Synthesis of convex hexoctahedral palladium@gold core-shell nanocrystals with {431} high-index facets with remarkable electrochemiluminescence activities

Bright luminol electrochemiluminescence mediated by a simple TEMPO radical for visualized multiplex detection

In this work, a series of 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) radicals bearing different functional groups were exploited as a simple catalyst to promote electrochemiluminescence (ECL) generation in luminol/H2O2 system. These TEMPO radicals were found to facilitate the electrochemical oxidation of H2O2 and luminol through different catalytic mechanisms, as well as the subsequent ECL generation of luminol/H2O2 system. The electrochemical oxidation and luminol ECL generation could be tuned by the functional group on the para-position of TEMPO, for which the structure/activity relationship was revealed. Finally, with the combination of enzymatic system, luminol ECL enhancement up to 9.6-fold was obtained through the catalysis of 4-hydroxyl-TEMPO. The enhanced luminol ECL allows acquiring brighter ECL images in a single-electrochemical system (SEES) for multiplex detection of cholesterol, H2O2 and glucose.

Wet-Chemical Synthesis of Concave Hexoctahedral Pd and Pd@Pt Nanocrystals for Methanol Electrooxidation

Nanocrystals (NCs) exposed with high-index facets usually show enhanced electrocatalytic performances. However, it is a great challenge to persevere with high-index facets against their high surface energy during the synthesis. Herein, we successfully synthesize concave hexoctahedral (c-HOH) Pd NCs exposed with 48 high-index {741} facets using a facile one-pot wet-chemical protocol. Control experiments illustrate that l-ascorbic acid plays a critical role in the formation of the c-HOH morphology, acting as both reducing and capping agents. Moreover, we can extend the synthesis for fabricating c-HOH Pd@Pt core-shell NCs by simply introducing a Pt precursor into the reaction solution, attaining remarkably boosted electrocatalysis for methanol electrooxidation reaction (MOR). Integrating the merits of {741} facets, concave structure, and ligand and strain effect of the core-shell structure, c-HOH Pd4@Pt1 core-shell NCs showed an excellent MOR mass activity of 1.18 A mgPGM-1 or 3.60 A mgPt-1, which is 3.80 or 11.61 times higher than that of commercial Pt/C, respectively.

A Carbonate-Involved Amplification Strategy for Cathodic Electrochemiluminescence of Luminol Triggered by the Catalase-like CoO Nanorods

The lumiol-O₂ electrochemiluminescence (ECL) system constantly emits bright light at positive potential. Notably, compared with the anodic ECL signal of the luminol-O₂ system, the great virtues of cathodic ECL are that it is simple and causes minor damage to biological samples. Unfortunately, little emphasis has been paid to cathodic ECL, owing to the low reaction efficacy between luminol and reactive oxygen species. The state-of-the-art work mainly focuses on improving the catalytic activity of the oxygen reduction reaction, which remains a significant challenge. In this work, a synergistic signal amplification pathway is established for luminol cathodic ECL. The synergistic effect is based on the decomposition of H₂O₂ by catalase-like (CAT-like) CoO nanorods (CoO NRs) and regeneration of H₂O₂ by a carbonate/bicarbonate buffer. Compared with Fe₂O₃ nanorod (Fe₂O₃ NR)- and NiO microsphere-modified glassy carbon electrodes (GCEs), the ECL intensity of the luminol-O₂ system is nearly 50 times stronger when the potential ranged from 0 to -0.4 V on the CoO NR-modified GCE in a carbonate buffer solution. The CAT-like CoO NRs decompose the electroreduction product H₂O₂ into OH^· and O₂^·-, which further oxidize HCO₃^- and CO₃^2- to HCO₃^· and CO₃^·-. These radicals very effectively interact with luminol to form the luminol radical. More importantly, H₂O₂ can be regenerated when HCO₃^· dimerizes to produce (CO₂)₂*, which provides a cyclic amplification of the cathodic ECL signal during the dimerization of HCO₃^·. This work inspires developing a new avenue to improve cathodic ECL and deeply understand the mechanism of a luminol cathodic ECL reaction.

High Chemical Potential Driven Amorphization of Pd-based Nanoalloys

Amorphous metals and alloys are promising candidates for superior catalysts in many catalytic and electrocatalytic reactions. It is of great urgency to develop a general method to construct amorphous alloys and further clarify the growth mechanism in a wet-chemical system. Herein, inspired by the conservation of energy during the crystallization process, amorphous PdCu nanoalloys have been successfully synthesized by promoting the chemical potential of the building blocks in solution. Benefiting from the abundant active sites and enhanced corrosion resistance, the synthesized amorphous PdCu nanostructures exhibit superior catalytic activity and durability over the face-centered cubic one in formic acid decomposition reaction. More importantly, the successful fabrications of amorphous PdFe, PdCo, and PdNi further demonstrate the universality of the above strategy. This proposed strategy is promising to diversify the amorphous family.

Enhancing Electrochemiluminescence Efficiency through Introducing Atomically Dispersed Ruthenium in Nickel-Based Metal-Organic Frameworks

The successful application of electrochemiluminescence (ECL) in various fields required continuous exploration of novel ECL signal emitters. In this work, we have proposed a pristine ECL luminophor named NiRu MOFs, which owned extremely high and stable ECL transmission efficiency and was synthesized via a straightforward two-step hydrothermal pathway. The foundation framework of pure Ni-MOFs with the initial structure was layered-pillared constructed by the coordinated octahedrally divalent between nickel and terephthalic acid (BDC). The terephthalates were coordinated and pillared directly to the nickel hydroxide layers and the three-dimensional framework was formed, which had a weak ECL response strength. Then, the ruthenium pyridine complex was recombined with pure Ni-MOFs to produce NiRu MOFs and part of the introduced ruthenium was atomically dispersed in the layered-pillared structure through an ion-exchange method, which led to the ECL luminous efficiency being significantly boosted more than pure Ni-MOFs. In order to verify the superiority of this newly synthesized illuminant, an ECL immunoassay model has been designed, and the results demonstrated that it had extremely strong and steady signal output in practical application. This study realized an efficient platform in ECL immunoassay application with the limit of detection of 0.32 pg mL^-1 for neuron-specific enolase (NSE). Therefore, the approach which combined the pristine pure Ni-MOFs and the star-illuminant ruthenium pyridine complex would provide a convenient and meaningful solution for exploring the next-generation ECL emitters.

A selective electrochemical chiral interface based on a carboxymethyl-β-cyclodextrin/Pd@Au nanoparticles/3D reduced graphene oxide nanocomposite for tyrosine enantiomer recognition

Palladium@gold nanoparticle modified three-dimensional-reduced graphene oxide was coupled with carboxymethyl-β-cyclodextrin to form a novel nanocomposite, which served as an effective chiral sensing interface for electrochemical enantiorecognition.

Surface lattice engineering for fine-tuned spatial configuration of nanocrystals

Hybrid nanocrystals combining different properties together are important multifunctional materials that underpin further development in catalysis, energy storage, et al., and they are often constructed using heterogeneous seeded growth. Their spatial configuration (shape, composition, and dimension) is primarily determined by the heterogeneous deposition process which depends on the lattice mismatch between deposited material and seed. Precise control of nanocrystals spatial configuration is crucial to applications, but suffers from the limited tunability of lattice mismatch. Here, we demonstrate that surface lattice engineering can be used to break this bottleneck. Surface lattices of various Au nanocrystal seeds are fine-tuned using this strategy regardless of their shape, size, and crystalline structure, creating adjustable lattice mismatch for subsequent growth of other metals; hence, diverse hybrid nanocrystals with fine-tuned spatial configuration can be synthesized. This study may pave a general approach for rationally designing and constructing target nanocrystals including metal, semiconductor, and oxide.

Light Scattering and Luminophore Enrichment-Enhanced Electrochemiluminescence by a 2D Porous Ru@SiO2 Nanoparticle Membrane and Its Application in Ultrasensitive Detection of Prostate-Specific Antigen

Electrochemiluminescence (ECL) by virtue of its controllability and versatility has emerged as a significant tool in bioassay, but how to integrate it with other (nano)materials and further break the limit of sensitivity for ultrasensitive detection still possess tremendous potential. Herein, a close-packed Ru@SiO₂ NP nanomembrane that serves as an enhanced substrate and luminophore enricher simultaneously was constructed by the liquid-liquid interface self-assembly method and applied for ECL-enhanced bioassay. The developed ECL electrode obtained ∼600-fold enhancement on ECL intensity compared with the bare ITO electrode and ∼21-fold enhancement compared with the SiO₂ NP nanomembrane electrode due to the dramatic light scattering of the 2D SiO₂ NPs and the enrichment of Ru(bpy)₃²⁺ molecules on the surface of the Ru@SiO₂ NP nanomembrane electrode. Based on the fascinating Ru@SiO₂ NP nanomembrane platform, we further constructed a label-free immunosensor for the detection of prostate-specific antigen (PSA). The as-fabricated Ru@SiO₂-nanomembrane ECL immunosensor exhibited good stability and performed ultrasensitive detection with an utmost low detection limit of 0.169 fg·mL^-1 (signal/noise = 3). Our work puts forward an effective solution benefiting for further improving ECL performance for ultrasensitive bioassays.

Controllable preparation of sea urchin-like Au NPs as a SERS substrate for highly sensitive detection of the toxic atropine

Branched Au nanoparticles (Au NPs) can significantly enhance the Raman signal of trace chemical substances, and have attracted the interest of researchers. However, there are still challenges to accurately prepare the morphology of branched Au NPs. In this work, we have successfully prepared sea urchin-like Au NPs and Au nanowires by using the seed-mediate growth method, with cetyltrimethylammonium bromide (CTAB) and glutathione as ligands, and ascorbic acid as a reducing agent. Using Au NPs with a tetrahexahedron (THH) morphology as seeds, and by simply changing the concentration of glutathione, we explored the growth process of sea urchin-like Au and Au nanowires. At low concentrations of glutathione, Au NPs will preferentially grow along the edges and corners of the THH Au seed, forming a core/satellite structure. As the concentration of glutathione increases, Au NPs will grow along the direction of glutathione, forming sea urchin-like Au NPs. To further increase the concentration of glutathione, we will prepare Au nanowires. In addition, we use the prepared Au NPs as a substrate material for surface-enhanced Raman (SERS) high-sensitivity detection. By using 4-aminothiophenol (4-ATP) as the test molecule, we evaluated the SERS effect of the prepared Au NPs with different morphologies. The results showed that sea urchin-like Au NPs have the best enhancement effect. The lowest concentrations of Rhodamine 6G and 4-ATP were 10-10 M and 10-12 M, respectively, using sea urchin Au NPs as the base material. Furthermore, we conducted a highly sensitive SERS detection of the poison atropine monohydrate, and the lowest detected concentration was 10-10 M.

A facile synthesis of Cu catalysts with multiple high-index facets for the suppression of competing H2 evolution during electrocatalytic CO2 reduction

The electrochemical CO₂ reduction reaction (CO₂RR) over the high-index facets of Cu nanoparticles (NPs) is favourable towards the formation of multi-carbon products, such as hydrocarbons and oxygenates. However, the facile synthesis of Cu NPs with multiple high-index facets remains a great challenge in the research community. Herein, we have prepared numerous Cu catalysts with flat surfaces by electropolishing polycrystalline Cu foils before and after annealing at different temperatures ranging from 200 °C to 1000 °C under an argon atmosphere. The individual electrode crystal orientations were investigated via X-ray diffraction (XRD) and electron backscattering diffraction (EBSD) techniques. As confirmed by the EBSD technique, the formation of high-index facets increases with an increase in the annealing temperature and reaches a high quantity of high-index facets enclosed mainly by (211) and (431) facets with about 94% of those on the electrode annealed at 1000 °C. As a possible application, we have used the different electrodes for CO₂RR at -1.0 V vs. RHE with special emphasis on the formation of H₂ gas and C1 products. Thus, the electrodes prepared at higher temperatures enable the suppression of competing H₂ evolution due to the increased amount of high-index facets. Moreover, the formation rates of C1 products were inhibited as well at the electrodes with increased number of high-index facets. The drops in the formation rates of both H₂ and C1 products indicate that they are consumed in the chemical reaction to commence the formation of multi-carbon products. However, further study is still required with superior attention on CO₂RR towards the C₂₊ product formation at a range of applied potentials.

Chiral metal surfaces for enantioselective processes

Chiral surfaces are critical components of enantioselective heterogeneous processes such as those used to prepare enantiomerically pure pharmaceuticals. While the majority of chiral surfaces in practical use are based on achiral materials whose surfaces have been modified with enantiomerically pure chiral adsorbates, there are many inorganic materials with valuable surface properties that could be rendered enantiospecific, if their surfaces were intrinsically chiral. This Perspective discusses recent developments in the fabrication of intrinsically chiral surfaces exhibiting enantiospecific adsorption, surface chemistry and electron emission. We propose possible paths to the scalable fabrication of high-surface-area, enantiomerically pure surfaces and discuss opportunities for future progress.

Identification of the Miller indices of a crystallographic plane: a tutorial and a comprehensive review on fundamental theory, universal methods based on different case studies and matters needing attention

Micro-/nanostructures exposed with special crystallographic planes (surface or crystal facets) exhibit distinctive physicochemical properties because of their unique atomic arrangements, resulting in their widespread applications in the fields of catalysis, energy conversion, sensors, electrical devices and so on. Therefore, tremendous progress has been made in facet-dependent investigation of various micro-/nanocrystals over the past decades. However, a lot of beginners including undergraduate students as well as graduate students lack systematic knowledge and don't know how to identify the Miller indices of a crystallographic plane in the actual research process. So far, to the best of our knowledge, there is no specialized review article in this respect. Herein, we present a tutorial and a comprehensive review on the identification of the Miller indices of a crystallographic plane, including fundamental theory, universal methods based on different case studies, and matters needing attention. Hopefully, this tutorial review will be a beneficial theoretical and practical reference for beginners currently focusing on the controllable preparation and facet-dependent investigation of micro-/nanocrystals.

Expanding the scope of chemiluminescence in bioanalysis with functional nanomaterials

Nanomaterial-enabled chemiluminescence (CL) detection has become a growing area of interest in recent years. We review the development of nanomaterial-based CL detection strategies and their applications in bioanalysis. Much progress has been achieved in the past decade, but most attempts still remain in the proof-of-concept stage. This review highlights recent advances in nanomaterials in CL detection and organizes them into three groups based on their role in detection: as a sensing platform, as a signal probe, and applications in homogeneous systems. Furthermore, we have discussed the critical challenges we are facing and future prospects of this field.

Surface faceting and compositional evolution of Pd@Au core–shell nanocrystals during in situ annealing

A step-wise transformation process of a Pd@Au nanoparticle both structurally and compositionally was observed. Monte Carlo simulation was used to explain the results.

Toward Rationally Designing Surface Structures of Micro- and Nanocrystallites: Role of Supersaturation

Tailoring the surface structures of nanocrystals is an exciting research area on account of appealing surface-dependent properties in various applications. Although significant progress has been made in recent years, current synthetic approaches are mainly dependent upon trial and error because of the ambiguous roles of various influencing factors in complicated environments. Therefore, a general theory for predicting and guiding the rationally controlled synthesis of micro- and nanocrystallites with specific surface structures is highly desired. Of note, previous research attention was mainly focused on the crystal growth in near equilibrium conditions. However, in supersaturated growth environments (nonequilibrium conditions), the corresponding crystal growth theories are still limited. Recently, the supersaturation-controlled surface structure strategy, which is derived from thermodynamics and the Thomson-Gibbs equation, has opened up a new avenue for the control the surface structures of crystals. This strategy involves manipulating the supersaturation of growth units to control the surface structure of micro- and nanocrystallites, as the surface energy of exposed facets is correlated to the supersaturation of growth blocks. Based on the proposed theory, micro- and nanocrystallites with various surface structures, especially high-energy facets, have been successfully synthesized by our group and other researchers in past years. In order to draw lessons from previous studies, it is imperative to give a timely research account related to the supersaturation strategy and corresponding applications in controlling surface structures of different crystallites. In this Account, we explore the supersaturation-controlled surface structure strategy to construct functional nanomaterials with desired architectures. First, we highlight the role of supersaturation of growth units from theoretical analysis after a short introduction of fundamental principles for crystal growth. Then, some detailed cases concerning evolution of surface structures are presented to highlight the key experimental factors involved in manipulating the supersaturation of growth units during synthetic processes. These factors include solvents, reaction rates, and additives in wet chemical routes as well as overpotential in electrochemical routes. In addition, we briefly discuss the role of supersaturation in growth kinetics with focus on explaining the formation of spherical micro- and nanocrystallites at extremely high supersaturation. Finally, a general summary of the supersaturation-dependent surface structure control and future prospects in this field are provided. It is expected that this Account will deepen the current understanding on fundamental principles behind the control of surface structures of micro- and nanocrystallites, which can help us to construct desirable nanomaterials and promote their practical applications.

Controllable corrosion-assisted fabrication of Au-Ag alloyed hollow nanocrystals for highly efficient and environmentally-stable SERS substrates

Surface enhanced Raman scattering (SERS) substrates with both high activity and long term chemical-stability have been expected in the practical application of the SERS-based detection. In this paper, Au-Ag bimetal nanocrystals are fabricated based on the template-etching reaction in the Ag nanocubes-contained cetylpyridinium chloride (CPC) aqueous solution via adding the HAuCl₄ solution. The obtained nanocrystals are Au-Ag alloyed and hollow in structure. Further, it has been found that with the increasing Au/Ag molar ratio, the shape of the alloyed nanocrystals evolve from the truncated nanocubes to the hollow boxes and then nanocages, showing the ever red-shifting surface plasmon resonance from the visible to the infrared region. The formation of the alloyed hollow nanocrystals is attributed to the preferential dissolution of the Ag nanocubes induced by CPC selective adsorption and the three to one galvanic replacement reaction between Ag and Au atoms. Importantly, such Au-Ag alloyed hollow nanocrystals, especially the ones with a low Au/Ag atomic ratio, show both high SERS activity and long term environmental stability compared with pure Ag or Au nanocrystals, and are the ideal candidate for the SERS substrate with practical application value. This work not only demonstrates the nanofabrication route to the alloyed hollow nanocrystals with controllable shapes and tunable optical properties in a large region, but also presents highly active and chemically-stable SERS substrates for the practical SERS-based detection.

MoS2 Quantum Dots as New Electrochemiluminescence Emitters for Ultrasensitive Bioanalysis of Lipopolysaccharide

Cd-based semiconductor quantum dots (QDs) with size-tunable luminescence and high quantum yield have become the most promising electrochemiluminescence (ECL) emitters. However, their unavoidable biotoxicity limited their applications in bioassays. Here, the nontoxic and economical MoS₂ QDs prepared by chemical exfoliation from the bulk MoS₂ were first investigated as new ECL emitters, and then the possible luminescence mechanism of MoS₂ QDs was studied using ECL-potential curves and differential pulse voltammetry (DPV) methods in detail. With MoS₂ QDs as the ECL emitters and triethylamine (TEA) as the efficient coreactant, a practical and label-free aptasensor for lipopolysaccharide (LPS) detection was constructed based on aptamer recognition-driven target-cycling synchronized rolling circle amplification. Comparing to conventional stepwise reactions, this target-cycling synchronized rolling circle amplification achieved more efficient signal amplification and simpler operation. The developed assay for LPS detection demonstrated a wide linear range of 0.1 fg/mL to 50 ng/mL with limit of detection down to 0.07 fg/mL. It is worth mentioning that MoS₂ QDs with stable ECL emission exhibited a great application potential in ECL bioanalysis and imaging as a new type of excellent emitter candidates.

Multifaceted Gold-Palladium Bimetallic Nanorods and Their Geometric, Compositional, and Catalytic Tunabilities

Kinetically controlled, seed-mediated co-reduction provides a robust and versatile synthetic approach to multimetallic nanoparticles with precisely controlled geometries and compositions. Here, we demonstrate that single-crystalline cylindrical Au nanorods selectively transform into a series of structurally distinct Au@Au-Pd alloy core-shell bimetallic nanorods with exotic multifaceted geometries enclosed by specific types of facets upon seed-mediated Au-Pd co-reduction under diffusion-controlled conditions. By adjusting several key synthetic parameters, such as the Pd/Au precursor ratio, the reducing agent concentration, the capping surfactant concentration, and foreign metal ion additives, we have been able to simultaneously fine-tailor the atomic-level surface structures and fine-tune the compositional stoichiometries of the multifaceted Au-Pd bimetallic nanorods. Using the catalytic hydrogenation of 4-nitrophenol by ammonia borane as a model reaction obeying the Langmuir-Hinshelwood kinetics, we further show that the relative surface binding affinities of the reactants and the rates of interfacial charge transfers, both of which play key roles in determining the overall reaction kinetics, strongly depend upon the surface atomic coordinations and the compositional stoichiometries of the colloidal Au-Pd alloy nanocatalysts. The insights gained from this work not only shed light on the underlying mechanisms dictating the intriguing geometric evolution of multimetallic nanocrystals during seed-mediated co-reduction but also provide an important knowledge framework that guides the rational design of architecturally sophisticated multimetallic nanostructures toward optimization of catalytic molecular transformations.

Kinetically controlled synthesis of nanoporous Au and its enhanced electrocatalytic activity for glucose-based biofuel cells

Nanoporous gold (NPG) structures, which possess abundant high-index facets, kinks, and steps, have been demonstrated as effective catalysts for the glucose electrooxidation in biofuel cells. Herein, we designed surface-clean NPG structures with high-index facets by a trisodium citrate (Na₃Cit) self-initiated reduction of chloroauric acid (HAuCl₄) in a water-ice bath followed by a kinetically controlled self-assembly manner. This strategy breaks through the traditional trisodium citrate thermal-reducing chloroauric acid approach where solutions are required to heat to a certain temperature for the reaction to initiate. However, herein, the surface-clean NPG structures yielded highly enhanced catalytic activity in glucose electrooxidation with approximately 9 A cm^-2 mg^-1 current density, which is over 20 times higher than that of Au nanoparticles devised by Turkevich (Turkevich-Au NPs) under the same conditions. This remarkable electrocatalytic activity could be ascribed to the large electrochemically active surface area, clean surface, and high-index facets or highly active sites of the porous structure. The employment of the surface-clean NPG with high-index facets for glucose electrooxidation promises a substantial improvement in the current biofuel cell technology and indicates the potential of biofuel cells in practical applications.

High-index faceted Au nanocrystals with highly controllable optical properties and electro-catalytic activity

We introduce a new and naturally abundant mild reducing agent, tannic acid, to improve the seed-mediated growth method for the synthesis of elongated tetrahexahedral Au nanocrystals enclosed with high-index (730) planes, at room-temperature. The control of the dimensions, plasmonics and electro-catalysis of such high-index faceted nanocrystals is remarkable.

Alloy oxidation as a route to chemically active nanocomposites of gold atoms in a reducible oxide matrix

While nanoparticles are being pursued actively for a number of applications, dispersed atomic species have been explored far less in functional materials architectures, primarily because composites comprising dispersed atoms are challenging to synthesize and difficult to stabilize against sintering or coarsening. Here we show that room temperature oxidation of Au-Sn alloys produces nanostructures whose surface is terminated by a reducible amorphous oxide that contains atomically dispersed Au. Analysis of the oxidation process shows that the dispersal of Au in the oxide can be explained by predominant oxygen anion diffusion and kinetically limited metal mass transport, which restrict phase separation due to a preferential oxidation of Sn. Nanostructures prepared by oxidation of nanoscale Au-Sn alloys with intermediate Au content (30-50%) show high activity in a CO-oxidation probe reaction due to a cooperative mechanism involving Au atoms as sites for CO adsorption and reaction to CO₂ embedded in a reducible oxide that serves as a renewable oxygen reservoir. Our results demonstrate a reliable approach toward nanocomposites involving oxide-embedded, atomically dispersed noble metal species.

Selectivity on Etching: Creation of High-Energy Facets on Copper Nanocrystals for CO2 Electrochemical Reduction

Creating high-energy facets on the surface of catalyst nanocrystals represents a promising method for enhancing their catalytic activity. Herein we show that crystal etching as the reverse process of crystal growth can directly endow nanocrystal surfaces with high-energy facets. The key is to avoid significant modification of the surface energies of the nanocrystal facets by capping effects from solvents, ions, and ligands. Using Cu nanocubes as the starting material, we have successfully demonstrated the creation of high-energy facets in metal nanocrystals by controlled chemical etching. The etched Cu nanocrystals with enriched high-energy {110} facets showed significantly enhanced activity toward CO2 reduction. We believe the etching-based strategy could be extended to the synthesis of nanocrystals of many other catalysts with more active high-energy facets.

Synthesis of octahedral, truncated octahedral, and cubic Rh2Ni nanocrystals and their structure-activity relationship for the decomposition of hydrazine in aqueous solution to hydrogen

We developed a co-reduction method to synthesize octahedral, truncated octahedral, and cubic Rh2Ni nanocrystals. The shape/size distribution, structural characteristics, and composition of the Rh2Ni nanocrystals are investigated, and their possible formation mechanism at high temperatures in margaric acid/1-aminoheptadecane solution in the presence of tetraethylgermanium and borane trimethylamine complexes is proposed. A preliminary probing of the structure-activity dependence of the surface "clean" Rh2Ni nanocrystals supported on carbon towards hydrazine (N2H4) in aqueous solution dehydrogenation revealed that the higher the percentage of {111} facets, the higher is the activity and H2 selectivity of the nanocrystals. This result was attributed to the {111} facets not only introducing more basic sites, but also weakening the interaction between the produced adspecies (including H2 and NHx) and surface metal atoms in comparison with those of {100} facets. Furthermore, the as-prepared Rh2Ni nanooctahedra exhibited 100% H2 selectivity and high activity at room temperature for H2 generation via N2H4 decomposition. The activation energy of the Rh2Ni nanooctahedra was 41.6 ± 1.2 kJ mol(-1). The Rh2Ni nanooctahedra were stable catalysts for the hydrolytic dehydrogenation of N2H4, providing 27 723 total turnovers in 30 h. Our work provides a new perspective concerning the possibility of constructing hydrogen-producing systems based on N2H4 and surface "clean" Rh2Ni nanocrystal catalysts with defined shapes supported on carbon that possess a competitive performance in comparison with NaBH4 and NH3BH3 hydrogen-producing systems for fuel cell applications.

Graphene Oxide-Assisted Synthesis of Pt-Co Alloy Nanocrystals with High-Index Facets and Enhanced Electrocatalytic Properties

Metal nanocrystals (NCs) are grown directly on the surface of reduced graphene oxide (rGO), which can maximize the rGO-NCs contact/interaction to achieve the enhanced catalytic activity. However, it is difficult to control the size and morphology of metal NCs by in situ method due to the effects of functional groups on the surface of GO, and as a result, the metal NCs/rGO hybrids are conventionally synthesized by two-step method. Herein, one-pot synthesis of Pt-Co alloy NCs is demonstrated with concave-polyhedrons and concave-nanocubes bounded by {hkl} and {hk0} high-index facets (HIFs) distributed on rGO. GO can affect the geometry and electronic structure of Pt-Co NCs. Thanks to the synergy of the HIFs and the electronic effect of the intimate contact/interaction between Pt-Co alloy and rGO, these as-prepared Pt-Co NCs/rGO hybrids presents enhanced catalytic properties for the electrooxidation of formic acid, as well as for the oxygen reduction reaction.

Fabrication of Pd/P nanoparticle networks with high activity for methanol oxidation

The as-prepared Pd/P nanoparticle networks efficiently exhibit electrocatalytic activity and stability for methanol oxidation.

Shape-controlled synthesis of Au–Pd bimetallic nanocrystals for catalytic applications

This review describes recent progress in the design and synthesis of shape-controlled Au–Pd bimetallic NCs and their emerging catalytic applications.

In situ electro-polymerization of nitrogen doped carbon dots and their application in an electrochemiluminescence biosensor for the detection of intracellular lead ions

Here, a sensitive electrochemiluminescence (ECL) biosensor using N doped carbon dots (N-CDs) as luminophores, and Pd–Au hexoctahedrons (Pd@Au HOHs) as enhancers, was developed for the detection of intracellular Pb²⁺.

Concave Rhombic Dodecahedral Au Nanocatalyst with Multiple High-Index Facets for CO2 Reduction

A concave rhombic dodecahedron (RD) gold nanoparticle was synthesized by adding 4-aminothiophenol (4-ATP) during growth from seeds. This shape is enclosed by stabilized facets of various high-indexes, such as (331), (221), and (553). Because it is driven thermodynamically and stabilized by 4-ATP ligands, the concave RD maintains its structure over a few months, even after rigorous electrochemical reactions. We discussed the mechanism of the shape evolution controlled by 4-ATP and found that both the binding energy of Au-S and the aromatic geometry of 4-ATP are major determinants of Au atom deposition during growth. As a possible application, we demonstrated that the concave RD exhibits superior electrocatalytic performance for the selective conversion of CO2 to CO in aqueous solution.

Sandwiched Electrochemiluminescent Peptide Biosensor for the Detection of Prognostic Indicator in Early-Stage Cancer Based on Hollow, Magnetic, and Self-Enhanced Nanosheets

Currently, peptide-based protein-recognition has been recognized as an effective and promising approach for protein assays. However, sandwiched peptide-based biosensor with high sensitivity and low background has not been proposed before. Herein, a sandwiched electrochemiluminescence (ECL) peptide-based biosensor is constructed for Cyclin A(2) (CA2), a prognostic indicator in early stage of multiple cancers, based on nanosheets with hollow, magnetic, and ECL self-enhanced properties. First, hollow and magnetic manganese oxide nanocrystals (H-Mn(3)O(4)) are synthesized using triblock copolymeric micelles with core-shell-corona architecture as templates. Then, polyethyleneimine (PEI) and the composite of platinum nanoparticles and tris (4,4'-dicarboxylicacid-2,2'-bipyridyl) ruthenium (II) (PtNPs-Ru) are immobilized on H-Mn(3)O(4) to form H-Mn(3)O(4) -PEI-PtNPs-Ru nanocomposite, in which PEI as coreactant can effectively enhance the luminous efficiency and PtNPs as nanochannels can greatly accelerate the electron transfer. Finally, due to the coordination between Eu(3+) and carboxyl, the obtained H-Mn(3)O(4) -PEI-PtNPs-Ru aggregates locally to form sheet-like nanostructures ((H-Mn(3)O(4) -PEI-PtNPs-Ru)(n) -Eu(3+)), by which the luminous efficiency is further increased. Based on the nanosheets and two designed peptides, a sandwiched ECL biosensor, using palladium nanocages synthesized through galvanic replacement reaction as substrate, is proposed for CA2 with a linear range from 0.001 to 100 ng mL(-1) and a detection limit of 0.3 pg mL(-1).

{331}-Faceted trisoctahedral gold nanocrystals: synthesis, superior electrocatalytic performance and highly efficient SERS activity

We investigate the effect of gold (Au) seeds prepared in cetyltrimethylammonium chloride solution (CTAC-Au seeds) on the index facets of trisoctahedral gold nanocrystals (TOH Au NCs). We demonstrate that monodisperse {331}-faceted TOH Au NCs with controllable sizes (from 60 to 255 nm) can be successfully prepared in high yield by using 3.0 nm CTAC-Au seeds or as-prepared 70 nm TOH Au NCs as seeds. We find that the electrocatalytic performance on methanol oxidation and surface enhancement Raman spectroscopy (SERS) activity of {331}-faceted TOH Au NCs is size-dependent. In comparison with well-known nanoporous gold (0.088 mA cm(-2)), {331}-faceted TOH Au NCs with sizes of 110 nm exhibit fairly high catalytic activity (0.178 mA cm(-2)) on methanol oxidation (1.0 M) in alkaline media due to the presence of increasing density of atomic steps, ledges, and kinks on the NC surfaces. Their current density is reduced by less than 7% after 500 cycling tests. {331}-Faceted TOH Au NCs with sizes of 175 nm exhibit the highest SERS activity for 4-aminothiophenol (4-ATP) molecules. The enhancement factors of a1 modes of 4-ATP molecules can reach the order of 10(9) when the 4-ATP concentration is 3 × 10(-6) M. Moreover, Raman signals (ag modes) of 4,4'-dimercaptoazobenzene (DMAB) molecules on TOH Au NCs are stronger than those on spherical Au NCs of comparable size due to the enhanced laser-induced transformation of 4-ATP molecules by high-index {331}-facets during SERS measurement. Furthermore, the SERS intensities of 4-methylbenzenethiol (4-MTP) molecules on TOH Au NCs are also higher than those on spherical Au NCs of comparable size due to sharp extremities.

Recent advances in electrochemiluminescence

The great success of electrochemiluminescence (ECL) for in vitro diagnosis (IVD) and its promising potential in light-emitting devices greatly promote recent ECL studies. More than 45% of ECL articles were published after 2010, and the first international meeting on ECL was held in Italy in 2014. This critical review discusses recent vibrant developments in ECL, and highlights novel ECL phenomena, such as wireless ECL devices, bipolar electrode-based ECL, light-emitting electrochemical swimmers, upconversion ECL, ECL resonance energy transfer, thermoresponsive ECL, ECL using shape-controlled nanocrystals, and ECL as an ion-selective electrode photonic reporter, a paper-based microchip, and a self-powered microfluidic ECL platform. We also comment on the latest progress in bioassays, light-emitting devices and, the computational approach for the ECL mechanism study. Finally, perspectives and key challenges in the near future are addressed (198 references).