Cu/NC@Co/NC composites derived from core-shell Cu-MOF@Co-MOF and their electromagnetic wave absorption properties

Recent advances in small-angle scattering techniques for MOF colloidal materials

This paper reviews the recent progress of small angle scattering (SAS) techniques, mainly including X-ray small angle scattering technique (SAXS) and neutron small angle scattering (SANS) technique, in the study of metal-organic framework (MOF) colloidal materials (CMOFs). First, we introduce the application research of SAXS technique in pristine MOFs materials, and review the studies on synthesis mechanism of MOF materials, the pore structures and fractal characteristics, as well as the spatial distribution and morphological evolution of foreign molecules in MOF composites and MOF-derived materials. Then, the applications of SANS technique in MOFs are summarized, with emphasis on SANS data processing method, structure modeling and quantitative structural information extraction. Finally, the characteristics and developments of SAS techniques are commented and prospected. It can be found that most studies on MOF materials with SAS techniques focus mainly on nanoporous structure characterization and the evolution of pore structures, or the spatial distribution of other foreign molecules loaded in MOFs. Indeed, SAS techniques take an irreplaceable role in revealing the structure and evolution of nanopores in CMOFs. We expect that this paper will help to understand the research status of SAS techniques on MOF materials and better to apply SAS techniques to conduct further research on MOF and related materials.

Strongly plasticized gelatin-based hydrogel for flexible encapsulation of complex-shaped electronic devices

The growth of environmentally sensitive complex-shaped electronic devices (ECEDs) has led to a surging demand for flexible electromagnetic wave (EMW) absorbers. Herein, the water loss property of hydrogel was ingeniously applied for the flexible encapsulation (FE) of ECEDs. To be specific, saturated state (SGT) hydrogels were prepared by chemical cross-linking, and the hydrogen bond dissipation network promoted FE. Additionally, SGT has an effective absorption bandwidth (EAB) of 6.04 GHz at 1.65 mm due to the presence of dipole polarization. With the loss of water, SGT transitions to its natural state (NGT), and the decreasing conductivity leads to better impedance matching. NGT exhibited a broader EAB (9.20 GHz at 2.65 mm) and also strength and lightness (density of 0.3 g cm-3). Furthermore, the semi-automatic reversible cyclic transformation between SGT and NGT gels further broadens application scenarios. GT gel combines self-encapsulation and self-optimized performance as a potential EMW absorber for FE.

Integrating Sulfur Doping with a Multi-Heterointerface Fe7S8/NiS@C Composite for Wideband Microwave Absorption

Heterointerface engineering is presently considered a valuable strategy for enhancing the microwave absorption (MA) properties of materials via compositional modification and structural design. In this study, a sulfur-doped multi-interfacial composite (Fe7S8/NiS@C) coated with NiFe-layered double hydroxides (LDHs) is successfully prepared using a hydrothermal method and post-high-temperature vulcanization. When assembled into twisted surfaces, the NiFe-LDH nanosheets exhibit porous morphologies, improving impedance matching, and microwave scattering. Sulfur doping in composites generates heterointerfaces, numerous sulfur vacancies, and lattice defects, which facilitate the polarization process to enhance MA. Owing to the controllable heterointerface design, the unique porous structure induced multiple heterointerfaces, numerous vacancies, and defects, endowing the Fe7S8/NiS@C composite with an enhanced MA capability. In particular, the minimum reflection loss (RLmin) value reached -58.1 dB at 15.8 GHz at a thickness of 2.1 mm, and a broad effective absorption bandwidth (EAB) value of 7.3 GHz is achieved at 2.5 mm. Therefore, the Fe7S8/NiS@C composite exhibits remarkable potential as a high-efficiency MA material owing to the synergistic effects of the polarization processes, multiple scatterings, porous structures, and impedance matching.

Hierarchical N-doped porous carbon scaffold Cu/Co-oxide with enhanced electrochemical sensing properties for the detection of glucose in beverages and ascorbic acid in vitamin C tablets

This research focuses on the development of a highly efficient electrocatalyst, CuxO/NPC@Co3O4/NPC-10-7, for detecting glucose and ascorbic acid. In a 0.1 M NaOH solution, the modified electrode exhibits a sensitivity of 3314.29 μA mM-1 cm-2 for glucose detection. The linear range for ascorbic acid sensing is 0.5 μM - 23.332 mM, with a detection limit as low as 0.24 μM. In a 0.1 M PBS solution, the linear range for ascorbic acid detection extends to 43.328 mM, which represents the best performance reported to date by chronoamperometry. Moreover, the electrode demonstrates high accuracy, with a recovery rate of 96.80 % - 103.60 % for glucose detection and a recovery rate of 95.25 % - 104.83 % for ascorbic acid detection. These results suggest that the CuxO/NPC@Co3O4/NPC-10-7 modified electrode shows significant potential for practical applications in food detection.

Contribution of 1O2 in the efficient degradation of organic pollutants with Cu0/Cu2O/CuO@N-C activated peroxymonosulfate: A Case study with tetracycline

Peroxymonosulfate-mediated advanced oxidation processes (PMS-AOPs) degrading organic pollutants (Tetracycline (TC) as an example) in water with singlet oxygen (1O2) as the main reactive oxygen has received more and more attention. However, the generation mechanism of 1O2 is still unclear. Consequently, this study investigates the 1O2 formation mechanism during the activated PMS process using a nitrogen-copper-loaded carbon-based material (Cu0/Cu2O/CuO@N-C), synthesized by thermally decomposing organobase-modified HKUST-1 via a one-pot method. It was discovered that incorporating an organobase (Benzylamine) into the metal organic framework (MOF) precursor directs the MOF's self-assembly process and supplements its nitrogen content. This modification modulates the Nx-Cu-Oy active site formation in the material, selectively producing 1O2. Additionally, 1O2 was identified as the dominant reactive oxygen species in the Cu0/Cu2O/CuO@N-C-PMS system, contributing to TC degradation with a rate of 70.82%. The TC degradation efficiency remained high in the pH range of 3-11 and sustained its efficacy after five consecutive uses. Finally, based on the intermediates of TC degradation, three possible degradation pathways were postulated, and a reduction in the ecotoxicity of the degradation products was predicted. This work presents a novel and general strategy for constructing nitrogen-copper-loaded carbon-based materials for use in PMS-AOPs.

Preparation of MIL-88(Fe)@Fe2O3@FeSiCr double core-shell-structural composites and their wave-absorbing properties

To tackle the aggravating electromagnetic wave (EMW) pollution issues, high-efficiency EMW absorption materials are being urgently explored. The FeSiCr soft magnetic alloy is one of the more widely used and well-received iron-based soft magnetic alloy materials with high permeability; however, the development of high-performance FeSiCr alloy wave-absorbing materials is still a major challenge. In this study, double core-shell-structured composites of MIL-88(Fe)@Fe2O3@FeSiCr were successfully prepared by the oxidative heat treatment of the flaky FeSiCr obtained after ball milling and then in situ composited with MIL-88(Fe). The heterogeneous interfacial composition and microstructure were regulated to balance the microwave-loss capability and impedance matching of the material, and an enhancement of the composite absorbing performance was achieved. The composite material had a reflection-loss minimization (RLmin) of -72.65 dB, corresponding to a frequency of 6.61 GHz, with an absorbing coating thickness of 2.97 mm and an effective absorbing bandwidth (RL ≤ -10 dB) of 2.38 GHz (5.42-7.80 GHz). The results of this study provide useful ideas for wave-absorbing materials by applying high permeability soft magnetic alloy micropowders.

Large Microsphere Structure of a Co/C Composite Derived from Co-MOF with Excellent Wideband Electromagnetic Microwave Absorption Performance

In the field of electromagnetic wave (EMW) absorption, carbon matrix materials based on metal-organic frameworks (MOFs) have drawn more interest as a result of their outstanding advantages, such as porous structure, lightweight, controlled morphology, etc. However, how to broaden the effective absorption bandwidth [EAB; reflection loss (RL) ≤ -10 dB] is still a challenge. In this paper, large microsphere structures of a Co/C composite composed of small particle clusters were successfully prepared by the solvothermal method and annealing treatment. At a filling ratio of 40 wt %, the Co/C composite shows attractive microwave absorption (MA) performance after being annealed at 600 °C in an atmosphere of argon. With an EAB of 6.32 GHz (9.92-16.24 GHz) and a thickness of just 2.57 mm, the minimum RL can be attained at -54.55 dB. Most importantly, the EAB can attain 7.12 GHz (10.88-18.0 GHz) when the thickness is 2.38 mm, which is larger than that of the majority of MOF-derived composites. The superior MA performance is strongly related to excellent impedance matching and a higher attenuation constant. This study provides a simple strategy for synthesizing a MOF-derived Co/C composite with a wide EAB.

Regulating conduction and polarization losses by adjusting bonded N in N-doped Cu/CuO/C composites

Conduction and polarization losses are the main forms of dielectric loss, and regulating these mechanisms is key to obtaining favorable electromagnetic wave absorption performance. In this study, the conversion of graphite N and pyridine N in Cu-based metal-organic framework (MOF)-derived composites was adopted to modulate conduction and polarization losses by tuning the pyrolysis temperature and Cu salt concentration. The results show that increasing the pyrolysis temperature facilitates the conversion of pyridine N to graphite N, which is beneficial for conduction loss. Moreover, increasing the Cu concentration promotes the transformation of pyridine N to graphite N as well as, and then promotes the reverse conversion of graphite N to pyridine N, which is conducive to defect-induced polarization. The unique layered Cu/CuO/C composite obtained at 700 °C with a moderate Cu content exhibited the optimal performance with an effective absorption bandwidth of 5.5 GHz (11.6 ∼ 17.1 GHz) at an ultra-thin thickness of 1.56 mm. This is owed to its favorable impedance matching, significant conduction loss, and polarization loss (defect-induced polarization and interfacial polarization). This study provides a novel strategy for regulating conduction and polarization losses.

Symbiotic strategy of Cu on CuFe2O4 realizing high-efficiency electromagnetic wave absorption

Low complex permittivity and easy magnetic agglomeration prevent ferrites from achieving high-efficiency electromagnetic wave (EMW) absorption owing to the resultant narrow absorption bandwidth. Existing composition- and morphology-controlled strategies have made limited progress in fundamentally improving the intrinsic complex permittivity and absorption performance of pure ferrite. In this study, Cu/CuFe₂O₄ composites were synthesized using a facile and low-energy sol-gel self-propagating combustion, and the metallic Cu content was adjusted by changing the ratio of the reductant (citric acid) to the oxidant (ferric nitrate). The symbiosis and coexistence of metallic Cu with ferritic CuFe₂O₄ increases the intrinsic complex permittivity of CuFe₂O₄, which can be regulated by changing the metallic Cu content_. Moreover, the unique ant-nest-like microstructure overcomes the issue of magnetic agglomeration. Because of the favorable impedance matching and strong dielectric loss (interfacial polarization and conduction loss) provided by the moderate metallic Cu content, S0.5 concurrently displays broadband absorption with an effective absorption bandwidth (EAB) of 6.32 GHz at an ultrathin thickness of 1.7 mm and strong absorption relying on minimum reflection loss (RL_min) of -48.81 dB at 4.08 GHz and 4.0 mm. This study provides a new perspective for improving the EMW absorption performance of ferrites.

Heterointerface construction for permalloy microparticles through the surface modification of bilayer metallic organic frameworks: Toward microwave absorption enhancement

Reasonable heterointerface modification can effectively regulate and enhance the microwave absorption of electromagnetic materials. The surface of magnetic permalloy (PM) microparticles is modified herein by coating double-layer metal organic frameworks (MOF), which are composed of a 2-methylimidazole cobalt salt (ZIF-67) layer and a 2-methylimidazole zinc salt (ZIF-8) layer. A stable heterointerface structure with cobalt/carbon (Co/C) and zinc/carbon (Zn/C) layers is formed on the surface of PM microparticles after pyrolysis. These particles include two types of composite particles of PM solely encapsulated by ZIF-67 or ZIF-8, PM@ZIF67 and PM@ZIF8, respectively, and two types of composite PM particles with a double-layered MOF outer shell structure obtained by exchanging the coating sequence (PM@ZIF8@ZIF67 and PM@ZIF67@ZIF8). Furthermore, the thermal decomposition temperature has a significant impact on the surface morphology and magnetic properties of the composite particles. After pyrolyzing at 500 °C, the PM@ZIF67@ZIF8 samples exhibit the highest microwave absorption performance among these samples. Specifically, the minimum reflection loss and effective absorption bandwidth of PM@ZIF67@ZIF8 after pyrolyzing at 500 °C can reach -47.3 dB at a matching thickness of 3.8 mm and 5.3 GHz at a matching thickness of 2.5 mm, respectively. A heterointerface with an electrical field orientation is created in the PM@ZIF67@ZIF8 particles, which effectively enhances the interface polarization and dipole polarization. Furthermore, the formation of a three-dimensional carbon network after pyrolysis is also useful for optimizing impedance matching and enhancing magneto-electric synergism.

Enhanced electromagnetic wave absorption of Fe3O4@MnO2@Ni-Co/C composites derived from Prussian blue analogues

Herein, Fe₃O₄@MnO₂@Ni-Co/C composites derived from PBAs were successfully fabricated. Firstly, Ni-Co Prussian blue analogues (Ni-Co PBAs) were used as precursors to derive a carbon layer on their surface by annealing treatment and subsequently translated into MnO₂@Ni-Co/C nanocubes after hydrothermal reactions. Fe₃O₄@MnO₂@Ni-Co/C composites were finally obtained after depositing Fe₃O₄ nanoparticles through the annealing process. Their electromagnetic wave (EMW) absorption performance apparently enhanced, thanks to the excellent impedance matching and strong attenuation derived from the synergy between the dielectric loss and the magnetic loss. In particular, the minimum reflection loss (RL_min) of Fe₃O₄@MnO₂@Ni-Co/C reached -41.2 dB with a thickness of 4.0 mm and the effective absorption bandwidth (EAB) reached 7.1 GHz with a thickness of 2.0 mm. Therefore, the results could be significant for synthesizing EMW absorbers with excellent performance, a broad bandwidth, strong absorption, thin thickness and light weight.

Texture Regulation of Metal-Organic Frameworks, Microwave Absorption Mechanism-Oriented Structural Optimization and Design Perspectives

Texture regulation of metal-organic frameworks (MOFs) is essential for controlling their electromagnetic wave (EMW) absorption properties. This review systematically summarizes the recent advancements in texture regulation strategies for MOFs, including etching and exchange of central ions, etching and exchange of ligands, chemically induced self-assembly, and MOF-on-MOF heterostructure design. Additionally, the EMW absorption mechanisms in approaches based on structure-function dependencies, including nano-micro topological engineering, defect engineering, interface engineering, and hybrid engineering, are comprehensively explored. Finally, current challenges and future research orientation are proposed. This review aims to provide new perspectives for designing MOF-derived EMW-absorption materials to achieve essential breakthroughs in mechanistic investigations in this promising field.

Low-Frequency Broadband Absorbing Coatings Based on MOFs: Design, Fabrication, Microstructure and Properties

Although most microwave absorbing materials (MAMs) have good absorption ability above 8 GHz, they perform poorly in the low-frequency range (1–8 GHz). Metal–organic frameworks (MOFs) derived carbon-based composites have been highly sought after in electromagnetic materials and functional devices, due to their high specific area, high porosity, high thermal stability, low reflection loss, and adjustable composition. In this review, we first introduce the three loss types of MAMs and argue that composite materials are effective ways to achieve broadband absorption. Secondly, the absorbing properties of traditional materials and MOF materials in the literature are compared, followed by a discussion of the promising strategies for designing MAMs with broadband absorption in low frequencies based on the recent progress. Finally, the main problems, fabrication methods, and applications are discussed for their future prospects.

Constructing ordered macropores in hollow Co/C polyhedral nanocages shell toward superior microwave absorbing performance

Rational design of porous carbon architecture is essential for superior microwave absorbing performance. Herein, we report a new type of hollow porous Co/C polyhedral nanocages with ordered macropores of  ∼60 nm (HP-Co/C) as microwave absorber, which were readily manufactured by epitaxial growth of ZIF-67/SiO₂ nanolayers on the surfaces of polyhedral ZIF-8 nanoparticle, and followed by simple calcination in Ar atmosphere and subsequent removal of SiO₂ with HF. The ordered macropores can effectively tune the electromagnetic parameters of HP-Co/C, affording the obtained HP-Co/C composites strong attenuation capability and excellent impedance matching characteristics for electromagnetic wave (EMW) absorption. As a result, the reflection loss (RL) and effective absorption bandwidth (EAB) of HP-Co/C prepared under pyrolysis temperature of 600 °C can reach up to -66.5 dB and 8.96 GHz, respectively, at filler fraction of only 15 wt%. Together, this study offers a new design philosophy to make lightweight and broadband microwave absorbent and can be extended to other types of microwave absorbers, significantly enriching the categories of the efficient microwave absorbing materials.

Recent Advancements in MOF/Biomass and Bio-MOF Multifunctional Materials: A Review

Metal–organic frameworks (MOFs) and their derivatives have delivered perfect answers in detection, separation, solving water and electromagnetic pollution and improving catalysis and energy storage efficiency due to their advantages including their highly tunable porosity, structure and versatility. Recently, MOF/biomass, bio-MOFs and their derivatives have gradually become a shining star in the MOF family due to the improvement in the application performance of MOFs using biomass and biomolecules. However, current studies lack a systematic summary of the synthesis and advancements of MOF/biomass, bio-MOFs and their derivatives. In this review, we describe their research progress in detail from the following two aspects: (1) synthesis of MOF/biomass using biomass as a template to achieve good dispersion and connectivity at the same time; (2) preparing bio-MOFs by replacing traditional organic linkers with biomolecules to enhance the connection stability between metal ions/clusters and ligands and avoid the formation of toxic by-products. This enables MOFs to possess additional unique advantages, such as improved biocompatibility and mechanical strength, ideal reusability and stability and lower production costs. Most importantly, this is a further step towards green and sustainable development. Additionally, we showcase some typical application examples to show their great potential, including in the fields of environmental remediation, energy storage and electromagnetic wave absorption.