Modulating Charges of Dual Sites in Multivariate Metal-Organic Frameworks for Boosting Selective Aerobic Epoxidation of Alkenes

Selective aerobic epoxidation of alkenes without any additives is of great industrial importance but still challenging because the competitive side reactions including C═C bond cleavage and isomerization are difficult to avoid. Here, we show fabricating Cu(I) single sites in pristine multivariate metal-organic frameworks (known as CuCo-MOF-74) via partial reduction of Cu(II) to Cu(I) ions during solvothermal reaction. Impressively, CuCo-MOF-74 is characteristic with single Cu(I), Cu(II), and Co(II) sites, and they exhibit the substantially enhanced selectivity of styrene oxide up to 87.6% using air as an oxidant at almost complete conversion of styrene, ∼25.8% selectivity increased over Co-MOF-74, as well as good catalytic stability. Contrast experiments and theoretical calculation indicate that Cu(I) sites contribute to the substantially enhanced selectivity of epoxides catalyzed by Co(II) sites. The adsorption of two O₂ molecules on dual Co(II) and Cu(I) sites is favorable, and the projected density of state of the Co-3d orbital is closer to the Fermi level by modulating with Cu(I) sites for promoting the activation of O₂ compared with dual-site Cu(II) and Co(II) and Co(II) and Co(II), thus contributing to the epoxidation of the C═C bond. When other kinds of alkenes are used as substrates, the excellent selectivity of various epoxides is also achieved over CuCo-MOF-74. We also prove the universality of fabricating Cu(I) sites in other MOF-74 with various divalent metal nodes.

Recent advanced development of metal-loaded mesoporous organosilicas as catalytic nanoreactors

Ordered periodic mesoporous organosilicas have been widely applied in adsorption/separation/sensor technologies and the fields of biomedicine/biotechnology as well as catalysis. Crucially, surface modification with functional groups and metal complexes or nanoparticle loading has ensured high efficacy and efficiency. This review will highlight the current state of design and catalytic application of transition metal-loaded mesoporous organosilica nanoreactors. It will outline prominent synthesis approaches for the grafting of metal complexes, metal salt adsorption and in situ preparation of metal nanoparticles, and summarize the catalytic performance of the resulting mesoporous organosilica hybrid materials. Finally, the potential prospects and challenges of metal-loaded mesoporous organosilica nanoreactors are addressed.

In Situ Study of the Wet Chemical Etching of SiO2 and Nanoparticle@SiO2 Core-Shell Nanospheres

The recent development of liquid cell (scanning) transmission electron microscopy (LC-(S)TEM) has opened the unique possibility of studying the chemical behavior of nanomaterials down to the nanoscale in a liquid environment. Here, we show that the chemically induced etching of three different types of silica-based silica nanoparticles can be reliably studied at the single particle level using LC-(S)TEM with a negligible effect of the electron beam, and we demonstrate this method by successfully monitoring the formation of silica-based heterogeneous yolk-shell nanostructures. By scrutinizing the influence of electron beam irradiation, we show that the cumulative electron dose on the imaging area plays a crucial role in the observed damage and needs to be considered during experimental design. Monte-Carlo simulations of the electron trajectories during LC-(S)TEM experiments allowed us to relate the cumulative electron dose to the deposited energy on the particles, which was found to significantly alter the silica network under imaging conditions of nanoparticles. We used these optimized LC-(S)TEM imaging conditions to systematically characterize the wet etching of silica and metal(oxide)-silica core-shell nanoparticles with cores of gold and iron oxide, which are representative of many other core-silica-shell systems. The LC-(S)TEM method reliably reproduced the etching patterns of Stöber, water-in-oil reverse microemulsion (WORM), and amino acid-catalyzed silica particles that were reported before in the literature. Furthermore, we directly visualized the formation of yolk-shell structures from the wet etching of Au@Stöber silica and Fe3O4@WORM silica core-shell nanospheres.

Ultrasmall Pd and PtPd nanoparticles for highly efficient catalysis directed by predesigned Morchella-inspired encapsulation

Although bio-inspired designs for ultrasmall metal nanoparticles (NPs) are likely to play an important role in exploring future heterogeneous catalysis materials, synthesizing these structures while retaining surface activity and avoiding aggregation is challenging. Inspired by the Morchella with the spatially and well-organized porous structures, we proposed a biological strategy to yield NPs with ultrasmall and highly dispersed while maintaining high catalytic activity through surfactin self-assembly. Here, multifunctional Morchella-like biological pores (MBP) nanomaterials (~28 nm) with reduction and encapsulation has been synthesized by surfactin self-assembly, then, ultrasmall PtPd (~2.90 nm) and Pd NPs (~2.87 nm) with coordinated sizes and well-dispersed have been successfully reduced and encapsulated inside the MBP. Notably, the synthesis possesses distinct advantages such as mild reaction conditions, strong controllability, good biological compatibility, low-toxicity and environmental friendliness. The as-prepared MBP-encapsulated ultrasmall PtPd and Pd NPs (M@MBP NPs) exhibited excellent catalytic activity and toxicity resistance for the ethanol oxidation reaction (EOR) in KOH, due to the synergistic effect of MBP and ultrasmall metal NPs. The current density of PtPd@MBP and Pd@MBP NPs were 3.35 and 2.72 A mg^-1, respectively. Such MBP synthesized and encapsulated nanoparticles open a new frontier for the design and preparation of NPs for various applications, such as catalysis, bioremediation and drug delivery.

Insight into the dissolution–crystallization strategy towards macro/meso/microporous Silicalite-1 zeolites and their performance in the Beckmann rearrangement of cyclohexanone oxime

A dissolution–crystallization strategy was investigated to synthesize macro/meso/microporous Silicalite-1.

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.

Accelerated catalytic activity of Pd NPs supported on amine-rich silica hollow nanospheres for quinoline hydrogenation

The ultra-small Pd NPs stabilized by the amine-rich silica hollow nanosphere with a TOF as high as 5052 h⁻¹ are among the most active solid catalysts for quinoline hydrogenation. The high catalytic activity could be mainly attributed to the ultra-small particle size and high surface electron density of Pd NPs.

Synthesis of double-shell hollow magnetic Au-loaded ellipsoids as highly active and recoverable nanoreactors

A schematic for the synthesis of double-shell magnetic Au-loaded ellipsoids (Fe@MO₂–Au@H–SiO₂) and the reaction mechanism for the catalytic reduction of 4-NP.

Cu nanoparticles immobilized on montmorillonite by biquaternary ammonium salts: a highly active and stable heterogeneous catalyst for cascade sequence to indole-2-carboxylic esters

Cu-Q-MMT catalyst was prepared by immobilizing Cu nanoparticals on the biquaternary ammonium salts modified montmorillonite and exhibited high activity for cascade sequence to indole-2-carboxylic esters.

Spindle-shaped nanoscale yolk/shell magnetic stirring bars for heterogeneous catalysis in macro- and microscopic systems

A new type of spindle-shaped nanoscale yolk/shell magnetic stirring bar containing noble metal nanoparticles was prepared. The as-synthesized Pd-Fe@meso-SiO2 not only showed impressive activity and stability as a heterogeneous catalyst in a macroscopic flask system, but also acted as an efficient nanoscale magnetic stir bar in a microscopic droplet system.

Mesoporous Au nanotube-constructed three-dimensional films with excellent SERS performance based on the nanofiber template-displacement reaction strategy

Mesoporous Au nanotube-constructed three-dimensional films with excellent SERS performance are fabricated by the nanofiber template-displacement reaction strategy.

Improved catalytic performance of encapsulated Ru nanowires for aqueous-phase Fischer–Tropsch synthesis

Ru–PVP nanowires encapsulated in ethane–silica hollow nanospheres could efficiently and steadily catalyze liquid-phase F–T synthesis with higher activity (activity: 6.35 versus 5.96 mol_CO mol⁻¹_Ru h⁻¹) and selectivity towards oxygenate products (41.3 versus 21.6%) than free Ru–PVP.

Yolk/shell nanoparticles: classifications, synthesis, properties, and applications

Core/shell nanoparticles were first reported in the early 1990s with a simple spherical core and shell structure, but the area is gradually diversifying in multiple directions such as different shapes, multishells, yolk/shell etc., because of the development of different new properties of the materials, which are useful for several advanced applications. Among different sub-areas of core/shell nanoparticles, yolk/shell nanoparticles (YS NPs) have drawn significant attention in recent years because of their unique properties such as low density, large surface area, ease of interior core functionalization, a good molecular loading capacity in the void space, tunable interstitial void space, and a hollow outer shell. The YS NPs have better properties over simple core/shell or hollow NPs in various fields including biomedical, catalysis, sensors, lithium batteries, adsorbents, DSSCs, microwave absorbers etc., mainly because of the presence of free void space, porous hollow shell, and free core surface. This review presents an extensive classification of YS NPs based on their structures and types of materials, along with synthesis strategies, properties, and applications with which one would be able to draw a complete picture of this area.

Ultra-small Au nanoparticles stabilized by silica hollow nanospheres for styrene oxidation with oxygen

Ultra-small Au nanoparticles stabilized by unique silica hollow nanosphere were utilized as efficient solid catalyst for styrene oxidation with oxygen.

The function-led design of Z-scheme photocatalytic systems based on hollow carbon nitride semiconductors

Hollow conjugated polymer nanospheres mimicking thylakoids act as a host scaffold that coassemble with CdS and Au as an electron mediator to construct an artificial Z-scheme photosynthesis system, which shows a highly efficient performance in photocatalytic water-splitting and CO₂reduction reaction under the irradiation of visible light.