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• A facile synthetic strategy for fabricating P-AuAgNRs with tunable plasmonic properties and localized high-index facets. • P-AuAgNRs possess high chemical stability in harsh corrosive environments. • P-AuAgNRs with dual functionality, as efficient surface catalysts and a Raman probe for the in situ monitoring of the catalytic oxidation of TMB and reduction of 4-NTP, exhibit superior catalytic performances. • The synergistic mechanisms between structural and chemical effects are responsible for the enhanced catalytic performance of P-AuAgNRs. Porous metal nanostructures exhibit excellent catalytic properties due to their high surface-to-volume ratios and abundant catalytic active sites. However, it is still challenging to control nanopores density and structural features in a facile route and the preparation of porous alloy nanorods for catalytic application has not been well explored. In this work, we demonstrate a synthetic strategy to fabricate highly porous Au–Ag alloy nanorods (P-AuAgNRs) by critically dealloying Ag atoms from homogeneous solid Au–Ag alloy nanorods (AuAgNRs). Combining the merits of the tunable plasmonic properties of noble metal nanorods, excellent stabilities of alloys, and superior catalytic activities of porous structures, we use the P-AuAgNRs as a Raman probe for the in situ monitoring of the catalytic oxidation of 3,3',5,5' tetramethylbenzidine (TMB) and reduction of 4-nitrothiophenol (4-NTP). We also compare their composition-dependent catalytic activities. The results show that P-AuAgNRs possess superior chemical stability and higher catalytic activity than those of core-shell structures due to synergistic structural and chemical mechanisms. This strategy provides a predictive design approach for the next-generation alloy catalysts with high-performance. [ABSTRACT FROM AUTHOR]

The sensitivity of plasmonic sensors in response to the refractive index changes of the surrounding medium is highly dependent on the shape of metal nanocrystals. In this work, the bulk refractive index sensitivities of dispersed and immobilized Au nanocrystals in different shapes (nanospheres, nanorods, nanobipyramids, and nanoplates) are investigated. The Au nanoplates exhibit the largest bulk refractive index sensitivity in solutions. The substrate effect, which is correlated with the fractional particle surface area in contact with the substrate, makes the Au nanoplates fall behind the nanorods and nanobipyramids because of their larger interfacial contact area. The single-particle dark-field scattering technique is employed for the detection of the spectral shift upon molecular adsorption. The oxygen plasma treatment is proved to be incapable of improving the molecular sensitivity because of the structural damage to the nanocrystals. The Au nanobipyramids possess the highest molecular sensitivity among the four types of the Au nanocrystals. The distinction in the tendency of the differently shaped Au nanocrystals between the bulk and molecular sensitivities is systematically studied by electrodynamic simulations. The molecular sensitivity measurements with short-chain molecules further verify the sensitivity difference of the differently shaped Au nanocrystals. Taken together, our study and understanding of the effect of the shape on the sensitivities of plasmonic metal nanocrystals will be valuable for the design of highly sensitive plasmonic sensors as well as for the development of plasmon-enabled spectroscopies.

Directional optical nanoantennas are often realized by nanostructured systems with ingenious or complex designs. Herein we report on the realization of directional scattering of visible light from a simple configuration made of single Ag nanorods supported on Si substrates, where the incident light can be routed toward the two flanks of each nanorod. Such an intriguing far-field scattering behavior, which has not been investigated so far, is proved to result from the near-field coupling between high-aspect-ratio Ag nanorods and high-refractive-index Si substrates. A simple and intuitive model is proposed, where the complicated plasmon resonance is found to be equivalent to several vertically aligned electric dipoles oscillating in phase, to understand the far-field properties of the system. The interference among the electric dipoles results in wavefront reshaping and sidewise light routing in a similar manner to the broadside antenna described in the traditional antenna theory, allowing for the naming of these Si-supported Ag nanorods as “broadside nanoantennas”. We have carried out comprehensive experiments to understand the physical origins behind and the affecting factors on the directional scattering behavior of such broadside nanoantennas.

Biosynthesis of gold nanostructures has drawn increasing concerns because of its green and sustainable synthetic process. However, biosynthesis of gold nanoplates is still a challenge because of the expensive source and difficulties of controllable formation of morphology and size. Herein, one-pot biosynthesis of gold nanoplates is proposed, in which cheap yeast was extracted as a green precursor. The morphologies and sizes of the gold nanostructures can be controlled via varying the pH value of the biomedium. In acid condition, gold nanoplates with side length from 1300 ± 200 to 300 ± 100 nm and height from 18 to 15 nm were obtained by increasing the pH value. Whereas, in neutral or basic condition, only gold nanoflowers and nanoparticles were obtained. It was determined that organic molecules, such as succinic acid, lactic acid, malic acid, and glutathione, which are generated in metabolism process, played important role in the reduction of gold ions. Besides, it was found that the gold nanoplates exhibited plasmonic property with prominent dipole infrared resonance in near-infrared region, indicating their potential in surface plasmon-enhanced applications, such as bioimaging and photothermal therapy.

Exploring highly efficient microwave absorption (MA) materials with a facile preparation method is of great significance for tackling electromagnetic pollution and remains a challenge. Herein, ternary MoO2/Mo2C/Mo2N composites with porous structures are fabricated by a simple precursor pyrolysis process. The unique structure and multiple components, which could generate sufficient heterogeneous interfaces, are conducive to improve impedance matching, trigger polarization loss, and strengthen conduction loss. Profiting from the synergistic effect of multiple dissipation mechanisms, the composites exhibit exceedingly good MA performance. The minimum reflection loss value reaches −38.0 dB at 10.4 GHz when the thickness is 2.0 mm, and the maximum effective absorbing bandwidth is 4.11 GHz ranged from 12.41 to 16.52 GHz when the thickness is 1.5 mm. These strategies pave opportunities for rational design of Mo-related composites for high-efficiency electromagnetic-wave absorption performance.

We report on a method for the preparation of uniform and length-variable Ag nanorods through anisotropic Ag overgrowth on high-purity Au nanobipyramids. The rod diameters can be roughly tailored from ∼20 nm to ∼50 nm by judicious selection of differently sized Au nanobipyramids. The rod lengths can be tuned from ∼150 nm to ∼550 nm by varying the Ag precursor amount during the overgrowth process and/or by anisotropic shortening through mild oxidation. The controllable aspect ratios, high purity, and high dimensional uniformity of these Ag nanorods enable the observation of Fabry–Pérot-like multipolar plasmon resonance modes in the colloidal suspensions at the ensemble level, which has so far been demonstrated only on Au nanorods prepared electrochemically with anodic aluminum oxide templates. Depending on the mode order and geometry of the Ag nanorods, the multipolar plasmon wavelengths can be readily tailored over a wide spectral range from the visible to near-infrared region. We have further elucidated the relationships between the multipolar plasmon wavelengths and the geometric dimensions of the Ag nanorods at both the ensemble and single-particle levels. Our results indicate that the Au nanobipyramid-directed, dimensionally controllable Ag nanorods will be an attractive and promising candidate for developing multipolar plasmon-based devices and applications.