Polypyrrole Shell Research Articles

A novel core–shell structure composed of polypyrrole shell and high-entropy oxide/carbon cloth core for high-performance supercapatteries

High-entropy oxides (HEOs) are promising candidates for supercapattery applications owing to their unique high entropy effect and abundant metal elements to provide high capacitance. However, their poor electrical conductivity, low specific capacitance, and limited stability still need to be addressed. Herein, coaxial core–shell structured electrodes (CoCrFeMnNi)3O4@CC-PPy are prepared by a two-step electrodeposition method. The core–shell electrode structure is formed by depositing (CoCrFeMnNi)3O4 (HEO) nanoparticles on a conductive carbon (CC) cloth followed by electrodeposition of a shell layer composed of highly conductive polypyrrole (PPy) nanospheres. The optimized HEO@CC-PPy-140s electrode prepared by electrodeposition for 140 s exhibits excellent specific capacitance reaching 791 F·g−1 at a current density of 0.5 A·g−1, and a specific capacitance retention of 63 % at a high current density of 10 A·g−1. Importantly, the use of HEO@CC-PPy as a negative electrode in a supercapattery device assembled with an electrodeposited NiCo2O4@CC positive electrode displays a high energy density of 49.2 Wh·kg−1 and good cycling stability, with a capacitance retention rate of 88.2 % after 3000 charge/discharge cycles. Overall, the proposed coaxial core–shell structure electrode design offers promising potential for the fabrication of supercapatteries with advanced characteristics.

Exploring glass fibers modification conditions and designing lightweight and efficient absorbers based on glass fiber @polypyrrole

Designability of glass fiber (GF) for microwave absorption is frequently neglected in buoyancy matrixes, which overcomes difficulties for their poor polarization loss to realize lightweight and efficient microwave absorption performance. In this study, GF coated with polypyrrole shell (GF@PPy) for multi-layered interface was successfully prepared through surface etching GF and then in-situ growth of PPy. According to the etching process of GF, GF@PPy-t40 (NaOH concentration with 16.67 mol/L, etching time with 40 min) demonstrates the efficient microwave absorption performance. Minimum reflection loss (RLmin) of GF@PPy-t40 (-10.40 dB, 3.0 mm) is 1.5 times that of GF@PPy-w10 (NaOH concentration with 2.78 mol/L) and 1.2 times that of GF@PPy-t60 (etching time with 60 min), which is ascribed to the enhancement of polarized sites caused by surface defects through appropriate etching concentration and time for NaOH. Based on the above etching conditions, we controlled the loading of in-situ polymerized PPy on GF through adjusting the concentration of pyrrole, realizing the impedance matching of 20 wt% GF@PPy in paraffin ring. GF@PPy-c60 (pyrrole concentration as 1.5 g) possesses the best microwave absorption performance, its RLmin is up to −30.40 dB (14.96 GHz, 1.5 mm) and effective absorption bandwidth (EAB) reaches to 4.8 GHz, which is ascribed to its excellent impedance matching. Especially, the density of GF@PPy-c60 can reach to 1.65 g cm−3, which is far below that of commercial GF (2.4–2.7 g cm−3). This modification lighters GF and effectively enhances microwave absorption performance, providing a basis for the radar stealth of GF in the marine environment.

Selective Adsorbent Design with Multifunctional Surfaces: Innovating Solutions for Heterogeneous Catalysis in Water.

Heterogeneous catalytic systems with water as the solvent often have the disadvantage of cross-contamination, while concerns about the purification and workup of the aqueous phase after reactions are rare in the lab or industry. In this context, designing and developing the functional selective solid adsorbent and revealing the adsorption mechanism can provide a new strategy and guidelines for constructing supported heterogeneous catalysts to address these issues. Herein, we report the stable composite adsorbent (Fe/ATP@PPy: magnetic Fe3O4/attapulgite with the polypyrrole shell) that features an integrated multifunctional surface, which can effectively tune the selective adsorption processes for Cu2+, Co2+, and Ni2+ ions and nitrobenzene via the cooperative chemisorption/physisorption in an aqueous system. The adsorption experiments showed that Fe/ATP@PPy displayed significantly higher adsorption selectivity for Ni2+ than Cu2+ and Co2+ ions, especially which exhibited an approximate 100.00% removal for both Ni2+ ions and nitrobenzene in the mixture system with a low concentration. Furthermore, combined tracking adsorption of Ni2+ ions and X-ray photoelectron spectroscopy characterization confirmed that the effective adsorption occurs via ion transfer coordination; the pathway was further validated at the molecular level through theoretical modeling. In addition, the selective adsorption mechanism was proposed based on the adsorption experiment, characterization, and the corresponding density functional theory calculation.

Wrinkle Structure Regulating Electromagnetic Parameters in Constructed Core-shell ZnFe2O4@PPy Microspheres as Absorption Materials.

Structure engineering of magnetic-dielectric multi-components is emerging as an effective approach for presuming high-performance electromagnetic (EM) absorption, but still faces bottlenecks due to the ambiguous regulation mechanism of surface morphology. Here, a novel wrinkled surface structure is tailored on the ZnFe2O4 microsphere via a spray-pyrolysis induced Kirkendall diffusion effect, the conductivity of the sample is affected, and a better impedance matching is adjusted by modulating the concentration of metal nitrate precursors. Driven by a vapor phase polymerization, conductive polypyrrole (PPy) shell are in situ decorated on the ZnFe2O4 microsphere surfaces, ingeniously constructing a core-shell ZnFe2O4@PPy composites. Moreover, a systematic investigation reveals that this unique wrinkled surface structure is highly dependent on the metal salt concentration. Optimized wrinkle ZnFe2O4@PPy composite exhibits a minimum reflection loss (RLmin) reached -41.0dB and the effective absorption bandwidth (EAB) can cover as wide as 4.1GHz. The enhanced interfacial polarization originated from high-density ZnFe2O4-PPy heterostructure, and the conduction loss of PPy contributes to the boosted dielectric loss capability. This study gives a significant guidance for preparing high-performance EM composites by tailoring the surface wrinkle structure.

Embedding cobalt polyoxometalate in polypyrrole shell for improved photoelectrochemical performance of BiVO4 core

Bismuth vanadate (BiVO4), as an appropriate semiconducting material with a narrow band gap and high light-harvesting, suffers from a high charge recombination rate and low photoactivity. To address these issues, in this work, the embedded cobalt polyoxometalate (POM) within the network of polypyrrole (PPy) coated on BiVO4 has been proposed to promote charge injection and separation. The photoanode based on BiVO4 was fabricated by electrophoretic deposition (EPD) under the optimized conditions. Conducting a comprehensive and fundamental study, we also implemented experiments to achieve the best conditions for BiVO4 preparation and the creation and optimization of PPy heterojunction with and without POM. The photoelectrochemical and physical analysis results revealed that the simultaneous incorporation of PPy and POM makes BiVO4 experience an impressive current enhancement, a 900% increase relative to bare BiVO4. Moreover, the hole extraction efficiency was enhanced to 93.7% from 15.12% (BiVO4), and charge separation yielded 33.83% from 24.47% (BiVO4). This study inspires promising studies on heterojunction formation through inorganic/organic semiconductor hybridization, achieved by molecular water oxidation co-catalysts like POM.

Cover Image, Volume 140, Issue 15

This cover by Miaotian Long describes a facile strategy to construct microencapsulated urea ammonium polyphosphate (PPy-UAPP) with a polypyrrole shell. The good compatibility between epoxy matrix and PPy-UAPP endows the resulting EP composites with a satisfactory balance between fire safety and mechanical properties. This work may open a new route for developing a super flame retardant and corresponding high-performance flame-retarded resins. DOI: 10.1002/app.53675

Bidirectional Tandem Electrocatalysis Manipulated Sulfur Speciation Pathway for High-Capacity and Stable Na-S Battery.

The sluggish polysulfide redox kinetics and the uncontrollable sulfur speciation pathway, leading to serious shuttling effect and high activation barrier associated with sulfur cathode. We describe here the use of core-shell structured composite matrixes containing abundant catalytic sites for nearly fully reversible cycling of sulfur cathodes for Na-S batteries. The bidirectional tandem electrocatalysis provide successive reversible conversion of both long- and short-chain polysulfides, whereas Fe2 O3 accelerates Na2 S8 /Na2 S6 to Na2 S4 conversion and the redox-active Fe(CN)6 4- -doped polypyrrole shell catalyzes Na2 S4 reduction to Na2 S. The electrochemically reactive Na2 S can be readily charged back to sulfur with minimal overpotential. Simultaneously, stable cycling of Na-S pouch cell with a high reversible capacity of 696 mAh g-1 is also demonstrated. The bidirectional confined tandem catalysis renders the manipulation of sulfur redox electrochemistry for practical Na-S cells.

Bidirectional Tandem Electrocatalysis Manipulated Sulfur Speciation Pathway for High‐Capacity and Stable Na‐S Battery

AbstractThe sluggish polysulfide redox kinetics and the uncontrollable sulfur speciation pathway, leading to serious shuttling effect and high activation barrier associated with sulfur cathode. We describe here the use of core–shell structured composite matrixes containing abundant catalytic sites for nearly fully reversible cycling of sulfur cathodes for Na‐S batteries. The bidirectional tandem electrocatalysis provide successive reversible conversion of both long‐ and short‐chain polysulfides, whereas Fe2O3 accelerates Na2S8/Na2S6 to Na2S4 conversion and the redox‐active Fe(CN)64−‐doped polypyrrole shell catalyzes Na2S4 reduction to Na2S. The electrochemically reactive Na2S can be readily charged back to sulfur with minimal overpotential. Simultaneously, stable cycling of Na‐S pouch cell with a high reversible capacity of 696 mAh g−1 is also demonstrated. The bidirectional confined tandem catalysis renders the manipulation of sulfur redox electrochemistry for practical Na‐S cells.

Smart Chemical Oxidative Polymerization Strategy To Construct Au@PPy Core-Shell Nanoparticles for Cancer Diagnosis and Imaging-Guided Photothermal Therapy.

Imaging-guided photothermal therapy (PTT) in a single nanoscale platform has aroused extensive research interest in precision medicine, yet only a few methods have gained wide acceptance. Thus, it remained an urgent need to facilely develop biocompatible and green probes with excellent theranostic capacity for superior biomedical applications. In this study, a smart chemical oxidative polymerization strategy was successfully developed for the synthesis of Au@PPy core-shell nanoparticles with polyvinyl alcohol (PVA) as the hydrophile. In the reaction, the reactant tetrachloroauric acid (HAuCl4) was reduced by pyrrole to fabricate a gold (Au) core, and pyrrole was oxidized to deposit around the Au core to form a polypyrrole (PPy) shell. The as-synthesized Au@PPy nanoparticles showed a regular core-shell morphology and good colloidal stability. Relying on the high X-ray attenuation of Au and strong near-infrared (NIR) absorbance of PPy and Au, Au@PPy nanoparticles exhibited excellent performance in blood pool/tumor imaging and PTT treatment by a series of in vivo experiments, in which tumor could be precisely positioned and thoroughly eradicated. Hence, the facile chemical oxidative polymerization strategy for constructing monodisperse Au@PPy core-shell nanoparticles with potential for cancer diagnosis and imaging-guided photothermal therapy shed light on an innovative design concept for the facile fabrication of biomedical materials.

Cyclodextrin-Functionalized Polypyrrole Particles for the Extraction of Aromatics from Water.

We describe the preparation of oil-in-water (o/w) colloidal particles with a polypyrrole (pPy) shell in which cyclodextrin has been incorporated at the oil-water interface via either physical adsorption or reaction with the pPy shell. The utility of these particles was assessed by the extraction of organic dyes from water. In all cases, we found that cyclodextrin incorporation significantly improved dye uptake, giving up to 78 ± 11% dye extraction in the case of a 100 ppm solution of 4-nitroaniline with a covalently incorporated cyclodextrin. We demonstrated the ability of our colloidal particles to extract nicotine-derived nitrosamine ketone (NNK), a potent carcinogen, from aqueous solution. By treating the solution containing 100 ppm NNK with our particles over 24 and 48 h, we found that NNK removal reached 65 ± 2 and 83 ± 1%, respectively. The uptake could be improved by re-treating a solution with additional freshly prepared particles, to achieve 95 ± 1% NNK extraction with a covalently incorporated cyclodextrin.

Preparation of double-yolk egg-like nanoreactor: Enhanced catalytic activity in Fenton-like reaction and insight on confinement effect

Peroxymonosulfate (PMS)-based Fenton-like reaction is an effective technique for the pollutant degradation, and the Co-based metal organic frameworks displayed the excellent activity for the PMS activation. Nevertheless, how to further improve the catalytic activity, suppress the leaching of toxic cobalt ions, and realize the rapid separation were still challenges for practical application. In this work, a novel solution was proposed: encapsulating Fe3O4 and Prussian blue analogue (PBA) into the polypyrrole (PPy) shell and constructing a “double-yolk egg-like” Fe3O4/PBA@PPy as a nanoreactor. In Fe3O4/PBA@PPy-10, the catalytic performance was remarkably enhanced with the help of confinement effect, and the degradation rate (0.38 L·min·mol−1) was 5.1 times than that of reference Fe3O4/PBA-10 (0.074 L·min·mol−1). In addition, the concentration of leached cobalt ions was reduced to only 0.174 mg/L by the protective function from the PPy shell. Moreover, the nanoreactor could be magnetically separated from the reaction solution due to the encapsulation of Fe3O4 nanospheres, and 84.5% of activity still preserved after the 4th cycle. The main active species involved in Fe3O4/PBA@PPy-10 system was 1O2, while that in reference Fe3O4/PBA-10 system was OH. Electron spin resonance analysis and radical trapping experiment revealed that the different catalytic mechanisms were attributed to the confinement effect inside the hollow cavity. This work not only presents a feasible way to prepare rarely-reported double-yolk egg-like nanoreactor, but also provides a new insight to solve the bottlenecks in Fenton-like reaction.

Rational construction of hierarchical porous FeP nanorod arrays encapsulated in polypyrrole for efficient and durable hydrogen evolution reaction

Employing an environmentally friendly and economical approach to significantly improve the electrocatalytic activity for hydrogen evolution reaction (HER) has attracted widespread attention because of its enormous value and challenge. Herein, we report a series of FeP nanorod arrays (FeP NRAs) with polypyrrole (PPy) shell coating on carbon textiles (CTs) to improve the HER performance. The composite combines the high conductivity of PPy and synergistic effect between FeP and PPy, where the PPy coating remarkably reduces the apparent activation energy for HER and increases the turnover frequency of catalysts, thus the electrocatalytic performance of [email protected]/CTs hybrid nanorod arrays is significantly improved. Among them, the [email protected]/CTs-5 h catalyst exhibit superior HER performance with a low onset over-potential of 103.1 mV and a small Tafel slope of 49.2 mV/dec at 10 mA cm−2, and as well as an excellent long-term stability during operation for 46 h. Notably, it shows efficient HER performance during various bending status, demonstrating that the stability and flexibility of [email protected]/CTs catalysts. The excellent electrocatalytic performance is promising for applications as a cost-effective non-noble-metal HER catalyst during electrochemical water splitting for large-scale hydrogen fuel production.

Engineering NH3-induced 1D self-assembly architecture with conductive polymer for advanced hybrid Na-CO2 batteries via morphology modulation

Designing catalytic cathodes with excellent electrocatalytic activities and durability for Na-CO 2 batteries has captured considerable attention so far. Here, a series of morphologically controlled low-crystalline CuCo 2 O 4 was prepared by thermal oxidation of self-assembled Cu-Co precursors ( p -CCO). One-dimensional (1D) rod-like of CuCo 2 O 4 was subsequently encapsulated in polypyrrole shell (PPy) by in-situ polymerization of pyrrole monomers as an advanced catalyst (CCO/PPy) for high-performance Na-CO 2 batteries. It was demonstrated that ammonia solution exerts an important influence on the surface morphology and size of the p -CCO crystallites by the rate of nucleation and growth. Particle size and 1D architecture modulation, associated with the encapsulation of conductive PPy effectively improve the directional transfer rate of ions and the conductivity of the electrode. More importantly, PPy introduction not only induces interfacial reconstruction of CuCo 2 O 4 , arousing more oxygen vacancies and catalytic active sites, but also contributes to the corrosion protection of the active material from the electrolyte during long-term operation. Bestowed by these advantages, the fabricated hybrid Na-CO 2 battery manifested prominent electrochemical performance with a superior areal discharge capacity of 31.3 mAh cm −2 , low discharge-charge voltage gap of 0.6 V, over 400 cycles. • The 1D rod-like CuCo 2 O 4 with oxygen vacancies was obtained by morphology modulation. • A mechanism for the directional growth of NH 3 -induced Cu-Co precursors was proposed. • CCO/PPy exhibited enriched active sites with superior CRR and CER performance. • A high areal capacity of 31.3 mAh·cm −2 and over 400 cycles were achieved.

High-performance Fe–N–C electrocatalysts with a “chain mail” protective shield

Nitrogen-coordinated iron atoms on carbon supports (Fe–N–C) are among the most promising noble-metal-free electrocatalysts for oxygen reduction reaction (ORR). However, their unsatisfactory stability limits their practical application. Herein, we demonstrate a dual-shell Fe–N–C electrocatalyst with excellent catalytic activity and long-term stability. Pyrrole and dopamine are sequentially polymerized on a fumed silica nanoparticle template. Metal precursor (FeCl 3 ) and pore formation agent (ZnCl 2 ) were loaded on the inner polypyrrole shell. During carbonization, the Zn evaporation creates abundant mesopores in the polydopamine-derived outer carbon shell, forming a “chain mail” like outer shell that protects Fe–N–C active sites loaded on the inner carbon shell and enables efficient mass transfer. Systematical tuning of the shield thickness and porosity affords the optimal electrocatalyst with a large surface area of 934 ​m 2 ​g −1 and a high Fe loading of 2.04 ​wt%. This electrocatalyst delivers excellent ORR activity and superior stability in both acidic and alkaline electrolytes. Primary Zn-air batteries fabricated from this electrocatalyst delivers a high-power density of 257 ​mW ​cm −2 and impressive durability of continuous discharging over 250 ​h. Creating a graphitic and porous carbon protective shell can be further extended to other electrocatalysts to enable their practical applications in energy conversion and storage.

Gold nanorod@void@polypyrrole yolk@shell nanostructures: Synchronous regulation of photothermal and drug delivery performance for synergistic cancer therapy

Synergistic therapy has been emerging as new trend for effective tumor treatment due to synchronous function and cooperative reinforcement of multi therapeutic modalities. Herein, gold nanorods (GNRs) encapsulated into polypyrrole (PPy) shell with tunable void space (GNRs@Void@PPy) showing yolk@shell nanostructures were innovatively designed. The exploitation of dual near-infrared (NIR) absorptive species offered synergistic enhancement of photothermal performance. In addition, the manipulation of the void space between them provided additional benefits of high drug encapsulation efficiency (92.6%) and, interestingly, tumor microenvironment and NIR irradiation triggered targeted drug releasing. Moreover, the GNRs@Void@PPy exhibited excellent biocompatibility, and optimal curative effect by chemo-photothermal synergistic therapy was achieved through both in vitro and in vivo antitumor activity investigation.

Facile fabrication of metal–organic framework derived Fe/Fe3O4/FeN/N-doped carbon composites coated with PPy for superior microwave absorption

At present, the magnetic metal/carbon composites have been widely explored for microwave absorption (MA), which effectively integrate the characteristics of magnetic and dielectric materials. As a typical material, metal–organic framework (MOF) shows tremendous potential as a precursor or template. However, its development is limited by the inferior impedance matching. Herein, a novel rod-like Fe/Fe3O4/FeN/N-doped carbon (FON/NC) composite was synthesized via dual-ligand strategy and following calcination. The outer polypyrrole (PPy) shell, obtained by a facile polymerization method, effectively optimized the impedance matching and observably enhanced the MA capacity. Both the multi-component loss mechanism and unique porous core–shell structures of MOF-derived composites were beneficial for microwave attenuation. The effects of filler loadings (20 wt%, 25 wt%, 30 wt% and 35 wt%) on electromagnetic (EM) properties of FON/NC@PPy composites were discussed. Remarkably, as-obtained composites exhibited a minimum reflection loss (RL) value of −60.08 dB at the layer thickness of merely 1.44 mm and the widest effective absorption bandwidth (EAB, RL ≤ −10 dB) of 5.06 GHz at 1.64 mm with 30 wt% filler loading. This work provides a great reference for designing MOF-derived absorbers with high MA performance.

Encapsulating manganese oxide nanoparticles within conducting polypyrrole via in situ redox reaction and oxidative polymerization for long-life lithium-ion batteries

Manganese oxides (MnOx) have been extensively investigated due to their extremely high theoretical capacities for application as conversion anodes in lithium-ion batteries. However, fully performing their theoretical performance still faces poor electric conductivity and serious volume change upon lithium insertion/extraction. Herein, we demonstrate encapsulating manganese oxide nanoparticles within a conducting polymer polypyrrole (PPy) shell as a facile strategy to overcome such flaws through in situ redox reaction and oxidative polymerization process. Such an in situ method combines the redox reaction between potassium permanganate and tetrahydrofuran to form MnOx nanoparticles and the subsequent oxidative polymerization of pyrrole to form a conductive polypyrrole coating shell by the oxidant KMnO4 into one step. For the as-fabricated products (MnOx@PPy), this tenderly introduced conductive PPy shell highly favors the fast electron transfer and preserves the electrode structure integrity upon repeated cycling. As the anode for LIBs, MnOx@PPy exhibits superior lithium storage performance with a high reversible capacity (1538 mAh·g−1), long-life cyclability (747 mAh·g−1 after 1000 cycles at 1.0C) and durable ratability (574 mAh·g−1 at 2.0C). This work demonstrates that the convenient in situ strategy to form conductive polymer coating shell is effective to improve the performance of conversion anodes and can be extended to other materials for energy storage applications.

A Highly Efficient One-for-All Nanodroplet for Ultrasound Imaging-Guided and Cavitation-Enhanced Photothermal Therapy.

BackgroundPhotothermal therapy (PTT) has attracted considerable attention for cancer treatment as it is highly controllable and minimally invasive. Various multifunctional nanosystems have been fabricated in an “all-in-one” form to guide and enhance PTT by integrating imaging and therapeutic functions. However, the complex fabrication of nanosystems and their high cost limit its clinical translation.Materials and MethodsHerein, a high efficient “one-for-all” nanodroplet with a simple composition but owning multiple capabilities was developed to achieve ultrasound (US) imaging-guided and cavitation-enhanced PTT. Perfluoropentane (PFP) nanodroplet with a polypyrrole (PPy) shell (PFP@PPy nanodroplet) was synthesized via ultrasonic emulsification and in situ oxidative polymerization. After characterization of the morphology, its photothermal effect, phase transition performance, as well as its capabilities of enhancing US imaging and acoustic cavitation were examined. Moreover, the antitumor efficacy of the combined therapy with PTT and acoustic cavitation via the PFP@PPy nanodroplets was studied both in vitro and in vivo.ResultsThe nanodroplets exhibited good stability, high biocompatibility, broad optical absorption over the visible and near-infrared (NIR) range, excellent photothermal conversion with an efficiency of 60.1% and activatable liquid-gas phase transition performance. Upon NIR laser and US irradiation, the phase transition of PFP cores into microbubbles significantly enhanced US imaging and acoustic cavitation both in vitro and in vivo. More importantly, the acoustic cavitation enhanced significantly the antitumor efficacy of PTT as compared to PTT alone thanks to the cavitation-mediated cell destruction, which demonstrated a substantial increase in cell detachment, 81.1% cell death in vitro and 99.5% tumor inhibition in vivo.ConclusionThe PFP@PPy nanodroplet as a “one-for-all” theranostic agent achieved highly efficient US imaging-guided and cavitation-enhanced cancer therapy, and has considerable potential to provide cancer theranostics in the future.

ZnFe2O4@PDA@Polypyrrole composites with efficient electromagnetic wave absorption properties in the 18–40 GHz region

ZnFe2O4@PDA@PPy composites with core/shell/shell structures were successfully prepared via two successive polymerization steps, with the electromagnetic wave (EMW) absorber properties of the composites then being evaluated in the 18–40 GHz region. Magnetic spherical zinc ferrite (ZnFe2O4) particles with diameters ~350 nm were first prepared and used as the core material, over which polydopamine (PDA) and polypyrrole (PPy) shells were successively deposited. The obtained ZnFe2O4@PDA@PPy composites exhibited outstanding EMW absorption properties in the 18–40 GHz, with the thickness of PDA layer and loading of the ZnFe2O4@PDA@PPy composites in the absorber influencing EMW absorption performance. For the composite with the optimal PDA shell thickness, a minimum reflection loss (RLmin) of − 65.66 dB at 24.46 GHz and an effective absorption bandwidth (EAB, reflection loss less than − 10 dB) of 19.07 GHz (18.74–37.81 GHz) was realized at an absorber thickness of 1.0 mm (17 wt% composite in PVDF). When the composite loading was 10 wt%, the RLmin was − 36.35 dB at 25.99 GHz with an EAB of 22 GHz (18–40 GHz) at a thickness of only 1.5 mm. The outstanding EMW absorption performance of the ZnFe2O4@PDA@PPy composites can be attributed to good impedance matching arising from magnetic losses (ZnFe2O4 particles), dielectric losses (ZnFe2O4, PDA and PPy) and interfacial relaxation losses (at ZnFe2O4–PDA–PPy–PVDF interfaces). This work supports the development of low-cost microwave absorbers in the 18–40 GHz region.

Ultra-broadband and covalently linked core–shell CoFe2O4@PPy nanoparticles with reduced graphene oxide for microwave absorption

Covalent bond usually ensures a stable connection between nonmetallic atoms. However, the traditional reflux method usually requires the construction of complex instruments and equipment with tedious steps to ensure airtightness and reaction stability. In this work, an advanced method is adopted to bind core–shell CoFe2O4@PPy and rGO tightly via the aid of 2-(1H-pyrrol-1-yl)ethanamine (PyEA), dispense with a high-temperature environment or protective gas. Cobalt ferrite core and polypyrrole shell collaborate to approach suitable magnetic and conduction loss, while reduced graphene oxide usually provides a stable sheet structure for interface multiple reflections, and replenish the insufficient dielectric loss. The filled biscuit-shaped covalently bond CoFe2O4@PPy-rGO has a fantastically broad absorption bandwidth of 13.12 GHz under the thickness of 3.6 mm, together with a minimum reflection loss of −50.1 dB at 6.56 GHz, achieving both impedance matching and attenuation matching, and effectively responding to all electromagnetic waves in the X and Ku bands. Thus, the covalently bonded CoFe2O4@PPy-rGO has potential application in broadband absorption.