Cu-Ag Bimetallic Core-shell Nanoparticles in Pores of a Membrane Microreactor for Enhanced Synergistic Catalysis

In situ confined encapsulation of ultrafine Fe2O3 nanoclusters in N/S co-doped graphene-based membranes for continuous chemical conversion

Membranes with catalytic function can provide an effective approach for simultaneously transforming reactants to industrial chemicals and separation. However, rational design of stable and high-quality catalytic membranes with controlled structure remains a big challenge. We report a strategy for in situ confined encapsulation of ultrafine Fe2O3 nanoclusters in nitrogen and sulfur co-doped graphene-based membranes for continuous chemical conversion. By manipulation of the active ferric catalytic center and surrounding coordination atoms in doped rGO nanosheets, multiple coordination structures were provided to achieve improved catalytic properties. Angstrom-level confined interlayer structure (∼8 Å) was constructed by external pressurization of Fe/NS-rGO nanosheets on membrane substrate, and the adsorption energy of 4-nitrophenol (4-NP) molecule between Fe/NS-rGO layers was much stronger than that in traditional nanometer-level confined space due to extra interactions, achieving the catalytic efficiency with a high Turnover Frequency (TOF) value (1596.0 h-1). The prepared ultrathin Fe/NS-rGO catalytic membrane also exhibited excellent water flux and rejection rate for small dye molecules, as well as long-term separation activity toward naphthol green B (NgB) for at least 130 h. The progress offers a viable route to the rational design of high-quality catalytic membranes with tailored structures and properties for wide applications.

Recent development of substrates for immobilization of bimetallic nanoparticles for wastewater treatment: a review

Bimetallic nanoparticles (BMNPs) have gained considerable attention due to their remarkable catalytic properties, making them invaluable in wastewater treatment applications. One of these challenges lies in the propensity of BMNPs to aggregate due to Van der Waals interactions, which can reduce their overall performance. Additionally, retrieving exhausted NPs from the treated solution for subsequent reuse remains a significant hurdle. Moreover, the leaching of NPs into the discharged wastewater can have harmful effects on humans as well as aquatic life. To overcome these issues, various substrates have been researched to maximize the efficiency and stability of the NPs. This review paper delves into the pivotal role of various substrates in immobilizing BMNPs, providing a comprehensive analysis of their performances, advantages, and drawbacks. The substrates encompass a diverse range of materials, including organic, inorganic, organic-inorganic, beads, fibers, and membranes. Each substrate type offers unique attributes, influencing the stability, efficiency, and recyclability of BMNPs. This review paper aims to provide an up-to-date and detailed analysis and comparison of the substrates used for the immobilization of BMNPs. This work further reviews the underlying mechanisms of the composites involved in treating pollutants from wastewater and how these mechanisms are enhanced by the synergistic effects produced by the substrate and BMNPs. Furthermore, the reusability and sustainability of these composites are discussed. Also, high-performing substrates are highlighted to give direction to future research focusing on the immobilization of BMNPs in the application of wastewater treatment.

Promising biomedical systems based on copper nanoparticles: Synthesis, characterization, and applications

Copper and copper oxide nanoparticles (CuNPs) have unique physicochemical properties that make them highly promising for biomedical applications. This review discusses the application of CuNPs in biomedicine, including diagnosis, therapy, and theranostics. Recent synthesis methods, with an emphasis on green approaches, are described, and the latest techniques for nanoparticle characterization are critically analyzed. CuNPs, including Cu2O, CuO, and Cu, have significant potential as anti-cancer agents, drug delivery systems, and photodynamic therapy enhancers, among other applications. While challenges such as ensuring biocompatibility and stability must be addressed, the state-of-the-art research reviewed here provides strong evidence for the efficacy and versatility of CuNPs. These multifunctional properties have been extensively researched and documented, showcasing the immense potential of CuNPs in biomedicine. Overall, the evidence suggests that CuNPs are a promising avenue for future research and development in biomedicine. We strongly support further progress in the development of synthesis and application strategies to enhance the effectiveness and safety of CuNPs for clinical purposes.

Integrated In Situ Fabrication of CuO Nanorod-Decorated Polymer Membranes for the Catalytic Flow-Through Reduction of p-Nitrophenol

We developed a novel method to fabricate copper nanorods in situ in a poly(ether sulfone) (15 wt %) casting solution by a sonochemical reduction of Cu2+ ions with NaBH4. The main twist is the addition of ethanol to remove excess NaBH4 through Cu(0) catalyzed ethanolysis. This enabled the direct use of the resulting copper-containing casting dispersions for membrane preparation by liquid nonsolvent-induced phase separation and led to full utilization of the copper source, generating zero metal waste. We characterized the copper nanorods as presented in the membranes via scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and UV/vis spectroscopy. We could demonstrate that the rapid immobilization from reducing conditions led to the membrane incorporation of copper nanorods in a state of high reactivity, which also promoted the complete oxidation to CuO after fabrication. We further observed a large aspect ratio and crystal straining of the nanorods, likely resulting from growth around the matrix polymer. The entanglement with poly(ether sulfone) further facilitated a selective presentation at the pore surface of the final CuO-decorated membranes. The membranes also exhibit high water permeances of up to 2800 L/m2hbar. Our catalytic membranes achieved exceptionally high activities in the aqueous flow-through reduction of p-nitrophenol (p-NP), with turnover frequencies of up to 115 h-1, even surpassing those of other state-of-the-art catalytic membranes that incorporate Pd or Ag. Additionally, we demonstrated that catalytic hydrolysis of the reducing agent in water can lead to hydrogen gas formation and blocking of active sites during continuous catalytic p-NP hydrogenation. We illustrated that the accompanying conversion loss can be mitigated by facilitated gas transport in the water-filled pores, which is dependent on the orientation of the pore size gradient and the flow direction.

Novel Capturer-Catalyst Microreactor System with a Polypyrrole/Metal Nanoparticle Composite Incorporated in the Porous Honeycomb-Patterned Film

A composite of polypyrrole/metal nanoparticles (PPy/MNPs) was selectively incorporated into the pores of a honeycomb-patterned porous polycaprolactone polymer film to fabricate a novel capturer-catalyst microreactor system. This fabrication involved a modified breath figure method, where the polymer solution containing metal ions as an oxidizing agent was cast under humid conditions along with the pyrrole monomer through an interfacial reaction in a one-step in situ process. The higher hydrophilicity of the metal ions compared to the polymer solution led to their self-assembly around the pore surface, resulting in the selective incorporation of the PPy/MNP composite into the porous film. Copper (Cu), silver (Ag), and gold (Au) were used for the PPy/MNP fabrication. Various methods characterized the fabricated film. Strong catalytic degradations of methylene blue and methyl orange were obtained with PCL-PPy/MNPs. Recycling experiments showed no loss of activity even after five cycles of recycling. Comparative analysis of PCL-PPy, PCL-MNP, and PCL-PPy/MNP results indicated the synergistic action of PPy and MNPs in dye degradation. High-performance liquid chromatography and mass spectroscopy analyses confirmed dye degradation after treatment with a fabricated microreactor. PPy might have acted as a capturer of the dye molecule and MNPs as a catalyst, thereby enhancing the efficiency of dye degradation. Additionally, the PCL-PPy/Cu composite exhibited strong antimicrobial properties against Gram-positive (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli) with no cytotoxicity as measured by the MTT assay. Therefore, the fabricated microreactor film has promising applications in various fields.

Thermodynamically and Kinetically Stabilized Pt Clusters Against Sintering on CeO2 Nanofibers Through Enclosing CeO2 Nanocubes

Sintering is a major concern for the deactivation of supported metals catalysts, which is driven by the force of decreasing the total surface energy of the entire catalytic system. In this work, a double-confinement strategy is demonstrated to stabilize 2.6 nm-Pt clusters against sintering on electrospun CeO2 nanofibers decorated by CeO2 nanocubes (m-CeO2 ). Thermodynamically, with the aid of CeO2 -nanocubes, the intrinsically irregular surface of polycrystalline CeO2 nanofibers becomes smooth, offering adjacent Pt clusters with decreased chemical potential differences on a relatively uniform surface. Kinetically, the Pt clusters are physically restricted on each facet of CeO2 nanocubes in a nanosized region. In situ high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) observation reveals that the Pt clusters can be stabilized up to 800 °C even in a high density, which is far beyond their Tammann temperature, without observable size growth or migration. Such a sinter-resistant catalytic system is endowed with boosted catalytic activity toward both the hydrogenation of p-nitrophenol after being aged at 500 °C and the sinter-promoting exothermic oxidation reactions (e.g., soot oxidation) at high temperatures over 700 °C. This work offers new opportunities for exploring sinter-resistant nanocatalysts, starting from the rational design of whole catalytic system in terms of thermodynamic and kinetic aspects.

Formation of Core-Shell AuCu@Ag Nanocrystals through the Nanoscale Kirkendall Effect

Polymetallic nanocrystals (NCs) consist of multiple metal elements. A powerful platform to achieve the flexible construction of polymetallic NCs is highly desired but challenging. Herein, we devise a model system that realizes metal atom diffusion between different NCs, resulting in the formation of polymetallic NCs. The differential bond strength between different metal atoms is proposed to initiate such metal atom diffusion, and the specific high surface-to-volume ratio of the NCs can expedite the diffusion process. Taking the Au-Cu-Ag trimetallic system as an example, core-shell AuCu@Ag NCs were successfully formed by combining AgCu NCs with Au NCs. The evolution process was explored, and the gradual fusion of simple NCs into AuCu@Ag NCs was unambiguously observed, which could be attributed to the larger bond strength of Au-Cu than that of Ag-Cu. This work offers an opportunity/platform in theory and experiment to expand the synthesis framework as well as the polymetallic NC list.

NIR-induced improvement of catalytic activity and antibacterial performance over AuAg nanorods in Rambutan-like Fe3O4@AgAu@PDA magnetic nanospheres

Pathogenic bacteria and difficult-to-degrade pollutants in water have been serious problems that always plague people. Therefore, finding a "one stone-two birds" method that can quickly catalyze the degradation of pollutants and show effective antibacterial behavior become an urgent requirement. This work reports a facile one-step strategy for fabricating a Rambutan-like Fe₃O₄@AgAu@PDA (Fe₃O₄@AgAu@Polydopamine) core/shell nanosphere with both catalytic and antibacterial activities which can be critically improved by externally applying an NIR laser irradiation (NIR, 808 nm) and a rotating magnetic field. Typically, the Rambutan-like Fe₃O₄@AgAu@PDA nanosphere have a rather rough surface due to the AuAg bimetallic nanorods sandwiched between the Fe₃O₄ core and the PDA shell. Owing to the penetrated PDA shell, AgAu nanorods show high and magnetically recyclable photothermal-enhanced catalytic activity for the reduction of 4-nitrophenol to 4-aminophenol and they can also be applied to initiate TMB oxidation under the help of NIR heating condition. Moreover, Fe₃O₄@AgAu@PDA shows a moderate antibacterial activity due to the weak release of Ag⁺. Under applying a rotating external magnetic field, the rough-surface Fe₃O₄@AgAu@PDA nanospheres produce a controllable magnetolytic force on the bacterial due to their good affinity. As a result, the Fe₃O₄@AgAu@PDA nanospheres show a "magnetolytic-photothermal-Ag⁺" synergistic antibacterial behavior against E. coli and S. aureus.

Carbonized wood impregnated with bimetallic nanoparticles as a monolithic continuous-flow microreactor for the reduction of 4-nitrophenol

Porous monolithic microreactors show great promise in catalytic applications, but are usually based on non-renewable materials. Herein, we demonstrate a Ni/Au nanoparticle-decorated carbonized wood (Ni/Au-CW) monolithic membrane microreactor for the efficient reduction of 4-nitrophenol. The hierarchical porous wood structure supports uniformly distributed heterobimetallic Ni/Au nanoparticles. As a consequence of these two factors, both mass diffusion and electron transfer are enhanced, resulting in a superior reduction efficiency of 99.5% as the liquor flows through the optimised Ni/Au-CW membrane. The reaction mechanism was investigated by electron paramagnetic resonance spectroscopy and density functional theory calculations. The proposed attraction-repulsion mechanism facilitated by the bimetallic nanoparticles has been ascribed to the different electronegativities of Ni and Au. The Ni/Au-CW membrane exhibits excellent catalytic performance and could be applicable to other catalytic transformations.

Magnetic-Field-Induced Improvement of Photothermal Sterilization Performance by Fe3O4@SiO2@Au/PDA Nanochains

Due to the abuse of antibiotics, the sensitivity of patients to antibiotics is gradually reduced. This work develops a Fe₃O₄@SiO₂@Au/PDA nanochain which shows an interesting magnetic-field-induced improvement of its photothermal antibacterial property. First, SiO₂ was wrapped on Fe₃O₄ nanospheres assembled in a chain to form a Fe₃O₄@SiO₂ nanocomposite with a chain-like nanostructure. Then, the magnetic Fe₃O₄@SiO₂@Au/PDA nanochains were prepared using in situ redox-oxidization polymerization. Under the irradiation of an 808 nm NIR laser, the temperature rise of the Fe₃O₄@SiO₂@Au/PDA nanochain dispersion was obvious, indicating that they possessed a good photothermal effect. Originating from the Fe₃O₄, the Fe₃O₄@SiO₂@Au/PDA nanochain showed a typical soft magnetic behavior. Both the NIR and magnetic field affected the antimicrobial performance of the Fe₃O₄@SiO₂@Au/PDA nanochains. Escherichia coli and Staphylococcus aureus were used as models to verify the antibacterial properties. The experimental results showed that the Fe₃O₄@SiO₂@Au/PDA nanochains exhibited good antibacterial properties under photothermal conditions. After applying a magnetic field, the bactericidal effect was further significantly enhanced. The above results show that the material has a broad application prospect in inhibiting the growth of bacteria.

Catalytic Membrane Nanoreactor with Cu-Agx Bimetallic Nanoparticles Immobilized in Membrane Pores for Enhanced Catalytic Performance

A catalytic membrane nanoreactor (CMNR) with Cu-Ag_x (where x is the millimolar concentration of AgNO₃) bimetallic catalysts immobilized in membrane pores has been fabricated via coupling flowing synthesis and replacement reaction. Surface characterization by transmission electron microscopy (TEM) gives obvious evidence of the formation of Cu-Ag bimetallic core-shell nanostructures with Ag islands deposited on the Cu core metal. An apparent high shift phenomenon for the Cu element and a low shift phenomenon for the Ag element was determined by X-ray photoelectron spectroscopy (XPS), indicating a close interaction with the transfer of electron density from the Cu atom to the Ag atom. The hydrogenation catalysis of p-nitrophenol (p-NP) was tested to evaluate the catalytic performance. During the catalytic process, the Cu core acts as an electron-deficient site to adsorb and activate the -NO₂ group for p-NP, and the Ag shell is beneficial for enhancing active H spilling to the Cu surface and then performing hydrogenation. A volcano-shaped apparent reaction rate constant can be achieved, which rises initially with the increasing Ag content and subsequently drops with a further increase in the Ag content. The highest value of 1071 min^-1 can be achieved for CMNR immobilized with Cu-Ag₂ owing to the suitable adsorption activation behavior and the best hydrogen spillover behavior.