Composite Absorbent Research Articles

Bamboo-Based Carbon/Co/CoO Heterojunction Structures Based on a Multi-Layer Periodic Matrix Array Can Be Used for Efficient Electromagnetic Attenuation.

With the popularization of wireless communication, radar, and electronic devices, the hidden harm of electromagnetic radiation is becoming increasingly serious. The design of green biomass carbon-based interface heterojunctions based on lightweight porous materials can effectively protect against electromagnetic radiation hazards. In this work, we constructed an anisotropic heterojunction interface with magnetic and dielectric coupling based on a honeycomb-like periodic matrix multi-layer array repeating unit. The removal of lignin components from bamboo through oxidation enriches the impregnation pores and uniform adsorption sites of the magnetic medium. Further, in situ pyrolysis promotes the formation of a large number of electric dipoles at the interface between the magnetic medium and dielectric coupling inside the periodic cell carbon skeleton, enhancing interface polarization and relaxation. Local carrier traps and uneven electromagnetic density enhance dielectric and hysteresis losses, resulting in excellent impedance matching. Therefore, the obtained bamboo-based carbon multiphase composite absorbent has satisfactory electromagnetic loss characteristics. At a thickness of 1.55 mm, the effective absorption bandwidth reaches 5.1 GHz, and the minimum reflection loss (RL) value reaches -54.7 dB. In addition, the far-field radar simulation results show that the sample has an excellent RCS (radar cross-section) reduction of 33.3 dB·m2. This work provides new directions for the diversified development of green biomass and the optimization of the design of magnetic and dielectric coupling in periodic array structures.

Synergistically magnetic and dielectric properties of two dimensional Fe3Al@PPy lamellae exhibiting broadband and strong electromagnetic wave absorption

Addressing the issue of low impedance characteristics is essential to improve the electromagnetic wave absorption performance of magnetic materials. Herein, two dimensional Fe3Al@polypyrrole (PPy) lamellae with synergistic magnetic and dielectric properties are fabricated by a mechanical alloying, ordering transformation and polymerization process, which exhibits excellent electromagnetic wave absorption performance. By carefully controlling the thickness of the PPy shell, the optimized Fe3Al@PPy lamellae show a minimum reflection loss of −45.6 dB and an effective absorption bandwidth of 9.1 GHz at a thickness of only 1.5 mm. The conformal growth of Fe3Al@PPy lamellae can induce strong interfacial polarization, dipole polarization, multiple scattering effect and magnetic loss behaviors for the attenuation of electromagnetic waves. This study demonstrates a facile strategy for the development of efficient Fe3Al@PPy composite absorbents showing great potential for practical applications.

Sustainable regeneration of transformer oil through composite adsorbent of chitosan and sepiolite: a biorefinery approach

ABSTRACT This study introduces an innovative biorefinery approach for sustainably regenerating transformer oil utilizing a composite adsorbent comprised of Chitosan (CS) and Sepiolite (SL). Surface modification analyses, employing BET, SEM, and FTIR techniques, unveiled enhanced adsorption capabilities attributed to pores and folds on the CS-SL composite surface, coupled with uniform SL distribution within the CS substrate. Through systematic evaluations based on color index and transmittance assessments across multiple samples, optimal regeneration was achieved with a 5% volume fraction of the composite absorbent, closely replicating fresh oil properties. Significant improvements were observed in acidity (−62.50%), moisture content (−44.44%), and viscosity (−27.93%), with slight changes in density and a notable rise in flash point (+31.82°C). Electrical properties showed enhancement, with breakdown voltage (+80.00%) and resistivity (+54.93%) increasing, while dissipation factor (−98.00%) and permittivity (−44.74%) decreased, indicating improved energy efficiency. Gas chromatography-mass spectrometry confirmed the removal of oxidation by-products. This study underscores the potential of CS-SL as a sustainable adsorbent for transformer oil regeneration, thereby making significant strides toward environmental sustainability within the framework of Sustainable Development Goals (SDGs) and the principles of biorefinery practices.

Methane adsorption effect of cyclodextrin-based metal-organic frameworks and ultra-fine water mist composite system in closed container

Natural gas, predominantly composed of methane, is a widely used energy source. Methane is prone to leakage during storage and usage, posing environmental risks. Currently, effective strategies to capture methane leaked in urban environments are lacking. This study investigates the synthesis of a non-toxic Cyclodextrin-based Metal-Organic Framework (CD-MOF) and its adsorption capacity for leaked methane in an ultrafine water mist composite solution system. CD-MOFs, utilizing β-cyclodextrin as the organic ligand and alkali metal potassium as the metal ion, were synthesized via solvothermal and methanol vapor diffusion method. The morphology, functional groups, and thermal properties of CD-MOFs were characterized by multiple techniques. The BET specific surface area, pore structure, and high-pressure methane adsorption capacity of the samples were investigated. Furthermore, CD-MOF, surfactant, and castor oil were combined to create a composite solution absorbent. The methane absorption efficacy of this ultra-fine water mist of absorbent was tested using a closed-container methane spray adsorption apparatus, and the compound solution ratio was optimized. The results indicate that CD-MOFs retain the parent cyclodextrin structure, and the methane adsorption capacity under high-pressure (35 bar) of CD-MOF synthesized by the sodium dodecyl sulfate-assisted solvothermal method reached 216.13 cm3/g. The composite solution with an appropriate proportion of surfactant, castor oil, and CD-MOF reached a methane absorption capacity of 5.7 % vol in enclosed spaces. The successful synthesis of CD-MOFs and the application of composite solutions with ultra-fine water mist offer innovative approaches and theoretical guidance for the emergency absorption and non-toxic disposal of leaked methane.

Facile synthesis of Co-loaded ceramic composite absorbents via gangue recycling

Coal gangue was recycled to synthesize ceramic-based microwave absorbents decorated with Co particles via a facile synthesis route. Co particles were uniformly loaded onto the ceramic matrix by pelletizing the gangue with concurrent spraying of a Co2+-containing solution, followed by in situ carbothermal reduction using the fixed carbon in the gangue as the reducing agent. The Co contents of the ceramic composites were precisely controlled by adjusting the concentration of Co2+ solution. The fixed carbon in the gangue was partially consumed, and the residual carbon in the composites resulted in more defects, and acted as a dielectric. Compared to gangue, the optimized composite exhibited excellent microwave absorbing properties with a minimum reflection loss of −48.2 dB and an effective absorption band of 4.3 GHz under a coating thickness of 1.5 mm. The excellent performance was mainly attributed to the enhanced impedance matching and multiple interface polarizations in the composite.

Removal of Nickel from Industrial Wastewater by an Agro-based Composite Adsorbent

For many years, especially in emerging nations like India, the environment has been threatened by the increased output of industrial wastes and heavy metal toxicity. The usage of inexpensive adsorbents has recently attracted a lot of attention in studies on the removal of heavy metals like nickel from industrial wastewater. The use of agro-based adsorbent is an alternative to conventionally used activated charcoal. In this research, adsorption experiments were carried out using agro-based adsorbent prepared from rice husk, wheat husk, and soybean husk to reduce nickel from industrial wastewater. The adsorption process is simple, economical, and effective is the most preferred method used for the removal of toxic metals like nickel from industrial wastewater. Adsorbents prepared from these husks can be effectively used for adsorption due to low cost & high availability. Characterization of agricultural material by various tests like XRF, proximate analysis, bulk density, and iodine number was conducted on agro-based adsorbents to know the co-relation between removal efficiency and adsorption capacity. The effect of turbidity and pH parameters on Ni removal efficiency is also studied. Results indicated that wheat husk adsorbent appeared to be the most effective for the adsorption of Ni from wastewater as compared to soybean husk and rice husk adsorbent. Wheat husk, soybean husk, and rice husk have removal efficiency in the range of 62.50 to 73.33. Composite absorbents CA-2 with the proportion of 50% wheat husk, 33% soybean husk, and 17% rice husk have 82.50% efficiency, and CA-3 has 80.83% efficiency in removing Nickel. Wheat husk adsorbent, CA-2, and CA-3 are more effectively and sustainably used for the treatment of industrial wastewater to remove heavy metals.

Polyvinyl Alcohol-Citric Acid: A New Material for Green and Efficient Removal of Cationic Dye Wastewater.

The citric acid (CA) cross-linked polyvinyl alcohol (PVA) adsorbent, PVA-CA, was efficiently synthesized and its application to the removal of dyes in water, particularly the cationic dye, methylene blue (MB), was thoroughly investigated. The morphologies and physiochemical characteristics of PVA-CA were fully characterized by SEM, FT-IR, XRD, TGA, BET, and XPS. The effects of contact time, adsorbent dosage, MB concentration, solution pH, and temperature on the adsorption performance were compared using controllable methods. The maximum adsorption capacity of PVA-CA was 709.86 mg g-1 and the removal rate remained high through several adsorption-desorption cycles, demonstrating that such a composite absorbent has a good adsorption performance and recoverability. Further analysis by the density functional theory (DFT) showed that van der Waals interactions, electrostatic interactions and hydrogen bonding interactions between PVA-CA and MB played significant roles in the adsorption mechanism.

Effective removal of Cr (VI) from aqueous solution by reinforced sodium alginate/polyethyleneimine/graphene oxide composite aerogels.

A reinforced composite aerogel absorbent was synthesized using a green chemistry method and an environmentally friendly freeze-drying technique. The absorbent consisted of sodium alginate, polyethyleneimine (PEI), and graphene oxide (GO). The ability of the absorbent to remove Cr (VI) ions from aqueous solutions was studied. PEI was a nitrogen source for Cr (VI) removal and a cross-linking agent for GO sheets, while SA was a reinforcing material. The aerogel was investigated using X-ray diffraction, scanning electron microscopy, Fourier transform infrared (FTIR) spectroscopy, texture analysis, Raman spectroscopy, and thermogravimetric analysis (TGA). Batch studies were conducted to investigate the effect of pH and contact time on adsorption. The results indicated that the SA/PEI/GO aerogel had a maximum adsorption capacity of 174.05 mg·g-1 for Cr (VI) at pH 2. The adsorption mechanism was described using the Langmuir isotherm and pseudo-second-order kinetic models. Thermodynamic studies revealed that the adsorption process was spontaneous and endothermic. The aerogel demonstrated good regeneration ability and satisfactory recovery for Cr (VI) even after five cycles. These findings suggest that the composite aerogel could be a promising adsorbent for efficiently removing Cr (VI) from wastewater.

Tunable Complex Permittivity and Strong Microwave Absorption Properties of Novel Dielectric-Conductive ZnO/C Hybrid Composite Absorbents

Modern electronic information technology has led social life into inevitable electromagnetic pollution, making microwave absorbing materials more and more important. Herein, dielectric-conductive ZnO/C hybrid composite absorbents were prepared by two-step carbonization with ZnO powders and glucose as critical materials. The electrical conductivity, complex permittivity, and reflection loss were analyzed to study the dielectric and microwave absorption properties. Results show that the prepared ZnO/C composite absorbents exist in the form of rod-like ZnO dispersed in the irregular block carbon, and the complex permittivity of the composite absorbents can be adjusted via varying the carbonization temperature. The minimum reflection loss of −25.64 dB is achieved at 1.8 mm thickness for the composite absorbent with 50 wt.% absorbent content as the final carbonization temperature is 750 °C, and the optimum effective absorption bandwidth is 2.21 GHz at 9.64–11.85 GHz. The excellent microwave absorption properties of ZnO/C composite absorbents are attributed to the combination actions of dipole polarization, conductance loss, and interface polarization, which is significant for the purposeful design of superior microwave-absorbing materials with dielectric and conductive absorbents.

Post-consumer plastics/CoxMn3–xO4 spinels derived Co/MnO@carbon nanotube composites towards advanced electromagnetic absorbents

Waste plastics and electromagnetic radiation pollution have been two serious issues that largely affect our environment. How to solve them in a single approach is a social and scientific challenge. In this work, advanced Co/MnO@carbon nanotube composite (Co/MnO@CNTs) absorbents were prepared via pyrolysis-catalysis conversion of face masks as post-consumer plastic waste with multi-scale designed CoxMn3–xO4 spinel pre-catalysts. The (nano)structure (e.g., MnO-carbon and Co-carbon hetero-interface), composition, and graphitic degree of the Co/MnO@CNTs absorbents were facilely controlled by varying the catalytic reaction temperature and the composition of spinel pre-catalysts. By constructing multi-loss mechanisms (e.g., magnetic loss, conductive loss, interface polarization loss, and defects-induced polarization loss), the largest effective absorption bandwidth (EAB) of the Co/MnO@CNTs/wax composites can reach as wide as 5.28 GHz at a thickness of 1.7 mm. When the content of the Co/MnO@CNTs absorbents is 17 wt%, the EAB and minimal reflection loss (RLmin) achieves 5.04 GHz and −38.1 dB, respectively. This work is based on a sustainable and cost-effective feedstock as well as an innovative method for the large-scale production of advanced CNTs-based materials in electromagnetic absorption application.

Construction and optimization of Fe3O4/C/ceramic composite absorbents by one-step recycling red mud and coal hydrogasification residue

Construction and optimization of Fe3O4/C/ceramic composite absorbents by one-step recycling red mud and coal hydrogasification residue

Fabrication, Properties, and Performance of Polymer-Clay Nanocomposites for Organic Dye Removal from Aqueous Media

Methylene blue dye (MB dye) is a harmful contaminant for wastewater streams of industries and is harmful to human and aquatic life. An ecofriendly sugar templating process was used to generate porous bentonite/polydimethylsiloxane (PB) and porous magnetite nanoparticles/bentonite/polydimethylsiloxane (PBNP) composite absorbents to remove MB dye in this study. During the infiltration of PDMS solution into the sugar template in the vacuum chamber, bentonite and magnetite particles were integrated on the surface of the PDMS, and the porous structure was generated during the leaching out of sugar particles in water. The absorbents were characterized using Fourier infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The absence of the methyl bond at 2924 cm-1 and phenol bond at 3325 cm-1 in the FTIR spectra of the formed membrane proves that the food grade sugar was completely removed. The SEM images confirm that porosity was achieved as well as uniform mixing of the in the formation of composite. MB dye was effectively removed from wastewater using the as-prepared composite as absorbent. The removal efficiencies of the composite PBNP and PB were ~91% and ~85%, respectively. The experimental data was applied to pseudo-first-order (PFO) and pseudo-second-order (PSO) kinetic models as well as the Dubinin-Radushkevich, Harkins-Jura, and Elovich models for the adsorption isotherm. The data was found to fit the pseudo-second-order and Elovich models, respectively. The results show that the presence of magnetite nanoparticles improved MB dye removal significantly.

MOFs derived Fe/Co/C heterogeneous composite absorbers for efficient microwave absorption

Microwave absorbing materials (MAMs) can effectively attenuate microwave energy and avoid the secondary pollution of microwaves, showing great research significance. However, most of the reported MAMs are short of efficient electromagnetic wave absorption ability in low-frequency microbands (such as S-band in 2–4 GHz). Herein, we proposed a "MOF on MOF" design to obtain a Fe/Co/C multicomponent composite through the synthesis of ion-ligand of two MOFs and subsequent high-temperature pyrolysis, realizing the broadband microwave absorption(MA) and superb electromagnetic wave absorption in S band. ZIF-67 was grown in situ on micron-scale spindle NH2-MIL-88B (Fe) as the bearing matrix to obtain the precursor composed of Fe-MOF and Co-MOF. After pyrolysis at high temperature in an inert atmosphere, the organic components are carbonized to form a carbon layer coated with magnetic nanoparticles composed of Fe and Co. The characteristics of a rich heterogeneous interface and large specific surface area enhance the polarization ability of composite absorbent and the conduction dissipation path of electromagnetic wave. Besides, the composite absorbent can cover the absorption demand of 2–18 GHz with an adjustable thickness. We believe that this composite design of multiple MOFs can provide a new reference for the realization of efficient microwave absorption.

Photoinduced phase transitions in nanogel particles for reversible CO2 capture

Solar energy has been utilized to strip CO2 for saving the CO2 capture energy consumption. However, a large temperature swing is necessary for higher regeneration efficiency, which also will result in a serious materials degradation. Herein, we report a photo triggered phase transition strategy for reversible capture CO2 using amine containing nanogel particles-based solvents with a small temperature swing. The composite absorbents were prepared by combing N-[3-(dimethylamino)propyl]methacrylamide containing nanogel particles with polydopamine. The phenomenon of photoinduced phase transition was observed in both nanogel particles-based solvents and the composite absorbents. Although the nanogel particles can release most of CO2 undergo a light irradiation, the composite absorbents present a more faster desorption rate than the former, which can be explained by an enhanced light absorbability and photothermal conversion efficiency of the latter. An average CO2 regeneration efficiency can reach up to 92.45% in five CO2 uptake and release cycles, indicating that the photo triggered phase transition can be used to develop energy efficient CO2 capture technology.

From the solid waste mixture of coal hydrogasification residue and red mud to efficient Fe3O4/C- and Fe/C-based composite microwave absorbents

Following the concept of sustainable development, magnetic particles/C-based composite microwave absorbing materials were prepared through reactions between two solid wastes: coal hydrogasification residue (CHR) and red mud (RM). At a fixed mass ratio of CHR to RM of 0.6:1, Fe3O4/C- and Fe/C-based composites could be obtained at 700 and 900 °C, respectively. A minimum microwave reflection loss of −48.3 dB and a largest effective absorption bandwidth of 4.5 GHz were achieved for the Fe/C-based composite with a simulated thickness of 1.5 mm. The Fe3O4/C-based composite exhibited slightly poorer performance because the fixed initial system could not guarantee impedance matching for both products. The strong intrinsic attenuation capacity of the materials mainly resulted from the dielectric loss, including conduction loss caused by graphite carbon as well as interfacial polarization relaxation loss arising from the numerous phase boundaries.

Fe3O4@PANI/chitosan composite aerogel with electromagnetic induction heating capacity toward efficient removing viscous oil

The leakage of oil will cause serious damage to the environment. However, it is a challenge for porous absorbents to quickly and completely absorb high viscosity oils such as crude oil or asphalt. Although there are some absorbents generating heat with the aid of sunlight or electricity to heat, thin, and absorb this viscous oil, these heating methods have defects such as inefficiency or unsafety. Herein, we utilize polyaniline and Fe3O4 to develop a chitosan composite aerogel absorbent with magnetism and conductivity so that it is able to generate heat in an alternating magnetic field, thus providing a safe, efficient, and non-contact method to clean up the viscous oil. The samples can be reused by extrusion, and the absorption process can be repeated without deterioration. Moreover, this absorbent can also be heated by sunlight, which realizes a strategy in which the absorbent absorbs the viscous oil under sunlight to conserve energy but switches to induction heating to rapidly clean up the oil spills in an emergency.

An efficient non-destructive separation method of road marking from asphalt pavement by microwave directional heating

In this paper, an efficient and non-destructive separation route of road marking from asphalt pavement was reported firstly via microwave directional heating. By accurately focusing microwave energy on a thin film and making it high temperature, the markings can be easily separated from the pavement surface. Microwave heating test results showed that when 25%wt composite microwave absorbent were added to the bonding layer and impedance-matching layer respectively, the heating rate of impedance-matching marking specimen surface was 34.56℃/min, 73.72% higher than that of the control group. The marking removal efficiency was calculated via Matlab digital image processing technology, showed that the average removal efficiency of impedance-matching marking specimens were 100.00%. The above findings show that marking removal method proposed in this study could significantly reduce the difficulty of removing markings on asphalt pavements and greatly improve the removal efficiency.

Sustainable Utilization of Solid Waste Fly Ash for Fabrication of CoNi@FA as Microwave Absorbent

Under the background of carbon peak and neutrality, the composite microwave absorbents are prepared using coal‐based solid waste fly ash (FA) as raw material, supporting the implementation of comprehensive utilization for FA and the low‐cost preparation for microwave absorbents. CoNi‐loaded FA composites (CoNi@FA) are prepared via a simple rotary evaporation and sintering process, involving the introduction of Co2+–Ni2+ into FA as well as the subsequent reduction process during which the CoNi alloy transforms from the metallic oxide. As expected, the CoNi@FA800 manifests excellent microwave absorption performance, and the minimum reflection loss (RLmin) value is −39.8 dB. The effective absorption bandwidth (EAB) is extended to 3.4 GHz when the coating thickness is 2.0 mm. These are attributed to the introduction of CoNi alloy, endowing CoNi@FA composites with proper impedance matching and attenuation characteristics. Thus, the CoNi@FA will be a potential candidate in the field of microwave absorbent, which not only realizes the resource utilization of FA efficiently, but also makes a compromise between economic and environmental benefit simultaneously.

A brand new two-phase wet oxidation absorption system for the simultaneous removal of SO2 and NOX from simulated marine exhaust gas

Marine engine exhaust emissions are increasingly harmful to the natural environment and human health and must be controlled. A self-synthesized amide (BAD, C12H25NO) in the laboratory shows a strong absorption capacity of nitric acid and nitrous acid, which may solve the problem that only using chlorine-based oxidant as an absorbent cannot completely absorb or retain NO2 produced by NO oxidation in previous studies. Based on Multiwfn and VMD (Visual Molecular Dynamics) program calculation, the formation mechanism of hydrogen bonds between BAD with nitric acid and nitrous acid was revealed by electrostatic potential (ESP) analysis and further confirmed by FT-IR (Fourier transform infrared spectroscopy) spectra research. Subsequently, simultaneous removal of SO2 and NOX from simulated flue gas was carried out by using NaClO/BAD as a two-phase composite absorbent, and the maximum removal efficiencies of SO2 and NOX were 98.9% and 86.6%, respectively. The recycling experiments and the engineering experiments showing that NaClO/BAD can solve the problem of absorption of NO2, and it can be a promising composite absorbent in wet desulfurization and denitrification of marine engine exhaust gas in practical applications.

Alginate-oil gelator composite foam for effective oil spill treatment

Oil spills threaten ecosystem and health seriously. Porous foams have been proved as ideal candidates for oil absorbents, however, many with poor oil retention (re-bleeding). Here, we creatively developed a composite foam oil absorbent capable of oil absorption and oil gelation, based on porous alginate foam and hydroxyl aluminum stearate oil gelator. The microstructure of alginate foam can be adjusted by the addition of t-butanol in the solvent, and long alkyl chains of gelator endow foam skeleton with good hydrophobicity, avoiding secondary pollution from traditional hydrophobic chemical modification. Interconnected skeleton decorated by oleophilic gelators contributes to high oil absorption. Oleophilic gelator can self-assemble into 3D network to entrap oils to form gels, giving rise to effective oil retention, realizing the integration of high oil absorption and oil retention. The natural abundant, low-cost composite foam would be promising for tackling oil spills.