Ke Xie

Trithiocarbonates as intrinsic photoredox catalysts and RAFT agents for oxygen tolerant controlled radical polymerization

This study reports the discovery that trithiocarbonate RAFT agents can significantly reduce the amount of dissolved oxygen when irradiated with visible light (λmax ≈ 460 nm) in the presence of a sacrificial tertiary amine. By taking advantage of this effect, we conducted a series of photo-CRPs of acrylates without the requirement of pre-degassing the reaction mixtures. In these systems, the trithiocarbonate plays a triple role of photocatalyst for oxygen removal, initiator, and RAFT agent for polymerization control. We believe this robust and facile synthetic method will be beneficial for cost-effective industrial applications as well as the laboratory-scale synthesis of functional polymeric materials.

The use of reduced copper metal-organic frameworks to facilitate CuAAC click chemistry.

A reduced copper metal-organic framework (rCu-MOF) containing CuI ions was prepared by reducing raw MOFs (Cu-BTC). A series of polymer functionalizations and coupling reactions could subsequently be achieved via CuAAC click chemistry, thus demonstrating the high activity, facile recyclability and good structural stability of rCu-MOFs for catalytic applications.

Continuous assembly of a polymer on a metal–organic framework (CAP on MOF): a 30 nm thick polymeric gas separation membrane

We have developed a bottom-up approach to fabricate an ultra-thin (∼30 nm), continuous and defect-free polymeric membrane on a rough micro-scale MOF layer. This polymer-on-MOF architecture exhibits a promising CO2/N2 separation performance with a CO2 permeance of >3000 GPU and a CO2/N2 selectivity of 34. To the best of our knowledge, this membrane has the best CO2/N2 separation performance compared to any other membrane reported in the open literature.

MOF-Mediated Destruction of Cancer Using the Cell’s Own Hydrogen Peroxide

A novel reduced iron metal-organic framework nanoparticle with cytotoxicity specific to cancer cells is presented. This nanoparticle was prepared via a hydrothermal method, reduced using hydroquinone, and finally conjugated with folic acid (namely, rMOF-FA). The synthesized nanoparticle shows the controlled release of iron in an acidic ex-vivo environment. Iron present on the rMOF-FA and released into solution can react with high levels of hydrogen peroxide found specifically in cancer cells to increase the hydroxyl radical concentration. The hydroxyl radicals oxidize proteins, lipids, and/or DNA within the biological system to decrease cell viability. In vitro experiments demonstrate that this novel nanoparticle is cytotoxic to cancer cells (HeLa) through generation of OH• inside the cells. At low concentrations of rMOF-FA, the cancer cell viability decreases dramatically, with no obvious reduction of normal cell (NIH-3T3) viability. The calculated half-maximum inhibitory concentration value (IC50) was 43 μg/mL for HeLa cells, which was significantly higher than 105 μg/mL for NIH-3T3. This work thus demonstrates a new type of agent for controlled hydroxyl radical generation using the Fenton reaction to kill the tumor cells.

Pd(0) loaded Zn2(azoBDC)2(dabco) as a heterogeneous catalyst

We report a novel Pd(0) loaded metal–organic framework (MOF) catalyst, namely Pd@Zn2(azoBDC)2(dabco). The efficient catalytic activity and good recyclability of the heterogeneous catalyst carrier are demonstrated through the probe reduction reaction of 4-nitrophenol (NP) to 4-aminophenol (AP) by sodium borohydride (NaBH4).

MOF Scaffold for a High‐Performance Mixed‐Matrix Membrane

A novel composite membrane consisting of an interconnected MOF scaffold coated with cross-linked poly(ethylene glycol) (PEG) has been developed. As a result of its unique structure, the membrane shows an exceptional 18-fold permeability enhancement as compared to pristine PEG membranes, without compromising the selectivity. This performance is unattainable with current mixed-matrix membranes (MMMs). Our optimized membrane has a permeability of 2700 Barrer with a CO2 /N2 selectivity of 35, which surpasses the latest Robeson upper bound.

Ultrathin Metal-Organic Framework Nanosheets as A Gutter Layer for Flexible Composite Gas Separation Membranes

Ultrathin metal-organic framework (MOF) nanosheets show great potential in various separation applications. In this study, MOF nanosheets are incorporated as a gutter layer in high-performance, flexible thin-film composite membranes (TFCMs) for CO2 separation. Ultrathin MOF nanosheets (∼3-4 nm) were prepared via a surfactant-assisted method and subsequently coated onto a flexible porous support by vacuum filtration. This produced an ultrathin (∼25 nm), extremely flat MOF layer, which serves as a highly permeable gutter with reduced gas resistance when compared with conventional polydimethylsiloxane gutter layers. Subsequent spin-coating of the ultrathin MOF gutter layer with a polymeric selective layer (Polyactive) afforded a TFCM exhibiting the best CO2 separation performance yet reported for a flexible composite membrane (CO2 permeance of ∼2100 GPU with a CO2/N2 ideal selectivity of ∼30). Several unique MOF nanosheets were examined as gutter layers, each differing with regard to structure and thickness (∼10 and ∼80 nm), with results indicating that flexibility in the ultrathin MOF layer is critical for optimized membrane performance. The inclusion of ultrathin MOF nanosheets into next-generation TFCMs has the potential for major improvements in gas separation performance over current composite membrane designs.