Enhancing photocatalytic performance of metal-organic frameworks for CO2 reduction by a bimetallic strategy

Metal-organic frameworks（MOFs） as a type of crystalline heterogeneous catalysts have shown potential application in photocatalytic CO₂ reduction.However,MOF catalysts with high efficiency and selectivity are still in pursuit.Herein,by a bimetallic strategy,the catalytic performance of a Co-MOF for photocatalytic CO₂ reduction was enhanced.Specifically,the Co-MOF based on 4,5-dicarboxylic acid（H₃ IDC） and4,4’-bipydine（4,4’-bpy） can catalyze CO₂ reductio...     

Isolated Square‐Planar Copper Center in Boron Imidazolate Nanocages for Photocatalytic Reduction of CO2 to CO

Photocatalytic reduction of CO₂ to value‐added fuel has been considered to be a promising strategy to reduce global warming and shortage of energy. Rational design and synthesis of catalysts to maximumly expose the active sites is the key to activate CO₂ molecules and determine the reaction selectivity. Herein, we synthesize a well‐defined copper‐based boron imidazolate cage (BIF‐29) with six exposed mononuclear copper centers for the photocatalytic reduction of CO₂. Theoretical calculations show a single Cu site including weak coordinated water delivers a new state in the conduction band near the Fermi level and stabilizes the *COOH intermediate. Steady‐state and time‐resolved fluorescence spectra show these Cu sites promote the separation of electron–hole pairs and electron transfer. As a result, the cage achieves solar‐driven reduction of CO₂ to CO with an evolution rate of 3334 μmol g^?1 h^?1 and a high selectivity of 82.6 %.     

A novel naphthalimide–glutathione chemosensor for fluorescent detection of Fe3+ and Hg2+ in aqueous medium and its application

By rationally introducing glutathione functionalized 1, 8–naphthalimide, a novel fluorescent chemosensor (NG) was successfully synthesized. NG can high selectively and sensitively recognize Fe³⁺/Hg²⁺ ions through quenching of fluorescence among all kinds of common metal ions in aqueous medium. The binding stoichiometry ratio of NG–Fe³⁺ is verified as 2:1and NG–Hg²⁺ as 1:2 confirmed by Job's plot method, FT-IR, ¹H NMR and ESI–MS spectrum, and the possible sensing mechanism were also proposed. The chemosensor NG toward Fe³⁺ and Hg²⁺ displays the excellent advantages of high selectivity and sensitivity, low detection limits (7.92?×?10^?8 and 4.22?×?10^?8?M), high association constants (3.37?×?10⁸ and 8.14?×?10⁴?M^?2), instataneous response (about 10s) and wide pH response range (3.0–8.0). Importantly, the chemosensor NG was successfully applied to determine Hg²⁺ in tap water. Meanwhile, the test strips based on NG were prepared, which could conveniently and efficiently detect Fe³⁺ and Hg²⁺. Moreover, the complex of NG and Fe³⁺ (NG–Fe³⁺) showed high selectivity and sensitivity for H₂PO₄￣ over many other anions in the same medium.     

Eosin Y‐Functionalized Conjugated Organic Polymers for Visible‐Light‐Driven CO2 Reduction with H2O to CO with High Efficiency

Visible‐light‐driven photoreduction of CO₂ to energy‐rich chemicals in the presence of H₂O without any sacrifice reagent is of significance, but challenging. Herein, Eosin Y‐functionalized porous polymers (PEosinY‐N, N=1–3), with high surface areas up to 610 m² g^?1, are reported. They exhibit high activity for the photocatalytic reduction of CO₂ to CO in the presence of gaseous H₂O, without any photosensitizer or sacrifice reagent, and under visible‐light irradiation. Especially, PEosinY‐1 derived from coupling of Eosin Y with 1,4‐diethynylbenzene shows the best performance for the CO₂ photoreduction, affording CO as the sole carbonaceous product with a production rate of 33 μmol g^?1 h^?1 and a selectivity of 92 %. This work provides new insight for designing and fabricating photocatalytically active polymers with high efficiency for solar‐energy conversion.     

Dispersed Nickel Cobalt Oxyphosphide Nanoparticles Confined in Multichannel Hollow Carbon Fibers for Photocatalytic CO2 Reduction

Materials for high‐efficiency photocatalytic CO₂ reduction are desirable for solar‐to‐carbon fuel conversion. Herein, highly dispersed nickel cobalt oxyphosphide nanoparticles (NiCoOP NPs) were confined in multichannel hollow carbon fibers (MHCFs) to construct the NiCoOP‐NPs@MHCFs catalysts for efficient CO₂ photoreduction. The synthesis involves electrospinning, phosphidation, and carbonization steps and permits facile tuning of chemical composition. In the catalyst, the mixed metal oxyphosphide NPs with ultrasmall size and high dispersion offer abundant catalytically active sites for redox reactions. At the same time, the multichannel hollow carbon matrix with high conductivity and open ends will effectively promote mass/charge transfer, improve CO₂ adsorption, and prevent the metal oxyphosphide NPs from aggregation. The optimized hetero‐metal oxyphosphide catalyst exhibits considerable activity for photosensitized CO₂ reduction, affording a high CO evolution rate of 16.6 μmol h^?1 (per 0.1 mg of catalyst).     

Regulation of Coordination Number over Single Co Sites: Triggering the Efficient Electroreduction of CO2

The design of active, selective, and stable CO₂ reduction electrocatalysts is still challenging. A series of atomically dispersed Co catalysts with different nitrogen coordination numbers were prepared and their CO₂ electroreduction catalytic performance was explored. The best catalyst, atomically dispersed Co with two‐coordinate nitrogen atoms, achieves both high selectivity and superior activity with 94 % CO formation Faradaic efficiency and a current density of 18.1 mA cm^?2 at an overpotential of 520 mV. The CO formation turnover frequency reaches a record value of 18 200 h^?1, surpassing most reported metal‐based catalysts under comparable conditions. Our experimental and theoretical results demonstrate that lower a coordination number facilitates activation of CO₂ to the CO₂^.? intermediate and hence enhances CO₂ electroreduction activity.     

Post-modification of metal-organic framework for improved CO2 photoreduction efficiency

Utilizing metal-organic frameworks (MOFs) to design photocatalysts for CO₂ reduction catalysts is an excellent idea but currently restricted by the relatively low activity. Enhancing CO₂ affinity and tuning the oxidation state of metal clusters in MOFs might be a solution to improve the catalytic performance. Herein, the Cl-bridge atoms in the metal clusters of a cobalt MOF were easily exchanged with OH^?, which simultaneously oxidized a portion of Co(II) to Co(III) and resulted in a much enhanced photocatalytic activity for CO₂ reduction. In contrast, the original framework does not exhibit such superior activity. Comprehensive characterizations on their physicochemical properties revealed that the introduction of hydroxyl group not only greatly increases the CO₂ affinity but also alters the oxidation state of metal clusters, resulting in significantly improved photocatalytic activities for CO₂ reduction. This work provides important insight into the design of efficient photocatalysts.     

A colorimetric squaraine-based probe and test paper for rapid naked eyes detection of copper ion (II)

A colorimetric probe N,N’-bis(2-methoxy-ethyl)-2,3,3-trimethyl-3H-squaraine (MOESQ) with H₂O solubility was synthesized to detect Cu²⁺. MOESQ exhibits good selectivity, high sensitivity and fast UV-Vis response toward Cu²⁺ over other competing ions in CH₃CN. The detection limit of MOESQ for Cu²⁺ in CH₃CN can reach 1.88?×?10^?7?molL^?1. By adsorbing MOESQ on the chromatography paper, a colorimetric test paper for Cu²⁺ was prepared, which could detect Cu²⁺ with the color change from blue to faint yellow even in the limit of detection concentration of 10^?6?molL^?1.     

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.     

Efficient Visible‐Light‐Driven Carbon Dioxide Reduction by a Single‐Atom Implanted Metal–Organic Framework

Modular optimization of metal–organic frameworks (MOFs) was realized by incorporation of coordinatively unsaturated single atoms in a MOF matrix. The newly developed MOF can selectively capture and photoreduce CO₂ with high efficiency under visible‐light irradiation. Mechanistic investigation reveals that the presence of single Co atoms in the MOF can greatly boost the electron–hole separation efficiency in porphyrin units. Directional migration of photogenerated excitons from porphyrin to catalytic Co centers was witnessed, thereby achieving supply of long‐lived electrons for the reduction of CO₂ molecules adsorbed on Co centers. As a direct result, porphyrin MOF comprising atomically dispersed catalytic centers exhibits significantly enhanced photocatalytic conversion of CO₂, which is equivalent to a 3.13‐fold improvement in CO evolution rate (200.6 μmol g^?1 h^?1) and a 5.93‐fold enhancement in CH₄ generation rate (36.67 μmol g^?1 h^?1) compared to the parent MOF.     

Single chemosensor for sensing multiple analytes: Selective fluorogenic detection of Cu2+ and Br−

A tripodal receptor R1 with a combination of nitrogen and oxygen-based binding sites was designed and used for the selective determination of Cu²⁺. The fluorescence emission profile of R1 in the presence of Cu²⁺ showed a marked enhancement in fluorescence intensity, indicating high selectivity among other metal ions. The R1–Cu²⁺ complex was further explored as a sensor for anion detection. Upon addition of Br^?, switching to a fluorescence “off” state was observed. The Br^? selectivity of the complex over a wide range of concentrations was observed via titrimetric analysis through changes in the emission spectra.     

A novel highly selective ratiometric fluorescent sensor for relay recognition of Zn2+ and H2PO4−

A novel fluorescent sensor (AQTF1) based on the N-(quinolin-8-yl) tetrahydrofuran-2-carboxamide was designed and synthesized. This new sensor demonstrated high selectivity for the Zn²⁺ without the interference from Cd²⁺. The detection limit of this probe was calculated to be 10.8 nM for Zn²⁺. The in situ prepared AQTF1-Zn²⁺ complex was used for detection of H₂PO₄^? and displayed good selectivity from the common anions. Furthermore, the AQTF1 displayed good ratiometric response for the relay recognition for Zn²⁺ and H₂PO₄^?.     

Coupling Benzylamine Oxidation with CO2 Photoconversion to Ethanol over a Black Phosphorus and Bismuth Tungstate S-Scheme Heterojunction

Photoconversion of CO₂ and H₂O into ethanol is an ideal strategy to achieve carbon neutrality. However, the production of ethanol with high activity and selectivity is challenging owing to the less efficient reduction half-reaction involving multi-step proton-coupled electron transfer (PCET), a slow C−C coupling process, and sluggish water oxidation half-reaction. Herein, a two-dimensional/two-dimensional (2D/2D) S-scheme heterojunction consisting of black phosphorus and Bi₂WO₆ (BP/BWO) was constructed for photocatalytic CO₂ reduction coupling with benzylamine (BA) oxidation. The as-prepared BP/BWO catalyst exhibits a superior photocatalytic performance toward CO₂ reduction, with a yield of 61.3 μmol g⁻¹ h⁻¹ for ethanol (selectivity of 91 %).In situ spectroscopic studies and theoretical calculations reveal that S-scheme heterojunction can effectively promote photogenerated carrier separation via the Bi−O−P bridge to accelerate the PCET process. Meanwhile, electron-rich BP acts as the active site and plays a vital role in the process of C−C coupling. In addition, the substitution of BA oxidation for H₂O oxidation can further enhance the photocatalytic performance of CO₂ reduction to C₂H₅OH. This work opens a new horizon for exploring novel heterogeneous photocatalysts in CO₂ photoconversion to C₂H₅OH based on cooperative photoredox systems.     

Transition Metal Doping Induces Ti3+ to Promote the Performance of SrTiO3@TiO2 Visible Light Photocatalytic Reduction of CO2 to Prepare C1 Product.

Transition metal Fe, Co, Ni and Cu doped strontium titanate-rich SrTiO₃@TiO₂ (STO@T) materials were prepared by hydrothermal method. The prepared doped materials exhibit better photocatalytic CO₂ reduction to CH₄ ability under visible light conditions. Among them, Fe-doped and undoped SrTiO₃@TiO₂ under visible light conditions CO₂ reduction products only CO, while M-STO@T (M=Co, Ni, Cu) samples converted CO₂ to CH₄. The average methane yield of Ni-doped STO@T samples are as high as 73.85 μmol g⁻¹ h⁻¹. The production of methane is mainly due to the increase in the response of the doped samples to visible light. And the increase in the separation rate of photogenerated electrons and holes and the efficiency of electron transport caused by the generation of impurity levels. The impurity level caused by Ti³⁺ plays an important role in the production of methane by CO₂ visible light reduction. Ni doping effectively improves the photocatalytic performance of STO@T and CO₂ reduction mechanism were explained.     

Palladium Single Atoms on TiO2 as a Photocatalytic Sensing Platform for Analyzing the Organophosphorus Pesticide Chlorpyrifos

Traditional methods for analyzing organophosphorus pesticide chlorpyrifos, usually require the tedious sample pretreatment and sophisticated bio‐interfaces, leading to the difficulty for real‐time analysis. Herein, we use palladium single‐atom (PdSA)/TiO₂ as a photocatalytic sensing platform to directly detect chlorpyrifos with high sensitivity and selectivity. PdSA/TiO₂, prepared by an in situ photocatalytic reduction of PdCl₄^2? on the TiO₂, shows much higher photocatalytic activity (10 mol g^?1 h^?1) for hydrogen evolution reaction than Pd nanoparticles (1.95 mol g^?1 h^?1), and excellent stability. In the presence of chlorpyrifos, the photocatalytic activity of PdSA/TiO₂ decreases. Through this inhibition effect the platform can realize a detection limit for chlorpyrifos of 0.01 ng mL^?1, much lower than the maximum residue limit (10 ppb) permitted by the U.S. Environmental Protection Agency.     

A Hybrid Co Quaterpyridine Complex/Carbon Nanotube Catalytic Material for CO2 Reduction in Water

Associating a metal‐based catalyst to a carbon‐based nanomaterial is a promising approach for the production of solar fuels from CO₂. Upon appending a Co^II quaterpyridine complex [Co(qpy)]²⁺ at the surface of multi‐walled carbon nanotubes, CO₂ conversion into CO was realized in water at pH 7.3 with 100 % catalytic selectivity and 100 % Faradaic efficiency, at low catalyst loading and reduced overpotential. A current density of 0.94 mA cm^?2 was reached at ?0.35 V vs. RHE (240 mV overpotential), and 9.3 mA cm^?2 could be sustained for hours at only 340 mV overpotential with excellent catalyst stability (89 095 catalytic cycles in 4.5 h), while 19.9 mA cm^?2 was met at 440 mV overpotential. Such a hybrid material combines the high selectivity of a homogeneous molecular catalyst to the robustness of a heterogeneous material. Catalytic performances compare well with those of noble‐metal‐based nano‐electrocatalysts and atomically dispersed metal atoms in carbon matrices.     

Supramolecular photocatalysts fixed on the inside of the polypyrrole layer in dye sensitized molecular photocathodes: application to photocatalytic CO2 reduction coupled with water oxidation

The development of systems for photocatalytic CO₂ reduction with water as a reductant and solar light as an energy source is one of the most important milestones on the way to artificial photosynthesis. Although such reduction can be performed using dye-sensitized molecular photocathodes comprising metal complexes as redox photosensitizers and catalyst units fixed on a p-type semiconductor electrode, the performance of the corresponding photoelectrochemical cells remains low, e.g., their highest incident photon-to-current conversion efficiency (IPCE) equals 1.2%. Herein, we report a novel dye-sensitized molecular photocathode for photocatalytic CO₂ reduction in water featuring a polypyrrole layer, [Ru(diimine)₃]²⁺ as a redox photosensitizer unit, and Ru(diimine)(CO)₂Cl₂ as the catalyst unit and reveal that the incorporation of the polypyrrole network significantly improves reactivity and durability relative to those of previously reported dye-sensitized molecular photocathodes. The irradiation of the novel photocathode with visible light under low applied bias stably induces the photocatalytic reduction of CO₂ to CO and HCOOH with high faradaic efficiency and selectivity (even in aqueous solution), and the highest IPCE is determined as 4.7%. The novel photocathode is coupled with n-type semiconductor photoanodes (CoO_x/BiVO₄ and RhO_x/TaON) to construct full cells that photocatalytically reduce CO₂ using water as the reductant upon visible light irradiation as the only energy input at zero bias. The artificial Z-scheme photoelectrochemical cell with the dye-sensitized molecular photocathode achieves the highest energy conversion efficiency of 8.3 × 10⁻²% under the irradiation of both electrodes with visible light, while a solar to chemical conversion efficiency of 4.2 × 10⁻²% is achieved for a tandem-type cell using a solar light simulator (AM 1.5, 100 mW cm⁻²).

A novel dye-sensitized molecular photocathode with polypyrrole networks exhibits high efficiency and durability for photocatalytic CO₂ reduction by using water as reductant and visible light as energy.     

Stable and Highly Efficient Electrochemical Production of Formic Acid from Carbon Dioxide Using Diamond Electrodes

High faradaic efficiencies can be achieved in the production of formic acid (HCOOH) by metal electrodes, such as Sn or Pb, in the electrochemical reduction of carbon dioxide (CO₂). However, the stability and environmental load in using them are problematic. The electrochemical reduction of CO₂ to HCOOH was investigated in a flow cell using boron‐doped diamond (BDD) electrodes. BDD electrodes have superior electrochemical properties to metal electrodes, and, moreover, are highly durable. The faradaic efficiency for the production of HCOOH was as high as 94.7 %. Furthermore, the selectivity for the production of HCOOH was more than 99 %. The rate of the production was increased to 473 μmol m^?2 s^?1 at a current density of 15 mA cm^?2 with a faradaic efficiency of 61 %. The faradaic efficiency and the production rate are almost the same as or larger than those achieved using Sn and Pb electrodes. Furthermore, the stability of the BDD electrodes was confirmed by 24 h operation.     

The effects of local environment towards yield and selectivity on photocatalytic CO2 reduction catalyzed by metal-organic framework

The CO₂ photoconversion is sensitive to the local reaction environment, of which activity and selectivity can be regulated by the change of reaction systems. This paper focuses on investigating the photocatalytic CO₂ reduction behaviors of MOFs with the involvement of water under different reaction modes, including gas-solid and liquid-solid systems. The CO₂ photoreduction in a liquid-solid system shows high performance in generating HCOOH with the selectivity of 100%. In contrast, the gas-solid system referring to the synergistic interaction of MOFs and H₂O vapor benefits to the formation of gas-phase products, such as CO and CH₄. The possible mechanisms of photocatalytic CO₂ reaction in two modes were investigated by in-situ Fourier-transform infrared spectroscopy, which indicates that the distinction in reaction consequence may result from the difference in CO₂ chemisorbed modes and the proton provision. The choice of reaction system plays an important role in the achievement of high efficiency and selectivity for photocatalytic CO₂ reduction, which is of great practical value in real-world applications.     

Stable Heterometallic Cluster‐Based Organic Framework Catalysts for Artificial Photosynthesis

A series of stable heterometallic Fe₂M cluster‐based MOFs ( NNU‐31‐M , M=Co, Ni, Zn) photocatalysts are presented. They can achieve the overall conversion of CO₂ and H₂O into HCOOH and O₂ without the assistance of additional sacrificial agent and photosensitizer. The heterometallic cluster units and photosensitive ligands excited by visible light generate separated electrons and holes. Then, low‐valent metal M accepts electrons to reduce CO₂, and high‐valent Fe uses holes to oxidize H₂O. This is the first MOF photocatalyst system to finish artificial photosynthetic full reaction. It is noted that NNU‐31‐Zn exhibits the highest HCOOH yield of 26.3 μmol g^?1 h^?1 (selectivity of ca. 100 %). Furthermore, the DFT calculations based on crystal structures demonstrate the photocatalytic reaction mechanism. This work proposes a new strategy for how to design crystalline photocatalyst to realize artificial photosynthetic overall reaction.