Molecular Compartments Created in Metal-Organic Frameworks for Efficient Visible-Light-Driven CO2 Overall Conversion

Construction of molecular compartments on the HKUST-1 for space-limited enhancement of visible light CO2 reduction

The construction of host structures with well-defined compartments that dispersedly accommodate catalytically active substances is a promising approach to significantly improve catalytic activity. Herein, we created separated compartments on the copper-based metal-organic framework (HKUST-1) by a mixed solvent-assisted approach and dispersedly confined tungstophosphoric acid hydrate (H3PW12O40) in its inner cavity structure to form the photocatalyst H3PW12O40@HKUST-1 with a novel "molecular compartment" structure. This structure not only enables the photosensitizer to be enriched in the interior of the "molecular compartment" structure to accelerate the photogenerated charge transfer but also creates a synergistic interaction between the H3PW12O40 units and the catalytic metal clusters in the main structure of the HKUST-1 to facilitate the photocatalytic CO2 reduction. H3PW12O40@HKUST-1 exhibits high CO2 to CO (415 μmol·g-1·h-1) and CH4 (37 μmol·g-1·h-1) conversion, corresponding to 73.9 % and 26.1 % selectivities for CO and CH4. This work provides a novel approach for the rational design of efficient catalysts for CO2 reduction.

Nanocatalysts encapsulated in metal-organic frameworks: Size control and positive influences

Beyond traditional porous materials, metal-organic frameworks (MOFs) have attracted considerable attention for fabricating encapsulated nanocatalysts in the pores/cavities/channels of MOFs due to the high surface area, porous structure, and a large variety of organic linkers. As the host for nanocatalyst encapsulation, MOFs can provide uniform hierarchical pores and channels that can accelerate the mass transfer and migration of reactants or products and various metal‑oxygen clusters and organic linkers, which may interact strongly with nanocatalysts. Herein, state-of-the-art advancements in the encapsulation of nanocatalysts, including catalyst nanoparticles, clusters, quantum dots, and single-atom catalysts, have been summarized. The synthetic methods for nanocatalysts in MOFs and the enhanced properties are especially discussed. Then, positive effects upon the encapsulation of nanocatalysts in MOFs, including tunable chemical environment and encapsulation effects have been explored. Notably, the catalytic activity and product selectivity can be much improved by regulating the chemical environment around nanocatalysts and the interaction between the active nanocatalysts and metal nodes or organic linkers. Finally, challenges and future perspectives in encapsulated nanocatalysts in MOFs are proposed. This review could shed light on the construction of stable nanocatalysts encapsulation in MOFs with maximum exposed active sites and excellent activity in significant reactions.

Rational Design of MOF-Based Multifunctional Bio-Nanoreactor for Efficient Detection and Photo-Degradation of Chloramphenicol

Food safety have received increasing attention in recent years, and rapid detection and thorough removal of organic contaminants is an important part of food safety control. In this work, a novel multi-functional photo-enzymatic nanoreactor HRP@Fe-NU-1003 is developed through the co-immobilization of horseradish peroxidase (HRP) and FeCl2 on a photosensitive metal-organic frameworks (MOF) NU-1003. The bio-nanocluster can serve as an efficient biosensor in the detection of chloramphenicol (CAP), with a detection limit of 15.38 pg mL-1, which is 62 times greater than that of the conventional HRP- enzyme-linked immunosorbent assay method. Besides its detecting capability, the nanoreactor also exhibits high efficiency in the photocatalytic degradation of CAP, which can remove 50 µg mL-1 of CAP thoroughly within 30 min, and the mineralization efficiency of CAP reaches 61%. In this material, Fe-NU-1003 not only acts as a protecting shell to prevent HRP from deactivation, but improves detecting sensitivity and photocatalytic performance. Mechanism studies show that FeCl2 enhances its photocatalytic performance through promoting electron (e-)-hole (h+) separation and photocurrent transfer. More importantly, the heterogeneous material possesses high stability and can be recycled at least five rounds while its photocatalytic performance maintained at a high level. This strategy provides a new approach for the detection and degradation of pollutants.

Steering electron flow by constructing an integrated structure in a metal-organic framework (MOF) via iminopyridine units for efficient CO2 photoreduction to C2H4 and C2H6

Selective photoreduction of CO2 to C2+ products has attracted increasing interest, but it remains challenging. Herein, we reported a novel strategy to steer electron flow by constructing integrated photocatalysts to achieve selective photoreduction of CO2 to C2H4 and C2H6. Using iminopyridine units in NH2-MIL-125(Ti) (Ti-MOF) as a tag, both the Ru photosensitizer and CuCo active sites were assembled within the Ti-MOF to form the integrated structure. Due to the strong interaction of the Ru photosensitizer and CuCo with Ti-MOF, the integrated CuCo/Ti-MOF-Py-Ru exhibited accelerated charge separation and migration efficiency, resulting in significant electron accumulation around CuCo. Compared with the discrete counterparts, the CO2 photoreduction products were upgraded from CO and CH4 to C2H4 and C2H6, with a high C2 selectivity of 86.1% over the integrated CuCo/Ti-MOF-Py-Ru, highlighting the critical role of the integrated structure in enhancing the selective CO2 photoreduction to C2+ products.

Regulated Second-sphere Coordination in Amorphous Metal-organic Framework for Efficient CO2 Fixation

The endeavor toward photocatalytic CO2 fixation is largely hampered by the rigid spatial configurations and inadequate orbital overlap between the catalytic site and CO2. Herein, we propose a second-sphere coordination regulation strategy by atomically tailoring the metal-metal coordination of the secondary building unit (SBU). Amorphous metal-organic framework (a-MOF) is constructed as proof-of-concept to achieve creative control over the second coordination sphere. Such architecture transforms rigid trinuclear nodes into flexible dinuclear motifs. This shift can open spatial proximity to access the guest molecules and optimize s-π* overlap by enabling orbital reorientation. Both in situ experiments and theoretical calculations verify second-sphere engineering endows the Lewis base sites with high electron donating capacity and promotes the electron injection into the π* anti-bonding orbitals of the CO2 molecule effectively. Hence, the a-MOF displays approximately double the yield in various photocatalytic CO2 reactions compared with its crystalline counterpart. Moreover, its photo-assisted Li-CO2 battery delivers higher discharging voltage and a fourfold increment of discharge capacity at 200 µA cm-2. The unique ability to tailor the secondary coordination sphere performs attractive merits governing the small molecule binding affinity, aiming to manipulate the local microenvironment of open metal sites for efficient CO2 fixation.

Mechanistic Insights Into H2O Dissociation in Overall Photo-/Electro-Catalytic CO2 Reduction

Photo-/electro-catalytic CO2 reduction with H2O to produce fuels and chemicals offers a dual solution to address both environmental and energy challenges. For a long time, catalyst design in this reaction system has primarily focused on optimizing reduction sites to improve the efficiency or guide the reaction pathway of the CO2 reduction half-reaction. However, less attention has been paid to designing activation sites for H2O to modulate the H2O dissociation half-reaction. Impressively, the rate-determining step in overall CO2 reduction is the latter, and it influences the evolution direction and formation energy of carbon-containing intermediates through the proton-coupled electron transfer process. Herein, we summarize the mechanism of the H2O dissociation half-reaction in modulating CO2 reduction performance based on cutting-edge research. These analyses aim to uncover the potential regulatory mechanisms by which H2O activation influences CO2 reduction pathways and conversion efficiency, and to establish a mechanism-structure-performance relationship that can guide the design and development of high-efficiency catalytic materials. A summary of advanced characterization techniques for investigating the dissociation mechanism of H2O is presented. We also discuss the challenges and offer perspectives on the future design of activation sites to improve the performance of photo-/electro-catalytic CO2 reduction.

Unraveling the Essential Role of Consecutive Protonation Steps in Photocatalytic CO2 Reduction when Using Au Nanorods in a MOF

The proton-coupled electron transfer process (PCET) plays a crucial role in both natural and artificial photosynthesis, including CO2 fixation chemistry. However, difficulties in capturing the transient intermediates generated during the protonation process impede the clarification of the fundamental mechanism behind photocatalytic CO2 reduction. Herein, we report a general killing two birds with one stone strategy by spatially confining Au nanorods within a typical porphyrin metal-organic framework (MOF). Interestingly, 2.4-fold increase in CH4/CO selectivity and 12-fold increase in CH4 production were observed after loading of Au nanorods, indicative of a strengthened protonation process in the photocatalytic CO2 reduction. More importantly, the plasmonic effect from Au nanorods simultaneously boosted the in situ Raman signals of *CO and *CHO intermediates on the Au-O-Zr active site. The evident protonation process was further clarified in a control H/D kinetic isotope experiment. This work highlights the significance of successive protonation steps for boosting CH4 production in photocatalytic CO2 reduction.

High-Performance Overall Water Splitting Dominated by Direct Ligand-to-Cluster Photoexcitation in Metal-Organic Frameworks

Expanding the spectral response of photocatalysts to facilitate overall water splitting (OWS) represents an effective approach for improving solar spectrum utilization efficiency. However, the majority of single-phase photocatalysts designed for OWS primarily respond to the ultraviolet region, which accounts for a small proportion of sunlight. Herein, we present a versatile strategy to achieve broad visible-light-responsive OWS photocatalysis dominated by direct ligand-to-cluster charge transfer (LCCT) within metal-organic frameworks (MOFs). Three synthesized OWS MOFs, namely Fe2MCbz (M2+ = Mn2+, Co2+, Ni2+), exhibited intrinsic OWS capability without the requirement for extra photosensitizer or sacrificial agent or cocatalyst. Among these, Fe2NiCbz was identified as the superior performer, and when dispersed with polyacrylonitrile nanofibers using electrospinning technology, it achieved the highest OWS rates of 170.2 and 85.1 μmol g-1 h-1 for H2 and O2 evolution, surpassing all previously documented MOF-based photocatalysts. Experimental and theoretical analyses revealed that direct LCCT played a crucial role in enhancing the photocatalytic efficiency, with exceptional performance of Fe2NiCbz attributed to its well-optimized energy level structures and highly efficient charge transfer mechanism. This work not only sets a benchmark in OWS MOF photocatalysts but also paves the way for maximizing solar spectrum utilization, thereby advancing renewable hydrogen production strategy.

Electron Microscopy Reveals Inhomogeneous Adsorption of Iodine and Concurrent Defect Formation in a Metal-Organic Framework

Adsorption behaviors are typically examined through adsorption isotherms, which measure the average adsorption amount as a function of partial pressure or time. However, this method is incapable of identifying inhomogeneities across the adsorbent, which may occur in the presence of strong intermolecular interactions of the adsorbate. In this study, we visualize the adsorption of molecular iodine (I2) in the metal-organic framework material MFM-300(Sc) using high-resolution scanning transmission electron microscopy (STEM). Our observations demonstrate that, counterintuitively, I2 adsorption in MFM-300(Sc) occurs in an inhomogeneous manner, regardless of the I2 uptake level. Even at adsorption saturation, corresponding to an average of 23 iodine atoms per unit cell, MOF channels with significantly varying iodine contents─from nearly empty to densely filled─coexist. Image simulations suggest that the most densely packed I2 may locally form the previously proposed triple-helix structure, corresponding to up to 142 iodine atoms per unit cell. Furthermore, STEM imaging reveals that I2 adsorption can induce the formation of structural defects, such as edge dislocations and stacking faults, within the MOF framework. These defects persist even after the complete removal of I2 molecules. Additionally, we have developed a surfactant-capping strategy to minimize the release of adsorbed I2 from MFM-300(Sc) and validated its effectiveness using STEM imaging.

Uniform single-crystal mesoporous metal-organic frameworks

The synthesis of mesoporous metal-organic frameworks (meso-MOFs) is desirable as these materials can be used in various applications. However, owing to the imbalance in structural tension at the micro-scale (MOF crystallization) and the meso-scales (assembly of micelles with MOF subunits), the formation of single-crystal meso-MOFs is challenging. Here we report the preparation of uniform single-crystal meso-MOF nanoparticles with ordered mesopore channels in microporous frameworks with definite arrangements, through a cooperative assembly method co-mediated by strong and weak acids. These nanoparticles feature a truncated octahedron shape with variable size and well-defined two-dimensional hexagonally structured (p6mm) columnar mesopores. Notably, the match between the crystallization kinetics of MOFs and the assembly kinetics of micelles is critical for forming the single-crystal meso-MOFs. On the basis of this strategy, we have constructed a library of meso-MOFs with tunable large pore sizes, controllable mesophases, various morphologies and multivariate components.

Tailoring d-Band Center of Single-Atom Nickel Sites for Boosted Photocatalytic Reduction of Diluted CO2 from Flue Gas

Photocatalytic reduction of diluted CO2 from anthropogenic sources holds tremendous potential for achieving carbon neutrality, while the huge barrier to forming *COOH key intermediate considerably limits catalytic effectiveness. Herein, via coordination engineering of atomically scattered Ni sites in conductive metal-organic frameworks (CMOFs), we propose a facile strategy for tailoring the d-band center of metal active sites towards high-efficiency photoreduction of diluted CO2. Under visible-light irradiation in pure CO2, CMOFs with Ni-O4 sites (Ni-O4 CMOFs) exhibits an outstanding rate for CO generation of 13.3 μmol h-1 with a selectivity of 94.5 %, which is almost double that of its isostructural counterpart with traditional Ni-N4 sites (Ni-N4 CMOFs), outperforming most reported systems under comparable conditions. Interestingly, in simulated flue gas, the CO selectivity of Ni-N4 CMOFs decreases significantly while that of Ni-O4 CMOFs is mostly unchanged, signifying the supremacy for Ni-O4 CMOFs in leveraging anthropogenic diluted CO2. In situ spectroscopy and density functional theory (DFT) investigations demonstrate that O coordination can move the center of the Ni sites' d-band closer to the Fermi level, benefiting the generation of *COOH key intermediate as well as the desorption of *CO and hence leading to significantly boosted activity and selectivity for CO2-to-CO photoreduction.

Novel Inorganic-Organic Dual-Photosensitizing Dinuclear-Metal Self-Assembly System for Efficient Artificial Photosynthesis without Sacrificial Electron Donors

Owing to the unique synergistic effect, dinuclear-metal-molecule-catalysts (DMCs) show excellent performance in catalytic fields. However, for overall photocatalytic CO2 reaction (CO2RR), it is still a challenge to construct well-matched photosensitizer (PS) components for DMCs-based photocatalysts. Inorganic-quantum-dot PS possesses capacities of multiple exciton generation and catalyzing water oxidation but is incompatible with DMCs. In contrast, organic PS can be covalently linked with DMCs but inescapable of using sacrificial electron donors. For overall photocatalytic CO2RR, organic-inorganic dual-photosensitizing system might be a promising candidate. Herein, we employed covalent-linking and electrostatic-driven approaches to construct the self-assembly of pyrene-sensitized Co2L DMCs (Py-Co2L) and perovskite (PVK) quantum dots, i.e., PVK@[Py-Co2L]. Using H2O as an electron donor, PVK@[Py-Co2L] realized 105.24 μmol ⋅ g-1⋅h-1 CO yield in photocatalytic CO2RR, much higher than PVK (15.44 μmol ⋅ g-1⋅h-1) and PVK@Co2L (32.30 μmol ⋅ g-1 ⋅ h-1), ascribing to the efficient photogenerated charge separation and transfer. The experimental results and theoretical investigations demonstrated that the pyrene linked on Co2L boosted the electron delivery from PVK to DMCs. Besides, this strategy could also be extended to the photocatalytic H2 evolution coupled with alcohol oxidation. As a proof-of-concept, our work lightens the integration of DMCs, organic and inorganic PS components, promoting the development of photocatalysis without sacrificial electron donors.

Beyond Tradition: A MOF-On-MOF Cascade Z-Scheme Heterostructure for Augmented CO2 Photoreduction

Metal-organic frameworks (MOFs) are rigorously investigated as promising candidates for CO2 capture and conversion. MOF-on-MOF heterostructures integrate bolstered charger carrier separation with the intrinsic advantages of MOF components, exhibiting immense potential to substantially escalate the efficiency of photocatalytic CO2 reduction (CO2RR). However, the structural and compositional complexity poses significant challenges to the controllable development of these heterostructures. Herein, a conventional MOF-on-MOF nanocomposite is readily optimized from a type II heterojunction to a state-of-the-art cascade Z-scheme configuration via the encapsulation of Pt nanoparticles (Pt NPs), establishing synergistic MOF-MOF and metal-MOF heterojunctions with reinforced built-in electric field. A cascade electron flow is thus propelled, vigorously separating the photogenerated charge carriers and profoundly extending their lifetimes. Collectively, the photocatalytic activity of the cascade Z-scheme is drastically promoted, exhibiting a nearly quintuple enhancement in the CO production rate over the original type II heterostructure. Moreover, the anti-sintering capacity of the developed nanocomposite is unveiled, elucidating its simultaneously improved activity and stability. These findings present unprecedented regulation over the configuration of a MOF-on-MOF heterojunction, substantially enriching the fundamental understanding and rational design strategies of composite materials.

Metal-Modified Zr-MOFs with AIE Ligands for Boosting CO2 Adsorption and Photoreduction

The design and synthesis of metal-organic frameworks (MOFs) with outstanding light-harvesting and photoexcitation for artificial photocatalytic CO2 reduction is an attractive but challenging task. In this work, a novel aggregation-induced emission (AIE)-active ligand, tetraphenylpyrazine (PTTBPC) is proposed and utilized for the first time to construct a Zr-MOF photocatalyst via coordination with stable Zr-oxo clusters. Zr-MOF is featured by a scu topology with a two-fold interpenetrated framework, wherein the PTTBPC ligands enable strong light-harvesting and photoexcitation, while the Zr-oxo clusters facilitate CO2 adsorption and activation, as well as offer potential sites for further metal modification. Consequently, the Zr-PTTBPC and its Co/Ni derivatives not only exhibit exceptional stability and high CO2 adsorption capability (73 cm3 g-1 at 273 K and 1 atm), but also demonstrate a CO production rate of up to 293.2 µmol g h-1 under 420 nm LED light that can be reused for at least three cycles. With insights from charge-carrier dynamics and theoretical calculations, the underlying mechanism is revealed, confirming that the single-phase multi-component synergy is the key for the outstanding photocatalytic CO2 reduction. This work showcases a brand-new type of MOF photocatalyst based on AIE ligands and their promising applications in photocatalytic C1 conversion.

Space Exploration of Metal-Organic Frameworks in the Mesopore Regime

ConspectusThe past decades have witnessed the proliferation of porous materials offering high surface areas and the revolution in gas storage and separation, where metal-organic frameworks (MOFs) stand out as an important family. Alongside the pursuit of higher surface area, the increase in the size of guests, such as nanoparticles and biomolecules, has also led to the demand for larger space defined by the pores and cages within the MOF structure, from the conventional micropore regime (<2 nm) toward the mesopore regime (2-50 nm). Among the essential elements in the design of MOFs, molecular building blocks, their coordination and spatial arrangement, the chemistry for molecular design, and coordination bonds have become relatively mature, offering precise control of the shape and environment of the molecularly defined 3D cages; however, the correlation between the geometrical parameters and the size of polyhedrons describing the cages, concerning the spatial arrangement of building blocks, is much less explored.In this Account, we made efforts to associate actual cage size with the critical geometrical components, vertices, edges, connectivity, rings, and underlying polyhedrons, as well as the combination of components of various types in the design of MOFs. Several trends were found, such as influence from connectivity and expansion efficiency, offering insights into the construction of 3D cages in MOFs. This enables the creation of extremely large mesoporous cages in MOFs with an internal diameter up to 11.4 nm from relatively small building blocks. Furthermore, we discuss a strategy of partial removal or replacement of organic linkers to construct mesoporous cages from readily known topologies.All of the above efforts urged us to ask the following questions: Is there any limit in the sculpting of the 3D space from molecules? How large an area can one chemical bond support? The answer to these questions will deepen the knowledge of efficient utilization of chemical bonds in the sculpting of 3D spaces and guide the design of larger mesopores. Several general geometrical principals emerged: (1) Expansion efficiency and radius are positively correlated with the number of vertices. (2) Increase in the number of vertices and decrease of their connectivity favor the construction and expansion of large cages. (3) The boundary of the 3D space constructed by the chemical bonds is related to the polyhedron type and determined by the energy involved in crystallinity. Such principals are likely to be applicable also in the design of isolated cages in supramolecular chemistry. In addition to the structural design and synthesis, the applications of these mesoporous cages in MOFs are also summarized.

Integration of Plasmonic Ag(I) Clusters and Fe(II) Porphyrinates into Metal-Organic Frameworks for Efficient Photocatalytic CO2 Reduction Coupling with Photosynthesis of Pure H2O2

Efficient photocatalytic CO2 reduction coupled with the photosynthesis of pure H2O2 is a challenging and significant task. Herein, using classical CO2 photoreduction site iron porphyrinate as the linker, Ag(I) clusters were spatially separated and evenly distributed within a new metal-organic framework (MOF), namely Ag27TPyP-Fe. With water as electron donors, Ag27TPyP-Fe exhibited remarkable performances in artificial photosynthetic overall reaction with CO yield of 36.5 μmol g-1 h-1 and ca. 100 % selectivity, as well as H2O2 evolution rate of 35.9 μmol g-1 h-1. Since H2O2 in the liquid phase can be more readily separated from the gaseous products of CO2 photoreduction, high-purity H2O2 with a concentration up to 0.1 mM was obtained. Confirmed by theoretical calculations and the established energy level diagram, the reductive iron(II) porphyrinates and oxidative Ag(I) clusters within an integrated framework functioned synergistically to achieve artificial photosynthesis. Furthermore, photoluminescence spectroscopy and photoelectrochemical measurements revealed that the robust connection of Ag(I) clusters and iron porphyrinate ligands facilitated efficient charge separation and rapid electron transfer, thereby enhancing the photocatalytic activity.

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.

Low-dose electron microscopy imaging for beam-sensitive metal-organic frameworks

Metal-organic frameworks (MOFs) have garnered significant attention in recent years owing to their exceptional properties. Understanding the intricate relationship between the structure of a material and its properties is crucial for guiding the synthesis and application of these materials. (Scanning) Transmission electron microscopy (S)TEM imaging stands out as a powerful tool for structural characterization at the nanoscale, capable of detailing both periodic and aperiodic local structures. However, the high electron-beam sensitivity of MOFs presents substantial challenges in their structural characterization using (S)TEM. This paper summarizes the latest advancements in low-dose high-resolution (S)TEM imaging technology and its application in MOF material characterization. It covers aspects such as framework structure, defects, and surface and interface analysis, along with the distribution of guest molecules within MOFs. This review also discusses emerging technologies like electron ptychography and outlines several prospective research directions in this field.

Engineering Single-Atom Sites with the Irving-Williams Series for the Simultaneous Co-photocatalytic CO2 Reduction and CH3CHO Oxidation

The bonding effects between 3d transition-metal single sites and supports originate from crystal field stabilization energy (CFSE). The 3d transition-metal atoms of the spontaneous geometrical distortions, that is the Jahn-Teller effect, can alter CFSE, thereby leading to the Irving-Williams series. However, engineering single-atom sites (SASs) using the Irving-Williams series as an ideal guideline has not been reported to date. Herein, alkynyl-linked covalent phenanthroline frameworks (CPFs) with phenanthroline units are developed to anchor the desired 3d single metal ions from d5 to d10 (Mn2+, Fe3+, Co2+, Ni2+, Cu2+, and Zn2+). The Irving-Williams series was employed to accurately predict the bonding effects between 3d transition-metal atoms and phenanthroline units. To verify this, theoretical calculations and experimental results reveal that Cu-SASs/CPFs exhibits higher stability and faster charge-transfer efficiency, far surpassing other metal-SASs/CPFs. As expected, Cu-SASs/CPFs demonstrates a high photoreduction of CO2-to-CO activity (~30.3 μmol ⋅ g-1 ⋅ h-1) and an exceptional photooxidation of CH3CHO-to-CH3COOH activity (~24.7 μmol ⋅ g-1 ⋅ h-1). Interestingly, the generated *O2 - is derived from the process of CO2 reduction, thereby triggering a CH3CHO oxidation reaction. This work provides a novel design concept for designing SASs by the Irving-Williams to regulate the catalytic performances.

Matched Redox Kinetics on Triazine-Based Carbon Nitride/Ni(OH)2 for Stoichiometric Overall Photocatalytic CO2 Conversion

Mismatched reaction kinetics of CO2 reduction and H2O oxidation is the main obstacle limiting the overall photocatalytic CO2 conversion. Here, a molten salt strategy is used to construct tubular triazine-based carbon nitride (TCN) with more adsorption sites and stronger activation capability. Ni(OH)2 nanosheets are then grown over the TCN to trigger a proton-coupled electron transfer for a stoichiometric overall photocatalytic CO2 conversion via "3CO2 + 2H2O = CH4 + 2CO + 3O2." TCN reduces the energy barrier of H2O dissociation to promote H2O oxidation to O2 and supply sufficient protons to Ni(OH)2, whereby the CO2 conversion is accelerated due to the enhanced proton-coupled electron transfer process enabled by the sufficient proton supply from TCN. This work highlights the importance of matching the reaction kinetics of CO2 reduction and H2O oxidation by proton-coupled electron transfer on stoichiometric overall photocatalytic CO2 conversion.

Recent advances in small-angle scattering techniques for MOF colloidal materials

This paper reviews the recent progress of small angle scattering (SAS) techniques, mainly including X-ray small angle scattering technique (SAXS) and neutron small angle scattering (SANS) technique, in the study of metal-organic framework (MOF) colloidal materials (CMOFs). First, we introduce the application research of SAXS technique in pristine MOFs materials, and review the studies on synthesis mechanism of MOF materials, the pore structures and fractal characteristics, as well as the spatial distribution and morphological evolution of foreign molecules in MOF composites and MOF-derived materials. Then, the applications of SANS technique in MOFs are summarized, with emphasis on SANS data processing method, structure modeling and quantitative structural information extraction. Finally, the characteristics and developments of SAS techniques are commented and prospected. It can be found that most studies on MOF materials with SAS techniques focus mainly on nanoporous structure characterization and the evolution of pore structures, or the spatial distribution of other foreign molecules loaded in MOFs. Indeed, SAS techniques take an irreplaceable role in revealing the structure and evolution of nanopores in CMOFs. We expect that this paper will help to understand the research status of SAS techniques on MOF materials and better to apply SAS techniques to conduct further research on MOF and related materials.

Microfluidic-Aerosol Hyphenated Synthesis of Metal-Organic Framework-Derived Hybrid Catalysts for CO2 Utilization

A new and efficient technique is developed by combining the hyphenated microfluidic- and aerosol-based synthesis with the coupled differential mobility analysis for the effective and continuous synthesis and simultaneous analysis of metal-organic frameworks (MOFs)-derived hybrid nanostructured products. HKUST-1, a copper-based MOF, is chosen as the representative to fabricate Cu-based hybrid catalysts for reverse water-gas shift (RWGS) reaction, an effective route for CO2 utilization. The effect of precursor concentration and carrier selection on the properties of the resulting products, including mobility size distribution, crystallization degree, surface area, and metal dispersion are investigated, as well as the correlation between the material properties of the synthesized catalysts and their catalytic performance in RWGS reaction in terms of conversion ratio/rate, selectivity, and operational stability. The results indicate that the continuous microfluidic droplet system can successfully synthesize MOF colloids, followed by the continuous production of MOF-derived hybrid materials through the tandem aerosol spray-drying-reaction system. High catalytic activity and low initiate temperature toward RWGS (turnover frequency = 0.0074 s-1; 450 °C) are achievable. The work facilitates the production and the designed concept of relevant MOF-derived hybrid nanostructured catalysts in the continuous synthesis system and the enhancement of applications in CO2 capture and utilization.

Sodium Dodecyl Sulfate-Adjusted Phase Composition of Hydrated Tungsten Oxides as Stable Self-Supporting Electrodes for Supercapacitors with High Volumetric Specific Capacitance

High pseudocapacitive activity of hydrated tungsten oxides (WO3·xH2O, x = 1 or 2) makes them promising materials for supercapacitors (SCs). During their synthesis, additives such as complexing agents and surfactants generally can only affect the morphology and/or size of the products. Here, we demonstrate that not only morphology and size of WO3·xH2O were affected, its phase composition could also change from WO3·2H2O to WO3·H2O simply by increasing the amount of sodium dodecyl sulfate (SDS) during its anodization synthesis. To the best of our knowledge, such a phenomenon has not been reported before. In addition, SDS introduced a special structure to the products, i.e., WO3·xH2O nanoplatelets constructed from nanoparticle multilayers with abundant nanogaps between the multilayers, which further arranged into nanoflowers with increased amounts of SDS. Benefiting from such a structure, low internal resistance, enhanced stability, and fast redox kinetics, the as-obtained WO3·xH2O/W-3 self-supporting electrode showed a high volumetric specific capacitance of 1402.92 F cm-3 and good cycling stability (a capacity retention of 106% after 10 000 cycles). In addition, an all-solid-state asymmetric SC device based on WO3·xH2O/W-3 delivered high a volumetric energy density of 44.0 mW h cm-3 at 0.5 W cm-3. Our method demonstrates a potential way to fabricate excellent self-supporting electrodes for SCs.