Practicable Zn metal batteries enabled by ultrastable ferromagnetic interface.

Rechargeable zinc (Zn) metal batteries (RZMBs) are demonstrated as sustainable and low-cost alternative in the energy storage industry of the future. However, the elusive Zn deposition behavior and water-originated parasitic reactions bring significant challenges to the fabrication and commercialization of Zn anodes, especially under high plating/stripping capacity. In this work, the ferromagnetic interface in conjunction with the magnetic field (MF) to effectively address these fabrication hurdles is proposed. The introduction of ferromagnetic layer with high chemical durability not only maintains the long-term regulating deposition steadily by magnetic field, but also plays a significant role in preventing side reactions, hence reducing gas production. These merits allow Zn-anode to achieve over 350 h steady Zn-deposition with a depth of discharge (DODZn) up to 82% and translates well to ZnFe-MF||V2O5 full cells, supporting stable cycling at high mass loading of 13.1 mg/cm2, which makes RZMBs configurations promising for commercial applications.

Multi-Scale Computer-Aided Design of Covalent Organic Frameworks for CO2 Capture in Wet Flue Gas.

Discovery of remarkable porous materials for CO2 capture from wet flue gas is of great significance to reduce the CO2 emissions, but elucidating the most critical structure features for boosting CO2 capture capabilities remains a great challenge. Here, machine-learning-assisted Monte Carlo computational screening on 516 experimental covalent organic frameworks (COFs) identifies the superior secondary building units (SBUs) for wet flue gas separation using COFs, which are tetraphenylporphyrin units for boosting CO2 adsorption uptake and functional groups for boosting CO2/N2 selectivity. Accordingly, 1233 COFs are assembled using the identified superior SBUs. Density functional theory calculation analysis on frontier orbitals, electrostatic potential, and binding energy reveals the influencing mechanism of the SBUs on the wet flue gas separation performance. The "electron-donating-induced vdW interaction" effect is discovered to construct the better-performing COFs, which can achieve high CO2 uptake of 4.4 mmol·g-1 with CO2/N2 selectivity of 104.8. Meanwhile, the "electron-withdrawing-induced vdW + electrostatic coupling interaction" effect is unearthed to construct the better-performing COFs with superior CO2/N2 selectivity, which can reach 277.6 with CO2 uptake of 2.2 mmol·g-1; in this case, H2O plays a positive contribution in improving CO2/N2 selectivity. This work provides useful guidelines for designing optimized two-dimensional-COF adsorbents for wet flue gas separation.

Telluride Nanocrystals with Adjustable Amorphous Shell Thickness and Core-Shell Structure Modulation by Aqueous Cation Exchange.

Engineering the structure of core-shell colloidal semiconductor nanoparticles (CSNPs) is attractive due to the potential to enhance photo-induced charge transfer and induce favorable optical and electronic properties. Nonetheless, the sensitivity of telluride CSNPs to high temperatures makes it challenging to precisely modulate their surface crystallinity. Herein, we have developed an efficient strategy for synthesizing telluride CSNPs with thin amorphous shells using aqueous cation exchange (ACE). By changing the synthesis temperature in the range of 40-110 °C, the crystallinity of the CdTe nanoparticles was controllable from perfect crystals with no detectable amorphous shell (c-CdTe) to a core-shell structure with a crystalline CdTe NP core covered by an amorphous shell of tunable thickness up to 7-8 nm (c@a-CdTe). A second ACE step transformed c@a-CdTe to crystalline CdTe@HgTe core-shell NPs. The c@a-CdTe nanoparticles synthesized at 60 °C and having a 4-5 nm thick amorphous shell exhibited the highest surface-enhanced Raman scattering activity with a high enhancement factor around 8.82 × 105, attributed to the coupling between the amorphous shell and the crystalline core.

POSS and imidazolium-constructed ionic porous hypercrosslinked polymers with multiple active sites for synergistic catalytic CO2 transformation.

In this work, we reported a facile one-pot approach to construct polyhedral oligomeric silsesquioxane (POSS) and imidazolium-based ionic porous hypercrosslinked polymers (denoted as iPHCPs) with multiple active sites towards efficient catalytic conversion of carbon dioxide (CO2) to high value-added cyclic carbonates. The targeted iPHCPs were synthesized from a rigid molecular building block octavinylsilsesquioxane (VPOSS) and a newly-designed phenyl-based imidazolium ionic crosslinker through the AlCl3-catalyzed Friedel-Crafts reaction. The desired multiple active sites come from the mixed anions including free Cl- and Br- anions, and in situ formed Lewis acidic metal-halogen complex anions [AlCl3Br]- within imidazolium moieties and POSS-derived Si-OH groups during the synthetic process. The typical polymer iPHCP-12 possesses a hierarchical micro-/mesoporous structure with a high surface area up to 537 m2 g-1 and shows a fluffy nano-morphology. By virtue of the co-existence of free nucleophilic Cl- and Br- anions, the metal complex anion [AlCl3Br]- with both electrophilic and nucleophilic characters and electrophilic hydrogen bond donor (HBD) Si-OH groups, iPHCP-12 is regarded as an efficient recyclable heterogeneous catalyst for synergistic catalytic conversion of CO2 with various epoxides into cyclic carbonates under mild conditions. The present work provides a succinct one-pot strategy to construct task-specific ionic porous hypercrosslinked polymers from easily available modules for the targeted catalytic applications.

Carbon/Sulfur Aerogel with Adequate Mesoporous Channels as Robust Polysulfide Confinement Matrix for Highly Stable Lithium-Sulfur Battery.

The ability to restrict the shuttle of lithium polysulfide (LiPSn) and improve the utilization efficiency of sulfur represents an important endeavor toward practical application of lithium-sulfur (Li-S) batteries. Herein, we report the crafting of a robust 3D graphene-wrapped, nitrogen-doped, highly mesoporous carbon/sulfur (G-NHMC/S) hierarchical aerogel as an effective polysulfide confinement matrix for a highly stable Li-S battery. Rich polar sites of NHMC firmly anchor LiPSn on the matrix surface. Porous NHMC provides ample space for accommodating sulfur and cushioning its volume expansion. Moreover, graphene wrapped on NHMC/S not only physically hinders the LiPSn shuttle but also interconnects the isolated NHMC/S, thus increasing electron transfer rate. Taken together, triple confinement of G-NHMC/S aerogel synergistically retains the soluble LiPSn and displays a specific capacity of 1322 mAh g-1 and 1000-cycle life. As such, rationally designed 3D carbon/sulfur aerogel affords a unique platform to impart high energy density and stable electrodes for energy storage devices.

Metalated-bipyridine-based porous hybrid polymers with POSS-derived Si-OH groups for synergistic catalytic CO2 fixation.

Herein, we construct a new series of N-heterocyclic ligand bipyridine-based porous hybrid polymers (denoted Bpy-PHPs) from the Heck reaction of a rigid building unit octavinylsilsesquioxane (VPOSS) and 5,5'-dibromo-2,2'-bipyridine. Surprisingly, the typical sample Bpy-PHP-4 was found to be a metal-/halogen-free heterogeneous catalyst in the cycloaddition reaction of CO2 with a few epoxides under atmospheric pressure. After coordination with ZnBr2, the resultant ZnBr2@Bpy-PHP-4 afforded largely enhanced heterogeneous catalytic activities upon the conversion of carbon dioxide (CO2) and various epoxides into cyclic carbonates without using any co-catalysts under mild conditions. The moderate catalytic activities of Bpy-PHP-4 may be due to the presence of hydrogen bond donors (HBDs), i.e., polyhedral oligomeric silsesquioxane (POSS)-derived Si-OH groups and N active sites from Bpy linkers. In comparison, the high catalytic efficiency of ZnBr2@Bpy-PHP-4 should be attributed to the synergistic catalysis of Si-OH groups, N active atoms, and Bpy-coordinated ZnBr2. Moreover, the catalyst ZnBr2@Bpy-PHP-4 can be easily recovered and reused ten times without any significant loss of catalytic activities. This work affords an efficient metal-based porous hybrid polymer heterogeneous catalyst for the cycloaddition reaction of CO2 and epoxides under mild and co-catalyst-free conditions.

An easy way to identify high performing covalent organic frameworks for hydrogen storage.

The complexity of secondary building units (SBUs), an indicator that can not only be calculated but also visually estimated, is proposed as a highly indicative predictor of hydrogen storage performance. With optimal pore sizes and void fractions, selecting COFs consisting of simple SBUs greatly improves the probability of top-performing COFs towards the ultimate DOE hydrogen storage target, as an easy principle for experimentalists to select hydrogen adsorbents.

Ultrathin Two-Dimensional Membranes Assembled by Ionic Covalent Organic Nanosheets with Reduced Apertures for Gas Separation.

Covalent organic frameworks (COFs) are a promising category of porous materials possessing extensive chemical tunability, high porosity, ordered arrangements at a molecular level, and considerable chemical stability. Despite these advantages, the application of COFs as membrane materials for gas separation is limited by their relatively large pore apertures (typically >0.5 nm), which exceed the sieving requirements for most gases whose kinetic diameters are less than 0.4 nm. Herein, we report the fabrication of ultrathin two-dimensional (2D) membranes through layer-by-layer (LbL) assembly of two kinds of ionic covalent organic nanosheets (iCONs) with different pore sizes and opposite charges. Because of the staggered packing of iCONs with strong electrostatic interactions, the resultant membranes exhibit features of reduced aperture size, optimized stacking pattern, and compact dense structure without sacrificing thickness control, which are suitable for molecular sieving gas separation. One of the hybrid membranes, TpEBr@TpPa-SO3Na with a thickness of 41 nm, shows a H2 permeance of 2566 gas permeation units (GPUs) and a H2/CO2 separation factor of 22.6 at 423 K, surpassing the recent Robeson upper bound along with long-term hydrothermal stability. This strategy provides not only a high-performance H2 separation membrane candidate but also an inspiration for pore engineering of COF or 2D porous polymer membranes.

Two-in-one: construction of hydroxyl and imidazolium-bifunctionalized ionic networks in one-pot toward synergistic catalytic CO2 fixation.

A succinct strategy was demonstrated for constructing a hydroxyl group and imidazolium-bifunctionalized ionic network via a one-pot quaternization. Key to success lies in the rational design of multi-imidazole precursor and hydroxyl-containing counterpart. Unique properties of the resultant ionic network render its high catalytic efficiency toward CO2 fixation under ambient conditions.

Facile synthesis of crystalline viologen-based porous ionic polymers with hydrogen-bonded water for efficient catalytic CO2 fixation under ambient conditions.

In this work, we report a series of crystalline viologen-based porous ionic polymers (denoted VIP-X, X = Cl or Br), that have in situ formed dicationic viologens paired with halogen anions and intrinsic hydrogen-bonded water molecules, towards metal-free heterogeneous catalytic conversion of carbon dioxide (CO2) under mild conditions. The targeted VIP-X materials were facilely constructed via the Menshutkin reaction of 4,4'-bipyridine with 4,4'-bis(bromomethyl)biphenyl (BCBMP) or 4,4'-bis(chloromethyl)biphenyl (BBMBP) monomers. Their crystalline and porous structures, morphological features and chemical structures and compositions were fully characterized by various advanced techniques. The optimal catalyst VIP-Br afforded a high yield of 99% in the synthesis of cyclic carbonate by CO2 cycloaddition with epichlorohydrin under atmospheric pressure (1 bar) and a low temperature (40 °C), while other various epoxides could be also converted into cyclic carbonates under mild conditions. Moreover, the catalyst VIP-Br could be separated easily and reused with good stability. The remarkable catalytic performance could be attributed to the synergistic effect of the enriched Br- anions and available hydrogen bond donors -OH groups coming from H-bonded water molecules.

Materials genomics methods for high-throughput construction of COFs and targeted synthesis.

Materials genomics represents a research mode for materials development, for which reliable methods for efficient materials construction are essential. Here we present a methodology for high-throughput construction of covalent organic frameworks (COFs) based on materials genomics strategy, in which a gene partition method of genetic structural units (GSUs) with reactive sites and quasi-reactive assembly algorithms (QReaxAA) for structure generation were proposed by mimicking the natural growth processes of COFs, leading to a library of 130 GSUs and a database of ~470,000 materials containing structures with 10 unreported topologies as well as the existing COFs. As a proof-of-concept example, two generated 3D-COFs with ffc topology and two 2D-COFs with existing topologies were successfully synthesized. This work not only presents useful genomics methods for developing COFs and largely extended the COF structures, but also will stimulate the switch of materials development mode from trial-and-error to theoretical prediction-experimental validation.

Constructing POSS and viologen-linked porous cationic frameworks induced by the Zincke reaction for efficient CO2 capture and conversion.

POSS and viologen-linked porous cationic frameworks (V-PCIF-X, X = Cl, Br) are constructed via the Zincke reaction between octa(aminophenyl)silsesquioxane and viologen linkers. The typical V-PCIF-Br has a high surface area with abundant ionic sites, micro-/mesopores and Si-OH groups, serving as an efficient porous adsorbent and metal-free catalyst for simultaneous CO2 capture and conversion.

An in situ self-assembly template strategy for the preparation of hierarchical-pore metal-organic frameworks.

Metal-organic frameworks (MOFs) have recently emerged as a new type of nanoporous materials with tailorable structures and functions. Usually, MOFs have uniform pores smaller than 2 nm in size, limiting their practical applications in some cases. Although a few approaches have been adopted to prepare MOFs with larger pores, it is still challenging to synthesize hierarchical-pore MOFs (H-MOFs) with high structural controllability and good stability. Here we demonstrate a facile and versatile method, an in situ self-assembly template strategy for fabricating stable H-MOFs, in which multi-scale soluble and/or acid-sensitive metal-organic assembly (MOA) fragments form during the reactions between metal ions and organic ligands (to construct MOFs), and act as removable dynamic chemical templates. This general strategy was successfully used to prepare various H-MOFs that show rich porous properties and potential applications, such as in large molecule adsorption. Notably, the mesopore sizes of the H-MOFs can be tuned by varying the amount of templates.

Effect of central metal ions of analogous metal-organic frameworks on adsorption of organoarsenic compounds from water: plausible mechanism of adsorption and water purification.

The adsorptive removal of organoarsenic compounds such as p-arsanilic acid (ASA) and roxarsone (ROX) from water using metal-organic frameworks (MOFs) has been investigated for the first time. A MOF, iron benzenetricarboxylate (also called MIL-100-Fe) exhibits a much higher adsorption capacity for ASA and ROX than activated carbon, zeolite (HY), goethite, and other MOFs. The adsorption of ASA and ROX over MIL-100-Fe is also much more rapid than that over activated carbon. Moreover, the used MIL-100-Fe can be recycled by simply washing with acidic ethanol. Therefore, it is determined that a MOF such as MIL-100-Fe can be used to remove organoarsenic compounds from contaminated water because of its high adsorption capacity, rapid adsorption, and ready regeneration. Moreover, only one of three analogous MIL-100 species (MIL-100-Fe, rather than MIL-100-Al or MIL-100-Cr) can effectively remove the organoarsenic compounds. This selective and high adsorption over MIL-100-Fe, different from other analogous MIL-100 species, can be explained (through calculations) by the facile desorption of water from MIL-100-Fe as well as the large (absolute value) replacement energy (difference between the adsorption energies of the organoarsenic compounds and water) exhibited by MIL-100-Fe. A plausible adsorption/desorption mechanism is proposed based on the surface charge of the MOFs, FTIR results, calculations, and the reactivation results with respect to the solvents used in the experiments.

Revealing the structure-property relationship of covalent organic frameworks for CO2 capture from postcombustion gas: a multi-scale computational study.

With the aid of multi-scale computational methods, a diverse set of 46 covalent organic frameworks (COFs), covering the most typical COFs synthesized to date, were collected to study the structure-property relationship of COFs for CO2 capture. For this purpose, CO2 capture from postcombustion gas (CO2-N2 mixture) under industrial vacuum swing adsorption (VSA) conditions was considered as an example. This work shows that adsorption selectivity, CO2 working capacity and the sorbent selection parameter of COFs all exhibit strong correlation with the difference in the adsorbility of adsorbates (ΔAD), highlighting that realization of large ΔAD can be regarded as an important starting point for designing COFs with improved separation performance. Furthermore, it was revealed that the separation performance of 2D-layered COFs can be greatly enhanced by generating "splint effects", which can be achieved through structural realignment to form slit-like pores with suitable size in the structures. Such "splint effects" in 2D-COFs can find their similar counterpart of "catenation effects" in 3D-COFs or MOFs. On the basis of these observations, a new design strategy was proposed to strengthen the separation performance of COFs. It could be expected that the information obtained in this work not only will enrich the knowledge of the structure-property relationship of COFs for separation, but also will largely facilitate their future applications to the fields related to energy and environmental science, such as natural gas purification, CO2, NO(x) and SO(x) capture, etc.