Ligand Defect-Induced Active Sites in Ni-MOF-74 for Efficient Photocatalytic CO2 Reduction to CO

Electrochemical Sensing toward Noninvasive Evaluation of High-Starch Food Digestion via Point-of-Use Monitoring Glucose Level in Saliva

To provide individuals with healthier and more reliable dietary recommendations for diabetic patients, a pragmatic electrochemical sensing toward in situ monitoring of glucose in saliva was designed for noninvasive evaluation of high-starch food digestion. The proposed sensor was constructed by exploiting a carbon-based nanostructure for electrical conductivity and Ni-based nanozyme toward direct catalytic oxidation of glucose for signal output. Particularly, the catalytic host-guest interaction between nanozyme and glucose was investigated to be a hydrogen bond via molecular docking, and the C11 and O5 sites in the glucose molecule were attacked during host-guest catalytic reaction through density functional theory (DFT) research. With merits of simplicity, sensitivity, and accuracy, the electrochemical sensor exhibited good performance for monitoring glucose with a detection limit of 10 μM (corresponding to 1.8 μg mL-1). Moreover, it was well qualified to point-of-use trace glucose levels in saliva, offering a promising tool for noninvasive evaluation of high-starch food digestion (e.g., Wheat bread, Steamed bun, and Shao-mai) at different times after meals and eventually yielding benefits to dietary recommendations for diabetic patients.

Functionalized Thorium-Based Metal-Organic Frameworks for the Photocatalytic Oxidation of 1, 5-Dihydroxynaphthalene

It is still a challenging task to rationally design metal-organic framework (MOF) crystal catalysts with excellent light absorption and charge transfer for efficient photocatalytic reactions. In this work, the hexanuclear thorium clusters, porphyrin derivative ligands, and linear carboxylic acid ligands were assemed into Th-based metal-organic frameworks (Th6-TCPP, Th6-Co-TCPP, and Th6-Ni-TCPP) by the mixed ligand method. The three prepared MOF crystals were applied in the photocatalytic oxidation of 1, 5-dihydroxynaphthalene (1, 5-DHN) for the synthesis of juglone. Among them, Th6-TCPP exhibited optimum photodynamic activity for production of reactive oxygen species. Under lillumination, Th6-TCPP resulted in photochemical reaction conversion rate up to 95 % for 9, 10-diphenylanthracene (DPA) and 54.5 % for 1, 5-DHN. The good catalytic effect was attributed to the large conjugate system of porphyrin and the enhanced photosensitivity of bipyridine.

Plasmonic Nanocrystal-MOF Nanocomposites as Highly Active Photocatalysts and Highly Sensitive Sensors for CO2 Reduction over a Wide Range of Solar Wavelengths

Plasmonic nanocrystals have the potential to be widely used in green energy-related applications, due to their excellent optical properties and high reactivity over a wide range of solar wavelengths. Another benefit of using plasmonic nanocrystals for optical applications is that these nanocrystals strongly enhance Raman scattering and are therefore widely used in sensors. Recently, nanocomposites of porous materials deposited on plasmonic nanocrystals are demonstrated to enhance chemical reactivity by concentrating reactants on the surface of plasmonic nanocrystals. Here, three different plasmonic nanocrystals producing plasmonic responses within 400-900 nm are used as templates, and MOF-801 (Zr-based MOF) is produced on these nanocrystals as photocatalysts for the CO2 reduction reaction. Using nanocomposites as CO2 reduction reaction photocatalysts, the CO2 conversion rate can reach >50% within 30 min. The CO2 reduction reactivity of nanocomposites can be improved by the composition and morphology of plasmonic nanocrystals (increased by 40-50%), due to stronger synergistic effects and higher surface area to volume ratio. This report demonstrates that by controlling the plasmonic responses of nanocrystals, it is possible to realize photocatalysts that can be used for CO2 reduction reactions over a wide range of solar wavelengths.

Assembling Giant Nanoclusters as Heterogeneous Catalysts for Effectively Converting CO2 to CO Under Visible Light

Heterometallic lanthanide-transition metal (3d-4f) nanoclusters with well-defined structures and multiple active sites are excellent vehicles for achieving efficient catalysis and studying heterometallic synergism. In this work, two closely related yet different high-nuclearity nanoclusters, 72-nuclear {Ni28RE44} (1, RE = Pr, Nd, Sm, Eu, and Gd) and 111-nuclear {Ni48La63} (2), are synthesized using a mixed-ligand strategy. Importantly, the crystal solids of these giant coordination clusters are insoluble when soaking in H2O/CH3CN and can be used as heterogeneous catalysts for visible-light-driven catalytic conversion of CO2 to CO. Cluster 2 exhibits a maximum CO production rate of 4800 µmol g-1 h-1 and a CO selectivity of 92% over H2. Furthermore, the catalytic properties are investigated of different rare earths in the cluster 1 series, found that 1-Eu exhibited superior catalytic performance under identical conditions, likely due to the lower reduction potential of the europium ions. This study represents the first report of 3d-4f heterometallic nanoclusters as heterogeneous catalysts for photocatalytic reaction and provides a reference for the study of high-nuclearity 3d-4f nanoclusters as catalysts for photocatalytic reduction of CO2 to CO.

Co-In Bimetallic Hydroxide Nanosheet Arrays With Coexisting Hydroxyl and Metal Vacancies Anchored on Rod-Like MOF Template for Enhanced Photocatalytic CO2 Reduction

Layered double hydroxides (LDHs) can serves as catalysts for CO2 photocatalytic reduction (CO2PR). However, the conventionally synthesized LDHs undergo undesired aggregation, which results in an insufficient number of active sites and limits the desirable electron transfer required for CO2PR. The metal-organic framework (MOF) template-grown LDHs demonstrate excellent promise for exploiting the strengths of both MOFs and LDHs. Herein, the in situ growth of MIL-68(In)-NH2 MOF-templated Co-In bimetallic catalyst (CoIn-LDH/MOF) having an ultrathin nanosheet morphology on the preserved rod-like MOF template is demonstrated. Compared to the conventionally grown bimetallic LDH (CoIn-LDH), CoIn-LDH/MOF not only exposes more active sites but also possesses hydroxyl vacancies (VOH) and Co vacancies (VCo). Thus, CoIn-LDH/MOF performs a higher CO generation rate of 2320 µmol g-1 h-1 during CO2PR, demonstrating improved activity and selectivity than those in CoIn-LDH. Experiments coupled with calculations reveal that the CoIn-LDH/MOF-driven CO2PR follows the *COOH pathway. The lower energy barriers for the formation of *COOH and CO(g) can be attributed to the coexistence of VOH and VCo in CoIn-LDH/MOF, effectively promoting charge transfer and enhancing CO2PR performance. This study provides a new strategy to obtain high-performant LDH-based catalysts with improved morphology.

Precision-Engineered Construction of Proton-Conducting Metal-Organic Frameworks

Proton-conducting materials have attracted considerable interest because of their extensive application in energy storage and conversion devices. Among them, metal-organic frameworks (MOFs) present tremendous development potential and possibilities for constructing novel advanced proton conductors due to their special advantages in crystallinity, designability, and porosity. In particular, several special design strategies for the structure of MOFs have opened new doors for the advancement of MOF proton conductors, such as charged network construction, ligand functionalization, metal-center manipulation, defective engineering, guest molecule incorporation, and pore-space manipulation. With the implementation of these strategies, proton-conducting MOFs have developed significantly and profoundly within the last decade. Therefore, in this review, we critically discuss and analyze the fundamental principles, design strategies, and implementation methods targeted at improving the proton conductivity of MOFs through representative examples. Besides, the structural features, the proton conduction mechanism and the behavior of MOFs are discussed thoroughly and meticulously. Future endeavors are also proposed to address the challenges of proton-conducting MOFs in practical research. We sincerely expect that this review will bring guidance and inspiration for the design of proton-conducting MOFs and further motivate the research enthusiasm for novel proton-conducting materials.

Controlled Synthesis of Preferential Facet-Exposed Fe-MOFs for Ultrasensitive Detection of Peroxides

Exposing different facets on metal-organic frameworks (MOFs) is highly desirable to enhance the performance for various applications, however, exploiting a concise and effective approach to achieve facet-controlled synthesis of MOFs remains challenging. Here, by modulating the ratio of metal precursors to ligands, the facet-engineered iron-based MOFs (Fe-MOFs) exhibits enhanced catalytic activity for Fenton reaction are explored, and the mechanism of facet-dependent performance is revealed in detail. Fully exposed (101) and (100) facets on spindle-shaped Fe-MOFs enable rapid oxidation of colorless o-phenylenediamine (OPD) to colored products, thereby establishing a dual-mode platform for the detection of hydrogen peroxide (H2O2) and triacetone triperoxide (TATP). Thus, a detection limit as low as 2.06 nm is achieved, and robust selectivity against a wide range of common substances (>16 types) is obtained, which is further improved by incorporating a deep learning architecture with an SE-VGG16 network model, enabling precise differentiation of oxidizing agents from captured images. The present strategy is expected will shine light on both the rational synthesis of nanomaterials with modulated morphologies and the exploitation of high-performance trace chemical sensors.