Metal Nanocrystals Research Articles

Single-Crystalline Mesoporous Palladium and Palladium-Copper Nanocubes for Highly Efficient Electrochemical CO 2 Reduction

Single-Crystalline Mesoporous Palladium and Palladium-Copper Nanocubes for Highly Efficient Electrochemical CO ₂ Reduction

Nanoparticles, Nanocrystals, and Quantum Dots: What are the Implications of Size in Colloidal Nanoscale Materials?

Semiconductor nanoparticles (NP) or nanocrystals (NC) have been investigated for many decades, with particular acceleration in interest upon the discovery of quantum confinement effects thereby yielding quantum dots (QD) from certain well-grown NC. The term NP is commonly used in the case of metal and wide gap semiconductor nanocrystals. The term NC is commonly used in semiconductor nanocrystals, whether covalent II-VI or ionic perovskites, that are colloidally grown. The term QD applies to select semiconductor nanocrystals for whom their size is on the order of the excitonic Bohr radius. In the case of colloidal particles on the nanometer length scale, these terms are often used carelessly and interchangeably. The words have specific meaning in relationship to specific physical effects which give rise to specific key processes that can be measured. Here, we provide a Perspective on the ways in which size confers function across different families of NP. In this way, we aim to find ways to identify their similarities and differences by providing the correct semantics for discussion of the salient processes.

Surface Chemistry of Metal Phosphide Nanocrystals

Semiconducting and metallic metal phosphide nanocrystals have gained increased attention in the materials science and engineering community due to their demonstrated and theoretical promise in both emissive and catalytic applications. Central to realizing the full potential of nanoscale metal phosphides is a thorough understanding of their surfaces and how surface chemistry impacts their function. In this review, we document what is known about the surface chemistry of metal phosphide nanocrystals, including both as synthesized and postsynthetically modified species, and draw a connection between surface chemistry and functional properties. This survey is intended to provide a comprehensive view of metal phosphide nanocrystal surface chemistry and how it differs across the families of phosphide materials. A clear distinction emerges between the semiconducting and metallic phosphides from both a synthetic and applied standpoint. We seek to expose key knowledge gaps and targets for further scientific and technological development.

Laser-Driven Growth of Semiconductor Nanowires from Colloidal Nanocrystals.

Semiconductor nanowire production through vapor- and solution-based processes has propelled nanowire systems toward a wide range of technological applications. Although vapor-based nanowire syntheses enable precise control over nanowire composition and phase, they typically employ batch processes with specialized pressure management systems, limiting throughput. Solution-based nanowire growth processes have improved scalability but can require even more extensive pressure and temperature management systems. Here, we demonstrate a solution-based nanowire growth process that utilizes the large Young-Laplace interfacial surface pressures and collective heating effects of colloidal metal nanocrystals under irradiation to drive nanowire growth photothermally. Laser irradiation of a solution containing metal nanocrystals and semiconductor precursors facilitates rapid heating, precursor decomposition, and nanowire growth on a benchtop in simple glassware under standard conditions, potentially enabling a range of solution-based experiments including in-line combinatorial identification of optimized reaction parameters, in situ measurements, and the production of nanowires with complex compositions.

Nickel(II) complexes with 2-Hfur and N-donors: The magnetic effects of the structural variations, thermal properties and antimycobacterial activity against Mycolicibacterium smegmatis

New complexes of nickel(II) with 2-furoic acid (2-Hfur) and different N-donor ligands of the composition [Ni(fur)2(phen)(H2O)2]·H2O (1) (phen = 1,10-phenantroline), [Ni(fur)2(2,2′-bpy)] (2, 2,2′-bpy = 2,2′-bipyridine), [Ni(fur)2(4,4′-bpy)(CH3OH)2]n (3, 4,4′-bpy = 4,4′-bipyridine), [Ni(fur)2(pz)4]·2MeCN (4) (pz = pyrazole) have been synthesized. The structure of the compounds was established by single crystal X-ray diffraction analysis. Complexes 1, 2, and 4 are mononuclear, complex 3 is a 1D coordination polymer. The DC magnetic susceptibility data measured for 2 and 3 are indicative of antiferromagnetic exchange interactions between the metal centers, which proved to be negligibly weak in 2 and more pronounced in 3. A quantum-chemical analysis of intermolecular (for 2) and intra- and interchain (for 3) magnetic exchange pathways confirms these findings, revealing the presence of magnetic chains formed by a network of very weak intermolecular antiferromagnetic exchange interactions in the crystal of 2 and a strengthening of antiferromagnetic exchange coupling in the polymeric chains of 3. Thermal behavior of 1 and 2 was studied by simultaneous thermal analysis (STA). According to PXRD data, the final thermolysis product of complex 2 is metal Ni nanocrystals (d = 14.7(3) nm). Analysis of the results of biological activity of 1–4in vitro against Mycolicibacterium smegmatis showed a low sensitivity of the mycobacterial wall to Ni2+ cations.

Prospects in Engineering Congested Molecular Diffusion at the Stabilizer Layer of Metal Nanocrystals for Ultrahigh Catalytic Activity

Electron transfer processes between a catalyst and a reactant molecule are inefficient beyond a couple of angstroms distance. However, the stabilizers of metal nanocrystals or ligands often create ...

Modelling of size-dependent thermodynamic properties of metallic nanocrystals based on modified Gibbs\u2013Thomson equation

In this paper, a new theoretical two-phase (solid–liquid) type model of melting temperature has developed based on the modified Gibbs–Thomson equation. Further, it is extended to derive other different size-dependent thermodynamic properties such as cohesive energy, Debye temperature, specific heat capacity, the thermal and electrical conductivity of metallic nanoparticles. Quantitative calculation of the effect of size on thermodynamic properties resulted in, varying linearly with the inverse of characteristic length of nanomaterials. The models are applied to Al, Pb, Ag, Sn, Mo, W, Co, Au and Cu nanoparticles of spherical shape. The melting temperature, Debye temperature, thermal and electrical conductivity are found to decrease with the decrease in particle size, whereas the cohesive energy and specific heat capacity are increased with the decrease in particle size. The present model is also compared with previous models and found consistent. The results obtained with this model validated with experimental and simulation results from several sources that show similar trends between the model and experimental results.Graphic abstract

Preparation and Catalytic Performance of Highly Stable Silica-Coated Gold Nanorods Supported on Alumina

Abstract Shape-controlled metal nanocrystals such as nanorods are attractive because of their potential novel catalytic properties. It is important to improve the stability of the shape-controlled nanocrystals to be applied as nanocatalysts. In this study, α-Al2O3-supported Au nanorods (AuNR/α-Al2O3) and silica-coated α-Al2O3-supported Au nanorods (SiO2/AuNR/α-Al2O3) were prepared as alcohol oxidation catalysts for the transformation of 1-phenylethyl alcohol to acetophenone. The formation rate of acetophenone over AuNR/α-Al2O3 is higher than that over α-Al2O3-supported spherical Au nanoparticles obtained by calcining AuNR/α-Al2O3. In addition, SiO2/AuNR/α-Al2O3 exhibits higher catalytic performance and thermal stability than those of AuNR/α-Al2O3 in alcohol oxidation.

Metal‐Semiconductor Heterostructures for Photoredox Catalysis: Where Are We Now and Where Do We Go?

AbstractThe ability of metal nanocrystals (NCs) to maneuver light, trap charge carriers, and enrich reactive sites for photoredox reactions has received considerable attention for constructing metal‐semiconductor heterostructures (MSHs) toward solar‐to‐chemical production. In this review, the comprehensive and fundamental understanding of the structure‐property‐catalysis interplays of MSHs is mainly described. The fundamentals, including basic concepts, and critical insights of MSH‐mediated photoredox catalysis, are first demonstrated. Particular focus is placed on the state‐of‐the‐art technological advances in monitoring the key photophysical/photochemical processes associated with MSH‐mediated photoredox catalysis, followed by highlighting the design parameters for high‐performance MSHs. Then, the applications of MSHs for solar energy conversion, especially for some emerging reaction types are discussed. This review is concluded by casting a perspective on the challenges as well as the opportunities for further promoting this burgeoning field.

Biaxial strained dual-phase palladium-copper bimetal boosts formic acid electrooxidation

Surface strain engineering is considered as an effective strategy to promote the electrocatalytic properties of noble metal nanocrystals. Herein, we construct a dual-phase palladium-copper (DP-PdCu) bimetallic electrocatalyst with remarkable biaxial strain via a one-pot wet-chemical approach for formic acid oxidation. The biaxial strain originates from the lattice mismatch between the disordered face-centered cubic (FCC) phase and ordered body-centered cubic (BCC) phase in each of DP-PdCu nanoparticles. The proportion of FCC and BCC phases and size of PdCu nanoparticles are dependent on the addition amount of capping agent, cetyltrimethylammonium bromide (CTAB). Density functional theory calculations reveal the downshift of d-band center of Pd atoms due to the interfacial strain, which weakens the adsorption strength of undesired intermediates. These merit the DP-PdCu catalyst with superior mass activity of 0.55 A·mgPd-1 and specific activity of 1.91 mA·cmPd-2 toward formic acid oxidation, outperforming the single FCC/BCC PdCu and commercial Pd/C catalysts. This will provide new insights into the structure design of high-performance electrocatalysts via strain engineering.

Ultrathin and Wavy PdB Alloy Nanowires with Controlled Surface Defects for Enhanced Ethanol Oxidation Electrocatalysis.

Engineering crystalline structures/defects and elemental compositions is synthetically critical to optimize surface features of noble metal nanocrystals and thus improve their catalytic performances in various reactions. In this manuscript, we report a facile one-step aqueous synthesis of one-dimensional (1D) noble metal-metalloid alloy nanowires (NWs) with an ultrathin and wavy morphology, controlled crystalline defects, and binary PdB compositions as a highly efficient catalyst toward the electrochemical ethanol oxidation reaction (EOR). We show that the utilization of hexadecylpyridinium chloride as functional surfactant is of great importance to confine in-the-columnar epitaxial nucleation of anisotropic ultrathin PdB NWs, while the attachment growth precisely controls their surface crystalline defects with a wavy morphology. Meanwhile, this strategy is synthetically universal and can be readily extended to engineer an ultrathin wavy morphology and crystalline defect of ternary PdMB (M = Cu and Pt) alloy NWs. Owing to multiple structural and compositional merits, resultant PdB alloy NWs synergistically expose more electrocatalytically active sites and also kinetically accelerate the removal of CO-related poisons, remarkably improving electrocatalytic EOR activity and stability compared to their counterpart catalysts. Besides, wavy PdB alloy NWs are also electrochemically more active for electrocatalytic oxidation of other alcohols (methanol, glycerol, and glucose). The findings reported here thus shed a bright light on rational design of the high-performance metal alloy catalysts for their potential applications in fine chemical synthesis, fuel cells, and beyond.

Electrophoretic Plasmonic Ink for Dynamic Color Display

AbstractPlasmonic metal nanostructures generate vivid colors with high spatial resolution. Active control of plasmonic pixels by electrical means, which is compatible with integrated circuit technologies, is a promising technique for dynamic full color reflective display. However, the development of electrical plasmonic display is still limited by the difficulties in cost‐effective construction of active plasmonic pixels over large areas. This study demonstrates the achievement of electrical plasmonic display in full color by electrophoretic movement control of plasmonic noble metal nanocrystals in an organic electrolyte solvent. The persistent issues of nanoparticle aggregation and irreversible deposition in electrophoresis are addressed through appropriate surface modifications of the plasmonic nanocrystals, enabling them as advantageous nanoscale colorful pigments with long‐term durability. A weak electric field therefore allows color display with high contrast, high saturation, and electrical reconfigurability. The ink containing plasmonic pigments is further assembled into microfluidic chips to display different characters. The strategy will pave the way towards the development of plasmonic electronic paper in full color.

X-ray sensitive high-Z metal nanocrystals for cancer imaging and therapy

Radiotherapy (RT) based on X-ray irradiation is a widely applied cancer treatment strategy in the clinic. However, treating cancer based on RT alone usually results in insufficient radiation energy deposition, which inevitably has serious side effects on healthy parts of the body. Interestingly, high atomic number (high-Z) metal nanocrystals as X-ray sensitizers can reduce the radiation dose effectively due to their high X-ray absorption, which has attracted increased attention in recent years. High-Z metal nanocrystals produce Auger and photoelectrons electrons under X-ray irradiation, which could generate large amounts of reactive oxygen species, and induce cellular damages. The sensitization effect of high-Z metal nanocrystals is closely related with their composition, morphologies, and size, which would strongly impact their performances in the application of cancer imaging and therapy. In this review, we summarize diverse types of X-ray sensitizers such as bismuth, hafnium, gold, and gadolinium for cancer RT and imaging applications. In addition, current challenges and the outlook of RT based on high-Z metal nanocrystals are also discussed.

Synthesis of silver nanocrystal with an excellent oxidase-like activity and its application in colorimetric detection of D-penicillamine

High-index facets of metal nanocrystal have often a higher catalytic activity compared with the low-index facets. However, the shape-controlled synthesis of silver nanocrystal still faces great challenges. In the study, we reported synthesis of silver nanocrystals using histidine-functionalized graphene quantum dots (His-GQDs) as a chelating agent and shape inducer. Silver ions were coordinated with His-GQDs to form stable complex and then heated at 180 °C for 3 h. The resulting Ag/His-GQD nanohybrid offers polygonal nanostructure. The architecture improves the exposure of high-index facets, leading to an improved oxidase-like activity. Ag/His-GQD was used as the mimetic enzyme for colorimetric detection of D-penicillamine. In the detection Ag/His-GQD catalyzes the oxidization of 3,3′,5,5′-tetramethylbenzidine into blue product. D-penicillamine can inhibit the catalytic activity of Ag/His-GQD and leads to a reduced oxidization rate, because sulfhydryl in D-penicillamine was combined with silver in the Ag/His-GQD to form Ag-S bond. The absorbance at 652 nm linearly decreases with increasing D-penicillamine concentration in the range from 0.1 to 1.25 μM with detection limit of 0.034 μM (S/N = 3). The proposed method exhibits a better sensitivity, selectivity and stability and was successfully applied in colorimetric detection of D-penicillamine. The study also provides a promising approach for synthesis of metal nanocrystals with excellent catalytic activity.

Facile synthesis of heterophase sponge-like Pd toward enhanced formic acid oxidation

The controllable preparation of noble metallic nanocrystals with a 3D architecture is of great interest for electrocatalysis applications due to their enhanced atomic utilization, facilitated mass transport, and other attractive properties. In this work, a facile, one-pot, and surfactant-free method of synthesizing heterophase sponge-like Pd (S-Pd) is developed. The prepared S-Pd has a four-fold higher peak current density and better durability than a commercial Pd/C catalyst for formic acid oxidation. It therefore has great potential as an anode catalyst for direct formic acid fuel cells.

Recent advances in nonmetallic atom-doped metal nanocrystals: Synthesis and catalytic applications

Metal nanocrystals have been recognized as the main catalytic materials in many fields, but insufficient activity and stability, as well as high prices, have limited their large-scale potential applications. As one of the extremely promising alternatives toward metal in boosting their catalytic performance, nonmetallic atoms-doped metal nanocrystals have recently received extensive attention because of their high efficiency, chemical and structural durability, abundant reserve, and low cost. In this review, we highlight the most recent progress in this field and provide insights into their catalytic applications. The metal-nonmetal nanocrystals prepared by doping metal nanocrystals with nonmetallic atoms are introduced and classified based on the types of nonmetallic atoms, including metal hydrides, borides, carbides, nitrides, oxides, phosphides, and chalcogenides. Besides, their applications in catalysis, especially in electrocatalysis and organic catalysis, have been summarized and discussed. Finally, the conclusions and perspectives are given for the catalysis-driven rational design of metal-nonmetal nanocrystals in this minireview.

Visible light photodegradation of dyes and paracetamol by direct sensitization mechanism onto metallic MoO2 nanocrystals

MoO2 nanocrystals were prepared by solvothermal treatment of a Mo chloromethoxide at 250 °C in oleic acid. The monoclinic MoO2 phase, with a mean crystallite size of 29 nm, formed through reduction of molybdenum bronzes. The as-prepared MoO2 nanocrystals were free from organics, allowing their use in photodegradation tests of organic pollutants (methylene blue, rhodamine B, paracetamol), without any preliminary purification treatment of the nanocrystals. It was found that MoO2 was an efficient adsorbent of methylene blue (43 mg g−1 for 1.5 × 10−4 M concentration) in the dark and an efficient photodegradation catalyst under visible light (all methylene blue removed from the solution after 240 min). From the analysis of the combined photodegradation tests of rhodamine B and paracetamol, it was clarified that direct sensitization was responsible for photodegradation. This finding was related to the work function value of metallic MoO2, placed at more negative values if compared with other metallic materials.

Liquid-Phase Synthesis, Sintering, and Transport Properties of Nanoparticle-Based Boron-Rich Composites

Nanostructuring boron-rich materials should significantly impact their thermal and electrical transport properties. Nonetheless, nanostructured monoliths of such materials could not be achieved in the 10 nm range so far, because of the large temperatures required to synthesize and produce boron-rich compounds. Such a nanostructuration may have important consequences for achieving a trade-off between enhanced electrical and low thermal conductivity in boron-rich materials, which are among the few materials enabling thermoelectric power generation above 1000 K thanks to their thermal stability, high positive Seebeck coefficients, and low thermal conductivity. In this study, we use a one-pot synthesis in inorganic molten salts to yield a nanocomposite consisting of metallic HfB2 nanocrystals dispersed in an insulating amorphous boron-rich matrix with a controlled volume fraction of nanocrystals from 16 to 56 vol %. We show that this controlled liquid-phase synthesis can be coupled to spark plasma sintering for densification preserving the nanostructure. The relationships between the reagent ratio in the liquid-phase synthesis, sintering conditions, and transport properties of the densified nanocomposites are then highlighted. We then design materials exhibiting metallic electrical conductivity related to the HfB2 nanocrystals, together with enhanced thermal dissipation attributed to the nanostructured amorphous boron matrix. Combined with the versatility offered by in-solution routes toward boride-based nanocomposites, this work opens a new avenue for tuning transport properties in boron-rich nanomaterials.

A General Approach for Monolayer Adsorption of High Weight Loadings of Uniform Nanocrystals on Oxide Supports

AbstractMonodispersed metal and semiconductor nanocrystals have attracted great attention in fundamental and applied research due to their tunable size, morphology, and well‐defined chemical composition. Utilizing these nanocrystals in a controllable way is highly desirable especially when using them as building blocks for the preparation of nanostructured materials. Their deposition onto oxide materials provide them with wide applicability in many areas, including catalysis. However, so far deposition methods are limited and do not provide control to achieve high particle loadings. This study demonstrates a general approach for the deposition of hydrophobic ligand‐stabilized nanocrystals on hydrophilic oxide supports without ligand‐exchange. Surface functionalization of the supports with primary amine groups either using an organosilane ((3‐aminopropyl)trimethoxysilane) or bonding with aminoalcohols (3‐amino‐1,2‐propanediol) were found to significantly improve the interaction between nanocrystals and supports achieving high loadings (>10 wt. %). The bonding method with aminoalcohols guarantees the opportunity to remove the binding molecules thus allowing clean metal/oxide materials to be obtained, which is of great importance in the preparation of supported nanocrystals for heterogeneous catalysis.

A General Approach for Monolayer Adsorption of High Weight Loadings of Uniform Nanocrystals on Oxide Supports.

Monodispersed metal and semiconductor nanocrystals have attracted great attention in fundamental and applied research due to their tunable size, morphology, and well-defined chemical composition. Utilizing these nanocrystals in a controllable way is highly desirable especially when using them as building blocks for the preparation of nanostructured materials. Their deposition onto oxide materials provide them with wide applicability in many areas, including catalysis. However, so far deposition methods are limited and do not provide control to achieve high particle loadings. This study demonstrates a general approach for the deposition of hydrophobic ligand-stabilized nanocrystals on hydrophilic oxide supports without ligand-exchange. Surface functionalization of the supports with primary amine groups either using an organosilane ((3-aminopropyl)trimethoxysilane) or bonding with aminoalcohols (3-amino-1,2-propanediol) were found to significantly improve the interaction between nanocrystals and supports achieving high loadings (>10 wt. %). The bonding method with aminoalcohols guarantees the opportunity to remove the binding molecules thus allowing clean metal/oxide materials to be obtained, which is of great importance in the preparation of supported nanocrystals for heterogeneous catalysis.