Interfacial nanodroplets guided construction of hierarchical Au, Au-Pt, and Au-Pd particles as excellent catalysts

Fast synthesis of nanoporous Cu/Ag bimetallic triangular nanoprisms via galvanic replacement for efficient 4-nitrophenol reduction

We report the synthesis of nanoporous Cu/Ag bimetallic triangular nanoprisms (BTNPs) using a galvanic replacement method. Based on ultraviolet-visible spectroscopy (UV-vis), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), X-ray diffraction (XRD), energy dispersive spectrometry (EDS), selected area electron diffraction (SAED) and X-ray photoelectron spectroscopy (XPS) analyses, the structure of Cu/Ag BTNPs was characterized. The prepared Cu/Ag BTNPs exhibited excellent catalytic activity and good cycling stability for the reduction of 4-nitrophenol (4-NP) due to the synergistic effect between Cu and Ag elements. The kinetic rate constant (k) and turnover frequency (TOF) values reached 331 × 10-3 s-1 and 500 × 10-3 s-1, respectively, which were higher than those of previously reported Cu, Ag, Au, Cu/Ag or Cu/Au-based catalysts. We hope that the development of promising routes for high-quality BTNPs can broaden their applications in catalysis and environmental sustainability.

Fabrication of Bimetallic Cu-Ag Nanoparticle-Decorated Poly(cyclotriphosphazene-co-4,4'-sulfonyldiphenol) and Its Enhanced Catalytic Activity for the Reduction of 4-Nitrophenol

We reported a study on the preparation of bimetallic Ag-Cu nanoparticles (NPs) impregnated on PZS poly(cyclotriphosphazene-co-4,4'-sulfonyldiphenol) nanotubes via a facile and efficient reduction method. Herein, PZS nanotubes consisting of enriched hydroxyl groups are fabricated through an in situ template method, and then, fluctuating the amount ratios of Cu and Ag precursors, bimetallic NPs can be fabricated on readily prepared PZS nanotubes using NaBH4 as a reductant, which results in a series of bimetallic catalysts having tunable catalytic activity. The characterization investigations of scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and Fourier transform infrared spectroscopy results show that Ag-Cu bimetallic NPs are well-dispersed, ultrasmall in size, and well-anchored on the surface of PZS nanotubes. In addition, to examine the catalytic activity and reusability of these nanocomposites, reduction of 4-nitrophenol to 4-aminophenol is utilized as a prototype reaction. The optimized Ag-Cu NPs with a copper ratio of 0.3% are well-stabilized by the organic-inorganic poly(cyclotriphosphazene-co-4,4'-sulfonyldiphenol) nanotubes. The obtained results show that bimetallic NPs have remarkably higher catalytic ability than that of their monometallic counterparts with maximum catalytic activity. These results are even better than those of noble metal-based bimetallic catalysts and pave the avenue to utilize the polyphosphazene polymer as a substrate material for highly effective bimetallic catalysts.

Copper/Zinc-Modified Palygorskite Protects Against Salmonella Typhimurium Infection and Modulates the Intestinal Microbiota in Chickens

Palygorskite (Pal), a clay nanoparticle, has been demonstrated to be a vehicle for drug delivery. Copper has antibacterial properties, and zinc is an essential micronutrient for intestinal health in animals and humans. However, whether copper/zinc-modified Pal (Cu/Zn-Pal) can protect chickens from Salmonella enterica subsp. enterica serovar Typhimurium (S. Typhimurium) infection remains unclear. In this study, three complexes (Cu/Zn-Pal-1, Cu/Zn-Pal-2, and Cu/Zn-Pal-3) were prepared, and Cu/Zn-Pal-1 was shown to be the most effective at inhibiting the growth of S. Typhimurium in vitro, whereas natural Pal alone had no inhibitory effect. In vivo, Cu/Zn-Pal-1 reduced S. Typhimurium colonization in the intestine of infected chickens and relieved S. Typhimurium-induced organ and intestinal mucosal barrier damage. Moreover, this reduction in Salmonella load attenuated intestinal inflammation and the oxidative stress response in challenged chickens. Additionally, Cu/Zn-Pal-1 modulated the intestinal microbiota in infected chickens, which was characterized by the reduced abundance of Firmicutes and the increased abundance of Proteobacteria and Bacteroidetes. Our results indicated that the Cu/Zn-Pal-1 complex may be an effective feed supplement for reducing S. Typhimurium colonization of the gut.

Polymeric nanodroplets: an emerging trend in gaseous delivery system

Currently, nanotechnology-based products are gaining tremendous interest in the development of nanocarriers for drug delivery and nano-diagnostic devices. Nanodroplets (NDs) emerge as novel carriers for delivery of gases and actives with a wide range of applications in fields of theranostics, drug delivery and diagnostic devices. NDs are multifunctional carriers composed of an outer shell of drug and polymer that encapsulates the inner core of gases and liquid molecules. This review focuses on properties of NDs, mathematical theories, different polymers used in the preparation of NDs, characterisation, animal models, toxicity and applications of NDs. These nanocarriers are advantageous due to their cost-effectiveness and compatibility with both gaseous and liquid core molecules. NDs are increasingly utilised in the field of healthcare due to their properties like large effective surface area for drug loading and target specificity. These nanocarriers are also employed in the treatment of hypoxia, multiple sclerosis and cancer. In the near future, NDs will advance in fields of personalised medicine and precise theranostics.

Shaping well-defined noble-metal-based nanostructures for fabricating high-performance electrocatalysts: advances and perspectives

This review highlights recent advances in shaping protocols and structure-activity relationships of noble-metal-based catalysts with well-defined nanostructures in electrochemical reactions.

Preparation of bimetallic Au/Pt nanotriangles with tunable plasmonic properties and improved photocatalytic activity

Bimetallic nanoparticles are widely used in chemical catalysis and energy conversion. Their practical performance can be better exploited through morphological control by adjusting the synthetic strategy. Herein, an aqueous phase route is used to achieve the controlled preparation of bimetallic Au/Pt and hollow Au/Pt/Au nanotriangles with tunable plasmonic properties and superior photocatalytic activity. By continuously adjusting the concentration of surfactant solution, the gradual growth orientation of Pt nanoparticles on Au nanotriangles is observed, which occurs first on the tips, then on the edges, and then on the facets. Three types of Au/Pt nanotriangles (including Pt on the tips (Au/Pt (tips)), Pt on the edges (Au/Pt (edges)), and Pt covering Au (Au@Pt)) with tunable plasmon resonance are obtained. Then, Au/Pt/Au nanotriangles with a hollow structure are synthesized based on Au/Pt (edges). By evaluating the reduction rate of p-nitrophenol under visible light irradiation, hollow Au/Pt/Au nanotriangles exhibit the best photocatalytic activity compared with Au and Au/Pt (edges). The hollow structure, high visible light absorption and a strong tip- and center-focused local electric field of Au/Pt/Au are thought to be responsible for their superior photocatalytic activity.

Dual-channel extraordinary ultraviolet transmission through an aluminum nanohole array

Ultraviolet (UV) surface plasmon (SP) has distinct applications in UV filters, high-density optical storage, spectral enhancement, optical detectors, and nanolithography, which are closely related to plasmon-induced extraordinary optical transmission (EOT). However, such EOT in the UV region has not been the subject of detailed research. We report UV transmission based on theoretical research using the finite-difference time-domain method, by modulating the Al thickness, hole size, array periodicity, and SiO₂ overlayer thickness. It is notable that we can obtain dual-channel UV transmission peaks with excellent qualities such as high transmissivity, zero cross-talk, narrow bandwidth, and perfect symmetry, by optimizing the parameters. The UV transmission peaks have been discovered to non-monotonously shift with increasing hole size. Although array periodicity has great influence on the transmission peak position, the peak energy in the UV region is much less than the value predicted by the well-known periodicity-related surface plasmon polariton (SPP) wavelength equation; the energy discrepancy in the UV region can reach above 20%, which is much larger than the value (typically 4%) in the visible-infrared region. Furthermore, the SiO₂ overlayer may significantly modify the transmission properties. The Al nanohole arrays have also been found to exhibit distinct multi-band UV electric field enhancement properties with special interface effect and size effect. Such extraordinary dual-channel UV transmission with zero cross-talk, based on a very simple Al nanohole array, has promising application in dual-channel UV filters, high-density optical storage, and plasmon-enhanced fluorescence/Raman spectroscopy, which generally involves two wavebands (writing/reading storage or exciting/emission wavelengths). This study is expected to broaden our fundamental understanding of the UV EOT phenomenon, and provide references for experimental research and application of deep-UV and near-UV-related dual-band plasmonic devices.

Photo-reduced Cu/CuO nanoclusters on TiO2 nanotube arrays as highly efficient and reusable catalyst

Non-noble metal nanoparticles are becoming more and more important in catalysis recently. Cu/CuO nanoclusters on highly ordered TiO₂ nanotube arrays are successfully developed by a surfactant-free photoreduction method. This non-noble metal Cu/CuO-TiO₂ catalyst exhibits excellent catalytic activity and stability for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) with the presence of sodium borohydride (NaBH₄). The rate constant of this low-cost Cu/CuO based catalyst is even higher than that of the noble metal nanoparticles decorated on the same TiO₂ substrate. The conversion efficiency remains almost unchanged after 7 cycles of recycling. The recycle process of this Cu/CuO-TiO₂ catalyst supported by Ti foil is very simple and convenient compared with that of the common powder catalysts. This catalyst also exhibited great catalytic activity to other organic dyes, such as methylene blue (MB), rhodamine B (RhB) and methyl orange (MO). This highly efficient, low-cost and easily reusable Cu/CuO-TiO₂ catalyst is expected to be of great potential in catalysis in the future.

Scalable Synthesis of Ag Networks with Optimized Sub-monolayer Au-Pd Nanoparticle Covering for Highly Enhanced SERS Detection and Catalysis

Highly porous tri-metallic Ag_xAu_yPd_z networks with a sub-monolayer bimetallic Au-Pd nanoparticle coating were synthesized via a designed galvanic replacement reaction of Ag nanosponges suspended in mixed solutions of HAuCl₄ and K₂PdCl₄. The resulting networks’ ligaments have a rough surface with bimetallic nanoparticles and nanopores due to removal of Ag. The surface morphology and composition are adjustable by the temperature and mixed solutions’ concentration. Very low combined Au and Pd atomic percentage (1−x) where x is atomic percentage of Ag leads to sub-monolayer nanoparticle coverings allowing a large number of active boundaries, nanopores, and metal-metal interfaces to be accessible. Optimization of the Au/Pd atomic ratio y/z obtains large surface-enhanced Raman scattering detection sensitivity (at y/z = 5.06) and a higher catalytic activity (at y/z = 3.55) toward reduction reactions as benchmarked with 4-nitrophenol than for most bimetallic catalysts. Subsequent optimization of x (at fixed y/z) further increases the catalytic activity to obtain a superior tri-metallic catalyst, which is mainly attributed to the synergy of several aspects including the large porosity, increased surface roughness, accessible interfaces, and hydrogen absorption capacity of nanosized Pd. This work provides a new concept for scalable synthesis and performance optimization of tri-metallic nanostructures.

Spontaneous Self-Formation of 3D Plasmonic Optical Structures

Self-formation of colloidal oil droplets in water or water droplets in oil not only has been regarded as fascinating fundamental science but also has been utilized in an enormous number of applications in everyday life. However, the creation of three-dimensional (3D) architectures by a liquid droplet and an immiscible liquid interface has been less investigated than other applications. Here, we report interfacial energy-driven spontaneous self-formation of a 3D plasmonic optical structure at room temperature without an external force. Based on the densities and interfacial energies of two liquids, we simulated the spontaneous formation of a plasmonic optical structure when a water droplet containing metal ions meets an immiscible liquid polydimethylsiloxane (PDMS) interface. At the interface, the metal ions in the droplet are automatically reduced to form an interfacial plasmonic layer as the liquid PDMS cures. The self-formation of both an optical cavity and integrated plasmonic nanostructure significantly enhances the fluorescence by a magnitude of 1000. Our findings will have a huge impact on the development of various photonic and plasmonic materials as well as metamaterials and devices.

How a Surface Nanodroplet Sits on the Rim of a Microcap

The location and morphology of femtoliter nanodroplets that nucleate and grow on a microcap-decorated substrate in contact with a liquid phase were investigated. We experimentally examined four different wetting combinations of the flat area and the microcaps. The results show that depending on the relative wettability, the droplets sit either on the plain surface or on the top of the microcap or on the rim of the microcap. The contact angle and, for the last case, the radial positions of the nanodroplets relative to the microcap center were characterized, in reasonable agreement with our theoretical analysis, which is based on an interfacial energy minimization argument. However, the experimental data show considerable scatter around the theoretical equilibrium curves, reflecting pinning and thus nonequilibrium effects. We also provide the theoretical phase diagram in parameter space of the contact angles, revealing under which conditions the nanodroplet will nucleate on the rim of the microcap.

Novel redox species polyaniline derivative-Au/Pt as sensing platform for label-free electrochemical immunoassay of carbohydrate antigen 199

A novel electrochemical redox-active nanocomposite was synthesized by a one-pot method using N,N'-diphenyl-p-phenylediamine as monomer, and HAuCl4 and K2PtCl4 as co-oxidizing agents. The as-prepared poly(N,N'-diphenyl-p-phenylediamine)-Au/Pt exhibited admirable electrochemical redox activity at 0.15 V, excellent H2O2 electrocatalytic ability and favorable electron transfer ability. Based on these, the evaluation of the composite as sensing substrate for label-free electrochemical immunosensing to the sensitive detection of carbohydrate antigen 199 was described. This technique proved to be a prospective detection tool with a wide liner range from 0.001 U mL(-1) to 40 U mL(-1), and a low detection limit of 2.3 × 10(-4) U mL(-1) (S/N = 3). In addition, this method was used for the analysis of human serum sample, and good agreement was obtained between the values and those of enzyme-linked immunosorbent assay, implying the potential application in clinical research. Importantly, the strategy of the present substrate could be extended to other polymer-based nanocomposites such as polypyrrole derivatives or polythiophene derivatives, and this could be of great significance for the electrochemical immunoassay.

Preparation of supported AuPd nanoalloys mediated by ionic liquid-like functionalized SBA-15: structural correlations concerning its catalytic activity

We report highly active catalysts based on mono- or bimetallic Au and Pd nanoparticles supported in ionic liquid-like modified SBA-15.

Novel electrochemical redox-active species: one-step synthesis of polyaniline derivative-Au/Pd and its application for multiplexed immunoassay

Electrochemical redox-active species play crucial role in electrochemically multiplexed immunoassays. A one-pot method for synthesizing four kinds of new electrochemical redox-active species was reported using HAuCl4 and Na2PdCl4 as dual oxidating agents and aniline derivatives as monomers. The synthesized polyaniline derivative-Au/Pd composites, namely poly(N-methyl-o-benzenediamine)-Au/Pd, poly(N-phenyl-o-phenylenediamine)-Au/Pd, poly(N-phenyl-p-phenylenediamine)-Au/Pd and poly(3,3',5,5'-tetramethylbenzidine)-Au/Pd, exhibited electrochemical redox activity at -0.65 V, -0.3 V, 0.12 V, and 0.5 V, respectively. Meanwhile, these composites showed high H2O2 electrocatalytic activity because of the presence of Au/Pd. The as-prepared composites were used as electrochemical immunoprobes in simultaneous detection of four tumor biomarkers (carcinoembryonic antigen (CEA), carbohydrate antigen 19-9 (CA199), carbohydrate antigen 72-4 (CA724), and alpha fetoprotein (AFP)). This immunoassay shed light on potential applications in simultaneous gastric cancer (related biomarkers: CEA, CA199, CA724) and liver cancer diagnosis (related biomarkers: CEA, CA199, AFP). The present strategy to the synthesize redox species could be easily extended to other polymers such as polypyrrole derivatives and polythiophene derivatives. This would be of great significance in the electrochemical detection of more analytes.

Formation, characterization and stability of oil nanodroplets on immersed substrates

Nanoscale oil droplets locating at solid-liquid interfaces significantly impact the interfacial properties, which are concerned in both industry applications and fundamental studies. This review article presents an overview of the current progress in nanodroplet research. We will start from the characterization of interfacial nanodroplets and the formation of interfacial nanodroplets by direct adsorption from emulsions and by the solvent exchange protocol. Then we will review the experimental and theoretical studies on the evolution of oil nanodroplets including spreading, dissolution, and detachment. We will also cover the emerging applications of the interfacial nanodroplets in the fields of surface functionalization and nanostructure engineering, and particularly, highlight the potential application as capping agents to obtain architectures on microparticle surface. Finally we propose the challenges and the opportunities in this area. In our opinion, the nanodroplets have not only of high relevance to practical applications, but also serve as a model system for understanding many interfacial phenomena, such as phase separation and wetting on a microscopic scale.

The significant impact of polydopamine on the catalytic performance of the carried Au nanoparticles

Mussel-inspired polydopamine catalyst carriers dramatically enhance the catalytic performance (∼450%) of Au nanoparticles in methylene blue reduction, which is attributed to the local enrichment mechanism caused by the favourable attractive interaction between the polydopamine and reactants.