Wanqin Jin

Subnanometer Two-Dimensional Graphene Oxide Channels for Ultrafast Gas Sieving

Two-dimensional (2D) materials with atomic thickness and extraordinary physicochemical properties exhibit unique mass transport behaviors, enabling them as emerging nanobuilding blocks for separation membranes. Engineering 2D materials into membrane with subnanometer apertures for precise molecular sieving remains a great challenge. Here, we report rational-designing external forces to precisely manipulate nanoarchitecture of graphene oxide (GO)-assembled 2D channels with interlayer height of ∼0.4 nm for fast transporting and selective sieving gases. The external forces are synergistic to direct the GO nanosheets stacking so as to realize delicate size-tailoring of in-plane slit-like pores and plane-to-plane interlayer-galleries. The 2D channels endow GO membrane with excellent molecular-sieving characteristics that offer 2-3 orders of magnitude higher H2 permeability and 3-fold enhancement in H2/CO2 selectivity compared with commercial membranes. Formation mechanism of 2D channels is proposed on the basis of the driving forces, nanostructures, and transport behaviors.

A ZIF-71 Hollow Fiber Membrane Fabricated by Contra-Diffusion

As a subclass of metal-organic framework materials, zeolitic imidazolate frameworks (ZIFs) have exhibited great potential for numerous applications because of their special three-dimensional structure. Up to now, utilizing ZIF membranes for liquid separations is still limited because it is very difficult to select suitable materials and to fabricate integrated membranes. In this work, a modified contra-diffusion method was carried out to prepare ZIF-71 hollow fiber membranes. The metals Zn(2+) and the organic links imidazole would meet and react on the interface of ceramic hollow fiber through diffusion. The as-prepared ZIF-71 membrane exhibits good performance in separation of ethanol-water mixtures.

Fabrication of supported mesoporous TiO2 membranes: matching the assembled and interparticle pores for an improved ultrafiltration performance.

We report the fabrication and ultrafiltration performances of an asymmetric composite membrane with a mesoporous TiO2 skin layer coated on a macroporous alumina support. Mesoporous TiO2 was first prepared and deposited on the substrate through a sol-gel process where a ethylene oxide and propylene oxide triblock polymer (PEO-PPO-PEO, P123) was used to modify the properties of the sols and also to introduce assembled pores in the skin layer. The obtained mesoporous TiO2 membrane was characterized by means of scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and nitrogen adsorption. We found that there were two types of wormlike mesopores present in the TiO2 membrane: interparticle and assembled pores. By carefully controlling the sol properties, we made the two types of pores match each other, which means the size of the interparticle pores is close or smaller than that of the assembled pores. This pore-size matching ensures a narrow pore-size distribution and, consequently, a good retention performance of the obtained TiO2 membrane. The pore size of the TiO2 membrane is ca. 6 nm, as revealed by both nitrogen adsorption and dextran separation experiments, and it has a pure water flux of 7.12 L/(m(2) x h x bar) and a cutoff molecular weight of 19 000 Da, which is very attractive for applications in the enrichment and separation of proteins and polypeptides.

Stretchable Ti3C2Tx MXene/Carbon Nanotube Composite Based Strain Sensor with Ultrahigh Sensitivity and Tunable Sensing Range

It remains challenging to fabricate strain-sensing materials and exquisite geometric constructions for integrating extraordinary sensitivity, low strain detectability, high stretchability, tunable sensing range, and thin device dimensions into a single type of strain sensor. A percolation network based on Ti3C2Tx MXene/carbon nanotube (CNT) composites was rationally designed and fabricated into versatile strain sensors. This weaving architecture with excellent electric properties combined the sensitive two-dimensional (2D) Ti3C2Tx MXene nanostacks with conductive and stretchable one-dimensional (1D) CNT crossing. The resulting strain sensor can be used to detect both tiny and large deformations with an ultralow detection limit of 0.1% strain, high stretchability (up to 130%), high sensitivity (gauge factor up to 772.6), tunable sensing range (30% to 130% strain), thin device dimensions (<2 μm), and excellent reliability and stability (>5000 cycles). The versatile and scalable Ti3C2Tx MXene/CNT strain sensors provide a promising route to future wearable artificial intelligence with comprehensive tracking ability of real-time and in situ physiological signals for health and sporting applications.

Fabrication of morphology-preserved microporous carbon from a zeolitic-like porous coordination polymer

A new zeolitic-like microporous coordination polymer (PCP), [Zn2(L)·2H2O]·guest (named NTU-17), with crb (BCT) topology was designed and prepared. Interestingly and unusually, it is the first time that such rod-shaped NTU-17 crystals could be converted to morphology-preserved carbon rods with exclusive micropores and a large surface area by using a facile method of direct thermal transformation. Gas adsorption and selectivity showed that these PCP dependent carbon rods are suitable solid adsorbents for CH4 purification.

Controlled flexibility of porous coordination polymers by shifting the position of the –CH3 group around coordination sites and their highly efficient gas separation

As an emerging class of crystalline materials, porous coordination polymers (PCPs) with regular and flexible nanopores have become particularly promising for adsorption applications. Here, we report a new method to synthesize PCPs with varied flexibility by shifting the position of the methyl group, the shortest alkyl chain, around the coordination sites of T-shaped ligands of H2NL1 (5-(2′-methyl-imidazol-1-yl)-isophthalic acid) and H2NL2 (5-(4′-methyl- imidazol-1-yl)-isophthalic acid). The two generated PCPs (NTU-40 and NTU-41) showed a significant change in gate opening pressure (P/P0: 0.25 to 0.0001) under the stimulus of N2 at 77 K. In addition, the square window (5 × 5 A2) of the one-dimensional (1D) zigzag channel was divided into two small triangular and straight channels in NTU-41. More importantly, the synergistic effect of structural flexibility, channel type and the micro-pores enabled highly efficient CO2/CH4 and C2H4/CH4 separation under both equilibrium state and dynamic conditions, as well as having good potential for challenging C2H4/C2H6 separation.

Incorporating Graphene Oxide into Alginate Polymer with a Cationic Intermediate To Strengthen Membrane Dehydration Performance

Two-dimensional graphene oxide (GO) in hybrid membranes provides fast water transfer across its surface due to the abundant oxygenated functional groups to afford water sorption and the hydrophobic basal plane to create fast transporting pathways. To establish more compatible and efficient interactions for GO and sodium alginate (SA) polymer chains, cations sourced from lignin are employed to decorate GO (labeled as cation-functionalized GO (CG)) nanosheets via cation-π and π-π interactions, providing more interactive sites to confer synergetic benefits with polymer matrix. Cations from CG are also functional to partially interlock SA chains and intensify water diffusion. And with the aid of two-dimensional pathways of CG, fast selective water permeation can be realized through hybrid membranes with CG fillers. In dehydrating aqueous ethanol solution, the hybrid membrane exhibits considerable performance compared with bare SA polymer membrane (long-term stable permeation flux larger than 2500 g m-2 h-1 and water content larger than 99.7 wt %, with feed water content of 10 wt % under 70 °C). The effects of CG content in SA membrane were investigated, and the transport mechanism was correspondingly studied through varying operation conditions and membrane materials. In addition, such a membrane possesses long-term stability and almost unchanged high dehydration capability.