环境响应型纳米粒子在不互溶两相间的相转移

纳米粒子在不互溶两相间的相转移在催化剂的循环利用、药物输送等领域发挥着重要的作用.环境响应性纳米粒子因兼具纳米粒子的优点和刺激响应的特性而受到了广泛的关注.环境响应型纳米粒子相转移的出现使相转移过程更为高效、可逆且智能化,已展现出了广阔的应用前景.本文综述了近年来环境响应型纳米粒子在不互溶两相间转移的研究进展,主要内容...     

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 N₂, and recovered ILs could be directly reused in the next process.     

Pivotal Role of the Basic Character of Organic and Salt Catalysts in C−N Bond Forming Reactions of Amines with CO2

Organocatalysts promote a range of C?N bond forming reactions of amines with CO₂. Herein, we review these reactions and attempt to identify the unifying features of the catalysts that allows them to promote a multitude of seemingly unrelated reactions. Analysis of the literature shows that these reactions predominantly proceed by carbamate salt formation in the form [BaseH][RR′NCOO]. The anion of the carbamate salt acts as a nucleophile in hydrosilane reductions of CO₂, internal cyclization reactions or after dehydration as an electrophile in the synthesis of urea derivatives. The reactions are enhanced by polar aprotic solvents and can be either promoted or hindered by H‐bonding interactions. The predominant role of all types of organic and salt catalysts (including ionic liquids, ILs) is the stabilization of the carbamate salt, mostly by acting as a base. Catalytic enhancement depends on the combination of the amine, the base strength, the solvent, steric factors, ion pairing and H‐bonding. A linear relationship between the base strength and the reaction yield has been demonstrated with IL catalysts in the synthesis of formamides and quinazoline‐2,4‐diones. The role of organocatalysts in the reactions indicates that all bases of sufficient strength should be able to catalyze the reactions. However, a physical limit to the extent of a purely base catalyzed reaction mechanism should exist, which needs to be identified, understood and overcome by synergistic or alternative methods.     

N‐Heterocyclic Olefin–Carbon Dioxide and –Sulfur Dioxide Adducts: Structures and Interesting Reactivity Patterns

Depending on the amount of methanol present in solution, CO₂ adducts of N‐heterocyclic carbenes (NHCs) and N‐heterocyclic olefins (NHOs) have been found to be in fully reversible equilibrium with the corresponding methyl carbonate salts [EMIm][OCO₂Me] and [EMMIm][OCO₂Me]. The reactivity pattern of representative 1‐ethyl‐3‐methyl‐NHO–CO₂ adduct 4 has been investigated and compared with the corresponding NHC–CO₂ zwitterion: The protonation of 4 with HX led to the imidazolium salts [NHO–CO₂H][X], which underwent decarboxylation to [EMMIm][X] in the presence of nucleophilic catalysts. NHO–CO₂ zwitterion 4 can act as an efficient carboxylating agent towards CH acids such as acetonitrile. The [EMMIm] cyanoacetate and [EMMIm]₂ cyanomalonate salts formed exemplify the first C?C bond‐forming carboxylation reactions with NHO‐activated CO₂. The reaction of the free NHO with dimethyl carbonate selectively led to methoxycarbonylated NHO, which is a perfect precursor for the synthesis of functionalized ILs [NHO–CO₂Me][X]. The first NHO‐SO₂ adduct was synthesized and structurally characterized; it showed a similar reactivity pattern, which allowed the synthesis of imidazolium methyl sulfites upon reaction with methanol.     

Catalytic and Asymmetric Fluorolactonisations of Carboxylic Acids through Anion Phase Transfer

Catalytic fluorolactonisations of aromatic carboxylic acids have been developed. The reactions proceed under mild conditions using the commercially available reagent Selectfluor. A weak phase transfer of the reagent mediated by Na₂CO₃ allows the reaction to be conducted in non‐polar solvents. Furthermore, by the use of a catalytic amount of (DHQ)₂PHAL (hydroquinine 1,4‐phthalazinediyl diether), the first asymmetric fluorolactonisation has been achieved. The corresponding isobenzofuran core can be found in many biologically active molecules.     

Efficient Conversion of Carbon Dioxide with Si‐Based Reducing Agents Catalyzed by Metal Complexes and Salts

Homogeneous metal complex and salt catalysts were developed for the reductive transformation of CO₂ with Si‐based reducing agents. Cu‐bisphosphine complexes were found to be excellent catalysts for the hydrosilylation of CO₂ with polymethylhydrosiloxane (PMHS). The Cu complexes also showed high catalytic activity and a wide substrate scope for formamide synthesis from amines, CO₂, and PMHS. Simple fluoride salts such as tetrabutylammonium fluoride acted as good catalysts for the reductive conversion of CO₂ to formic acid in the presence of hydrosilane, disilane, and metallic Si. Based on the kinetics, isotopic experiments, and in‐situ NMR measurements, the reaction mechanism for both catalyst systems, the Cu complex and the fluoride salt, have been proposed.     

Metal‐Free Reduction of CO2 with Hydroboranes: Two Efficient Pathways at Play for the Reduction of CO2 to Methanol

Guanidines and amidines prove to be highly efficient metal‐free catalysts for the reduction of CO₂ to methanol with hydroboranes such as 9‐borabicyclo[3.3.1]nonane (9‐BBN) and catecholborane (catBH). Nitrogen bases, such as 1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (TBD), 7‐methyl‐1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (Me‐TBD), and 1,8‐diazabicycloundec‐7‐ene (DBU), are active catalysts for this transformation and Me‐TBD can catalyze the reduction of CO₂ to methoxyborane at room temperature with TONs and TOFs of up to 648 and 33 h^?1 (25 °C), respectively. Formate HCOOBR₂ and acetal H₂C(OBR₂)₂ derivatives have been identified as reaction intermediates in the reduction of CO₂ with R₂BH, and the first C?H‐bond formation is rate determining. Experimental and computational investigations show that TBD and Me‐TBD follow distinct mechanisms. The N?H bond of TBD is reactive toward dehydrocoupling with 9‐BBN and affords a novel frustrated Lewis pair (FLP) that can activate a CO₂ molecule and form the stable adduct 2 , which is the catalytically active species and can facilitate the hydride transfer from the boron to the carbon atoms. In contrast, Me‐TBD promotes the reduction of CO₂ through the activation of the hydroborane reagent. Detailed DFT calculations have shown that the computed energy barriers for the two mechanisms are consistent with the experimental findings and account for the reactivity of the different boron reductants.     

Computational Design of New Heterofullerene‐Based Biomimetic α‐Carbonic Anhydrase Analogues

The biomimetic CO₂ hydration activity of Ru/Rh‐doped fullerenes was revealed by using density functional theory calculations. The mechanism of CO₂ hydration on the proposed heterofullerenes followed the mechanistic action of α‐carbonic anhydrases, and consisted of the adsorption and deprotonation of H₂O, CO₂ interaction with hydroxyl groups, CO₂ bending, and proton transfer to give the product. Free‐energy landscapes for the reaction showed the catalysts to be active for the reaction. H₂O adsorption over the catalysts was exergonic whereas CO₂ adsorption over the catalyst–OH complex was observed to be an endergonic process. Intramolecular proton transfer resulting in the final product, , was found to be the rate‐limiting step for the reaction on C₅₆N₃M (M=Ru/Rh), whereas H₂O dissociation was found to be the rate‐limiting step for the reaction on C₅₉M (M=Ru/Rh). C₅₆N₃M catalysts were found to be superior to C₅₉M catalysts for biomimetic CO₂ hydration, as indicated by the free‐energy landscapes and energy requirements.     

Formation of Gas‐Phase Formate in Thermal Reactions of Carbon Dioxide with Diatomic Iron Hydride Anions

The hydrogenation of carbon dioxide involves the activation of the thermodynamically very stable molecule CO₂ and formation of a C−H bond. Herein, we report that HCO₂⁻ and CO can be formed in the thermal reaction of CO₂ with a diatomic metal hydride species, FeH⁻. The FeH⁻ anions were produced by laser ablation, and the reaction with CO₂ was analyzed by mass spectrometry and quantum‐chemical calculations. Gas‐phase HCO₂⁻ was observed directly as a product, and its formation was predicted to proceed by facile hydride transfer. The mechanism of CO₂ hydrogenation in this gas‐phase study parallels similar behavior of a condensed‐phase iron catalyst.     

An ATR‐FTIR Study on the Effect of Molecular Structural Variations on the CO2 Absorption Characteristics of Heterocyclic Amines,Part II

This paper reports on an ATR‐FTIR spectroscopic investigation of the CO₂ absorption characteristics of a series of heterocyclic diamines: hexahydropyrimidine (HHPY), 2‐methyl and 2,2‐dimethylhexahydropyrimidine (MHHPY and DMHHPY), hexahydropyridazine (HHPZ), piperazine (PZ) and 2,5‐ and 2,6‐dimethylpiperazine (2,6‐DMPZ and 2,5‐DMPZ). By using in situ ATR‐FTIR the structure–activity relationship of the reaction between heterocyclic diamines and CO₂ is probed. PZ forms a hydrolysis‐resistant carbamate derivative, while HHPY forms a more labile carbamate species with increased susceptibility to hydrolysis, particularly at higher CO₂ loadings (>0.5 mol CO₂/mol amine). HHPY exhibits similar reactivity toward CO₂ to PZ, but with improved aqueous solubility. The α‐methyl‐substituted MHHPY favours HCO₃^? formation, but MHHPY exhibits comparable CO₂ absorption capacity to conventional amines MEA and DEA. MHHPY show improved reactivity compared to the conventional α‐methyl‐ substituted primary amine 2‐amino‐2‐methyl‐1‐propanol. DMHHPY is representative of blended amine systems, and its reactivity highlights the advantages of such systems. HHPZ is relatively unreactive towards CO₂. The CO₂ absorption capacity C_A (mol CO₂/mol amine) and initial rates of absorption R_IA (mol CO₂/mol amine min^?1) for each reactive diamine are determined: PZ: C_A=0.92, R_IA=0.045; 2,6‐DMPZ: C_A=0.86, R_IA=0.025; 2,5‐DMPZ: C_A=0.88, R_IA=0.018; HHPY: C_A=0.85, R_IA=0.032; MHHPY: C_A=0.86, R_IA=0.018; DMHHPY: C_A=1.1, R_IA=0.032; and HHPZ: no reaction. Calculations at the B3LYP/6‐31+G** and MP2/6‐31+G** calculations show that the substitution patterns of the heterocyclic diamines affect carbamate stability, which influences hydrolysis rates.     

An FTIR Spectroscopic Study on the Effect of Molecular Structural Variations on the CO2 Absorption Characteristics of Heterocyclic Amines

Herein, the reaction between CO₂ and piperidine, as well as commercially available functionalised piperidine derivatives, for example, those with methyl‐, hydroxyl‐ and hydroxyalkyl substituents, has been investigated. The chemical reactions between CO₂ and the functionalised piperidines were followed in situ by using attenuated total reflectance (ATR) FTIR spectroscopy. The effect of structural variations on CO₂ absorption was assessed in relation to the ionic reaction products identifiable by IR spectroscopy, that is, carbamate versus bicarbonate absorbance, CO₂ absorption capacity and the mass‐transfer coefficient at zero loading. On absorption of CO₂, the formation of the carbamate derivatives of the 3‐ and 4‐hydroxyl‐, 3‐ and 4‐hydroxymethyl‐, and 4‐hydroxyethyl‐substituted piperidines were found to be kinetically less favourable than the carbamate derivatives of piperidine and the 3‐ and 4‐methyl‐substituted piperidines. As the CO₂ loading of piperidine and the 3‐ and 4‐methyl‐ and hydroxyalkyl‐substituted piperidines exceeded 0.5 moles of CO₂ per mole of amine, the hydrolysis of the carbamate derivative of these amines was observed in the IR spectra collected. From the subset of amines analysed, the 2‐alkyl‐ and 2‐hydroxyalkyl‐substituted piperidines were found to favour bicarbonate formation in the reaction with CO₂. Based on IR spectral data, the ability of these amines to form the carbamate derivatives was also established. Computational calculations at the B3LYP/6‐31+G** and MP2/6‐31+G** levels of theory were also performed to investigate the electronic/steric effects of the substituents on the reactivity (CO₂ capture performance) of different amines, as well as their carbamate structures. The theoretical results obtained for the 2‐alkyl‐ and 2‐hydroxyalkyl‐substituted piperidines suggest that a combination of both the electronic effect exerted by the substituent and a reduction in the exposed area of the nitrogen atom play a role in destabilising the carbamate derivative and increasing its susceptibility to hydrolysis. A theoretical investigation into the structure of the carbamate derivatives of these amines revealed shorter N? C bond lengths and a less‐delocalised electron distribution in the carboxylate moiety.     

New Device for Adding Polar Modifiers to Carbon Dioxide Mobile Phase for Supercritical Fluid Chromatography

Abstract

Adding additional components to supercritical carbon dioxide in supercritical fluid chromatography can extend or significantly alter the fluid solvating properties. Polar samples which are difficult to be analyzed with pure supercritical CO₂ because of their high polarity can be separated by adding polar modifiers to supercritical CO₂. In this paper, a new mixing device using a teflon high capacity filter for adding polar modifiers to carbon dioxide mobile phase is introduced. This new mixing device could keep the amount of modifier in the mobile phase constant for a much longer time than a saturator column. The amount of water or methanol dissolved in supercritical CO₂ was measured by amperometric microsensor which is made of thin film of perfluorosulfonate ionomer(PFSI).     

The Functionality of Surface Hydroxy Groups on the Selectivity and Activity of Carbon Dioxide Reduction over Cuprous Oxide in Aqueous Solutions

Carbon dioxide (CO₂) reduction in aqueous solutions is an attractive strategy for carbon capture and utilization. Cuprous oxide (Cu₂O) is a promising catalyst for CO₂ reduction as it can convert CO₂ into valuable hydrocarbons and suppress the side hydrogen evolution reaction (HER). However, the nature of the active sites in Cu₂O remains under debate because of the complex surface structure of Cu₂O under reducing conditions, leading to limited guidance in designing improved Cu₂O catalysts. This paper describes the functionality of surface‐bonded hydroxy groups on partially reduced Cu₂O(111) for the CO₂ reduction reaction (CO₂RR) by combined density functional theory (DFT) calculations and experimental studies. We find that the surface hydroxy groups play a crucial role in the CO₂RR and HER, and a moderate coverage of hydroxy groups is optimal for promotion of the CO₂RR and suppression of the HER simultaneously. Electronic structure analysis indicates that the charge transfer from hydroxy groups to coordination‐unsaturated Cu (Cu_CUS) sites stabilizes surface‐adsorbed COOH*, which is a key intermediate during the CO₂RR. Moreover, the CO₂RR was evaluated over Cu₂O octahedral catalysts with {111} facets and different surface coverages of hydroxy groups, which demonstrates that Cu₂O octahedra with moderate coverage of hydroxy groups can indeed enhance the CO₂RR and suppress the HER.     

Cu–N Dopants Boost Electron Transfer and Photooxidation Reactions of Carbon Dots

The broadband light‐absorption ability of carbon dots (CDs) has inspired their application in photocatalysis, however this has been impeded by poor electron transfer inside the CDs. Herein, we report the preparation of Cu–N‐doped CDs (Cu‐CDs) and investigate both the doping‐promoted electron transfer and the performance of the CDs in photooxidation reactions. The Cu–N doping was achieved through a one‐step pyrolytic synthesis of CDs with Na₂[Cu(EDTA)] as precursor. As confirmed by ESR, FTIR, and X‐ray photoelectron spectroscopies, the Cu species chelates with the carbon matrix through Cu–N complexes. As a result of the Cu–N doping, the electron‐accepting and ‐donating abilities were enhanced 2.5 and 1.5 times, and the electric conductivity was also increased to 171.8 μs cm^?1. As a result of these enhanced properties, the photocatalytic efficiency of CDs in the photooxidation reaction of 1,4‐dihydro‐2,6‐dimethylpyridine‐3,5‐dicarboxylate is improved 3.5‐fold after CD doping.     

Three‐Phase Photocatalysis for the Enhanced Selectivity and Activity of CO2 Reduction on a Hydrophobic Surface

The photocatalytic CO₂ reduction reaction (CRR) represents a promising route for the clean utilization of stranded renewable resources, but poor selectivity resulting from the competing hydrogen evolution reaction (HER) in aqueous solution limits its practical applicability. In the present contribution a photocatalyst with hydrophobic surfaces was fabricated. It facilitates an efficient three‐phase contact of CO₂ (gas), H₂O (liquid), and catalyst (solid). Thus, concentrated CO₂ molecules in the gas phase contact the catalyst surface directly, and can overcome the mass‐transfer limitations of CO₂, inhibit the HER because of lowering proton contacts, and overall enhance the CRR. Even when loaded with platinum nanoparticles, one of the most efficient HER promotion cocatalysts, the three‐phase photocatalyst maintains a selectivity of 87.9 %. Overall, three‐phase photocatalysis provides a general and reliable method to enhance the competitiveness of the CRR.     

Reductive Activation of Small Molecules by Anionic Coinage Metal Atoms and Clusters in the Gas Phase

Metal atoms and clusters exhibit chemical properties that are significantly different or totally absent in comparison to their bulk counterparts. Such peculiarity makes them potential building units for the generation of novel catalysts. Investigations of the gas‐phase reactions between size‐ and charge‐selected atoms/clusters and small molecules have provided fundamental insights into their intrinsic reactivity, thus leading to a guiding principle for the rational design of the single‐atom and cluster‐based catalysts. Especially, recent gas‐phase studies have elucidated that small molecules such as O₂, CO₂, and CH₃I can be catalytically activated by negatively‐charged atoms/clusters via donation of a partial electronic charge. This Minireview showcases typical examples of such “reductive activation” processes promoted by anions of metal atoms and clusters. Here, we focus on anionic atoms/clusters of coinage metals (Cu, Ag, and Au) owing to the simplicity of their electronic structures. The determination of a correlation between their activation modes and the electronic structures might be helpful for the future development of innovative coinage metal catalysts.     

Methanol Synthesis at a Wide Range of H2/CO2 Ratios over a Rh‐In Bimetallic Catalyst

There is increasing interest in capturing H₂ generated from renewables with CO₂ to produce methanol. However, renewable hydrogen production is expensive and in limited quantity compared to CO₂. Excess CO₂ and limited H₂ in the feedstock gas is not favorable for CO₂ hydrogenation to methanol, causing low activity and poor methanol selectivity. Now, a class of Rh‐In catalysts with optimal adsorption properties to the intermediates of methanol production is presented. The Rh‐In catalyst can effectively catalyze methanol synthesis but inhibit the reverse water‐gas shift reaction under H₂‐deficient gas flow and shows the best competitive methanol productivity under industrially applicable conditions in comparison with reported values. This work demonstrates a strong potential of Rh‐In bimetallic composition, from which a convenient methanol synthesis based on flexible feedstock compositions (such as H₂/CO₂ from biomass derivatives) with lower energy cost can be established.     

Reforming of CH4 with CO2 over Rh/H-Beta:Effect of Rhodium Dispersion on the Catalytic Activity and Coke Resistance

The effect of Rh dispersion on reforming of CH₄ with CO₂ over H‐Beta supported Rh catalysts has been investigated. The CH₄ and CO₂ conversion over the catalysts increase with increasing Rh loading from 0.5 wt% to 4.0 wt% in the reaction temperature range of 823–1123 K. The high TOF of CH₄ over 0.5 wt% and 1.0 wt% Rh/H‐beta may be attributed to high dispersion of rhodium species. The catalysts before and after the reaction were characterized by XRD, TEM, and TG‐DTA and the results indicate the catalysts with Rh loading of 0.5 wt% and 1.0 wt% exhibiting high resistance to coke. Under controllable conditions, we confirm that the coke is originated from methane dissociation and can be substantially oxidized by active oxygen species dissociated from the adsorbed carbon dioxide on the catalyst with high dispersion of Rh species.     

Catalysis of N‐Methylaniline‐Blocked Polyisocyanate‐Hydroxyl‐Terminated Polybutadiene Cure Reaction

Catalysis of cure reaction between N‐methylaniline‐blocked polyisocyanate and hydroxyl‐terminated polybutadiene was investigated using a variety of tertiary amine and organotin catalysts. The catalytic activity of amine and organotin compounds was determined from the cure‐time results. It was found that the activity of the catalyst depends upon the steric constrain around the catalytic center. The organotin compounds showed higher catalytic activity than the amine catalysts. FTIR results obtained under isothermal condition revealed that DABCO selectively catalyze the urethane formation reaction, whereas DBTDL catalyze both the allophanate formation and urethane formation reactions during curing process. The synergistic effect of amine and organotin mixed catalysts on the cure reaction was also investigated.     

Electrons Mediate the Gas‐Phase Oxidation of Formic Acid with Ozone

Gas‐phase reactions of CO₃^.? with formic acid are studied using Fourier transform ion cyclotron resonance (FT‐ICR) mass spectrometry. Signal loss indicates the release of a free electron, with the formation of neutral reaction products. This is corroborated by adding traces of SF₆ to the reaction gas, which scavenges 38 % of the electrons. Quantum chemical calculations of the reaction potential energy surface provide a reaction path for the formation of neutral carbon dioxide and water as the thermochemically favored products. From the literature, it is known that free electrons in the troposphere attach to O₂, which in turn transfer the electron to O₃. O₃^.? reacts with CO₂ to form CO₃^.?. The reaction reported here formally closes the catalytic cycle for the oxidation of formic acid with ozone, catalyzed by free electrons.