Electrocatalysis CO2 to Tunable Syngas upon Fe Clusters Catalyst Dispersed on Bamboo-like NCTs.

Herein, we report a catalyst of Fe@NBCT with a high performance in electrocatalytic CO2 to syngas with tunable H2/CO ratio. Both in situ synchrotron radiation Fourier transform infrared spectra (SR-FTIR) and density functional theory (DFT) calculation proved that the differing N-doping carbon matrix and Fe nanoclusters (NCs) play dramatic roles in tuning the ratio of syngas during the electrocatalytic carbon dioxide reduction reaction (EC-CO2RR) process.

Ferrocene-Functionalized Crystalline Biomimetic Catalysts for Efficient CO2 Photoreduction.

Photoreducing carbon dioxide (CO2) into highly valued chemicals or energy products has been recognized as one of the most promising proposals to degrade atmospheric CO2 concentration and achieve carbon neutrality. Adenine with a photosensitive amino group and aromatic nitrogen atom can strongly interact with CO2 and has been authenticated for its catalytic activity for the CO2 photoreduction reaction (CO2RR). Herein, two adenine-constructed crystalline biomimetic photocatalysts (Co2-AW and Co2-AF) were designed and synthesized to achieve CO2RR. Between them, Co2-AF displayed higher photocatalytic activity (225.8 µmol g-1 h-1) for CO2-to-HCOOH conversion than that of Co2-AW. It was found that the superior charge transfer capacity of the functional ferrocene group in Co2-AF is the primary reason to facilitate the photocatalytic performance efficiently. Additionally, this work also demonstrated the great potential of the ferrocene group as an electron donor and mediator in improving the photocatalytic activity of crystalline coordination catalysts.

Design of Binary Cu-Fe Sites Coordinated with Nitrogen Dispersed in the Porous Carbon for Synergistic CO2 Electroreduction.

To relieve the green gas emission and involve the carbon neutral cycle, electrochemical reduction of CO2 attracts more and more attention. Herein, a biatomic site catalyst of Cu-Fe coordinated with the nitrogen, which is doped in the carbon matrix (denoted as Cu-Fe-N6 -C), is designed. The as-obtained Cu-Fe-N6 -C exhibits higher performance than that of Cu-N-C and Fe-N-C, owing to bimetallic sites, proving synergistic functions based on different molecules and their interfaces. Cu-Fe-N6 -C shows high selectivity toward CO, with high Faradaic efficiency (98% at -0.7 V), and maintaining 98% of its initial selectivity after 10 h electrolysis. The experimental results and theoretical calculations reveal that the synergistic catalysis of different metallic sites enlarges the adsorption enthalpy of CO2 , reducing the activation energy result in generating high selectivity, activity, stability, and low impedance.

Adenine Components in Biomimetic Metal-Organic Frameworks for Efficient CO2 Photoconversion.

Visible-light driven photoconversion of CO2 into energy carriers is highly important to the natural carbon balance and sustainable development. Demonstrated here is the adenine-dependent CO2 photoreduction performance in green biomimetic metal-organic frameworks. Photocatalytic results indicate that AD-MOF-2 exhibited a very high HCOOH production rate of 443.2 µmol g-1 h-1 in pure aqueous solution, and is more than two times higher than that of AD-MOF-1 (179.0 µmol g-1 h-1 ) in acetonitrile solution. Significantly, experimental and theoretical evidence reveal that the CO2 photoreduction reaction mainly takes place at the aromatic nitrogen atom of adenine molecules through a unique o-amino-assisted activation rather than at the metal center. This work not only serves as an important case study for the development of green biomimetic photocatalysts used for artificial photosynthesis, but also proposes a new catalytic strategy for efficient CO2 photoconversion.

Sub-Nanometer Mono-Layered Metal-Organic Frameworks Nanosheets for Simulated Flue Gas Photoreduction.

The dilemma between the thickness and accessible active site triggers the design of porous crystalline materials with mono-layered structure for advanced photo-catalysis applications. Here, a kind of sub-nanometer mono-layered nanosheets (Co-MOF MNSs) through the exfoliation of specifically designed Co3 cluster-based metal-organic frameworks (MOFs) is reported. The sub-nanometer thickness and inherent light-sensitivity endow Co-MOF MNSs with fully exposed Janus Co3 sites that can selectively photo-reduce CO2 into formic acid under simulated flue gas. Notably, the production efficiency of formic acid by Co-MOF MNSs (0.85 mmol g-1 h-1) is ≈13 times higher than that of the bulk counterpart (0.065 mmol g-1 h-1) under a simulated flue gas atmosphere, which is the highest in reported works up to date. Theoretical calculations prove that the exposed Janus Co3 sites with simultaneously available sites possess higher activity when compared with single Co site, validating the importance of mono-layered nanosheet morphology. These results may facilitate the development of functional nanosheet materials for CO2 photo-reduction in potential flue gas treatment.

Electronic Tuning of CO2 Interaction by Oriented Coordination of N-Rich Auxiliary in Porphyrin Metal-Organic Frameworks for Light-Assisted CO2 Electroreduction.

The efficient CO2 electroreduction into high-value products largely relies on the CO2 adsorption/activation or electron-transfer of electrocatalysts, thus site-specific functionalization methods that enable boosted related interactions of electrocatalysts are much desired. Here, an oriented coordination strategy is reported to introduce N-rich auxiliary (i.e., hexamethylenetetramine, HMTA) into metalloporphyrin metal organic frameworks (MOFs) to synthesize a series of site-specific functionalized electrocatalysts (HMTA@MOF-545-M, M = Fe, Co, and Ni) and they are successfully applied in light-assisted CO2 electroreduction. Noteworthy, thus-obtained HMTA@MOF-545-Co presents approximately two times enhanced CO2 adsorption-enthalpy and electrochemical active surface-area with largely decreased impedance-value after modification, resulting in almost twice higher CO2 electroreduction performance than its unmodified counterpart. Besides, its CO2 electroreduction performance can be further improved under light-illumination and displays superior FECO (≈100%), high CO generation rate (≈5.11 mol m-2  h-1 at -1.1 V) and energy efficiency (≈70% at -0.7 V). Theoretical calculations verify that the oriented coordination of HMTA can increase the charge density of active sites, almost doubly enhance the CO2 adsorption energy, and largely reduce the energy barrier of rate determining step for the boosted performance improvement. This work might promote the development of modifiable porous crystalline electrocatalysts in high-efficiency CO2 electroreduction.

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.

A new supramolecular catalytic system: the self-assembly of Rh8 cage host anthracene molecules for [4 + 4] cycloaddition induced by UV irradiation.

The supramolecular assembly, used as a molecular reactor, is of great significance in host-guest chemistry. In this work, we used a tetratopic pyridyl ligand as a building block to hierarchically combine a slightly twisted cuboid with half-sandwich rhodium fragments. The cuboid directionally self-assembled hydrophobic pockets that can encapsulate conjugated molecules like anthracene (ANT) as guests in solutions, by supramolecular interactions including hydrogen bonding and hydrophobic interactions. The array of the ANT molecules in the confined pockets was subjected to a [4 + 4] photocycloaddition reaction under UV light irradiation as an external stimulus in a methanol solution. Furthermore, the mechanism underlying the process was proposed. The cuboid was fully characterized by 1H NMR, single-crystal X-ray diffraction (SCXRD), and mass spectrometry (MS), and its host-guest and cycloaddition processes were monitored by 1H NMR spectroscopy and UV-visible spectrophotometry.

Hydrophobic Polyoxometalate-Based Metal-Organic Framework for Efficient CO2 Photoconversion.

A novel polyoxometalate (POM)-based metal-organic framework, TBA5[P2Mo16VMo8VIO71(OH)9Zn8(L)4] (NNU-29), was in situ synthesized and applied into CO2 photoreduction. The selection of porous material containing a reductive POM cluster is considered to be helpful for CO2 reduction; meanwhile, a hydrophobic-group-modified organic ligand enables NNU-29 to exhibit good chemical stability and restrains hydrogen generation to some extent. In the photocatalytic CO2 reduction, the yield of HCOO- reached 35.2 µmol in the aqueous solution with selectivity of 97.9% after 16 h.

Enhanced Breakthrough Efficiency by a Chemically Stable Porous Coordination Polymer with Optimized Nanochannel.

High separation efficiency is very important for process of pressure swing adsorption (PSA) in the industry. Herein, we propose a fine design of chemically stable porous coordination polymers (PCPs) with optimized nanochannel by strategy of inserting and shifting shortest alkyl group on T-shaped ligand. Remarkably, the synergistic effect of optimized nanochannel, unique crystal morphology and fitted channel enable sharply enhanced breakthrough efficiency of C2H6/4/CH4, 1.17 or 0.77 g of CH4 can be separated from corresponding dual mixtures (2/8, v/v) by 1 g of NTU-25 at 273 K, which was further validated and understood by controlled experiments and density functional theory (DFT) computations.

Stepwise assembly of a semiconducting coordination polymer [Cd8S(SPh)14(DMF)(bpy)]n and its photodegradation of organic dyes.

Chalcogenolate clusters can be interlinked with organic linkers into semiconducting coordination polymers with photocatalytic properties. Here, discrete clusters of Cd8S(SPh)14(DMF)3 were interlinked with 4,4'-bipyridine into a one dimensional coordination polymer of [Cd8S(SPh)14(DMF)(bpy)]n with helical chains. A stepwise mechanism for the assembly of the coordination polymer in DMF was revealed by an ex situ dynamic light scattering study. The cluster was electrostatically neutral and showed a penta-supertetrahedral structure. During the assembly each cluster was interlinked with two 4,4'-bipyridine molecules, which replaced the two terminal DMF molecules of the clusters. In their solid-state forms, the cluster and the coordination polymer were semiconductors with wide band gaps of 3.08 and 2.80 ev. They photocatalytically degraded rhodamine B and methylene blue in aqueous solutions. The moderate conditions used for the synthesis could allow for further in situ studies of the reaction-assembly of related clusters and coordination polymers.

Keggin POM microtubes: a coincident product of crystal growth and species transformation.

Microtubes of alpha-K4SiW12O40 with the length around 1 cm and inner diameter and wall thickness in the ranges of 7-55 mum and 3-15 mum, respectively, were copiously fabricated by a one-step, template-free aqueous synthesis. The formation mechanism is discussed. The discovered tubular structure of the polyoxometalate is believed to be promising for use in templates, as a precursor of tungsten oxide ceramic microtubes, and for other uses associated with tubular structures.