Fabrication of Supported AuPt Alloy Nanocrystals with Enhanced Electrocatalytic Activity for Formic Acid Oxidation through Conversion Chemistry of Layer-Deposited Pt(2+) on Au Nanocrystals

Synthesis of Eu3+-Doped NaGd9Si6O26 Sub-Microcrystals from a NaGdF4@SiO2 Structure

Rare earth silicate phosphors of high quantum efficiency with a stable performance are promising materials in the fields of display and illumination. The grain sizes of products synthesized via the conventional solid-state reaction method are usually too large to satisfy the requirements of color cast and extraction efficiency in high-resolution light-emitting devices (LEDs). We designed a synthetic route and successfully fabricated rare earth silicate NaGd₉Si₆O₂₆ (NGSO) sub-microcrystals with a size ranging from 550 to 1200 nm. The reaction mechanism and optical properties were systematically investigated. The quantum efficiency of Eu³⁺-activated NGSO sub-microcrystals was about 36.6%. The LED encapsulated with these sub-microcrystals showed lower color deviation and higher lumen efficiency and lumen flux compared to that with NGSO fabricated using the conventional solid state reaction method.

The enhancement in the performance of ultra-small core-shell Au@AuPt nanoparticles toward HER and ORR by surface engineering

In this work, ultra-small core-shell (USCS) Au_38.4@Au_4.1Pt_57.5 nanoparticles (NPs) with an optimal Pt-to-Au ratio were successfully prepared by the optimal etching treatment of USCS Au@AuPt NPs by Fe(III) ions to remove some exposed Au atoms on their outermost surfaces. The as-prepared USCS Au_38.4@Au_4.1Pt_57.5 NPs with Fe(III)-etching treatment for 2 h loaded on carbon black as catalysts (USCS^2h Au_38.4@Au_4.1Pt_57.5-NP/C catalysts) exhibit superior electrocatalytic activity and durability for both the hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) in acidic media. For instance, the overpotential of USCS^2h Au_38.4@Au_4.1Pt_57.5-NP/C catalysts toward the HER is 13 mV at a current density of -10 mA cm^-2 (η₁₀ = 13 mV), which is much better than that of commercial Pt/C catalysts (η₁₀ = 31 mV). Moreover, their mass activity (63.8 A mg_Pt^-1) is about 16.4 times larger than that of commercial Pt/C catalysts (3.9 A mg_Pt^-1). In addition, they also present better long-term stability. Furthermore, they also show an improved activity toward the ORR in terms of the half-wave potential (E_1/2) (0.89 V vs. RHE), which is more positive by about 38 mV than commercial Pt/C catalysts (0.852 V). In addition, they also show a higher kinetic current density (14.22 mA cm^-2 at 0.85 V) and better long-term durability. This etching-treatment strategy can be extended to further improve the catalytic performance of ultra-small Au-based bimetallic or multi-metallic NPs by surface engineering.

Bioinspired Pd-Cu Alloy Nanoparticles as Accept Agent for Dye Degradation Performances

Dye degradation is a key reaction in organic decomposition production through electron donor transferring. Palladium (Pd) is the best-known element for synthesis Pd-based catalyst, the surface status determines the scope of relative applications. Here we first prepare Pd-Cu alloy nanoparticles (NPs) by co-reduction of Cu(acac)₂ (acac = acetylacetonate) and Pd(C₅HF₆O₂)₂ in the presence of sodium borohydride (NaBH₄) and glutathione (GSH). The obtained Pd-Cu is about ~10 nm with super-hydrophilicity in aqueous mediums. The structural analysis clearly demonstrated the uniform distribution of Pd and Cu element. The colloidal solution keeps stability even during 30 days. Bimetallic Pd-Cu NPs shows biocompatibility in form of cell lines (IMEF, HACAT, and 239 T) exposed to colloidal solution (50 µg mL^-1) for 2 days. It shows the catalytic multi-performance for dye degradation such as methyl orange (MO), rhodamine B (RhB), and methylene blue (MB), respectively. The as-synthesized nanoparticles showed one of the best multiple catalytic activities in the industrially important (electro)-catalytic reduction of 4-nitrophenol (4-NP) to corresponding amines with noticeable reduced reaction time and increased rate constant without the use of any large area support. In addition, it exhibits peroxidase-like activity in the 3, 3', 5, 5'-Tetramethylbenzidine (TMB) color test and exhibit obvious difference with previous individual metal materials. By treated with high intensity focused ultrasound filed (HIFU), Pd-Cu NPs might be recrystallized and decreased the diameters than before. The enhancement in catalytic performance is observed obviously. This work expedites rational design and synthesis of the high-hierarchy alloy catalyst for biological and environment-friendly agents.

Solid-State Reaction Synthesis of Nanoscale Materials: Strategies and Applications

Nanomaterials (NMs) with unique structures and compositions can give rise to exotic physicochemical properties and applications. Despite the advancement in solution-based methods, scalable access to a wide range of crystal phases and intricate compositions is still challenging. Solid-state reaction (SSR) syntheses have high potential owing to their flexibility toward multielemental phases under feasibly high temperatures and solvent-free conditions as well as their scalability and simplicity. Controlling the nanoscale features through SSRs demands a strategic nanospace-confinement approach due to the risk of heat-induced reshaping and sintering. Here, we describe advanced SSR strategies for NM synthesis, focusing on mechanistic insights, novel nanoscale phenomena, and underlying principles using a series of examples under different categories. After introducing the history of classical SSRs, key theories, and definitions central to the topic, we categorize various modern SSR strategies based on the surrounding solid-state media used for nanostructure growth, conversion, and migration under nanospace or dimensional confinement. This comprehensive review will advance the quest for new materials design, synthesis, and applications.

Spatially Confined Formation and Transformation of Nanocrystals within Nanometer-Sized Reaction Media

The extensive research performed in the past two decades has enabled the production of a range of colloidal nanocrystals, mostly through solution-based procedures that generate and transform nanostructures in bulk-phase solutions containing precursors and surfactants. However, the understanding and control of each nanocrystal (trans)formation step during the synthesis are still complicated because of the high complexity of this process, in which multiple diverse events such as nucleation, subsequent growth, attachment, and ripening occur simultaneously in bulk suspensions. Unlike well-established solution-based methods, solid-state reactions, which had been at the forefront of traditional inorganic materials chemistry, are quite rarely utilized in the realm of nanomaterials because of the high temperatures required for most solid-state reactions, as a result of which the clusters and NCs are prone to migrate through the bulk reaction medium and sinter together uncontrollably into large particles. We have been pursuing the "nanospace-confined approach" to explore the use of a variety of solid and hollow silica nanoparticles as either solid-state or solution-phase reaction media to carry out the syntheses and transformations of nanocrystals in a unique microenvironment, partitioning the reactants, intermediates, and transition states from the rest of the bulk reaction medium. Such nanoconfined systems have the potential not only to enable efficient and selective nanocrystal conversion chemistries but also to provide fundamental understanding pertaining to the synthetic evolution of nanostructures and transient mechanistic steps. The unique spaces with sizes of a few tens of nanometers inside nanoconfined systems offer the opportunity to observe and elucidate novel deconvoluted chemical phenomena that are impossible to investigate in bulk systems, and comprehensive understanding of nanoconfined chemistry can be implicated in explaining and controlling the macroscopic chemical behaviors. This Account describes our focused research on developing spatially confined platforms for nanocrystal syntheses and transformations, highlighting our diversity-oriented strategy, namely, the "postdecoration approach", which results in the evolution of new nanocatalytic sites in a preformed cavity for diversifying and controlling their morphologies, number, density and combinations. We discuss key examples of the "nanoconfined solid-state conversion approach" that involve novel reactions of nanocrystals within thermally stable solid silica nanospheres to synthesize and transform complex hybrid nanocrystals with increased complexity and functionality. In addition, an enlightening discussion of the examples of nanocrystal syntheses and conversions in nanoconfined solutions inside enclosed and exposed cavities of silica nanospheres is included. Finally, the important applications of nanospace-confined systems in various fields are also briefly discussed.

Design of Ultrathin Pt-Based Multimetallic Nanostructures for Efficient Oxygen Reduction Electrocatalysis

Nanocatalysts with high platinum (Pt) utilization efficiency are attracting extensive attention for oxygen reduction reactions (ORR) conducted at the cathode of fuel cells. Ultrathin Pt-based multimetallic nanostructures show obvious advantages in accelerating the sluggish cathodic ORR due to their ultrahigh Pt utilization efficiency. A focus on recent important developments is provided in using wet chemistry techniques for making/tuning the multimetallic nanostructures with high Pt utilization efficiency for boosting ORR activity and durability. First, new synthetic methods for multimetallic core/shell nanoparticles with ultrathin shell sizes for achieving highly efficient ORR catalysts are reviewed. To obtain better ORR activity and stability, multimetallic nanowires or nanosheets with well-defined structure and surface are further highlighted. Furthermore, ultrathin Pt-based multimetallic nanoframes that feature 3D molecularly accessible surfaces for achieving more efficient ORR catalysis are discussed. Finally, the remaining challenges and outlooks for the future will be provided for this promising research field.

Confined Nucleation and Growth of PdO Nanocrystals in a Seed-Free Solution inside Hollow Nanoreactor

This paper reports a novel and adaptable hollow nanoreactor system containing a solution of cucurbituril (CB) inside a silica nanoparticle (CB@h-SiO₂) which enables the nucleation and formation of nanocrystals (NCs) to be confined at the seed-free interior solution inside the cavity. The above nanospace confinement strategy restricted the volume of medium available for NC formation to the solution inside the cavity to a few tens of nanometers in size and allowed homogeneous NC nucleation to be examined. Harboring of CB@h-SiO₂ in a Pd²⁺ complex solution confined the nucleation and formation of PdO NCs to the well-isolated nanosized cavity protected by the silica nanoshell, allowing the convoluted formation of clustered PdO NCs to be thoroughly examined. The corresponding temporal investigation indicated that PdO NC clusters evolved via a distinct pathway combining dendritic growth on early nucleated seed NCs and attachment of small intermediate clusters. In addition, the explored strategy was used to fabricate a recyclable nanocatalyst system for selective catalytic oxidation of cinammyl alcohols, featuring a cavity-included Fe₃O₄/PdO nanocomposite.

Selective Deposition of an Ultrathin Pt Layer on a Au-Nanoisland-Modified Si Photocathode for Hydrogen Generation

Platinum, being the most efficient and stable catalyst, is used in photoelectrochemical (PEC) devices. However, a minimal amount of Pt with maximum catalytic activity is required to be used to minimize the cost of production. In this work, we use an environmentally friendly, cost-effective, and less Pt-consuming method to prepare PEC devices for the hydrogen evolution reaction (HER). The Pt monolayer catalyst is selectively deposited on a Au-nanoisland-supported boron-doped p-type Si (100) photocathode. The PEC device based on the Si photocathode with an ultralow loading of the Pt catalyst exhibits a comparable performance for the HER to that of devices with a thick Pt layer. In addition, we demonstrate that by using a thin TiO₂ layer deposited by atomic layer deposition photo-oxidation of the Si photocathode can be blocked resulting in a stable PEC performance.

Hexagonal tungsten oxide nanoflowers as enzymatic mimetics and electrocatalysts

Tungsten oxide (WO_x) has been widely studied for versatile applications based on its photocatalytic, intrinsic catalytic, and electrocatalytic properties. Among the several nanostructures, we focused on the flower-like structures to increase the catalytic efficiency on the interface with both increased substrate interaction capacities due to their large surface area and efficient electron transportation. Therefore, improved WO_x nanoflowers (WONFs) with large surface areas were developed through a simple hydrothermal method using sodium tungstate and hydrogen chloride solution at low temperature, without any additional surfactant, capping agent, or reducing agent. Structural determination and electrochemical analyses revealed that the WONFs have hexagonal Na_0.17WO_3.085·0.17H₂O structure and exhibit peroxidase-like activity, turning from colorless to blue by catalyzing the oxidation of a peroxidase substrate, such as 3,3′,5,5′-tetramethylbenzidine, in the presence of H₂O₂. Additionally, a WONF-modified glassy carbon electrode was adopted to monitor the electrocatalytic reduction of H₂O₂. To verify the catalytic efficiency enhancement by the unique shape and structure of the WONFs, they were compared with calcinated WONFs, cesium WO_x nanoparticles, and other peroxidase-like nanomaterials. The results indicated that the WONFs showed a low Michaelis-Menten constant (k_m), high maximal reaction velocity (v_max), and large surface area.

Ultralong PtNi alloy nanowires enabled by the coordination effect with superior ORR durability

Ultralong PtNi nanowires were prepared by taking advantage of the coordination effect to delicately control the reduction and alloying kinetics.