Tunable Carrier Type of a Semiconducting 2D Metal-Organic Framework Cu3(HHTP)2

Direct Electrodeposition of Electrically Conducting Ni3(HITP)2 MOF Nanostructures for Micro-Supercapacitor Integration

Micro-supercapacitors emerge as an important electrical energy storage technology expected to play a critical role in the large-scale deployment of autonomous microdevices for health, sensing, monitoring, and other IoT applications. Electrochemical double-layer capacitive storage requires a combination of high surface area and high electronic conductivity, with these being attained only in porous or nanostructured carbons, and recently found also in conducting metal-organic frameworks (MOFs). However, techniques for conformal deposition at micro- and nanoscale of these materials are complex, costly, and hard to upscale. Herein, the study reports direct, one step non-sacrificial anodic electrochemical deposition of Ni3(2,3,6,7,10,11-hexaiminotriphenylene)2 - Ni3(HITP)2, a porous and electrically conducting MOF. Employing this strategy enables the growth of Ni3(HITP)2 films on a variety of 2D substrates as well as on 3D nanostructured substrates to form Ni3(HITP)2 nanotubes and Pt@ Ni3(HITP)2 core-shell nanowires. Based on the optimal electrodeposition protocols, Ni3(HITP)2 films interdigitated micro-supercapacitors are fabricated and tested as a proof of concept.

Photocatalytic Hydrogen Peroxide Production through Functionalized Semiconductive Metal-Organic Frameworks

Hydrogen peroxide (H2O2) holds significance as a vital chemical with the potential to serve as an energy carrier. Compared with the conventional anthraquinone process, photocatalytic H2O2 production has emerged as an appealing alternative because of its energy efficiency and environmental sustainability. However, the existing photocatalysts suffer from low catalytic efficiency, limited tunability of optical properties, and reliance on sacrificial agents due to high energy loss caused by inefficient charge separation. Therefore, developing catalysts with tunable optical properties and efficient charge separation is desirable. In this work, we introduce postsynthetic functionalization into an electrically conductive metal-organic framework, namely, DPT-MOF. Leveraging DPT (3,6-di(4-pyridyl)-1,2,4,5-tetrazine) as a pillar ligand, we exploited click-type chemistry to manipulate band position and charge separation efficiency, allowing for photocatalytic nonsacrificial H2O2 production. Notably, the fluorine-functionalized MOF exhibited the highest H2O2 production rate of 1676 μmol g-1 h-1 under visible light in O2-saturated water among our other samples. This high production rate is attributed to the tuned electronic structure and prolonged charge lifetime facilitated by the fluorine groups. This work highlights the effectiveness of postsynthetic methodology in tuning optical properties, opening a promising avenue for advancing the field of semiconductive MOF-based photocatalysis.

Controlling Film Formation and Host-Guest Interactions to Enhance the Thermoelectric Properties of Nickel-Nitrogen-Based 2D Conjugated Coordination Polymers

2D conjugated coordination polymers (cCPs) based on square-planar transition metal-complexes (such as MO4, M(NH)4, and MS4, M = metal) are an emerging class of (semi)conducting materials that are of great interest for applications in supercapacitors, catalysis, and thermoelectrics. Finding synthetic approaches to high-performance nickel-nitrogen (Ni-N) based cCP films is a long-standing challenge. Here, a general, dynamically controlled on-surface synthesis that produces highly conductive Ni-N-based cCP films is developed and the thermoelectric properties as a function of the molecular structure and their dependence on interactions with ambient atmosphere are studied. Among the four studied cCPs with different ligand sizes hexaminobenzene- and hexaaminotriphenylene-based films exhibit record electrical conductivity (100-200 S cm-1) in this Ni-N based cCP family, which is one order of magnitude higher than previous reports, and the highest thermoelectric power factors up to 10 µW m-1 K-2 among reported 2D cCPs. The transport physics of these films is studied and it is shown that depending on the host-guest interaction with oxygen/water the majority carrier type and the value of the Seebeck coefficient can be largely regulated. The high conductivity is likely reflecting good interconnectivity between (small) ordered domains and grain boundaries supporting disordered metallic transport.

In situ synthesis of self-supporting conductive CuCo-based bimetal organic framework for sensitive nonenzymatic glucose sensing in serum and beverage

Most MOFs are associated with the inherent defect of low conductivity, limiting their further application in electrochemical sensing. Herein, a self-supporting conductive CuCo-based bimetal organic framework with HHTP as the organic ligand was in situ synthesized on carbon cloth via a one-step hydrothermal method, namely CuCo-MOF/CC. Benefiting from the advantages of electrical conductivity and bimetallic synergies, CuCo-MOF/CC exhibited remarkable electrocatalytic performance toward glucose. Consequently, the prepared sensor demonstrated an outstanding sensitivity of 9317 μA mM-1 cm-2, a wide range of 0.25-2374.5 μM, a low determination limit (0.27 μM), and a rapid response time (1.6 s). The reproducibility, stability, and selectivity were also proved to be satisfactory. Furthermore, the remarkable feasibility of proposed sensor was confirmed in serum and beverages. With the convenience of the one-step hydrothermal method and portability of self-supporting electrode, CuCo-MOF/CC has emerged as a promising candidate for commercial glucose sensors.

Evaluation of triphenylene-based MOF ultrathin films for lithium batteries

Metal-organic frameworks (MOFs) are attractive candidates to meet the requirement of next-generation batteries, as functional materials with a high surface area, well-defined metal centers, and organic linkers through coordination bonds. Due to their great tunability, MOFs have been investigated as electrodes or electrolytes in lithium batteries and more recently as protective layers in anode-less batteries. Here, we synthesize a Ni₃(HHTP)₂ MOF directly at the air-liquid interface of a Langmuir trough and grow the electrode on a conductive substrate by the transference process. The characterization during Langmuir film formation shows that the addition of crystallization time during the compression process enhances the formation of 2D crystalline domains, as observed by in situ grazing-incidence X-ray diffraction. Next, the transferred Ni₃(HHTP)₂ ultrathin films were studied as working electrodes in Li batteries in a half-cell configuration and compared with bare copper. The results show that the Ni₃(HHTP)₂ film protects the Cu collector from oxidation, and the negative charge accumulates in the organic ligand during the lithiation process while Ni^II oxidizes to Ni^III, unlike other triphenylene-based MOFs with Cu^II or Co^II metal nodes. The galvanostatic plating-stripping cycles of the batteries show that the inclusion of the crystallization time improves the coulombic efficiency, especially significantly in the first cycles when the SEI is formed. This work shows the Langmuir technique as a useful tool to test MOF based materials for batteries with the advantages of using a low amount of raw materials and without the need to introduce additives (binder and electron conductor) in the electrodes. The electrochemical study of this type of electrode allows a first screening to synthesize electrodes based on MOFs and can be a tool for the preparation of protective coatings under optimized conditions.

Transformation of a copper-based metal-organic polyhedron into a mixed linker MOF for CO2 capture

A new mixed linker metal-organic framework (MOF) has been synthesized from a copper-based metal-organic polyhedron (MOP-1) and 2,2'-bipyridine (2,2'-bipy). The CuMOF-Bipy with a formula of [Cu₂(2,2'-bpy)₂(m-BDC)₂]_n is comprised of a binuclear Cu(II) node coordinated to 2,2'-bipy, and isophthalic acid (m-BDC), which bridges to neighboring nodes. The crystal structure of CuMOF-Bipy consists of a stacked two-dimensional framework with the sql topology. CuMOF-Bipy was characterized by single-crystal X-ray diffraction (SC-XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and CO₂ sorption. CuMOF-Bipy was shown to have one-dimensional sinusoidal channels that allow diffusion of CO₂ but not N₂.

Fluorine extraction from organofluorine molecules to make fluorinated clusters in yttrium MOFs

A new rare earth based two-dimensional coordination network and a three-dimensional metal-organic framework (MOF) have been synthesized using bicinchoninic acid (BCA) and yttrium(iii) ions. Yttrium dimer nodes are formed in the absence of a modulator, resulting in a 2D layered coordination network (Y-BCA-2D). The presence of fluorinating agents, e.g., 2-fluorobenzoic acid (2-FBA), 2,6-difluorobenzoic acid (2,6-DFBA), and perfluorohexanoic acid (PFHxA) result in μ₃-F bridged metal hexaclusters (Y₆F₈) that form a three-dimensional MOF (Y-BCA-3D). It was found that Y³⁺ can break highly stable C-F bonds in aromatic and aliphatic fluorinated compounds. Single-crystal X-ray diffraction (SC-XRD) shows the presence of fluorine in the metal cluster which was confirmed by energy dispersive X-ray spectroscopy (EDS). High resolution X-ray photoelectron spectroscopy (XPS) and ¹⁹F Nuclear Magnetic Resonance (NMR) also verify the presence of metal-fluorine bonds in the cluster. The Y-BCA-3D MOF selectively adsorbs CO₂ but not N₂.

Conjugated Metal-Organic Macrocycles: Synthesis, Characterization, and Electrical Conductivity

The dimensional reduction of solids into smaller fragments provides a route to achieve new physical properties and gain deeper insight into the extended parent structures. Here, we report the synthesis of CuTOTP-OR (TOTP^n- = 2,3,6,7-tetraoxidotriphenylene), a family of copper-based macrocycles that resemble truncated fragments of the conductive two-dimensional (2D) metal-organic framework Cu₃(HHTP)₂ (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene). The planar metal-organic macrocycles self-assemble into ordered nanotubes with internal diameters of ∼2 nm and short interlayer distances of ∼3.20 Å. Strong π-π stacking interactions between macrocycles facilitate out-of-plane charge transport, and pressed pellet conductivities as high as 2(1) × 10^-3 S cm^-1 are observed. Peripheral alkyl functionalization enhances solution processability and enables the fabrication of thin-film field-effect transistor devices. Ambipolar charge transport is observed, suggesting that similar behavior may be operative in Cu₃(HHTP)₂. By coupling the attractive features of metal-organic frameworks with greater processability, these macrocycles enable facile device integration and a more nuanced understanding of out-of-plane charge transport in 2D conductive metal-organic frameworks.