Controlled Synthesis of Palladium Nanoparticles with Size-Dependent Catalytic Activities Enabled by Organic Molecular Cages

Isomorphous Substitution of Organic Cage Crystal by Pd Nanoclusters for Selective Hydrogenation

For supporting active metal, the cavity confinement and mass transfer facilitation lie not in one sack, a trade-off between high activity and good stability of the catalyst is present. Porous organic cages (POCs) are expected to break the trade-off when metal particles are properly loaded. Herein, three organic cages (CC3, RCC3, and FT-RCC3) are employed to support Pd nanoclusters for catalytic hydrogenation. Subnanometer Pd clusters locate differently in different cage frameworks by using the same reverse double-solvents approach. Compared with those encapsulated in the intrinsic cavity of RCC3 and anchored on the outer surface of CC3, the Pd nanoclusters orderly assembled in FT-RCC3 crystal via isomorphous substitution exhibit superior activity, high selectivity, and good stability for semi-hydrogenation of phenylacetylene. Isomorphous substitution of FT-RCC3 crystal by Pd nanoclusters is originated from high crystallization capacity of FT-RCC3 and specific interaction of each Pd nanocluster with four cage windows. Both confinement function and H2 accumulation capacity of FT-RCC3 are fully utilized to support active Pd nanoclusters for efficient selective hydrogenation. The present results provide a new perspective to the heterogeneous catalysis field in terms of crystalizing metal nanoclusters in POC framework and outside the cage for making the best use of both parts.

Advances in Matrix-Supported Palladium Nanocatalysts for Water Treatment

Advanced catalysts are crucial for a wide range of chemical, pharmaceutical, energy, and environmental applications. They can reduce energy barriers and increase reaction rates for desirable transformations, making many critical large-scale processes feasible, eco-friendly, energy-efficient, and affordable. Advances in nanotechnology have ushered in a new era for heterogeneous catalysis. Nanoscale catalytic materials are known to surpass their conventional macro-sized counterparts in performance and precision, owing it to their ultra-high surface activities and unique size-dependent quantum properties. In water treatment, nanocatalysts can offer significant promise for novel and ecofriendly pollutant degradation technologies that can be tailored for customer-specific needs. In particular, nano-palladium catalysts have shown promise in degrading larger molecules, making them attractive for mitigating emerging contaminants. However, the applicability of nanomaterials, including nanocatalysts, in practical deployable and ecofriendly devices, is severely limited due to their easy proliferation into the service environment, which raises concerns of toxicity, material retrieval, reusability, and related cost and safety issues. To overcome this limitation, matrix-supported hybrid nanostructures, where nanocatalysts are integrated with other solids for stability and durability, can be employed. The interaction between the support and nanocatalysts becomes important in these materials and needs to be well investigated to better understand their physical, chemical, and catalytic behavior. This review paper presents an overview of recent studies on matrix-supported Pd-nanocatalysts and highlights some of the novel emerging concepts. The focus is on suitable approaches to integrate nanocatalysts in water treatment applications to mitigate emerging contaminants including halogenated molecules. The state-of-the-art supports for palladium nanocatalysts that can be deployed in water treatment systems are reviewed. In addition, research opportunities are emphasized to design robust, reusable, and ecofriendly nanocatalyst architecture.

Cage-Confinement Induced Emission Enhancement

As a proof-of-concept study, Imi-cage and Phos-cage organic molecular cages (OMCs) containing the triphenylphosphine (TPP) moiety, a nonclassic AIE luminogen (AIEgen), have been designed to demonstrate the cage-confinement induced emission enhancement (CCIEE). Thanks to the confinement effect of OMCs, the rigid Imi-cage exhibits much higher photoluminescence (PL) quantum yield (Φ_PL) than the open-shell Semicage and small molecule TPP in both solution and amorphous solid states. The emission of Phos-cage could be further enhanced in crystalline solid state with a remarkably high Φ_PL of 97.6% (vs 3.47% of crystalline TPP) benefiting from AIE enabled by the highly ordered molecular packing. The novel strategy of CCIEE via confining an AIEgen into an OMC to achieve a significant emission enhancement will shed light on the development of solid-state highly fluorescent materials. The fluorescent nature of Imi-cage was further exploited for the ultrahighly sensitive detection of the explosive picric acid.

Encapsulation of Metal Clusters within Porous Organic Materials: From Synthesis to Catalysis Applications

Metal clusters (MCs) with dimensions between a single metal atom and nanoparticles of >2 nm usually possess distinct geometric and electronic structures, their outstanding performance in catalysis applications have underpinned a broad research interest. However, smaller-sized MCs are easily deactivated by migration coalescence during the catalysis process because of their high surface energy. Therefore, the search of an appropriate stabilizer for MCs is urgently demanded. In recent years, porous organic polymers (POPs) and organic molecular cages (OMCs), as emerging functional materials, have attracted significant attention. Benefiting from the spatial confinement, encapsulating MCs into these porous organic materials is a promising approach to guarantee the uniform size distribution and stability. In this review, we aim to provide a comprehensive summary of the recent progress in the synthetic strategies and catalysis applications of the encapsulated MCs, and seek to uncover promising ideas that can stimulate future developments at both the fundamental and applied levels.