Absorbers with lightweight, low filler loading and broad absorption band are highly desirable for electromagnetic wave absorption field. Here, hollow Co1–xS microspheres constructed by nanosheets are ...fabricated via a facile synthetic method based on hydrothermal route. As an efficient wave absorber, the Co1–xS hollow spheres demonstrate excellent microwave absorption performance. With a weight content of only 3 wt%, the maximum reflection loss (RL) can reach as strong as −46.1 dB at 13.92 GHz and its qualified frequency bandwidth (with RL value over −10 dB) remarkably achieves 5.6 GHz, covering 35% of the entire measured bandwidth. In addition, compared with other cobalt sulfides (such as CoS2 and Co9S8), the Co1–xS microspheres with hollow structure exhibit more superior absorption intensity and broader qualified bandwidth. Therefore, this work provides a promising approach for the design and synthesis of hollow Co1–xS microspheres with lightweight and high‐performance microwave absorption.
The hollow Co1–xS microspheres with understanding microwave absorption performance are successfully fabricated through a facile hydrothermal route. The RLmax can reach to −46.1 dB at 13.92 GHz with an ultralow filler loading (3 wt%) and the effective frequency bandwidth is up to 5.6 GHz. Moreover, the possible wave absorption mechanism is also depicted comprehensively in this article.
Reduced graphene oxide (rGO)/Ni hybrids with different mass ratio are successful synthesized in order to tune the microwave absorption together with the electromagnetic shielding performance. By ...properly adjusting the permittivity and permeability derived from different contents of the rGO and Ni, an rGO/Ni composite with excellent microwave absorption properties is obtained. An optimal reflection loss value of −39.03 dB at 13 GHz is achieved for the composite with rGO/Ni ratio of 1:1, and the bandwidth less than −10 dB can reach up to 4.3 GHz (from 11 to 15.3 GHz) with a thickness of 2.0 mm. Furthermore, the composite with rGO/Ni ratio of 4:1 shows superior electromagnetic shielding performance as high as 52 dB, which far surpasses the best value for most carbon-based materials. Fundamental mechanisms for absorbing and shielding performance are discussed.
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The recent HAWC observations of a very-high-energy γ-ray halo around Geminga and Monogem indicate a very slow diffusion of cosmic rays that results in a tiny contribution of positrons from these two ...pulsars to the local flux. This makes the cosmic positron excess anomaly observed by PAMELA and AMS-02 even more puzzling. However, from the boron-to-carbon ratio data one can infer that the average diffusion coefficient in the Galaxy should be much larger. In this work we propose a two-zone diffusion model in which the diffusion is slow only in a small region around the source, outside of which the propagation is as fast as usual. We find that this scenario can naturally explain the positron excess data with parameters even more reasonable than those in the conventional one-zone diffusion model. The reason is that during the lifetime of Geminga (∼300 kyr), the electrons/positrons have propagated too far away with a fast diffusion and led to a low local flux. The slow-diffusion region in the two-zone model helps to confine the electrons/positrons for a long time and lead to an enhancement of the local flux. So under the constraint of the HAWC observations, pulsars are still the probable origin of the cosmic-ray positron excess.
Two Pt single‐atom catalysts (SACs) of Pt‐GDY1 and Pt‐GDY2 were prepared on graphdiyne (GDY)supports. The isolated Pt atoms are dispersed on GDY through the coordination interactions between Pt atoms ...and alkynyl C atoms in GDY, with the formation of five‐coordinated C1‐Pt‐Cl4 species in Pt‐GDY1 and four‐coordinated C2‐Pt‐Cl2 species in Pt‐GDY2. Pt‐GDY2 shows exceptionally high catalytic activity for the hydrogen evolution reaction (HER), with a mass activity up to 3.3 and 26.9 times more active than Pt‐GDY1 and the state‐of‐the‐art commercial Pt/C catalysts, respectively. Pt‐GDY2 possesses higher total unoccupied density of states of Pt 5d orbital and close to zero value of Gibbs free energy of the hydrogen adsorption (|ΔGPtH*
|) at the Pt active sites, which are responsible for its excellent catalytic performance. This work can help better understand the structure–catalytic activity relationship in Pt SACs.
All by their selves: Two Pt single‐atom catalysts, anchored on the support of graphdiyne with tuned coordination environments, were developed. Their structure–catalytic performance relationship for hydrogen evolution were investigated.
Controlling the architectures and crystal phases of metal@semiconductor heterostructures is very important for modulating their physicochemical properties and enhancing their application ...performances. Here, a facile one‐pot wet‐chemical method to synthesize three types of amorphous SnO2‐encapsulated crystalline Cu heterostructures, i.e., hemicapsule, yolk–shell, and core–shell nanostructures, in which unconventional crystal phases (e.g., 2H, 4H, and 6H) and defects (e.g., stacking faults and twin boundaries) are observed in the crystalline Cu cores, is reported. The hemicapsule Cu@SnO2 heterostructures, with voids that not only expose the Cu core with unconventional phases but also retain the interface between Cu and SnO2, show an excellent electrocatalytic CO2 reduction reaction (CO2RR) selectivity toward the production of CO and formate with high Faradaic efficiency (FE) above 90% in a wide potential window from −1.05 to −1.55 V (vs reversible hydrogen electrode (RHE)), and the highest FE of CO2RR (95.3%) is obtained at −1.45 V (vs RHE). This work opens up a new way for the synthesis of new heterostructured nanomaterials with promising catalytic application.
Three types of Cu@SnO2 nanostructures with hemicapsule, yolk–shell, and core–shell architectures are synthesized, in which a series of unconventional phases of Cu (i.e., 2H, 4H, and 6H) is observed. The obtained hemicapsule heterostructures exhibit superior CO2 reduction reaction selectivity toward CO and formate with high Faradaic efficiency (above 90%) in a wide potential window, outperforming their yolk–shell and core–shell counterparts.
Heterogeneous noble‐metal‐based catalysis plays an essential role in the production of fine chemicals. Rh‐based catalysts are one of the most active candidates for indole synthesis. However, it is ...still highly desired to develop heterogeneous Rh‐based catalysts with high activity and selectivity. In this work, a general, facile wet‐chemical method is reported to synthesize ultrathin amorphous/crystalline heterophase Rh and Rh‐based bimetallic alloy nanosheets (NSs), including RhCu, RhZn, and RhRu. Impressively, the amorphous/crystalline heterophase Rh NSs exhibit enhanced catalytic activity toward the direct synthesis of indole compared to the crystalline counterpart. Importantly, the obtained amorphous/crystalline heterophase RhCu alloy NSs can further enhance the selectivity to indole of >99.9% and the conversion is 100%. This work demonstrates the importance of phase engineering and metal alloying in the rational design and synthesis of tandem heterogeneous catalysts toward fine chemical synthesis.
Ultrathin Rh and RhM (M = Cu, Zn, Ru) alloy nanosheets with amorphous/crystalline heterophases are successfully synthesized. In tandem catalysis to directly synthesize indole, the amorphous/crystalline heterophase Rh nanosheets (NSs) outperform their crystalline counterpart, demonstrating much higher catalytic activity. Impressively, the amorphous/crystalline heterophase RhCu NSs show dramatically enhanced indole selectivity of over 99.9% and excellent activity.
Strongly coupled Nafion molecules and ordered porous CdS networks are fabricated for visible‐light photoelectrochemical (PEC) hydrogen evolution. The Nafion layer coating shifts the band position of ...CdS upward and accelerates charge transfer in the photoelectrode/electrolyte interface. It is highly expected that the strong coupling effect between organic and inorganic materials will provide new routes to advance PEC water splitting.
The use of DNA‐based nanomaterials in biomedical applications is continuing to grow, yet more emphasis is being put on the need for guaranteed structural stability of DNA nanostructures in ...physiological conditions. Various methods have been developed to stabilize DNA origami against low concentrations of divalent cations and the presence of nucleases. However, existing strategies typically require the complete encapsulation of nanostructures, which makes accessing the encased DNA strands difficult, or chemical modification, such as covalent crosslinking of DNA strands. We present a stabilization method involving the synthesis of DNA brick nanostructures with dendritic oligonucleotides attached to the outer surface. We find that nanostructures assembled from DNA brick motifs remain stable against denaturation without any chemical modifications. Furthermore, densely coating the outer surface of DNA brick nanostructures with dendritic oligonucleotides prevents nuclease digestion.
Brick by brick: DNA brick nanostructures with binding domains of 13 nt or longer are stable in solutions with low divalent salt concentration. Coating these DNA bricks with dendritic oligonucleotides increases their resistance to DNAse I, enhancing their biocompatible stability.
Recent advances in fluorescence super-resolution microscopy have allowed subcellular features and synthetic nanostructures down to 10-20 nm in size to be imaged. However, the direct optical ...observation of individual molecular targets (∼5 nm) in a densely packed biomolecular cluster remains a challenge. Here, we show that such discrete molecular imaging is possible using DNA-PAINT (points accumulation for imaging in nanoscale topography)-a super-resolution fluorescence microscopy technique that exploits programmable transient oligonucleotide hybridization-on synthetic DNA nanostructures. We examined the effects of a high photon count, high blinking statistics and an appropriate blinking duty cycle on imaging quality, and developed a software-based drift correction method that achieves <1 nm residual drift (root mean squared) over hours. This allowed us to image a densely packed triangular lattice pattern with ∼5 nm point-to-point distance and to analyse the DNA origami structural offset with ångström-level precision (2 Å) from single-molecule studies. By combining the approach with multiplexed exchange-PAINT imaging, we further demonstrated an optical nanodisplay with 5 × 5 nm pixel size and three distinct colours with <1 nm cross-channel registration accuracy.
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