A review of physical, chemical and biological synthesis methods of bimetallic nanoparticles and applications in sensing, water treatment, biomedicine, catalysis and hydrogen storage

This article provides an in-depth analysis of various fabrication methods of bimetallic nanoparticles (BNP), including chemical, biological, and physical techniques. The review explores BNP's diverse uses, from well-known applications such as sensing water treatment and biomedical uses to less-studied areas like breath sensing for diabetes monitoring and hydrogen storage. It cites results from over 1000 researchers worldwide and >300 peer-reviewed articles. Additionally, the article discusses current trends, actionable recommendations, and the importance of synthetic analysis for industry players looking to optimize manufacturing techniques for specific applications. The article also evaluates the pros and cons of various fabrication methods, highlighting the potential of plant extract synthesis for mass production of capped BNPs. However, it warns that this method may not be suitable for certain applications requiring ligand-free surfaces. In contrast, physical methods like laser ablation offer better control and reactivity, especially for applications where ligand-free surfaces are critical. The report underscores the environmental benefits of plant extract synthesis compared to chemical methods that use hazardous chemicals and pose risks to extraction, production, and disposal. The article emphasizes the need for life cycle assessment (LCA) articles in the literature, given the growing volume of research on nanotechnology materials. This article caters to researchers at all stages and applies to various fields applying nanomaterials.

Chameleon Multienvironment Nanoreactors

Nanoreactors consisting of hydrophilic porous SiO₂ shells and amphiphilic copolymer cores have been prepared, which can easily self-tune their hydrophilic/hydrophobic balance depending on the environment and exhibit chameleon-like behavior. The accordingly obtained nanoparticles show excellent colloidal stability in a variety of solvents with different polarity. Most importantly, thanks to the assistance of the nitroxide radicals attached to the amphiphilic copolymers, the synthesized nanoreactors show high catalytic activity for model reactions in both polar and nonpolar environments and, more particularly, realize a high selectivity for the products resulting from the oxidation of benzyl alcohol in toluene.

Yolk-shell smart Pickering nanoreactors for base-free one-pot cascade Knoevenagel-Hydrogenation with high catalytic efficiency in water

In present work, Au@Pd nanoparticles, catalytic active centers, were first implanted in amphiphilic hollow vinyl-pyridyl groups-doped periodic mesoporous organosilica (PMO) shells, and we got yolk–shell smart Pickering Au@Pd@Py-PMO nanoreactors. Two...

Salt of Organosilicon Framework as a Novel Emulsifier for Various Water-Oil Biphasic Systems and a Catalyst for Dibromination of Olefins in an Aqueous Medium

Pickering emulsifiers are significant for organic reactions in an aqueous medium because they have the ability of emulsifying water-oil biphasic systems. For this reason, 2,5-bis[(E)-2-(triethoxysilyl)vinyl]pyridine [BTOSVP] containing a pyridine bridging group was selected as a precursor to prepare a novel salt of organosilicon framework (SOF), an amphiphilic mesoporous pyridine hydrobromide nanosphere. We first synthesized a mesoporous organosilicon framework made up of organic groups containing vinyl groups, pyridine groups, and so forth. Then, hydrobromic acid was added to protonate the pyridine groups in the mesoporous organosilicon framework. Eventually, pyridine hydrobromide salt was formed on the surfaces of channels, and the SOF was successfully prepared for the first time. Pyridine hydrobromide salt can be ionized in water into protonated pyridine cations located on the SOF surfaces and free Br-anions swimming around the protonated pyridine cations because of the electrostatic interaction. In the water-oil biphasic systems, hydrophilicity of SOF originates from the protonated pyridine cations and the lipophilicity of SOF comes from organic groups in the framework; thus, this new kind of SOF can be used as a new generation of solid Pickering emulsifiers. Most importantly, the mesoporous SOF nanosphere can also be used as a catalyst for significantly improved dibromination of olefins in an aqueous medium.

Ultrasmall amphiphilic zeolitic nanoreactors for the aerobic oxidation of alcohols in water

Organic reactors in a green solvent (water) is the goal of sustainable development. Green nanoreactors with excellent amphiphilicity and catalytic activity are strongly desired. Herein, a novel amphiphilic nanoreactor Pd@amZSM-5 with ultrasmall size has been successfully synthesized via a simple one-step oil bath method, subjected to the modification-etching-modification strategy and in situ reduction of Pd2+. Ultrasmall Pd@amZSM-5 nanoreactors (60 nm) with hierarchical structures showed outstanding amphiphilicity for forming Pickering emulsions with fine uniform droplets (50 μm). Fine droplets formed short diffusion distances, which can significantly improve the catalytic activity in biphasic reactions. Moroever, the ultrasmall Pd@amZSM-5 nanoreactors demonstrated excellent catalytic activity for the selective oxidation of alcohols in water using air as the oxidant. Alkali was not present in the reaction system. The hydrophilic aminopropyl groups on the surface of the Pd@amZSM-5 nanoreactors not only changed the affinity of the zeolite surface and provided targeting points for Pd nanoparticles but also provided an alkaline environment for the selective oxidation of alcohols. The ultrasmall Pd@amZSM-5 nanoreactors presented excellent universality for aromatic alcohols (with >90% conversion and >90% selectivity) and allylic alcohols (with 100% conversion and 100% selectivity).

The Isocyanurate-Carbamate-Bridged Hybrid Mesoporous Organosilica: An Exceptional Anchor for Pd Nanoparticles and a Unique Catalyst for Nitroaromatics Reduction

Hybridisation of mesoporous organosilicas (MO) to reinforce the surface capability in adsorption and stabilisation of noble metal nanoparticles is of great attention in generating/supporting noble metal within their matrices and transforming them into efficient heterogeneous catalysts. Here, we used a unique hybrid of organic-inorganic mesoporous silica in which pore profile pattern was similar to the well-known mesoporous silica, SBA-15 for catalysis. This hybrid mesoporous organosilica was further engaged as a support in the synthesis and stabilisation of Pd nanoparticles on its surface, and then, the obtained Pd-supported MO was employed as a heterogeneous green catalyst in the conversion of aqueous p-nitrophenol (PNP) to p-aminophenol (PAP) at room temperature with efficient recyclability.

Eyeball-Like Yolk-Shell Bimetallic Nanoparticles for Synergistic Photodynamic-Photothermal Therapy

Noble metal-based nanomaterials offer great potential as cargoes for multifunctional cancer treatment. In this research, Au eyeball-like nanoparticles (NPs) with open-mouthed Pd shells were synthesized and their surface was functionalized with cell-targeting ligand folic acid (FA) and photodynamic agent Chlorin e6 (Ce6). Due to the broad near-infrared (NIR) absorption band of eyeball-like bimetallic Au and Pd, the photothermal therapy effects of this nanomaterial were studied in MCF-7 cancer cells. The anchored Ce6 not only addressed the hypoxia issue of tumor cells but also exhibited remarkable photodynamic efficacy upon irradiation. Results showed that the obtained Au@Pd-PEG-FA-Ce6 (APPFC) NPs were selectively accumulated at the tumor site and induced cell apoptosis effectively due to the target specificity and synergistic phototherapy effect. The high specificity, desirable biosafety, fast delivery, and drug functionalization demonstrated eyeball-like Au@Pd NPs are promising candidate for multifunctional therapy of breast cancer.

Polyoxometalates encapsulated into hollow double-shelled nanospheres as amphiphilic nanoreactors for an effective oxidative desulfurization

Although some catalytic hollow nanoreactors have been fabricated in the past, the encapsulated active species focus on metal nanoparticles, and a method for polyoxometalate (POM)-containing hollow nanoreactors has seldom been developed. Herein, we report a synthetic strategy towards POM-based amphiphilic nanoreactors, where the hollow mesoporous double-shelled SiO₂@C nanospheres were used to encapsulate Keggin-type H₃PMo₁₂O₄₀ (PMo₁₂). The outer hydrophobic carbon shell was beneficial for the enrichment of the organic substrate around the nanoreactor and simultaneously prevented the deposition of POMs on the outer surface of the nanoreactor. The inner hydrophilic silica cavity was modified by two types of organosilanes, which not only created an amphiphilic cavity environment but also acted as an anchor to mobilize PMo₁₂. As the POM nanoreactor had the hydrophilic@hydrophobic SiO₂@C shell and an amphiphilic cavity, both dibenzothiophene (DBT) and H₂O₂ could smoothly diffuse into the nanosized cavity, where the DBT was effectively oxidized (conversion: >99%) by the immobilized PMo₁₂ under mild conditions. Importantly, the control experiments indicated that the confined effect of nanoreactor, amphiphilic SiO₂@C double-shell, unique cavity environment, and mesoporous channels accounted for an excellent catalytic performance. Moreover, the nanoreactor was robust and could be reused for five cycles without loss of activity.

Mesoporous Silica Nanosheets with Tunable Pore Lengths Supporting Metal Nanoparticles for Enhanced Hydrogenation Reactions

The channel lengths of mesoporous materials have a crucial impact on the catalytic performances of as-loaded active components. However, it remains a challenge to precisely tune the mesochannel length in a wide range from ≤50 nm to 200 nm. In this paper, we developed a top-down strategy, that is to say, crushing hollow microspheres, for preparing mesoporous silica nanosheets (MSSs) with perpendicular mesochannels and tunable thicknesses. Owing to the heterogeneous growth of the mesoporous silica layer on the surfaces of polystyrene microspheres (hard template), it was achieved to regulate the mesochannel length continuously in the range of 20–200 nm. The obtained materials were characterized by X-ray diffraction (XRD), nitrogen sorption, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The effect of channel lengths on the catalytic activity of metal nanoparticles was then investigated in the selective hydrogenation reaction of nitroarenes. It was found that a short channel not only favored dispersing metal nanoparticles uniformly and then avoiding pore blocking, but also improved the accessibility of metal nanoparticles largely during reactions.

An amphiphilic organosilicon framework (AOF): a new solid Pickering catalyst carrier

The amphiphilicity of the AOF carrier originates from the amphiphilic pyridine groups in the frameworks of the nanoparticles.

Janus N-Doped Carbon@Silica Hollow Spheres as Multifunctional Amphiphilic Nanoreactors for Base-Free Aerobic Oxidation of Alcohols in Water

The hydrophobicity/hydrophilicity of nanocatalysts has a significant impact on their performances via modulating the adsorption, transfer, and desorption of reactants/products. In this work, we reported a novel multifunctional amphiphilic nanoreactor composed of Janus nitrogen-doped carbon@silica hollow nanostructure and ultrasmall Pt nanoparticles. The core/shell polybenzoxazine@mesosilica spheres were used as the precursor for pyrolysis. It was found that the internal polybenzoxazine was decomposed from interior to exterior and transformed into a nitrogen-doped carbon hollow shell that partly embedded into the mesosilica layer, forming the Janus hollow spheres. The obtained nanoreactor showed remarkable activity and selectivity for base-free aerobic oxidation of alcohols in water using air as the oxidant. A one-pot oxidation-condensation cascade reaction was also successfully demonstrated to synthesize imines from alcohols and amines with good yields. The sorption analyses revealed that the superior hydrophilicity/hydrophobicity strengthened both adsorption of hydrophobic alcohols from water and desorption of byproduct water molecules from the active sites. The doped nitrogen atoms in the carbon matrix were used not only as anchoring sites for stabilizing ultrasmall Pt nanoparticles but also as basic active sites for accelerating the deprotonation process. Moreover, due to the anchoring effect of nitrogen and the extremely stable amphiphilicity, this nanoreactor exhibited excellent catalytic stability.

Molecular simulations of water adsorption and transport in mesopores with varying hydrophilicity arrangements

The adsorption and transport of water in an open cylindrical mesopore with two different inner surface arrangements of hydrophilicities were examined by molecular simulations. The first model has a weak hydrophilic surface at both entrances of the pore and a stronger hydrophilic surface in the mid-section. The second pore has stronger hydrophilic surfaces at the entrances and weaker in the middle region. The simulation results show that the water adsorption isotherms obtained from Grand Canonical Monte Carlo simulations and pore filling curves acquired from Grand Canonical Molecular Dynamics simulations change depending on the arrangement of the strong and weak hydrophilic surfaces. In the first model, water condensation focuses on the mid-section forming a liquid bridge or a film, which creates a concave meniscus accelerating subsequent adsorption within the pore. Two bridges form in the entrance regions, where a cavity naturally occurs in between the films, in the second model. The different filling and emptying mechanisms clearly change the adsorption-desorption characteristics for the two pore types, but the second type generally showed faster transitions overall. Flux and meniscus analysis also reveals a circulating flow at the menisci of the interfaces within the pore. The results are expected to be valuable in understanding the effects of interior surface modification of nanopores in future applications.

Immobilization of catalytic virus-like particles in a flow reactor

A functional microfluidic reactor is constructed by the immobilization of gold containing virus-based protein cages that catalyze the reduction of nitro-arenes with high efficiency.

Fabrication of Ellipsoidal Silica Yolk-Shell Magnetic Structures with Extremely Stable Au Nanoparticles as Highly Reactive and Recoverable Catalysts

A novel strategy was reported for the fabrication of yolk-shell magnetic MFSVmS-Au nanocomposites (NCs) consisting of double-layered ellipsoidal mesoporous silica shells, numerous sub-4 nm Au nanoparticles (NPs), and magnetic Fe central cores. The hierarchical FSVmS NCs with ellipsoidal α-Fe₂O₃@mSiO₂/mSiO₂ as yolks/shells were first prepared through the facile sol-gel template-assisted method, and plenty of extremely stable ultrafine Au NPs were postencapsulated within interlayer cavities through the unique deposition-precipitation method mediated with Au(en)₂Cl₃ compounds. Notably, ethylenediamine ligands were used to synthesize the stable cationic complexes, [Au(en)₂]³⁺, that readily underwent the deprotonation reaction to chemically modify negatively charged mesoporous silica under alkaline conditions. The subsequent two-stage programmed hydrogen annealing initiated the in situ formation of Au NPs and the reduction of α-Fe₂O₃ to magnetic Fe, where the synthesized Au NPs were highly resistant to harsh thermal sintering even at 700 °C. Given its structural superiority and magnetic nature, the MFSVmS-Au was demonstrated to be a highly efficient and recoverable nanocatalyst with superior activity and reusability toward the reduction of 4-nitrophenol to 4-aminophenol, and the pristine morphology was retained after six recycling tests.

Silver-Free Gold Nanocages with Near-Infrared Extinctions

This article reports the preparation of silver-free Au nanocages from cubic palladium templates. Pd nanocubes were subjected to galvanic replacement with Au³⁺ to produce Pd@Au nanocages having tunable dimensions (i.e., edge length, gold layer thickness, and hollow pore size), which allowed selectable positioning of the optical extinction maxima from the visible to the near infrared. These new nanocages circumvent the problems associated with previous Ag-derived gold alloy nanocages, which suffer from the toxicity of residual silver and the possible fragmentation of such alloyed nanostructures, thereby limiting their potential applications. In contrast, the present materials represent stable, nontoxic, tunable, and hollow plasmonic nanostructures.

Turning the Halide Switch in the Synthesis of Au-Pd Alloy and Core-Shell Nanoicosahedra with Terraced Shells: Performance in Electrochemical and Plasmon-Enhanced Catalysis

Au-Pd nanocrystals are an intriguing system to study the integrated functions of localized surface plasmon resonance (LSPR) and heterogeneous catalysis. Gold is both durable and can harness incident light energy to enhance the catalytic activity of another metal, such as Pd, via the SPR effect in bimetallic nanocrystals. Despite the superior catalytic performance of icosahedral (IH) nanocrystals compared to alternate morphologies, the controlled synthesis of alloy and core-shell IH is still greatly challenged by the disparate reduction rates of metal precursors and lack of continuous epigrowth on multiply twinned boundaries of such surfaces. Herein, we demonstrate a one-step strategy for the controlled growth of monodisperse Au-Pd alloy and core-shell IH with terraced shells by turning an ionic switch between [Br(-)]/[Cl(-)] in the coreduction process. The core-shell IH nanocrystals contain AuPd alloy cores and ultrathin Pd shells (<2 nm). They not only display more than double the activity of the commercial Pd catalysts in ethanol electrooxidation attributed to monatomic step terraces but also show SPR-enhanced conversion of 4-nitrophenol. This strategy holds promise toward the development of alternate bimetallic IH nanocrystals for electrochemical and plasmon-enhanced catalysis.

Macroporous TiO2encapsulated Au@Pd bimetal nanoparticles for the photocatalytic oxidation of alcohols in water under visible-light

A novel macroporous photocatalyst Au@Pd@TiO₂has been reported and showed excellent catalytic activity and stability in the aerobic oxidation of alcohols in water at ambient temperature when using air as the oxidizing agent under visible light irradiation.

Characterisation of gold catalysts

Au-based catalysts have established a new important field of catalysis, revealing specific properties in terms of both high activity and selectivity for many reactions.

Pd(0) encapsulated nanocatalysts as superior catalytic systems for Pd-catalyzed organic transformations

In the last decade, Pd(0) nanoparticles have attracted increasing attention due to their outstanding utility as nanocatalysts in a wide variety of key chemical reactions.