Axially twinned nanodumbbell with a Pt bar and two Rh@Pt balls designed for high catalytic activity

Designing Sites in Heterogeneous Catalysis: Are We Reaching Selectivities Competitive With Those of Homogeneous Catalysts?

A critical review of different prominent nanotechnologies adapted to catalysis is provided, with focus on how they contribute to the improvement of selectivity in heterogeneous catalysis. Ways to modify catalytic sites range from the use of the reversible or irreversible adsorption of molecular modifiers to the immobilization or tethering of homogeneous catalysts and the development of well-defined catalytic sites on solid surfaces. The latter covers methods for the dispersion of single-atom sites within solid supports as well as the use of complex nanostructures, and it includes the post-modification of materials via processes such as silylation and atomic layer deposition. All these methodologies exhibit both advantages and limitations, but all offer new avenues for the design of catalysts for specific applications. Because of the high cost of most nanotechnologies and the fact that the resulting materials may exhibit limited thermal or chemical stability, they may be best aimed at improving the selective synthesis of high value-added chemicals, to be incorporated in organic synthesis schemes, but other applications are being explored as well to address problems in energy production, for instance, and to design greener chemical processes. The details of each of these approaches are discussed, and representative examples are provided. We conclude with some general remarks on the future of this field.

Structure-intensified PtCoRh spiral nanowires as highly active and durable electrocatalysts for methanol oxidation

Platinum (Pt)-based nanocatalysts with a high density of surface atomic steps hold great prospects in electrocatalysis. However, the structural instability under harsh redox conditions is still a rigorous challenge. Here, we demonstrate that ternary PtCoRh alloyed spiral nanowires (SNWs), which have the advantages of one-dimensional nanowires, alloy synergy, surface atomic steps, and anti-corrosive Rh incorporation, can serve as active and robust MOR electrocatalysts in acidic media. The results showed that the Pt₇₇Co₁₁Rh₁₂ SNWs delivered the highest mass activity (1.48 A mg^-1) and specific activity (4.76 mA cm^-2), as well as the best durability in the long-term MOR test, compared with the Pt₈₅Co₁₀Rh₅ and Pt₈₅Co₁₅ SNWs and Pt black. Further inspections of the morphology, composition, and electronic structure revealed that the incorporated Rh atoms not only stabilized the highly rugged SNWs and the easily leaching Co atoms but also delicately tuned the electron transfer among the three metallic elements, leading to the enhancement of MOR activity, structural stability and anti-CO-poisoning ability. Our work provides a rational strategy for the development of highly efficient and durable alcohol oxidation electrocatalysts.

A sandwich-type electrochemical immunosensor based on RhPt NDs/NH2-GS and Au NPs/PPy NS for quantitative detection hepatitis B surface antigen

In this work, a sandwich-type electrochemical immunosensor was fabricated to quantitatively detect hepatitis B surface antigen (HBsAg). The immunosensor was based on Rh core and Pt shell nanodendrites loaded onto amino group functionalized graphene nanosheet (RhPt NDs/NH₂-GS) as label and gold nanoparticles loaded onto polypyrrole nanosheet (Au NPs/PPy NS) as platform. RhPt NDs with abundant catalytic active sites because of the branched core-shell structure, RhPt NDs/NH₂-GS as the label displayed high catalytic activity, amplifying the current signal of the immunosensor. Additionally, Au NPs/PPy NS enhanced the electron transfer and provided a good microenvironment to immobilize antibodies effectively, thus improving the sensitivity of the immunosensor. Based on above advantages, the immunosensor emerged a linear concentration ranging from 0.0005 to 10 ng/mL, a low detection limit of 166 fg/mL for HBsAg (S/N = 3) and good stability, selectivity, reproducibility. Furthermore, the satisfactory accuracy in analysis of actual serum samples implied the immunosensor had promising prospect in clinical analysis applications.

Efficient oxygen reduction catalysis by subnanometer Pt alloy nanowires

The common knowledge is that Pt and Pt alloy nanoparticles (NPs) less than 2 nm are not desirable for oxygen reduction reaction (ORR). However, whether the same trend is expected in Pt-based nanowires (NWs) and nanoplates remains questionable because there is no scalable approach to make such Pt nanostructures. We report a general approach for preparing subnanometer Pt alloy NWs with a diameter of only 4 to 5 atomic layer thickness, ranging from monometallic Pt NWs to bimetallic PtNi and PtCo NWs and to trimetallic PtNiCo NWs. In a sharp contrast to Pt alloy NPs, the subnanometer Pt alloy NWs demonstrate exceptional mass and specific activities of 4.20 A/mg and 5.11 mA/cm² at 0.9 V versus reversible hydrogen electrode (RHE), respectively, 32.3 and 26.9 times higher than those of the commercial Pt/C. Density functional theory simulations reveal that the enhanced ORR activities are attributed to the catalytically active sites on high-density (111) facets in the subnanometer Pt alloy NWs. They are also very stable under the ORR condition with negligible activity decay over the course of 30,000 cycles. Our work presents a new approach to maximize Pt catalytic efficiency with atomic level utilization for efficient heterogeneous catalysis and beyond.

Facet-controlled {100}Rh-Pt and {100}Pt-Pt dendritic nanostructures by transferring the {100} facet nature of the core nanocube to the branch nanocubes

Facet-controlled dendritic nanostructures are expected to exhibit excellent catalytic properties because both aggregation-free nature and controlled facet-originated activity and selectivity can be accomplished. However, such examples are extremely rare due to the incompatibility of the dendrite formation process with the usage of surface-stabilizing moieties, which are typically used to control facets. Herein, we demonstrate that regiospecific growth on a facet-controlled core nanoparticle can induce the facet-control of the branch nanoparticles. Specifically, facet-controlled dendritic nanostructures of {100}Rh-Pt and {100}Pt-Pt can be conveniently prepared by transferring the crystallographic behaviour of the {100}Pt dendritic core nanocube to the {100}Rh or {100}Pt branch nanocubes.

Rod-like β-FeOOH@poly(dopamine)–Au–poly(dopamine) nanocatalysts with improved recyclable activities

A novel rod-like β-FeOOH@poly(dopamine)–Au–poly(dopamine) core–shell nanocomposite with significantly improved recyclability is developed for catalysis.

Rationally synthesized five-fold twinned core-shell Pt3Ni@Rh nanopentagons, nanostars and nanopaddlewheels for selective reduction of a phenyl ring of phthalimide

Surface-energy fine-tuned five-fold twinned nanostructures with a core-shell Pt3Ni@Rh structural motif, namely, a core-shell Pt3Ni@Rh pentagon, a core-shell Pt3Ni@Rh starfish, and a paddlewheel with a Pt3Ni crankshaft and two Rh five-fold starfish wheels, are prepared by rationally designed stepwise heteroepitaxial growth. Unusual selective hydrogenation of the phenyl ring in phthalimide is accomplished with moderately active core-shell Pt3Ni@Rh pentagons and starfish-like nanoparticles. The most active paddlewheel structure proceeds to further reduce one carbonyl group, indicating the sequential nature of phthalimide reduction by Rh nanoparticle catalysis.

One pot synthesis of nanoscale phase-segregated PdPt nanoarchitectures via unusual Pt-doping induced structural reorganization of a Pd nanosheet into a PdPt nanotent

Pt-doping of an ultrathin Pd nanosheet results in the unprecedented structural rearrangement of a Pd nanosheet into a PdPt nanotent structure, in which a tripod stands on a triangular nanosheet. Further growth of Pt phase on this nanotent structure is dependent on the presence of surface-stabilizing CO molecules, leading to the formation of two distinct nanoscale phase segregated structures with respective structural features of a popped out Pt facet and an overgrown Pt layer.

Seed-assisted synthesis of Pd@Au core-shell nanotetrapods and their optical and catalytic properties

The synthesis of noble metal nanostructures with special morphology, structure, composition, and size has been an attractive research area because of their valuable applications in various fields, including optics, electronics, sensing and catalysis. In this work, the first Pd@Au core-shell nanotetrapods (Pd@Au CSNTPs) were synthesized through a facile seeded growth method. Specifically, Pd nanotetrapods were utilized as the substrate for Au coating through chemically reducing HAuCl4 with ascorbic acid (AA) in the presence of polyvinylpyrrolidone (PVP). The morphology, composition, and structure of Pd@Au CSNTPs were fully characterized by scanning and transmission electron microscopy, energy dispersive spectroscopy element mapping, X-ray powder diffraction, X-ray photoelectron spectroscopy techniques, etc. Different from conventional spherical Au nanoparticles, the Pd@Au CSNTPs had a very wide surface plasmon resonance (SPR) absorption band in the visible and near-infrared regions (500-1400 nm), showing special SPR absorption features. Meanwhile, the Pd@Au CSNTPs exhibited remarkably enhanced catalytic activity for the hydrogenation reduction of nitro functional groups and the C=N bond because of their specific structural characteristics.

One-pot synthesis of ultralong coaxial Au@Pt nanocables with numerous highly catalytically active perpendicular twinning boundaries and Au@Pt core-shell bead structures

Ultralong coaxial Au@Pt nanocables prepared by one-pot synthesis exhibit excellent electrocatalytic activity due to structural features of (1) numerous twinning boundaries and (2) lattice mismatch between the core and the shell.

RhPt flowerlike bimetallic nanocrystals with tunable composition as superior electrocatalysts for methanol oxidation

For the first time, composition-tunable, high-yield, RhPt flowerlike bimetallic nanocrystals were successfully synthesized through an aqueous solution approach. The electrocatalytic activity of these RhPt nanoalloys toward methanol oxidation was investigated and compared to the activity of commercial Pt black and commercial Ru50Pt50/C. The RhPt flowerlike bimetallic nanoallys have shown composition-dependent and superior catalytic properties relative to those of commercial Pt black and commercial Ru50Pt50/C. The peak current density and mass current value of Rh19Pt81 nanoalloys are 0.75 mA cm(-2) and 0.12 mA μg(-1), respectively. For commercial Pt black, they are 0.48 mA cm(-2) and 0.074 mA μg(-1), and for commercial Ru50Pt50/C, they are 0.28 mA cm(-2) and 0.10 mA μg(-1). Moreover, the chronoamperometric measurements show that the RhPt flowerlike nanoalloys have excellent stability over commercial Pt black and commercial Ru50Pt50/C.

Twinning boundary-elongated hierarchical Pt dendrites with an axially twinned nanorod core for excellent catalytic activity

Introduction of twinning boundary elongation and lattice mismatch to the hierarchical and dendritic Pt₃Ni@Pt nanostructures by heteroepitaxial twinning transfer from five-fold twinned Pt₃Ni nanorods leads to great enhancement of the electrocatalytic performance in MOR and ORR.

Facile synthesis of PdPt nanoalloys with sub-2.0 nm islands as robust electrocatalysts for methanol oxidation

The high-yield, composition-tunable PdPt nanoalloys with sub-2.0 nm islands were first achieved through a facile aqueous approach.

Growth of nanobipyramid by using large sized Au decahedra as seeds

Au nanobipyramids (NBPs) are important nanostructures which attract much attention due to their unique structure, optical, and catalytic properties. The controlled synthesis of Au NBPs and corresponding mechanistic study are highly desirable for both fundamental research and practical applications. Herein, we demonstrate a strategy that large sized Au decahedra with well-defined shape act as seeds for growing NBPs. Furthermore, through using different sized decahedra seeds with edge from 25 to 49 nm, various sized NBPs can be easily prepared (longitudinal length from 110 to 210 nm; transverse length from 36 to 70 nm). Our study provides hard evidence for the growth of NBPs that they surely stem from the overgrowth on penta-twinned decahedra. Because these used large size seeds have well-defined shape and structure, the growth of the NBPs can be easily determined. Results show that the formation of NBPs is primarily determined by the molar ratio of Au(3+) and Au seeds (MRAA). MRAA less than 4 only causes size enhancement and no significant shape change. In cases of MRAA higher than 4 and lower than 8, quasi-nanorods are produced. When MRAA range from 8 to 10, NBPs form and the yield is higher than 90%. The effect of reaction time and temperature also are vital to the growth of NBPs. These prepared NBPs are found to exhibit excellent surface enhanced Raman scattering (SERS) performance because of many present hotspots, edges, steps, and tips on their surfaces.