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We report a new design of polymer phenylacetylene (PA) ligands and the ligand exchange methodology for colloidal noble metal nanoparticles (NPs). PA-terminated poly(ethylene glycol) (PEG) can bind to metal NPs through acetylide (M-C≡C-R) that affords a high grafting density. The ligand–metal interaction can be switched between σ bonding and extended π backbonding by changing grafting conditions. The σ bonding of PEG–PA with NPs is strong and it can compete with other capping ligands including thiols, while the π backbonding is much weaker. The σ bonding is also demonstrated to improve the catalytic performance of Pd for ethanol oxidation and prevent surface absorption of the reaction intermediates. Those unique binding characteristics will enrich the toolbox in the control of colloidal surface chemistry and their applications using polymer ligands.

Uricase-catalyzed uric acid (UA) degradation has been applied for hyperuricemia therapy, but this medication is limited by H2O2accumulation, which can cause oxidative stress of cells, resulting in many other health issues. Herein, we report a robust cubic hollow nanocage (HNC) system based on polyvinylpyrrolidone-coated PdPt3and PdIr3to serve as highly efficient self-cascade uricase/peroxidase mimics to achieve the desired dual catalysis for both UA degradation and H2O2elimination. These HNCs have hollow cubic shape with average wall thickness of 1.5 nm, providing desired synergy to enhance catalyst’s activity and stability. Density functional theory calculations suggest the PdIr3HNC surface tend to promote OH*/O* desorption for better peroxidase-like catalysis, while the PdPt3HNC surface accelerates the UA oxidation by facilitating O2-to-H2O2conversion. The dual catalysis power demonstrated by these HNCs in cell studies suggests their great potential as a new type of nanozyme for treating hyperuricemia.

Core@shell nanoparticles (NPs) have been widely explored to enhance catalysis due to the synergistic effects introduced by their nanoscale interface and surface structures. However, creating a catalytically functional core@shell structure is often a synthetic challenge due to the need to control the shell thickness. Here, we report a one-step synthetic approach to core–shell CuPd@Pd NPs with an intermetallic B2-CuPd core and a thin (∼0.6 nm) Pd shell. This core@shell structure shows enhanced activity toward selective hydrogenation of Ar-NO2and allows one-pot tandem hydrogenation of Ar-NO2to Ar-NH2and its condensation with Ar-CHO to form Ar-N═CH-Ar. DFT calculations indicate that the B2-CuPd core promotes the Pd shell binding to Ar-NO2more strongly than to Ar-CHO, thereby selectively activating Ar-NO2. The chemoselective catalysis demonstrated by B2-CuPd@Pd can be extended to a broader scope of substrates, allowing green chemistry synthesis of a wide range of functional chemicals and materials.

Polymer N-heterocyclic carbenes (NHCs) are a class of robust surface ligands to provide superior colloidal stability for metal nanoparticles (NPs) under various harsh conditions. We report a general method to prepare polymeric NHCs and demonstrate that these polymer NHC–AgNPs are stable against oxidative etching and show high peroxidase activity. We prepared three imidazolium-terminated poly(methyl methacrylate) (PMMA), polystyrene (PS), and poly(2-(2-methoxyethoxy)ethyl methacrylate) (PMEO2MA) through atom-transfer radical polymerization with an imidazole-containing initiator. The imidazolium end group was further converted to NHC–Ag(I) in the presence of Ag2O at room temperature. Polymer NHC–Ag(I) can transmetalate to AgNPs through ligand exchange at the interface of oil/water within 2 min. All the three polymers can modify metal NPs, such as AgNPs, Ag nanowires, and AuNPs, providing excellent thermal, oxidative, and chemical stabilities for AgNPs. As an example, in the presence of hydrogen peroxide, AgNPs modified by polymer NHCs were resistant against oxidative etching with a rate of ∼700 times slower than those grafted with thiolates. AgNPs modified by polymer NHCs also showed higher peroxidase activity, 4 times more active than those capped by citrate and polyvinylpyrrolidone (PVP) and 2 times more active than those with polymer thiolate. Our studies demonstrate a great potential of using polymer NHCs to stabilize metallic NPs for various applications.

We report a new form of catalyst based on ferromagnetic hexagonal-close-packed (hcp) Co nanosheets (NSs) for selective CO2RR to ethanal, CH3CHO. In all reduction potentials tested from −0.2 to −1.0 V (vs RHE) in 0.5 M KHCO3solution, the reduction yields ethanal as a major product and ethanol/methanol as minor products. At −0.4 V, the Faradaic efficiency (FE) for ethanal reaches 60% with current densities of 5.1 mA cm–2and mass activity of 3.4 A g–1(total FE for ethanal/ethanol/methanol is 82%). Density functional theory (DFT) calculations suggest that this high CO2RR selectivity to ethanal on the hcp Co surface is attributed to the unique intralayer electron transfer, which not only promotes [OC–CO]* coupling but also suppresses the complete hydrogenation of the coupling intermediates to ethylene, leading to highly selective formation of CH3CHO.

While nanoscale mimics of peroxidase have been extensively developed over the past decade or so, their catalytic efficiency as a key parameter has not been substantially improved in recent years. Herein, we report a class of highly efficient peroxidase mimic–nickel–platinum nanoparticles (Ni–Pt NPs) that consist of nickel-rich cores and platinum-rich shells. The Ni–Pt NPs exhibit a record high catalytic efficiency with a catalytic constant (Kcat) as high as 4.5 × 107s–1, which is ∼46- and 104-fold greater than the Kcatvalues of conventional Pt nanoparticles and natural peroxidases, respectively. Density functional theory calculations reveal that the unique surface structure of Ni–Pt NPs weakens the adsorption of key intermediates during catalysis, which boosts the catalytic efficiency. The Ni–Pt NPs were applied to an immunoassay of a carcinoembryonic antigen that achieved an ultralow detection limit of 1.1 pg/mL, hundreds of times lower than that of the conventional enzyme-based assay.

Enabling catalysts to promote multistep chemical reactions in a tandem fashion is an exciting new direction for the green chemistry synthesis of materials. Nanoparticle (NP) catalysts are particularly well suited for tandem reactions due to the diverse surface-active sites they offer. Here, we report that AuPd alloy NPs, especially 3.7 nm Au42Pd58NPs, catalyze one-pot reactions of formic acid, diisopropoxy-dinitrobenzene, and terephthalaldehyde, yielding a very pure thermoplastic rigid-rod polymer, polybenzoxazole (PBO), with a molecular weight that is tunable from 5.8 to 19.1 kDa. The PBO films are more resistant to hydrolysis and possess thermal and mechanical properties that are superior to those of commercial PBO, Zylon. Cu NPs are also active in catalyzing tandem reactions to form PBO when formic acid is replaced with ammonia borane. Our work demonstrates a general approach to the green chemistry synthesis of rigid-rod polymers as lightweight structural materials for broad thermomechanical applications.

We report a chemical method to synthesize size-controllable SmCo5nanoparticles (NPs) and to stabilize the NPs against air oxidation by coating a layer of N-doped graphitic carbon (NGC). First 10 nm CoO and 5 nm Sm2O3NPs were synthesized and aggregated in reverse micelles of oleylamine to form SmCo-oxide NPs with a controlled size (110, 150, or 200 nm). The SmCo-O NPs were then coated with polydopamine and thermally annealed to form SmCo-O/NGC NPs, which were further embedded in CaO matrix and reduced with Ca at 850 °C to give SmCo5/NGC NPs of 80, 120, or 180 nm, respectively. The 10 nm NGC coating efficiently stabilized the SmCo5NPs against air oxidation at room temperature or at 100 °C. The magnetization value of the 180 nm SmCo5/NGC NPs was stabilized at 86.1 emu/g 5 days after air exposure at room temperature and dropped only 1.7% 48 h after air exposure at 100 °C. The stable SmCo5/NGC NPs were aligned magnetically in an epoxy resin, showing a square-like hysteresis behavior with their Hcreaching 51.1 kOe at 150 K and 21.9 kOe at 330 K and their Mrstabilized at around 84.8 emu/g. Our study demonstrates a new strategy for synthesizing and stabilizing SmCo5NPs for high-performance nanomagnet applications in a broad temperature range.

While various effects of physicochemical parameters (e.g., size, facet, composition, and internal structure) on the catalytic efficiency of nanozymes (i.e., nanoscale enzyme mimics) have been studied, the strain effect has never been reported and understood before. Herein, we demonstrate the strain effect in nanozymes by using Pd octahedra and icosahedra with peroxidase-like activities as a model system. Strained Pd icosahedra were found to display 2-fold higher peroxidase-like catalytic efficiency than unstrained Pd octahedra. Theoretical analysis suggests that tensile strain is more beneficial to OH radical (a key intermediate for the catalysis) generation than compressive strain. Pd icosahedra are more active than Pd octahedra because icosahedra amplify the surface strain field. As a proof-of-concept demonstration, the strained Pd icosahedra were applied to an immunoassay of biomarkers, outperforming both unstrained Pd octahedra and natural peroxidases. The findings in this research may serve as a strong foundation to guide the design of high-performance nanozymes.

Tuning the performance of nanoparticle (NP) catalysts by controlling the NP surface strain has evolved as an important strategy to optimize NP catalysis in many energy conversion reactions. Here, we present our new study on using an eigenforce model to predict and experiments to verify the strain-induced catalysis enhancement of the oxygen reduction reaction (ORR) in the presence of L10-CoMPt NPs (M = Mn, Fe, Ni, Cu, Ni). The eigenforce model allowed us to predict anisotropic (that is, two-dimensional) strain levels on distorted Pt(111) surfaces. Experimentally, by preparing a series of 5 nm L10-CoMPt NPs, we could push the ORR catalytic activity of these NPs toward the optimum region of the theoretical two-dimensional volcano plot predicted for L10-CoMPt. The best ORR catalyst in the alloy NP series we studied is L10-CoNiPt, which has a mass activity of 3.1 A/mgPtand a specific activity of 9.3 mA/cm2at room temperature with only 15.9% loss of mass activity after 30 000 cycles at 60 °C in 0.1 M HClO4.

Understanding the Cu-catalyzed electrochemical CO2reduction reaction (CO2RR) under ambient conditions is both fundamentally interesting and technologically important for selective CO2RR to hydrocarbons. Current Cu catalysts studied for the CO2RR can show high activity but tend to yield a mixture of different hydrocarbons, posing a serious challenge on using any of these catalysts for selective CO2RR. Here, we report a new perovskite-type copper(I) nitride (Cu3N) nanocube (NC) catalyst for selective CO2RR. The 25 nm Cu3N NCs show high CO2RR selectivity and stability to ethylene (C2H4) at −1.6 V (vs reversible hydrogen electrode (RHE)) with the Faradaic efficiency of 60%, mass activity of 34 A/g, and C2H4/CH4molar ratio of >2000. More detailed electrochemical characterization, X-ray photon spectroscopy, and density functional theory calculations suggest that the high CO2RR selectivity is likely a result of (100) Cu(I) stabilization by the Cu3N structure, which favors CO–CHO coupling on the (100) Cu3N surface, leading to selective formation of C2H4. Our study presents a good example of utilizing metal nitrides as highly efficient nanocatalysts for selective CO2RR to hydrocarbons that will be important for sustainable chemistry/energy applications.

Intermetallic nanoparticles (NPs) described in this Account are a class of metallic alloy NPs within which metal atoms are bonded via strong d-orbital interaction and ordered anisotropically in a specific crystallographic direction. Compared to the common metallic alloy NPs with solid solution structure, intermetallic NPs are generally more stable against chemical oxidation and etching. The strict stoichiometry requirement, well-defined atom binding environment and layered atomic arrangement also make intermetallic NPs an ideal model for understanding their physical and catalytic properties. This account summarizes the synthetic principles and strategies developed to obtain monodisperse intermetallic NPs, especially tetragonal L10-NPs. The thermodynamics and kinetics involved in the conversion between disordered and ordered structures are briefly discussed. The synthetic methods are grouped into two slightly different categories: solution-phase synthesis followed by solid state annealing and direct solution-phase synthesis. In the former method, high-surface-area supports are often needed to disperse NPs and to prevent them from aggregation, while in the latter method such supports are not required since the structure conversion temperature is lowered to a level that the conversion can proceed in the solution reaction condition. In any of these two synthetic approaches, various factors influencing intermetallic structure formation should be carefully controlled to ensure more complete structural transition within NPs. Using representative synthetic examples, we highlight the strategies explored to facilitate the formation of intermetallic structure, including the introduction of vacancies/defects within NP structures and the control of atom addition rate/seed-mediated diffusion to lower the energy barrier. These strategies illustrate how the concept of thermodynamics and kinetics can be used to design the synthesis of intermetallic NPs. Additionally, to correlate NP structure and catalysis, we introduce briefly the d-band theory to explain how the electronic, strain and ensemble effects can be used to tune NP catalysis. We focus specifically on Pt-, Pd-, and Au-based L10-NPs and demonstrate how these L10-NPs could be prepared to show much enhanced catalysis for electrochemical reactions, including oxygen reduction reaction (ORR), hydrogen evolution reaction (HER), formic acid oxidation reaction (FAOR), and thermo-oxidation reaction of CO. Due to the enhanced metal atom stability in the “sandwich”-type structure, the roles of the first-row transition metal atoms in catalysis are better understood to achieve catalysis optimization. This concept can be extended to other alloy NPs, demonstrating great potentials in using intermetallic structures to control NP reduction and oxidation catalysis for important chemical and energy applications.

Transition-metal nitrides (TMNs), especially iron-based TMNs, have high electrical conductivity, superior chemical stability and unique oxygen-reaction ability, and have emerged as a new form of noble metal-free electrocatalysts. In this paper, we demonstrate that the ORR-active/OER-inert single function catalyst Fe-N can be made as the OER/ORR-active bifunctional catalyst Co-Fe-N by controlled substitution of Fe with Co. To obtain atomic insights of the Co-enhanced OER catalysis, we develop a new exfoliation method to prepare atomically thin (1.1 nm) nanosheets (NSs) of CoxFe1-xN0.5(x = 0, 0.05, 0.1, 0.15 and 0.2). Our studies show that both electronic structure and local binding environment of Fe are modified by Co substitution and the Co-Fe-N NSs show a volcano−like OER catalysis with Co0.15Fe0.85N0.5NSs being the most efficient OER catalyst, showing the lowest overpotential of 266 mV at 10 mA cm−2, a Tafel slope of ∼30 mV dec−1, and excellent stability in the 1.0 M KOH OER condition. Density functional theory (DFT) calculations suggest that the Co-Fe sites in the Co0.15Fe0.85N0.5structure are optimized to promote OH* to O* conversion, O*-O* coupling and O2formation. The Co0.15Fe0.85N0.5NSs are a class of new noble-metal-free catalyst for OER.

Stabilizing transition metals (M) in MPt alloy under acidic conditions is challenging, yet crucial to boost Pt catalysis toward oxygen reduction reaction (ORR). We synthesized ∼9 nm hard-magnet core/shell L10-CoPt/Pt nanoparticles with 2–3 atomic layers of strained Pt shell for ORR. At 60°C in acid, the hard-magnet L10-CoPt better stabilizes Co (5% loss after 24 hr) than soft-magnet A1-CoPt (34% loss in 7 hr). L10-CoPt/Pt achieves mass activities (MA) of 0.56 A/mgPtinitially and 0.45 A/mgPtafter 30,000 voltage cycles in the membrane electrode assembly at 80°C, exceeding the DOE 2020 targets on Pt activity and durability (0.44 A/mgPtin MA and <40% loss in MA after 30,000 cycles). Density functional theory calculations suggest that the ligand effect of Co and the biaxial strain (−4.50%/−4.25%) of the Pt shell weaken the binding of oxygenated species, leading to enhanced ORR performance in fuel cells.

We report a new strategy of controlling catalytic activity and selectivity of Cu nanoparticles (NPs) for the ammonia borane initiated hydrogenation reaction. Cu NPs are active and selective for chemoselective reduction of nitrostyrene to vinylaniline under ambient conditions. Their activity, selectivity, and more importantly, stability are greatly enhanced by their anchoring on WO2.72nanorods, providing a room-temperature full conversion of nitrostyrene selectively to vinylaniline (>99% yield). Compared with all other catalysts developed thus far, our new Cu/WO2.72catalyst shows much enhanced hydrogenation selectivity and stability without the use of pressured hydrogen. The synthetic approach demonstrated here can be extended to prepare various M/WO2.72catalysts (M = Fe, Co, Ni), with M being stabilized for many chemical reactions.

This paper provides an overview of the synthetic techniques used to prepare colloidal nanocrystals (NCs) of controlled composition, size, shape, and internal structure and the methods for manipulation of these materials into ordered NC assemblies (superlattices). High-temperature solution-phase synthesis (100-300[degrees]C) is followed by size-selective separation techniques in the preparation of monodisperse NC samples tunable in size from ~1 to 15 nm in diameter with [is less than]5% standard deviation. Each NC consists of a crystalline inorganic core coordinated by an organic monolayer. These monodisperse NC samples enable systematic studies of structural, electronic, magnetic, and optical properties of materials as a function of size evolution from molecular species ([is less than]100 atoms) to bulk solids ([is greater than]100 000 atoms). We illustrate size-dependent properties for magnetic materials using Co and for semi-conducting materials using PbSe. These NC samples are sufficiently uniform in size to self-assemble into close-packed, ordered NC superlattices, also known as colloidal crystals.

NixWO2.72nanorods (NRs) are synthesized by a one-pot reaction of Ni(acac)2and WCl4. In the rod structure, Ni(II) intercalates in the defective perovskite-type WO2.72and is stabilized. The NixWO2.72NRs show the x-dependent electrocatalysis for the oxygen evolution reaction (OER) in 0.1 M KOH with Ni0.78WO2.72being the most efficient, even outperforming the commercial Ir-catalyst. The synthesis is not limited to NixWO2.72but can be extended to MxWO2.72(M = Co, Fe) as well, providing a new class of oxide-based catalysts for efficient OER and other energy conversion reactions.

Efficient C–C bond cleavage and oxidation of alcohols to CO2is the key to developing highly efficient alcohol fuel cells for renewable energy applications. In this work, we report the synthesis of core/shell Au/Pt nanowires (NWs) with stepped Pt clusters deposited along the ultrathin (2.3 nm) stepped Au NWs as an active catalyst to effectively oxidize alcohols to CO2. The catalytic oxidation reaction is dependent on the Au/Pt ratios, and the Au1.0/Pt0.2NWs have the largest percentage (∼75%) of stepped Au/Pt sites and show the highest activity for ethanol electro-oxidation, reaching an unprecedented 196.9 A/mgPt(32.5 A/mgPt+Au). This NW catalyst is also active in catalyzing the oxidation of other primary alcohols, such as methanol, n-propanol, and ethylene glycol. In situ X-ray absorption spectroscopy and infrared spectroscopy are used to characterize the catalyst structure and to identify key reaction intermediates, providing concrete evidence that the synergy between the low-coordinated Pt sites and the stepped Au NWs is essential to catalyze the alcohol oxidation reaction, which is further supported by DFT calculations that the C–C bond cleavage is indeed enhanced on the undercoordinated Pt–Au surface. Our study provides important evidence that a core/shell structure with stepped core/shell sites is essential to enhance electrochemical oxidation of alcohols and will also be central to understanding electro-oxidation reactions and to the future development of highly efficient direct alcohol fuel cells for renewable energy applications.

Functional nanoparticles (NPs) have been studied extensively in the past decades for their unique nanoscale properties and their promising applications in advanced nanosciences and nanotechnologies. One critical component of studying these NPs is to prepare monodisperse NPs so that their physical and chemical properties can be tuned and optimized. Solution phase reactions have provided the most reliable processes for fabricating such monodisperse NPs in which metal–ligand interactions play essential roles in the synthetic controls. These interactions are also key to stabilizing the preformed NPs for them to show the desired electronic, magnetic, photonic, and catalytic properties. In this Account, we summarize some representative organic bipolar ligands that have recently been explored to control NP formation and NP functions. These include aliphatic acids, alkylphosphonic acids, alkylamines, alkylphosphines, and alkylthiols. This ligand group covers metal–ligand interactions via covalent, coordination, and electrostatic bonds that are most commonly employed to control NP sizes, compositions, shapes, and properties. The metal–ligand bonding effects on NP nucleation rate and growth can now be more thoroughly investigated by in situspectroscopic and theoretical studies. In general, to obtain the desired NP size and monodispersity requires rational control of the metal/ligand ratios, concentrations, and reaction temperatures in the synthetic solutions. In addition, for multicomponent NPs, the binding strength of ligands to various metal surfaces needs to be considered in order to prepare these NPs with predesigned compositions. The selective ligand binding onto certain facets of NPs is also key to anisotropic growth of NPs, as demonstrated in the synthesis of one-dimensional nanorods and nanowires. The effects of metal–ligand interactions on NP functions are discussed in two aspects, electrochemical catalysis for CO2reduction and electronic transport across NP assemblies. We first highlight recent advances in using surface ligands to promote the electrochemical reduction of CO2. Several mechanisms are discussed, including the modification of the catalyst surface environment, electron transfer through the metal–organic interface, and stabilization of the CO2reduction intermediates, all of which facilitate selective CO2reduction. These strategies lead to better understanding of molecular level control of catalysis for further catalyst optimization. Metal–ligand interaction in magnetic NPs can also be used to control tunneling magnetoresistance properties across NPs in NP assemblies by tuning NP interparticle spacing and surface spin polarization. In all, metal–ligand interactions have yielded particularly promising directions for tuning CO2reduction selectivity and for optimizing nanoelectronics, and the concepts can certainly be extended to rationalize NP engineering at atomic/molecular precision for the fabrication of sensitive functional devices that will be critical for many nanotechnological applications.

Metal nanoparticles (MNPs) are essential catalyst components in electrochemical energy conversion and storage devices, including fuel cells, Li-air batteries and water-splitting systems. Syntheses of monodisperse MNPs with controlled sizes, shapes and structures is key to fully harvesting their catalytic capabilities. This review first outlines the fundamentals of the synthesis of monodisperse MNPs by organic solution phase reactions. It then summaries common strategies applied to tailor MNP size, shape and structure. The review further highlights recent advances of using MNPs as efficient catalysts to catalyze some representative reactions that related to energy conversions, including oxygen reduction reaction, hydrogen evolution reaction, CO2reduction reaction, methanol/formic acid oxidation reaction, and oxygen evolution reaction.

Monodisperse Cu nanoparticles (NPs) assembled on a pyridinic-N rich graphene (p-NG) support show a Cu NP mass- and size-dependent catalysis for the selective electrochemical reduction of CO2to ethylene (C2H4). For the 7nm Cu NPs assembled on the p-NG with the p-NG/Cu mass ratio of 1:1, the C2H4formation Faradaic efficiency and hydrocarbon selectivity reach 19% and 79% respectively at −0.9V (vs reversible hydrogen electrode). The p-NG itself can catalyze the CO2reduction to formate, but in the composite p-NG-Cu structure, the pyridinic-N functions as a CO2and proton absorber, facilitating hydrogenation and carbon–carbon coupling reactions on Cu for the formation of C2H4. The work demonstrates a new strategy to improve Cu NP catalytic activity and selectivity for the electrochemical reduction of CO2for sustainable chemistry and energy applications.

Addressed herein is a facile protocol for the synthesis and assembly of FePd alloy nanoparticles (NPs) on reduced graphene oxide (rGO) to catalyze transfer hydrogenation of nitroarenes to anilines under ambient conditions. 3.5 nm FePd NPs were synthesized by using a surfactant-assisted co-reduction method that allowed NP composition control. FePd NPs were then assembled on rGO viaa liquid-phase self-assembly method and studied as catalysts to promote hydrogen transfer from ammonia borane (AB) to numerous nitroarenes in aqueous methanol solutions at room temperature. Among three different rGO–FePd, the commercial C–Pd and rGO–Pd catalysts tested, rGO–Fe48Pd52showed the highest efficiency in converting nitroarenes to anilines, achieving >90% yields within 10–20 min of reactions. Our work demonstrates an efficient and selective approach to transfer hydrogenation of nitroarenes to anilines.

We report a strategy to coat Fe3O4nanoparticles (NPs) with tetrathiafulvalene-fused carboxylic ligands (TTF-COO−) and to control electron conduction and magnetoresistance (MR) within the NP assemblies. The TTF-COO-Fe3O4NPs were prepared by replacing oleylamine (OA) from OA-coated 5.7 nm Fe3O4NPs. In the TTF-COO-Fe3O4NPs, the ligand binding density was controlled by the ligand size, and spin polarization on the Fe3O4NPs was greatly improved. As a result, the interparticle spacing within the TTF-COO-Fe3O4NP assemblies are readily controlled by the geometric length of TTF-based ligand. The shorter the distance and the better the conjugation between the TTF’s HOMO and LUMO, the higher the conductivity and MR of the assembly. The TTF-coating further stabilized the Fe3O4NPs against deep oxidation and allowed I2-doping to increase electron conduction, making it possible to measure MR of the NP assembly at low temperature (<100 K). The TTF-COO-coating provides a viable way for producing stable magnetic Fe3O4NP assemblies with controlled electron transport and MR for spintronics applications.

We report the synthesis of core/shell face-centered tetragonal (fct)-FePd/Pd nanoparticles (NPs) viareductive annealing of core/shell Pd/Fe3O4NPs followed by temperature-controlled Fe etching in acetic acid. Among three different kinds of core/shell FePd/Pd NPs studied (FePd core at ∼8 nm and Pd shell at 0.27, 0.65, or 0.81 nm), the fct-FePd/Pd-0.65 NPs are the most efficient catalyst for the oxygen reduction reaction (ORR) in 0.1 M HClO4with Pt-like activity and durability. This enhanced ORR catalysis arises from the desired Pd lattice compression in the 0.65 nm Pd shell induced by the fct-FePd core. Our study offers a general approach to enhance Pd catalysis in acid for ORR.

The effect of elastic strain on catalytic activity of platinum (Pt) toward oxygen reduction reaction (ORR) is investigated through dealloyed Pt–Cu thin films; stress evolution in the dealloyed layer and the mass of the Cu removed are measured in real-time during electrochemical dealloying of (111)-textured thin-film PtCu (1:1, atomic ratio) electrodes. In situstress measurements are made using the cantilever-deflection method, and nanogravimetric measurements are made using an electrochemical quartz crystal nanobalance. Upon dealloying via successive voltammetric sweeps between −0.05 and 1.15 V vs standard hydrogen electrode, compressive stress develops in the dealloyed Pt layer at the surface of thin-film PtCu electrodes. The dealloyed films also exhibit enhanced catalytic activity toward ORR compared with polycrystalline Pt. In situnanogravimetric measurements reveal that the mass of dealloyed Cu is approximately 210 ± 46 ng/cm2, which corresponds to a dealloyed layer thickness of 1.2 ± 0.3 monolayers or 0.16 ± 0.04 nm. The average biaxial stress in the dealloyed layer is estimated to be 4.95 ± 1.3 GPa, which corresponds to an elastic strain of 1.47% ± 0.4%. In addition, density functional theory calculations have been carried out on biaxially strained Pt(111) surface to characterize the effect of strain on its ORR activity; the predicted shift in the limiting potentials due to elastic strain is found to be in good agreement with the experimental shift in the cyclic voltammograms for the dealloyed PtCu thin film electrodes.

Due to their size and tailorable physicochemical properties, nanomaterials are an emerging class of structures utilized in biomedical applications. There are now many prominent examples of nanomaterials being used to improve human health, in areas ranging from imaging and diagnostics to therapeutics and regenerative medicine. An overview of these examples reveals several common areas of synergy and future challenges. This Nano Focus discusses the current status and future potential of promising nanomaterials and their translation from the laboratory to the clinic, by highlighting a handful of successful examples.

Ordered assemblies of nanoparticles remain challenging to fabricate, yet could open the door to many potential applications of nanomaterials. Here, we demonstrate that locally ordered arrays of nanoparticles, using electrophoretic deposition, can be extended to produce long-range order among the constituents. Voronoi tessellations along with multiple statistical analyses show dramatic increases in order compared with previously reported assemblies formed through electric field-assisted assembly. Based on subsequent physical measurements of the nanoparticles and the deposition system, the underlying mechanisms that generate increased order are inferred.

Using positron emission tomography (PET) imaging to monitor and quantitatively analyze the delivery and localization of Au nanomaterials (NMs), a widely used photothermal agent, is essential to optimize therapeutic protocols to achieve individualized medicine and avoid side effects. Coupling radiometals to Au NMs viaa chelator faces the challenges of possible detachment of the radiometals as well as surface property changes of the NMs. In this study, we reported a simple and general chelator-free 64Cu radiolabeling method by chemically reducing 64Cu on the surface of polyethylene glycol (PEG)-stabilized Au NMs regardless of their shape and size. Our 64Cu-integrated NMs are proved to be radiochemically stable and can provide an accurate and sensitive localization of NMs through noninvasive PET imaging. We further integrated 64Cu onto arginine-glycine-aspartic acid (RGD) peptide modified Au nanorods (NRs) for tumor theranostic application. These NRs showed high tumor targeting ability in a U87MG glioblastoma xenograft model and were successfully used for PET image-guided photothermal therapy.

In a solution-phase synthesis of nanocrystals (NCs), organic surfactants play an important role in size and shape control as well as in facilitating the stable dispersion of NCs in solvents. However, in order to use these NCs for electrical applications, the surfactants must be removed effectively. Here we report that monodisperse indium tin oxide (ITO) NCs were synthesized and stabilized with oleate/oleylamine ligands, and these long-chain surfactants were readily substituted with tetrabutylammonium hydroxide (TBAOH), forming a stable methanol dispersion. Uniform assemblies of ITO NCs were made by spin-coating the ITO–TBAOH NC dispersions with an assembly thickness controllable from 68 to 260 nm by the NC solution concentration. An annealing treatment at 120 °C and 300 °C under Ar + 5% H2for 1 h effectively removed the TBAOH, and the ITO NC assemblies showed high transparency (>88%) and low resistivity (2.6 × 10–3Ω·cm). Our new approach to surface modification of ITO NCs with a volatile surfactant followed by film deposition is an effective strategy for fabricating ITO NC films by a solution process with desired transparency and conductivity for transparent electrode applications.

Determining the atomic-scale structure of nanosized particles remains a challenge and crucial goal for today’s science and technology. We investigate the atomic-scale structure of 3–8 nm Au particles obtained by a fast solution reaction and find it to be of a noncrystallographic icosahedral type, in particular, close to the particles’ surface. This noncrystallographic structure may well explain the previously observed but poorly understood enhancement of the particles’ catalytic properties. Our finding demonstrates that together with size the structure type of nanosized particles can be used as a tunable parameter for achieving improved functionality.

Surfactant-mediated synthesis of monodisperse CeO2nanoplates (15 nm × 50 nm, 2 nm thick) was conducted by the thermal decomposition of cerium acetate in 1-octadecene. X-ray diffraction patterns indicated selective (200) plane growth of fluorite cubic CeO2in the CeO2nanoplates, and transmission electron microscopy revealed that most of the side surfaces exhibited {200} lattice fringes. Smaller amounts of surfactants resulted in larger nanoplates composed of assemblies of small CeO2nanoparticles (NPs). The formation of this polycrystalline structure of assembled NPs is preferable to induce stability by decreasing the surface energy and positive charge of the NPs. The bandgap energy of CeO2nanoplates for direct transitions was larger than that for polyhedral CeO2NPs.

Monodisperse 8 nm CoPd nanoparticles (NPs) with controlled compositions were synthesized by the reduction of cobalt acetylacetonate and palladium bromide in the presence of oleylamine and trioctylphosphine. These NPs were active catalysts for hydrogen generation from the hydrolysis of ammonia borane (AB), and their activities were composition dependent. Among the 8 nm CoPd catalysts tested for the hydrolysis of AB, the Co35Pd65NPs exhibited the highest catalytic activity and durability. Their hydrolysis completion time and activation energy were 5.5 min and 27.5 kJ mol–1, respectively, which were comparable to the best Pt-based catalyst reported. The catalytic performance of the CoPd/C could be further enhanced by a preannealing treatment at 300 °C under air for 15 h with the hydrolysis completion time reduced to 3.5 min. This high catalytic performance of Co35Pd65NP catalyst makes it an exciting alternative in pursuit of practical implementation of AB as a hydrogen storage material for fuel cell applications.

We and others have recently proposed the synthesis of composite nanoparticles that offer strongly enhanced functionality. Here we have used a flower-shaped Au−Fe3O4nanoparticle as a template to construct an optical probe containing Cy5.5-GPLGVRG-TDOPA on the iron oxide surface and SH-PEG5000on the gold surface that can be specifically activated by matrix metalloproteinases expressed in tumors. Gold nanoparticles have excellent quenching properties, but labile surface chemistry in vivo; on the other hand, iron oxide nanoparticles afford robust surface chemistry, but are suboptimal as energy receptors. By a marriage of the two, we have produced a unified structure with performance that is unachievable with the separate components. Our results are a further demonstration that the architecture of nanoparticles can be modulated to tailor their function as molecular imaging/therapeutic agents.

Monodisperse polyhedral nanoparticles (NPs) and nanorods (NRs) of cerium dioxide, CeO2, were synthesized by thermal decomposition of ammonium cerium(IV) nitrate, (NH4)2Ce(NO3)6, at 180 °C in an organic solution of oleylamine (OAm) and/or oleic acid (OA). The 4 nm CeO2NPs were synthesized in diphenyl ether solution of OAm and OA with the molar ratio of Ce/OAm/OA = 1:3:3, while the 6 nm CeO2NPs were made in 1-octadecene solution of OAm with Ce/OAm = 1:6. The NRs were formed in 1-octadecene with Ce/OAm/OA = 1:3:1.5. The CeO2NPs were assembled on γ-Al2O3via polyvinylpyrrolidone and were annealed at 500 °C under air to remove organic coating. They were well-dispersed on Al2O3and showed the increased oxygen storage capacity compared to the physical mixture of aggregated CeO2and γ-Al2O3powder. The reported CeO2NPs are promising for oxygen storage and release applications.

Metallmantel: Kern‐Schale‐Nanopartikel von Pd/Au und Pd/Au/FePt wurden mit Palladium (5 nm Durchmesser), einer Goldschale (1–2 nm) und einer FePt‐Schale (2 nm) synthetisiert. Die Synthese ist sehr gut steuerbar, sodass die katalytischen Pd/Au‐Eigenschaften durch die Schalendicke eingestellt werden können. Das Verfahren gibt einen Ausblick auf zukünftige Entwicklungen von Mehrkomponenten‐Nanopartikeln für fortgeschrittene Katalyseanwendungen.

Magnetic nanoparticles (MNPs) have been explored extensively as contrast agents for magnetic resonance imaging (MRI) or as heating agents for magnetic fluid hyperthermia (MFH) [1]. To achieve optimum operation conditions in MRI and MFH, these NPs should have well-controlled magnetic properties and biological functionalities. Although numerous efforts have been dedicated to the investigations on MNPs for biomedical applications [2-5], the NP optimizations for early diagnostics and efficient therapeutics are still far from reached. Recent efforts in NP syntheses have led to some promising MNP systems for sensitive MRI and efficient MFH applications. This review summarizes these advances in the synthesis of monodisperse MNPs as both contrast probes in MRI and as therapeutic agents via MFH. It will first introduce the nanomagnetism and elucidate the critical parameters to optimize the superparamagnetic NPs for MRI and ferromagnetic NPs for MFH. It will further outline the new chemistry developed for making monodisperse MNPs with controlled magnetic properties. The review will finally highlight the NP functionalization with biocompatible molecules and biological targeting agents for tumor diagnosis and therapy.

Transition‐metal phosphide nanowires were facilely synthesized by Ullmann‐type reactions between transition metals and triphenylphosphine in vacuum‐sealed tubes at 350–400 °C. The phase (stoichiometry) of the phosphide products is controllable by tuning the metal/PPh3molar ratio and concentration, reaction temperature and time, and heating rate. Six classes of iron, cobalt, and nickel phosphide (Fe2P, FeP, Co2P, CoP, Ni2P, and NiP2) nanostructures were prepared to demonstrate the general applicability of this new method. The resulting phosphide nanostructures exhibit interesting phase‐ and composition‐dependent magnetic properties, and magnetic measurements suggested that the Co2P nanowires with anti‐PbCl2structure show a ferromagnetic–paramagnetic transition at 6 K, while the MnP‐structured CoP nanowires are paramagnetic with Curie–Weiss behavior. Moreover, GC‐MS analyses of organic byproducts of the reaction revealed that thermally generated phenyl radicals promoted the formation of transition‐metal phosphides under synthetic conditions. Our work offers a general method for preparing one‐dimensional nanoscale transition‐metal phosphides that are promising for magnetic and electronic applications.

Rh‐odin's masterpiece: Coupling N‐(rhodamine‐6G)lactam‐ethylenediamine to Fe3O4nanoparticles through a polyethylene glycol chain renders the rhodamine unit more water soluble and useful for sensitive and selective detection of FeIIIat the 2 ppb level in water. This sensitivity is also demonstrated in HeLa cells, thus indicating potential applications of this detection method in biological systems.

This review focuses on the recent advances in the synthesis of nanoparticle (NP) catalysts of Pt‐, Pd‐ and Au‐based NPs as well as composite NPs. First, new developments in the synthesis of single‐component Pt, Pd and Au NPs are summarized. Then the chemistry used to make alloy and composite NP catalysts aiming to enhance their activity and durability for fuel cell reactions is outlined. The review next introduces the exciting new research push in developing CoN/C and FeN/C as non‐Pt catalysts. Examples of size‐, shape‐ and composition‐dependent catalyses for oxygen reduction at cathode and formic acid oxidation at anode are highlighted to illustrate the potentials of the newly developed NP catalysts for fuel cell applications.

Hantelförmige Au‐Fe3O4‐Nanopartikelund ihre separaten Gegenstücke, Au und Fe3O4, wurden hinsichtlich ihrer Effizienz bei der H2O2‐Reduktion verglichen. Die höhere Aktivität der Au‐Fe3O4‐Nanopartikel wird auf die Polarisation von Fe3O4durch Au zurückgeführt. Die Aktivität lässt sich außerdem noch über die Nanopartikelgröße einstellen.

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Fe3BO5nanorods with diameters from 4 nm to 16 nm and length from 43 nm to 60 nm are synthesized by a facile thermal decomposition of iron acetylacetonate and t‐butylamine borane (TBAB). TBAB is used to control the 1D growth and the aspect ratio of the nanorods. These Fe3BO5nanorods are antiferromagnetic with TN= 174 K, which is higher than that of bulk Fe3BO5(114 K).

Au nanowires were produced at the interface of air/water by immersing a Au coated platinum tip into the growth solution containing CTAB, HAuCl4, and ascorbic acid. The Au coating layer is composed of 10−30 nm Au islands and these Au islands initiated the growth of Au crystals, which further produced Au nanowires via the template effect of the aligned cationic surfactant CTAB monolayer at the interface.

Thin is in!Recent advance in solution‐phase synthesis has led to the formation of ultrathin single‐crystalline Au nanowires with diameters of less than 10 nm. This Focus Review summarizes these syntheses and provides an exciting example of the electron transport in the ultrathin Au nanowires to demonstrate their great potential for nanoelectronic applications.

Oberflächenmodifizierte Fe3O4‐Nanopartikel(NPs) werden durch den Austausch von Oleylamin‐Schutzgruppen gegen [(η5‐Semichinon)Mn(CO)3]‐Einheiten erhalten. Sie können als Keim oder Templat bei der Bildung kristalliner Koordinationspolymere wirken, die die superparamagnetischen Fe3O4‐NPs dann einschließen. Hybride magnetische Eigenschaften resultieren, wenn paramagnetische Metallzentren wie Mn2+in die Polymere eingeführt werden (siehe Bild).

Surfacemodified Fe3O4nanoparticlesNPs can be obtained by substituting η5semiquinoneMnCO3 for oleylamine surface protecting groups. The resulting NP can function as a nucleus or template to generate crystalline coordination polymers that contain superparamagnetic Fe3O4NPs. Hybridized magnetic properties can be obtained by introducing paramagnetic metal nodes, such as Mn2+, into the polymers see picture.

It has been a long-standing challenge to create and identify the active sites of heterogeneous catalysts, because it is difficult to precisely control the interfacial chemistry at the molecular level. Here we report the synthesis and catalysis of a heteroleptic gold trihydride nanocluster, [Au22H3(dppe)3(PPh3)8]3+[dppe = 1,2-bis(diphenylphosphino)ethane, PPh3= triphenylphosphine]. The Au22H3core consists of two Au11units bonded via six uncoordinated Au sites. The three H atoms bridge the six uncoordinated Au atoms and are found to play a key role in catalyzing electrochemical reduction of CO2to CO with a 92.7% Faradaic efficiency (FE) at −0.6 V (vs RHE) and high reaction activity (134 A/gAumass activity). The CO current density and FECOremained nearly constant for the CO2reduction reaction for more than 10 h, indicating remarkable stability of the Au22H3catalyst. The Au22H3catalytic performance is among the best Au-based catalysts reported thus far for electrochemical reduction of CO2. Density functional theory (DFT) calculations suggest that the hydride coordinated Au sites are the active centers, which facilitate the formation of the key *COOH intermediate.

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FexPt100-xnanoparticles of different compositions (x63, 58, 54, 42, 15, and 0) were prepared and loaded onto a glassy carbon (GC) electrode where their catalytic activities in the electroreduction of oxygen were examined and compared. Cyclic and rotating disk voltammetric studies of the resulting FexPt100-x/GC electrodes showed that the catalytic activity for oxygen reduction exhibited a peak-shape dependence on the particle composition (x). Among the series of nanocatalysts under study, Fe42Pt58particles showed the maximum activity for O2reduction in terms of the reduction overpotential and current density. This was accounted for by the effects of the Fe content on the electronic structures of the Pt active sites and the resulting Pt−O interactions. Kinetic analyses showed that direct four-electron reduction of adsorbed oxygen occurred on these catalyst surfaces. Additionally, the rate constant of O2reduction increased with increasing Pt content in the alloy particles; yet, at x≤ 42, the rate constant exhibited only a very small increment. These studies suggest that the Fe42Pt58particles might represent an optimal composition for oxygen reduction among the series of nanoparticle catalysts under the present study.

Functionalization of monodisperse superparamagnetic magnetite (Fe3O4) nanoparticles for cell specific targeting is crucial for cancer diagnostics and therapeutics. Targeted magnetic nanoparticles can be used to enhance the tissue contrast in magnetic resonance imaging (MRI), to improve the efficiency in anticancer drug delivery, and to eliminate tumor cells by magnetic fluid hyperthermia. Herein we report the nucleus‐targeting Fe3O4nanoparticles functionalized with protein and nuclear localization signal (NLS) peptide. These NLS‐coated nanoparticles were introduced into the HeLa cell cytoplasm and nucleus, where the particles were monodispersed and non‐aggregated. The success of labeling was examined and identified by fluorescence microscopy and MRI. The work demonstrates that monodisperse magnetic nanoparticles can be readily functionalized and stabilized for potential diagnostic and therapeutic applications.