In conclusion, the results of this study showed that the hybrid adsorbents have a larger absorption amount and the other two adsorbents have a higher absorption speed to reach equilibrium conditions in the process of removing zinc and cadmium metals from the stock solution. other: All the necessary information is available inside the text.

Antifungal Hybrid Graphene-Transition-Metal Dichalcogenides Aerogels with an Ionic Liquid Additive as Innovative Absorbers for Preventive Conservation of Cultural Heritage.

The use and integration of novel materials are increasingly becoming vital tools in the field of preventive conservation of cultural heritage. Chemical factors, such as volatile organic compounds (VOCs), but also environmental factors such as high relative humidity, can lead to degradation, oxidation, yellowing, and fading of the works of art. To prevent these phenomena, highly porous materials have been developed for the absorption of VOCs and for controlling the relative humidity. In this work, graphene and transition-metal dichalcogenides (TMDs) were combined to create three-dimensional aerogels that absorb certain harmful substances. More specifically, the addition of the TMDs molybdenum disulfide and tungsten disulfide in such macrostructures led to the selective absorption of ammonia. Moreover, the addition of the ionic liquid 1-hexadecyl-3-methylimidazolium chloride promoted higher rates of VOCs absorption and anti-fungal activity against the fungus Aspergillus niger. These two-dimensional materials outperform benchmark porous absorbers in the absorption of all the examined VOCs, such as ammonia, formic acid, acetic acid, formaldehyde, and acetaldehyde. Consequently, they can be used by museums, galleries, or even storage places for the perpetual protection of works of art.

Preparatiοn οf pοrοus hydrοxyapatite-metakaοlin geοpοlymer granules fοr adsοrptiοn applicatiοns using pοlyethylene glycοl as pοrοgen agent and sοdium dοdecyl sulfate as aniοnic surfactant.

This study investigated the elaboration of novel porous absorbent granules by mixing powdered hydroxyapatite, metakaolin, sodium metasilicate, polyethylene glycol, and sodium dodecyl sulfate (SDS), an anionic surfactant. The effect of sodium dodecyl sulfate (SDS) was then studied by introducing it as a powder to the powdered mixture or dissolved into the granulation fluid. Characterization of the granules indicated that the incorporation of SDS dissolved in the granulation fluid into the G-PEG granules improved their specific surface area (97.9 m2/g) and porosity, resulting in a synergistic increase in the adsorption of crystal violet and methylene blue dyes compared to G-PEG granules and hydroxyapatite or metakaolin geopolymer alone. Moreover, the granules exhibited satisfactory compressive strength of 0.81MPa, making them suitable for large-scale adsorption columns. Finally, the regeneratiοn prοcess οf the granules was modeled and optimized by using surface response methodology based on Box-Behnken design. The granules cοuld be regenerated fοr eight cycles under οptimum cοnditiοns οf acetic acid cοncentratiοn οf 0.72 mοl/L, a temperature οf 323K, and a cοntact time οf 173.22min, withοut a significant lοss in the adsοrptiοn capacity οr degradatiοn οf the granules. These results suggest that the pοrοus granules prepared in this study have pοtential tο be used in industrial wastewater treatment.

Thermo-mechanical performance enhancement of volumetric solar receivers using graded porous absorbers

The potential of graded porous absorbers in enhancing the thermo-mechanical performance of a volumetric solar receiver is investigated. A coupled numerical model is developed and simulations are conducted on various configurations with porosity and pore size variations in axial, radial, and bidirectional arrangements. The performance of graded configurations is first compared with a representative uniform configuration, and then the optimal configurations within each arrangement are further analyzed to determine the overall best configuration. The parametric study reveals conflicting thermo-mechanical performances in majority of the arrangements. The configurations with a porosity range of 0.9–0.95 and a pore size range of 2–4 mm exhibit the best performance across all variations. Among the best configurations, the bidirectional configuration with radially decreasing porosity and axially increasing pore size demonstrates the best performance with an increase of 8.96 % in air outlet temperature and a decrease of 22.7 % and 4 % in Failure Index and pressure drop, respectively. Bidirectional configuration maintained superior performance over the receiver length range of 1–6 cm and velocity range of 0.4–2.4 m/s. The results underscore the suitability of certain graded arrangements for achieving improved thermal performance while ensuring higher mechanical safety.

Eco-friendly disposable porous absorbents from gluten proteins through diverse plastic processing techniques

The production of biodegradable gluten-based protein foams showing complete natural degradation in soil after 26 days is reported, as an alternative to commercial foams in disposable sanitary articles that rely on non-biodegradable materials. The foams were developed from an extensive evaluation of different foaming methodologies (oven expansion, compression moulding, and extrusion), resulting in low-density foams (ca. 400 kg/m3) with homogenous pore size distributions. The products showed the ability to absorb 3–4 times their weight, reaching ranges for their use as absorbents in single-use disposable sanitary articles. An additional innovative contribution is that these gluten foams were made from natural and non-toxic wheat protein, glycerol, sodium and ammonium bicarbonate, making them useful as fossil-plastic-free replacements for commercial products without the risk of having micro-plastic and chemical pollution. The impact of different processing conditions on forming the porous biopolymer network is explained, i.e., temperature, pressure, and extensive shear forces, which were also investigated for different pH/chemical conditions. The development of micro-plastic-free foams mitigating environmental pollution and waste while using industrial co-products is fundamental for developing large-scale production of single-use items. A sanitary pad prototype is demonstrated as an eco-friendly material alternative that paves the way for sustainable practices in manufacturing, and contributes to the global effort in combating plastic pollution and waste management challenges, Sustainable Development Goals: 12, 13, 14, and 15.

Eco-friendly bacterial cellulose/MXene aerogel with excellent photothermal and electrothermal conversion capabilities for efficient separation of crude oil/seawater mixture

Developing novel absorbent materials targeting high-efficiency, low-energy-consumption, and environmental-friendly oil spill cleanup is still a global issue. Porous absorbents endowed with self-heating function are an attractive option because of that they are able to in-situ heat crude oil and dramatically reduce oil viscosity for efficient remediation. Herein, we facilely prepared an eco-friendly multifunctional bacterial cellulose/MXene aerogel (P-SBC/MXene aerogel) for rapid oil recovery. Thanks to excellent full solar spectrum absorption (average absorbance = 96.6 %), efficient photo-thermal conversion, and superior electrical conductivity (electrical resistance = 36 Ω), P-SBC/MXene aerogel exhibited outstanding photothermal and electrothermal capabilities. Its surface temperature could quickly reach 93 °C under 1.0 kW/m2 solar irradiation and 124 °C under 3.0 V voltage respectively, enabling effective heat transfer toward spilled oil. The produced heat significantly decreased crude oil viscosity, allowing P-SBC/MXene aerogel to rapidly absorb oil. By combining solar heating and Joule heating, P-SBC/MXene aerogel connected to a pump-assisted absorption device was capable of achieving all-weather crude oil removal from seawater (crude oil flux = 630 kg m−2 h−1). More notably, P-SBC/MXene aerogel showed splendid outdoor crude oil separation performance. Based on remarkable crude oil/seawater separation ability, the versatile aerogel provides a promising way to deal with large-area oil spills.

A Solar Evaporator Based on Polypyrrole Coated 3D Carbon Nanotube Materials for Efficient Solar-Driven Vapor Generation.

Highly porous light absorbers are fabricated based on polypyrrole (PPy)-coated carbon nanotube (CNT). Carbon nanotube sponge (CNTS) or carbon nanotube array (CNTA) with three-dimensional (3D) network structure is the framework of porous light absorbers. Both PPy@CNTS and PPy@CNTA composites exhibit excellent light absorption of the full solar spectrum. The CNTS and CNTA with porous structures have extremely large effective surface area for light absorption and for water evaporation that has great practical benefit to the solar-driven vapor generation. The PPy layer on CNT sidewalls significantly improves the hydrophilicity of porous CNTS and CNTA. The good wettability of water on CNT sidewalls makes water transport in porous CNT materials highly efficient. The PPy@CNTS and PPy@CNTA light absorbers achieve high water evaporation rates of 3.35 and 3.41kg m-2 h-1 , respectively, under 1-sun radiation. The orientation of nano channels in CNTA-based light absorbers also plays an important role in the solar-driven vapor generation. The water transport and vapor escape are more efficient in CNTA-based light absorbers as compared to the CNTS-based light absorbers due to the relatively short path for the water transport and the vapor escape in CNTA-based light absorbers.