Colloid Science of Metal Nanoparticle Catalysts in 2D and 3D Structures. Challenges of Nucleation, Growth, Composition, Particle Shape, Size Control and Their Influence on Activity and Selectivity

The effect of ligands on the size distribution of copper nanoclusters: Insights from molecular dynamics simulations

Controlling the size distribution in the nucleation of copper particles is crucial for achieving nanocrystals with desired physical and chemical properties. However, their synthesis involves a complex system of solvents, ligands, and copper precursors with intertwining effects on the size of the nanoclusters. We combine molecular dynamics simulations and density functional theory calculations to provide insights into the nucleation mechanism in the presence of a triphenyl phosphite ligand. We identify the crucial role of the strength of the metal-phosphine interaction in inhibiting the cluster's growth. We demonstrate computationally several practical routes to fine-tune the interaction strength by modifying the side groups of the additive. Our work provides molecular insights into the complex nucleation process of protected copper nanocrystals, which can assist in controlling their size distribution and, eventually, their morphology.

A review on the applications of zinc tungstate (ZnWO4) photocatalyst for wastewater treatment

The monoclinic wolframite-phase structure of ZnWO₄ materials has been frequently synthesised, characterised, and applied in optical fibres, environmental decontamination, electrochemistry, photonics, catalysis, and not limited to magnetic applications. However, the problems of crystal growth conditions and mechanisms, growth, the crystal quality, stability, and the role of synthesis parameters of ZnWO₄ nanoparticles remain a challenge limiting its commercial applications. This review presents recent advances of ZnWO₄ as an advanced multi-functional material for Industrial wastewater treatment. The review also examines the influence of the synthesis parameters on the properties of ZnWO₄ and provides insight into new perspectives on ZnWO₄-based photocatalyst. Many researches have shown significant improvement in the efficiency of ZnWO₄ by mixing with polymers and doping with metals, nonmetals, and other nanoparticles. The review also provides information on the mechanism of doping ZnWO₄ with metals, non-metals, metalloids, metals oxides, and polymers based on different synthesis methods for bandgap reduction and extension of its photocatalytic activity to the visible region. The doped ZnWO₄ photocatalyst was a more effective and environmentally friendly material for removing organic and inorganic contaminants in industrial wastewater than ordinary ZnWO₄ nanocrystalline under suitable growth conditions.

Biosynthesized Bimetallic (ZnOSnO2) Nanoparticles for Photocatalytic Degradation of Organic Dyes and Pharmaceutical Pollutants

The quest for eco-friendly synthetic routes that can be used for the development of multifunctional materials, in particular for water treatment, has reinforced the use of plant extracts as replacement solvents. In this study, bimetallic ZnOSnO2 nanoparticles of different ratios were synthesized using the Sutherlandia frutescens (S. frutescens) plant and tested for the degradation of methylene blue dye and the antibiotics sulfisoxazole and sulfamethoxazole. From the analysis, FTIR confirmed the formation of bimetallic nanoparticles in all ratios within the fingerprint region. SEM revealed homogenous and heterostructures of tubular and spherical structures, with the size distribution ranging from 5–60 nm, respectively. XRD confirmed the formation and the crystallinity of the bimetallic nanoparticles, UV-Vis confirmed the optical properties of the materials and the bandgap values were found between 3.08 and 3.3 eV. From the surface area analysis, type III isotherm and mesoporous structures were confirmed. The photocatalytic activity of these ratios was investigated against MB dye and the antibiotics SSX and SMX. The highest degradation of 88% for MB was obtained using the 50:50 loading ratio at 150 min with a fast kinetic rate of 0.0008 min−1. Furthermore, the holes were the species found to be responsible for the degradation of MB. The SSX and SMX antibiotics exhibited a 66% and 70% degradation, respectively. From this analysis, it can be noted that it is possible to synthesize environmentally safe materials that can be used to degrade various pollutants in our water streams.

The two-step electrosynthesis of nanocomposites of Ag, Au, and Pd nanoparticles with iron(ii) oxide-hydroxide

The two-step electrosynthesis of metal nanoparticle (MNP, M = Ag, Pd, and Au) nanocomposites with iron oxide-hydroxide FeO-xFe(OH)2 was investigated.

MoS2 nanosheets/silver nanoparticles anchored onto textile fabric as "dip catalyst" for synergistic p-nitrophenol hydrogenation

Attaining a synergistic merge between the performance of homogenous catalysts and the recyclability of heterogeneous catalysts remains until now a concerning issue. The main challenge is to design efficient, low-cost catalyst with outstanding reusability, facile recovery, and ease of retrieval and monitoring between the reuses. Despite the vast efforts in the development of silver nanoparticle-based catalyst for the reaction of hydrogenation of 4-nitrophenol, the aforementioned criteria are infrequently found in a chosen system. Herein, we report a MoS₂ nanosheet/silver nanoparticle-anchored PES-based textile as an efficient and recyclable "dip catalyst" for the 4-NP hydrogenation in the presence of sodium bohydride as model reaction. The textile fabric-based catalyst was processed via a simple sono-coating approach using MoS₂ nanosheets as first coating layer followed by an in situ deposition of silver nanoparticles. The "dip catalyst" fabric is rapidly and easily removed from the reaction and then reinserted in the batch system to attain over 10 reaction cycles. Additionally, the produced textile materials were characterized via spectroscopic and microscopic tools such as FTIR, XRD, SEM, and EDX. Moreover, the sources of the high catalytic activity are also discussed and a plausible reaction mechanism is suggested. The present study demonstrates the potential of metal nanoparticle-textile material combination for future applications in chemical sustainable catalysis for environmental remediation purposes.

Importance of Surface Topography in Both Biological Activity and Catalysis of Nanomaterials: Can Catalysis by Design Guide Safe by Design?

It is acknowledged that the physicochemical properties of nanomaterials (NMs) have an impact on their toxicity and, eventually, their pathogenicity. These properties may include the NMs’ surface chemical composition, size, shape, surface charge, surface area, and surface coating with ligands (which can carry different functional groups as well as proteins). Nanotopography, defined as the specific surface features at the nanoscopic scale, is not widely acknowledged as an important physicochemical property. It is known that the size and shape of NMs determine their nanotopography which, in turn, determines their surface area and their active sites. Nanotopography may also influence the extent of dissolution of NMs and their ability to adsorb atoms and molecules such as proteins. Consequently, the surface atoms (due to their nanotopography) can influence the orientation of proteins as well as their denaturation. However, although it is of great importance, the role of surface topography (nanotopography) in nanotoxicity is not much considered. Many of the issues that relate to nanotopography have much in common with the fundamental principles underlying classic catalysis. Although these were developed over many decades, there have been recent important and remarkable improvements in the development and study of catalysts. These have been brought about by new techniques that have allowed for study at the nanoscopic scale. Furthermore, the issue of quantum confinement by nanosized particles is now seen as an important issue in studying nanoparticles (NPs). In catalysis, the manipulation of a surface to create active surface sites that enhance interactions with external molecules and atoms has much in common with the interaction of NP surfaces with proteins, viruses, and bacteria with the same active surface sites of NMs. By reviewing the role that surface nanotopography plays in defining many of the NMs’ surface properties, it reveals the need for its consideration as an important physicochemical property in descriptive and predictive toxicology. Through the manipulation of surface topography, and by using principles developed in catalysis, it may also be possible to make safe-by-design NMs with a reduction of the surface properties which contribute to their toxicity.

Recent advances in catalytic systems in the prism of physicochemical properties to remediate toxic CO pollutants: A state-of-the-art review

Carbon monoxide (CO) is the most harmful pollutant in the air, causing environmental issues and adversely affecting humans and the vegetation and then raises global warming indirectly. CO oxidation is one of the most effective methods of reducing CO by converting it into carbon dioxide (CO₂) using a suitable catalytic system, due to its simplicity and great value for pollution control. The CO oxidation reaction has been widely studied in various applications, including proton-exchange membrane fuel cell technology and catalytic converters. CO oxidation has also been of great academic interest over the last few decades as a model reaction. Many review studies have been produced on catalysts development for CO oxidation, emphasizing noble metal catalysts, the configuration of catalysts, process parameter influence, and the deactivation of catalysts. Nevertheless, there is still some gap in a state of the art knowledge devoted exclusively to synergistic interactions between catalytic activity and physicochemical properties. In an effort to fill this gap, this analysis updates and clarifies innovations for various latest developed catalytic CO oxidation systems with contemporary evaluation and the synergistic relationship between oxygen vacancies, strong metal-support interaction, particle size, metal dispersion, chemical composition acidity/basicity, reducibility, porosity, and surface area. This review study is useful for environmentalists, scientists, and experts working on mitigating the harmful effects of CO on both academic and commercial levels in the research and development sectors.

Cu oxide deposited on shape-controlled ceria nanocrystals for CO oxidation: influence of interface-driven oxidation states on catalytic activity

The polar CeO2 (100) surface facets contribute considerably to the formation of surface hydroxyl groups, which are necessary for selective, stable Cu1+ state loading and enhancement of CO oxidation activity.

Nanoscale Spatial Distribution of Supported Nanoparticles Controls Activity and Stability in Powder Catalysts for CO Oxidation and Photocatalytic H2 Evolution

Supported metal nanoparticles are essential components of high-performing catalysts, and their structures are intensely researched. In comparison, nanoparticle spatial distribution in powder catalysts is conventionally not quantified, and the influence of this collective property on catalyst performance remains poorly investigated. Here, we demonstrate a general colloidal self-assembly method to control uniformity of nanoparticle spatial distribution on common industrial powder supports. We quantify distributions on the nanoscale using image statistics and show that the type of nanospatial distribution determines not only the stability, but also the activity of heterogeneous catalysts. Widely investigated systems (Au-TiO2 for CO oxidation thermocatalysis and Pd-TiO2 for H2 evolution photocatalysis) were used to showcase the universal importance of nanoparticle spatial organization. Spatially and temporally resolved microkinetic modeling revealed that nonuniformly distributed Au nanoparticles suffer from local depletion of surface oxygen, and therefore lower CO oxidation activity, as compared to uniformly distributed nanoparticles. Nanoparticle spatial distribution also determines the stability of Pd-TiO2 photocatalysts, because nonuniformly distributed nanoparticles sinter while uniformly distributed nanoparticles do not. This work introduces new tools to evaluate and understand catalyst collective (ensemble) properties in powder catalysts, which thereby pave the way to more active and stable heterogeneous catalysts.

Designing Nanoparticles and Nanoalloys for Gas-Phase Catalysis with Controlled Surface Reactivity Using Colloidal Synthesis and Atomic Layer Deposition

Supported nanoparticles are commonly applied in heterogeneous catalysis. The catalytic performance of these solid catalysts is, for a given support, dependent on the nanoparticle size, shape, and composition, thus necessitating synthesis techniques that allow for preparing these materials with fine control over those properties. Such control can be exploited to deconvolute their effects on the catalyst's performance, which is the basis for knowledge-driven catalyst design. In this regard, bottom-up synthesis procedures based on colloidal chemistry or atomic layer deposition (ALD) have proven successful in achieving the desired level of control for a variety of fundamental studies. This review aims to give an account of recent progress made in the two aforementioned synthesis techniques for the application of controlled catalytic materials in gas-phase catalysis. For each technique, the focus goes to mono- and bimetallic materials, as well as to recent efforts in enhancing their performance by embedding colloidal templates in porous oxide phases or by the deposition of oxide overlayers via ALD. As a recent extension to the latter, the concept of area-selective ALD for advanced atomic-scale catalyst design is discussed.

Engineering Nanoscale Interfaces of Metal/Oxide Nanowires to Control Catalytic Activity

The interfacial effect between a metal catalyst and its various supporting transition metal oxides on the catalytic activity of heterogeneous catalysis has been extensively explored; engineering interfacial sites of metal supported on metal oxide has been found to influence catalytic performance. Here, we investigate the interfacial effect of Pt nanowires (NWs) vertically and alternatingly stacked with titanium dioxide (TiO₂) or cobalt monoxide (CoO) NWs, which exhibit a strong metal-support interaction under carbon monoxide (CO) oxidation. High-resolution nanotransfer printing based on nanoscale pattern replication and e-beam evaporation were utilized to obtain the Pt NWs cross-stacked on the CoO or TiO₂ NW on the silicon dioxide (SiO₂) substrate with varying numbers of nanowires. The morphology and interfacial area were precisely determined by means of atomic force microscopy and scanning electron microscopy. The cross-stacked Pt/TiO₂ NW and Pt/CoO NW catalysts were estimated with CO oxidation under 40 Torr CO and 100 Torr O₂ from 200 to 240 °C. Higher catalytic activity was found on the Pt/CoO NW catalyst than on Pt/TiO₂ NWs and Pt NWs, which indicates the significance of nanoscale metal-oxide interfaces. As the number of nanowire layers increased, the catalytic activity became saturated. Our study demonstrates the interfacial role of nanoscale metal-oxide interfaces under CO oxidation, which has intriguing applications in the smart design of catalytic materials.

Fabrication of nanohybrids assisted by protein-based materials for catalytic applications

Protein units and architectures were applied as supports in the synthesis of metal and metal oxide nanoparticles for environmentally benign catalytic applications.

Pyroelectric synthesis of Au/Pt bimetallic nanoparticles–BaTiO3 hybrid nanomaterials

This paper introduces an approach to synthesize bimetallic nanoparticles under an alternating temperature field in aqueous solution. During the synthesis, pyro-catalytic barium titanate is used as the substrate to reduce the metallic ions dispersed in the solution due to the generated charges at the surface of pyro-materials under temperature oscillation. Chloroauric acid and potassium tetrachloroplatinate are used as precursors to produce gold/platinum bimetallic nanoparticles through a pyro-catalytic process. Transmission electron microscopy characterization, in combination with energy dispersive X-ray spectroscopy mapping, demonstrates that the bimetallic nanoparticle is composed of an Au core and Au/Pt alloy shell structure. Compared to the conventional approaches, the pyroelectric synthesis approach demonstrated in this work requires no toxic reducing agents and waste heat can be used as a thermal energy source in the synthesis. Hence, it offers a potential “green” synthetic method for bimetallic nanoparticles.

A “green” synthetic approach to Au/Pt bimetallic nanoparticles under an alternating temperature field.

Well-Defined Materials for Heterogeneous Catalysis: From Nanoparticles to Isolated Single-Atom Sites

The use of well-defined materials in heterogeneous catalysis will open up numerous new opportunities for the development of advanced catalysts to address the global challenges in energy and the environment. This review surveys the roles of nanoparticles and isolated single atom sites in catalytic reactions. In the second section, the effects of size, shape, and metal-support interactions are discussed for nanostructured catalysts. Case studies are summarized to illustrate the dynamics of structure evolution of well-defined nanoparticles under certain reaction conditions. In the third section, we review the syntheses and catalytic applications of isolated single atomic sites anchored on different types of supports. In the final part, we conclude by highlighting the challenges and opportunities of well-defined materials for catalyst development and gaining a fundamental understanding of their active sites.

Probing Atomic Distributions in Mono- and Bimetallic Nanoparticles by Supervised Machine Learning

Properties of mono- and bimetallic metal nanoparticles (NPs) may depend strongly on their compositional, structural (or geometrical) attributes, and their atomic dynamics, all of which can be efficiently described by a partial radial distribution function (PRDF) of metal atoms. For NPs that are several nanometers in size, finite size effects may play a role in determining crystalline order, interatomic distances, and particle shape. Bimetallic NPs may also have different compositional distributions than bulk materials. These factors all render the determination of PRDFs challenging. Here extended X-ray absorption fine structure (EXAFS) spectroscopy, molecular dynamics simulations, and supervised machine learning (artificial neural-network) method are combined to extract PRDFs directly from experimental data. By applying this method to several systems of Pt and PdAu NPs, we demonstrate the finite size effects on the nearest neighbor distributions, bond dynamics, and alloying motifs in mono- and bimetallic particles and establish the generality of this approach.

Superior activity and selectivity of heterogenized cobalt catalysts for hydrogenation of nitroarenes

The development of improved catalysts based on Co nanoparticles supported on ordered mesoporous carbon CMK-3 for the highly selective hydrogenation of nitroarenes is described.

Gas-phase synthesis of morphology-controlled Pt nanoparticles and their impact on cinnamaldehyde hydrogenation

Pt nanoparticles of which morphology is controlled by gas-phase synthesis using carbon monoxide as a protective agent show high catalytic activity and selectivity for cinnamaldehyde hydrogenation.

The effect of the oxidation states of supported oxides on catalytic activity: CO oxidation studies on Pt/cobalt oxide

The strong metal–oxide interaction of platinum nanoparticles (PtNPs) deposited on two types of cobalt oxides, CoO and Co₃O₄, was investigated using CO oxidation.

"Weakly Ligated, Labile Ligand" Nanoparticles: The Case of Ir(0) n ·(H+Cl-) m

It is of considerable interest to prepare weakly ligated, labile ligand (WLLL) nanoparticles for applications in areas such as chemical catalysis. WLLL nanoparticles can be defined as nanoparticles with sufficient, albeit minimal, surface ligands of moderate binding strength to meta-stabilize nanoparticles, initial stabilizer ligands that can be readily replaced by other, desired, more strongly coordinating ligands and removed completely when desired. Herein, we describe WLLL nanoparticles prepared from [Ir(1,5-COD)Cl]₂ reduction under H₂, in acetone. The results suggest that H⁺Cl^--stabilized Ir(0) _n nanoparticles, herein Ir(0) _n ·(H⁺Cl^-) _a , serve as a WLLL nanoparticle for the preparation of, as illustrative examples, five specific nanoparticle products: Ir(0) _n ·(Cl^-Bu₃NH⁺) _a , Ir(0) _n ·(Cl^-Dodec₃NH⁺) _a , Ir(0) _n ·(POct₃)_0.2n (Cl^-H⁺) _b , Ir(0) _n ·(POct₃)_0.2n , and the γ-Al₂O₃-supported heterogeneous catalyst, Ir(0) _n ·(γ-Al₂O₃) _a (Cl^-H⁺) _b . (where a and b vary for the differently ligated nanoparticles; in addition, solvent can be present as a nanoparticle surface ligand). With added POct₃ as a key, prototype example, an important feature is that a minimum, desired, experimentally determinable amount of ligand (e.g., just 0.2 equiv POct₃ per mole of Ir) can be added, which is shown to provide sufficient stabilization that the resultant Ir(0) _n ·(POct₃)_0.2n (Cl^-H⁺) _b is isolable. Additionally, the initial labile ligand stabilizer HCl can be removed to yield Ir(0) _n ·(POct₃)_0.2n that is >99% free of Cl^- by a AgCl precipitation test. The results provide strong support for the weakly ligated, labile ligand nanoparticle concept and specific support for Ir(0) _n ·(H⁺Cl^-) _a as a WLLL nanoparticle.

Catalytic Oxidation of Benzyl Alcohol Using Nanosized Cu/Ni Schiff-Base Complexes and Their Metal Oxide Nanoparticles

In this work, nanosized Cu and Ni Schiff-base complexes, namely ahpvCu, ahpnbCu, and ahpvNi, incorporating imine ligands derived from the condensation of 2-amino-3-hydroxypyridine, with either 3-methoxysalicylaldehyde (ahpv) or 4-nitrobenzaldehyde (ahpnb), were synthesized using sonochemical approach. The structure and properties of the new ligands and their complexes with Ni(II) and Cu(II) were determined via infrared (IR), nuclear magnetic resonance (NMR), electronic spectra (UV-Vis), elemental analysis (CHN), thermal gravimetric analysis (TGA), molar conductivity (Λm), and magnetic moment (μeff). The combined results revealed the formation of 1:1 (metal: ligand) complexes for ahpvCu and ahpvNi and 1:2 for ahpnbCu. Additionally, CuO and NiO nanoparticles were prepared by calcination of the respective nanosized Cu/Ni complexes at 500 °C, and characterized by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). Significantly, the as-prepared nanosized Schiff-base Cu/Ni complexes and their oxides showed remarkable catalytic activity towards the selective oxidation of benzyl alcohol (BzOH) in aqueous H2O2/ dimethylsulfoxide (DMSO) solution. Thus, catalytic oxidation of BzOH to benzaldehyde (BzH) using both ahpvCu complex and CuO nanoparticles in H2O2/DMSO media at 70 °C for 2 h yielded 94% and 98% BzH, respectively, with 100% selectivity.

Metal Catalysts for Heterogeneous Catalysis: From Single Atoms to Nanoclusters and Nanoparticles

Metal species with different size (single atoms, nanoclusters, and nanoparticles) show different catalytic behavior for various heterogeneous catalytic reactions. It has been shown in the literature that many factors including the particle size, shape, chemical composition, metal-support interaction, and metal-reactant/solvent interaction can have significant influences on the catalytic properties of metal catalysts. The recent developments of well-controlled synthesis methodologies and advanced characterization tools allow one to correlate the relationships at the molecular level. In this Review, the electronic and geometric structures of single atoms, nanoclusters, and nanoparticles will be discussed. Furthermore, we will summarize the catalytic applications of single atoms, nanoclusters, and nanoparticles for different types of reactions, including CO oxidation, selective oxidation, selective hydrogenation, organic reactions, electrocatalytic, and photocatalytic reactions. We will compare the results obtained from different systems and try to give a picture on how different types of metal species work in different reactions and give perspectives on the future directions toward better understanding of the catalytic behavior of different metal entities (single atoms, nanoclusters, and nanoparticles) in a unifying manner.

Electrochemical processes on solid shaped nanoparticles with defined facets

This 2007 Chemistry Nobel prize update covers scientific advances of the past decade in our understanding of electrocatalytic processes on surfaces of nanoscale shape-controlled polyhedral solids. It is argued that the field of chemical reaction processes on solid surfaces has recently been paying increasing attention to the fundamental understanding of electrified solid-liquid interfaces and toward the operando study of the minute fraction of catalytically active, structurally dynamic non-equilibrium Taylor-type surface sites. Meanwhile, despite mounting evidence of acting as structural proxies in some cases, the concept of catalytic structure sensitivity of well-defined nanoscale solid surfaces continues to be a key organizing principle for the science of shape-controlled nanocrystals and, hence, constitutes a central recurring theme in this review. After addressing key aspects and recent progress in the wet-chemical synthesis of shaped nanocatalysts, three areas of electrocatalytic processes on solid shape-controlled nanocrystals of current scientific priority are discussed in more detail: the oxygen electroreduction on shape-controlled Pt-Ni polyhedra with its technological relevance for low temperature fuel cells, the CO₂ electroreduction to hydrocarbons on Cu polyhedra and the puzzling interplay between chemical and structural effects, and the electrocatalytic oxygen evolution reaction from water on shaped transition metal oxides. The review closes with the conclusion that Surface Science and thermal catalysis, honored by Ertl's Nobel prize a decade ago, continue to show major repercussions on the emerging field of Interface Science.

Towards the continuous production of Pt-based heterogeneous catalysts using microfluidic systems

The continuous production of Pt-based heterogeneous catalysts based on ultra-small (<2 nm) noble metal nanoparticles deposited on mesoporous ordered silica and their catalytic activity in VOC abatement are here reported. Microfluidic reactors can be used not only to enable the fast and controlled production of ultra-small Pt nanoparticles (NPs), but also alloyed NPs including PtPd, PtRu and PtRh can be formed in short residence times (between 60 s and 5 min). A novel continuous and homogeneous loading of these catalytic NPs on SBA-15 used as a mesoporous support is also here reported. This procedure eases the NP loading and minimizes washing post-treatments. A 12-fold decrease in the synthesis time was obtained when using this microfluidic reactor compared to the traditional batch production of Pt NPs. Microflow and batch type reactors yielded a Pt precursor conversion to generate Pt NPs with a 90% and 85% yield, respectively. Under the same conditions, the productivity of the microfluidic system (27 mg Pt NPs per h) was twice the one achieved in the conventional batch type reactor. The catalytic performance of the supported catalysts separately prepared by microfluidics and by conventional impregnation under the same conditions and with the same noble metal loading was also compared in the n-hexane abatement as a model of VOCs. Both catalysts were active in the VOC oxidation reaction but a 95% reduction in the catalyst synthesis time was obtained when using the catalysts produced in the microfluidic platform. For this reaction a long-term activity test was successfully carried out at 175 °C during 30 h on stream using the heterogeneous catalyst prepared by using the flow reactor.

A critical role of catalyst morphology in low-temperature synthesis of carbon nanotube-transition metal oxide nanocomposite

The effect of the catalyst morphology on the growth of carbon nanotubes (CNT) on nanostructured transition metal oxides was investigated to study a novel low-temperature synthetic route to functional CNT-transition metal oxide nanocomposites. Among several nanostructured manganese oxides with various morphologies and structures, only exfoliated 2D nanosheets of layered MnO₂ acted as an effective catalyst for the chemical vapor deposition of CNT at low temperatures of 400-500 °C, which emphasizes the critical role of the catalyst morphology in CNT growth. Heat treatment of the MnO₂ nanosheets under a C₂H₂ flow induced the deposition of CNT, as well as a phase transition to a 2D ordered assembly of MnO nanoparticles. The resulting CNT-MnO nanocomposites displayed excellent functionalities in Li-ion electrodes with huge discharge capacities and good rate characteristics, which highlights the usefulness of the present method for studying functional CNT-metal oxide nanocomposites. Electron microscopy and density functional theory calculations propose a formation mechanism via the efficient adsorption of carbon on the MnO₂ nanosheets followed by the surface diffusion of carbon. It is of prime importance that the substitution of Fe for layered MnO₂ nanosheets remarkably improved the efficiency of the formation of CNT by enhancing the surface adsorption of carbon species. This is the first report of the efficient growth of CNT at a very low temperature of 400 °C. The universal merit of the 2D nanosheet morphology was confirmed by the successful synthesis of a CNT-TiO₂ nanocomposite with exfoliated titanate nanosheets. The present study demonstrates that employing exfoliated transition metal oxide nanosheets as catalysts provides an efficient low-temperature synthetic route to functional CNT-transition metal oxide nanocomposites.

Facet-mediated growth of silver nanoparticles on biaxial calcium fluoride nanorod arrays

The surface orientation of metal nanoparticles is critical to their physical and chemical properties. This study aims on the understanding of the effect of surface orientation as well as heterogeneous epitaxy of metal nanoparticles at an interface between two materials with a large lattice mismatch. Silver nanoparticles of different diameters were grown on arrays of calcium fluoride (CaF₂) nanorods using oblique angle deposition as a model system for this study. Scanning electron microscopy and transmission electron microscopy (TEM) imaging were used to verify that the nanoparticles were selectively grown on the desired {111} facets of the nanorod tips. Using selected area diffraction and dark field imaging in TEM, it was shown that the nanoparticles were grown at a (111) orientation at the CaF₂ interface with large lattice strains. Thus biaxially textured CaF₂ nanorod arrays can be used as a catalytic support.

Highly active Pd–Ni nanocatalysts supported on multicharged polymer matrix

In this article, we report the synthesis of mono- and bimetallic Pd–Ni nanocomposites supported on a multicharged polymeric matrix for catalytic applications.