Metal Sites Research Articles

Construction of One-Dimensional Covalent-Organic Framework Coordinated with Main Group Metals for Selective Electrochemical Synthesis of H2O2.

Covalent-organic frameworks (COFs) are promising electrocatalysts for the selective synthesis of H2O2 through the two-electron oxygen reduction reaction (2e- ORR). However, the design and synthesis of efficient and stable COF-based electrocatalysts is still challenging. In this work, a predesigned 1,10-phenanthroline-based one-dimensional COF (PYTA-PTDE-COF) was constructed to anchor main group metal (In, Sn, and Sb) as electrocatalysts toward 2e- ORR. The catalysts are featured with fully exposed metalated side chains. Structural characterization revealed that PYTA-PTDE-M's (M = In, Sn, and Sb) are all quite similar, except for the coordinated metal ions with the maintenance of good crystallinity. They all exhibited satisfying activity and selectivity toward 2e- ORR under alkaline conditions. Among them, PYTA-PTDE-Sb exhibited the best performance (Eonset is 0.765 V, the H2O2 selectivity is 96%, and the yield rate is 209.2 mmol gcat-1 h-1). Moreover, it also delivered superior stability with almost no attenuation of current density during the long-time test. Theoretical calculations revealed that the Sb metal site in the COFs has the lowest adsorption strength of *OOH, which could be the main reason for its superior selectivity. The PYTA-PTDE-Sb assembled zinc-air battery realizes not only the supply of clean energy but also the production of green chemicals, showing it is highly promising in practical applications. This work offers an example for designing main group metal-coordinated 1D COFs and reveals fundamental structure-activity relationship toward 2e- ORR.

Establishing a Robust Nonlinear Targeted Switch for C1 Electroproduction in Atomic Alloy Cox/Pd Bimetallenes

Establishing a targeted switch for CO2 conversion under electric drive is essential for achieving carbon‐balance by enabling selective chemicals. However, engineering the topological assembly of active sites to precisely regulate the competing pathways for various intermediates has been plagued by unclear structure‐function relationships. To tailor the CO/formate pathways, herein we established a robust nonlinear targeted switch with tunable active Cox sites integrated into Pd metallene, which involves Co1/Pd single‐atom alloy (favoring CO) and Co2/Pd diatomic alloy (favoring formate). Transitioning from Co1/Pd to Co2/Pd atomic alloy bimetallenes resulted in a nonlinear, high‐contrast flip in selectivity, surpassing 94% for CO and formate productions in both H‐cell and flow cell. Furthermore, the superior selectivity and current efficiency for CO (> 80 %) and formate (> 88%) were consistently maintained at ‐150 mA cm‐2 over continuous 200 h. Theoretical simulations and in‐situ spectroscopy analyses unveiled that appropriate adjacent metal site combinations (Pd‐Pd, Pd‐Co and Co‐Co) lead to tunable dz2 band center and a nonlinear shift in preferred adsorption configurations of intermediates, dictating the C1 pathways. Our finding reveals a desired switch in C1 selectivity and robust stability within Cox/Pd system, providing a new perspective for fine‐tuning energy conversion processes through specific topological assembly.

Molten Salt-Assisted Synthesis of Ferric Oxide/M-N-C Nanosheet Electrocatalysts for Efficient Oxygen Reduction Reaction.

Efficient, stable, and low-cost oxygen reduction catalysts are the key to the large-scale application of metal-air batteries. Herein, high-dispersive Fe2O3 nanoparticles (NPs) with abundant oxygen vacancies uniformly are anchored on lignin-derived metal-nitrogen-carbon (M-N-C) hierarchical porous nanosheets as efficient oxygen reduction reaction (ORR) catalysts (Fe2O3/M-N-C, M═Cu, Mn, W, Mo) based on a general and economical KCl molten salt-assisted method. The combination of Fe with the highly electronegative O induces charge redistribution through the Fe-O-M structure, thereby reducing the adsorption energy of oxygen-containing substances. The coupling effect of Fe2O3 NPs with M-N-C expedites the catalytic activity toward ORR by promoting proton generation on Fe2O3 and transfer to M-N-C. Experimental and theoretical calculation further revealed the remarkable electronic structure evolution of the metal site during the ORR process, where the emission density and local magnetic moment of the metal atoms change continuously throughout their reaction. The unique layered porous structure and highly active M-N4 sites resulted in the excellent ORR activity of Fe2O3/Cu-N-C with the onset potential of 0.977V, which is superior to Pt/C. This study offers a feasible strategy for the preparation of non-noble metal catalysts and provides a new comprehension of the catalytic mechanism of M-N-C catalysts.

Establishing a Robust Nonlinear Targeted Switch for C1 Electroproduction in Atomic Alloy Cox/Pd Bimetallenes.

Establishing a targeted switch for CO2 conversion under electric drive is essential for achieving carbon-balance by enabling selective chemicals. However, engineering the topological assembly of active sites to precisely regulate the competing pathways for various intermediates has been plagued by unclear structure-function relationships. To tailor the CO/formate pathways, herein we established a robust nonlinear targeted switch with tunable active Cox sites integrated into Pd metallene, which involves Co1/Pd single-atom alloy (favoring CO) and Co2/Pd diatomic alloy (favoring formate). Transitioning from Co1/Pd to Co2/Pd atomic alloy bimetallenes resulted in a nonlinear, high-contrast flip in selectivity, surpassing 94% for CO and formate productions in both H-cell and flow cell. Furthermore, the superior selectivity and current efficiency for CO (> 80 %) and formate (> 88%) were consistently maintained at -150 mA cm-2 over continuous 200 h. Theoretical simulations and in-situ spectroscopy analyses unveiled that appropriate adjacent metal site combinations (Pd-Pd, Pd-Co and Co-Co) lead to tunable dz2 band center and a nonlinear shift in preferred adsorption configurations of intermediates, dictating the C1 pathways. Our finding reveals a desired switch in C1 selectivity and robust stability within Cox/Pd system, providing a new perspective for fine-tuning energy conversion processes through specific topological assembly.

Dual Metallosalen-Based Covalent Organic Frameworks for Artificial Photosynthetic Diluted CO2 Reduction.

Directly converting CO2 in flue gas using artificial photosynthetic technology represents a promising green approach for CO2 resource utilization. However, it remains a great challenge to achieve efficient reduction of CO2 from flue gas due to the decreased activity of photocatalysts in diluted CO2 atmosphere. Herein, we designed and synthesized a series of dual metallosalen-based covalent organic frameworks (MM-Salen-COFs, M: Zn, Ni, Cu) for artificial photosynthetic diluted CO2 reduction and confirmed their advantage in comparison to that of single metal M-Salen-COFs. As a results, the ZnZn-Salen-COF with dual Zn sites exhibits a prominent visible-light-driven CO2-to-CO conversion rate of 150.9 μmol g-1 h-1 under pure CO2 atmosphere, which is ~6 times higher than that of single metal Zn-Salen-COF. Notably, the dual metal ZnZn-Salen-COF still displays efficient CO2 conversion activity of 102.1 μmol g-1 h-1 under diluted CO2 atmosphere from simulated flue gas conditions (15 % CO2), which is a record high activity among COFs- and MOFs-based photocatalysts under the same reaction conditions. Further investigations and theoretical calculations suggest that the synergistic effect between the neighboring dual metal sites in the ZnZn-Salen-COF facilitates low concentration CO2 adsorption and activation, thereby lowering the energy barrier of the rate-determining step.

Dual Metallosalen‐based Covalent Organic Frameworks for Artificial Photosynthetic Diluted CO2 Reduction

Directly converting CO2 in flue gas using artificial photosynthetic technology represents a promising green approach for CO2 resource utilization. However, it remains a great challenge to achieve efficient reduction of CO2 from flue gas due to the decreased activity of photocatalysts in diluted CO2 atmosphere. Herein, we designed and synthesized a series of dual metallosalen‐based covalent organic frameworks (MM‐Salen‐COFs, M: Zn, Ni, Cu) for artificial photosynthetic diluted CO2 reduction and confirmed their advantage in comparison to that of single metal M‐Salen‐COFs. As a results, the ZnZn‐Salen‐COF with dual Zn sites exhibits a prominent visible‐light‐driven CO2‐to‐CO conversion rate of 150.9 μmol g−1 h−1 under pure CO2 atmosphere, which is ~6 times higher than that of single metal Zn‐Salen‐COF. Notably, the dual metal ZnZn‐Salen‐COF still displays efficient CO2 conversion activity of 102.1 μmol g−1 h−1 under diluted CO2 atmosphere from simulated flue gas conditions (15% CO2), which is a record high activity among COFs‐ and MOFs‐based photocatalysts under the same reaction conditions. Further investigations and theoretical calculations suggest that the synergistic effect between the neighboring dual metal sites in the ZnZn‐Salen‐COF facilitates low concentration CO2 adsorption and activation, thereby lowering the energy barrier of the rate‐determining step.

Facile and scalable method to synthesize MOFs/PET composite fibers for indoor VOCs adsorption

Volatile organic compounds (VOCs) that are emitted into indoor environments pose significant risks to human health, necessitating air purification to protect individuals from VOC-induced harm. Metal–organic frameworks (MOFs) are characterized by their extensive porosity and accessible metal sites and have attracted significant interest owing to their efficacy in VOC adsorption. However, the inherent difficulty in collecting powdered MOFs hinders their practical application. Thus, integrating MOFs with textiles presents an innovative solution for overcoming these challenges. In this study, MOFs/PET composite textiles (MOFs@STP-PET) were synthesized via an in-situ growth process on polyethylene terephthalate (PET) fiber substrates using thermal crosslinking coating and pre-soaked seed hot-solvent methodologies. The capacities of the composites to adsorb and mitigate VOCs, including benzene and formaldehyde, were evaluated. The presence of carboxyl groups (–COOH) on the polyacrylic acid coating facilitated the chelation of metal ions via electrostatic interactions, providing a foundation for MOF growth. Moreover, the obtained textiles exhibited good adsorption performance. Notably, the 10 % breakthrough time of ethylbenzene on the U6N@STP-PET textile increased to 267.9 min, resulting in a maximum adsorption capacity of 4.3 mg/g. Uniformly anchored MOFs on the fiber surface ensured a high specific surface area of 292.3 m2/g, further enhancing adsorption capabilities. In addition, the textile exhibited excellent mechanical properties, with a tensile strength of approximately 20 MPa. This straightforward, effective, and scalable approach paves the way for the development of novel VOC adsorption materials and holds promise for improving indoor air quality.

Reusable fluorescence nanoprobe based on DNA-functionalized metal-organic framework for ratiometric detection of mercury (II) ions.

Areusable fluorescent nanoprobewas developedusing DNA-functionalized metal-organic framework (MOF) for ratiometric detection of Hg2+. We utilized a zirconium-based MOF (UiO-66) to encapsulate tris(bipyridine) ruthenium(II) chloride (Ru(bpy)32+), resulting in Ru(bpy)32+@UiO-66 (RU) with red fluorescence. The unsaturated metal sites in UiO-66 facilitate the attachment of thymine-rich single-strand DNA (T-ssDNA) through Zr-O-P bond, producing T-ssDNA-functionalized RU complex (RUT). The T-ssDNA selectively binds to Hg2+, forming stable T-Hg2+-T base pairs and folding into double-stranded DNA, which permits the intercalation of SYBR Green I (SGI) and activates its green fluorescence. In the presence of Hg2+, SGI fluorescence increases in a dose-dependent manner, while Ru(bpy)32+ fluorescence remains constant. This fluorescence contrast enables RUT to serve as an effective ratiometric nanoprobe for Hg2+ detection, with a detection limit of 3.37 nM. Additionally, RUT demonstrates exceptional reusability due to the ability of cysteine to remove Hg2+, given its stronger affinity for thiol groups. The RUT was successfully applied to detect Hg2+ in real water samples. This work advances the development of ratiometric fluorescence nanoprobe based on DNA-functionalized MOFs.

Loading Dyes into Chiral Cd/Zn-Metal-Organic Frameworks for Efficient Full-Color Circularly Polarized Luminescence.

Host-guest chemistry of chiral metal-organic frameworks (MOFs) has endowed them with circularly polarized luminescence (CPL), it is still limited for MOFs to systematically tune full-color CPL emissions and sizes. This work directionally assembles the chiral ligands, metal sites and organic dyes to prepare a series of crystalline enantiomeric D/L-Cd/Zn-n MOFs (n=1~5, representing the adding amount of dyes), where D/L-Cd/Zn with the formula of Cd2(D/L-Cam)2(TPyPE) and Zn2(D/L-Cam)2(TPyPE) (D/L-Cam=D/L-camphoric acid, TPyPE=4,4',4'',4'''-(1,2-henediidenetetra-4,1-phenylene)tetrakis[pyridine]) were used as the chiral platforms. The framework-dye-enabled emission and through-space chirality transfer facilitate D/L-Cd/Zn-n bright full-color CPL activity. The ideal yellow CPL of D-Cd-5 and D-Zn-4, with |glum| as 4.9 × 10-3 and 1.3×10-3 and relatively high photoluminescence quantum yield of 40.79 % and 45.40 %, are further assembled into a white CPL light-emitting diode. The crystal sizes of D/L-Cd/Zn-n were found to be strongly correlated to the types and additional amounts of organic dyes, that the positive organic dyes allow for the preparation of > 7 mm bulks and negative dyes account for sub-20 μm particles. This work opens a new avenue to fabricate full-color emissive CPL composites and provides a potentially universal method for controlling the size of optical platforms.

Ammonia Storage in Metal-Organic Framework Materials: Recent Developments in Design and Characterization.

Since the advent of the Haber-Bosch process in 1910, the global demand for ammonia (NH3) has surged, driven by its applications in agriculture, pharmaceuticals, and energy. Current methods of NH3 storage, including high-pressure storage and transportation, present significant challenges due to their corrosive and toxic nature. Consequently, research has turned towards metal-organic framework (MOF) materials as potential candidates for NH3 storage due to their potential high adsorption capacities and structural tunability. MOFs are coordination networks composed of metal nodes and organic linkers, offering unprecedented porosity and surface area, and allowing incorporation of various functional groups and metal sites that can enhance NH3 adsorption. However, the stability of MOFs in the presence of NH3 is a significant concern since many degrade upon exposure to NH3, primarily due to ligand displacement and framework collapse. To address this, recent studies have focused on the synthesis and postsynthetic modification of MOFs to enhance both NH3 uptake and stability. In this Account, we summarize recent developments in the design and characterization of MOFs for NH3 storage. The choice of metal centers in MOFs is crucial for stability and performance. High-valence metals such as AlIII and TiIV form strong metal-linker bonds, enhancing the stability of the framework to NH3. The MFM-300 series of materials composed of high-valence 3+ and 4+ metal ions and carboxylic linkers demonstrates high stability and high NH3 uptake capacities. Ligand functionalization is another effective strategy for improving the NH3 adsorption. Polar functional groups such as -NH2, -OH, and -COOH enhance the interaction between the framework and NH3, particularly at low partial pressures, while postsynthetic modification allows fine-tuning of these functionalities to optimize the framework for higher adsorption capacities and stability. For example, MFM-303(Al), incorporating free carboxylic acid groups, exhibits a high NH3 packing density comparable to that of solid NH3. Creating defect sites by removing linkers or adding metal ions increases the number of active sites available for NH3 adsorption and shows promise for enhancing uptake. UiO-66, a stable MOF framework, can be modified to include defect sites, significantly enhancing the level of NH3 uptake. The full characterization of MOFs and especially their interactions with NH3 are vital for understanding and improving their performance. Techniques such as neutron powder diffraction (NPD), inelastic neutron scattering (INS), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), electron paramagnetic resonance (EPR) spectroscopy, and solid-state nuclear magnetic resonance (ssNMR) spectroscopy can elucidate host-guest interactions and binding dynamics between NH3 and the framework structure and afford crucial information for the future design and rational development of new sorbents. This Account highlights our current strategies for the synthesis and characterization of MOFs for NH3 capture, providing an overview of this rapidly evolving field.

Hierarchically Ordered Pore Engineering of Carbon Supports with High-Density Edge-Type Single-Atom Sites to Boost Electrochemical CO2 Reduction.

Metal sites at the edge of the carbon matrix possess unique geometric and electronic structures, exhibiting higher intrinsic activity than in-plane sites. However, creating single-atom catalysts with high-density edge sites remains challenging. Herein, the hierarchically ordered pore engineering of metal-organic framework-based materials to construct high-density edge-type single-atomic Ni sites for electrochemical CO2 reduction reaction (CO2RR) is reported. The created ordered macroporous structure can expose enriched edges, further increased by hollowing the pore walls, which overcomes the low edge percentage in the traditional microporous substrates. The prepared single-atomic Ni sites on the ordered macroporous carbon with ultra-thin hollow walls (Ni/H-OMC) exhibit Faraday efficiencies of CO above 90% in an ultra-wide potential window of 600mV and a turnover frequency of 3.4×104h-1, much superior than that of the microporous material with dominant plane-type sites. Theory calculations reveal that NiN4 sites at the edges have a significantly disrupted charge distribution, forming electron-rich Ni centers with enhanced adsorption ability with *COOH, thereby boosting CO2RR efficiency. Furthermore, a Zn-CO2 battery using the Ni/H-OMC cathode shows an unprecedentedly high power density of 15.9mW cm-2 and maintains an exceptionally stable charge-discharge performance over 100h.

Fabrication of Hofmann-type metal-organic framework based mixed-matrix membranes for efficient CH4/N2 separation

The analogous physical and chemical properties of methane (CH4) and nitrogen (N2) pose a great challenge for their separation. Mixed-matrix membranes (MMMs), combining the good separation performance of fillers and easy processability of polymers, are expected to address this challenging task. In this work, one Hofmann-type metal-organic framework (MOF), CoNi-DABCO, featuring abundant oppositely adjacent open metal sites, narrow pore size, and strong binding affinity toward CH4, is introduced into the polymer of polydimethylsiloxane to fabricate MMMs. The presence of CoNi-DABCO in the membranes could enhance the adsorption capacity for CH4, thus facilitating the transport of CH4 molecules through the membranes. Specially, the MMM containing 20 wt% CoNi-DABCO displays a high CH4 permeability of 1285 Barrer and maintains a good CH4/N2 mixed-gas selectivity of 3.7. Furthermore, the MMMs show good pressure resistance (up to 10 bar) and long-term stability for 30 days. This study suggests the potential of Hofmann-type MOF in the development of high-performance membranes for CH4/N2 separation.

Controlling Chlorine-Doped Nickel Diselenide Ultrathin Nanosheets through Steric Effects: An Electrocatalyst for Oxygen Evolution Reaction and Urea Oxidation Reaction.

Exploration of electrocatalysts suitable for the oxygen evolution reaction (OER) and urea oxidation reaction (UOR) is essential for electrocatalytic hydrogen production. In this work, a ligand substitution strategy is used to synthesize ultrathin-nanosheet electrocatalysts of Cl-doped NiSe2 (NiSe2-a and NiSe2-b), which exhibit high-electrocatalytic activity during OER and UOR. NiSe2-a and NiSe2-b only need an overpotential of 227 and 268 mV, respectively, to achieve a current density of 10 mA cm-2 during OER. Furthermore, NiSe2-a with its smaller steric effects exhibits excellent catalytic performance for UOR, requiring an ultralow potential of 1.360 V to deliver a current density of 100 mA cm-2. This excellent performance can be attributed to the nonmetallic elements (Se and Cl) modulating and optimizing the charge state of the metal sites, thereby increasing the electrocatalytic activity. Overall, this work provides an unparalleled example of tuning space structures to design efficient electrocatalysts and has promising industrial applications.

Designing a one-dimensional photonic crystal sensor for dimethyl methylphosphonate detection leveraging a hydrogen-bonding-based acidic strategy

Chemical warfare agents (CWAs) are extremely toxic chemicals, necessitating rapid, easy-to-use, sensitive and selective sensors for detection. Dimethyl methylphosphonate (DMMP) serves as a simulant of nerve agents and is commonly used to evaluate the efficacy of sensors in detecting these hazardous compounds. In this context, this paper proposes a one-dimensional (1D) photonic crystal (PC) gas sensor functionalised with UIO-66-COOH, leveraging a hydrogen-bonding-based acidic strategy, for rapid and sensitive DMMP detection. To optimise DMMP uptake, the organic ligand, UIO-66, is functionalised by grafting additional carboxyl groups to facilitate hydrogen-bonding interactions with the PO groups of organophosphorus gases such as DMMP. Subsequently, attenuated total reflection surface-enhanced infrared absorption spectroscopy is performed to quantitatively monitor the impact of strong interactions between the PC bonds and PO bonds of DMMP and the adsorption sites of metal–organic frameworks (MOFs) during adsorption. The results reveal an increase in the number of hydrogen-bonding sites available for DMMP adsorption, thus promoting hydrogen-bonding interactions. Furthermore, density functional theory calculations are employed to analyse the presence and strength of hydrogen bonds between the MOFs and DMMP. The results reveal that the chemisorption energy of UIO-66-COOH exceeds those of its variants, corroborating the findings of sensing experiments. Overall, the developed 1D PC gas sensor comprising UIO-66-COOH/TiO2 demonstrates excellent stability and reproducibility, with a limit of detection of 0.3 ppm. This sensor also demonstrates enhanced selectivity towards organophosphorus gases compared to volatile organic compounds.

Machine Learning Predictions of Methane Storage in MOFs: Diverse Materials, Multiple Operating Conditions, and Reverse Models.

A machine learning (ML) model is developed for predicting useable methane (CH4) capacities in metal-organic frameworks (MOFs). The model applies to a wide variety of MOFs, including those with and without open metal sites, and predicts capacities for multiple pressure swing conditions. Despite its wider applicability, the model requires only 5 measurable structural features as input, yet achieves accuracies that surpass less-general models. Application of the model to a database of more than a million hypothetical MOFs identified several hundred whose capacities surpass that of the benchmark MOF, UMCM-152. Guided by the computational predictions, one of the promising candidates, UMCM-153, was synthesized and demonstrated to achieve superior volumetric capacity for CH4. Feature importance analyses reveal that pore volume and gravimetric surface area are the most important features for predicting CH4 capacity in MOFs. Finally, a reverse ML model is demonstrated. This model predicts the set of elementary MOF structural properties needed to achieve a desired CH4 capacity for a prescribed operating condition.

Engineering Coordinatively Unsaturated Metal Sites in 2D Metal‐Porphyrin Frameworks for Initiator‐Free, Broadband Photocatalytic Synthesis of Ultrahigh Molecular Weight Polymers

Engineering Coordinatively Unsaturated Metal Sites in 2D Metal‐Porphyrin Frameworks for Initiator‐Free, Broadband Photocatalytic Synthesis of Ultrahigh Molecular Weight Polymers

Simultaneous construction of Zr-β zeolite with high content and high accessibility of framework Zr sites in the conversion of ethanol to 1,3-butadiene: Mechanisms and synergistic effects

Metallosilicate zeolites, represented by Zr-β zeolite, possess unique porosity and tunable acidity, showing great potential in the conversion of ethanol to 1,3-butadiene. However, there still remains potential for further improvement of catalytic activity and stability by breaking the bottleneck framework metal site content and microporosity diffusion. In this paper, a novel Zr-β zeolite with both high content and high accessibility of framework Zr sites was successfully synthesized via the combination strategy of “Improved Decomposition Reconstruction” and “Silanization.” Based on the activity evaluation experiments of key reaction steps and in situ DRIFTS in the conversion of ethanol to 1,3-butadiene, the enhanced activity and stability are due to the synergistic effects of the content and accessibility of framework Zr sites, which both facilitate reactant conversion and inhibit the covering of active sites or the plugging of pore channels by polymerized heavy compounds. The prepared zeolite demonstrates excellent performance with a total conversion of 66 % and a 1,3-butadiene selectivity above 67 % in 100 h, along with good regenerability.

Efficient Formaldehyde Gas Sensing Performance via Promotion of Oxygen Vacancy on In-Doped LaFeO3 Nanofibers.

Perovskite oxide LaFeO3(LFO) emerges as a potential candidate for formaldehyde (HCHO) detection due to its exceptional electrical conductivity and abundant active metal sites. However, the sensitivity of the LFO sensor needs to be further enhanced. Herein, a series of LaxIn1-xFeO3 (x = 1.0, 0.9, 0.8, and 0.7) nanofibers (LxIn1-xFO NFs) with different ratios of La/In were obtained via the electrospinning method followed by a calcination process. Among all these LxIn1-xFO NFs sensors, the sensor based on the L0.8In0.2FO NFs possessed the maximum response value of 18.8 to 100 ppm HCHO at the operating temperature of 180 °C, which was 4.47 times higher than that based on pristine LFO NFs (4.2). Furthermore, the L0.8In0.2FO NFs sensor also exhibited a rapid response/recovery time (2 s/22 s), exceptional repeatability, and long-term stability. This excellent gas sensing performance of the L0.8In0.2FO NFs can be attributed to the large number of oxygen vacancies induced by the replacement of the A-site La3+ by In3+, the large specific surface area, and the porous structure. This research presents an approach to enhance the HCHO gas sensing capabilities by adjusting the introduced oxygen vacancies through the doping of A-sites in perovskite oxides.

Regulating electron transfer between valence-variable cuprum and cerium sites within bimetallic metal–organic framework towards enhanced catalytic hydrogenation performance

Modulating the electron distribution between active sites in metal–organic frameworks (MOFs) offers a promising strategy for optimizing their catalytic performance. In this study, we employed a novel heterovalent substitution strategy to synthesize bimetallic organic frameworks (CuxCey-BTC) that feature dual active sites with copper (Cu) and cerium (Ce), Our objective was to achieve efficient hydrogenation of dicyclopentadiene (DCPD) by regulating the electron transfer between the valence-variable Cu and Ce species. The designed CuxCey-BTC were characterized using various spectroscopic and microscopic techniques, along with density functional theory (DFT) calculations, confirming the successful incorporation of bimetallic nodes within the framework structure and the electron transfer between them. The transfer of electrons from the less electronegative Ce to the Cu sites promotes the chemisorption of hydrogen gas (H2) on the electron-rich Cu sites, thereby optimizing the activation of the CC bond in DCPD. The Cu4Ce-BTC catalyst demonstrated exceptional performance, achieving complete conversion of DCPD and significantly surpassing monometallic MOFs. Moreover, we proposed a plausible pathway for the hydrogenation of DCPD. This work highlights the synergistic effects between bimetallic centers and offers a novel strategy to improve the MOFs’ catalytic activity by modulating electron distribution between dual active sites.

Platinum modification of metallic cobalt defect sites for efficient electrocatalytic oxidation of 5-hydroxymethylfurfural

Co3O4 possesses both direct and indirect oxidation effects and is considered as a promising catalyst for the oxidation of 5-hydroxymethylfurfural (HMF). However, the enrichment and activation effects of Co3O4 on OH− and HMF are weak, which limits its further application. Metal defect engineering can regulate the electronic structure, optimize the adsorption of intermediates, and improve the catalytic activity by breaking the symmetry of the material, which is rarely involved in the upgrading of biomass. In this work, we prepare Co3O4 with metal defects and load the precious metal platinum at the defect sites (Pt-Vco). The results of in-situ characterizations, electrochemical measurements, and theoretical calculations indicate that the reduction of Co–Co coordination number and the formation of Pt–Co bond induce the decrease of electron filling in the antibonding orbitals of Co element. The resulting upward shift of the d-band center of Co combined with the characteristic adsorption of Pt species synergically enhances the enrichment and activation of organic molecules and OH− species, thus exhibiting excellent HMF oxidation activity (including a lower onset potential (1.14 V) and 19 times higher current density than pure Co3O4 at 1.35 V). In summary, this work explores the adsorption enhancement mechanism of metal defect sites modified by precious metal in detail, provides a new option for improving the HMF oxidation activity of cobalt-based materials, broadens the application field of metal defect based materials, and gives an innovative guidance for the functional utilization of metal defect sites in biomass conversion.