Ultrasmall Metal Nanoparticles Research Articles

Selective electrocatalytic oxidation of ammonia to nitrogen by using titanium dioxide nanorod array decorated with ultrasmall Ir nanoparticles and non-noble metal Fe nanoparticles

Electrochemical ammonia oxidation process through active chlorine has been proposed as a potentially effective method for ammonia removal. Currently, most of the anodes require to use high-stable TiO2 loaded with large particles of noble metal Ru or Ir, which have low activity and high cost. Herein, we prepare ultrasmall and uniform metal nanoparticles of Ir on TiO2 to remove ammonia. Moreover, we use non-noble metal Fe to replace noble metals. The ammonia removal efficiency of Fe/TiO2 under 2 VVS Ag / AgCl during 2 h is 100 % and 94 % of ammonia is converted to N2. The Fe/TiO2 anodes not only have higher catalytic activity but also show excellent stability and reusability. Fe/TiO2 anodes still exhibit excellence activity and selectivity after 1 year. As a common metal, Fe will have more application space than iridium in ammonia removal for its low cost and selectively high efficiency.

Accelerating water dissociation at hierarchical nanostructured electrocatalyst for efficient hydrogen evolution

The sluggish kinetics of the water electrolysis reaction is a key issue for hydrogen production, so the rational design of a high-efficiency hydrogen evolution reaction (HER) electrocatalyst with various structures has attracted extensive attention. Herein, a coaxial hierarchical three-dimensional (3D) nanostructure, Pt@Mo–S–Ni-CNTs, was prepared. In this nanostructure, carbon nanotubes (CNTs) as the core, Mo–S–Ni ultrathin nanosheets as shells, and ultrasmall metal nanoparticles (NPs) were grown uniformly on the surface of Mo–S–Ni nanosheets (NSs). At a current density of 10 mA m−2, the catalyst under investigation has remarkable hydrogen evolution reaction (HER) activity under acidic conditions. The overpotential (η10) is measured to be 61.2 mV, while the Tafel slope is determined to be 40.2 mV dec−1. Meanwhile, in an alkaline medium, η10 is 80.5 mV and the Tafel slope is 52.3 mV dec−1. It also shows great mass activities of 1.32 A mg−1 and 1.86 A mg−1, which are higher than those of commercial Pt/C HER catalysts. Impressively, the excellent HER activity and durability of Pt@Mo–S–Ni-CNTs are mainly attributed to the close binding effects among Pt, MoS2, and NiS. Theoretical simulations show that the MoS2/NiS interfaces facilitate H2O dissociation and that Platinum (Pt) enhances the absorption of hydrogen atoms (H) and increases the charge transfer kinetics of the Mo–S–Ni, thus significantly improving the HER activity. This work highlights the importance of engineering interface nanosheets based on transition-metal dichalcogenides for enhanced HER performance.

Bottom-Up Construction of Metal-Organic Framework Loricae on Metal Nanoclusters with Consecutive Single Nonmetal Atom Tuning for Tailored Catalysis.

The introduction of single or multiple heterometal atoms into metal nanoparticles is a well-known strategy for altering their structures (compositions) and properties. However, surface single nonmetal atom doping is challenging and rarely reported. For the first time, we have developed synthetic methods, realizing "surgery"-like, successive surface single nonmetal atom doping, replacement, and addition for ultrasmall metal nanoparticles (metal nanoclusters, NCs), and successfully synthesized and characterized three novel bcc metal NCs Au38I(S-Adm)19, Au38S(S-Adm)20, and Au38IS(S-Adm)19 (S-Adm: 1-adamantanethiolate). The influences of single nonmetal atom replacement and addition on the NC structure and optical properties (including absorption and photoluminescence) were carefully investigated, providing insights into the structure (composition)-property correlation. Furthermore, a bottom-up method was employed to construct a metal-organic framework (MOF) on the NC surface, which did not essentially alter the metal NC structure but led to the partial release of surface ligands and stimulated metal NC activity for catalyzing p-nitrophenol reduction. Furthermore, surface MOF construction enhanced NC stability and water solubility, providing another dimension for tunning NC catalytic activity by modifying MOF functional groups.

Small-size and well-dispersed Fe nanoparticles embedded in carbon rods for efficient oxygen reduction reaction.

The preparation of ultra-small and well-dispersed metal nanoparticles (NPs) is of great importance for promoting oxygen reduction. Here, a metal (Fe and Zn) NP (7 nm) based catalyst derived from a Zn-based metal-organic framework was obtained by a vapor adsorption strategy, demonstrating a high half-wave potential (0.868 V) and power density (196 mW cm-2).

Anti-galvanic reaction induced interfacial engineering to reconstruct ternary colloid satellite platform for exceptionally high-performance redox-responsive sensor

The anti-galvanic reaction (AGR), which is a classic galvanic reaction (GR) with an opposite effect, is a unique phenomenon associated with the quantum size effect. This reaction involves the interaction between metal ions and nanoclusters, offering opportunities to create well-defined nanomaterials and diverse reductive behavior. In hence, in our work, we utilize the AGR to generate gold (Au), silver (Ag), and copper (Cu) satellite nanoclusters which have superior electromagnetic properties for Surface-enhanced Raman spectroscopy (SERS) sensor. As the AGR process, weak oxidant Cu2+ is selected to etched matrix Au@Ag NPs, reduced to Cu(0) or Cu(1) and generated the ultrasmall metal nanoparticles (Ag). To facilitate the AGR, we introduce the nucleophilic thiol 4-mercaptopyridine (4-Mpy) to bridge the metal ions or ultrasmall metal nanoparticles to reconstruct the satellite nanoclusters. These experimental displays that the AGR based biosensors has highly sensitivity for reductive molecule glucose. The liner ranges from 1 mmol/L to 1 nmol/L and alongs with a correlation coefficient and detection limit (LOD) of 0.999 and 0.14 nmol/L. Moreover, the AGR based biosensors exhibits remarkable stability and high repeatability with RSD 1.3 %. The food samples are tested to further investigate the accuracy and reliability of the method, which provides a novel and effective SERS method for the reduction molecules detection.

Highly Stable and Selective Catalysts for m-Cresol Hydrogenolysis to Aromatics

Deoxygenation is an essential link for upgrading bio-based low-value phenolics to aromatics, which is achieved through the catalytic hydrogenation way. Herein, we designed and synthesized kinds of Ni-confined catalysts via tailoring the preparation procedures. The highest hydroxyl hydrogenolysis performance (r[garomatics·gNi–1·h–1] = 103.5 at 290 °C) in vapor m-cresol conversion so far was obtained over Ni@Silicalite-1 prepared via the in situ encapsulation method due to the average 2.5 nm Ni nanoparticles uniformly encapsulated within silicalite-1 crystals for improving the shape selectivity with the vertical adsorption mode of phenolics. The appropriate porosities are proven to play a crucial role in shape-selective catalysis for hydroxyl hydrogenolysis of m-cresol. In addition, Ni@Silicalite-1 showed outstanding stability in 200 h long run with 95.5% conversion and 74.2% aromatics yield without obvious deactivation. This work provided a novel insight into tuning hydroxyl hydrogenolysis of phenolics by designing metal@zeolite catalysts with different microenvironments and ultrasmall metal nanoparticles.

Locking Effect in Metal@MOF with Superior Stability for Highly Chemoselective Catalysis

Ultrasmall metal nanoparticles (NPs) show high catalytic activity in heterogeneous catalysis but are prone to reunion and loss during the catalytic process, resulting in low chemoselectivity and poor efficiency. Herein, a locking effect strategy is proposed to synthesize high-loading and ultrafine metal NPs in metal-organic frameworks (MOFs) for efficient chemoselective catalysis with high stability. Briefly, the MOF ZIF-90 with aldehyde groups cooperating with diamine chains via aldimine condensation was interlocked, which was employed to confine in situ formation of Au NPs, denoted as Au@L-ZIF-90. The optimized Au@La-ZIF-90 has highly dispersed Au NPs (2.60 ± 0.81 nm) with a loading amount around 22 wt % and shows a great performance toward 3-aminophenylacetylene (3-APA) from the selective hydrogenation of 3-nitrophenylacetylene (3-NPA) with a high yield (99%) and excellent durability (over 20 cycles), far superior to contrast catalysts without chains locking and other reported catalysts. In addition, experimental characterization and systematic density functional theory calculations further demonstrate that the locked MOF modulates the charge of Au nanoparticles, making them highly specific for nitro group hydrogenation to obtain 3-APA with high selectivity (99%). Furthermore, this locking effect strategy is also applicable to other metal nanoparticles confined in a variety of MOFs, and all of these catalysts locked with chains show great selectivity (≥90%) of 3-APA. The proposed strategy in this work provides a novel and universal method for precise control of the inherent activity of accessible metal nanoparticles with a programmable MOF microenvironment toward highly specific catalysis.

Simple Synthesis of Monodisperse Ultrasmall Au Icosahedral Nanoparticles

Ultrasmall metal nanoparticles (NPs) with a mean diameter below 2 nm are being intensively studied due to their unique structural and chemical properties. At such small sizes, metal particles can appear as various polyhedra with different atomic structures depending on whether electronic effects, surface energy, or the nucleation mechanism govern their crystallization. Therefore, the synthesis of monodisperse nanoparticles of a very small size and well-defined structure requires a good understanding of the different steps of the crystallization process, which can be achieved by conducting and coupling in situ studies at different length and time scales. In this article, we describe the synthesis of ultrasmall gold NPs by reduction of HAuCl4 in solution of oleylamine (OY) in hexane using trialkylsilanes as reducing agents. Thanks to time-resolved in situ small-angle X-ray scattering and X-ray absorption spectroscopy kinetic studies, a competition between nucleation of Au NPs from a solution containing Au(III) clusters and crystallization of a lamellar phase of composition OY-Au(I)-Cl was revealed. In situ X-ray diffraction and pair distribution function (PDF) analysis showed that the first chemical pathway leads to icosahedral NPs while the reduction of OY-Au(I)-Cl leads to fcc NPs. Increasing the reaction rate, achieved by adjusting the silane concentration, changing the nature of the silane (triethylsilane instead of triisopropylsilane), and/or increasing the temperature of reaction, avoided the formation of the Au(I) lamellar phase as the intermediate, leading to monodisperse Au NPs with an icosahedral structure. This fairly simple liquid-phase synthesis method yields highly concentrated suspensions of icosahedral gold NPs, paving the way for their future use in practical applications such as catalysis.

Pd nanoparticle-decorated covalent organic frameworks for enhanced photocatalytic tetracycline hydrochloride degradation and hydrogen evolution.

In this study, we synthesized novel bipyridine-based, sp2-carbon-linked COFs with the incorporation of ultra-small metal nanoparticles for enhanced photocatalytic tetracycline hydrochloride degradation and hydrogen evolution. The obtained photocatalyst exhibits strong visible light absorption and modulated electronic structure, owing to charge transfer between the metal and COFs, resulting in tuned proton absorption/desorption energy. As a result, the Pd-COFs exhibit remarkable photocatalytic activities for both tetracycline hydrochloride removal and hydrogen evolution. Specifically, the rate constant of photocatalytic tetracycline hydrochloride removal reaches 0.03406 min-1 with excellent stability and the photocatalytic hydrogen evolution rate reaches 98.17 mmol g-1 h-1, outperforming the-state-of-the-art photocatalysts with noble Pt loading.

Efficient Enzyme‐Metal Hybrid Catalysts Constructed with Polymer

AbstractRational design and construction of enzyme‐metal hybrid catalysts (EMHCs) with high activity and stability is challenging. Introducing polymers into EMHCs is a promising way to enhance the catalytic performance by controlling the synthesis of ultrasmall metal nanoparticles on enzymes, and altering the surface properties of EMHCs, which has been wildly applied in organic synthesis and biomedicine. This review summarizes three representative strategies for the construction of EMHCs with polymers, including: using enzyme‐polymer conjugate as nanoreactors, using polymers as self‐assemble modules, and using polymers as surface modifiers. The effects of polymers on morphology and catalytic activity of EMHCs are discussed. Finally, the research directions of this field are proposed.

In Situ Confinement of Ultrasmall Metal Nanoparticles in Short Mesochannels for Durable Electrocatalytic Nitrate Reduction with High Efficiency and Selectivity.

Electrocatalytic reduction is a sustainable approach for NO3 - removal and high-value N-containing compounds manufacturing, which, however, is strongly obstructed by sluggish kinetics, low selectivity, and poor stability. Herein, the in situ confinement of ultrasmall CuPd alloy nanoparticles in mesochannels of conductive core-shell structured carbon nanotubes@mesoporous carbon substrates (CNTs@mesoC@CuPd) via a simple molecule-mediated interfacial assembly method is reported. As a catalyst for electrocatalytic NO3 - reduction, the CNTs@mesoC@CuPd shows a splendid conversion efficiency (100%), N2 selectivity (98%), cycling stability (>30days), and removal capacity as high as 30000mgNg-1 CuPd, which are much superior to most of the prior reports. Notably, experimental (in situ testing and isotopic labeling) and theoretical results unveil that bimetallic and monometallic catalysts for electrocatalytic NO3 - reduction exhibit exclusive selectivity for N2 and NH3 , respectively. This in situ confinement strategy is universal for the synthesis of stable and highly accessible metallic catalysts, which opens an appealing way to synthesize advanced catalysts with high activity, selectivity, and stability.

In-situ synthesis of ultra-small Ni nanoparticles anchored on palygorskite for efficient reduction of 4-nitrophenol

4-nitrophenol (4-NP) is an environmental pollutant with high toxicity and strong stability, which is difficult to degrade naturally. Reduction of 4-NP to 4-aminophenol (4-AP), an important chemical intermediate, is an economical and green method. The reduction process demands high-efficient catalysts, and ultra-small metal nanoparticles (NPs) are the great potential ones. Herein, ultra-small and monodisperse Ni nanoparticles (NiNPs) (5.1 nm) were successfully anchored on palygorskite (Pal), using nickel silicate (NiSi) as a welding-like joint, and the ultimate catalysts were NiNPs/NiSi/Pal nanocomposites. The NiNPs were in-situ reduced from the NiSi precursor, which was previously and in-situ grown on Pal. The size of NiNPs was adjustable by the NiSi precursor, while the size of the NiSi precursor was controlled by the etching degree cations of the crystal structure of Pal. The etching degree affected the amounts of octahedral released from Pal, and thus affected the amounts of freshly exposed SiO- bonds, which could capture Ni2+ ions, form SiONi bonds and promote the generation of NiSi. The as-prepared NiNPs/NiSi/Pal nanocomposites exhibited excellent catalytic activity for the reduction of 4-NP (52.67 × 10-3 s−1), and satisfactory recyclability. The excellent catalytic performance is mainly attributed to the full exposure of ultra-small NiNPs, which provides enough active sites and enables fast electron transfer between the catalysts and substrates. It is expected that the work could develop a new avenue for designation of ultra-small and monodisperse non-precious metal NPs, and contribute to the treatment of waste water containing 4-NP.

Botryoidal nanolignin channel stabilized ultrasmall PdNP incorporating with filter membrane for enhanced removal of Cr(VI) via synergetic filtration and catalysis

Catalytic membrane technology, as a combination of membrane separation and catalysis, is a high-efficiency and feasible route for wastewater remediation. The controllable synthesis of ultrasmall metal nanoparticles on the membrane to maximize the size effect is a challenging task yet. Herein, the filter paper-based botryoidal nanolignin channel stabilized ultrasmall PdNP membrane (Pd@LNP/FP) was prepared by chemical crosslinking of epichlorohydrin (EPI), the nanolignin (LNP) serves as both reducing and capping agent for the in-situ synthesis of ultrasmall PdNP with enhanced active sites. The mean size of PdNP was effectively tuned from 1.76 to 2.09 nm by varying the LNP loading amount of composite membranes. The botryoidal LNP supported on FP also provides the nanoscale channel to keep reactants on active sites of ultrasmall PdNP to improve the catalytic performance of Pd@LNPE/FP. The complete removal of hazardous Cr(VI) required only 2.5 min using Pd@LNPE/FP membrane, the pseudo-first-order rate constant (k) is 1.2725 min−1, much higher than that of the Pd@LNPp/FP membrane prepared by physical composite (0.2885 min−1). Moreover, the rapid filtration-catalysis removal of Cr(VI) can be achieved by twice filtration, demonstrating the high efficiency and feasibility of Pd@LNPE/FP via synergetic filtration enrichment and catalysis reduction.

DNA-Assisted Creation of a Library of Ultrasmall Multimetal/Metal Oxide Nanoparticles Confined in Silica.

Supported ultrasmall metal/metal oxide nanoparticles (UMNPs) with sizes in the range of 1-5nm exhibit unique properties in sensing, catalysis, biomedicine, etc. However, the metal-support and metal-metal precursor interactions were not as well controlled to stabilize the metal nanoparticles on/in the supports. Herein, DNA is chosen as a template and a ligand for the silica-supported UMNPs, taking full use of its binding ability to metal ions via either electrostatic or coordination interactions. UMNPs thus are highly dispersed in silica via self-assembly of DNA and DNA-metal ion interactions with the assistance of a co-structural directing agent (CSDA). A large number of metal ions are easily retained in the mesostructured DNA-silica materials, and their growth is controlled by the channels after calcination. Based on this directing concept, a material library, consisting of 50 mono- and 54 bicomponent UMNPs confined within silica and with narrow size distribution, is created. Theoretical calculation proves the indispensability of DNA with combination of several organics in the synthesis of ultrasmall metal nanoparticles. The Pt-silica and Pt/Ni-silica chosen from the library exhibit good catalytic performance for toluene combustion. This generalizable and straightforward synthesis strategy is expected to widen the corresponding applications of supported UMNPs.

Robust continuous synthesis and in situ deposition of catalytically active nanoparticles on colloidal support materials in a triphasic flow millireactor

• A triphasic flow millireactor for nanoparticle synthesis and deposition is designed. • Tunability of nanoparticle loading on the support is demonstrated. • A versatile method shown for various support materials – TiO 2 , Al 2 O 3 and CeO 2 . • Mono-/bi-/tri- metallics nanoparticles are deposited on colloidal support material. Ultra-small noble metal nanoparticles, such as palladium, platinum and rhodium, are invaluable catalysts for the synthesis of a plethora of materials, ranging from pharmaceutical drugs to polymers and fertilizers due to their high catalytic activities and large surface area-to-volume ratios. In practice, these particles are typically deposited on larger-sized support materials to stabilize them against agglomeration, whilst maintaining catalytic activity. We choose colloidal deposition as the process to synthesize supported nanoparticles, as it enables the deposition of nanoparticles with complex compositions and shapes on the support material, since the physical properties of the colloid nanoparticles are not affected by the deposition process. In this paper, we demonstrate a robust triphasic flow millireactor for catalytic nanoparticle synthesis and their facile in situ deposition onto colloidal support materials with tunable metal loading from 5% to 23% and a high degree of control over the spatial distribution on the support material. We highlight the consistency and quality of the supported nanoparticles produced by the flow synthesis compared to their batch-synthesized counterparts. We also demonstrate the versatility of our method for different nanoparticles types, including bi-/tri-metallics (Pd 5 Pt 5 , Rh 5 Pt 5 , Ru 5 Pt 5 and Rh 3 Pd 4 Pt 5 ) and three different support materials - titania, alumina and ceria.

Synthesis of ultrasmall metal nanoparticles and continuous shells at the liquid/liquid interface in Ouzo emulsions.

Herein, we report a novel method to synthesize metal nanoparticle-shells (NP-shells) and continuous shells at the liquid/liquid interface, via an interfacial reaction in an Ouzo emulsion. Ouzo emulsions spontaneously form submicronic droplets with a narrow size distribution, without any energy-intensive process. The Ouzo system in this work comprises water, tetrahydrofuran (THF) and butylated hydroxytoluene (BHT), and forms BHT-rich droplets (∼100 nm). The addition of a reducing agent (NaBH4) in the aqueous phase, and of a metal precursor (AuPPh3Cl and/or Pd(PPh3)2Cl2) in the BHT-rich droplets, results in the formation of Au nanoparticles (AuNPs), continuous Pd shells, or bimetallic shells, at the interface of the droplets. Control over the NP-shell size was achieved by the addition of a water-soluble polymer during the synthesis, which in turn leads to smaller NP-shells.

Ultrasmall Luminescent Metal Nanoparticles: Surface Engineering Strategies for Biological Targeting and Imaging.

In the past decade, ultrasmall luminescent metal nanoparticles (ULMNPs, d < 3 nm) have achieved rapid progress in addressing many challenges in the healthcare field because of their excellent physicochemical properties and biological behaviors. With the sharp shrinking size of large plasmonic metal nanoparticles (PMNPs), the contributions from the surface characteristics increase significantly, which brings both opportunities and challenges in the application‐driven surface engineering of ULMNPs toward advanced biological applications. Here, the systematic advancements in the biological applications of ULMNPs from bioimaging to theranostics are summarized with emphasis on the versatile surface engineering strategies in the regulation of biological targeting and imaging performance. The efforts in the surface functionalization strategies of ULMNPs for enhanced disease targeting abilities are first discussed. Thereafter, self‐assembly strategies of ULMNPs for fabricating multifunctional nanostructures for multimodal imaging and nanomedicine are discussed. Further, surface engineering strategies of ratiometric ULMNPs to enhance the imaging stability to address the imaging challenges in complicated bioenvironments are summarized. Finally, the phototoxicity of ULMNPs and future perspectives are also reviewed, which are expected to provide a fundamental understanding of the physicochemical properties and biological behaviors of ULMNPs to accelerate their future clinical applications in healthcare.

Site-Specified Two-Dimensional Heterojunction of Pt Nanoparticles/Metal-Organic Frameworks for Enhanced Hydrogen Evolution.

Heterojunction nanostructures usually exhibit enhanced properties in compariosn with their building blocks and are promising catalyst candidates due to their combined surface and unique interface. Here, for the first time we realized the oriented growth of ultrasmall metal nanoparticles (NPs) on metal-organic framework nanosheets (MOF NSs) by precisely regulating the reduction kinetics of metal ions with solvents. In particular, a rapid reduction of metal ions leads to the random distribution of metal NPs on the surface of MOF NSs, while a slow reduction of metal ions results in the oriented growth of NPs on the edge of MOF NSs. Impressively, the strong synergy between Pt NPs and MOF NSs significantly enhances the hydrogen evolution reaction (HER) performance, and the optimal catalyst displays HER activities superior to those of a composite with a random growth of Pt NPs and commercial Pt/C under both acidic and alkaline conditions. Moreover, the versatility of such oriented growth has been extended to other metal NPs, such as Pd, Ag, and Au. We believe this work will promote research interest in material design for many potential applications.

Reversible isomerization of metal nanoclusters induced by intermolecular interaction

Reversible isomerization of metal nanoclusters induced by intermolecular interaction

Compression‐Driven Internanocluster Reaction for Synthesis of Unconventional Gold Nanoclusters

AbstractCan the active kernels in ultrasmall metal nanoparticles (nanoclusters, NCs) react with one another, or can the internanocluster reaction occur when they are in close enough proximity? To resolve this fundamental issue, we investigated the solid‐state internanocluster reaction of the most studied gold NC Au25(SR)18 (SR: thiolate). A novel NC was produced by increasing the pressure to 5 GPa, whose composition was determined to be Au32(SC2H4Ph)24 by mass spectrometry and thermogravimetric analysis. As revealed by single‐crystal X‐ray crystallography, the structure, a bicuboid Au14 kernel and three pairs of interlocked trimetric staples, has not been reported and endows the NC with obvious photoluminescence. DFT calculations indicate that the staples contribute substantially to the absorption properties. Further experiments reveal the pressure (internanocluster distance) can tune the internanocluster reaction, and the resulting product is not necessarily the thermodynamic product.