Metastable intermetallic compound Zn3Co alloying from porous coordination polymer pyrolysis

ZIF-67 derived Co nanoparticles on ZIF-Derived carbon for hydrogen spillover and storage

This chapter describes our studies on the silica coating of metal-related nanoparticles, or the fabrication of core-shell particles composed of metal-related nanoparticle cores and silica shells, along with their various properties. Various metal-related nanoparticles such as metallic nanoparticles, metallic alloy nanoparticles, and nanoparticles containing metallic nanoparticles were successfully coated with silica by a sol-gel process. Nanoparticles of metallic cobalt (Co) and metallic copper (Cu) are easily oxidized in air and in aqueous solutions exposed to air. Nevertheless, the crystallization of metallic Co nanoparticles with no oxidation of the metallic Co was boosted by annealing even in the atmosphere, and the crystallized nanoparticles exhibited magnetic properties. For metallic Cu, an absorption peak derived from the surface plasmon resonance (SPR) of metallic Cu nanoparticles was caught for a colloidal solution of silica-coated metallic Cu nanoparticles. Accordingly, silica coating was confirmed to chemically stabilize the core nanoparticles via the physical barrier of the silica shells. For metallic gold (Au) and metallic silver (Ag), the optical spectra of silica-coated metallic nanoparticle colloidal solutions coincided with the forecast of Mie theory, which confirmed that most metallic nanoparticles were coated with silica shells with no aggregation. The silica-coated metallic Au nanoparticle colloidal solution exhibited strong X-ray absorption, which is applicable to X-ray imaging. In addition to the silica coating of nanoparticles with a single metal component, silica coating was also successfully performed on nanoparticles of an alloy of metallic platinum (Pt) and metallic ruthenium, nanoparticles of an alloy of metallic Co and metallic Pt, and multilayered nanoparticles composed of metallic Au, silica, and gadolinium compound, which exhibited catalytic activity, magnetic properties, and magnetic resonance imaging ability, respectively. The abovementioned core nanoparticles were spherical. In contrast, the silica coating of metallic Au nanorods (AuNRs), which are not spherical, was also performed successfully. The silica-coated AuNR colloidal solution had an SPR peak in the near-infrared region, so that cancer cells in culture medium died from a temperature rise given by photothermal conversion via near-infrared laser irradiation.

Hydrotalcite-derived well-dispersed and thermally stable cobalt nanoparticle catalyst for ammonia decomposition

In solid oxide CO2 electrolysis cells, moderate activity and coking of the cathode are major issues that hinder commercialization of this important technology. It has been already shown that cathodes based on a mixed conducting oxide decorated with well-dispersed metal nanoparticles, which were grown via an exsolution process, are highly resilient to carbon deposition. Using perovskite-type oxides that contain reducible transition metals, such nanoparticles can be obtained in situ under sufficiently reducing conditions. However, the direct catalytic effect of exsolved metal nanoparticles on the CO2 splitting reaction has not yet been explored thoroughly (e.g. by employing well-defined model systems), thus, an in-depth understanding is still lacking. In this study, we aim at providing a crucial piece of insight into high-temperature electrochemical CO2 splitting on exsolution-decorated electrodes: we present the results of combined Near Ambient Pressure X-ray Photoelectron Spectroscopy (NAP-XPS) and electrochemical measurements on three different ferrite perovskites, which were employed as thin film model electrodes. The investigated materials are: La0.6Ca0.4FeO3-δ (LCF), Nd0.6Ca0.4FeO3-δ (NCF), and Pr0.6Ca0.4FeO3-δ (PCF). The results obtained allow us to directly link the electrode's CO2 splitting activity to their surface chemistry. Especially, the electro-catalytic activity of the materials decorated with and without metallic iron nanoparticles was in focus. Our experiments reveal that in contrast to their beneficial role in H2O electrolysis, exsolved Fe0 metal particles deteriorate CO2 electrolysis activity. This behavior contrasts with expectations derived from earlier reports on porous samples, and is likely a consequence of the differences between the CO2 splitting and H2O splitting mechanism.

Studying catalytic processes at the molecular level is extremely challenging, due to the structural and chemical complexity of the materials used as catalysts and the presence of reactants and products in the reactor's environment. The most common materials used on catalysts are transition metals and their oxides. The importance of multifunctional active sites at metal/oxide interfaces has been long recognized, but a molecular picture of them based on experimental observations is only recently emerging. The initial approach to interrogate the surface chemistry of catalysts at the molecular level consisted of studying metal single crystals as models for reactive metal centers, moving later to single crystal or well-defined thin film oxides. The natural next iteration consisted in the deposition of metal nanoparticles on well-defined oxide substrates. Metal nanoparticles contain undercoordinated sites, which are more reactive. It is also possible to create architectures where oxide nanoparticles are deposited on top of metal single crystals, denominated inverse catalysts, leading in this case to a high concentration of reactive cationic sites in direct contact with the underlying fully coordinated metal atoms. Using a second oxide as a support (host), a multifunctional configuration can be built in which both metal and oxide nanoparticles are located in close proximity. Our recent studies on copper-based catalysts are presented here as an example of the application of these complementary model systems, starting from the creation of undercoordinated sites on Cu(111) and Cu2O(111) surfaces, continuing with the formation of mixed-metal copper oxides, the synthesis of ceria nanoparticles on Cu(111) and the codeposition of Cu and ceria nanoparticles on TiO2(110). Catalysts have traditionally been characterized before or after reactions and analyzed based on static representations of surface structures. It is shown here how dynamic changes on a catalyst's chemical state and morphology can be followed during a reaction by a combination of in situ microscopy and spectroscopy. In addition to determining the active phase of a catalyst by in situ methods, the presence of weakly adsorbed surface species or intermediates generated only in the presence of reactants can be detected, allowing in turn the comparison of experimental results with first principle modeling of specific reaction mechanisms. Three reactions are used to exemplify the approach: CO oxidation (CO + 1/2O2 → CO2), water gas shift reaction (WGSR) (CO + H2O → CO2 + H2), and methanol synthesis (CO2 + 3H2 → CH3OH + H2O). During CO oxidation, the full conversion of Cu(0) to Cu(2+) deactivates an initially outstanding catalyst. This can be remedied by the formation of a TiCuOx mixed-oxide that protects the presence of active partially oxidized Cu(+) cations. It is also shown that for the WGSR a switch occurs in the reaction mechanism, going from a redox process on Cu(111) to a more efficient associative pathway at the interface of ceria nanoparticles deposited on Cu(111). Similarly, the activation of CO2 at the ceria/Cu(111) interface allows its facile hydrogenation to methanol. Our combined studies emphasize the need of searching for optimal metal/oxide interfaces, where multifunctional sites can lead to new efficient catalytic reaction pathways.

Review: 42 refs.

Metallic nanoparticles (NPs), either supported on a porous oxide framework or finely dispersed within an oxide matrix, find applications in catalysis, plasmonics, nanomagnetism and energy conversion, among others. The development of synthetic routes that enable to control the morphology, chemical composition, crystal structure and mutual interaction of metallic and oxide phases is necessary in order to tailor the properties of this class of nanomaterials. With this work, we aim at developing a novel method for the synthesis of metal/oxide nanocomposites based on the assembly of NPs formed by gas phase condensation of metal vapors in a He/O2 atmosphere. This new approach relies on the independent evaporation of two metallic precursors with strongly different oxidation enthalpies. Our goal is to show that the precursor with less negative enthalpy gives birth to metallic NPs, while the other to oxide NPs. The selected case study for this work is the synthesis of a Fe-Co/TiOx nanocomposite, a system of great interest for its catalytic and magnetic properties. By exploiting the new concept, we achieve the desired target, i.e., a nanoscale dispersion of metallic alloy NPs within titanium oxide NPs, the structure of which can be tailored into TiO1-δ or TiO2 by controlling the synthesis and processing atmosphere. The proposed synthesis technique is versatile and scalable for the production of many NPs-assembled metal/oxide nanocomposites.

In this review, we have presented the controlled synthesis of Fe-based metal and oxide nanoparticles with large size by chemical methods. The issues of the size, shape and morphology of Fe nanoparticles are discussed in the certain ranges of practical applications in biology and medicine. The homogeneous nanosystems of Fe-based metal and oxide nanoparticles with various sizes and shapes from the nano-to-micro ranges can be used in order to meet the demands of the treatments of dangerous tumors and cancers through magnetic hyperthermia and magnetic resonance imaging (MRI). In this context, the polyhedral Fe-based metal and oxide nanoparticles having large size in the ranges from 1000 nm to 5000 nm can be potentially used in magnetic hyperthermia and MRI in the innovative drug delivery, diagnosis, treatment, and therapy of tumor and cancer diseases because of their very high bio-adaptability. We have suggested that high stability and durability of Fe-based metal and oxide nanoparticles are very crucial to recent magnetic hyperthermia and MRI technology. The roles of various Fe-based nanostructures are focused in biomedical applications of tumors and cancers diagnostics, targeted drug delivery, and magnetic hyperthermia. Finally, Fe-based, α-, β- and γ-Fe2O3, and Fe3O4-based nanoparticles are shortly discussed in various potential applications in catalysis, biology, and medicine.

Spherical polyelectrolyte brushes as nanoreactors for the generation of metallic and oxidic nanoparticles: Synthesis and application in catalysis

Since the 1980s [1,2], colloidal systems such as microemulsions (ME) have been widely investigated, especially for the synthesis of nanomaterials for various applications.[...]

Developing highly active and stable nonprecious metal catalysts for electrochemical reactions is desirable but remains a great challenge. Herein, we report a novel metal-ion adsorption-pyrolysis strategy for the controllable zeolitic imidazolate framework-8 derived synthesis of individual high-quality N-doped carbon nanotubes embedded with well-dispersed nonprecious metal nanoparticles, which exhibit superior electrocatalytic activity and stability for electrochemical CO2 reduction reaction, oxygen reduction reaction, and oxygen evolution reaction. Experimental analysis and density functional theory calculations indicate that the remarkable electrocatalytic activities are mainly attributed to the interface effects for the efficient electron transfer from metal nanoparticles to the N-doped carbon shell, as well as the large specific areas, unique tube structures, appropriate doping, high graphitization degree, and robust frameworks. The high reaction stability is attributed to the multiwalled graphitic carbon shells efficiently preventing metal nanoparticles from aggregation, corrosion, and oxidation. This novel synthetic strategy presents a facile universality for synthesizing N-doped carbon nanotube structures and will provide a guideline for developing low-cost, highly active, and stable electrocatalytic materials for sustainable energy conversion.

Catalytic and fluorescence studies with copper nanoparticles synthesized in polysorbates of varying hydrophobicity

Metal–organic frameworks (MOFs) have attracted considerable attention on account of their applications in molecular separations, gas storage, catalysis, and chemical sensing. Recently, there has been a growing interest in using these highly ordered microporous architectures as host matrices or templates with incorporated metal or metal oxide nanoclusters or nanoparticles (NPs). Such hybrid NPMOF structures are promising materials for gas storage and catalysis. The strategies available for the incorporation of metal or metal oxide NPs into MOFs include solvent-free gasphase loading, solution impregnation, incipient wetness impregnation, solid grinding, and microwave irradiation. Most of these techniques, however, involve relatively cumbersome processes such as pretreating the MOF (e.g., by solvent exchange or MOF activation) or particle loading (by introduction of reducing agents, heating, irradiation, etc.), and none allows any spatial control over the NP loading within the MOF crystals. Here, we describe a procedure in which reaction-diffusion processes inside the MOF crystals mediate the deposition of NPs either in a uniform or in a location-specific fashion, with the latter leading to the formation of core/shell architectures (which are of interest in the context of multistep catalysis). In our method, cyclodextrin-based MOF (CD-MOF) crystals are immersed in a metal (here, Ag or Au) salt solution, and the OH counterions—which are homogenously distributed in the CD-MOF at concentrations of about 1.33m—reduce this salt to the respective metal NPs. By coupling the diffusion of salt precursors with their reduction inside the CD-MOFs it is possible to deposit the NPs only at the core of the MOF crystal and such that the thickness of the NP-free shell depends on the concentration of the HAuCl4 used. Subsequent deposition of another type of NPs gives rise to core/ shell architectures. NPs of all types can be readily liberated by dissolving the CD-MOFs in water—for the core/shell NP/CDMOFs, the release of the two different types of NPs is then sequential. Two types of millimeter-sized CD-MOFs were used. The first type was synthesized from g-cyclodextrin (g-CD) and RbOH following the reported procedures (see Experimental Section for details). As illustrated in Figure 1a–c, these Rb-CD-MOF single crystals (for powder X-ray diffraction (PXRD) spectra, see Section 1 in the Supporting Information) were rectangular prisms up to about 2 2 1 mm in size with nanosized cavities (ca. 1.7 nm across) and 1D channels connecting them (channel cross-section: ca. 8 8 ). The second type of MOFwas also made from g-CD, but CsOH was used as the alkali metal source. These Cs-CDMOF crystals also comprised cavities of approximately 1.7 nm in diameter connected by channels with cross-sections of about 8 8 2 (Figure 1a,b). Following the procedure described in the Experimental Section, Cs-CD-MOF single crystals were grown that had an overall truncated-octahedron shape and the diameters of these crystals were up to 5 mm (Figure 1d, see also the PXRD spectra in Section 2 of the Supporting Information). In the context of the present work, the key feature of the CD-MOFs is that they contain hydroxide counterions (one per metal center) which can work either alone or cooperatively with the cyclodextin units to reduce metal salt Figure 1. a) A unit cell of Rbor Cs-CD-MOF crystals synthesized from g-CD and RbOH or CsOH, respectively (red: oxygen; gray: carbon; purple: Rb or Cs). b) The 1D channels in Rbor Cs-CD-MOF crystals. c) and d) The optical images of the millimeter-sized Rb-CD-MOF and Cs-CD-MOF crystals, respectively.

Optoelectronic performance analysis of perpendicularly aligned conformally coated GaAs0.99Bi0.01/ZnO/ITO core–shell nanowire solar cell having a core length of 1 μm, core diameter of 160 nm, shell thickness of 10 nm and period of 280 nm, decorated with Au metal nanoparticles(MNPs) of variable diameters at the core–shell interface is done employing FDTD method. Diameter optimization of MNPs with four different diameters values around core GaAs0.99Bi0.01 nanowire is accomplished in terms of maximum short circuit current density (Jsc), which offered an optimized diameter combination of D1 = D2 = 50 nm and D3 = 34 nm, D4 = 10 nm, resulting in a maximum Jsc of 32.6 mA cm−2. A detailed analysis of the electric field profile including its top view and longitudinal view is presented to investigate the distribution of electric field upon optical illumination at different wavelength range. The overall photo generation rate profile is also presented to focus on the localized surface plasmon resonance effect caused by the metal nanoparticles (MNPs). In order to boost the electrical performance, a thin coating of electron selective ZnO shell is used around p type GaAs0.99Bi0.01core, which aids in charge carrier separation, thereby improving open circuit voltage (Voc) and overall power conversion efficiency (PCE). The electrical characteristics of bare NW and MNP decorated GaAs0.99Bi0.01/ZnO core–shell nanowire solar cell for different MNP diameters have been compared. For the optimized diameter combination, as stated above, a Voc of 941 mV, Jsc of 28 mA cm−2, FF of 84.35% and PCE of 22.19% is obtained for SRV of 105 cm s−1 at the interfaces and SRH recombination lifetime as less as 10 ns. For SRV of 105 cm s−1 at the interfaces and SRH recombination lifetime of 1 μs, this proposed structure can achieve a Voc of 1.06 V, Jsc of 31.5 mA cm−2, PCE of 29.37% and FF of 87.88% for equal diameters of D1 = D2 = D3 = D4 = 50 nm.

This study describes a simple green method for the synthesis of Limnophila rugosa leaf-extract-capped silver and gold nanoparticles without using any expensive toxic reductant or stabilizer. The noble metal nanoparticles were characterized by Fourier transform infrared (FTIR) microscopy, powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray analysis (EDX), high-resolution transmission electron microscopy (HR-TEM), selected area electron diffraction (SAED), and dynamic light scattering (DLS) method. It has been found that the biosynthesized silver and gold nanoparticles are nearly spherical in shape with a mean particle size distribution of 87.5 nm and 122.8 nm, respectively. XRD and SAED patterns confirmed the crystalline nanostructure of the metal nanoparticles. FTIR spectra revealed the functional groups of biomolecules presented in the extract possibly responsible for reducing metallic ions and stabilizing formed nanoparticles. The biosynthesized metal nanoparticles have potential application in catalysis. Compared to previous reports, Limnophila rugosa leaf-extract-capped silver and gold nanoparticles exhibited a good catalytic activity in the reduction of several derivatives of nitrophenols including 1,4-dinitrobenzene, 2-nitrophenol, 3-nitrophenol, and 4-nitrophenol.