Yiyin Mao

Ultrafast viscous water flow through nanostrand-channelled graphene oxide membranes

Pressure-driven ultrafiltration membranes are important in separation applications. Advanced filtration membranes with high permeance and enhanced rejection must be developed to meet rising worldwide demand. Here we report nanostrand-channelled graphene oxide ultrafiltration membranes with a network of nanochannels with a narrow size distribution (3-5 nm) and superior separation performance. This permeance offers a 10-fold enhancement without sacrificing the rejection rate compared with that of graphene oxide membranes, and is more than 100 times higher than that of commercial ultrafiltration membranes with similar rejection. The flow enhancement is attributed to the porous structure and significantly reduced channel length. An abnormal pressure-dependent separation behaviour is also reported, where the elastic deformation of nanochannels offers tunable permeation and rejection. The water flow through these hydrophilic graphene oxide nanochannels is identified as viscous. This nanostrand-channelling approach is also extendable to other laminate membranes, providing potential for accelerating separation and water-purification processes.

Flexible CuO nanosheets/reduced-graphene oxide composite paper: binder-free anode for high-performance lithium-ion batteries.

Flexible free-standing CuO nanosheets (NSs)/reduced graphene oxide (r-GO) hybrid lamellar paper was fabricated through vacuum filtration and hydrothermal reduction processes. A unique three-dimensional nanoporous network was achieved with CuO NSs homogeneously embedded within the r-GO layers. This hybrid lamellar composite paper was examined as a binder-free anode for lithium ion batteries, and demonstrated excellent cyclic retention with the specific capacity of 736.8 mA h g(-1) after 50 cycles. This is much higher than 219.1 mA h g(-1) of the pristine CuO NSs and 60.2 mA h g(-1) of r-GO film at the same current density of 67 mA g(-1). The high capacitance and excellent cycling performance were generated from the integrated nanoporous structure compose of CuO NSs spaced r-GO layers, which offered an efficient electrically conducting channels, favored electrolyte penetration, and buffered to the volume variations during the lithiation and delithiation process. These outstanding electrochemical capabilities of CuO NSs/r-GO paper holds great promise for flexible binder-free anode for lithium ion batteries.

Two-Dimensional Titanium Carbide for Efficiently Reductive Removal of Highly Toxic Chromium(VI) from Water

Two dimensional (2-D) Ti3C2Tx nanosheets are obtained by etching bulk Ti3C2Tx powders in HF solution and delaminating ultrasonically, which exhibit excellent removal capacity for toxic Cr(VI) from water, due to their high surface area, well dispersibility, and reductivity. The Ti3C2Tx nanosheets delaminated by 10% HF solution present more efficient Cr(VI) removal performance with capacity of 250 mg g(-1), and the residual concentration of Cr(VI) in treated water is less than 5 ppb, far below the concentration (0.05 ppm) of Cr(VI) in the drinking water standard recommended by the World Health Organization. This kind of 2-D Ti3C2Tx nanosheet can not only remove Cr(VI) rapidly and effectively in one step from aqueous solution by reducing Cr(VI) to Cr(III) but also adsorb the reduced Cr(III) simultaneously. Furthermore, these reductive 2-D Ti3C2Tx nanosheets are generally explored to remove other oxidant agents, such as K3[Fe(CN)6], KMnO4, and NaAuCl4 solutions, by converting them to low oxidation states. These significantly expand the potential applications of 2-D Ti3C2Tx nanosheets in water treatment.

Ultrafast Molecule Separation through Layered WS2 Nanosheet Membranes

Two-dimensional layered materials have joined in the family of size-selective separation membranes recently. Here, chemically exfoliated tungsten disulfide (WS2) nanosheets are assembled into lamellar thin films and explored as an ultrafast separation membrane for small molecules with size of about 3 nm. Layered WS2 membranes exhibit 5- and 2-fold enhancement in water permeance of graphene oxide membranes and MoS2 laminar membranes with similar rejection, respectively. To further increase the water permeance, ultrathin nanostrands are used as templates to generate more fluidic channel networks in the WS2 membrane. The water permeation behavior and separation performance in the pressure loading-unloading process reveal that the channels created by the ultrathin nanostrands are cracked under high pressure and result in a further 2-fold increase of the flux without significantly degrading the rejection for 3 nm molecules. This is supported by finite-element-based mechanical simulation. These layered WS2 membranes demonstrate up to 2 orders of magnitude higher separation performance than that of commercial membranes with similar rejections and hold the promising potential for water purification.

Foldable interpenetrated metal-organic frameworks/carbon nanotubes thin film for lithium–sulfur batteries

Lithium–sulfur batteries are promising technologies for powering flexible devices due to their high energy density, low cost and environmental friendliness, when the insulating nature, shuttle effect and volume expansion of sulfur electrodes are well addressed. Here, we report a strategy of using foldable interpenetrated metal-organic frameworks/carbon nanotubes thin film for binder-free advanced lithium–sulfur batteries through a facile confinement conversion. The carbon nanotubes interpenetrate through the metal-organic frameworks crystal and interweave the electrode into a stratified structure to provide both conductivity and structural integrity, while the highly porous metal-organic frameworks endow the electrode with strong sulfur confinement to achieve good cyclability. These hierarchical porous interpenetrated three-dimensional conductive networks with well confined S8 lead to high sulfur loading and utilization, as well as high volumetric energy density.

CuO nanosheets/rGO hybrid lamellar films with enhanced capacitance

CuO nanosheets (NSs)/reduced graphene oxide (rGO) hybrid lamellar films were prepared by vacuum filtration of CuO NSs/GO composite dispersions, followed by hydrothermal reduction. The CuO NSs/GO composite dispersions were assembled electrostatically by mixing a negatively charged GO sheets aqueous solution with a positively charged CuO NSs aqueous dispersion at room temperature. The prepared CuO NSs/rGO hybrid lamellar films exhibited a specific capacitance of 163.7 F g(-1), which is much higher than the 69.7 F g(-1) of CuO NSs and 66.0 F g(-1) of rGO. The effective specific capacitance was 82.5 F g(-1) after 1000 cycles, which was more than two times the 32.7 F g(-1) of CuO NSs electrodes. The synergistic redox activity of the CuO NSs, in combination with the high electronic conductivity of the rGO and the unique CuO NSs spaced sandwich-like porous structures, dominated the excellent capacitance of CuO NSs/rGO hybrid lamellar films. The sandwiched, lamellar, porous structures not only provide plenty of paths for electrolyte-ion access to the CuO NSs but also expose the rGO sheets to the electrolyte as much as possible. This process provides a potential way to synthesise metal oxide/GO composite electrodes for capacitors.

General incorporation of diverse components inside metal-organic framework thin films at room temperature

Porous metal-organic frameworks (MOFs) demonstrate great potential for numerous applications. Although hetero-functional components have been encapsulated within MOF crystalline particles, the uniform incorporation of functional species with different sizes, shapes and functions in MOF thin films with dual properties, especially at room temperature and without the degradation of the MOF framework, remains a significant challenge towards further enriching their functions for various purposes. Here we report a general method that can rapidly encapsulate diverse functional components, including small ions, micrometre-sized particles, inorganic nanoparticles and bioactive proteins, in MOF thin films at room temperature via a metal-hydroxide-nanostrand-assisted confinement technique. These functional component-encapsulated MOF composite thin films exhibit synergistic and size-selective catalytic, bio-electrochemical, conductive and flexible functionalities that are desirable for thin film devices, including catalytic membrane reactors, biosensors and flexible electronic devices.

Pressure-Assisted Synthesis of HKUST‑1 Thin Film on Polymer Hollow Fiber at Room Temperature toward Gas Separation

The scalable fabrication of continuous and defect-free metal-organic framework (MOF) films on the surface of polymeric hollow fibers, departing from ceramic supported or dense composite membranes, is a huge challenge. The critical way is to reduce the growth temperature of MOFs in aqueous or ethanol solvents. In the present work, a pressure-assisted room temperature growth strategy was carried out to fabricate continuous and well-intergrown HKUST-1 films on a polymer hollow fiber by using solid copper hydroxide nanostrands as the copper source within 40 min. These HKUST-1 films/polyvinylidenefluoride (PVDF) hollow fiber composite membranes exhibit good separation performance for binary gases with selectivity 116% higher than Knudsen values via both inside-out and outside-in modes. This provides a new way to enable for scale-up preparation of HKUST-1/polymer hollow fiber membranes, due to its superior economic and ecological advantages.

Polystyrene Sulfonate Threaded through a Metal–Organic Framework Membrane for Fast and Selective Lithium‐Ion Separation

Extraction of lithium ions from salt-lake brines is very important to produce lithium compounds. Herein, we report a new approach to construct polystyrene sulfonate (PSS) threaded HKUST-1 metal-organic framework (MOF) membranes through an in situ confinement conversion process. The resulting membrane PSS@HKUST-1-6.7, with unique anchored three-dimensional sulfonate networks, shows a very high Li+ conductivity of 5.53×10-4  S cm-1 at 25 °C, 1.89×10-3  S cm-1 at 70 °C, and Li+ flux of 6.75 mol m-2  h-1 , which are five orders higher than that of the pristine HKUST-1 membrane. Attributed to the different size sieving effects and the affinity differences of the Li+ , Na+ , K+ , and Mg2+ ions to the sulfonate groups, the PSS@HKUST-1-6.7 membrane exhibits ideal selectivities of 78, 99, and 10296 for Li+ /Na+ , Li+ /K+ , Li+ /Mg2+ and real binary ion selectivities of 35, 67, and 1815, respectively, the highest ever reported among ionic conductors and Li+ extraction membranes.

HKUST-1 Membranes Anchored on Porous Substrate by Hetero MIL-110 Nanorod Array Seeds

Great anchors and seeds: Hetero-seeding growth processes and anchored nanorod arrays were successfully utilized in the synthesis of HKUST-1 membranes. These arrays were firmly anchored on porous substrates by using a MIL-110 nanorod array as both the anchor and seed. The resulting HKUST-1 membranes demonstrated good separation factors for binary gases exceeding the Knudson selectivity.