A Highly Efficient and Stable Palladium Catalyst Entrapped within the Cross-Linked Chitosan Membrane for Heck Reactions

In this study, chitosan directly cross-linked by Pd^II cation membranes (Pd-<i>cr</i>-CSM) with good mechanical strength and thermal stabilities have been prepared. Although the prepared Pd-<i>cr</i>-CSM has neither open porous structure nor high specific surface areas, it has similar good catalytic activity and much higher stability as compared with typical prepared chitosan-stabilized palladium heterogeneous catalysts for Heck reactions. It is highly active for the Heck reactions of aryl iodides and bromides with a strong electron-withdrawing group at a palladium catalyst loading of 0.15 mol %. It can be recycled 12 times in dimethyl sulfoxide (DMSO) solution or 7 times in aqueous solution. The high activity and extreme stability of the Pd-<i>cr</i>-CSM catalyst are mainly attributed to the well-entrapped palladium nanoparticles inside the chitosan matrix, which might catalyze the coupling reactions in the free volume holes (open spaces) of the swollen cross-linked chitosan gel networks

Incorporating Zwitterionic Graphene Oxides into Sodium Alginate Membrane for Efficient Water/Alcohol Separation

For the selective water-permeation across dense membrane, constructing continuous pathways with high-density ionic groups are of critical significance for the preferential sorption and diffusion of water molecules. In this study, zwitterionic graphene oxides (PSBMA@GO) nanosheets were prepared and incorporated into sodium alginate (SA) membrane for efficient water permeation and water/alcohol separation. The two-dimensional GO provides continuous pathway, while the high-density zwitterionic groups on GO confer electrostatic interaction sites with water molecules, leading to high water affinity and ethanol repellency. The simultaneous optimization of the physical and chemical structures of water transport pathway on zwitterionic GO surface endows the membrane with high-efficiency water permeation. Using dehydration of water/alcohol mixture as the model system, the nanohybrid membranes incorporating PSBMA@GO exhibit much higher separation performance than the SA membrane and the nanohybrid membrane utilizing unmodified GO as filler (with the optimal permeation flux of 2140 g m^–2 h^–1, and separation factor of 1370). The study indicates the great application potential of zwitterionic graphene materials in dense water-permeation membranes and provides a facile approach to constructing efficient water transport pathway in membrane

High-Performance Composite Membrane with Enriched CO₂‑philic Groups and Improved Adhesion at the Interface

A novel strategy to design a high-performance composite membrane for CO₂ capture via coating a thin layer of water-swellable polymers (WSPs) onto a porous support with enriched CO₂-philic groups is demonstrated in this study. First, by employing a versatile platform technique combining non-solvent-induced phase separation and surface segregation, porous support membranes with abundant CO₂-philic ethylene oxide (EO) groups at the surface are successfully prepared. Second, a thin selective layer composed of Pebax MH 1657 is deposited onto the support membranes via dip coating. Because of the water-swellable characteristic of Pebax and the enriched EO groups at the interface, the composite membranes exhibit high CO₂ permeance above 1000 GPU with CO₂/N₂ selectivity above 40 at a humidified state (25 °C and 3 bar). By tuning the content of the PEO segment at the interface, the composite membranes can show either high CO₂ permeance up to 2420 GPU with moderate selectivity of 46.0 or high selectivity up to 109.6 with fairly good CO₂ permeance of 1275 GPU. Moreover, enrichment of the PEO segment at the interface significantly improves interfacial adhesion, as revealed by the T-peel test and positron annihilation spectroscopy measurement. In this way, the feasibility of designing WSP-based composite membranes by enriching CO₂-philic groups at the interface is validated. We hope our findings may pave a generic way to fabricate high-performance composite membranes for CO₂ capture using cost-effective materials and facile methods

Encaging Palladium Nanoparticles in Chitosan Modified Montmorillonite for Efficient, Recyclable Catalysts

Metal nanoparticles, once supported by a suitable scaffolding material, can be used as highly efficient heterogeneous catalysts for numerous organic reactions. The challenge, though, is to mitigate the continuous loss of metals from the supporting materials as reactions proceed, so that the catalysts can be recycled multiple times. Herein, we combine the excellent chelating property of chitosan (CS) and remarkable stability of montmorillonite (MMT) into a composite material to support metal catalysts such as palladium (Pd). The in situ reduction of Pd²⁺ into Pd⁰ in the interstices of MMT/CS composites effectively encages the Pd⁰ nanoparticles in the porous matrices, while still allowing for reactant and product molecules of relatively small sizes to diffuse in and out the matrices. The prepared Pd⁰@MMT/CS catalysts are highly active for the Heck reactions of aromatic halides and alkenes, and can be recycled 30 times without significant loss of activities. Positron annihilation lifetime analysis and other structural characterization methods are implemented to elucidate the unique compartmentalization of metal catalysts in the composite matrices. As both CS and MMT are economical and abundant materials in nature, this approach may facilitate a versatile platform for developing highly recyclable, heterogeneous catalysts containing metal nanoparticles

Hydrogenated Oxygen-Deficient Blue Anatase as Anode for High-Performance Lithium Batteries

Blue oxygen-deficient nanoparticles of anatase TiO₂ (H-TiO₂) are synthesized using a modified hydrogenation process. Scanning electron microscope and transmission electron microscope images clearly demonstrate the evident change of the TiO₂ morphology, from 60 nm rectangular nanosheets to much smaller round or oval nanoparticles of ∼17 nm, after this hydrogenation treatment. Importantly, electron paramagnetic resonance and positronium annihilation lifetime spectroscopy confirm that plentiful oxygen vacancies accompanied by Ti³⁺ are created in the hydrogenated samples with a controllable concentration by altering hydrogenation temperature. Experiments and theory calculations demonstrate that the well-balanced Li⁺/e^– transportation from a synergetic effect between Ti³⁺/oxygen vacancy and reduced size promises the optimal H-TiO₂ sample a high specific capacity, as well as greatly enhanced cycling stability and rate performance in comparison with the other TiO₂