Wood-Derived Freestanding Carbon-Based Electrode with Hierarchical Structure for Industrial-Level Hydrogen Production.

The sustainable and scalable fabrication of low-cost, efficient, and durable electrocatalysts that operate well at industrial-level current density is urgently needed for large-scale implementation of the water splitting to produce hydrogen. In this work, an integrated carbon electrode is constructed by encapsulating Ni nanoparticles within N-doped carbonized wood framework (Ni@NCW). Such integrated electrode with hierarchically porous structure facilitates mass transfer process for hydrogen evolution reaction (HER). Ni@NCW electrode can be employed directly as a robust electrocatalyst for HER, which affords the industrial-level current density of 1000 mA cm-2 at low overpotential of 401 mV. The freestanding binder-free electrode exhibits extraordinary stability for 100 h. An anion exchange membrane water electrolysis (AEMWE) electrolyzer assembled with such freestanding carbon electrode requires only a lower cell voltage of 2.43 V to achieve ampere-level current of 4.0 A for hydrogen production without significant performance degradation. These advantages reveal the great potential of this strategy in designing cost-effective freestanding electrode with monometallic, bimetallic, or trimetallic species based on abundant natural wood resources for water splitting.

Stabilizing electron-rich Ni single-atoms on black phosphorus nanosheets boosts photocatalytic carbon dioxide reduction.

The development of unique single-atom catalysts with electron-rich feature is essential to promoting the photocatalytic CO2 reduction, yet remains a big challenge. Here, a conceptionally new single-atom catalyst constructed from atomically dispersed Ni-P3 species on black phosphorus (BP) nanosheets (BP-Ni) is synthesized for realizing highly efficient visible-light-driven CO2 reduction when trapping photogenerated electrons from homogeneous light absorbers in the presence of triethanolamine as the sacrificial agent. Both the experimental and theoretical calculation data reveal that the Ni-P3 species on BP nanosheets own the electron-rich feature that can improve the photogenerated charge separation efficiency and lower the activation barrier of CO2 conversion. This unique feature makes BP-Ni exhibit the much higher activity as cocatalyst in the photocatalytic CO2 reduction than BP nanosheets. The BP-Ni can also be applied as a cocatalyst for enhanced photocatalytic CO2 reduction after combining with CdSe/S colloidal crystal photocatalyst. The present study offers valuable inspirations for the design and construction of effective catalytic sites toward photocatalytic CO2 reduction reactions.

Pathway Complexity in Nanotubular Supramolecular Polymerization: Metal-Organic Nanotubes with a Planar-Chiral Monomer.

Here, we report an anomalous pathway complexity in the supramolecular polymerization of a chiral monomer, which displays an unusual chiroptical feature that does not follow any of the known stereochemical rules such as "chiral self-sorting" and "majority rule". We newly developed a planar-chiral ferrocene-cored tetratopic pyridyl monomer FcL, which underwent AgBF4-mediated supramolecular polymerization to give nanotubes FcNTs composed of metal-organic nanorings FcNRs. Although FcNRs must be homochiral because of a strong geometrical constraint, FcNRs were formed even efficiently from racemic FcL and AgBF4. Detailed studies revealed the presence of two competing pathways for producing homochiral FcNRs as the constituents of FcNTs: (i) spontaneous cyclization of initially formed acyclic polymers -[FcL-Ag+]n- and (ii) template (FcNR)-assisted cyclization via a Ag+···Ag+ metallophilic interaction. The dominance of the two pathways changes depending on the %ee of chiral FcL. Namely, when the %ee of FcL is high, -[FcL-Ag+]n- must contain sufficiently long homochiral sequences that can be readily cyclized into FcNRs. Meanwhile, when the %ee of FcL is low, the homochiral sequences in -[FcL-Ag+]n- must be short and therefore are hardly eligible for spontaneous cyclization. Why were FcNRs formed? Even though the probability is very low, homochiral -[FcL-Ag+]n- can be statistically generated and undergo spontaneous cyclization to give FcNRs minutely. We found that FcNRs can be amplified by heterochirally templating their own synthesis using metallophilic interaction. Because of this stereochemical preference, the growth of FcNRs into FcNTs via the template-assisted mechanism occurs only when both (R,R)FcL and (S,S)FcL are present in the polymerization system.

Accumulated Lattice Strain as an Internal Trigger for Spontaneous Pathway Selection.

Multicomponent crystallization is universally important in various research fields including materials science as well as biology and geology, and presents new opportunities in crystal engineering. This process includes multiple kinetic and thermodynamic events that compete with each other, wherein "external triggers" often help the system select appropriate pathways for constructing desired structures. Here we report an unprecedented finding that a lattice strain accumulated with the growth of a crystal serves as an "internal trigger" for pathway selection in multicomponent crystallization. We discovered a "spontaneous" crystal transition, where the kinetically preferred layered crystal, initially formed by excluding the pillar component, carries a single dislocation at its geometrical center. This crystal "spontaneously" liberates a core region to relieve the accumulated lattice strain around the dislocation. Consequently, the liberated part becomes dynamic and enables the pillar ligand to invade the crystalline lattice, thereby transforming into a thermodynamically preferred pillared-layer crystal.

Functional metal-organic framework-based nanocarriers for accurate magnetic resonance imaging and effective eradication of breast tumor and lung metastasis.

The use of nanoscale metal-organic frameworks (MOFs) as drug delivery vehicles has attracted considerable attention in tumor therapy. In this study, novel biocompatible MOF-based nanocarriers were used as part of a facile and reproducible strategy for precision cancer theranostics. Both diagnostic (Mn2+) and therapeutic compounds (doxorubicin, DOX) were incorporated into the multifunctional MOF-based nanocarriers, which exhibited high colloidal stability and promoted T1-weighted proton relaxivity and low-pH-activated drug release. The obtained MOF-based nanocarriers exhibited significantly high cellular uptake and efficient intracellular drug delivery into cancer cells, which resulted in high apoptosis and cytotoxicity, in addition to effectively inhibiting the migration of 4T1 breast cancer cells. Moreover, the MOF-based nanocarriers could intensively deliver diagnostic and therapeutic agents to tumors to enable precise visualization of the nanocarrier accumulation and accurate tumor positioning, diagnosis, and imaging-guided therapy using magnetic resonance imaging (MRI). In addition, the functional MOF-based nanocarriers exhibited effective ablation of the primary breast cancer, as well as significant inhibition of lung metastasis with a high survival rate. Therefore, the developed nanocarriers represent a viable platform for cancer theranostics.

Sulfonated Sub-Nanochannels in a Robust MOF Membrane: Harvesting Salinity Gradient Power.

We developed a robust, crack-free ultrathin zeolite- imidazole framework (ZIF-8) membrane in-built with a sulfonate-ion-containing polymer (ZIFHep) via a vapor-assisted in situ conversion process. The sulfonated sub-nanochannels of the ZIFHep membrane afforded a rapid and selective transport of Li+ over counteranions and other alkali ions due to electrostatic repulsion and optimal transport kinetics of cation-sulfonate ion pairs. A salinity gradient power generator (SGPG) was built by using the ZIFHep membrane as a cell separator coupled with a pair of Ag/AgCl porous membrane electrodes. At a salinity gradient of 105, such a power generator presented a significantly decreased internal resistance (25.6 Ω), three-order of magnitude lower than that reported previously, and an output power as high as 9.03 µW.

Stepwise Expansion of Layered Metal-Organic Frameworks for Nonstochastic Exfoliation into Porous Nanosheets.

A layered metal-organic framework (MOF) with a porous kagomé lattice, kgmSMe, was synthesized by complexation of 5-methylthioisophthalate (SMe-ip) with Cu2+ in MeOH. As observed by powder XRD, kgmSMe (state I), when immersed in aprotic polar solvents such as THF, underwent stepwise interlayer expansion into a monolayer-expanded state (state III) through a bilayer-expanded state (state II). We successfully obtained the single-crystal structures of states I-III. Of interest, when further immersed in appropriate solvents, state II and III crystals preferentially exfoliated into bilayer and monolayer MOF nanosheets, respectively. The stepwise expansion followed by exfoliation, thus developed, may enable a nonstochastic approach to the selective synthesis of ultrathin porous nanosheets from layered MOF crystals.

Crystalline Nanochannels with Pendant Azobenzene Groups: Steric or Polar Effects on Gas Adsorption and Diffusion?

An azobenzene-containing, zirconium-based metal-organic framework (AzoMOF), upon irradiation with ultraviolet (UV) light at 365 ± 10 nm, underwent trans-to-cis isomerization of its azobenzene pendants to furnish the cis-isomer content of 21% (AzoMOF21%) in 30 min at the photostationary state and underwent backward isomerization into AzoMOF1% upon either irradiation with visible light (420-480 nm) or heating. When the cis-isomer content increased, the diffusion rate and amount of CO2 adsorbed into the nanochannels of AzoMOF decreased considerably. When erythrosine B, a polarity-probing guest, was used, it showed a red shift upon exposure of AzoMOF20%⊃EB to visible light, indicating that the interior environment of AzoMOF turns less polar as the trans-isomer content becomes higher. In sharp contrast, the adsorption profiles of AzoMOF15% and AzoMOF1% for Ar having an analogous kinetic diameter to CO2 but no quadrupole moment and a smaller polarizability were virtually identical to one another. Therefore, it is likely that CO2 experiences a dominant effect of a polar effect rather than a steric effect in the crystalline nanochannels.

Ultrafast molecule separation through layered WS(2) 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.

The highly enhanced performance of lamellar WS2 nanosheet electrodes upon intercalation of single-walled carbon nanotubes for supercapacitors and lithium ions batteries.

Hybrid lamellar porous electrodes with excellent electrochemical performance were successfully fabricated by homogeneously intercalating single-walled carbon nanotubes into the lamellar assembled WS2 nanosheets through vacuum filtration.

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.

Laminar MoS2 membranes for molecule separation.

For the first time, a laminar separation membrane was assembled from atom-thick MoS2 sheets and exhibited a water permeance of 245 L h(-1) m(-2) bar(-1), which was 3-5 times higher than that of graphene oxide membranes without degradation of the rejection ratio (89%) for Evans blue molecules.

[Fe(CN)6]4- decorated mesoporous gelatin thin films for colorimetric detection and as sorbents of heavy metal ions.

[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.

Salt concentration, pH and pressure controlled separation of small molecules through lamellar graphene oxide membranes.

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.

Room temperature synthesis of free-standing HKUST-1 membranes from copper hydroxide nanostrands for gas separation.

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.