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Utilizing weak interactions to effectively recover and separate precious metals in solution is of great importance but the practice remains a challenge. Herein, we report a novel strategy to achieve precise recognition and separation of gold by regulating the hydrogen‐bond (H‐bond) nanotrap within the pore of covalent organic frameworks (COFs). It is found that both COF‐HNU25 and COF‐HNU26 can efficiently capture AuIII with fast kinetics, high selectivity, and uptake capacity. In particular, the COF‐HNU25 with the high density of H‐bond nanotraps exhibits an excellent gold uptake capacity of 1725 mg g−1, which is significantly higher than that (219 mg g−1) of its isostructural COF (COF‐42) without H‐bond nanostrap in the pores. Importantly, the uptake capacity is strongly correlated to the number of H‐bonds between phenolic OH in the COF and [AuCl4]− in water, and multiple H‐bond interactions are the key driving force for the excellent gold recovery and reusability of the adsorbent. [ABSTRACT FROM AUTHOR]

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/H2O. 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Breaking point: An effective reductive cleavage of inert aryl CO bonds with an inexpensive iron catalyst has been developed. During this process, the reduction of the arene rings was not observed. This catalytic system also enabled the selective cleavage of the β‐O‐4 linkage of lignin model compounds under an atmosphere of hydrogen, thus offering an opportunity for the depolymerization of lignin. [ABSTRACT FROM AUTHOR]

Fluorescent single crystals that respond to multiple external stimuli are of great interest in molecular machines, sensors, and displays. The integration of photo‐ or acid‐induced fluorescence enhancement and bending in one organic crystal, however, has not been reported yet. Herein, we report the interesting plastic photomechanical bending and switching on of the fluorescence of an azine crystal in a single‐crystal transformation, due to extended π‐conjugation and molecular slippage. Moreover, the fluorescent plastic bending driven by multiple volatile acid vapors was firstly observed, and attributed to the synergistic effect of push–pull electronic structure and hydrogen bonding. The single crystal also shows high elasticity under external force. In addition, reversible fluorescence switching can be triggered by grinding and solvent fuming, as well as by the adsorption and desorption of HCl vapor. The integration of plastic, elastic bending and switch‐on fluorescence into one single crystal provides a new strategy for next‐generation smart materials. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Photoelectrochemical (PEC) reduction of carbon dioxide (CO2) is a potential method for production of fuels and chemicals from a C1 feedstock accumulated in the atmosphere. However, the low solubility of CO2 in water, and complicated processes associated with capture and conversion, render CO2 conversion inefficient. A new concept is proposed in which a PEC system is used to capture and convert CO2 into formic acid. The process is assisted by an ionic liquid (1-aminopropyl-3-methylimidazolium bromide) aqueous solution, which functions as an absorbent and electrolyte at ambient temperature and pressure. Within this PEC reduction strategy, the ionic liquid plays a critical role in promoting the conversion of CO2 to formic acid and suppressing the reduction of H2O to H2. At an applied voltage of 1.7 V, the Faradaic efficiency for formic acid production is as high as 94.1 % and the electro-to-chemical efficiency is 86.2 %. [ABSTRACT FROM AUTHOR]