Zr-Based MOF-Stabilized CO2-Responsive Pickering Emulsions for Efficient Reduction of Nitroarenes.

A Pickering emulsion is a natural microreactor for interfacial catalysis in which an emulsifier is critical. Recently, a metal-organic framework (MOF) has attracted attention to emulsify water-organic mixtures for constructing a Pickering emulsion. However, a few stimuli-responsive Pickering emulsions based on MOFs have been reported, and the MOF emulsifiers cannot be regenerated at room temperature. Herein, the Zr-MOF with a rodlike morphology is synthesized using ionic liquid as a modulator and then modified with n-(trimethoxysilylpropyl)imidazole (C3im) to prepare a series of functionalized Zr-MOFs (MOF-C3im). It is found that MOF-C3im is an excellent emulsifier to construct stable and CO2-responsive Pickering emulsions even at low content (>0.20 wt %). Notably, the emulsification and demulsification of the emulsions can be easily and reversibly switched by bubbling of CO2 and N2 alternatively at room temperature because CO2 and imidazole molecules anchored on the Zr-MOF underwent a reversible acid-base reaction, resulting in an obvious change in the wettability of the emulsifier. As a proof of concept, the reduction reactions of nitrobenzene have been successfully carried out in these Pickering emulsions, demonstrating the efficient integration as a microreactor for chemical reaction, product separation, and emulsifier recycling under ambient conditions. This strategy provides an innovative option to develop stimulus-responsive Pickering emulsions for sustainable chemical processes.

Efficient Capture and Low Energy Release of NH3 by Azophenol Decorated Photoresponsive Covalent Organic Frameworks.

In NH3 capture technologies, the desorption process is usually driven by high temperature and low pressure (such as 150-200°C under vacuum), which accounts for intensive energy consumption and CO2 emission. Developing light responsive adsorbent is promising in this regard but remains a great challenge. Here, we for the first time designed and synthesized a light responsive azophenol-containing covalent organic framework (COF), COF-HNU38, to address this challenge. We found that at 25 °C and 1.0 bar the cis -COF exhibited a NH3 uptake capacity of 7.7 mmol g-1 and a NH3/N2 selectivity of 158. In the adsorbed NH3, about 29.0% could be removed by vis-light irradiated cis-trans isomerization at 25 °C, and the remaining NH3 might be released at 25 °C under vacuum. Almost no decrease in adsorption capacity was observed after eight adsorption-desorption cycles. As such, an efficient NH3 capture and low energy release strategy was established thanks to the multiple hydrogen bond interactions (which are strong in total but weak in individuals) between NH3 and the smart COF, and the increase in polarity and in number of hydrogen bond sites after the trans-cis isomerization process.

Ingenious Artificial Leaf Based on Covalent Organic Framework Membranes for Boosting CO2 Photoreduction.

Covalent organic frameworks (COFs) hold the potential in converting CO2 with water into value-added fuels and O2 to save the deteriorating ecological environment. However, reaching high yield and selectivity is a grand challenge under metal-, photosensitizer-, or sacrificial reagent-free conditions. Here, inspired by microstructures of natural leaves, we designed triazine-based COF membranes with the integration of steady light-harvesting sites, efficient catalytic center, and fast charge/mass transfer configuration to fabricate a novel artificial leaf for the first time. Significantly, a record high CO yield of 1240 µmol g-1 in a 4 h reaction, approximately 100% selectivity, and a long lifespan (at least 16 cycles) were achieved under gas-solid conditions without using any metal, photosensitizer, or sacrificial reagent. Unlike the existing knowledge, the chemical structural unit of triazine-imide-triazine and the unique physical form of the COF membrane are predominant for such a remarkable photocatalysis. This work opens a new pathway to simulating photosynthesis in leaves and may motivate relevant research in the future.

Isomerization of DASA Molecules in the Nanopores of Metal-Organic Frameworks: What Determines Its Reversibility?

In recent years, light-responsive molecules have been incorporated in metal-organic frameworks (MOFs) to fabricate light-responsive intelligent devices, where reversible isomerization of the guest molecules in the nanopores is crucial. However, how to design a porous environment of MOFs to achieve a reversible isomerization remains unknown until now. In this work, donor-acceptor Stenhouse adducts (DASAs), a new kind of visible light responsive compound, were confined in the nanopores of different MOFs to study their isomerization upon visible-light irradiation/mild heating. We found that the polarity of the pore environment is the key to control the reversibility of isomerization of such guest molecules. Under the guidance of this principle, MIL-53(Al) was screened to investigate the proton conductivity and switching performance of the DASA-confined MOF. The proton conductance was up to 0.013 S cm-1 at 80 °C and 98 % RH, and at least 30 switching cycles were achieved thanks to the Grotthuss-type mechanism and the low polarity of MIL-53(Al) pore environment.

Simultaneous screening of 33 restricted substances in polymer materials using pyrolysis/thermal desorption gas chromatography-mass spectrometry.

The purpose of this study was to offer a quick and efficient method to screen for multiple restricted additives in polymer materials. A solvent-free pyrolysis gas chromatography-mass spectrometry method was developed to simultaneously screen 33 restricted substances, comprising 7 phthalates, 15 bromine flame retardants, 4 phosphorus flame retardants, 4 ultraviolet stabilizers, and 3 bisphenols. The pyrolysis technique and temperatures affecting additive desorption were studied. Under optimized conditions, the instrument sensitivity was confirmed using in-house reference materials at concentrations of 100 mg/kg and 300 mg/kg. The linear range was between 100 and 1000 mg/kg in 26 compounds, and in the other compounds it was between 300 and 1000 mg/kg. In this study, in-house reference materials, certified reference materials, and proficiency testing samples were used for method verification. The relative standard deviation of this method was less than 15%, and recoveries ranged from 75.9 to 107.1% for most of the compounds, with a few exceeding 120%. Furthermore, the screening method was verified with 20 plastic products used in daily life and 170 recycled plastic particle samples from imports. The experimental results showed that phthalates were the main additives in plastic products, and among 170 recycled plastic particle samples, 14 samples were found to contain restricted additives. The main additives in recycled plastics were bis(2-ethylhexyl) phthalate, di-iso-nonyl phthalate, hexabromocyclododecane, and 2,2',3,3',4,4',5,5',6,6'-decabromodiphenyl ether at concentrations between 374 and 34785 mg/kg, except for some results that exceeded the maximum measured value of the instrument. Compared with traditional methods, an important advantage is that this method simultaneously tests for 33 additives without sample pretreatment, covering a variety of additives limited by laws and regulations, and therefore can provide more comprehensive and thorough inspections.

Impacts of land use/land cover and soil property changes on soil erosion in the black soil region, China.

Soil erosion (SE) is seriously threatening grain production and the ecological environment in the black soil region. Understanding the impact of changes in land use/land cover (LULC) and soil properties on SE is critical for agricultural sustainability and soil management. However, the contribution of soil property changes to SE is often ignored in existing studies. This study analyzed changes in LULC and soil properties from 1980 to 2020 in the black soil region, China. Then, the revised universal soil loss equation was used to explore the spatiotemporal changes of SE from 1980 to 2020. Finally, the contribution of LULC change and soil property change to SE was separated by scenario comparison. The results showed that cropland increased (by 24,157 km2) at the expense of grassland and forest from 1980 to 2020. Sand in cropland decreased by 21.95%, while the silt, clay, and SOC increased by 21.37%, 1.43%, and 15.38%, respectively. Soil erodibility in cropland increased greatly (+9.85%), while in forest and grassland decreased (-6.05% and -4.72%). LULC change and soil properties change together aggravated SE in the black soil region. LULC change and soil property change resulted in a 22% increase in SE, of which LULC change resulted in a 14% increase, and soil property change resulted in an 8% increase. Agricultural development policy was the main reason driving LULC change. The combination of LULC change, climatic factors, and long-term tillage resulted in changes in soil properties. Ecosystem management and policy can reduce SE through vegetation restoration and soil improvement. This study can provide important references for soil conservation and agricultural development in the black soil region.

Bismuth-Decorated Honeycomb-like Carbon Nanofibers: An Active Electrocatalyst for the Construction of a Sensitive Nitrite Sensor.

The existence of carcinogenic nitrites in food and the natural environment has attracted much attention. Therefore, it is still urgent and necessary to develop nitrite sensors with higher sensitivity and selectivity and expand their applications in daily life to protect human health and environmental safety. Herein, one-dimensional honeycomb-like carbon nanofibers (HCNFs) were synthesized with electrospun technology, and their specific structure enabled controlled growth and highly dispersed bismuth nanoparticles (Bi NPs) on their surface, which endowed the obtained Bi/HCNFs with excellent electrocatalytic activity towards nitrite oxidation. By modifying Bi/HCNFs on the screen-printed electrode, the constructed Bi/HCNFs electrode (Bi/HCNFs-SPE) can be used for nitrite detection in one drop of solution, and exhibits higher sensitivity (1269.9 µA mM-1 cm-2) in a wide range of 0.1~800 µM with a lower detection limit (19 nM). Impressively, the Bi/HCNFs-SPE has been successfully used for nitrite detection in food and environment samples, and the satisfactory properties and recovery indicate its feasibility for further practical applications.

Anchoring LiCl in the Nanopores of Metal-Organic Frameworks for Ultra-High Uptake and Selective Separation of Ammonia.

Ammonia (NH3 ) is an important chemical raw material and a unique carbon-free fuel with high hydrogen energy density. Thus, NH3 capture, storage, and desorption are of significant importance. However, high capacity capture, low energy desorption, and selective separation of NH3 are still challengs so far. Here, we report high-performance hybrid sorbents by anchoring LiCl in the nanopores of MIL-53-(OH)2 metal-organic frameworks (MOFs). It is found that the optimal composite shows a capture capacity of 33.9 mmol g-1 NH3 at 1.0 bar and 25 °C, which far exceeds the current record among the reported porous materials. Notably, the excellent capture capacity at low pressure and high temperature makes it possible to selectively capture NH3 from NH3 /N2 , NH3 /CO2 , and NH3 /H2 O. It is revealed that synergistic action of NH3 coordination to the highly dispersed Li+ in the MOF nanopores and hydrogen bonding of NH3 with Cl- account for such an excellent capture and selectivity performance.

An Ultrastable Crystalline Acylhydrazone-Linked Covalent Organic Framework for Efficient Removal of Organic Micropollutants from Water.

As an important member of crystalline porous polymers, acylhydrazone-linked covalent organic frameworks (COFs) have gained much attention in recent years. However, the low structural stability imparts a limit on their practical applications. To tackle this problem, we report a simple strategy to increase the chemical stability of acylhydrazone-linked COFs by incorporating azobenzene groups in the conjugated framework. Through reinforcing the π-π stacking interactions between the adjacent layers with increased π-surface, it is surprising to find that the resulting materials exhibit extreme stability in harsh environments, such as in strong acid, strong base, aqueous educing agent and boiling water, even exposed to air for one year. As a proof-of-concept, such frameworks have been used to remove various organic micropollutants such as antibiotics, plastic components, endocrine disruptors, and carcinogens from water with high capacity, fast speed and excellent reusability over a wide pH range at environmentally relevant concentrations. The results provide a new avenue to significantly enhance the stability of COFs for practical applications.

Light-Responsive, Reversible Emulsification and Demulsification of Oil-in-Water Pickering Emulsions for Catalysis.

Pickering emulsions are an excellent platform for interfacial catalysis. However, developing simple and efficient strategies to achieve product separation and catalyst and emulsifier recovery is still a challenge. Herein, we report the reversible transition between emulsification and demulsification of a light-responsive Pickering emulsion, triggered by alternating between UV and visible light irradiation. The Pickering emulsion is fabricated from Pd-supported silica nanoparticles, azobenzene ionic liquid surfactant, n-octane, and water. This phase behavior is attributed to the adsorption of azobenzene ionic liquid surfactant on the surface of the nanoparticles and the light-responsive activity of ionic liquid surfactant. The Pickering emulsion can be used as a microreactor that enables catalytic reaction, product separation as well as emulsifier and catalyst recycling. Catalytic hydrogenation of unsaturated hydrocarbons at room temperature and atmospheric pressure has been performed in this system to demonstrate product separation and emulsifier and catalyst re-use.

Management of type B aortic dissection with an isolated left vertebral artery.

OBJECTIVE: The objective of this study was to report our single-center experience of thoracic endovascular aortic repair (TEVAR) and concomitant procedures in patients with type B aortic dissection (TBAD) with an isolated left vertebral artery (ILVA) and the early to midterm outcomes in these patients. METHODS: Between March 2011 and June 2018, there were 31 patients (27 men; median age, 55 years; range, 31-66 years) with TBAD and an ILVA who received TEVAR and concomitant procedures in our center. Demographics, coexisting medical conditions, imaging features, operation details, and follow-up outcomes in these patients were retrospectively collected and analyzed. RESULTS: All patients received aortic stent grafts; nine patients also received chimney stents, and 10 patients received aortic arch bypasses. The technical success rate was 96.8% (30/31), with only one patient (3.2%) showing immediate type IA endoleak. One patient experienced transient neurologic deficit, and a puncture-related femoral artery pseudoaneurysm was observed in one patient; both recovered completely before their hospital discharge. There was no death in the early term. The median duration of follow-up was 33 months (range, 2-90 months). Reintervention for a type II endoleak by using coils to seal the origin of the left subclavian artery was performed in one (3.1%) case 72 months postoperatively. One (3.2%) death occurred 42 months after operation as a result of rectal cancer. No neurologic deficits, chimney stent occlusions, or bypass occlusions were observed during the follow-up period. CONCLUSIONS: Our limited experience reveals that TEVAR and concomitant procedures are relatively safe and viable for treatment of TBAD with an ILVA. Further studies with larger samples of patients and longer follow-ups are needed to confirm these findings.

Aqueous systems of a surface active ionic liquid having an aromatic anion: phase behavior, exfoliation of graphene flakes and its hydrogelation.

Surface active ionic liquid (SAIL) induced hydrogelation, in the absence of additives, is important considering the properties of soft-hydrogels that can be utilized in different applications. The present study is concerned with the phase behavior and hydrogelation of a SAIL, 1-hexadecyl-3-methylimidazolium p-toluenesulfonate, [C16mim][PTS]. The obtained information about the phase behavior along with the surfactant like behavior of the SAIL was exploited for effective exfoliation of graphene-flakes from graphite in aqueous medium that remain stable for at least one month. Thus the obtained dispersion of graphene-flakes was subsequently hydrogelated exploiting the observations made from the phase behavior of the SAIL, via entanglement of long worm-like micelles of the SAIL formed at higher concentration. The obtained graphene-flake based hydrogels were found to be equally stable as compared to the blank hydrogel as well as against centrifugation. The low melting point of hydrogel facilitates the extraction of graphene-flakes from the hydrogel matrix by heating and diluting the gel and there is no sign of agglomeration in the extracted graphene-flakes even if the extraction is carried out after a period of three months. The present work is an exemplary study on exfoliation, hydrogelation and extraction of graphene-flakes from a hydrogel, when required, using a SAIL and is expected to provide a new platform for utilization of SAILs for efficient graphene exfoliation and subsequent preparation of functional materials.

Photo-Triggered Reversible Phase Transfer of Azobenzene-Based Ionic Liquid Surfactants between Oil and Water.

The reversible phase transfer of compounds between two immiscible liquid phases has many applications in a wide range of fields, and ionic liquids have been widely used as potential functional solvents and catalysts. However, photo-triggered reversible phase transfer of ionic liquids between the organic phase and water phase has not been reported so far. In the present work, the reversible phase transfer of six kinds of azobenzene-based ionic liquid surfactants between the organic phase and water phase is investigated by alternative irradiation of UV and visible light. Factors affecting the transfer efficiency, such as chemical structure and concentration of the ionic liquid surfactants, equilibrium photo-isomerization degree, and the aggregation state of ionic liquid surfactants are investigated in detail. It is shown that transfer efficiency greater than 89% was achieved under optimal conditions, equilibrium photo-isomerization degree of the ionic liquid surfactants is the main factor to determine their transfer efficiencies, and the aggregation of cis-isomers is not beneficial for the transfer.

Cu(I)/Ionic Liquids Promote the Conversion of Carbon Dioxide into Oxazolidinones at Room Temperature.

Recently, the efficient chemical fixation of carbon dioxide (CO2) into high value chemicals without using noble metal catalysts has become extremely appealing from the viewpoint of sustainable chemistry. In this work, a one-pot three component reaction of propargylic alcohols, anines and CO2 that can proceed in an atom economy and environmentally benign manner by combination of CuI and tetrabutylphosphonium imidazol ([P4444][Im]) as a catalyst was described. Catalysis studies indicate that this catalytic system is an effective catalyst for the conversion of CO2 into oxazolidinones at room temperature and ambient pressure without any solvent. The results provide a useful way to design novel noble metal-free catalyst systems for the transformation of CO2 into other valuable compounds.

Reply to the Correspondence on "Preorganization and Cooperation for Highly Efficient and Reversible Capture of Low-Concentration CO2 by Ionic Liquids".

The water content is crucial to the preparation of [P4442 ][Suc] and its capture of CO2 . The use of a large amount of water in the preparation of this ionic liquid results in the significant formation of the byproduct succinamate anions and difficulties in water removal, which strongly reduces the capacity of CO2 absorption through a bicarbonate mechanism. By contrast, the addition of a small amount of water maintains a high absorption capacity through cooperation.

Visible Light-Controlled Inversion of Pickering Emulsions Stabilized by Functional Silica Microspheres.

A new class of donor-acceptor Stenhouse adduct (DASA)-functionalized silica microspheres (SMs) is designed and described to formulate Pickering emulsions with inversion property and large polarity change upon visible light irradiation. By tuning the hydrophilicity of the functional SM particles with visible light, these Pickering emulsions can easily perform inversion from water-in-oil to oil-in-water. The inversion performance of the emulsions is ascribed to DASA photoisomerization from an extended, hydrophobic, and intensely purple-colored triene to a compact, zwitterionic, and colorless cyclopentenone upon irradiation with visible light. This unique inversion behavior has been applied to control encapsulation and the release of fluorescein sodium salt.

A reversible conductivity modulation of azobenzene-based ionic liquids in aqueous solutions using UV/vis light.

Photo-induced conductivity modulation of stimuli-responsive materials is of great importance from the viewpoint of fundamental research and technology. In this work, 5 new kinds of azobenzene-based photo-responsive ionic liquids were synthesized and characterized, and UV/vis light modulation of their conductivity was investigated in an aqueous solution. The factors affecting the conductivity modulation of the photo-responsive fluids, such as photo-isomerization efficiency, photo-regulation aggregation, concentration and chemical structure of the ionic liquids, were examined systematically. It was found that the conductivity of the ionic liquids in water exhibited a significant increase upon UV light irradiation and the ionic liquids with a shorter alkyl spacer in the cation showed a more remarkable photo-induced conductivity enhancement with a maximum increase of 150%. In addition, the solution conductivity was restored (or very close) to the initial value upon an alternative irradiation with visible light. Thus, the solution conductivity can be modulated using alternative irradiation with UV and visible light. Although the reversible photo-isomerization of the azobenzene group under UV/vis irradiation is the origin of the conductivity modulation, the photo-regulated aggregation of the ionic liquid in water is indispensable for the maximum degree of conductivity modulation because UV irradiation can weaken, even break the aggregated cis-isomers of the ionic liquids in an aqueous solution.

Reversible Phase Transfer of Carbon Dots between an Organic Phase and Aqueous Solution Triggered by CO2.

Carbon dots (CDs) have attracted increasing attention in applications such as bio-imaging, sensors, catalysis, and drug delivery. However, unlike metallic and semiconductor nanoparticles, the transfer of CDs between polar and non-polar phases is little understood. A class of amine-terminated CDs is developed and their phase transfer behavior has been investigated. It is found that these CDs can reversibly transfer between aqueous and organic solvents by alternatively bubbling and removing CO2 at atmospheric pressure. The mechanism of such CO2 -switched phase transfer involves reversible acid-base reaction of amine-terminated CDs with CO2 and the reversible formation of hydrophilic ammonium salts. By using the CDs as catalysts, the phase transfer is applied in the Knoevenagel reaction for efficient homogeneous reaction, heterogeneous separation, and recycling of the catalysts.

Preorganization and Cooperation for Highly Efficient and Reversible Capture of Low-Concentration CO2 by Ionic Liquids.

A novel strategy based on the concept of preorganization and cooperation has been designed for a superior capacity to capture low-concentration CO2 by imide-based ionic liquids. By using this strategy, for the first time, an extremely high gravimetric CO2 capacity of up to 22 wt % (1.65 mol mol-1 ) and excellent reversibility (16 cycles) have been achieved from 10 vol. % of CO2 in N2 when using an ionic liquid having a preorganized anion. Through a combination of quantum-chemical calculations and spectroscopic investigations, it is suggested that cooperative interactions between CO2 and multiple active sites in the preorganized anion are the driving force for the superior CO2 capacity and excellent reversibility.

Reversible Switching of Amphiphilic Self-Assemblies of Ionic Liquids between Micelle and Vesicle by CO2.

The creation of CO2-responsive materials that undergo structural transition between micelle and vesicle is of great importance from both theoretical and practical points of view. In this work, we have developed a series of CO2-responsive single-tailed amphiphilic ionic liquids (ILs) composed of N-alkyl-N-methyldiethanolamine cation [CnMDEA](+) (n = 8, 10, 12, 14, 16, 18) and 2-pyrrolidinone [2-Pyr](-) anion. The aggregation behavior and self-assembly structures of the ILs in aqueous solution have been investigated by conductivity, surface tension, dynamic light scattering, cryogenic transmission electron microscopy, small-angle X-ray scattering, and nuclear magnetic resonance spectroscopy. For the first time, CO2 driven reversible switching of self-assembly between spherical micelle and unilamellar vesicle is found for [CnMDEA][2-Pyr] (n = 16, 18) in aqueous solutions at 20 °C and atmospheric pressure. It is shown that the mechanism behind the reversible micelle to vesicle transition involves the formation of carbamate anion from the reaction between [2-Pyr](-) and CO2.