In Situ Formation of Z-Scheme Bi₂WO₆/WO₃ Heterojunctions for Gas-Phase CO₂ Photoreduction with H₂O by Photohydrothermal Treatment

We report a new photohydrothermal method to prepare a Bi2WO6/WO3 catalytic material for CO2 photoreduction by solar concentrators. The photohydrothermal treatment improves the physico-chemical properties of the Bi2WO6/WO3 material and forms well contact Bi2WO6/WO3 heterojunctions, which increase the maximum reaction rate of CO2 photoreduction to 8.2 times under the simulated light, and the hydrocarbon yield under the real concentrating solar light achieves thousands of μmol·gcata−1. The reason for the high activity is attributed to the direct Z-scheme effect of Bi2WO6/WO3 heterojunctions and the photothermal effect during the course. These findings highlight the utilization of solar energy in CO2 photoreduction and open avenues for the rational design of highly efficient photocatalysts

Covalent Organic Frameworks with Ionic Liquid-Moieties (ILCOFs): Structures, Synthesis, and CO2 Conversion

CO2, an acidic gas, is usually emitted from the combustion of fossil fuels and leads to the formation of acid rain and greenhouse effects. CO2 can be used to produce kinds of value-added chemicals from a viewpoint based on carbon capture, utilization, and storage (CCUS). With the combination of unique structures and properties of ionic liquids (ILs) and covalent organic frameworks (COFs), covalent organic frameworks with ionic liquid-moieties (ILCOFs) have been developed as a kind of novel and efficient sorbent, catalyst, and electrolyte since 2016. In this critical review, we first focus on the structures and synthesis of different kinds of ILCOFs materials, including ILCOFs with IL moieties located on the main linkers, on the nodes, and on the side chains. We then discuss the ILCOFs for CO2 capture and conversion, including the reduction and cycloaddition of CO2. Finally, future directions and prospects for ILCOFs are outlined. This review is beneficial for academic researchers in obtaining an overall understanding of ILCOFs and their application of CO2 conversion. This work will open a door to develop novel ILCOFs materials for the capture, separation, and utilization of other typical acid, basic, or neutral gases such as SO2, H2S, NOx, NH3, and so on

Effects of Different Ions and Temperature on Corrosion Behavior of Pure Iron in Anoxic Simulated Groundwater

As a typical material of the insert in high-level radioactive waste (HLW) geological disposal canisters, iron-based materials will directly contact with groundwater after the failure of a metallic canister, acting as a chemical barrier to prevent HLW leaking into groundwater. In this paper, anoxic groundwater was simulated by mixing 10 mM NaCl and 2 mM NaHCO3 purged by Ar gas (containing 0.3% CO2) with different added ions (Ca2+, CO32− and SiO32−) and operation temperatures (25, 40 and 60 °C). An electrochemical measurement, immersion tests and surface characterization were carried out to study the corrosion behavior of pure iron in the simulated groundwater. The effects of Ca2+ on the corrosion behavior of iron is negligible, however, Cl− plays an important role in accelerating the corrosion activity with the increased concentration and temperature. With increased concentrations of CO32− and SiO32−, the corrosion resistance of iron is largely improved, which is attributed to the formation of a uniform passivation film. The independent effects of temperature on the corrosion behavior of iron are resulted from the repeated passivation–dissolution processes in the formation of the passivation film, resulting from the synergistic effects of CO32−/SiO32− and Cl−. The formation of ferric silicate is dominant in the passivation film with the addition of SiO32−, which effectively protects the iron surface from corrosion

Tuning the Hydrophilicity and Hydrophobicity of the Respective Cation and Anion: Reversible Phase Transfer of Ionic Liquids

The separation and recycling of catalyst and cocatalyst from the products and solvents are of critical importance. In this work, a class of functionalized ionic liquids (ILs) were designed and synthesized, and by tuning the hydrophilicity and hydrophobicity of cation and anion, respectively, these ILs could reversibly transfer between water and organics triggered upon undergoing a temperature change. From a combination of multiple spectroscopic techniques, it was shown that the driving force behind the transfer was originated from a change in conformation of the PEG chain of the IL upon temperature variation. By utilizing the novel property of this class of ILs, a highly efficient and controllable CuI-catalyzed cycloaddition reaction was achieved wherein the IL was used to entrain, activate, and recycle the catalyst, as well as to control the reaction.</p

Remarkable synergistic effect between copper(I) and ionic liquids for promoting chemical fixation of CO2

Recently, efficient chemical conversion of CO2 into high value chemicals at room temperature and atmospheric pressure without using noble metal catalysts remains a great challenge. In this work, we find that the carboxylative cyclization of propargylic alcohols with CO2 can proceed at 60 degrees C and ambient pressure by using a combination of CuI and an ionic liquid (IL) 1,8-diazabicyclo-[5.4.0]-7-undecenium trifluoroethanol ([DBUH] [TFE]) as catalyst. By simple extraction after the reactions, a series of desired products have been obtained in good to excellent yields with this highly efficient catalyst system. Spectroscopic investigations and DFT calculations demonstrate that such a high efficiency originates from remarkable synergistic catalysis between Cu(I) and the IL on substrates. In addition, it is worth noting that this catalyst system also works well for the carboxylative cyclization of propargylic amines even at ambient temperature and pressure, with the highest turnover number among the reported base metals catalytic systems.</p

Recent Advances in Carbon-Silica Composites: Preparation, Properties, and Applications

The thermal catalytic conversion of biomass is currently a prevalent method for producing activated carbon with superb textural properties and excellent adsorption performance. However, activated carbon suffers severely from its poor thermal stability, which can easily result in spontaneous burning. In contrast, silica material is famed for its easy accessibility, high specific surface area, and remarkable thermal stability; however, its broader applications are restricted by its strong hydrophilicity. Based on this, the present review summarizes the recent progress made in carbon-silica composite materials, including the various preparation methods using diverse carbon (including biomass resources) and silica precursors, their corresponding structure–function relationship, and their applications in adsorption, insulation, batteries, and sensors. Through their combination, the drawbacks of the individual materials are circumvented while their original advantages are maintained. Finally, several bottlenecks existing in the field of carbon-silica composites, from synthesis to applications, are discussed in this paper, and possible solutions are given accordingly

Acylamido-Based Anion-Functionalized Ionic Liquids for Efficient SO₂ Capture through Multiple-Site Interactions

Acid gases such as SO₂ can be absorbed by ionic liquids (ILs) because of their unique properties. In this work, we developed a new approach for improving SO₂ absorption by novel acylamido-based anion-functionalized ILs. Several kinds of such ILs with different structures of acylamido group (anionic acylamide) were designed, prepared, and used for efficient capture of SO₂. It was shown that these acylamido-based ILs strongly interacted with SO₂, resulting in a very high SO₂ capacity up to ∼4.5 mol SO₂ per mole of IL. The interactions between acylamido-based ILs and SO₂ were investigated by FT-IR, NMR, and quantum chemical calculations. It was found that the dramatic enhancement of SO₂ absorption capacity was originated from the multiple-site interactions such as N···S and CO···S interactions between the anion and SO₂. Furthermore, the captured SO₂ was easy to release by heating or bubbling N₂ through the SO₂-saturated ILs. This novel strategy provides an excellent alternative to current SO₂ capture technologies

Reversible Hydrophobic-Hydrophilic Transition of Ionic Liquids Driven by Carbon Dioxide

Ionic liquids (ILs) with a reversible hydrophobic-hydrophilic transition were developed, and they exhibited unique phase behavior with H2O: monophase in the presence of CO2, but biphase upon removal of CO2 at room temperature and atmospheric pressure. Thus, coupling of reaction, separation, and recovery steps in sustainable chemical processes could be realized by a reversible liquid-liquid phase transition of such IL-H2O mixtures. Spectroscopic investigations and DFT calculations showed that the mechanism behind hydrophobic-hydrophilic transition involved reversible reaction of CO2 with anion of the ILs and formation of hydrophilic ammonium salts. These unique IL-H2O systems were successfully utilized for facile one-step synthesis of Au porous films by bubbling CO2 under ambient conditions. The Au porous films and the ILs were then separated simultaneously from aqueous solutions by bubbling N-2, and recovered ILs could be directly reused in the next process.</p

Limited Number of Active Sites Strategy for Improving SO₂ Capture by Ionic Liquids with Fluorinated Acetylacetonate Anion

SO₂ capture is highly important because this acid gas can react with moisture in the atmosphere to produce acid rain, a kind of atmospheric pollution. In this contribution, we show how SO₂ can be efficiently absorbed by a new class of fluorinated acetylacetonate ionic liquids (FILs) with limited number of active sites in the anions. The absorption of SO₂ by these functionalized FILs is investigated under different partial pressures and temperatures, and a high SO₂ capacity up to 4.27 and 1.82 mol SO₂ per mol IL can be achieved under 1 and 0.1 bar, respectively, compared with 1.43 and 0.24 mol SO₂ per mol [TFSI]-based FIL ([TFSI] = bis­(trifluoromethylsulfonyl)­imide anion). From a combined study of quantum chemical calculations, FT-IR and NMR analysis, it is found that the high SO₂ absorption capacities by fluorinated acetylacetonate task-specific FILs can be ascribed to the multiple-site interactions between SO₂ and limited number of active sites in the anions. Furthermore, the FILs can be easily regenerated and the SO₂ absorption process could be recycled