Unprecedented acid-tolerant ultrathin membranes with finely tuned sub-nanopores for energetic-efficient molecular sieving

Azo-PMA nanopores of sub-20 nm length for unimolecular resolution of nucleic acids and proteins

Owing to the facile fabrication and surface modification, the cost-effective polymer nanopores are widely employed in unimolecular determination of biomacromolecules and selective sensing of small molecules, nanoparticles and biomarkers. However, the documented polymer nanochannels are generally microscale in length with low spatial resolution. We herein synthesized azobenzene side-chain polymer (Azo-PMA) and spin-coated on silicon nitride membrane to obtain a polymer film of nanoscale thickness for further nanopore generation via controlled dielectric breakdown (CDB) approach. The Azo-PMA nanopores demonstrate good ions transporting activities, pH tolerance and stability in high concentration of electrolyte with low ionic current noise. In addition, the azobenzene-containing polymer nanopores exhibit photo-response upon UV/Vis. light irradiation. The Azo-PMA nanopore devices are utilized for linear and quadruple nucleic acids discrimination, sensing of proteins with distinct shapes and sizes, as well as the single amino acid resolution with good capture rate and sensitivity. We established an unimolecular sensing platform using polymer nanopores for nucleic acids and proteins detection with good spatial resolution, which will be an addition for the nanopore-carrier material exploration and applications in potential genomics and proteomics with high spatiotemporal resolution and low cost.

Tailoring the characteristics of polyacrylonitrile nanofiltration membranes for nickel removal from wastewater: The influence of binary solvents and pore-forming agents

This work presents the results of an investigation on the physiochemical and structural characteristics of polyacrylonitrile (PAN) nanofiltration (NF) membranes prepared using a novel concept of binary solvents for nickel (Ni) removal from wastewater streams. The thermodynamic and kinetic aspects are emphasized aiming to optimize dope formulation, membrane performance, and durability. The fabricated membranes were characterized by scanning electron microscopy (SEM), porosimetry, tensile stress/strain, and flux and rejection. Results revealed that the use of an equal (1:1) mixture of n-methyl-2-pyrrolidone (NMP) and dimethylformamide (DMF) as dope solvents led to the formation of membranes with enhanced performance, offering pure water flux of 2.33 L·m-2·h-1·bar-1 and Ni rejection of 90.84%. Moreover, the incorporation of 0.5 wt.% PEG as a pore-forming agent to the dope solution further boosted pure water flux to 4.97 L·m-2·h-1·bar-1 with negligible impact on Ni rejection. Besides attractive performance, the adopted strategy offered membranes of exceptionally high flexibility with no sign of defect or failure especially during module fabrication and testing enabling smooth and hassle-free scale-up and extension to other applications. PRACTITIONER POINTS: Optimized solvent mixture: A 1:1 blend of n-methyl-2-pyrrolidone (NMP) and dimethylformamide (DMF) as solvents resulted in enhanced membrane performance. High flux and Ni rejection: The fabricated membranes exhibited a pure water flux of 2.33 L·m-2·h-1·bar-1 and a remarkable Ni rejection of 90.84%. PEG enhancement: Incorporating 0.5 wt.% PEG as a pore-forming agent further improved the membrane's pure water flux to 4.97 L·m-2·h-1·bar-1, without compromising Ni rejection. Exceptional flexibility: The adopted strategy yielded membranes with exceptional flexibility, making them suitable for scale-ups and other applications.

Design and Synthesis of Transferrable Macro-Sized Continuous Free-Standing Metal-Organic Framework Films for Biosensor Device

Metal organic framework (MOF) films have attracted abundant attention due to their unique characters compared with MOF particles. But the high-temperature reaction and solvent corrosion limit the preparation of MOF films on fragile substrates, hindering further applications. Fabricating macro-sized continuous free-standing MOF films and transferring them onto fragile substrates are a promising alternative but still challenging. Here, a universal strategy to prepare transferrable macro-sized continuous free-standing MOF films with the assistance of oxide nanomembranes prepared by atomic layer deposition and studied the growth mechanism is developed. The oxide nanomembranes serve not only as reactant, but also as interfacial layer to maintain the integrality of the free-standing structure as the stacked MOF particles are supported by the oxide nanomembrane. The centimeter-scale free-standing MOF films can be transferred onto fragile substrates, and all in one device for glucose sensing is assembled. Due to the strong adsorption toward glucose molecules, the obtained devices exhibit outstanding performance in terms of high sensitivity, low limit of detection, and long durability. This work opens a new window toward the preparation of MOF films and MOF film-based biosensor chip for advantageous applications in post-Moore law period.

Regulating the thickness of nanofiltration membranes for efficient water purification

Fabrication of an organic polymer nanofiltration membrane with both high water permeability and high salt rejection is still a big challenge. Herein, phytic acid (PhA)-modified graphene oxide (GO) was used as the membrane thickness modifier, which was introduced into the thin-film nanoparticle composite (TFN) membrane via in situ interfacial polymerization (IP) on a porous substrate. The water flux of the optimally tuned TFN-GP-0.2 composite membrane is 48.9 L m-2 h-1, which is 1.3 times that of the pristine thin-film composite (TFC) nanofiltration membrane (37.9 L m-2 h-1) (GP represents the PhA modified GO composite). The rejection rate of 2000 ppm MgSO4 for TFN-GP-0.2 membranes was maintained at 97.5%. The increased water flux of the TFN-GP composite membrane compared to that of the TFN nanofiltration membrane was mainly attributed to enhanced hydrophilicity and reduced thickness of the polyamide (PA) layer. Molecular dynamics (MD) simulations confirm that the diffusion rate of amine monomers is reduced by the presence of a GP complex in the IP process, which facilitates the formation of PA layer with thinner thickness. In addition, the TFN-GP-0.2 composite membrane also showed good long-term stability; after 12 h of continuous operation, the water flux only decreased by 0.1%. This study sheds new light on the development of GO-based nanofiltration for potential implementation, as well as a unique concept for manufacturing high-performance nanofiltration membranes.

Ionic Sieving at Sub-Angstrom Precision Enabled by Metal Organic Frameworks

The demand for cesium is expanding rapidly in light of its necessity in high-tech industries. Thus, technologies that can efficiently extract cesium from the sources are critically needed. Here, the metal-organic framework (MOF) membranes created from -Cl and -NH2 functionalized MIL-53 enabled highly selective transport of cesium ions. The angstrom-scale pore windows in these MOFs conduct Cs+ ions at high throughput, 2 orders of magnitude faster than other marginally larger ions. Ascribed to size sieving effects, MIL-53-NH2 containing 6.6 Å size channels realized an exceedingly high Cs+/Li+ selectivity up to ∼315. The rapid transport of Cs+ ions relative to other ions is greatly dependent on the precision of the angstrom-scale pores. Our work highlights the enormous potential of realizing high ion selectivity with MOFs and drives the further development of these materials in a variety of advanced separations.