Accelerating Charge Kinetics in Photocatalytic CO2 Reduction by Modulating the Cobalt Coordination in Heterostructures of Cadmium Sulfide/Metal-Organic Layer.

Artificial photocatalytic CO2 reduction (CO2R) holds great promise to directly store solar energy into chemical bonds. The slow charge and mass transfer kinetics at the triphasic solid-liquid-gas interface calls for the rational design of heterogeneous photocatalysts concertedly boosting interfacial charge transfer, local CO2 concentration, and exposure of active sites. To meet these requirements, in this study heterostructures of CdS/MOL (MOL = metal-organic layer) furnishing different redox Co sites are fabricated for CO2R photocatalysts. It is found that the coordination environment of Co is key to photocatalytic activity. The best catalyst ensemble comprising ligand-chelated Co2+ with the bipyridine electron mediator demonstrates a high CO yield rate of 1523 µmol h-1 gcat -1, selectivity of 95.8% and TON of 1462.4, which are ranked among the best seen in literature. Comprehensive photochemical and electroanalytical characterizations attribute the high CO2R performance to the improved photocarrier separation and charge kinetics originated from the proper energy band alignment and coordination chemistry. This work highlights the construction of 2D heterostructures and modulation of transition metal coordination to expedite the charge kinetics in photocatalytic CO2 reduction.

Nanoscale Metal-Organic Layer Reprograms Cellular Metabolism to Enhance Photodynamic Therapy and Antitumor Immunity.

Abnormal cancer metabolism causes hypoxia and immunosuppressive tumor microenvironment (TME), which limits the antitumor efficacy of photodynamic therapy (PDT). Herein, we report a photosensitizing nanoscale metal-organic layer (MOL) with anchored 3­bromopyruvate (BrP), BrP@MOL, as a metabolic reprogramming agent to enhance PDT and antitumor immunity. BrP@MOL inhibited mitochondrial respiration and glycolysis to oxygenate tumors and reduce lactate production. This metabolic reprogramming enhanced reactive oxygen species generation during PDT and reshaped the immunosuppressive TME to enhance antitumor immunity. BrP@MOL-mediated PDT inhibited tumor growth by >90% with a 40% cure rate, rejected tumor re-challenge, and prevented lung metastasis. Further combination with immune checkpoint blockade potently regressed the tumors with >98% tumor inhibition and an 80% cure rate.

Building 2D/2D CdS/MOLs Heterojunctions for Efficient Photocatalytic Hydrogen Evolution.

2D lamellar materials can offer high surface area and abundant reactive sites, thus showing an appealing prospect in photocatalytic hydrogen evolution. However, it is still difficult to build cost-efficient photocatalytic hydrogen evolution systems based on 2D materials. Herein, an in situ growth method is employed to build 2D/2D heterojunctions, with which 2D Ni-based metal-organic layers (Ni-MOLs) are closely grown on 2D porous CdS (P-CdS) nanosheets, affording traditional P-CdS/Ni-MOL heterojunction materials. Impressively, the optimized P-CdS/Ni-MOL catalyst exhibits superior photocatalytic hydrogen evolution performance, with an H2 yield of 29.81 mmol g-1 h-1 . This value is 7 and 2981 times higher than that of P-CdS and Ni-MOLs, respectively, and comparable to those of reported state of the art catalysts. Photocatalytic mechanism studies reveal that the enhanced photocatalytic performance can be attributed to the 2D/2D intimate interface between P-CdS and Ni-MOLs, which facilitates the fast charge carriers' separation and transfer. This work provides a strategy to develop 2D MOL-based photocatalysts for sustainable energy conversion.

Cost-Effective 2D Ultrathin Metal-Organic Layers with Bis-Metallic Catalytic Sites for Visible Light-Driven Photocatalytic CO2 Reduction.

As novel generated 2D materials, metal-organic layers (MOLs) have recently emerged as a potential platform for photocatalytic CO2 reduction reaction (PCO2 RR). Such 2D structures negate the blemish of low-density catalytic sites and low electron transmission efficiency on the surface of metal organic frameworks (MOFs), while retaining the advantage of low expenditure when using earth-abundant metal nodes and meritorious applicability in the PCO2 RR. Herein, it is reported that the 2D ultrathin layer material with bis-metallic catalytic sites (Ni-O metal node and the Ni-N metal site) from bidentate ligand 2,2'-bipyridine-5,5'-dicarboxylate (H2 bpydc) and nickel(II) remarkably boosts the visible light-driven PCO2 RR performance with a CO yield of 2400 mmol g-1 for 18 h and a selectivity up to 99 %. Consequently, the effects of morphology, catalytic sites and intrinsic properties on PCO2 RR efficiency have been investigated in detail. In this context, the ultrathin layer structure has been elucidated as the key point to facilitate electron transfer efficiency. Notably, the bis-metallic catalytic sites with reasonable distance between two adjacent metals presumably induce synergistic effect and offer a guiding ideology for further designing high performance photocatalysts.

Electrochemical Enzyme Sensor Based on the Two-Dimensional Metal-Organic Layers Supported Horseradish Peroxidase.

Metal-organic frames (MOFs) have recently been used to support redox enzymes for highly sensitive and selective chemical sensors for small biomolecules such as oxygen (O2), hydrogen peroxide (H2O2), etc. However, most MOFs are insulative and their three-dimensional (3D) porous structures hinder the electron transfer pathway between the current collector and the redox enzyme molecules. In order to facilitate electron transfer, here we adopt two-dimensional (2D) metal-organic layers (MOLs) to support the HRP molecules in the detection of H2O2. The correlation between the current response and the H2O2 concentration presents a linear range from 7.5 µM to 1500 µM with a detection limit of 0.87 µM (S/N = 3). The sensitivity, reproducibility, and stability of the enzyme sensor are promoted due to the facilitated electron transfer.

Metal-Organic Layers Hierarchically Integrate Three Synergistic Active Sites for Tandem Catalysis.

We report the design of a bifunctional metal-organic layer (MOL), Hf12 -Ru-Co, composed of [Ru(DBB)(bpy)2 ]2+ [DBB-Ru, DBB=4,4'-di(4-benzoato)-2,2'-bipyridine; bpy=2,2'-bipyridine] connecting ligand as a photosensitizer and Co(dmgH)2 (PPA)Cl (PPA-Co, dmgH=dimethylglyoxime; PPA=4-pyridinepropionic acid) on the Hf12 secondary building unit (SBU) as a hydrogen-transfer catalyst. Hf12 -Ru-Co efficiently catalyzed acceptorless dehydrogenation of indolines and tetrahydroquinolines to afford indoles and quinolones. We extended this strategy to prepare Hf12 -Ru-Co-OTf MOL with a [Ru(DBB)(bpy)2 ]2+ photosensitizer and Hf12 SBU capped with triflate as strong Lewis acids and PPA-Co as a hydrogen transfer catalyst. With three synergistic active sites, Hf12 -Ru-Co-OTf competently catalyzed dehydrogenative tandem transformations of indolines with alkenes or aldehydes to afford 3-alkylindoles and bisindolylmethanes with turnover numbers of up to 500 and 460, respectively, illustrating the potential use of MOLs in constructing novel multifunctional heterogeneous catalysts.

Tailoring Crystal Facets of Metal-Organic Layers to Enhance Photocatalytic Activity for CO2 Reduction.

It is common that different crystal facets in metal and metal oxide nanocrystals display different catalytic performances, whereas such phenomena have been rarely documented in metal-organic frameworks (MOFs). Herein, we demonstrate for the first time that a nickel metal-organic layer (MOL) exposing rich (100) crystal facets (Ni-MOL-100) shows a much higher photocatalytic CO2 -to-CO activity than the one exposing rich (010) crystal facets (Ni-MOL-010) and its bulky counterpart (bulky Ni-MOF), with a catalytic activity up to 2.5 and 4.6 times more active than Ni-MOL-010 and bulky Ni-MOF, respectively. Theoretical studies reveal that the two coordinatively unsaturated NiII ions with a close distance of 3.50 Šon the surface of Ni-MOL-100 enables synergistic catalysis, leading to more favorable energetics in CO2 reduction than that of Ni-MOL-010.

Metal-Organic Layers Leading to Atomically Thin Bismuthene for Efficient Carbon Dioxide Electroreduction to Liquid Fuel.

Electrochemical reduction of CO2 to valuable fuels is appealing for CO2 fixation and energy storage. However, the development of electrocatalysts with high activity and selectivity in a wide potential window is challenging. Herein, atomically thin bismuthene (Bi-ene) is pioneeringly obtained by an in situ electrochemical transformation from ultrathin bismuth-based metal-organic layers. The few-layer Bi-ene, which possesses a great mass of exposed active sites with high intrinsic activity, has a high selectivity (ca. 100 %), large partial current density, and quite good stability in a potential window exceeding 0.35 V toward formate production. It even deliver current densities that exceed 300.0 mA cm-2 without compromising selectivity in a flow-cell reactor. Using in situ ATR-IR spectra and DFT analysis, a reaction mechanism involving HCO3 - for formate generation was unveiled, which brings new fundamental understanding of CO2 reduction.

Functionalization of Zirconium-Based Metal-Organic Layers with Tailored Pore Environments for Heterogeneous Catalysis.

Intriguing properties and functions are expected to implant into metal-organic layers (MOLs) to achieve tailored pore environments and multiple functionalities owing to the synergies among multiple components. Herein, we demonstrate a facile one-pot synthetic strategy to incorporate multiple functionalities into stable zirconium MOLs via secondary ligand pillaring. Through the combination of Zr6 -BTB (BTB=benzene-1,3,5-tribenzoate) layers and diverse secondary ligands (including ditopic and tetratopic linkers), 31 MOFs with multi-functionalities were systematically prepared. Notably, a metal-phthalocyanine fragment was successfully incorporated into this Zr-MOL system, giving rise to an ideal platform for the selective oxidation of anthracene. The organic functionalization of two-dimensional MOLs can generate tunable porous structures and environments, which may facilitate the excellent catalytic performance of as-synthesized materials.

Two-Dimensional Metal-Organic Layers as a Bright and Processable Phosphor for Fast White-Light Communication.

A metal-organic layer (MOL) is a new type of 2D material that is derived from metal-organic frameworks (MOFs) by reducing one dimension to a single layer or a few layers. Tetraphenylethylene-based tetracarboxylate ligands (TCBPE), with aggregation-induced emission properties, were assembled into the first luminescent MOL by linking with Zr6 O4 (OH)6 (H2 O)2 (HCO2 )6 clusters. The emissive MOL can replace the lanthanide phosphors in white light emitting diodes (WLEDs) with remarkable processability, color rendering, and brightness. Importantly, the MOL-WLED exhibited a physical switching speed three times that of commercial WLEDs, which is crucial for visible-light communication (VLC), an alternative wireless communication technology to Wi-Fi and Bluetooth, by using room lighting to carry transmitted signals. The short fluorescence lifetime (2.6 ns) together with high quantum yield (50 %) of the MOL affords fast switching of the assembled WLEDs for efficient information encoding and transmission.

Surface Modification of Two-Dimensional Metal-Organic Layers Creates Biomimetic Catalytic Microenvironments for Selective Oxidation.

Microenvironments in enzymes play crucial roles in controlling the activities and selectivities of reaction centers. Herein we report the tuning of the catalytic microenvironments of metal-organic layers (MOLs), a two-dimensional version of metal-organic frameworks (MOFs) with thickness down to a monolayer, to control product selectivities. By modifying the secondary building units (SBUs) of MOLs with monocarboxylic acids, such as gluconic acid, we changed the hydrophobicity/hydrophilicity around the active sites and fine-tuned the selectivity in photocatalytic oxidation of tetrahydrofuran (THF) to exclusively afford butyrolactone (BTL), likely a result of prolonging the residence time of reaction intermediates in the hydrophilic microenvironment of catalytic centers. Our work highlights new opportunities in using functional MOLs as highly tunable and selective two-dimensional catalytic materials.

Nanoscale Metal-Organic Layers for Deeply Penetrating X-ray-Induced Photodynamic Therapy.

We report the rational design of metal-organic layers (MOLs) that are built from [Hf6 O4 (OH)4 (HCO2 )6 ] secondary building units (SBUs) and Ir[bpy(ppy)2 ]+ - or [Ru(bpy)3 ]2+ -derived tricarboxylate ligands (Hf-BPY-Ir or Hf-BPY-Ru; bpy=2,2'-bipyridine, ppy=2-phenylpyridine) and their applications in X-ray-induced photodynamic therapy (X-PDT) of colon cancer. Heavy Hf atoms in the SBUs efficiently absorb X-rays and transfer energy to Ir[bpy(ppy)2 ]+ or [Ru(bpy)3 ]2+ moieties to induce PDT by generating reactive oxygen species (ROS). The ability of X-rays to penetrate deeply into tissue and efficient ROS diffusion through ultrathin 2D MOLs (ca. 1.2 nm) enable highly effective X-PDT to afford superb anticancer efficacy.

Self-Supporting Metal-Organic Layers as Single-Site Solid Catalysts.

Metal-organic layers (MOLs) represent an emerging class of tunable and functionalizable two-dimensional materials. In this work, the scalable solvothermal synthesis of self-supporting MOLs composed of [Hf6O4(OH)4(HCO2)6] secondary building units (SBUs) and benzene-1,3,5-tribenzoate (BTB) bridging ligands is reported. The MOL structures were directly imaged by TEM and AFM, and doped with 4'-(4-benzoate)-(2,2',2''-terpyridine)-5,5''-dicarboxylate (TPY) before being coordinated with iron centers to afford highly active and reusable single-site solid catalysts for the hydrosilylation of terminal olefins. MOL-based heterogeneous catalysts are free from the diffusional constraints placed on all known porous solid catalysts, including metal-organic frameworks. This work uncovers an entirely new strategy for designing single-site solid catalysts and opens the door to a new class of two-dimensional coordination materials with molecular functionalities.

Pyrenetetrasulfonate-grafted 2D ultrathin metal-organic layer as new electrochemiluminescence emitters for ultrasensitive microRNA-21 assay.

The exploration of novel electrochemiluminescence (ECL) luminophores with excellent ECL properties is a current research hotspot in the ECL field. Herein, a novel high-efficiency Ru-complex-free ECL emitter PyTS-Zr-BTB-MOL has been prepared by using porous ultrathin Zr-BTB metal-organic layer (MOL) as carrier to coordinatively graft the cheap and easily available polycyclic aromatic hydrocarbon (PAH) derivative luminophore PyTS whose ECL performance has never been investigated. Gratifyingly, the ECL intensity and efficiency of PyTS-Zr-BTB-MOL were markedly enhanced compared to both PyTS monomers and PyTS aggregates. The main reason was that the distance between pyrene rings was greatly expanded after the PyTS grafting on the Zr6 clusters of Zr-BTB-MOL, which overcame the aggregation-caused quenching (ACQ) effect of PyTS and thus enhanced the ECL emission. Meanwhile, the porous nanosheet structure of PyTS-Zr-BTB-MOL could distinctly increase the exposure of PyTS luminophores and shorten the diffusion paths of coreactants and electrons/ions, which effectively promoted the electrochemical excitation of more PyTS luminophores and thus achieved a further ECL enhancement. In light of the remarkable ECL property of PyTS-Zr-BTB-MOL, it was employed as an ECL indicator to build a novel high-sensitivity ECL biosensor for microRNA-21 determination, possessing a satisfactory response range (100 aM to 100 pM) and an ultralow detection limit (10.4 aM). Overall, this work demonstrated that using MOLs to coordinatively graft the PAH derivative luminophores to eliminate the ACQ effect and increase the utilization rate of the luminophores is a promising and efficient strategy to develop high-performance Ru-complex-free ECL materials for assembling ultrasensitive ECL biosensing platforms.

2D Nano-Sonosensitizers Facilitate Energy Transfer to Enhance Sonodynamic Therapy.

Although sonodynamic therapy (SDT) has shown promise for cancer treatment, the lack of efficient sonosensitizers (SSs) has limited the clinical application of SDT. Here, a new strategy is reported for designing efficient nano-sonosensitizers based on 2D nanoscale metal-organic layers (MOLs). Composed of Hf-oxo secondary building units (SBUs) and iridium-based linkers, the MOL is anchored with 5,10,15,20-tetra(p-benzoato)porphyrin (TBP) sensitizers on the SBUs to afford TBP@MOL. TBP@MOL shows 14.1- and 7.4-fold higher singlet oxygen (1 O2 ) generation than free TBP ligands and Hf-TBP, a 3D nanoscale metal-organic framework, respectively. The 1 O2 generation of TBP@MOL is enhanced by isolating TBP SSs on the SBUs of the MOL, which prevents aggregation-induced quenching of the excited sensitizers, and by triplet-triplet Dexter energy transfer between excited iridium-based linkers and TBP SSs, which more efficiently harnesses broad-spectrum sonoluminescence. Anchoring TBP on the MOL surface also enhances the energy transfer between the excited sensitizer and ground-state triplet oxygen to increase 1 O2 generation efficacy. In mouse models of colorectal and breast cancer, TBP@MOL demonstrates significantly higher SDT efficacy than Hf-TBP and TBP. This work uncovers a new strategy to design effective nano-sonosensitizers by facilitating energy transfer to efficiently capture broad-spectrum sonoluminescence and enhance 1 O2 generation.

A 2D Nanoradiosensitizer Enhances Radiotherapy and Delivers STING Agonists to Potentiate Cancer Immunotherapy.

Despite potent preclinical antitumor activity, activation of stimulator of interferon genes (STING) has shown modest therapeutic effects in clinical studies. Many STING agonists, including 2',3'-cyclic guanosine monophosphate-adenosine monophosphate (cGAMP), show poor pharmacokinetic properties for sustaining STING activation in tumors and achieving optimal antitumor efficacy. Improved delivery of STING agonists and their effective combination with other treatments are needed to enhance their therapeutic effects. Herein, a 2D nanoplatform, cGAMP/MOL, is reported via conjugating cGAMP to a nanoscale metal-organic layer (MOL) for simultaneous STING activation and radiosensitization. The MOL not only exhibits strong radiosensitization effects for enhanced cancer killing and induction of immunogenic cell death, but also retains cGAMP in tumors for sustained STING activation. Compared to free cGAMP, cGAMP/MOL elicits stronger STING activation and regresses local tumors upon X-ray irradiation. Further combination with an immune checkpoint inhibitor bridges innate and adaptive immune systems by activating the tumor microenvironment to elicit systemic antitumor responses.

Photocatalytic CO2 Conversion Using Metal-Containing Coordination Polymers and Networks: Recent Developments in Material Design and Mechanistic Details.

International guidelines have progressively addressed global warming which is caused by the greenhouse effect. The greenhouse effect originates from the atmosphere's gases which trap sunlight which, as a consequence, causes an increase in global surface temperature. Carbon dioxide is one of these greenhouse gases and is mainly produced by anthropogenic emissions. The urgency of removing atmospheric carbon dioxide from the atmosphere to reduce the greenhouse effect has initiated the development of methods to covert carbon dioxide into valuable products. One approach that was developed is the photocatalytic transformation of CO2. Photocatalysis addresses environmental issues by transferring CO2 into value added chemicals by mimicking the natural photosynthesis process. During this process, the photocatalytic system is excited by light energy. CO2 is adsorbed at the catalytic metal centers where it is subsequently reduced. To overcome several obstacles for achieving an efficient photocatalytic reduction process, the use of metal-containing polymers as photocatalysts for carbon dioxide reduction is highlighted in this review. The attention of this manuscript is directed towards recent advances in material design and mechanistic details of the process using different polymeric materials and photocatalysts.

Regulating Hydrogenation Chemoselectivity of α,ß-Unsaturated Aldehydes by Combination of Transfer and Catalytic Hydrogenation.

Two hydrogenation mechanisms, transfer and catalytic hydrogenation, were combined to achieve higher regulation of hydrogenation chemoselectivity of cinnamyl aldehydes. Transfer hydrogenation with ammonia borane exclusively reduced C=O bonds to get cinnamyl alcohol, and Pt-loaded metal-organic layers efficiently hydrogenated C=C bonds to synthesize phenyl propanol with almost 100 % conversion rate. The hydrogenation could be performed under mild conditions without external high-pressure hydrogen and was applicable to various α,ß-unsaturated aldehydes.

Two-Dimensional Metal-Organic Layers for Electrochemical Acceptorless Dehydrogenation of N-Heterocycles.

The catalytic acceptorless dehydrogenation (CAD) is an attractive synthetic route to unsaturated compounds because of its high atomic efficiency. Here we report electrochemical acceptorless dehydrogenation of N-heterocycles to obtain quinoline or indole derivatives using metal-organic layer (MOL) catalyst. MOL is the two-dimensional version of metal-organic frameworks (MOF), and it can be constructed on conductive multi-walled carbon nanotubes via facile solvothermal synthesis to overcome the conductivity constraint for MOFs in electrocatalysis. TEMPO-OPO3 2- was incorporated into the system through a ligand exchange with capping formate on the MOL surface to serve as the active catalytic centers. The hybrid catalyst is efficient in the organic conversion and can be readily recycled and reused.

Highly stable Ru-complex-grafted 2D metal-organic layer with superior electrochemiluminescent efficiency as a sensing platform for simple and ultrasensitive detection of mucin 1.

This work utilized ultrathin metal-organic layer (MOL) to immobilize luminophores for effectively shortening the ion/electron-transport distance and relieving the diffusional constraints of ion/electron, which greatly enhanced the ECL efficiency and intensity. Moreover, the MOL's immobilization amount of luminophores should be higher than these of bulk MOFs because MOLs possess more accessible postmodification sites for the luminophores with minimal diffusion barriers. As expected, our proof-of-concept experiment indicated that the Hf-MOL's loading number of Ru(bpy)2(mcpbpy)2+ was about 1.74 times that of a 3D mesoporous MOF (PCN-777), and the ECL efficiency and intensity of PEI@Ru-Hf-MOL were around 1.27 times and 14.5 times those of PEI@Ru-PCN-777, respectively. In view of these merits, this work utilized the prepared PEI@Ru-Hf-MOL as a highly efficient sensing platform for simple, rapid and sensitive detection of mucin 1, which exhibited a broad linearity from 1 fg/mL to 10 ng/mL and a low detection limit of 0.48 fg/mL. This work provided a practicable strategy to develop high-performance ECL materials, and therefore opened up a new avenue to design ultrasensitive ECL biosensors, which expanded the application potential of MOLs in ECL assays.