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

Supramolecular Engineering of Metal-Organic Membranes with Metal-Support Interactions for Nanoconfined Synergistic Catalysis

Continuous-flow nanoconfined catalysis is crucial for rapid and efficient water purification but is challenging for traditional reactors. Supramolecular metal-organic membranes, with their intrinsically rich metal nodes, present promising opportunities for heterogeneous nano-catalysis. However, achieving a uniform distribution and stabilization of exposed metal active sites remains a challenge. Here, a phosphotungstic acid (H3PW12O40: PW12) modulated interfacial coordination strategy is introduced to engineer a thin palladium-1,3,5-triformylphloroglucinol (Pd-Tp) nanofilm. The strong electrostatic-dominated interaction between the fourfold hollow site of PW12 and PdII enables in situ confined reduction, facilitating the enhanced loading and uniform distribution of cluster-shaped Pd-PW12 nanoparticles within the thin layer. The coordination between hydrophilic PW12 and Tp leads to competition with PdCl4 2- during film formation, giving rise to thinner, more hydrophilic, and loose-structured membranes. Importantly, the PCM/NaBH4 system exhibits a superior reducibility and electron transfer capacity, enabling efficient degradation of a range of organic contaminants, attributed to the robust metal-support interactions. The PCM achieves a degradation rate constant of the target pollutant 4-nitrophenol (97.8 ms-1), which is 175 times faster than that of the control HCM (0.56 ms-1). This study highlights the role of phosphotungstic acid in the microstructure modulation of metal-organic membrane and enhanced metal-support interaction for nanoconfined synergistic catalysis.

Tempospatially Confined Catalytic Membranes for Advanced Water Remediation

The application of homogeneous catalysts in water remediation is limited by their excessive chemical and energy input, weak regenerability, and potential leaching. Heterogeneous catalytic membranes (CMs) offer a new approach to facilitate efficient, selective, and continuous pollutant degradation. Thus, integrating membranes and continuous filtration with heterogeneous advanced oxidation processes (AOPs) can promote thermodynamic and kinetic mass transfers in spatially confined intrapores and facilitate diffusion-reaction processes. Despite the remarkable advantages of heterogeneous CMs, their engineering application is practically restricted due to the fuzzy design criteria for specific applications. Herein, the recent advances in CMs for advanced water remediation are critically reviewed and the design flow for tempospatially confined CMs is proposed. Further, state-of-the-art CM materials and their catalytic mechanisms are reviewed, after which the tempospatial confinement mechanisms comprising the nanoconfinement effect, interface effect, and kinetic mass transfer are emphasized, thus clarifying their roles in the construction and performance optimization of CMs. Additionally, the fabrication methods for CMs based on their catalysts and pore sizes are summarized and an overview of their application and performance evaluations is presented. Finally, future directions for CMs in materials research and water treatment, are presented.

3D-Continuous Nanoporous Covalent Framework Membrane Nanoreactors with Quantitatively Loaded Ultrafine Pd Nanocatalysts

The confinement effect of catalytic nanoreactors containing metal catalysts within nanometer-sized volumes has attracted significant attention for their potential to enhance reaction rate and selectivity. Nevertheless, unregulated catalyst loading, aggregation, leaching, and limited reusability remain obstacles to achieving an efficient nanoreactor. A robust and durable catalytic membrane nanoreactor prepared by incorporating palladium nanocatalysts within a 3D-continuous nanoporous covalent framework membrane is presented. The reduction of palladium precursor occurs on the pore surface within 3D nanochannels, producing ultrafine palladium nanoparticles (Pd NPs) with their number density adjustable by varying metal precursor concentrations. The precise catalyst loading enables controlling the catalytic activity of the reactor while preventing excess metal usage. The facile preparation of Pd NP-loaded free-standing membrane materials allows hydrodechlorination in both batch and continuous flow modes. In batch mode, the catalytic activity is proportional to the loaded Pd amount and membrane area, while the membrane retains its activity upon repeated use. In continuous mode, the conversion remains above 95% for over 100 h, with the reactant solution passing through a single 50 µm-thick Pd-loaded membrane. The efficient nanoporous film-type catalytic nanoreactor may find applications in catalytic reactions for small chemical devices as well as in conventional chemistry and processes.