Nanoscale Magnetic Stirring Bars for Heterogeneous Catalysis in Microscopic Systems

ZnS Nanoseeds Sealed in N, P, S Co-Doped Carbon Hollow Rhombic Dodecahedra as a Superlithiophilic Host for Dendrite-Free Lithium Metal Anodes

Lithium (Li) metal is considered a hopeful anode for next-generation Li-ion batteries thanks to its ultra-high theoretical specific capacity, extra-low theoretical density, and low negative potential. However, the uncontrolled growth of Li dendrites and volume fluctuation during plating/stripping processes severely hamper its commercial application. Herein, ZnS seeds sealed in N, P, S co-doped carbon hollow rhombic dodecahedra (ZnS@NPS-C HRD) is fabricated as a superlithiophilic host for Li metal anodes (LMAs) to solve the above problems. In addition, the Li nucleation and deposition mechanism on ZnS@NPS-C HRD is investigated by in situ optical microscopy, ex-situ X-ray diffraction, scanning electron microscopy, and theoretical calculations. Owing to the synergistic strategy of ZnS seeds-inducing nucleation and Li-limited growth, the as-prepared composite exhibits stability for 300 cycles in asymmetric cells and a long lifespan over 1100 h in symmetric cells. Moreover, the ZnS@NPS-C HRD@Li|LiFePO4 full cell demonstrates a reversible capacity of 100.91 mAh g-1 after 400 cycles at 1 C.

Light and Magnetism Orchestrating Aquatic Pollutant-Degradation Robots in Programmable Trajectories

Interfacial floating robots have promising applications in carriers, environmental monitoring, water treatment, and so on. Even though, engineering smart robots with both precisely efficient navigation and elimination of water pollutants in long term remains a challenge, as the superhydrophobicity greatly lowers resistance for aquatic motion while sacrificing chemical reactivity of the surface. Here, a pollutant-removing superhydrophobic robot integrated with well-assembled iron oxide-bismuth sulfide heterojunction composite minerals, which provide both light and magnetic propulsion, and the ability of catalytic degradation, is reported. The motion velocity of the robot reaches up to 51.9 mm s-1 within only 300 ms of acceleration under the orchestration of light, and brakes rapidly (≈200-300 ms) once turn off the light. And magnetism extends the robot to work in broad range of surface tensions in any programmable trajectory. Besides, purification of polluted water is efficiently achieved in situ and the degradation efficiency exhibits eightfold enhancements under the effect of light-triggered photothermal behavior coupled with magnetic induction, overcoming the dilemma of efficient motion with catalytic superhydrophobicity. This strategy developed here provides guidelines for the explorations of high-performance smart devices.

Shaping Liquid Droplets on an Active Air-Ferrofluid Interface

An air-liquid interface is important in many biological and industrial applications, where the manipulation of liquids on the air-liquid interface can have a significant impact. However, current manipulation techniques on the interface are mostly limited to transportation and trapping. Here, we report a magnetic liquid shaping method that can squeeze, rotate, and shape nonmagnetic liquids on an air-ferrofluid interface with programmable deformation. We can control the aspect ratio of the ellipse and generate repeatable quasi-static shapes of a hexadecane oil droplet. We can rotate droplets and stir liquids into spiral-like structures. We can also shape phase-changing liquids and fabricate shape-programmed thin films at the air-ferrofluid interface. The proposed method may potentially open up new possibilities for film fabrication, tissue engineering, and biological experiments that can be carried out at an air-liquid interface.

Design of Raman reporter-embedded magnetic/plasmonic hybrid nanostirrers for reliable microfluidic SERS biosensors

Magnetic-based microfluidic SERS biosensors hold great potential in various biological analyses due to their integrated advantages including easy manipulation, miniaturization and ultrasensitivity. However, it remains challenging to collect reliable SERS nanoprobe signals for quantitative analysis due to the irregular aggregation of magnetic carriers in a microfluidic chamber. Here, magnetic/plasmonic hybrid nanostirrers embedded with a Raman reporter are developed as capture carriers to improve the reliability of microfluidic SERS biosensors. Experimental results revealed that SERS signals from magnetic hybrid nanostirrers could serve as microenvironment beacons of their irregular aggregation, and a signal filtering method was proposed through exploring the relationship between the intensity range of beacons and the signal reproducibility of SERS nanoprobes using interleukin 6 as a model target analyte. Using the signal filtering method, reliable SERS nanoprobe signals with high reproducibility could be picked out from similar microenvironments according to their beacon intensity, and then the influence of irregular aggregation of magnetic carriers on the SERS nanoprobe could be eliminated. The filtered SERS nanoprobe signals also exhibited excellent repeatability from independent tests, which lay a solid foundation for a reliable working curve and subsequent accurate bioassay. This study provides a simple but promising route for reliable microfluidic SERS biosensors, which will further promote their practical application in biological analysis.

Self-Assembly of Magnetic Nanochains in an Intrinsic Magnetic Dipole Force-Dominated Regime

Magnetic nanoparticle chains offer the anisotropic magnetic properties that are often desirable for micro- and nanoscale systems; however, to date, large-scale fabrication of these nanochains is limited by the need for an external magnetic field during the synthesis. In this work, the unique self-assembly of nanoparticles into chains as a result of their intrinsic dipolar interactions only is examined. In particular, it is shown that in a high concentration reaction regime, the dipole-dipole coupling between two neighboring magnetic iron cobalt (FeCo) nanocubes, was significantly strengthened due to small separation between particles and their high magnetic moments. This dipole-dipole interaction enables the independent alignment and synthesis of magnetic FeCo nanochains without the assistance of any templates, surfactants, or even external magnetic field. Furthermore, the precursor concentration ([M] = 0.016, 0.021, 0.032, 0.048, 0.064, and 0.096 m) that dictates the degree of dipole interaction is examined-a property dependent on particle size and inter-particle distance. By varying the spinner speed, it is demonstrated that the balance between magnetic dipole coupling and fluid dynamics can be used to understand the self-assembly process and control the final structural topology from that of dimers to linear chains (with aspect ratio >10:1) and even to branched networks. Simulations unveil the magnetic and fluid force landscapes that determine the individual nanoparticle interactions and provide a general insight into predicting the resulting nanochain morphology. This work uncovers the enormous potential of an intrinsic magnetic dipole-induced assembly, which is expected to open new doors for efficient fabrication of 1D magnetic materials, and the potential for more complex assemblies with further studies.

Self-Healing Polymeric Soft Actuators

Natural evolution has provided multicellular organisms with sophisticated functionalities and repair mechanisms for surviving and preserve their functions after an injury and/or infection. In this context, biological systems have inspired material scientists over decades to design and fabricate both self-healing polymeric materials and soft actuators with remarkable performance. The latter are capable of modifying their shape in response to environmental changes, such as temperature, pH, light, electrical/magnetic field, chemical additives, etc. In this review, we focus on the fusion of both types of materials, affording new systems with the potential to revolutionize almost every aspect of our modern life, from healthcare to environmental remediation and energy. The integration of stimuli-triggered self-healing properties into polymeric soft actuators endow environmental friendliness, cost-saving, enhanced safety, and lifespan of functional materials. We discuss the details of the most remarkable examples of self-healing soft actuators that display a macroscopic movement under specific stimuli. The discussion includes key experimental data, potential limitations, and mechanistic insights. Finally, we include a general table providing at first glance information about the nature of the external stimuli, conditions for self-healing and actuation, key information about the driving forces behind both phenomena, and the most important features of the achieved movement.

Ni-Pd-Incorporated Fe3O4 Yolk-Shelled Nanospheres as Efficient Magnetically Recyclable Catalysts for Reduction of N-Containing Unsaturated Compounds

The use of metal-based heterogeneous catalysts for the degradation of N-containing organic dyes has attracted much attention due to their excellent treatment efficiency and capability. Here, we report the synthesis of heterometals (Ni and Pd)-incorporated Fe3O4 (Ni-Pd/Fe3O4) yolk-shelled nanospheres for the catalytic reduction of N-containing organic dyes using a facile combination of solvothermal treatment and high-temperature annealing steps. Benefiting from the magnetic properties and the yolk-shelled structure of the Fe3O4 support, as well as the uniformly dispersed active heterometals incorporated in the shell and yolk of spherical Fe3O4 nanoparticles, the as-prepared Ni-Pd/Fe3O4 composite shows excellent recyclability and enhanced catalytic activity for three N-containing organic dyes (e.g., 4-nitrophenol, Congo red, and methyl orange) compared with its mono metal counterparts (e.g., Ni/Fe3O4 and Pd/Fe3O4). In the 4-nitrophenol reduction reaction, the catalytic activity of Ni-Pd/Fe3O4 was superior to many Fe3O4-supported nanocatalysts reported within the last five years. This work provides an effective strategy to boost the activity of iron oxide-based catalytic materials via dual or even multiple heterometallic incorporation strategy and sheds new light on environmental catalysis.

Bioinspired construction of magnetic nano stirring rods with radially aligned dual mesopores and intrinsic rapid adsorption of palladium

Quick and precise recovery of palladium (Pd) from electronic waste remains a serious task, owing to the strong acid and complexity of chemical compounds in leachate. Here, bioinspired construction of magnetic nano stirring rod with radially aligned dual mesopores and abundant 8-aminoquinoline (MNSR-DM-AQ) is proposed for selective and rapid extraction of Pd(II) from highly acidic sample solutions. Benefit from the unique dual mesoporous (12.4 nm and 3.6 nm) and the stirring motion under an external magnetic field, MNSR-DM-AQ possesses enhanced adsorption capacity and kinetics, achieving 11.62 mg g^-1 (97.2 % of the maximum adsorption capacity) in 15 min. Distribution coefficient (K_D = 299.0 mL g^-1), separation factor (α above 25.54) and concentration factor (CF = 230.2 mL g^-1) reveal the excellent selectivity of MNSR-DM-AQ towards Pd(II) when comparing with the coexisting ions (Ca(II), Co(II), Cu(II), Fe(II), Mg(II), Ni(II), Pb(II), Zn(II)). The adsorption mechanisms of MNSR-DM-AQ are ion exchange and chelation due to a strong affinity between Pd(II) and N. Meanwhile, 96.82 % of the captured Pd(II) can be easily eluted within 15 min, and the adsorption capacity remains stable after five adsorption-desorption cycles. It is worthwhile to mention that MNSR-DM-AQ exhibits a high adsorption capacity of 8.39 mg g^-1 from leachate of abandoned high-voltage patch capacitor, which is greatly desired in Pd(II) extraction from electronic waste.

Nanozymatic magnetic nanomixers for enzyme immobilization and multiplexed detection of metabolic disease biomarkers

Nanozymes with enzyme-mimicking catalytic activity and unique functions have stimulated increasing interest in the biosensing field. Herein, we report a magnetic nanozyme (MNE) with integrated superior peroxidase-like activity and efficient mixing ability. This nanozymatic magnetic nanomixer is synthesized by depositing a Fe2+-doped polydopamine coating on the surface of well-aligned magnetic nanoparticles to form a rigid chain-like nanostructure. Polydopamine coating of the nanozymatic MNE allows for efficient immobilization of natural enzymes such as glucose oxidase, cholesterol oxidase or urate oxidase to produce a series of enzymes-immobilized MNE (MNE@enzymes) with intrinsic multienzyme cascade properties. These MNE@enzymes show synchronously rotating capability in spinning magnetic fields, which leads to an 80∼100% improvement in their overall catalytic efficiencies. In the on-chip detection of small molecular metabolites (i.e., glucose, cholesterol, and uric acid), the rotating MNE@enzymes lead to detection sensitivities 2.1∼4.3 times higher than those of the static ones. Importantly, the consistent performance of the rotating MNE@enzymes offers the possibility of integrating the detection of glucose, free cholesterol and uric acid into a single multiplexing microchip assay with smartphone readout, affording an improved sensitivity, good selectivity and reliability. The designed enzymes-loaded MNEs holds great promise in developing rapid and ultrasensitive measurements of diverse targets of healthcare concerns using portable devices.

Self-Stirring Microcatalysts: Large-Scale, High-Throughput, and Controllable Preparation and Application

Herein, we introduce a strategy to develop a kind of unprecedented microcatalyst, which owns self-stirring and catalytic performance based on pneumatic printing and magnetic field induction technology. A spindle-shaped microcatalyst based on metal-organic frameworks (MOFs) with a certain aspect ratio and size can be obtained by tuning the printing parameters and the intensity of the magnetic field. One nozzle can print 18 000 microcatalysts per hour, which provides a prerequisite for the realization of large-scale production in the industrial field. Furthermore, this strategy can be widely applied to a variety of other heterogeneous catalysts, such as mesoporous SiO₂, zeolite, metallic oxide, and so on. To demonstrate the superiority of the printed catalyst, the series of printed microcatalysts were evaluated by various catalytic reactions including liquid-phase hydrogenation, microdroplet dye-fading, and photocatalytic degradation in microreactor, all of which exhibited excellent catalytic performance.

Soft Magnetic Microrobot Doped with Porous Silica for Stability-Enhanced Multimodal Locomotion in a Nonideal Environment

As an emerging field of robotics, magnetic-field-controlled soft microrobot has broad application prospects for its flexibility, locomotion diversity, and remote controllability. Magnetic soft microrobots can perform multimodal locomotion under the control of a magnetic field, which may have potential applications in precision medicine. However, previous research studies mainly focus on new locomotion in a relatively ideal environment, lacking exploration on the ability of magnetic microrobot locomotion to resist external disturbances and proceed in a nonideal environment. Here, a porous silica-doped soft magnetic microrobot is constructed for enhanced stability of multimodal locomotion in the nonideal biological environment. Porous silica spheres are doped into a NdFeB-silicone elastomer base, improving adhesion properties and refining the comprehensive mechanical properties of the microrobot. Multimodal locomotions are achieved, and the influence of porous silica doping on the stability of each locomotion in a nonideal environment is explored in depth. Motions in nonideal circumstances such as climbing, loading, current rushing, wind blowing, and obstacle hindering are conducted successfully with porous silica doping. Such a stability-enhanced multimodal locomotion system can be used in biocatalysis and thrombus removal, and its prospect for precision medicine is highlighted by in vivo demonstration of multimodal locomotion with nonideal disturbance.

Integration of Palladium Nanoparticles with Surface Engineered Metal-Organic Frameworks for Cell-Selective Bioorthogonal Catalysis and Protein Activity Regulation

Bioorthogonal catalysis provides a powerful tool to perform non-natural chemical reactions in living systems to dissect complex intracellular processes. Its potency to precisely regulate cellular function, however, is limited by the lack of bioorthogonal catalysts with cell selectivity. Herein, we report that palladium nanoparticles deposited on metal-organic frameworks, Pd@UiO-66, are highly efficient for intracellular bioorthogonal catalysis. In addition, introducing a cancer cell-targeting aptamer, AS1411, onto Pd@UiO-66 enables a threefold enhancement of catalysis efficiency in cancer cells. Moreover, AS1411@Pd@UiO-66 is effective in activating chemically caged 4-hydroxytamoxifen to regulate the activity of a protein destabilizing domain, ER50, and therefore protein function selectively in cancer cells. We show that the control over the activity of a bacterial effector, OspF, using AS1411@Pd@UiO-66 inactivates mitogen-activated protein kinase (MAPK) signaling of cancer cells to selectively prohibit tumor cell growth. We believe that the strategy developed herein for cell-selective bioorthogonal catalysis can expand the chemical biology toolbox for spatiotemporal control of protein function for advanced therapeutic applications.

Bioinspired Magnetic Nanochains for Medicine

Superparamagnetic iron oxide nanoparticles (SPIONs) have been widely used for medicine, both in therapy and diagnosis. Their guided assembly into anisotropic structures, such as nanochains, has recently opened new research avenues; for instance, targeted drug delivery. Interestingly, magnetic nanochains do occur in nature, and they are thought to be involved in the navigation and geographic orientation of a variety of animals and bacteria, although many open questions on their formation and functioning remain. In this review, we will analyze what is known about the natural formation of magnetic nanochains, as well as the synthetic protocols to produce them in the laboratory, to conclude with an overview of medical applications and an outlook on future opportunities in this exciting research field.

Reversible filtration redox of methylene blue in dimethylsulfoxide by manganese oxide loaded carbonaceous nanofibrous membrane through Fenton-like oxidation

The reversible redox of methylene blue in organic solvents was highly attractive, yet was rarely reported. In this study, we realized the continuous filtration redox of methylene blue (MB) in dimethylsulfoxide (DMSO) through Fenton-like oxidization by using MnO₂ loaded carbonaceous nanofibrous membrane (cPAN-MnO₂). The carbonaceous nanofibrous membrane (cPAN) was fabricated through electrospun of polyacrylonitrile and subsequent carbonization. The obtained cPAN nanofibrous membrane showed excellent stability in polar DMSO. MnO₂ can be readily coated on cPAN nanofibers through an in situ redox reaction between cPAN and potassium permanganate. The fabricated cPAN-MnO₂ membrane exhibited instantaneous reduction property towards MB in DMSO during a gravity-driven continuous filtration process. Interestingly, MB reduction was initiated by a typical Fenton-like oxidization, where hydroxyl radicals were firstly generated from hydrogen peroxide catalyzed by MnO₂ in DMSO. Then hydroxyl radicals attacked DMSO to further produce methyl radicals, which resulted in the reduction of MB. In addition, MB reduction process in DMSO was reversible. Our study provides a novel strategy for continuous redox of MB in polar organic solvent and might give new ideas for MB applications.

Metallically gradated silicon nanowire and palladium nanoparticle composites as robust hydrogenation catalysts

Heterogeneous catalysis of alkenes to alkanes is of great importance in chemical industry, but more efficient and reusable heterogeneous catalysts are still demanded. Here, we report a metallically gradated composite of a silicon nanowire array and palladium nanoparticles which are reused for the hydrogenation of an alkene. The catalyst promotes the hydrogenation of stilbene with atmospheric hydrogen (0.1 MPa) to give diphenylethane quantitatively. The recovered catalyst can be reused, and mediates the reaction without loss of yield more than one hundred times, whereas the stability of Pd/C degrades rapidly over 10 cycles of reuse. The catalyst allows the hydrogenation of a variety of alkenes, including tetra-substituted olefins. Structural investigation reveals that palladium nanoparticles are metallically gradated onto the silicon nanowire array under mild conditions by agglomeration of palladium silicide, as confirmed by XAFS and XPS together with argon-ion sputtering. This means of metal agglomeration immobilization may be applicable to the preparation of a variety of metal nanoparticle catalysts.

Synthesis of Podlike Magnetic Mesoporous Silica Nanochains for Use as Enzyme Support and Nanostirrer in Biocatalysis

Magnetic mesoporous materials have attracted great interest due to their combined property of magnetic nanomaterials and mesoporous materials as well as their potential applications in catalysis, bioenrichment, drug delivery, nanoreactors, etc. In this study, one-dimensional (1D) podlike magnetic mesoporous silica nanochains with tunable hollow space (Fe₃O₄@nSiO₂@void@mSiO₂ nanochain named as podlike 1D magnetic mesoporous silica (PL-MMS) nanochain) are rationally synthesized for the first time through a controlled magnetic-induced interface coassembly approach. The obtained PL-MMS possesses a tunable diameter (300-500 nm), large and perpendicular mesopores (8.2 nm) in the outer shell, a silica-protected magnetic-responsive core, and a high surface area (325 m²/g). Benefiting from the large voids and unique mesopores, these mesoporous nanochains exhibit superior performance in enzyme (lipase with a size of 4.0 nm) immobilization with a high loading capacity of 223 μg/mg, and the immobilized lipase demonstrates enhanced catalytic activity in different pH values and temperatures as well as excellent tolerance of organic solvent.

Synthesis of cube–rod–tube triblock asymmetric nanostructures for enhanced heterogeneous catalysis

A triblock asymmetric nanostructure is fabricated via a sequential growth process, which can be used as an active nano stir bar with accelerated catalytic performance.

Magnetic Actuation Multifunctional Platform Combining Microdroplets Delivery and Stirring

Multifunctional droplets manipulation devices are in urgent need for various laboratory operations such as chemical reaction and biological analysis. However, most current techniques that achieved a controllable droplet transport system mainly rely on passive diffusion for mixing, limiting their practical applications. Here, we develop a magnetic controlled dimple on slippery surface (MCDSS) that enables arbitrary direction or even uphill droplet transport through the synergy between gravitational force and asymmetrical droplet deformation. Further experiments demonstrate that our system could also be used for stirring microdroplets and accelerating the mixing speed by more than one hundred times. In addition, the microstir strategy could help to avoid locally uneven production of precipitation or gas in heterogeneous reactions. This combination of droplet delivery and agitation may have a promising future for application in various fields, for example, laboratory-on-a-chip platforms and microengines.

Fabrication of multifunctional integrated catalysts by decorating confined Ag nanoparticles on magnetic nanostirring bars

Catalysis benefits from biomimetic materials with sophisticated structures because a variety of functions can be integrated into one structure, satisfying the demands of a diverse range of applications. Magnetic catalysts have been widely used in various applications, but the magnetic components are most commonly used for recycling. In this study, we report the fabrication of magnetic nanocatalysts composed of a support of magnetic nanobars and Ag nanoparticles confined between two silica layers. Notably, the catalysts are constructed as nanoscale stirring bars that are able to generate disturbances at this scale. More importantly, the catalysts can be applied in both macro- and micro-systems, effectively addressing the conventional mixing method. The catalysts can then be conveniently separated from the system after use. The performances of magnetic nanoscale catalysts are well maintained through recycling.

Nanoparticle-Encapsulated Hollow Porous Polymeric Nanosphere Frameworks as Highly Active and Tunable Size-Selective Catalysts

We report the use of hyper-cross-linked polymers for synthesis of hollow porous polymeric nanosphere frameworks (HPPNFs) as highly efficient yolk-shell structured catalysts. This approach involves encapsulation of ligand-free metal nanoparticles within the hyper-cross-linked HPPNFs, giving rise to remarkable catalytic activity as well as outstanding reusability toward hydrogenation. By tuning the molecular size of the reactant, we demonstrate intrinsic size selectivity precisely defined by the HPPNF-based catalyst. Because the solvent polarity determines the porosity of the HPPNFs, it provides guidance to design a class of responsive and functional soft materials for use in catalysis technology.

Synthesis of Ni3Si4O10(OH)2 Porous Microspheres as Support of Pd Catalyst for Hydrogenation Reaction

Nickel phyllosilicates have attracted much attention owing to their potential applications in various fields. Herein, Ni₃Si₄O₁₀(OH)₂ porous microspheres (NiSi-PMs) with a diameter of 1.2 to 3.2 μm were successfully fabricated via a urea-assisted hydrothermal method, and subsequently used to prepare supported Pd catalyst. Characterizations of the NiSi-PMs and the obtained catalyst, combined with the catalytic performance for the hydrogenation reaction, are presented and discussed. The BET surface area and pore volume of the NiSi-PMs were 196.2 m² g^-1 and 0.70 cm³ g^-1, respectively. The Pd/NiSi-PMs catalyst exhibited remarkable catalytic activity for the hydrogenation of styrene under mild conditions, with a turnover frequency of 5234 h^-1, and the catalyst was recovered and recycled for six consecutive cycles without any discernible loss of activity. H₂-TPR and H₂-TPD revealed that the activity of the catalysts was closely related to the adsorption property for hydrogen. The present Ni₃Si₄O₁₀(OH)₂ supported Pd catalyst afforded a promising and competitive candidate for heterogeneous catalysis.

Magnetically-actuated artificial cilium: a simple theoretical model

We propose a theoretical model for a magnetically-actuated artificial cilium in a fluid environment and investigate its dynamical behaviour, using both analytical calculations and numerical simulations. The cilium consists of a spherical soft magnet, a spherical hard magnet, and an elastic spring that connects the two magnetic components. Under a rotating magnetic field, the cilium exhibits a transition from phase-locking at low frequencies to phase-slipping at higher frequencies. We study the dynamics of the magnetic cilium in the vicinity of a wall by incorporating its hydrodynamic influence, and examine the efficiency of the actuated cilium in pumping viscous fluids. This cilium model can be helpful in a variety of applications such as transport and mixing of viscous solutions at small scales and fabricating microswimmers.

Wet-Chemistry Strong Metal-Support Interactions in Titania-Supported Au Catalysts

Classical strong metal-support interactions (SMSI), which play a crucial role in the preparation of supported metal nanoparticle catalysts, is one of the most important concepts in heterogeneous catalysis. The conventional wisdom for construction of classical SMSI involves in redox treatments at high-temperatures by molecular oxygen or hydrogen, sometimes causing sintered metal nanoparticles before SMSI formation. Herein, we report that the aforementioned issue can be effectively avoided by a wet-chemistry methodology. As a typical example, we demonstrate a new concept of wet-chemistry SMSI (wcSMSI) that can be constructed on titania-supported Au nanoparticles (Au/TiO₂-wcSMSI), where the key is to employ a redox interaction between Au^δ+ and Ti³⁺ precursors in aqueous solution. The wcSMSI is evidenced by covering Au nanoparticles with the TiO _x overlayer, electronic interaction between Au and TiO₂, and suppression of CO adsorption on Au nanoparticles. Owing to the wcSMSI, the Au-TiO _x interface with an improved redox property is favorable for oxygen activation, accelerating CO oxidation. In addition, the oxide overlayer efficiently stabilizes the Au nanoparticles, achieving sinter-resistant Au/TiO₂-wcSMSI catalyst in CO oxidation.

An intramolecular relay catalysis strategy for Knoevenagel condensation and 1,3-dipolar cycloaddition domino reactions

A relay catalysis strategy was established by using a bifunctional catalyst which was prepared by immobilization of organic chains containing secondary amine and Cu(ii) complex onto silica-coated nano-Fe₃O₄. The simply prepared nanoparticles acted as efficient, intramolecular relays and magnetically recyclable base-metal bifunctional catalysts for Knoevenagel condensation and 1,3-dipolar cycloaddition domino reactions to prepare 5-substituted 1H-tetrazoles with excellent yields.

A magnetically recoverable bifunctional catalyst was synthesized and effectively used in Knoevenagel condensation and 1,3-dipolar cycloaddition domino reactions.

Metal-Organic-Framework-Derived Co3 S4 Hollow Nanoboxes for the Selective Reduction of Nitroarenes

MOF-derived Co₃ S₄ /CN hollow nanoboxes (CN=nitrogen-doped carbon) was used to catalyze the chemoselective reduction of nitroarenes to anilines under mild reaction conditions with H₂ as the reducing agent. The catalyst provides high conversion efficiencies and selectivities for a variety of nitroarene substrates that contain electron-donating or electron-withdrawing substituents under mild reaction conditions (in methanol at 60 °C). Further, the nanobox inhibits both dehalogenation and vinyl hydrogenation reactions, which are common limitations of state-of-the-art Pd-based catalysts. Because the reactions result in pure aniline products, the need for separation by column chromatography is eliminated. The resulting anilines are easily separated from the methanolic reaction solution in just three simple steps (centrifugation, decantation, and drying). If employed in industrial processes, catalysts of this kind would significantly reduce the amount of waste organic solvent generated and thus satisfy the need for sustainable chemical processes.

Bifunctional nanoscale magnetic chains with high saturation magnetization and catalytic activity

The conventional stirring method cannot be employed for chip-on-lab reactions such as microfluidic and microdroplet reactions as well as nanoscale reactions. Therefore, it is necessary to design a nanoscale magnetic stirrer with a high magnetic response towards the external magnetic field. In this work, one dimentional core@shell structured Fe-Fe₂O₃@poly(cyclotriphosphazene-co-4,4'-sulfonyldiphenol) magnetic nanochains modified by nickel hydroxide (denoted as Fe-Fe₂O₃@PZS@Ni(OH)₂ NCs) as nanoscale magnetic stirrer and recyclable self-mixing nanocatalysts are successfully prepared through three steps: synthesis of Fe-Fe₂O₃ nanochains (NCs) with high saturation magnetization, coating with poly (cyclotriphosphazene-co-4,4'-sulfonyldiphenol) (PZS), and nickel hydroxide's anchoring on the surface of Fe-Fe₂O₃@PZS NCs. The cross-linked polymer PZS is used to protect Fe-Fe₂O₃ NCs from chemical corrosion and as a platform for subsequent immobilization of nickel hydroxide. Characterization results show that the Fe-Fe₂O₃@PZS@Ni(OH)₂ NCs own chainlike structure and high saturation magnetization of 103 emu g^-1 at room temperature, exhibiting high magnetic response to the external rotating magnetic field. In the macro-reaction system for 4-nitrophenol (4-NP) reduction, the as-prepared Fe-Fe₂O₃@PZS@Ni(OH)₂ NCs show an apparent rate constant of about 0.60 min^-1. Furthermore, the Fe-Fe₂O₃@PZS@Ni(OH)₂ catalyst is reused ten times while no obvious loss of catalytic activity was observed. In the micro-reaction system, the Fe-Fe₂O₃@PZS@Ni(OH)₂ NCs also display good magnetic response and favorable catalytic activity for the hydrogenation of methylene blue. These results indicate that the bifunctional Fe-Fe₂O₃@PZS@Ni(OH)₂ NCs with high saturation magnetization have great potential as excellent nanocatalysts and as promising nanoscale magnetic stirrers.

Controllable Synthesis of Multiheteroatoms Co-Doped Hierarchical Porous Carbon Spheres as an Ideal Catalysis Platform

The synthesis of porous carbon spheres with hierarchical porous structures coupled with the doping of heteroatoms is particularly important for advanced applications. In this research, a new route for efficient and controllable synthesis of hierarchical porous carbon spheres co-doped with nitrogen, phosphorus, and sulfur (denoted as NPS-HPCs) was reported. This new approach combines in situ polymerization of hexachlorocyclophosphazene and 4,4'-sulfonyldiphenol with the self-assembly of colloidal silica nanoparticles (SiO₂ NPs). After pyrolysis and subsequent removal of the SiO₂ NPs, the resulting NPS-HPCs possess a high surface area (960 m²/g) as well as homogeneously distributed N, P, and S heteroatoms. The NPS-HPCs are shown to be an ideal support for anchoring highly dispersed and uniformly sized noble metal NPs for heterogeneous catalysis. As a proof of concept, Pd NPs are loaded onto the NPS-HPCs using only methanol as a reductant at room temperature. The prepared Pd/NPS-HPCs are shown to exhibit high activity, excellent stability, and recyclability for hydrogenation of nitroarenes.

A Magnetic-Field Guided Interface Coassembly Approach to Magnetic Mesoporous Silica Nanochains for Osteoclast-Targeted Inhibition and Heterogeneous Nanocatalysis

1D core-shell magnetic materials with mesopores in shell are highly desired for biocatalysis, magnetic bioseparation, and bioenrichment and biosensing because of their unique microstructure and morphology. In this study, 1D magnetic mesoporous silica nanochains (Fe₃ O₄ @nSiO₂ @mSiO₂ nanochain, Magn-MSNCs named as FDUcs-17C) are facilely synthesized via a novel magnetic-field-guided interface coassembly approach in two steps. Fe₃ O₄ particles are coated with nonporous silica in a magnetic field to form 1D Fe₃ O₄ @nSiO₂ nanochains. A further interface coassembly of cetyltrimethylammonium bromide and silica source in water/n-hexane biliquid system leads to 1D Magn-MSNCs with core-shell-shell structure, uniform diameter (≈310 nm), large and perpendicular mesopores (7.3 nm), high surface area (317 m² g^-1 ), and high magnetization (34.9 emu g^-1 ). Under a rotating magnetic field, the nanochains with loaded zoledronate (a medication for treating bone diseases) in the mesopores, show an interesting suppression effect of osteoclasts differentiation, due to their 1D nanostructure that provides a shearing force in dynamic magnetic field to induce sufficient and effective reactions in cells. Moreover, by loading Au nanoparticles in the mesopores, the 1D Fe₃ O₄ @nSiO₂ @mSiO₂ -Au nanochains can service as a catalytically active magnetic nanostirrer for hydrogenation of 4-nitrophenol with high catalytic performance and good magnetic recyclability.

Enhancing reaction rate in a Pickering emulsion system with natural magnetotactic bacteria as nanoscale magnetic stirring bars

Pickering emulsion is emerging as an advanced platform for catalysis because of the large oil/water interface area for reaction and its superior efficiency. How to enhance the mass transportation within the micro-droplets is the biggest obstacle in further improving the efficiency of the Pickering emulsion system. In this study, we propose and solve this problem for the first time using natural magnetotactic bacteria as nanoscale magnetic stirring bars, which can be encapsulated into each micro-droplet and used to stir the solution to accelerate the mass transportation under an external magnet, and thus significantly enhance the reaction rate of Pickering emulsion. Taking the epoxidation of cyclooctene in the Pickering emulsion system as a demonstration, the reaction rate was enhanced three times with nanoscale magnetic stirring bars compared to that of traditional Pickering emulsion, and was even thirty times higher than that of conventional stirrer-driven biphasic systems. We envision that this strategy will bring biphasic reactions with fundamental innovations toward more green, efficient and sustainable chemistry.

Erbium oxide as a novel support for palladium nanocatalysts with strong metal–support interactions: remarkable catalytic performance in hydrogenation reactions

The SMSI effect and strong chemisorption of H₂ on Pd–Er₂O₃ nanocatalysts significantly improve the catalytic performance for the hydrogenation reactions.

Smart construction of palladium@polypyrrole nanocomposite coating on a magnetic support as a highly efficient and recyclable catalyst

Herein is reported a facile and smart approach to fabricating polystyrene/Fe₃O₄/palladium@polypyrrole nanocomposite particles with high catalytic activity and stability for the degradation of methylene blue by NaBH₄.

Oxygen deficient Pr6O11 nanorod supported palladium nanoparticles: highly active nanocatalysts for styrene and 4-nitrophenol hydrogenation reactions

The design and development of highly efficient and long lifetime Pd-based catalysts for hydrogenation reactions have attracted significant research interest over the past few decades. Rational selection of supports for Pd loadings with strong metal-support interaction (SMSI) is beneficial for boosting catalytic activity and stability. In this context, we have developed a facile approach for uniformly immobilizing ultra-small Pd nanoparticles (NPs) with a clean surface on a Pr₆O₁₁ support by a hydrogen thermal reduction method. The hydrogenations of p-nitrophenol and styrene are used as model reactions to evaluate the catalytic efficiency. The results show highly efficient styrene hydrogenation performance under 1 atm H₂ at room temperature with a TOF value as high as 8957.7 h⁻¹, and the rate constant value of p-nitrophenol reduction is 0.0191 s⁻¹. Strong metal-support interaction and good dispersion of Pd nanoparticles, as demonstrated by XPS and HRTEM results, contribute to the excellent hydrogenation performance. Electron paramagnetic resonance (EPR) results suggest the presence of oxygen vacancies in the support, which serve as electron donors and enhance the adsorption and activation of reactants and subsequent conversion into products. Moreover, the catalyst can be recovered and reused up to 10 consecutive cycles without marked loss of activity. Overall, our results indicate that oxygen-deficient Pr₆O₁₁ nanorods (NRs) not only play a role as support but also work as the promoter to substantially boost the catalytic activities for organic transformations, therefore, providing a novel strategy to develop other high-performance nanostructured catalysts for environmental sustainability.

Oxygen-deficient Pd/Pr₆O₁₁ nanocatalysts with strong metal-support interaction exhibit highly efficient styrene and 4-NP hydrogenation reactions performance.

Electrochemical Conversion of Fe3O4 Magnetic Nanoparticles to Electroactive Prussian Blue Analogues for Self-Sacrificial Label Biosensing of Avian Influenza Virus H5N1

A serious impetus always exists to exploit new methods to enrich the prospect of nanomaterials. Here, we report electrochemical conversion (ECC) of magnetic nanoparticles (MNPs) to electroactive Prussian blue (PB) analogues accompanied by three interfacial effects and its exploitation for novel label self-sacrificial biosensing of avian influenza virus H5N1. The ECC method involves a high-potential step to create strong acidic condition by splitting H₂O to release Fe³⁺ from the MNPs, and then a low-potential step leading to the reduction of coexisting K₃Fe(CN)₆ and Fe³⁺ to K₄Fe(CN)₆ and Fe²⁺, respectively, which react to form PB analogues. Unlike conventional solid/liquid electrochemical interfaces that need a supply of reactants by transportation from bulk solution and require additional template to generate porosity, the proposed method introduces MNPs on the electrode surface and makes them natural nanotemplates and nanoconfined sources of reactants. Therefore, the method presents interesting surface templating, generation-confinement, and refreshing effects/modes, which benefit the produced PB with higher porosity and electrochemical activity, and 3 orders of magnitude lower requirement for reactant concentration compared with conventional methods. Based on the ECC methods, a sandwich immunosensor is designed for rapid detection of avian influenza virus H5N1 using MNPs as self-sacrificial labels to produce PB for signal amplification. Taking full advantages of the high abundance of Fe in MNPs and three surface effects, the ECC method endows the biosensing technology with high sensitivity and a limit of detection down to 0.0022 hemagglutination units, which is better than those of most reported analogues. The ECC method may lead to a new direction for application of nanomaterials and new electrochemistry modes.

Highly dispersed ultra-small Pd nanoparticles on gadolinium hydroxide nanorods for efficient hydrogenation reactions

Heterogeneous catalytic hydrogenation reactions are of great importance to the petrochemical industry and fine chemical synthesis. Herein, we present the first example of gadolinium hydroxide (Gd(OH)₃) nanorods as a support for loading ultra-small Pd nanoparticles for hydrogenation reactions. Gd(OH)₃ possesses a large number of hydroxyl groups on the surface, which act as an ideal support for good dispersion of Pd nanoparticles. Gd(OH)₃ nanorods are prepared by hydrothermal treatment, and Pd/Gd(OH)₃ catalyst with a low loading of 0.95 wt% Pd is obtained by photochemical deposition. The catalytic hydrogenation of p-nitrophenol (4-NP) to p-aminophenol (4-AP) and styrene to ethylbenzene is performed as a model reaction. The obtained Pd/Gd(OH)₃ catalyst displays excellent activity as compared to other reported heterogeneous catalysts. The rate constant of 4-NP reduction is measured to be 0.047 s^-1 and the Pd/Gd(OH)₃ nanocatalyst shows no marked loss of activity even after 10 consecutive cycles. Additionally, the hydrogenation of styrene to ethylbenzene over Pd/Gd(OH)₃ nanorods exhibits a turnover frequency (TOF) as high as 6159 h^-1 with 100% selectivity. Moreover, the catalyst can be recovered by centrifugation and recycled for up to 5 consecutive cycles without obvious loss of activity. Our results indicate that Gd(OH)₃ nanorods act as a promoter to enhance the catalytic activity by providing a synergistic effect from the strong metal support interaction and the large surface area for high dispersion of small sized Pd nanoparticles enriched with hydroxyl groups on the surface. The high performance of Pd/Gd(OH)₃ in heterogeneous catalysis offers a new, efficient and facile strategy to explore other metal hydroxides or oxides as supports for organic transformations.