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The conventional method for synthesizing gold nanobipyramids (AuNBPs) is well established. However, the cytotoxicity resulting from the conjugates between hexadecyltrimethylammonium bromide (CTAB) and gold limits their biomedical applications. This study introduces a dual surfactant approach with CTAB and sodium oleate (NaOL) in the seed‐mediated synthesis of the AuNBPs, which can significantly reduce the CTAB concentration to 10 mM. Additionally, optimal growth conditions are achieved by varying the volumes of seed solution, AgNO3, and HCl. Under low CTAB concentrations, AuNBPs with tunable sizes and localized surface plasmon resonances between 600 and 1200 nm are successfully synthesized, as characterized by UV–vis‐NIR spectroscopy, transmission electron microscopy (TEM), and finite‐difference time‐domain (FDTD) simulations. This work demonstrates a method for synthesizing AuNBPs at low CTAB concentrations using binary surfactants and provides a framework applicable to the synthesis of other metallic nanomaterials. [ABSTRACT FROM AUTHOR]

Surface plasmon resonance of precious metal gold nanorods can be tuned by controlling the aspect ratio, and they find widespread applications in biotechnology, imaging, sensing, optoelectronics, photonics, and catalysis. Here, a method is proposed for the controlled etching of gold nanorods within mesoporous silica shells by using a certain concentration of H2O2 at room temperature. In the experiments, the amount of HCl is varied to adjust the acidity and/or change the amount of H2O2 to control the speed of corrosion, achieving controllable adjustment of the aspect ratio of the gold nanorods. The extinction spectra show that under the action of H2O2 and HCl, the longitudinal plasmonic resonance of the gold nanorods shifted to shorter wavelengths, and the intensity of the longitudinal plasmonic resonance decreased. The more hydrochloric acid or hydrogen peroxide added, the faster the corrosion rate of the gold nanorods, and the faster the blue shift of the longitudinal plasmonic resonance. In addition, the intensity of the extinction spectra at 320 nm increased linearly versus time, which can also be used to monitor the etching process. By corroding gold nanorods to control the plasmonic resonances, gold nanorods can find broader applications. [ABSTRACT FROM AUTHOR]

A versatile method is invented to self‐assemble gold nanoparticles (GNPs) into nanoclusters (NCs) of various morphologies. By storing the particles in toluene, a highly non‐polar solvent, under conditions that ensure particle stability, the success rate of subsequent assembly can be enhanced. Additionally, conducting particle self‐assembly at a stirring speed of 200 rpm allows the NCs to maintain a spherical shape. The relative standard deviation (RSD) of Raman spectral peaks of multiple NCs used as surface‐enhanced Raman spectroscopy (SERS) substrates is calculated to be less than 10%, effectively addressing the issue of low repeatability when using NCs as SERS substrates. Furthermore, even at an analyte concentration reduced to 10−9 m, a SERS characteristic peak intensity of approximately 2 × 103 is measurable, demonstrating the high sensitivity of the assembled structures. Finally, by detecting SERS signals from NCs of varying sizes, the intensities of characteristic peaks tend to converge, eliminating the influence of morphology and size on SERS detection. [ABSTRACT FROM AUTHOR]

Colloidal gold nanorods (GNRs) have demonstrated their potential to absorb light within specific wavelength bands and induce photothermal effects. However, the unpredictability and lack of adjustability in the broadband spectrum formed by the self-assembly of gold nanospheres or the coupling of various sizes of GNRs have posed significant challenges. To address this, we have developed broadband GNRs (BGNRs) with a predictable and adjustable extinction band in the visible and near-infrared regions. The BGNRs were synthesized by simply mixing GNRs with different aspect ratios, allowing for control over the bandwidths and positions of the extinction bands. Subsequently, the BGNRs were coated with silica and underwent surface modification. The resulting BGNRs@SiO2 were then mixed with either polydimethylsiloxane (PDMS) or polyvinylidene fluoride (PVDF) to create BGNRs@SiO2/PDMS (or PVDF) films. The BGNRs@SiO2/PDMS and BGNRs@SiO2/PVDF films both exhibit excellent photothermal performance properties. Additionally, the light absorption intensity of the BGNRs@SiO2/PVDF film linearly increases upon folding, leading to significantly enhanced photothermal performance after folding. This work demonstrates that plasmonic colloidal GNRs, without the need for coupling, can yield predictable and adjustable extinction bands. This finding holds great promise for future development and practical applications, particularly in the transfer of these properties to films. [ABSTRACT FROM AUTHOR]

Transferring gold nanorods (GNRs) from an aqueous solution to a non‐polar solvent enhances self‐assembly, promotes biocompatibility, and boosts surface‐enhanced Raman scattering (SERS). However, the strong attachment ability of toxic hexadecyltrimethylammonium bromide (CTAB) to GNRs presents a significant challenge in the fall of CTAB and combining with other substances for self‐assembly and SERS applications. We propose a solution that employs ethanol as a 'catalyst' to lower the critical micelle concentration (CMC) of CTAB and efficiently combine it with the organosilanes formed by the hydrolysis of mercaptopropyltrimethoxysilane (MPS) and octadecyltrimethoxysilane (ODS). The samples were characterized by UV‐vis‐NIR spectroscopy, transmission electron microscopy (TEM), and energy disperse spectroscopy (EDS) mapping. A detailed interpretation of the phase transfer processes was provided. The modified particles were effectively dispersed in toluene and formed thin films at the air‐water interface through self‐assembly, which was confirmed by scanning electron microscopy (SEM) and optical microscopy. These films can serve as a platform for SERS. [ABSTRACT FROM AUTHOR]

In this study, we synthesized Au-Cu2O core–shell nanoparticles (Au@Cu2O NPs) with epitaxial Cu2O shell, which have highly improved catalytic performances in methyl orange reduction reaction. We have obtained Au@Cu2O NPs with different sizes at low temperatures by changing the amount of Cu2+ precursor. Both Au and Cu2O are catalytic materials, especially Cu2O, as a p-type semiconductor, whose catalytic ability depends on the crystalline facets. Catalytic reduction of methyl orange (MO) was used as a model system to explore the catalytic properties of Au@Cu2O nanocomposite. In comparison to pure Au and Cu2O NPs, the catalytic performance of Au@Cu2O has a noticeable improvement. The best catalytic rate was ~ 22 times faster than that of AuNRs and ~ 4 times than that of Cu2O NPs. By studying the catalytic mechanism, it is supposed that the Schottky barrier at the Au-Cu2O interfaces leads to the charge separation, which is beneficial to catalysis. Therefore, the Au@Cu2O NPs we designed with controllable shell thickness is an ideal composite material in the catalyst domain. [ABSTRACT FROM AUTHOR]

The localized surface plasmon resonances (LSPRs) in plasmonic nanoparticles have been used in accelerating photocatalytic reactions under light illumination. To improve the catalytic performance, bimetallic nanoparticles composed of a plasmonic core and a catalytic shell, where LSPR-excited hot electrons and the intrinsic catalytic active sites work synergistically, have attracted much attention. Despite progress in designing bimetallic catalysts, balancing the strong LSPR and catalytic sites remains challenging. Here, a trimetallic nanostructure containing a gold nanorod (AuNR) core and a silver–platinum (AgPt) hollow alloy shell was designed and used as a plasmon-mediated photocatalyst for methylene blue reduction reaction. Specifically, the AuNRs covered by a thin layer of Ag (Au@Ag) were used as the template to deposit Pt, forming a Au@AgPt trimetallic nanostructure. By changing the Ag and/or Pt precursor concentration, the external layer could be varied from AgPt heterostructure and AgPt hollow alloy shell to AuAgPt alloy dendrites. Using methylene blue as a model system, the photocatalytic reduction reaction was studied by adding the obtained nanoparticles as catalysts under visible and near-infrared light irradiation. The optimal photocatalytic performance of the trimetallic nanoparticles was seen with the AgPt hollow alloy shell, and the reaction rate is ∼7 times higher than that of the reaction without catalysts and ∼3 times higher than that of monometallic AuNRs, bimetallic Au@Ag, and Au@Pt nanorods. Plasmon energy transfer from the AuNRs to the AgPt layer, which enhances the charge-carrier generation, is responsible for outstanding photocatalytic performance. The approach used here to synthesize Au@AgPt trimetallic nanostructures is suitable for the design of other multimetallic photocatalysts. [ABSTRACT FROM AUTHOR]

The roles of CTAB and Ag+ have been discovered and given us a deeper understanding of the seed-mediated method in the gold nanorods synthesis. Former work used binary surfactants CTAB + NaOL (sodium oleate) to greatly improve the dimensional tunability and monodispersity of gold nanorods. However, they only used a few of the concentration combinations of the binary surfactants, and the influence of NaOL under this method has not been systematically studied. In this work, we carried out systematic experiments under the variation of NaOL and used transmission electron microscopy and UV–vis-near-infrared spectroscopy to monitor the growth process of the gold nanorods. The results showed that the NaOL contributed to the symmetry breaking process. We discovered the ideal ranges of NaOL concentration under different concentrations of CTAB (10–40 mM). Lower concentrations of NaOL produced many impurities, such as Au spheres, while higher concentrations of NaOL led to the decrease of monodispersity of the obtained gold nanorods. A growth model based on the balance of diffusion/reduction of the growth solution has been proposed in order to explain the formation of the gold nanorods. [ABSTRACT FROM AUTHOR]

Because of the decrease in the band gap and the carrier recombination rate, the visible light photocatalysis performance of the mixed-phase TiO2 with oxygen vacancies is better than that of the pure-phase TiO2. In this study, two different acids were separately applied in the hydrothermal synthesis of TiO2 nanoparticles without any post-heat treatment. The reaction was carried out at a relatively low temperature not exceeding 140∘C. Both kinds of crystallized TiO2 powders show much more band gap reduction than that of commercial Degussa P25 TiO2 nanoparticles, which can be attributed to the oxygen vacancies. Under the visible light illumination-assisted photocatalytic degradation of methyl orange in water, the two mixed-phase TiO2 powders exhibited a steady photocatalytic activity upon increasing to five cycles. The highest photocatalytic efficiency of the two powders is 2.7 times than that of the P25 powder, which is regarded as an excellent photocatalyst for water purification. Mixed-phase TiO2 nanoparticles were synthesized by acid-assisted hydrothermal synthesis at 140∘C without any post-calcination. Compared with P25, the specific surface area of H-TiO2 (by HCl) and A-TiO2 (by acetic acid) is larger. At the same time, H-TiO2 and A-TiO2 have excellent photocatalytic performances when assisting in the degradation of methyl orange in water under visible light illumination. The stable high photocatalytic performance and the simple preparation methods of the H-TiO2 and A-TiO2 nanoparticles will promote the industrial application. [ABSTRACT FROM AUTHOR]

Metamaterials, subwavelength nanostructured materials, can exhibit novel optical properties such as a negative index of refraction. Dielectric core–nanoparticle satellite clusters, termed "metamolecules," can have strong optical magnetic resonances in the visible wavelength range—a requirement to achieve negative refractive index materials. However, achieving the desired photonic properties is challenging due to limited control in forming the metamolecule structures. Here, polystyrene (PS) core–gold nanoparticle (AuNP) satellite metamolecules with highly ordered single layers (monolayers) of AuNPs are fabricated and single particle spectroscopy, electron tomography structural measurements, and electrodynamics simulations are conducted to study the photonic properties of metamolecules constituted of ≈100 AuNPs. The simulated and experimental spectra of the many metamolecules studied, including excitation with azimuthally and radially polarized light, are in excellent agreement. It is shown that the scattering properties of the metamolecules are dominated by the AuNPs near the "equator" of the cluster, and that backscattering is strongly suppressed when different multipolar modes (e.g., dipolar and quadrupolar) of electric or optical magnetic character have comparable intensity due to the π‐phase shift of their scattering. Both the optical excitation fields and the ordering of the nanoparticles within metamolecules affect their optical excitation and scattering properties, providing new insights into designing novel photonic metamaterials. [ABSTRACT FROM AUTHOR]

ZnO nanowire arrays were grown on semi-insulating intrinsic GaAs substrates, and controlled arsenic-doping process was carried out to realize the n-ZnO/p-ZnO nanowire array/GaAs structures. The constructed ZnO nanowire homojunctions demonstrated a clear rectifying behavior and the turn-on voltage was above 4.0 V. The corresponding ultraviolet electroluminescence spectra were obtained for the applied forward voltage above 30 V (20 mA). The distinct ultraviolet electroluminescence peak, centered at 382 nm, is nonlinearly enhanced with an increase in the applied forward voltage. The origin of the strong ultraviolet electroluminescence was discussed in terms of the controlled arsenic-doping process. [ABSTRACT FROM AUTHOR]