Excellent NiO–Ni Nanoplate Microwave Absorber via Pinning Effect of Antiferromagnetic–Ferromagnetic Interface

Materials with strong magnetic property that can provide excellent microwave absorption performance are highly desirable, especially if their dielectric and magnetic properties can be easily modulated, which make minimal thickness and ultrawide bandwidth become achievable. The magnetic properties of ferromagnetic (FM) and antiferromagnetic (AFM) composite materials are closely related to their ratio of composition, size, morphology, and structure. AFM–FM composites have become a popular alternative for microwave absorption; however, the controllable design and preparation need to be urgently optimized. Here, we have successfully prepared a series of platelike NiO–Ni composites and demonstrated the potential of such composites for microwave absorption. Strong magnetic coupling was found from NiO–Ni nanoparticles by electron holography, which makes NiO–Ni composites a highly efficient microwave absorber (strong reflection loss: −61.5 dB and broad bandwidth: 11.2 GHz, reflection loss < −10 dB). Our findings are helpful to develop a strong microwave absorber based on magnetic coupling

Tailoring Au–Ag–S Composite Microstructures in One-Pot for Both SERS Detection and Photocatalytic Degradation of Plasticizers DEHA and DEHP

We report a facile single-step one-pot solvothermal process for tailoring the Au–Ag–S microstructures as bifunctional substrates for both surface-enhanced Raman scattering (SERS) detection and photocatalytic degradation of plasticizers diethylhexyl phthalate (DEHP) and diethylhexyl adipate (DEHA). Typically, two different microstructures, the Ag₂S particles inlaid Au microflowers (Ag₂S–Au MFs) and Au particles decorated AgAuS microsheets (Au–AgAuS MSs) were obtained. The Ag₂S–Au MF substrates finally turned out to provide 0.9 × 10^–9 and 0.9 × 10^–7 M of the limits of detection (LODs) for DEHP and DEHA in orange juice. And on the other hand, the Au–AgAuS MSs achieved complete degradation of DEHP and DEHA (1 × 10^–5 M) after 20 and 25 min of UV light irradiation, respectively. It is believed that the facile preparation and appreciable SERS and catalytic activities of these Au–Ag–S microstructures would make much sense to develop novel multifunctional sensing and monitoring devices

Graphene Oxide-Wrapped Co₃O₄/NiO Micron Flowers as an Anode of Lithium-Ion Batteries with Enhanced Rate Performance and Cycling Stability

A graphene oxide-wrapped Co3O4/NiO (denoted as CNO/GO) micron flower is successfully synthesized by a rapid solvothermal method, which is formed through interpenetrating nanosheets. Nanosheets with a large specific surface area expose a large number of active sites for an electrochemical reaction. Moreover, abundant pores formed during the interpenetration of nanosheets are instrumental in providing enough buffer space to relieve the large volume expansion from the repeated lithium insertion/delithiation processes, and the tightly wrapped GO can effectively sustain the stability of the CNO micron flower structure during the long-term cycle processes. The reversible specific capacity as high as 602.9 mA h g–1 is maintained after 800 cycles at 5000 mA g–1. In addition, GO with good conductivity can greatly enhance the conductivity of CNO micron flowers, accelerate the transfer of electrons, and then achieve a high rate performance (the reversible specific capacity is 570.2 mA h g–1 at 10 000 mA g–1). This work provides a viable method for synthesizing the CNO micron flowers as a promising high-performance transition metal oxide anode for lithium-ion batteries

Synthesis of Co₃O₄/VG/CNT Composite Microspheres with Excellent Lithium Storage Performance

In order to improve the conductivity of Co3O4, Co3O4/VG/CNT composite microspheres were prepared by facile spray drying method and subsequently plasma-enhanced chemical vapor deposition method. A three-dimensional conductivity network was constructed by vertical graphenes and CNTs distributed throughout the microspheres, the transmission of electrons was greatly promoted, excellent rate performance was realized, and the high average reversible specific capacity of 526 mA h g–1 was still retained at 1000 mA g–1. Besides, thanks to the abundant pores distributed in the whole microspheres, the stress could be greatly released during the repeated charging/discharging processes, long cycling stability could be achieved, and the reversible specific capacity as high as 396 mA h g–1 was retained after 1000 cycles at 800 mA g–1. The preparation of Co3O4/VG/CNT composite microspheres can provide a new idea for high-performance lithium-ion battery anode materials

Biomimetic Synthesis of Multilayered Aragonite Aggregates Using Alginate as Crystal Growth Modifier

Polysaccharides were believed to play an important role in the mineralization process of many organisms. As the source of continuously and uniformly releasing alginate molecules and Ca2+, alginate/Ca nanospherical gel was employed in the solution to induce the nucleation and growth of CaCO3. Time-resolved transmission electron microscopy (TEM) was applied to study the crystallization at a very early stage. It was found that the initially formed lens-like vaterite particles gradually dissolved from the middle of the particle and released alginate molecules and Ca2+ back into the system. As reaction time increased, the released substances were involved in the next stage of crystallization of CaCO3, in the form of needle-like and shuttle-like aragonite particles sequentially depending on the concentration of alginate molecules and Ca2+. “Egg-box” conformation of alginate and Ca2+ was considered a skeleton for the growth of such aragonite particles. Notably, shuttle-like aragonite particles were composed of “bricks” of several hundred nanometers in size, which were very similar to biogenetic nacreous layers in shells

Graphene Oxide-Wrapped Porous Hollow Co₃O₄ Microspheres with Enhanced Lithium Storage Performance

Porous hollow Co3O4 microspheres wrapped with graphene oxide were synthesized by a step solvothermal method and subsequent heat treatment. Benefiting from the design of special porous hollow microspheres, the effective specific surface area was greatly increased, the sufficient contact between the porous hollow Co3O4 microspheres and electrolyte was achieved, and then a charge specific capacity of 888.59 mA h g–1 was gained. Meanwhile, partial stress from the charging/discharging process was greatly relieved due to the abundant pores and hollow structure, excellent cycling stability was realized, and the charge specific capacity of the 1000th cycle was 465.75 mA h g–1 at 5 C (1 C = 890 mA g–1). In addition, the conductivity of Co3O4 microspheres was effectively improved due to the tight package of graphene oxide to Co3O4 microspheres, and superior rate performance was attained (280.99 mA h g–1 at 10 C)

Insight into Surface Electronic Effects on Pd Nanostructures as Efficient Electrocatalysts

Although the unique properties of nanomaterials have endowed enzyme-mimic catalysts with broad applications, the development of catalysts still relies on trial-and-error strategies without predictive indicators. Surface electronic structures have rarely been studied in enzyme-mimic catalysts. Herein, we present a platform for understanding the impact of surface electronic structures on electrocatalysis toward H2O2 decomposition, using the Pd icosahedra (Pd ico), Pd octahedra (Pd oct) and Pd cubic nanocrystals as electrocatalysts. The electronic properties on Pd were modulated with a correlation of surface orientation. We revealed the relationship between the electronic properties and electrocatalytic performance, in which the surface electron accumulation can boost the electrocatalytic activity of the enzyme-mimic catalysts. As a result, the Pd icodimer exhibits the highest electrocatalytic and sensing efficiency. This work offers new perspectives for the investigation of structure–activity relationships and provides an effective knob for utilizing the surface electronic structures to boost the catalytic performance for enzyme-mimics

Direct Imaging Au Nanoparticle Migration Inside Mesoporous Silica Channels

Supported metal nanoparticle (NP) catalysts have been widely used in many industry processes and catalytic reactions. Catalyst deactivation is mainly caused by the sintering of supported metal NPs. Hence, understanding the metal NPs’ sintering behaviors has great significance in preventing catalyst deactivation. Here we report the metal particle migration inside/between mesochannels by scanning transmission electron microscopy and electron energy loss spectroscopy via an in situ TEM heating technique. A sintering process is proposed that particle migration predominates, driven by the difference of gravitational potential from the height of the uneven internal surface of the mesopores; when the distance of the gold nanoparticles with a size of about 3 and 5 nm becomes short after migration, the coalescence process is completed, which is driven by an “octopus-claw-like” expansion of a conduction electron cloud outside the Au NPs. The supports containing an abundance of micropores help to suppress particle migration and coalescence. Our findings provide the understanding toward the rational design of supported industrial catalysts and other nanocomposites with enhanced activity and stability for applications such as batteries, catalysis, drug delivery, gas sensors, and solar cells

Control over Different Crystallization Stages of CaCO₃-Mediated by Silk Fibroin

The crystallization process of CaCO3-mediated by the addition of silk fibroin at different crystalline stages was examined. During earlier stages of crystallization, time-resolved transmission electron microscopy (TEM) was applied to demonstrate that the crystallization of an amorphous precursor was based on randomly oriented domains. Different addition times of silk fibroin primarily led to two kinds of morphology of CaCO3, that is, lens-like and multilayered vaterite. Additionally, the thickness or number of layers of such vaterite would increase with the delay of silk fibroin addition, ascribing to the control of silk fibroin over different basic units during the aggregation and reorientation process. It was found that those squeezed-out silk fibroins, which probably resulted from the relatively weak interaction between silk fibroin chains and (001) plane of vaterite phase during the crystallization process could lead to the formation of oblate aggregates via vectorial assembly of units with consistent orientation (nanoparticle for lens-like vaterite or flake for layered vaterite) and inhibition to the growth of (001) faces of fused intermediates. For comparison, the crystallization process of CaCO3 regulated by poly (acrylic acid) (PAA) was observed by cryoSEM, presenting a “stepwise aggregation” pathway to form spherical polycrystals which may be attributed to strong electrostatic interaction between carboxyl groups in PAA chains and nanoparticles. Therefore, the extent of binding affinity between organic and inorganic substances was proposed to be relevant to the reconstructuring process and the morphologies of final product

Enhanced Polarization from Hollow Cube-like ZnSnO₃ Wrapped by Multiwalled Carbon Nanotubes: As a Lightweight and High-Performance Microwave Absorber

Polarization and conduction loss play fundamentally important roles in the nonmagnetic microwave absorption process. In this paper, a uniform and monodisperse hollow ZnSnO₃ cube wrapped by multiwalled carbon nanotubes (ZSO@CNTs) was successfully synthesized via facile hydrothermal treatment. A reasonable mechanism related to Ostwald ripening was proposed to design the varied ZSO@CNTs for the special hollow conductive network. Scanning electron microscopy images clearly indicate that reaction temperature is the key factor for the composite structure, which has a significant effect on its electromagnetic properties. Electron holography proves the inhomogeneous distribution of charge density in the ZSO@CNT system, leading to the occurrence of interface polarization. Complex permittivity properties of ZSO@CNT composites under different reaction temperatures were investigated to optimize the morphology that can distinctly enhance microwave absorption performance. The maximum reflection loss that the ZSO@CNT-130 °C composite can reach is −52.1 dB at 13.5 GHz, and the absorption bandwidths range from 11.9 to 15.8 GHz with a thickness as thin as 1.6 mm. Adjusting the simulation thicknesses from 1 to 5 mm, the efficient absorption bandwidth (RL < −10 dB) that the ZSO@CNT composite could reach was 14.16 GHz (88.8% of 2–18 GHz). The excellent microwave absorption performance may be attributed to the synergistic effects of polarization, conduction loss, and special hollow cage structure. It is proposed that the specially controlled structure could provide an effective path for achieving a high-performance microwave absorber