Aerobically Autoxidized Self-Charge Concept Derived from Synergistic Pyrrolic Nitrogen and Catechol Configurations in N, O Co-Doped Carbon Cathode Material.

Aerobically autoxidized self-charging concept has drawn significant attraction due to its promising chemical charge features without external power supply. Particularly, heteroatom-doped carbon materials with abundant oxidizable sites and good conductivity are expected to be ideal cathode materials. However, there is no well-defined aerobically autoxidized self-charging concept based on heteroatom-doped carbon materials, significantly hindering the design of related carbon cathodes. An aerobically autoxidized self-chargeable concept derived from synergistic effect of pyrrolic nitrogen and catechol configuration in carbon cathode using model single pyrrolic nitrogen and oxygen (N-5, O) co-doped carbon and O-enriched carbon is proposed. First, self-charging of N-5, O co-doped carbon cathode can be achieved by aerobic oxidation of pyrrolic nitrogen and catechol to oxidized pyrrolic nitrogen and ortho-quinone configurations, respectively. Second, introducing a single pyrrolic nitrogen configuration enhanced acidic wettability of N-5, O co-doped carbon facilitating air self-charge/galvanic discharge involving proton removal/introduction. Third, synergistic effect of pyrrolic nitrogen and hydroxyl species with the strong electron-donating ability to conjugated carbon-based backbone endows N-5, O co-doped carbon with a higher highest occupied molecular orbital (HOMO) energy level more susceptible to oxidation charging. The assembled Cu/Carbon batteries can drive a timer after every air-charging run. This promising aerobically autoxidized self-charging concept can inspire exploring high-efficiency self-charging devices.

Unprecedented 100% conversion from pyridinic to pyrrolic nitrogen configuration for electrochemically active nitrogen-doped carbon materials.

Nitrogen-doped carbons with promising electrochemical performance exhibit a strong dependence on nitrogen configuration. Therefore, accurate control of nitrogen configurations is crucial to clarify their influence. Unfortunately, there is still no well-defined conversion route to finely control nitrogen configuration. Herein, we proposed the concept of 100% conversion from pyridinic to pyrrolic nitrogen in carbon materials through low-temperature pyrolysis and alkali activation of hydroxypyridine-3-halophenol-formaldehyde resins. Their dehalogenation pyrolysis promotes formation of carbon intermediates and conversion of tautomeric pyridone and hydroxypyridine into pyrrolic and pyridinic nitrogen through eliminating carbonyl and hydroxyl functionalities, respectively. Continuous thermal alkali activation introduces hydroxyl groups into carbon materials, converting pyridinic species to intermediate hydroxypyridine and pyridone; subsequently, these configurations transform to pyridinic and pyrrolic nitrogen, respectively, and finally, an excessive alkali ensures 100% conversion from pyridinic to pyrrolic nitrogen. NaOH activation for pyrrolic and pyridinic nitrogen co-doped carbon and KOH activation for model nitrogen-containing compounds including acridine, phenanthridine, and acridone further confirm that alkali activation plays an indispensable role in 100% conversion from pyridinic to pyrrolic units through the tautomeric hydroxypyridine and pyridone intermediates. Low-temperature alkali-induced controllable conversion of nitrogen configuration in carbon materials is suitable modulating nitrogen configurations for almost all nitrogen-doped carbon materials in electrochemical applications.

Proof of Aerobically Autoxidized Self-Charge Concept Based on Single Catechol-Enriched Carbon Cathode Material.

HIGHLIGHTS: An air-breathing chemical self-charge concept of oxygen-enriched carbon cathode. The oxygen-enriched carbon material with abundant catechol groups. Rapid air-oxidation chemical self-charge of catechol groups. The self-charging concept has drawn considerable attention due to its excellent ability to achieve environmental energy harvesting, conversion and storage without an external power supply. However, most self-charging designs assembled by multiple energy harvesting, conversion and storage materials increase the energy transfer loss; the environmental energy supply is generally limited by climate and meteorological conditions, hindering the potential application of these self-powered devices to be available at all times. Based on aerobic autoxidation of catechol, which is similar to the electrochemical oxidation of the catechol groups on the carbon materials under an electrical charge, we proposed an air-breathing chemical self-charge concept based on the aerobic autoxidation of catechol groups on oxygen-enriched carbon materials to ortho-quinone groups. Energy harvesting, conversion and storage functions could be integrated on a single carbon material to avoid the energy transfer loss among the different materials. Moreover, the assembled Cu/oxygen-enriched carbon battery confirmed the feasibility of the air-oxidation self-charging/electrical discharging mechanism for potential applications. This air-breathing chemical self-charge concept could facilitate the exploration of high-efficiency sustainable air self-charging devices.

Physicochemical and Structural Properties of Gluten-Konjac glucomannan Conjugates Prepared by Maillard Reaction.

Gluten (Glu) is important to wheat products by forming a three-dimensional matrix. This study aimed to investigate the physicochemical and structural properties of gluten after conjugation with konjac glucomannan (KGM) through the Maillard reaction. The study revealed that the degree of graft increased with the prolonged reaction time. The Glu-KGM conjugates were possessed of increased ß-sheet but decreased α-helix and ß-turn, as well as unfolding and loose tertiary structures as the reaction proceeded. Among three different proportions, the Glu-KGM 1:1 conjugate was proved to have the most excellent foaming and emulsifying properties, and could form more rigid and firm gelation structures, which could be related to the decreased particle size and increased zeta potential of the conjugate. Overall, the physicochemical and structural properties of gluten were significantly related to the KGM ratios as well as the reaction period.

Architecture inspired structure engineering toward carbon nanotube hybrid for microwave absorption promotion.

Constructing sophisticated 3D structure has been shown to be fruitful in developing carbon nanotubes (CNTs) microwave absorbers (MAs). However, issues with the unclear electromagnetic (EM) responding synergy of CNTs toward substrate and the limited dissipation property caused by the large dense CNTs networks throughout the reported models still need to be resolved. Inspired by the creeper-window-room-structured architecture, an analogous conformal nanostructure of amorphous carbon/CNTs (N-AC/CNTs) hybrid is constructed through an in situ autocatalytic planting approach. By this model, not only the inheritance of frequency dependence characteristic but the co-inheritance of lossy behavior and impedance matching is demonstrated. Moreover, by virtue of the unique structure, a synergistic reinforcing dielectric loss from conductive loss and dielectric polarization was introduced. Therefore, N-AC/CNTs-750 shows impressive EM performance. This work hereby unveils the synergy of EM response from CNTs toward substrate, and provides a pioneering insight into developing architecture-inspired structure engineering to construct high-performance MAs.

Reconfigurable Inverse Opal Structure Film for a Rewritable and Double-Sided Photonic Crystal Paper.

A rewritable photonic crystal (PC) paper as an environmentally friendly and low-resource-consuming material for information storage and spreading has gradually become a research hotspot. In this work, a novel rewritable PC paper with inkless writing and double-sided rewritability properties was developed. A double-sided epoxy resin PC paper exhibiting an inverse opal structure and a bright structural color was fabricated using the sacrificial template method. Carbon black was doped into the material to increase color saturation and purity while preventing light transmission and protecting the double-sided structural color from interference. The force of sliding friction and deformation triggered by capillary pressure as well as swelling-triggered recovery of the inverse opal structure led to an easy rewriting of the PC paper. The PC paper exhibited excellent rewritability even after 50 runs of the rewriting process. Given the inkless and double-sided rewriting, this study provides a new method for the preparation of rewritable PC papers.

Yolk-Shell Fe3 O4 @Void@N-Carbon Nanostructures Based on One-Step Deposition of SiO2 and Resorcinol-3-Aminophenol-Formaldehyde (R-APF) Cocondensed Resin Dual Layers onto Fe3 O4 Nanoclusters.

Yolk-shell magnetic nanoparticles@nitrogen-enriched Carbon nanostructures with a magnetic core and a hollow nitrogen-enriched carbon shell exhibit considerable promise in various applications, such as drug delivery, heterogenous catalysts, removal of metal ions and organic pollutants, and screening of biomolecules, due to their strong magnetic response, unique cavities, and the selective absorption ability of nitrogen-enriched groups. However, their complicated synthesis always involves possible surface modification, layer-by-layer deposition of a sacrificial middle layer and an outer nitrogen-enriched layer on magnetic nanoparticles, subsequent carbonization, and final removal of the sacrificial middle layer. Herein, yolk-shell Fe3 O4 @nitrogen-enriched carbon nanostructures are constructed based on NH4 + ion-induced one-step deposition of SiO2 and Resorcinol-3-aminophenol-formaldehyde cocondensed resin (R-APF) dual layers onto poly acrylic acid-modified Fe3 O4 nanoclusters without any extra surface modification. The N-Carbon shell thickness of the yolk-shell Fe3 O4 @Void@N-Carbon nanostructure can be finely tailored though tailoring the feeding amount of aminophenol and resorcinol to tune the thickness of the outer R-APF resin shell onto Fe3 O4 @SiO2 intermediate particles. This NH4 + ion-induced one-pot deposition of double layers can effectively promote synthesis efficiency of this kind of yolk-shell nanostructure.

Single-site pyrrolic-nitrogen-doped sp2-hybridized carbon materials and their pseudocapacitance.

Integrating nitrogen species into sp2-hybridized carbon materials has proved an efficient means to improve their electrochemical performance. Nevertheless, an inevitable mixture of nitrogen species in carbon materials, due to the uncontrolled conversion among different nitrogen configurations involved in synthesizing nitrogen-doped carbon materials, largely retards the precise identification of electrochemically active nitrogen configurations for specific reactions. Here, we report the preparation of single pyrrolic N-doped carbon materials (SPNCMs) with a tunable nitrogen content from 0 to 4.22 at.% based on a strategy of low-temperature dehalogenation-induced and subsequent alkaline-activated pyrolysis of 3-halogenated phenol-3-aminophenol-formaldehyde (X-APF) co-condensed resins. Additionally, considering that the pseudocapacitance of SPNCMs is positively dependent on the pyrrolic nitrogen content, it could be inferred that pyrrolic nitrogen species are highly active pseudocapacitive sites for nitrogen-doped carbon materials. This work gives an ideal model for understanding the contribution of pyrrolic nitrogen species in N-doped carbon materials.

Fabrication of Three-Dimensional Flower-like Heterogeneous Fe3O4/Fe Particles with Tunable Chemical Composition and Microwave Absorption Performance.

Heterogeneous Fe3O4 and Fe composites are highly desirable for microwave absorption application because of their complementary electromagnetic (EM) properties. With three-dimensional (3D) Fe2O3 as a sacrificing template, we realize the construction of Fe3O4/Fe composites with tunable chemical composition, and more importantly, these composites inherit the unique 3D microstructure from their precursor. The change in chemical composition produces significant impacts on the EM functions of these composites. On the one hand, dielectric loss can be improved greatly through positive interfacial polarization and reach the peak when the mass contents of Fe3O4 and Fe are 72.1 and 27.9 wt %, respectively. On the other hand, high Fe content slightly pulls down magnetic loss in the low-frequency range but favors strong magnetic loss in the high-frequency range because of the breakthrough of Snoek's limitation. The attenuation constant reveals that dielectric loss dominates overall consumption of incident EM waves. As a result, the optimized composite, F-350 (the reduction of Fe2O3 is conducted at 350 °C), shows the best microwave absorption performance, whose strongest reflection loss is -56.0 dB at 17.5 GHz and the effective bandwidth can cover the frequency range of 12.0-15.5 GHz with the thickness of 1.5 mm. Furthermore, an ultrawide effective bandwidth of 15.3 GHz can be achieved with the integrated thickness of 1.0-5.0 mm. Such a performance is superior to those of many reported Fe3O4/Fe composites, and a comparative analysis manifests that good microwave absorption of F-350 is also benefited from its unique 3D architecture.

Monomer Protonation-Dependent Surface Polymerization to Achieve One-Step Grafting Cross-Linked Poly(4-Vinylpyridine) Onto Core-Shell Fe3 O4 @SiO2 Nanoparticles.

Functional polymer-grafting silica nanoparticles hold great promise in diverse applications such as molecule recognition, drug delivery, and heterogeneous catalysis due to high density and uniform distribution of functional groups and their tunable spatial distance. However, conventional grafting methods from monomers mainly consist of one or more extra surface modification steps and a subsequent surface polymerization step. A monomer protonation-dependent surface polymerization strategy is proposed to achieve one-step uniform surface grafting of cross-linked poly(4-vinylpyridine) (P4VP) onto core-shell Fe3 O4 @SiO2 nanostructures. At an approximate pH, partially protonated 4VP sites in aqueous solution can be strongly adsorbed onto deprotonated silanol groups (SiO- ) onto Fe3 O4 @SiO2 nanospheres to ensure prior polymerization of these protonated 4VP sites exclusively onto Fe3 O4 @SiO2 nanoparticles and subsequent polymerization of other 4VP and divinylbenzene monomers harvested by these protonated 4VP monomers onto Fe3 O4 @SiO2 nanoparticles, thereby achieving direct grafting of cross-linked P4VP macromolecules onto Fe3 O4 @SiO2 nanoparticles.

Hierarchical AuNPs-Loaded Fe3O4/Polymers Nanocomposites Constructed by Electrospinning with Enhanced and Magnetically Recyclable Catalytic Capacities.

Gold nanoparticles (AuNPs) have attracted widespread attention for their excellent catalytic activity, as well as their unusual physical and chemical properties. The main challenges come from the agglomeration and time-consuming separation of gold nanoparticles, which have greatly baffled the development and application in liquid phase selective reduction. To solve these problems, we propose the preparation of polyvinyl alcohol(PVA)/poly(acrylic acid)(PAA)/Fe3O4 nanocomposites with loaded AuNPs. The obtained PVA/PAA/Fe3O4 composite membrane by electrospinning demonstrated high structural stability, a large specific surface area, and more active sites, which is conducive to promoting good dispersion of AuNPs on membrane surfaces. The subsequently prepared PVA/PAA/Fe3O4@AuNPs nanocomposites exhibited satisfactory nanostructures, robust thermal stability, and a favorable magnetic response for recycling. In addition, the PVA/PAA/Fe3O4@AuNPs nanocomposites showed a remarkable catalytic capacity in the catalytic reduction of p-nitrophenol and 2-nitroaniline solutions. In addition, the regeneration studies toward p-nitrophenol for different consecutive cycles demonstrate that the as-prepared PVA/PAA/Fe3O4@AuNPs nanocomposites have outstanding stability and recycling in catalytic reduction.

In Situ Confined Growth Based on a Self-Templating Reduction Strategy of Highly Dispersed Ni Nanoparticles in Hierarchical Yolk-Shell Fe@SiO2 Structures as Efficient Catalysts.

Ni-based magnetic catalysts exhibit moderate activity, low cost, and magnetic reusability in hydrogenation reactions. However, Ni nanoparticles anchored on magnetic supports commonly suffer from undesirable agglomeration during catalytic reactions due to the relatively weak affinity of the magnetic support for the Ni nanoparticles. A hierarchical yolk-shell Fe@SiO2 /Ni catalyst, with an inner movable Fe core and an ultrathin SiO2 /Ni shell composed of nanosheets, was synthesized in a self-templating reduction strategy with a hierarchical yolk-shell Fe3 O4 @nickel silicate nanocomposite as the precursor. The spatial confinement of highly dispersed Ni nanoparticles with a mean size of 4 nm within ultrathin SiO2 nanosheets with a thickness of 2.6 nm not only prevented their agglomeration during catalytic transformations but also exposed the abundant active Ni sites to reactants. Moreover, the large inner cavities and interlayer spaces between the assembled ultrathin SiO2 /Ni nanosheets provided suitable mesoporous channels for diffusion of the reactants towards the active sites. As expected, the Fe@SiO2 /Ni catalyst displayed high activity, high stability, and magnetic recoverability for the reduction of nitroaromatic compounds. In particular, the Ni-based catalyst in the conversion of 4-nitroamine maintained a rate of over 98 % and preserved the initial yolk-shell structure without any obvious aggregation of Ni nanoparticles after ten catalytic cycles, which confirmed the high structural stability of the Ni-based catalyst.

UV-Triggered Self-Healing of a Single Robust SiO2 Microcapsule Based on Cationic Polymerization for Potential Application in Aerospace Coatings.

UV-triggered self-healing of single microcapsules has been a good candidate to enhance the life of polymer-based aerospace coatings because of its rapid healing process and healing chemistry based on an accurate stoichiometric ratio. However, free radical photoinitiators used in single microcapsules commonly suffer from possible deactivation due to the presence of oxygen in the space environment. Moreover, entrapment of polymeric microcapsules into coatings often involves elevated temperature or a strong solvent, probably leading to swelling or degradation of polymer shell, and ultimately the loss of active healing species into the host matrix. We herein describe the first single robust SiO2 microcapsule self-healing system based on UV-triggered cationic polymerization for potential application in aerospace coatings. On the basis of the similarity of solubility parameters of the active healing species and the SiO2 precursor, the epoxy resin and cationic photoinitiator are successfully encapsulated into a single SiO2 microcapsule via a combined interfacial/in situ polymerization. The single SiO2 microcapsule shows solvent resistance and thermal stability, especially a strong resistance for thermal cycling in a simulated space environment. In addition, the up to 89% curing efficiency of the epoxy resin in 30 min, and the obvious filling of scratches in the epoxy matrix demonstrate the excellent UV-induced healing performance of SiO2 microcapsules, attributed to a high load of healing species within the capsule (up to 87 wt %) and healing chemistry based on an accurate stoichiometric ratio of the photoinitiator and epoxy resin at 9/100. More importantly, healing chemistry based on a UV-triggered cationic polymerization mechanism is not sensitive to oxygen, extremely facilitating future embedment of this single SiO2 microcapsule in spacecraft coatings to achieve self-healing in a space environment with abundant UV radiation and oxygen.

Nitrogen-Enriched Fe3O4@Carbon Nanospheres Derived from Fe3O4@3-Aminophenol/Formaldehyde Resin Nanospheres Based on a Facile Hydrothermal Strategy: Towards a Robust Catalyst Scaffold for Platinum Nanocrystals.

Robust nitrogen-enriched Fe3O4@carbon nanospheres have been fabricated as a catalyst scaffold for Pt nanoparticles. In this work, core-shell Fe3O4@3-aminophenol/formaldehyde (APF) nanocomposites were first synthesized by a simple hydrothermal method, and subsequently carbonized to Fe3O4@N-Carbon nanospheres for in situ growth of Pt nanocrystals. Abundant amine groups were distributed uniformly onto Fe3O4@N-Carbon nanospheres, which not only improved the dispersity and stability of the Pt nanocrystals, but also endowed the Pt-based catalysts with good compatibility in organic solvents. The dense three-dimensional cross-linked carbon shell protects the Fe3O4 cores against damage from harsh chemical environments, even in aqueous HCl (up to 1.0 M) or NaOH (up to 1.0 M) solutions under ultrasonication for 24 hours, which indicates that it can be used as a robust catalyst scaffold. In the reduction of nitrobenzene compounds, the Fe3O4@N-Carbon@Pt nanocatalysts show outstanding catalytic activity, stability, and recoverability.

Fabrication of hierarchical Fe3O4@SiO2@P(4VP-DVB)@Au nanostructures and their enhanced catalytic properties.

Hierarchical Fe3O4@SiO2@P(4VP-DVB)@Au nanostructures were prepared in which the slightly cross-linked, thin poly(4-vinylpyridine-co-divinylbenzene) (P(4VP-DVB)) shells were constructed onto Fe3O4@SiO2 nanospheres, followed by in situ embedding of gold nanocrystals homogeneously into the P4VP chains. These slightly cross-linked chains, easily swollen by the reactants, make the gold nanocrystals accessible to the reactants, and the thin shell (about 15 nm) reduces the diffusion distance of the reactants to the active gold nanocrystals (about 5 nm), thereby enhancing their catalytic activity and utility. At the same time, confinement of gold nanocrystals within the P4VP shells prevents their migration and coagulation during catalytic transformations. Hence the nanocomposites exhibit high activity (up to 4369.5 h(-1) of turnover frequency (TOF)) and controllable magnetic recyclability without any significant loss of gold species after ten runs of catalysis in the reduction of 4-nitrophenol.

Facile hydrogen-bond-assisted polymerization and immobilization method to synthesize hierarchical Fe3O4@poly(4-vinylpyridine-co-divinylbenzene)@Au nanostructures and their catalytic applications.

Hierarchical Fe3O4@poly(4-vinylpyridine-co-divinylbenzene)@Au (Fe3O4@P(4-VP-DVB)@Au) nanostructures were fabricated successfully by means of a facile two-step synthesis process. In this study, well-defined core-shell Fe3O4@P(4-VP-DVB) microspheres were first prepared with a simple polymerization method, in which 4-VP was easily polymerized on the surface of Fe3O4 nanoparticles by means of strong hydrogen-bond interactions between -COOH groups on poly(acrylic acid)-modified Fe3O4 nanoparticles and a 4-VP monomer. HAuCl4 was adsorbed on the chains of a P(4-VP) shell and then reduced to Au nanoparticles by NaBH4, which were embedded into the P(4-VP) shell of the composite microspheres to finally form the Fe3O4@P(4-VP-DVB)@Au nanostructures. The obtained Fe3O4@P(4-VP-DVB)@Au catalysts with different Au loadings were applied in the reduction of 4-nitrophenol (4-NP) and exhibited excellent catalytic activity (up to 3025 h(-1) of turnover frequency), facile magnetic separation (up to 31.9 emu g(-1) of specific saturation magnetization), and good durability (over 98 % of conversion of 4-NP after ten runs of recyclable catalysis and almost negligible leaching of Au).