Continuously Producing Highly Concentrated and Pure Acetic Acid Aqueous Solution via Direct Electroreduction of CO2.

It is crucial to achieve continuous production of highly concentrated and pure C2 chemicals through the electrochemical CO2 reduction reaction (eCO2RR) for artificial carbon cycling, yet it has remained unattainable until now. Despite one-pot tandem catalysis (dividing the eCO2RR to C2 into two catalytical reactions of CO2 to CO and CO to C2) offering the potential for significantly enhancing reaction efficiency, its mechanism remains unclear and its performance is unsatisfactory. Herein, we selected different CO2-to-CO catalysts and CO-to-acetate catalysts to construct several tandem catalytic systems for the eCO2RR to acetic acid. Among them, a tandem catalytic system comprising a covalent organic framework (PcNi-DMTP) and a metal-organic framework (MAF-2) as CO2-to-CO and CO-to-acetate catalysts, respectively, exhibited a faradaic efficiency of 51.2% with a current density of 410 mA cm-2 and an ultrahigh acetate yield rate of 2.72 mmol m-2 s-1 under neutral conditions. After electrolysis for 200 h, 1 cm-2 working electrode can continuously produce 20 mM acetic acid aqueous solution with a relative purity of 95+%. Comprehensive studies revealed that the performance of tandem catalysts is influenced not only by the CO supply-demand relationship and electron competition between the two catalytic processes in the one-pot tandem system but also by the performance of the CO-to-C2 catalyst under diluted CO conditions.

Efficient Capture and Electroreduction of Dilute CO2 into Highly Pure and Concentrated Formic Acid Aqueous Solution.

High-purity CO2 rather than dilute CO2 (15 vol %, CO2/N2/O2 = 15:80:5, v/v/v) similar to the flue gas is currently used as the feedstock for the electroreduction of CO2, and the liquid products are usually mixed up with the cathode electrolyte, resulting in high product separation costs. In this work, we showed that a microporous conductive Bi-based metal-organic framework (Bi-HHTP, HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) can not only efficiently capture CO2 from the dilute CO2 under high humidity but also catalyze the electroreduction of the adsorbed CO2 into formic acid with a high current density of 80 mA cm-2 and a Faradaic efficiency of 90% at a very low cell voltage of 2.6 V. Importantly, the performance in a dilute CO2 atmosphere was close to that under a high-purity CO2 atmosphere. This is the first catalyst that can maintain exceptional eCO2RR performance in the presence of both O2 and N2. Moreover, by using dilute CO2 as the feedstock, a 1 cm-2 working electrode coating with Bi-HHTP can continuously produce a 200 mM formic acid aqueous solution with a relative purity of 100% for at least 30 h in a membrane electrode assembly (MEA) electrolyzer. The product does not contain electrolytes, and such a highly concentrated and pure formic acid aqueous solution can be directly used as an electrolyte for formic acid fuel cells. Comprehensive studies revealed that such a high performance might be ascribed to the CO2 capture ability of the micropores on Bi-HHTP and the lower Gibbs free energy of formation of the key intermediate *OCHO on the open Bi sites.

Molecular-Sieving Separation of Methanol/Benzene Azeotrope by a Flexible Metal-Organic Framework.

Separation of methanol/benzene azeotrope mixtures is very challenging not only by the conventional distillation technique but also by adsorbents. In this work, we design and synthesize a flexible Ca-based metal-organic framework MAF-58 consisting of cheap raw materials. MAF-58 shows selective methanol-induced pore-opening flexibility. Although the opened pores are large enough to accommodate benzene molecules, MAF-58 shows methanol/benzene molecular sieving with ultrahigh experimental selectivity, giving 5.1 mmol g-1 high-purity (99.99%+) methanol and 2.0 mmol g-1 high-purity (99.97%+) benzene in a single adsorption/desorption cycle. Computational simulations reveal that the preferentially adsorbed, coordinated methanol molecules act as the gating component to selectively block the diffusion of benzene, offering a new gating adsorption mechanism.

Metal-Organic Framework Based Sensors for Benzene Vapor.

Sensing of benzene vapor is a hot spot due to the volatile drastic carcinogen even at trace concentration. However, achieving convenient and rapid detection is still a challenge. As a sort of functional porous material, metal-organic frameworks (MOFs) have been developed as detection sensors by adsorbing benzene vapor and converting it into other signals (fluorescence intensity/wavelength, chemiresistive, weight or color, etc.). Supramolecular interaction between benzene molecules and the host framework, aperture size/shape and structural flexibility are influential factors in the performance of MOF-based sensors. Therefore, enhancing the host-guest interactions between the host framework and benzene molecules, or regulating the diffusion rate of benzene molecules by changing the aperture size/shape and flexibility of the host framework to enhance the detection signal are effective strategies for constructing MOF-based sensors. This concept highlights several types of MOF-based sensors for the detection of benzene vapor.

Rapid and Visual Detection of Volatile Amines Based on Their Gas-Solid Reaction with Tetrachloro-p-Benzoquinone.

The detection of volatile amines is necessary due to the serious toxicity hazards they pose to human skin, respiratory systems, and nervous systems. However, traditional amines detection methods require bulky equipment, high costs, and complex measurements. Herein, we report a new simple, rapid, convenient, and visual method for the detection of volatile amines based on the gas-solid reactions of tetrachloro-p-benzoquinone (TCBQ) and volatile amines. The gas-solid reactions of TCBQ with a variety of volatile amines showed a visually distinct color in a time-dependent manner. Moreover, TCBQ can be easily fabricated into simple and flexible rapid test strips for detecting and distinguishing n-propylamine from other volatile amines, including ethylamine, n-butyamine, n-pentamine, n-butyamine and dimethylamine, in less than 3 s without any equipment assistance.

High-Pressure Molecular Sieving of High-Humidity C2H4/C2H6 Mixture by a Hydrophobic Flexible Metal-Organic Framework.

Molecular sieving is an ideal separation mechanism, but controlling pore size, restricting framework flexibility, and avoiding strong adsorption are all very challenging. Here, we report a flexible adsorbent showing molecular sieving at ambient temperature and high pressure, even under high humidity. While typical guest-induced transformations are observed, a high transition pressure of 16.6 atm is observed for C2H4 at 298 K because of very weak C2H4 adsorption (~16 kJ mol-1). Also, C2H6 is completely excluded below the pore-opening pressure of 7.7 atm, giving single-component selectivity of ca. 300. Quantitative high-pressure column breakthrough experiments using 1:1 C2H4/C2H6 mixture at 10 atm as input confirms molecular sieving with C2H4 adsorption of 0.73 mmol g-1 or 32 cm3(STP) cm-3 and negligible C2H6 adsorption of 0.001(2) mmol g-1, and the adsorbent can be completely regenerated by inert gas purging. Furthermore, it is highly hydrophobic with negligible water adsorption, and the C2H4/C2H6 separation performance is unaffected at high humidity.

Reverse Separation of Carbon Dioxide and Acetylene in Two Isostructural Copper Pyridine-Carboxylate Frameworks.

Separating acetylene from carbon dioxide is important but highly challenging due to their similar molecular shapes and physical properties. Adsorptive separation of carbon dioxide from acetylene can directly produce pure acetylene but is hardly realized because of relatively polarizable acetylene binds more strongly. Here, we reverse the CO2 and C2H2 separation by adjusting the pore structures in two isoreticular ultramicroporous metal-organic frameworks (MOFs). Under ambient conditions, copper isonicotinate (Cu(ina)2), with relatively large pore channels shows C2H2-selective adsorption with a C2H2/CO2 selectivity of 3.4, whereas its smaller-pore analogue, copper quinoline-5-carboxylate (Cu(Qc)2) shows an inverse CO2/C2H2 selectivity of 5.6. Cu(Qc)2 shows compact pore space that well matches the optimal orientation of CO2 but is not compatible for C2H2. Neutron powder diffraction experiments confirmed that CO2 molecules adopt preferential orientation along the pore channels during adsorption binding, whereas C2H2 molecules bind in an opposite fashion with distorted configurations due to their opposite quadrupole moments. Dynamic breakthrough experiments have validated the separation performance of Cu(Qc)2 for CO2/C2H2 separation.

"Ship-in-a-Bottle" Integration of Ditin(IV) Sites into a Metal-Organic Framework for Boosting Electroreduction of CO2 in Acidic Electrolyte.

The electrochemical CO2 reduction reaction (eCO2RR) under acidic conditions has become a promising way to achieve high CO2 utilization because of the inhibition of undesirable carbonate formation that typically occurs under neutral and alkaline conditions. Herein, unprecedented and highly active ditin(IV) sites were integrated into the nanopores of a metal-organic framework, namely NU-1000-Sn, by a "ship-in-a-bottle" strategy. NU-1000-Sn delivers nearly 100% formic acid Faradaic efficiency at an industry current density of 260 mA cm-2 with a high single-pass CO2 utilization of 95% in an acidic solution (pH = 1.67). No obvious degradation was observed over 15 hours of continuous operation at the current density of 260 mA cm-2, representing the remarkable eCO2RR performance in acidic electrolyte to date. The mechanism study shows that both oxygen atoms of the key intermediate *HCOO can coordinate to the two adjacent Sn atoms in a ditin(IV) site simultaneously. Such bridging coordination is conducive to the hydrogenation of CO2, thus leading to high performance.

Highly Efficient Electroreduction of CO2 to Ethanol via Asymmetric C-C Coupling by a Metal-Organic Framework with Heterodimetal Dual Sites.

The electroreduction of CO2 into value-added liquid fuels holds great promise for addressing global environmental and energy challenges. However, achieving highly selective yielding of multi-carbon oxygenates through the electrochemical CO2 reduction reaction (eCO2RR) is a formidable task, primarily due to the sluggish asymmetric C-C coupling reaction. In this study, a novel metal-organic framework (CuSn-HAB) with unprecedented heterometallic Sn···Cu dual sites (namely, a pair of SnN2O2 and CuN4 sites bridged by µ-N atoms) was designed to overcome this limitation. CuSn-HAB demonstrated an impressive Faradic efficiency (FE) of 56(2)% for eCO2RR to alcohols, achieving a current density of 68 mA cm-2 at a low potential of -0.57 V (vs RHE). Notably, no significant degradation was observed over a continuous 35 h operation at the specified current density. Mechanistic investigations revealed that, in comparison to the copper site, the SnN2O2 site exhibits a higher affinity for oxygen atoms. This enhanced affinity plays a pivotal role in facilitating the generation of the key intermediate *OCH2. Consequently, compared to homometallic Cu···Cu dual sites (generally yielding ethylene product), the heterometallic dual sites were proved to be more thermodynamically favorable for the asymmetric C-C coupling between *CO and *OCH2, leading to the formation of the key intermediate *CO-*OCH2, which is favorable for yielding ethanol product.

Synergistic Effect in a Metal-Organic Framework Boosting the Electrochemical CO2 Overall Splitting.

It is a very important but still challenging task to develop bifunctional electrocatalysts for highly efficient CO2 overall splitting. Herein, we report a stable metal-organic framework (denoted as PcNi-Co-O), composed of (2,3,9,10,16,17,23,24-octahydroxyphthalocyaninato)nickel(II) (PcNi-(O-)8) ligands and the planar CoO4 nodes, for CO2 overall splitting. When working as both cathode and anode catalysts (i.e., PcNi-Co-O||PcNi-Co-O), PcNi-Co-O achieved a commercial-scale current density of 123 mA cm-2 (much higher than the reported values (0.2-12 mA cm-2)) with a Faradic efficiency (CO) of 98% at a low cell voltage of 4.4 V. Mechanism studies suggested the synergistic effects between two active sites, namely, (i) electron transfer from CoO4 to PcNi sites under electric fields, resulting in the raised oxidizability/reducibility of CoO4/PcNi sites, respectively; (ii) the energy-level matching of cathode and anode catalysts can reduce the energy barrier of electron transfer between them and improve the performance of CO2 overall splitting.

Dicopper(I) Sites Confined in a Single Metal-Organic Layer Boosting the Electroreduction of CO2 to CH4 in a Neutral Electrolyte.

It is challenging and important to achieve high performance for an electrochemical CO2 reduction reaction (eCO2RR) to yield CH4 under neutral conditions. So far, most of the reported active sites for eCO2RR to yield CH4 are single metal sites; the performances are far below the commercial requirements. Herein, we reported a nanosheet metal-organic layer in single-layer, namely, [Cu2(obpy)2] (Cuobpy-SL, Hobpy = 1H-[2,2']bipyridinyl-6-one), possessing dicopper(I) sites for eCO2RR to yield CH4 in a neutral aqueous solution. Detailed examination of Cuobpy-SL revealed high performance for CH4 production with a faradic efficiency of 82(1)% and a current density of ∼90 mA cm-2 at -1.4 V vs. reversible hydrogen electrode (RHE). No obvious degradation was observed over 100 h of continuous operation, representing a remarkable performance to date. Mechanism studies showed that compared with the conventional single-copper sites and completely exposed dicopper(I) sites, the dicopper(I) sites in the confined space formed by the molecular stacking have a strong affinity to key C1 intermediates such as *CO, *CHO, and *CH2O to facilitate the CH4 production, yet inhibiting C-C coupling.

Optimizing the Spatial Density of Single Co Sites via Molecular Spacing for Facilitating Sustainable Water Oxidation.

Advances in single-atom (-site) catalysts (SACs) provide a new solution of atomic economy and accuracy for designing efficient electrocatalysts. In addition to a precise local coordination environment, controllable spatial active structure and tolerance under harsh operating conditions remain great challenges in the development of SACs. Here, we show a series of molecule-spaced SACs (msSACs) using different acid anhydrides to regulate the spatial density of discrete metal phthalocyanines with single Co sites, which significantly improve the effective active-site numbers and mass transfer, enabling one of the msSACs connected by pyromellitic dianhydride to exhibit an outstanding mass activity of (1.63 ± 0.01) × 105 A·g-1 and TOFbulk of 27.66 ± 1.59 s-1 at 1.58 V (vs RHE) and long-term durability at an ultrahigh current density of 2.0 A·cm-2 under industrial conditions for oxygen evolution reaction. This study demonstrates that the accessible spatial density of single atom sites can be another important parameter to enhance the overall performance of catalysts.

Molecule-Enhanced Electrocatalysis of Sustainable Oxygen Evolution Using Organoselenium Functionalized Metal-Organic Nanosheets.

Remolding the reactivity of metal active sites is critical to facilitate renewable electricity-powered water electrolysis. Doping heteroatoms, such as Se, into a metal crystal lattice has been considered an effective approach, yet usually suffers from loss of functional heteroatoms during harsh electrocatalytic conditions, thus leading to the gradual inactivation of the catalysts. Here, we report a new heteroatom-containing molecule-enhanced strategy toward sustainable oxygen evolution improvement. An organoselenium ligand, bis(3,5-dimethyl-1H-pyrazol-4-yl)selenide containing robust C-Se-C covalent bonds equipped in the precatalyst of ultrathin metal-organic nanosheets Co-SeMON, is revealed to significantly enhance the catalytic mass activity of the cobalt site by 25 times, as well as extend the catalyst operation time in alkaline conditions by 1 or 2 orders of magnitude compared with these reported metal selenides. A combination of various in situ/ex situ spectroscopic techniques, ab initio molecular dynamics, and density functional theory calculations unveiled the organoselenium intensified mechanism, in which the nonclassical bonding of Se to O-containing intermediates endows adsorption-energy regulation beyond the conventional scaling relationship. Our results showcase the great potential of molecule-enhanced catalysts for highly efficient and economical water oxidation.

Molecular Design of a Metal-Nitrosyl Ferroelectric with Reversible Photoisomerization.

The development of photo-responsive ferroelectrics whose polarization may be remotely controlled by optical means is of fundamental importance for basic research and technological applications. Herein, we report the design and synthesis of a new metal-nitrosyl ferroelectric crystal (DMA)(PIP)[Fe(CN)5(NO)] (1) (DMA = dimethylammonium, PIP = piperidinium) with potential phototunable polarization via a dual-organic-cation molecular design strategy. Compared to the parent non-ferroelectric (MA)2[Fe(CN)5(NO)] (MA = methylammonium) material with a phase transition at 207 K, the introduction of larger dual organic cations both lowers the crystal symmetry affording robust ferroelectricity and increases the energy barrier of molecular motions, endowing 1 with a large polarization of up to 7.6 µC cm-2 and a high Curie temperature (Tc) of 316 K. Infrared spectroscopy shows that the reversible photoisomerization of the nitrosyl ligand is accomplished by light irradiation. Specifically, the ground state with the N-bound nitrosyl ligand conformation can be reversibly switched to both the metastable state I (MSI) with isonitrosyl conformation and the metastable state II (MSII) with side-on nitrosyl conformation. Quantum chemistry calculations suggest that the photoisomerization significantly changes the dipole moment of the [Fe(CN)5(NO)]2- anion, thus leading to three ferroelectric states with different values of macroscopic polarization. Such optical accessibility and controllability of different ferroelectric states via photoinduced nitrosyl linkage isomerization open up a new and attractive route to optically controllable macroscopic polarization.

Fluorescent Probes with Variable Intramolecular Charge Transfer: Constructing Closed-Circle Plots for Distinguishing D2O from H2O.

It is difficult to distinguish between H2O and D2O due to their very similar properties. Triphenylimidazole derivatives with carboxyl groups (TPI-COOH-2R) show intramolecular charge transfer that responds to polarities and pH of solvents. Here, a series of TPI-COOH-2R with very high photoluminescence quantum yields (73-98%) were synthesized to distinguish D2O from H2O by the method of wavelength-changeable fluorescence. In a mixed THF/water solution, the increase of H2O and D2O contents will separately induce different pendulum-type fluorescence variations and form plots of closed circles with the same starting and ending points from which a THF/water ratio that displays the most different emission wavelengths (up to 53 nm with an LOD of 0.064 vol %) can be determined to further distinguish D2O from H2O. This is proved to be originated from the various Lewis acidities between H2O and D2O. The results of theoretical calculations and experiments suggest that, for different substituent groups in TPI-COOH-2R, an appropriate electron-donating effect is beneficial to distinguish between H2O and D2O, while the electron-pulling effect is adverse. Moreover, because the potential hydrogen/deuterium exchange does not affect the as-responsive fluorescence, this method is reliable. And this work provides a new strategy for the design of fluorescent probes for D2O.

Microfluidic characterization of single-cell biophysical properties and the applications in cancer diagnosis.

Single-cell biophysical properties play a crucial role in regulating cellular physiological states and functions, demonstrating significant potential in the fields of life sciences and clinical diagnostics. Therefore, over the last few decades, researchers have developed various detection tools to explore the relationship between the biophysical changes of biological cells and human diseases. With the rapid advancement of modern microfabrication technology, microfluidic devices have quickly emerged as a promising platform for single-cell analysis offering advantages including high-throughput, exceptional precision, and ease of manipulation. Consequently, this paper provides an overview of the recent advances in microfluidic analysis and detection systems for single-cell biophysical properties and their applications in the field of cancer. The working principles and latest research progress of single-cell biophysical property detection are first analyzed, highlighting the significance of electrical and mechanical properties. The development of data acquisition and processing methods for real-time, high-throughput, and practical applications are then discussed. Furthermore, the differences in biophysical properties between tumor and normal cells are outlined, illustrating the potential for utilizing single-cell biophysical properties for tumor cell identification, classification, and drug response assessment. Lastly, we summarize the limitations of existing microfluidic analysis and detection systems in single-cell biophysical properties, while also pointing out the prospects and future directions of their applications in cancer diagnosis and treatment.

Strepolyketide D, a new SEK15-derived polyketide compound from salt-lake-derived Streptomyces sp. DBC5.

A new SEK15-derived polyketide compound, strepolyketide D (1), was isolated from salt-lake-derived Streptomyces sp. DBC5, together with two known analogues (2-3). Their structures were elucidated based on spectroscopic analysis of IR, MS, 1 D and 2 D NMR. Compound 2 elicited moderate antioxidation with IC50 value of 39.26 µg/ml. The results of the study revealed that salt-lake actinomycetes of Lake Dabancheng appear to have immense potential as a source of polyketide compounds.

Isolated Tin(IV) Active Sites for Highly Efficient Electroreduction of CO2 to CH4 in Neutral Aqueous Solution.

The development of efficient electrocatalysts with non-copper metal sites for electrochemical CO2 reduction reactions (eCO2 RR) to hydrocarbons and oxygenates is highly desirable, but still a great challenge. Herein, a stable metal-organic framework (DMA)4 [Sn2 (THO)2 ] (Sn-THO, THO6- = triphenylene-2,3,6,7,10,11-hexakis(olate), DMA = dimethylammonium) with isolated and distorted octahedral SnO6 2- active sites is reported as an electrocatalyst for eCO2 RR, showing an exceptional performance for eCO2 RR to the CH4 product rather than the common products formate and CO for reported Sn-based catalysts. The partial current density of CH4 reaches a high value of 34.5 mA cm-2 , surpassing most reported copper-based and all non-Cu metal-based catalysts. Our experimental and theoretical results revealed that the isolated SnO6 2- active site favors the formation of key *OCOH species to produce CH4 and can greatly inhibit the formation of *OCHO and *COOH species to produce *HCOOH and *CO, respectively.

Nonlinear Optical Glass-Ceramic From a New Polar Phase-Transition Organic-Inorganic Hybrid Crystal.

Melt-quenched glasses of organic-inorganic hybrid crystals, i.e., hybrid glasses, have attracted increasing attention as an emerging class of hybrid materials with beneficial processability and formability in the past years. Herein, we present a new hybrid crystal, (Ph3 PEt)3 [Ni(NCS)5 ] (1, Ph3 PEt+ =ethyl(triphenyl)phosphonium), crystallizing in a polar space group P1 and exhibiting thermal-induced reversible crystal-liquid-glass-crystal transitions with relatively low melting temperature of 132 °C, glass-transition temperature of 40 °C, and recrystallization on-set temperature of 78 °C, respectively. Taking advantage of such mild conditions, we fabricated an unprecedented hybrid glass-ceramic thin film, i.e., a thin glass uniformly embedding inner polar micro-crystals, which exhibits a much enhanced intrinsic second-order nonlinear optical effect, being ca. 25.6 and 3.1 times those of poly-crystalline 1 and KH2 PO4 , respectively, without any poling treatments.

Simultaneous Capture of CO2 Boosting Its Electroreduction in the Micropores of a Metal-organic Framework.

Integration of CO2 capture capability from simulated flue gas and electrochemical CO2 reduction reaction (eCO2 RR) active sites into a catalyst is a promising cost-effective strategy for carbon neutrality, but is of great difficulty. Herein, combining the mixed gas breakthrough experiments and eCO2 RR tests, we showed that an Ag12 cluster-based metal-organic framework (1-NH2 , aka Ag12 bpy-NH2 ), simultaneously possessing CO2 capture sites as "CO2 relays" and eCO2 RR active sites, can not only utilize its micropores to efficiently capture CO2 from simulated flue gas (CO2 : N2 =15 : 85, at 298 K), but also catalyze eCO2 RR of the adsorbed CO2 into CO with an ultra-high CO2 conversion of 60 %. More importantly, its eCO2 RR performance (a Faradaic efficiency (CO) of 96 % with a commercial current density of 120 mA cm-2 at a very low cell voltage of -2.3 V for 300 hours and the full-cell energy conversion efficiency of 56 %) under simulated flue gas atmosphere is close to that under 100 % CO2 atmosphere, and higher than those of all reported catalysts at higher potentials under 100 % CO2 atmosphere. This work bridges the gap between CO2 enrichment/capture and eCO2 RR.