Artificial photosynthetic system for diluted CO2 reduction in gas-solid phase.

Rational design of robust photocatalytic systems to direct capture and in-situ convert diluted CO2 from flue gas is a promising but challenging way to achieve carbon neutrality. Here, we report a new type of host-guest photocatalysts by integrating CO2-enriching ionic liquids and photoactive metal-organic frameworks PCN-250-Fe2M (M = Fe, Co, Ni, Zn, Mn) for artificial photosynthetic diluted CO2 reduction in gas-solid phase. As a result, [Emim]BF4(39.3 wt%)@PCN-250-Fe2Co exhibits a record high CO2-to-CO reduction rate of 313.34 µmol g-1 h-1 under pure CO2 atmosphere and 153.42 µmol g-1 h-1 under diluted CO2 (15%) with about 100% selectivity. In scaled-up experiments with 1.0 g catalyst and natural sunlight irradiation, the concentration of pure and diluted CO2 (15%) could be significantly decreased to below 85% and 10%, respectively, indicating its industrial application potential. Further experiments and theoretical calculations reveal that ionic liquids not only benefit CO2 enrichment, but also form synergistic effect with Co2+ sites in PCN-250-Fe2Co, resulting in a significant reduction in Gibbs energy barrier during the rate-determining step of CO2-to-CO conversion.

Solid-Liquid-Gas Three-Phase Indirect Electrolysis Enabled by Affinity Auxiliary Imparted Covalent Organic Frameworks.

The design of efficient heterogeneous redox mediators with favorable affinity to substrate and electrolyte are much desired yet still challenging for the development of indirect electrolysis system. Herein, for the first time, we have developed a solid-liquid-gas three-phase indirect electrolysis system based on a covalent organic framework (Dha-COF-Cu) as heterogeneous redox mediator for S-S coupling reaction. Dha-COF-Cu with the integration of high porosity, nanorod morphology, abundant hydroxyl groups and active Cu sites is much beneficial for the adsorption/activation of thiols, uniform dispersion and high wettability in electrolyte, and efficient interfacial electron transfer. Notably, Dha-COF-Cu as solid-phase redox mediator exhibits excellent electrocatalytic efficiency for the formation of value-added liquid-phase S-S bond product (yields up to 99 %) coupling with the generation of gas-phase product of H2 (~1.40 mmol g-1 h-1), resulting in a powerful three-phase indirect electrolysis system. This is the first work about COFs that can be applied in three-phase indirect electrolysis system, which might promote the development of porous crystalline materials in this field.

Constructing Functional Radiation-Resistant Thorium Clusters for Catalytic Redox Reactions.

When catalytic reactions are interfered with by radiation sources, thorium clusters are promising as potential catalysts due to their superior radiation resistance. However, there is currently very little research on the design synthesis and catalytic application of radiation-stable thorium clusters. In this work, we have elaborately engineered and fabricated three high-nuclear thorium cluster catalysts denoted as Th12L3-MA12, Th12L3-MA6-BF6, and Th12L3-Fcc12, which did not undergo any significant alterations in their molecular structures and compositions after irradiation with 690 kGy γ-rays. We systematically investigated the photocatalytic/thermocatalytic properties of these radiation-resistant thorium clusters for the first time and found that γ-rays could not alter their catalytic activities. In addition, it was found that ligand engineering could modulate the catalytic activity of thorium clusters, thus expanding the range of catalytic applications of thorium clusters, including reduction reactions (nitroarene reduction) and some oxidation reactions (N-heterocyclic oxidative dehydrogenation and diphenylmethane oxidation). Meanwhile, all of these organic transformation reactions achieved a >80% conversion and nearly 100% product selectivity. Radiation experiments combined with DFT calculations showed that the synergistic catalysis of thorium-oxo core and ligands led to the generation of specific active species (H+, O2•-, or tBuO/tBuOO•) and activation of substrate molecules, thus achieving superior catalytic performance. This work is not only the first to develop radiation-resistant thorium cluster catalysts to perform efficient redox reactions but also provides design ideas for the construction of high-nuclearity thorium clusters under mild conditions.

Hybrid Membrane of Sulfonated Poly(aryl ether ketone sulfone) Modified by Molybdenum Clusters with Enhanced Proton Conductivity.

Developing novel proton exchange membranes (PEMs) with low cost and superior performance to replace Nafion is of great significance. Polyoxometalate-doped sulfonated poly(aryl ether ketone sulfone) (SPAEKS) allows for the amalgamation of the advantages in each constituent, thereby achieving an optimized performance for the hybrid PEMs. Herein, the hybrid membranes by introducing 2MeIm-{Mo132} into SPAEKS are obtained. Excellent hydrophilic properties of 2MeIm-{Mo132} can help more water molecules be retained in the hybrid membrane, providing abundant carriers for proton transport and proton hopping sites to build successive hydrophilic channels, thus lowering the energy barrier, accelerating the proton migration, and significantly fostering the proton conductivity of hybrid membranes. Especially, SP-2MIMo132-5 exhibits an enhanced proton conductivity of 75 mS cm-1 at 80 °C, which is 82.9% higher than pristine SPAEKS membrane. Additionally, this membrane is suitable for application in proton exchange membrane fuel cells, and a maximum power density of 266.2 mW cm-2 can be achieved at 80 °C, which far exceeds that of pristine SPAEKS membrane (54.6 mW cm-2). This work demonstrates that polyoxometalate-based clusters can serve as excellent proton conduction sites, opening up the choice of proton conduction carriers in hybrid membrane design and providing a novel idea to manufacture high-performance PEMs.

Anisotropically Hybridized Porous Crystalline Li-S Battery Separators.

Anisotropically hybridized porous crystalline Li-S battery separators based on porous crystalline materials that can meet the multiple functionalities of both anodic and cathodic sides are much desired for Li-S battery yet still challenging in directional design. Here, an anisotropically hybridized separator (CPM) based on an ionic liquid-modified porphyrin-based covalent-organic framework (COF-366-OH-IL) and catalytically active metal-organic framework (Ni3 (HITP)2 ) that can integrate the lithium-polysulfides (LiPSs) adsorption/catalytic conversion and ion-conduction sites together to directionally meet the requirements of electrodes is reported. Remarkably, the-obtained separator exhibits an exceptional high Li+ transference-number (tLi+  = 0.8), ultralow polarization-voltage (<30 mV), high initial specific-capacity (921.38 mAh g-1 at 1 C), and stable cycling-performance, much superior to polypropylene and monolayer-modified separators. Moreover, theoretical calculations confirm the anisotropic effect of CPM on the anodic side (e.g., Li+ transfer, LiPSs adsorption, and anode-protection) and cathodic side (e.g., LiPSs adsorption/catalysis). This work might provide a new perspective for separator exploration.

Achieving High Photo/Thermocatalytic Product Selectivity and Conversion via Thorium Clusters with Switchable Functional Ligands.

Structural exploration and functional application of thorium clusters are still very rare on account of their difficult synthesis caused by the susceptible hydrolysis of thorium element. In this work, we elaborately designed and constructed four stable thorium clusters modified with different functionalized capping ligands, Th6-MA, Th6-BEN, Th6-C8A, and Th6-Fcc, which possessed nearly the same hexanuclear thorium-oxo core but different capabilities in light absorption and charge separation. Consequently, for the first time, these new thorium clusters were treated as model catalysts to systematically investigate the light-induced oxidative coupling reaction of benzylamine and thermodriven oxidation of aniline, achieving >90% product selectivity and approximately 100% conversion, respectively. Concurrently, we found that thorium clusters modified by switchable functional ligands can effectively modulate the selectivity and conversion of catalytic reaction products. Moreover, catalytic characterization and density functional theory calculations consistently indicated that these thorium clusters can activate O2/H2O2 to generate active intermediates O2·-/HOO· and then improved the conversion of amines efficiently. Significantly, this work represents the first report of stable thorium clusters applied to photo/thermotriggered catalytic reactions and puts forward a new design avenue for the construction of more efficient thorium cluster catalysts.

Nickel Glyoximate Based Metal-Covalent Organic Frameworks for Efficient Photocatalytic Hydrogen Evolution.

Metal-covalent organic frameworks (MCOFs) have been recently received wide attention owing to the homogeneous distribution of active metal centers that are beneficial for enhancing the application potentials. However, metal complex based functional building blocks for MCOFs synthesis are limited. Herein, two new MCOFs (Ni-Py-COF and Ni-Bn-COF) were constructed via a novel nickel glyoximate based building block. Splendid photocatalytic activity on hydrogen evolution from water and great long-term recyclability were achieved using these nickel glyoximate based MCOFs as photocatalysts. Excitingly, even without the addition of Pt co-catalyst, the hydrogen evolution rates (HER) of Ni-Py-COF reached up to 626 µmol g-1 h-1 , which is better than many porous organic polymers. This work not only expands the type of building units for MCOFs, but also provides meaningful insights for developing stable, efficient and earth-abundant photocatalysts toward H2 generation.

In Situ Synthesis of Surface-Mounted Novel Nickel(II) Trimer-Based MOF on Nickel Oxide Hydroxide Heterostructures for Enhanced Methanol Electro-Oxidation.

Engineering the heterogeneous interface fusing MOFs and inorganic active component is an effective strategy to improve the electrochemical performance. Herein, we report a new Ni3-based MOF (denoted as CTGU-24) with an infrequent two-fold interpenetrating 3D (3,8)-connected network constructed from Ni(II) trimer and mixed tripodal tectonics for the electrocatalytic methanol oxidation reaction (MOR). In order to improve its stability and activities, the heterogeneous hybrid CTGU-24@NiOOH has been fabricated successfully via the first preparation of the NiOOH nanosphere and then in situ formation of CTGU-24 decorated on the NiOOH surface. Moreover, the integration of CTGU-24@NiOOH and different additives [acetylene black (AB) and ketjen black (KB)], resulting in the optimized hybrid sample AB&CTGU-24@NiOOH (4:4). It attains better MOR performance with an area-specific peak current density of 34.53 mA·cm-2 than pure CTGU-24 (14.99 mA·cm-2) and improved durability in an alkali medium. The new findings indicate that the CTGU-24@NiOOH heterostructure formed in situ and the integration of moderate additives are critical to optimizing and improving electrocatalytic activity of pure MOF crystalline material.

Implanting Polypyrrole in Metal-Porphyrin MOFs: Enhanced Electrocatalytic Performance for CO2RR.

Metal-organic frameworks (MOFs) with plenty of active sites and high porosity have been considered as an excellent platform for the electroreduction of CO2, yet they are still restricted by the low conductivity or low efficiency. Herein, we insert the electron-conductive polypyrrole (PPy) molecule into the channel of MOFs through the in situ polymerization of pyrrole in the pore of MOF-545-Co to increase the electron-transfer ability of MOF-545-Co and the obtained hybrid materials present excellent electrocatalytic CO2RR performance. For example, FECO of PPy@MOF-545-Co can reach up to 98% at -0.8 V, almost 2 times higher than that of bare MOF-545-Co. The high performance might be attributed to the incorporation of PPy that can serve as electric cables in the channel of MOF to facilitate electron transfer during the CO2RR process. This attempt might provide new insights to improve the electrocatalytic performance of MOFs for CO2RR.

Predesign of Catalytically Active Sites via Stable Coordination Cluster Model System for Electroreduction of CO2 to Ethylene.

Purposefully designing the well-defined catalysts for the selective electroreduction of CO2 to C2 H4 is an extremely important but challenging work. In this work, three crystalline trinuclear copper clusters (Cu3 -X, X=Cl- , Br- , NO3 - ) have been designed, containing three active Cu sites with the identical coordination environment and appropriate spatial distance, delivering high selectivity for the electrocatalytic reduction of CO2 to C2 H4 . The highest faradaic efficiency of Cu3 -X for CO2 -to-C2 H4 conversion can be adjusted from 31.90 % to 55.01 % by simply replacing the counter anions (NO3 - , Cl- , Br- ). The DFT calculation results verify that Cu3 -X can facilitate the C-C coupling of identical *CHO intermediates, subsequently forming molecular symmetrical C2 H4 product. This work provides an important molecular model system and a new design perspective for electroreduction of CO2 to C2 products with symmetrical molecular structure.

POMOF/SWNT Nanocomposites with Prominent Peroxidase-Mimicking Activity for l-Cysteine "On-Off Switch" Colorimetric Biosensing.

In order to explore novel colorimetric biosensors with high sensibility and selectivity, two new Keggin polyoxometalates (POMs)-based Cu-trz (1,2,4-triazole) metal-organic frameworks (MOFs) with suitable specific surface areas and multiple active sites were favorably fabricated; then single-walled carbon nanotubes (SWNTs) were merged with new POMOFs to construct POMOF/SWNT nanocomposites. Herein, POMOF/SWNT nanocomposites as peroxidase mimics were explored for the first time, and the peroxidase-mimicking activity of the prepared POMOF/SWNT nanocomposites is heavily dependent on the mass ratio of POMOFs and SWNTs, in which the maximum activity is achieved at the mass ratio of 2.5:1 (named PMNT-2). More importantly, PMNT-2 exhibits the lowest limit of detection (0.103 µM) among all reported materials to date and the assumable selectivity toward l-cysteine (l-Cys) detection. With these findings, a convenient, sensitive, and effective "on-off switch" colorimetric platform for l-Cys detection has been successfully developed, providing a promising prospect in the biosensors and clinical diagnosis fields.

Polyoxometalate-Based Metal-Organic Frameworks with Conductive Polypyrrole for Supercapacitors.

Metal-organic frameworks (MOFs) with high porosity could act as an ideal substitute for supercapacitors, but their poor electrical conductivities limit their electrochemical performances. In order to overcome this problem, conductive polypyrrole (PPy) has been introduced and a novel nanocomposite resulting from polyoxometalate (POM)-based MOFs (NENU-5) and PPy has been reported. It comprises the merits of POMs, MOFs, and PPy. Finally, the highly conductive PPy covering the surfaces of NENU-5 nanocrystallines can effectively improve the electron/ion transfer among NENU-5 nanocrystallines. The optimized NENU-5/PPy nanocomposite (the volume of Py is 0.15 mL) exhibits high specific capacitance (5147 mF·cm-2), larger than that of pristine NENU-5 (432 mF·cm-2). Furthermore, a symmetric supercapacitor device based on a NENU-5/PPy-0.15 nanocomposite possesses an excellent areal capacitance of 1879 mF·cm-2, which is far above other MOF-based supercapacitors.

Polyoxometalate-Decorated g-C3 N4 -Wrapping Snowflake-Like CdS Nanocrystal for Enhanced Photocatalytic Hydrogen Evolution.

Photocatalytic hydrogen evolution technology is recognized as a promising approach to relieving the growing energy crisis. Therefore, the development of a stable high-performance photocatalyst has long been the focus of research. In this work, quaternary composite materials involving a snowflake-like CdS nanocrystal wrapped by different amounts of polyoxometalate-decorated g-C3 N4 and polypyrrole (GPP@CdS) have been synthesized as photocatalysts for hydrogen production under visible-light irradiation. It has been revealed that the best composite (40 % GPP@CdS composite) exhibits hydrogen production activity of 1321 µmol, which exceeds that of CdS by a factor of more than two, and can be used in at least seven cycles with negligible loss of activity. The enhanced photocatalytic performance has been primarily attributed to the efficient synergy of CdS, g-C3 N4 , polypyrrole (PPy), and the polyoxometalate Ni4 (PW9 )2 . It should be noted that the introduction of PPy and g-C3 N4 into the title composite simultaneously promotes electron/hole pair separation and photocatalytic stability, whereas Ni4 (PW9 )2 serves as an efficient electron modulator and extra catalytic active site.

Correction: A microporous Cu-MOF with optimized open metal sites and pore spaces for high gas storage and active chemical fixation of CO2.

Correction for 'A microporous Cu-MOF with optimized open metal sites and pore spaces for high gas storage and active chemical fixation of CO2' by Chao-Ying Gao et al., Chem. Commun., 2016, 52, 11147-11150.

Syntheses of Exceptionally Stable Aluminum(III) Metal-Organic Frameworks: How to Grow High-Quality, Large, Single Crystals.

The difficulty of obtaining large single crystals of aluminum carboxylate metal-organic frameworks (MOFs) for structure determinations has limited the development of these water and thermally stable MOFs. Herein, how large single crystals of known MIL-53(Al) and the first two tetrahedral ligand-based, visible-light-absorbing 3D Al-MOFs, [Al3 (OH)3 (HTCS)2 ] (AlTCS-1) and [Al5 O2 (OH)3 (TCS)2 (H2 O)2 ] (AlTCS-2; TCS=tetrakis(4-oxycarbonylphenyl)silane), are obtained in the presence of hydrofluoric or formic acid for conventional single-crystal diffraction measurements is presented. The technique of obtaining those single crystals has potential to be a general method for obtaining large and good-quality single crystals of Al-MOFs. AlTCS-1 and -2 are stable over a wide pH range (1-11), and AlTCS-1 is even stable in aqua regia solution for at least 24 h. The BET specific surface areas of AlTCS-1 and -2 are 11 and 1506 m2 g-1 , respectively. AlTCS-2 takes up 51 cm3 (STP) g-1 CO2 and 15 cm3 (STP) g-1 CH4 at 298 K and 1 bar, which is relatively high among MOF materials. AlTCS-1 takes up 30 cm3 g-1 CO2 and 4.2 cm3 g-1 CH4 at 298 K and 1 bar. The rapid and stable photocurrent responses of AlTCS-1 and -2 under UV and visible-light illumination are observed. Moreover, AlTCS-1 photocatalyzes the water-splitting reaction under visible light with an average hydrogen evolution efficiency of 50 µmol g-1 h-1 for the first 10 h in a mixture of water and triethanolamine.

Controllable porosity conversion of metal-organic frameworks composed of natural ingredients for drug delivery.

Two extremely rare ß-cyclodextrin (ß-CD) supported metal-organic frameworks (MOFs), CD-MOF-1 and CD-MOF-2, were induced to crystallize for the first time through a template-induced approach. The targeted CD-MOFs were employed to perform controlled drug delivery and cytotoxicity assays that confirmed their favourable biological potential of being used as drug carriers.

Bimetallic Carbides-Based Nanocomposite as Superior Electrocatalyst for Oxygen Evolution Reaction.

The development of highly efficient and low-cost oxygen evolution electrocatalysts is extremely imperative for the new energy technology. Transition metal carbides have been investigated as remarkable hydrogen evolution reaction (HER) electrocatalysts but undesired oxygen evolution reaction (OER) electrocatalysts and need further study. Here, a cobalt-molybdenum-based bimetallic carbide coated by N-doped porous carbon and anchored on N-doped reduced graphene oxide film (Co6Mo6C2/NCRGO) is synthesized by directly carbonizing the Co-doped polyoxometalate/conductive polymer/graphene oxide (Co-PCG) precursors. The precise control of the Co/Mo molar ratio in the Co-PCG precursor is of critical importance to synthesize pure phase bimetallic carbide of Co6Mo6C2. As the highly active and robust OER electrocatalyst, the Co6Mo6C2/NCRGO composite exhibits excellent activity in alkaline solution, affording a low overpotential of 260 mV versus RHE at 10 mA cm-2, a small Tafel slope of 50 mV dec-1, as well as long-term stability. The superior OER performances are strongly associated with the active Co6Mo6C2 particles, polypyrrole (PPy)-derived N-doped porous carbon, and the conductive RGO films. Remarkably, it is the first evidence that the bimetallic carbides were used as the OER catalysts with such high OER activity.

Efficient Electrocatalyst for the Hydrogen Evolution Reaction Derived from Polyoxotungstate/Polypyrrole/Graphene.

Efficient hydrogen evolution reaction (HER) from water by electrocatalysis using cost-effective materials is critical to realize the clean hydrogen production. Herein, with controlling the structure and composition of polyoxotungstate/conductive polypyrrole/graphene (PCG) precursor precisely and followed by a temperature-programmed reaction, we developed a highly active and stable catalyst: NC@Wx C/NRGO (NC: nitrogen-doped porous carbon, NRGO: nitrogen-doped reduced graphene oxide). The composite presents splendid performance towards HER in acidic media, with a small onset overpotential of 24 mV versus RHE (reversible hydrogen electrode), a low Tafel slope of 58.4 mV dec-1 , a low overpotential of 100 mV at 10 mA cm-2 , and remarkable long-term cycle stability. This is one of the highest HER catalysts among the tungsten carbide-based materials ever reported.

Polyoxomolybdate-Polypyrrole/Reduced Graphene Oxide Nanocomposite as High-Capacity Electrodes for Lithium Storage.

A nanocomposite polyoxomolybdate (PMo12)-polypyrrole (PPy)/reduced graphene oxide (RGO) is fabricated by using a simple one-pot hydrothermal method as an electrode material for lithium-ion batteries. This facile strategy skillfully ensures that individual polyoxometalate (POM) molecules are uniformly immobilized on the RGO surfaces because of the wrapping of polypyrrole (PPy), which avoids the desorption and dissolution of POMs during cycling. The unique architecture endows the PMo12-PPy/RGO with the lithium storage behavior of a hybrid battery-supercapacitor electrode: the nanocomposite with a lithium storage capacity delivers up to 1000 mAh g-1 at 100 mA g-1 after 50 cycles. Moreover, it still demonstrates an outstanding rate capability and a long cycle life (372.4 mAh g-1 at 2 A g-1 after 400 cycles). The reversible capacity of this nanocomposite has surpassed most pristine POMs and POMs-based electrode materials reported to date.

A microporous Cu-MOF with optimized open metal sites and pore spaces for high gas storage and active chemical fixation of CO2.

A microporous Cu-MOF with optimized open metal sites and pore space was constructed based on a designed bent ligand; it exhibits high-capacity multiple gas storage under atmospheric pressure and efficient catalytic activity for chemical fixation of CO2 under mild conditions.