Maximizing the Catalytic Activity of Nanoparticles through Monolayer Assembly on Nitrogen‐Doped Graphene

Highly Ordered Nanoassemblies of Janus Spherocylindrical Nanoparticles Adhering to Lipid Vesicles

In recent years, there has been a heightened interest in the self-assembly of nanoparticles (NPs) that is mediated by their adsorption onto lipid membranes. The interplay between the adhesive energy of NPs on a lipid membrane and the membrane's curvature energy causes it to wrap around the NPs. This results in an interesting membrane curvature-mediated interaction, which can lead to the self-assembly of NPs on lipid membranes. Recent studies have demonstrated that Janus spherical NPs, which adhere to lipid vesicles, can self-assemble into well-ordered nanoclusters with various geometries, including a few Platonic solids. The present study explores the additional effect of geometric anisotropy on the self-assembly of Janus NPs on lipid vesicles. Specifically, the current study utilized extensive molecular dynamics simulations to investigate the arrangement of Janus spherocylindrical NPs on lipid vesicles. We found that the additional geometric anisotropy significantly expands the range of NPs' self-assemblies on lipid vesicles. The specific geometries of the resulting nanoclusters depend on several factors, including the number of Janus spherocylindrical NPs adhering to the vesicle and their aspect ratio. The lipid membrane-mediated self-assembly of NPs, demonstrated by this work, provides an alternative cost-effective route for fabricating highly engineered nanoclusters in three dimensions. Such structures, with the current wide range of material choices, have great potential for advanced applications, including biosensing, bioimaging, drug delivery, nanomechanics, and nanophotonics.

Nanoparticles insertion and dimerization in polymer brushes

Molecular dynamics simulations are conducted to systematically investigate the insertion of spherical nanoparticles (NPs) in polymer brushes as a function of their size, strength of their interaction with the polymers, polymer grafting density, and polymer chain length. For attractive interactions between the NPs and the polymers, the depth of NPs' penetration in the brush results from a competition between the enthalpic gain due to the favorable polymer-NP interaction and the effect of osmotic pressure resulting from displaced polymers by the NP's volume. A large number of simulations show that the average depth of the NPs increases by increasing the strength of the interaction strength. However, it decreases by increasing the NPs' diameter or increasing the polymer grafting density. While the NPs' effect on the polymer density is local, their effect on their conformations is long-ranged and extends laterally over length scales larger than the NP's size. This effect is manifested by the emergence of laterally damped oscillations in the normal component of the chains' radius of gyration. Interestingly, we found that for high enough interaction strength, two NPs dimerize in the polymer brush. The dimer is parallel to the substrate if the NPs' depth in the brush is shallow. However, the dimer is perpendicular to the substrate if the NPs' are deep in the brush. These results imply that polymer brushes can be used as a tool to localize and self-assemble NPs in polymer brushes.

Enabling Pd Catalytic Selectivity via Engineering Intermetallic Core@Shell Structure

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-NO2 and allows one-pot tandem hydrogenation of Ar-NO2 to Ar-NH2 and 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-NO2 more 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.

Non-close-packed hexagonal self-assembly of Janus nanoparticles on planar membranes

The adhesion modes of an ensemble of spherical Janus nanoparticles on planar membranes are investigated through large-scale molecular dynamics simulations of a coarse-grained implicit-solvent model. We found that the Janus nanoparticles adhering to planar membranes exhibit a rich phase behavior that depends on their adhesion energy density and areal number density. In particular, effective repulsive membrane-curvature-mediated interactions between the Janus nanoparticles lead to their self-assembly into an ordered hexagonal superlattice at intermediate densities and intermediate to high adhesion energy density, with a lattice constant determined by their areal density. The melting behavior of the hexagonal superlattice proceeds through a two-stage melting scenario in agreement with the Kosterlitz-Thouless-Halperin-Nelson-Young classical theory of two-dimensional melting.

Recent Advances and Perspectives on Supported Catalysts for Heterogeneous Hydrogen Production from Ammonia Borane

Ammonia borane (AB), a liquid hydrogen storage material, has attracted increasing attention for hydrogen utilization because of its high hydrogen content. However, the slow kinetics of AB hydrolysis and the indefinite catalytic mechanism remain significant problems for its large-scale practical application. Thus, the development of efficient AB hydrolysis catalysts and the determination of their catalytic mechanisms are significant and urgent. A summary of the preparation process and structural characteristics of various supported catalysts is presented in this paper, including graphite, metal-organic frameworks (MOFs), metal oxides, carbon nitride (CN), molybdenum carbide (MoC), carbon nanotubes (CNTs), boron nitride (h-BN), zeolites, carbon dots (CDs), and metal carbide and nitride (MXene). In addition, the relationship between the electronic structure and catalytic performance is discussed to ascertain the actual active sites in the catalytic process. The mechanism of AB hydrolysis catalysis is systematically discussed, and possible catalytic paths are summarized to provide theoretical considerations for the designing of efficient AB hydrolysis catalysts. Furthermore, three methods for stimulating AB from dehydrogenation by-products and the design of possible hydrogen product-regeneration systems are summarized. Finally, the remaining challenges and future research directions for the effective development of AB catalysts are discussed.

Lipid vesicles induced ordered nanoassemblies of Janus nanoparticles

Since many advanced applications require specific assemblies of nanoparticles (NPs), considerable efforts have been made to fabricate nanoassemblies with specific geometries. Although nanoassemblies can be fabricated through top-down approaches, recent advances show that intricate nanoassemblies can also be obtained through self-assembly, mediated for example by DNA strands. Here, we show, through extensive molecular dynamics simulations, that highly ordered self-assemblies of NPs can be mediated by their adhesion to lipid vesicles (LVs). Specifically, Janus NPs are considered so that the amount by which they are wrapped by the LV is controlled. The specific geometry of the nanoassembly is the result of effective curvature-mediated repulsion between the NPs and the number of NPs adhering to the LV. The NPs are arranged on the LV into polyhedra which satisfy the upper limit of Euler's polyhedral formula, including several deltahedra and three Platonic solids, corresponding to the tetrahedron, octahedron, and icosahedron.

Interfacial Colloidal Self-Assembly for Functional Materials

ConspectusSelf-assembly bridges nanoscale and microscale colloidal particles into macroscale functional materials. In particular, self-assembly processes occurring at the liquid/liquid or solid/liquid/air interfaces hold great promise in constructing large-scale two- or three-dimensional (2D or 3D) architectures. Interaction of colloidal particles in the assemblies leads to emergent collective properties not found in individual building blocks, offering a much larger parameter space to tune the material properties. Interfacial self-assembly methods are rapid, cost-effective, scalable, and compatible with existing fabrication technologies, thus promoting widespread interest in a broad range of research fields.Surface chemistry of nanoparticles plays a predominant role in driving the self-assembly of nanoparticles at water/oil interfaces. Amphiphilic nanoparticles coated with mixed polymer brushes or mussel-inspired polydopamine were demonstrated to self-assemble into closely packed thin films, enabling diverse applications from electrochemical sensors and catalysis to surface-enhanced optical properties. Interfacial assemblies of amphiphilic gold nanoparticles were integrated with graphene paper to obtain flexible electrodes in a modular approach. The robust, biocompatible electrodes with exceptional electrocatalytic activities showed excellent sensitivity and reproducibility in biosensing. Recyclable catalysts were prepared by transferring monolayer assemblies of polydopamine-coated nanocatalysts to both hydrophilic and hydrophobic substrates. The immobilized catalysts were easily recovered and recycled without loss of catalytic activity. Plasmonic nanoparticles were self-assembled into a plasmonic substrate for surface-enhanced Raman scattering, metal-enhanced fluorescence, and modulated fluorescence resonance energy transfer (FRET). Strong Raman enhancement was accomplished by rationally directing the Raman probes to the electromagnetic hotspots. Optimal enhancement of fluorescence and FRET was realized by precisely controlling the spacing between the metal surface and the fluorophores and tuning the surface plasmon resonance wavelength of the self-assembled substrate to match the optical properties of the fluorescent dye.At liquid/solid interfaces, infiltration-assisted (IFAST) colloidal self-assembly introduces liquid infiltration in the substrate as a new factor to control the degree of order of the colloidal assemblies. The strong infiltration flow leads to the formation of amorphous colloidal arrays that display noniridescent structural colors. This method is compatible with a broad range of colloidal particle inks, and any solid substrate that is permeable to dispersing liquids but particle-excluding is suitable for IFAST colloidal assembly. Therefore, the IFAST technology offers rapid, scalable fabrication of structural color patterns of diverse colloidal particles with full-spectrum coverage and unprecedented flexibility. Metal-organic framework particles with either spherical or polyhedral morphology were used as ink particles in the Mayer rod coating on wettability patterned photopapers, leading to amorphous photonic structures with vapor-responsive colors. Anticounterfeiting labels have also been developed based on the complex optical features encoded in the photonic structures.Interfacial colloidal self-assembly at the water/oil interface and IFAST assembly at the solid/liquid/air interface have proven to be versatile fabrication platforms to produce functional materials with well-defined properties for diverse applications. These platform technologies are promising in the manufacturing of value-added functional materials.

Membrane-mediated dimerization of spherocylindrical nanoparticles

We present a numerical investigation of the modes of adhesion and endocytosis of two spherocylindrical nanoparticles (SCNPs) on planar and tensionless lipid membranes, using systematic molecular dynamics simulations of an implicit-solvent model, with varying values of the SCNPs' adhesion strength and dimensions. We found that at weak values of the adhesion energy per unit of area, ξ, the SCNPs are monomeric and adhere to the membrane in the parallel mode. As ξ is slightly increased, the SCNPs dimerize into wedged dimers, with an obtuse angle between their major axes that decreases with increasing ξ. However, as ξ is further increased, we found that the final adhesion state of the two SCNPs is strongly affected by the initial distance, d₀, between their centers of mass, upon their adhesion. Namely, the SCNPs dimerize into wedged dimers, with an acute angle between their major axes, if d₀ is relatively small. However, for relatively high d₀, they adhere individually to the membrane in the monomeric normal mode. For even higher values of ξ and small values of d₀, the SCNPs cluster into tubular dimers. However, they remain monomeric if d₀ is high. Finally, the SCNPs endocytose either as a tubular dimer, if d₀ is low or as monomers for large d₀, with the onset value of ξ of dimeric endocytosis being lower than that of monomeric endocytosis. Dimeric endocytosis requires that the SCNPs adhere simultaneously at nearby locations.

2D FeP Nanoframe Superlattices via Space-Confined Topochemical Transformation

Self-assembled nanocrystal superlattices represent an emergent class of designer materials with potentially programmable functionalities. The ability to construct hierarchically structured nanocrystal superlattices with tailored geometry and porosity is critical for extending their applications. Here, 2D superlattices comprising monolayer FeP nanoframes are synthesized through a space-confined topochemical transformation approach induced by the Kirkendall effect, using carbon-coated Fe₃ O₄ nanocube superlattices as a precursor. The particle shape and the close-packed nature of Fe₃ O₄ nanocubes as well as the interconnected carbon layer network contribute to the topochemical transformation process. The resulting 2D FeP nanoframe superlattices possess several unique and advantageous structural features that are unavailable in conventional 3D nanocrystal superlattices, which make them particularly attractive for catalytic applications. As a proof of concept, such 2D FeP nanoframe superlattices are harnessed as highly efficient and durable electrocatalysts for the hydrogen evolution reaction, the performance of which is superior to that of most FeP-based catalysts reported previously. This topochemical transformation approach is scalable and general, representing a new route of designing hierarchical superlattices with highly open features that cannot be accessible by traditional self-assembly methods.

The Hydrogen-Storage Challenge: Nanoparticles for Metal-Catalyzed Ammonia Borane Dehydrogenation

Dihydrogen is one of the sustainable energy vectors envisioned for the future. However, the rapidly reversible and secure storage of large quantities of hydrogen is still a technological and scientific challenge. In this context, this review proposes a recent state-of-the-art on H₂ production capacities from the dehydrogenation reaction of ammonia borane (and selected related amine-boranes) as a safer solid source of H₂ by hydrolysis (or solvolysis), catalyzed by nanoparticle-based systems. The review groups the results according to the transition metals constituting the catalyst with a mention to their current cost and availability. This includes the noble metals Rh, Pd, Pt, Ru, Ag, as well as cheaper Co, Ni, Cu, and Fe. For each element, the monometallic and polymetallic structures are presented and the performances are described in terms of turnover frequency and recyclability. The structure-property links are highlighted whenever possible. It appears from all these works that the mastery of the preparation of catalysts remains a crucial point both in terms of process, and control and understanding of the electronic structures of the elaborated nanomaterials. A particular effort of the scientific community remains to be made in this multidisciplinary field with major societal stakes.

Mechanistic Insight into the Synergetic Interaction of Ammonia Borane and Water on ZIF-67-Derived Co@Porous Carbon for Controlled Generation of Dihydrogen

Regarding dihydrogen as a clean and renewable energy source, ammonia borane (NH₃BH₃, AB) was considered as a chemical H₂-storage and H₂-delivery material due to its high storage capacity of dihydrogen (19.6 wt %) and stability at room temperature. To advance the development of efficient and recyclable catalysts for hydrolytic dehydrogenation of AB with parallel insight into the reaction mechanism, herein, ZIF-67-derived fcc-Co@porous carbon nano/microparticles (cZIF-67_nm/cZIF-67_μm) were explored to promote catalytic dehydrogenation of AB and generation of H_2(g). According to kinetic and computational studies, zero-order dependence on the concentration of AB, first-order dependence on the concentration of cZIF-67_nm (or cZIF-67_μm), and a kinetic isotope effect value of 2.45 (or 2.64) for H₂O/D₂O identify the Co-catalyzed cleavage of the H-OH bond, instead of the H-BH₂NH₃ bond, as the rate-determining step in the hydrolytic dehydrogenation of AB. Despite the absent evolution of H_2(g) in the reaction of cZIF-67 and AB in the organic solvents (i.e., THF or CH₃OH) or in the reaction of cZIF-67 and water, Co-mediated activation of AB and formation of a Co-H intermediate were evidenced by theoretical calculation, infrared spectroscopy in combination with an isotope-labeling experiment, and reactivity study toward CO₂-to-formate/H₂O-to-H₂ conversion. Moreover, the computational study discovers a synergistic interaction between AB and the water cluster (H₂O)₉ on fcc-Co, which shifts the splitting of water into an exergonic process and lowers the thermodynamic barrier for the generation and desorption of H_2(g) from the Co-H intermediates. With the kinetic and mechanistic study of ZIF-67-derived Co@porous carbon for catalytic hydrolysis of AB, the spatiotemporal control on the generation of H_2(g) for the treatment of inflammatory diseases will be further investigated in the near future.

Nanoparticle-Catalyzed Green Chemistry Synthesis of Polybenzoxazole

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 Au₄₂Pd₅₈ NPs, 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.

Recent developments of nanocatalyzed liquid-phase hydrogen generation

Hydrogen is the most effective and sustainable carrier of clean energy, and liquid-phase hydrogen storage materials with high hydrogen content, reversibility and good dehydrogenation kinetics are promising in view of "hydrogen economy". Efficient, low-cost, safe and selective hydrogen generation from chemical storage materials remains challenging, however. In this Review article, an overview of the recent achievements is provided, addressing the topic of nanocatalysis of hydrogen production from liquid-phase hydrogen storage materials including metal-boron hydrides, borane-nitrogen compounds, and liquid organic hydrides. The state-of-the-art catalysts range from high-performance nanocatalysts based on noble and non-noble metal nanoparticles (NPs) to emerging single-atom catalysts. Key aspects that are discussed include insights into the dehydrogenation mechanisms, regenerations from the spent liquid chemical hydrides, and tandem reactions using the in situ generated hydrogen. Finally, challenges, perspectives, and research directions for this area are envisaged.

Atom transfer between precision nanoclusters and polydispersed nanoparticles: a facile route for monodisperse alloy nanoparticles and their superstructures

Reactions between atomically precise noble metal nanoclusters (NCs) have been studied widely in the recent past, but such processes between NCs and plasmonic nanoparticles (NPs) have not been explored earlier. For the first time, we demonstrate spontaneous reactions between an atomically precise NC, Au25(PET)18 (PET = 2-phenylethanethiol), and polydispersed silver NPs with an average diameter of 4 nm and protected with PET, resulting in alloy NPs under ambient conditions. These reactions were specific to the nature of the protecting ligands as no reaction was observed between the Au25(SBB)18 NC (SBB = 4-(tert-butyl)benzyl mercaptan) and the very same silver NPs. The mechanism involves an interparticle exchange of the metal and ligand species where the metal-ligand interface plays a vital role in controlling the reaction. The reaction proceeds through transient Au25-xAgx(PET)n alloy cluster intermediates as observed in time-dependent electrospray ionization mass spectrometry (ESI MS). High-resolution transmission electron microscopy (HRTEM) analysis of the resulting dispersion showed the transformation of polydispersed silver NPs into highly monodisperse gold-silver alloy NPs which assembled to form 2-dimensional superlattices. Using NPs of other average sizes (3 and 8 nm), we demonstrated that size plays an important role in the reactivity as observed in ESI MS and HRTEM.

Recent advances in graphene monolayers growth and their biological applications: A review

Development of two-dimensional high-quality graphene monolayers has recently received great concern owing to their enormous applications in diverging fields including electronics, photonics, composite materials, paints and coatings, energy harvesting and storage, sensors and metrology, and biotechnology. As a result, various groups have successfully developed graphene layers on different substrates by using the chemical vapor deposition method and explored their physical properties. In this direction, we have focused on the state-of-the-art developments in the growth of graphene layers, and their functional applications in biotechnology. The review starts with the introduction, which contains outlines about the graphene and their basic characteristics. A brief history and inherent applications of graphene layers followed by recent developments in growth and properties are described. Then, the application of graphene layers in biodevices is reviewed. Finally, the review is summarized with perspectives and future challenges along with the scope for future technological applications.

Type-II/type-II band alignment to boost spatial charge separation: a case study of g-C3N4 quantum dots/a-TiO2/r-TiO2 for highly efficient photocatalytic hydrogen and oxygen evolution

Efficient spatial charge separation and transfer that are critical factors for solar energy conversion primarily depend on the energetic alignment of the band edges at interfaces in heterojunctions. Herein, we first report that constructing a 0D/0D type-II(T-II)/T-II heterojunction is an effective strategy to ingeniously achieve long-range charge separation by taking a ternary heterojunction of TiO2 and graphitic carbon nitride (g-C3N4) as a proof-of-concept. Incorporating g-C3N4 quantum dots (QCN), as the third component, into the commercial P25 composed of anatase (a-TiO2) and rutile (r-TiO2) can be realized via simply mixing the commercially available Degussa P25 and QCN solution followed by heat treatment. The strong coupling and matching band structures among a-TiO2, r-TiO2 and QCN result in the construction of novel T-II/T-II heterojunctions, which would promote the spatial separation and transfer of photogenerated electrons and holes. Moreover, QCN plays a key role in reinforcing light absorption. Particularly, the unique 0D/0D architecture possesses the advantages of abundant active sites for the photocatalytic reaction. As a result, the optimized QCN/a-TiO2/r-TiO2 heterojunctions exhibit enhanced photocatalytic H2 and O2 evolution, especially the hydrogen evolution rate (49.3 μmol h-1) is 11.7 times that of bare P25 under visible light irradiation, and sufficient catalytic stability as evidenced by the recycling experiments. The remarkably enhanced photocatalytic activity can be attributed to the synergistic effects of the energy level alignment at interfaces, the dimensionality and component of the heterojunctions. This work provides a stepping stone towards the design of novel heterojunctions for photocatalytic water splitting.

Monodisperse nanoparticles for catalysis and nanomedicine

The growth and breadth of nanoparticle (NP) research now encompasses many scientific and technologic fields, which has driven the want to control NP dimensions, structures and properties. Recent advances in NP synthesis, especially in solution phase synthesis, and characterization have made it possible to tune NP sizes and shapes to optimize NP properties for various applications. In this review, we summarize the general concepts of using solution phase chemistry to control NP nucleation and growth for the formation of monodisperse NPs with polyhedral, cubic, octahedral, rod, or wire shapes and complex multicomponent heterostructures. Using some representative examples, we demonstrate how to use these monodisperse NPs to tune and optimize NP catalysis of some important energy conversion reactions, such as the oxygen reduction reaction, electrochemical carbon dioxide reduction, and cascade dehydrogenation/hydrogenation for the formation of functional organic compounds under greener chemical reaction conditions. Monodisperse NPs with controlled surface chemistry, morphologies and magnetic properties also show great potential for use in biomedicine. We highlight how monodisperse iron oxide NPs are made biocompatible and target-specific for biomedical imaging, sensing and therapeutic applications. We intend to provide readers some concrete evidence that monodisperse NPs have been established to serve as successful model systems for understanding structure-property relationships at the nanoscale and further to show great potential for advanced nanotechnological applications.

Competitive self-assembly driven as a route to control the morphology of poly(tannic acid) assemblies

With an attempt to develop some supermolecular assemblies of a particular structure through a controllable method, the present study developed two distinct assembly patterns for Poly(Tannic Acid) (PTA) by means of adjusting the components and composition of a binary solvent system. The assembly mechanism was explored through the comparison of theoretical calculations and experimental results with respect to how solvent sets affect the nature of intermolecular interactions among oligomers. The results indicate that the morphology of the aggregates of PTA is determined from the nature of the intermolecular interactions among oligomers. While a cuboid shaped aggregate is likely the result of π-π stacking self-assembly, a sphere shaped morphology is formed through intermolecular hydrogen bonding among the oligomers. The results of the present work provide valuable resources to tune the aggregation morphology by quantitatively adjusting the physical properties of the binary solvent.

SiO2-Encompassed Co@N-Doped Porous Carbon Assemblies as Recyclable Catalysts for Efficient Hydrolysis of Ammonia Borane

The development of earth-abundant catalysts for efficient hydrolysis of ammonia borane is of great importance in the conversion and utilization of hydrogen energy. Here, we report the synthesis of SiO₂-encompassed Co@N-doped porous carbon assemblies as a new type of recyclable catalyst for the purpose by calcination of zeolitic imidazolate framework-67@SiO₂ microtubes at high temperatures under an N₂ atmosphere. We find that the surface layer of SiO₂ in the precursor microtubes is essential for the production of efficient catalysts by supplying an additional surface for Co nanoparticle dispersion in an effort to reduce their size. In addition, the SiO₂ layer renders a highly ordered arrangement of Co@N-doped porous carbon within the catalysts, possibly allowing the ease of mass transfer of ammonia borane within the catalysts. The optimized catalysts obtained via calcination at 800 °C show a set of remarkable catalytic benefits, including a high hydrogen generation rate of 8.4 mol min^-1 mol_(Co)^-1, a relatively low activation energy of 36.1 kJ mol^-1, and a remarkable reusability (at least 10 times). Our results can provide new insight into the design and synthesis of highly ordered SiO₂-supported catalysts for different reactions.

Ultra-small and recyclable zero-valent iron nanoclusters for rapid and highly efficient catalytic reduction of p-nitrophenol in water

The synthesis of nanoscale zero-valent iron (NZVI) nanoclusters with dimensions ranging from 20 to 100 nm for the control of environmental pollutants has received substantial attention. However, due to the strong van der Waals and magnetic attraction forces of ZVI, synthesizing ZVI nanoclusters with a subnanometre size while retaining their surface activity and avoiding aggregation is challenging. Moreover, NZVI particles can be oxidized easily after the removal of contaminants even in anoxic environments, which makes the recovery and recycling of the particles very difficult. Here, for the first time, ultra-small zero-valent iron (ZVI) nanoclusters are successfully prepared in a micelle assisted method under mild conditions, and can be recycled simply. It is found that by encapsulating Fe3+ within the micelles, controlling the release of sulfur ions (S2-) from thiourea and forming the FeS nanoparticles as intermediates, the ZVI nanoclusters are produced with a precisely controlled size (<1 nm). A large number of zero-valent iron nanoclusters were assembled into quasi-spherical assemblages (with around 5 nm size), in which most of the nanoclusters exist discretely because of being coated by entangled hydrocarbon chains of the surfactant. The ZVI nanoclusters (with a diameter of <1 nm) exhibit excellent dispersibility and accessibility in solution, presenting significantly enhanced catalytic activity in the removal of p-nitrophenol from water. The as-prepared ZVI nanoclusters possess excellent stability and durability with the aid of NaBH4. Their catalytic activity/reusability can be comparable to those of the commonly used noble metal catalysts.

Superfine CoNi alloy embedded in Al2O3 nanosheets for efficient tandem catalytic reduction of nitroaromatic compounds by ammonia borane

Tunable Co_xNi_1−x/Al₂O₃ nanocatalysts have been prepared and used for the efficient tandem catalytic dehydrogenation of ammonia borane and hydrogenation of nitroaromatics.

Nitrogen-doped graphene and graphene quantum dots: A review onsynthesis and applications in energy, sensors and environment

Doping of nitrogen is a promising strategy to modulate chemical, electronic, and structural functionalities of graphene (G)and graphene quantum dots (GQDs) for their outstanding properties in energy and environmental applications.This paper reviews various synthesis approaches of nitrogen-doped graphene (N-G) and nitrogen-doped graphene quantum dots (N-GQDs).;Thermal, ultrasonic, solvothermal, hydrothermal, and electron-beam methods have been applied to synthesize N-G and N-GQDs.These nitrogen-doped carbon materials are characterized to obtain their structural configurations in order to achieve better performance in their applications compared to only either graphene or graphene quantum dots.Both N-G and N-GQDs may be converted into functional materials by integrating with other compounds such as metal oxides/nitrides, polymers, and semiconductors.These functional materials demonstrate superior performance over N-G and N-GQDs materials.Examples of applications of N-G and N-GQDs include supercapacitors, batteries, sensors, fuel cells, solar cells, and photocatalyst.

Graphene Derivative in Magnetically Recoverable Catalyst Determines Catalytic Properties in Transfer Hydrogenation of Nitroarenes to Anilines with 2-Propanol

Here, we report transfer hydrogenation of nitroarenes to aminoarenes using 2-propanol as a hydrogen source and Ag-containing magnetically recoverable catalysts based on partially reduced graphene oxide (pRGO) sheets. X-ray diffraction and X-ray photoelectron spectroscopy data demonstrated that, during the one-pot catalyst synthesis, formation of magnetite nanoparticles (NPs) is accompanied by the reduction of graphene oxide (GO) to pRGO. The formation of Ag⁰ NPs on top of magnetite nanoparticles does not change the pRGO structure. At the same time, the catalyst structure is further modified during the transfer hydrogenation, leading to a noticeable increase of sp² carbons. These carbons are responsible for the adsorption of substrate and intermediates, facilitating a hydrogen transfer from Ag NPs and creating synergy between the components of the catalyst. The nitroarenes with electron withdrawing and electron donating substituents allow for excellent yields of aniline derivatives with high regio and chemoselectivity, indicating that the reaction is not disfavored by these functionalities. The versatility of the catalyst synthetic protocol was demonstrated by a synthesis of an Ru-containing graphene derivative based catalyst, also allowing for efficient transfer hydrogenation. Easy magnetic separation and stable catalyst performance in the transfer hydrogenation make this catalyst promising for future applications.