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Metal-organic frameworks (MOFs) have drawn great interest in several applications. MOFs can be successfully synthesized by metal oxide or hydroxide, but the synthesis of MOFs membranes has been rarely reported. Here we found the CuO nanosheets (CuO NSs) were highly positively charged and reactive enough to form HKUST-1 powders in trimesic acid (H3BTC) ethanol-water solution even at room temperature. Thus we design a self-confined and healing strategy to prepared well-intergrown HKUST-1 membranes on macroporous support by solid-to-solid conversion from CuO NSs film. During the growth process, HKUST-1 (Cu3(BTC)2⋅3H2O) crystals are self-confined and tightly intergrown. The gaps and defects are healed with elongation growth time, resulting in a continuous and well-intergrown HKUST-1 membrane. The continuous and well intergrown HKUST-1 thin membranes demonstrate good gas separation performance. The process presented here may pave a new way to prepare MOFs membranes by using active metal oxide nanostructures.

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.

A facile template approach is developed to prepare highly conductive and flexible reduced graphene oxide (rGO) paper with hierarchical porous structures. When used as an electrode for a capacitor, these porous carbon layers demonstrate an enhanced electrochemical performance due to their large ion-accessible surface area and efficient electrolyte-ion transport pathways. The porous rGO electrode delivers a specific capacity of 173.5 F g−1, almost 1.8 times higher than 95.1 F g−1 of packed rGO. More importantly, the porous electrode also exhibits a good electrochemical performance with an energy density of 28.5 W h kg−1 and power density of 4000 W kg−1, as well as excellent cycling stability with 101.5% of its initial capacitance after 2000 charge–discharge cycles at a current density of 5 A g−1.

We developed a new approach to synthesize MOF seeds by directly growing ZIF-8 seeds from zinc hydroxide nanostrands (ZHNs)/gelatin composite thin films. The ZIF-8 seeds were anchored firmly and partially in the gelatin film, which could overcome the poor bonding between the substrate and the MOF layer. Using these seeds, after second growth, a dense and well intergrown ZIF-8/gelatine thin film composite membrane was obtained. The different proportions of gelatin mixed with ZHNs influenced the density of the seeds, accordingly affecting the quality of the final ZIF-8/gelatin membranes. The continuous and well intergrown membranes with a ZIF-8 layer of about 2 μm, exhibited H2 permeance of 7.68 × 10−6 mol s−1 Pa−1 m−2 at room temperature, with ideal selectivities for H2/CH4 and H2/N2 gases of 14.2 and 9.4, respectively, far beyond the Knudsen selectivity. Similarly, an HKUST-1 seeds/gelatin thin film was also synthesized. This process holds the potential for synthesis of other MOF membranes on various substrates.

Tubular MOP-18 crystals have been successfully prepared by cooling-induced crystallization from copper hydroxide nanostrands and 5-dodecyloxybenzene-1,3-dicarboxylic acid DMF (N,N-dimethyl-formamide)–ammonia solution. The dependence of the crystal morphologies on the cooling rate is investigated in detail. A slower cooling rate results in larger and longer MOP-18 tubes. The ammonia in the DMF solution plays a crucial role in the formation of MOP-18 tubes. It deprotonates the acid ligand to trigger the nucleation of MOP-18 and leads the growth of tubular crystals. A “diffusion driven instability” growth mechanism is proposed. The outside surfaces of the crystals have a better supply of material from the surrounding solution and maintain continuous growth, while the inner cavity part not only have a worse supply of material but the inner walls also dissolve in order to balance the local saturated solubility of MOP-18 in DMF at a certain temperature, and results in the formation of tubes.

ZnO micro-hexagons with controllable morphologies were synthesized with the assist of benzenedicarboxylic acid (BDC) from zinc hydroxide nanostrands at 120 °C. With increasing the concentration of BDC, the structures evolved from hexagonal disks to hexagonal pyramids and eventually to coarse hexagonal pyramid flakes. The reason was that the growth along the c axis was preferentially suppressed at relatively low BDC concentration, while at higher concentration, the BDC could uniformly adsorbed on the whole surface. The photoluminescence properties of the obtained ZnO hexagons were also investigated at room and low temperature. The ZnO hexagonal disks with lowest defect showed the best optical performance.

Well-intergrown ZIF-8 membranes are prepared directly from zinc hydroxide nanostrands without any modification of the substrate in ethanol–water at room temperature in a short time and exhibit high molecular sieving performance for gas separation after secondary growth. This strategy exhibits excellent reproducibility and versatility and is suitable for large-scale production.

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.

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.

Ultrathin gelatin films were prepared by filtering gelatin on a porous nanofibrous scaffold and cross-linked by glutaraldehyde. The gelatin thin films were obtained by using a copper hydroxide nanostrand scaffold after removal of the scaffold. At relative high pressure, the rejection properties of these gelatin films became worse due to mechanical fouling. However, the gelatin/carbon nanotube composite thin films prepared on a single-walled carbon nanotube scaffold could sustain a pressure up to 18 bars with more than 90% rejection for 2–3 nm molecules. The carbon nanotube layer dramatically increased the mechanical properties of the gelatin layer. The pressure dynamically controlled the network structure of the gelatin layer. The corresponding separation performances were investigated in detail. The gelatin films could be as thin as 62 nm. These gelatin films can separate 865 Dalton Direct Yellow 50 molecules at a rate of magnitude one to two orders higher than that of commercially available membranes with similar rejections.

Nanofibrous materials have been extensively investigated and used as building blocks for various nanodevices, due to their unique one-dimensional structures. Recently, novel membranes constructed by using nanofibers have been reported by various techniques. Here, we will give a critical review of our recent research on the general solution processed unique sub-3 nm thin metal hydroxide nanofibers and their application for constructing ultrathin separation membranes via filtration technique. The superior separation performances of these membranes hold the promising future for pressure-driven membrane separation processes.

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.

Hierarchical porous materials are promising for catalyst, separation and sorption applications. A ligand-assisted etching process is developed for template-free synthesis of hierarchical mesoporous MOFs as single crystals and well-intergrown membranes at 40 °C. At 223 K, the hierarchical porous structures significantly improve the CO2 capture capacity of HKUST-1 by more than 44 % at pressures up to 20 kPa and 13 % at 100 kPa. Even at 323 K, the enhancement of CO2 uptake is above 25 % at pressures up to 20 kPa and 7 % at 100 kPa. The mesoporous structures not only enhance the CO2 uptake capacity but also improve the diffusion and mass transportation of CO2 . Similarly, well-intergrown mesoporous HKUST-1 membranes are synthesized, which hold the potential for film-like porous devices. Mesoporous MOF-5 crystals are also obtained by a similar ligand-assisted etching process. This may provide a facile way to prepare hierarchical porous MOF single crystals and membranes for wide-ranging applications.

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.

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.

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.

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.

Large scale, robust, well intergrown free-standing HKUST-1 membranes were converted from copper hydroxide nanostrand free-standing films in 1,3,5-benzenetricarboxylic acid water–ethanol solution at room temperature, and explored for gas separation. The truncated crystals are controllable and favorable for the dense intergrowth.

Nanofibrous materials have been extensively investigated and used as building blocks for various nanodevices, due to their unique one-dimensional structures. Recently, novel membranes constructed by using nanofibers have been reported by various techniques. Here, we will give a critical review of our recent research on the general solution processed unique sub-3 nm thin metal hydroxide nanofibers and their application for constructing ultrathin separation membranes via filtration technique. The superior separation performances of these membranes hold the promising future for pressure-driven membrane separation processes.

Oriented MIL-110 nanorod arrays on porous anodic aluminum oxide membrane were successfully prepared through a hetero-metal hydroxide nanostrand-assisted growth process in H3BTC aqueous solution. This process provides an environmentally friendly method for synthesis of MIL-110 nanorod arrays without using toxic metal ionic sources and organic solvents.

Cuboctahedral and octahedral HKUST-1 seeds were quickly prepared on a porous anodic alumina oxide support at room temperature within one hour, from water–ethanol and ethanol solvents. The cuboctahedral seeds were favourable for the synthesis of continuous and well intergrown HKUST-1 membranes. However, the octahedral seeds could not produce high quality HKUST-1 membranes. Interestingly, both the shape of the seeds and growth habits of the HKUST-1 seed and crystals in different solvents also determines the final quality of the HKUST-1 membranes. The gas separation performance of the well intergrown HKUST-1 membrane is good and beyond the Knudsen selectivity.

For the first time, pressure, salt concentration and pH demonstrated advantages for tuning the nanochannels within lamellar graphene oxide (LGO) membranes to control the separation of small molecules. This provides a new avenue for designing and engineering efficient LGO membranes for molecular separation.

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.

[Fe(CN)6](4-) decorated mesoporous gelatin films, acting as colorimetric sensors and sorbents for heavy metal ions, were prepared by incorporating [Fe(CN)6](4-) ions into the mesoporous gelatin films through electrostatic interaction. Gelatin-Prussian blue (PB) and gelatin-PB analogue composite films were successfully synthesized by immersing the [Fe(CN)6](4-) decorated gelatin films into aqueous solutions of metal ions, such as Fe(3+), Cu(2+), Co(2+), Pb(2+) and Cd(2+) (all as nitrates). The in situ formation process of PB or its analogues in the films was investigated using quartz crystal microbalance (QCM) measurements. According to the different colors of the PB nanoparticles and its analogues, the [Fe(CN)6](4-) decorated mesoporous gelatin films demonstrated colorimetric sensor abilities for detecting the corresponding metal ions by the naked eye with sufficient sensitivity at 1 ppm level and a quite short response time of 5 minutes. Moreover, due to the [Fe(CN)6](4-) functionality and other functional groups of gelatin itself, this [Fe(CN)6](4-) decorated mesoporous gelatin film shows a tens times higher adsorption ability for heavy metal ions in water than that of activated carbon. Due to both the efficient detection and high adsorption ability for heavy metal ions, this film has wide potential applications for the detection and purification of heavy metal ions from polluted water.

In this paper, Au nanoparticle (NP)–gelatin mesoporous composite thin films were successfully prepared by the formation of Au NPs in the mesoporous gelatin films through in situ reduction of HAuCl4 at room temperature. The mesoporous gelatin films were prepared by using copper hydroxide nanostrands as both the assembling frames and the pore generators. It was found that both the trace aldehyde groups of the glutaraldehyde cross-linker and the reduction groups of gelatin contributed to the formation of Au NPs. The Au NPs were homogeneously formed and dispersed in the gelatin films. The effects of pH and the reduction time on the formation of the Au NPs were investigated in detail. These Au NP–gelatin mesoporous composite films demonstrated superior catalytic properties for the reduction of o-nitroaniline to 1,2-benzenediamine, and several to tens times higher activity than those reported of the Au NP–polymer (or oxide) composites. Similarly, Pt NP–gelatin mesoporous composite films were also prepared. This process is general and simple for other functional composite films.