Ultrahigh Selectivity Research Articles

A Bioinspired Free-Standing 2D Crown-Ether-Based Polyimine Membrane for Selective Proton Transport.

Biological proton channels play important roles in the delicate metabolism process, arousing great interest in mimicking selective proton transport. Herein, we designed a bioinspired proton transport membrane by bringing flexible 14-crown-4 (14C4) units into rigid frameworks of polyimine films by an interfacial Schiff base reaction. The Young's modulus of the membrane reaches ~8.2 GPa. The 14C4 units could grab water forming hydrogen bond-water networks and acting as jumping sites to lower the energy barrier of proton transport. The molecular chains present a vertical orientation to the membrane, and the ions travel between the quasi-planar molecular sheets. Also, the 14C4 moieties could bond alkali ions via host-guest interaction. Thus, the ion conductance follows H+ ≫ K+ > Na+> Li+, and an ultrahigh selectivity of H+/Li+ (~215) is resulted. This study provides an effective avenue for developing ion-selective membranes by embedding macrocycles motif with inherent cavities.

A Bioinspired Free‐Standing 2D Crown‐Ether‐Based Polyimine Membrane for Selective Proton Transport

AbstractBiological proton channels play important roles in the delicate metabolism process, and have led to great interest in mimicking selective proton transport. Herein, we designed a bioinspired proton transport membrane by incorporating flexible 14‐crown‐4 (14C4) units into rigid frameworks of polyimine films by an interfacial Schiff base reaction. The Young's modulus of the membrane reaches about 8.2 GPa. The 14C4 units could grab water, thereby forming hydrogen bond‐water networks and acting as jumping sites to lower the energy barrier of proton transport. The molecular chains present a vertical orientation to the membrane, and the ions travel between the quasi‐planar molecular sheets. Furthermore, the 14C4 moieties could bond alkali ions through host–guest interactions. Thus, the ion conductance follows H+≫K+>Na+>Li+, and an ultrahigh selectivity of H+/Li+ (ca. 215) is obtained. This study provides an effective avenue for developing ion‐selective membranes by embedding macrocycle motifs with inherent cavities.

Multiplex detection of clinical pathogen nucleic acids via a three-way junction structure-based nucleic acid circuit.

Nucleic acid testing technology has made considerable progress in the last few years. However, there are still many challenges in the clinical application of multiple nucleic acid assays, such as how to ensure accurate results, increase speed and decrease cost. Herein, a three-way junction structure has been introduced to specifically translate analytes of loop-mediated isothermal amplification to a catalytic hairpin assembly. For different analyses, a well-optimized nucleic acid circuit can be directly applied to detection, through only one-component replacement, which only not avoids duplicate sequence design but also saves detection cost. Thanks to this design, multiple and logical analysis can be easily realized in a single reaction with ultra-high sensitivity and selectivity. In this paper, Mycoplasma pneumoniae and Streptococcus pneumoniae can be clearly distinguished from the clinical mixed sample with negative control or one analyte in one tube single fluorescence channel. The fair experimental results of actual clinical samples provide a strong support for the possibility of clinical application of this methodology.

Enhancing the electrocatalytic performance of nitrate reduction to ammonia by in-situ nitrogen leaching

Electrochemical nitrate reduction reaction (NITRR) is regarded as a “two birds-one stone” method for the treatment of nitrate contaminant in polluted water and the synthesis of valuable ammonia, which is retarded by the lack of highly reactive and selective electrocatalysts. Herein, for the first time, nickel foam supported Co4N was designed as a high-performance NITRR catalyst by an in-situ nonmetal leaching-induced strategy. At the optimal potential, the Co4N/NF catalyst achieves ultra-high Faraday efficiency and NH3 selectivity of 95.4% and 99.4%, respectively. Ex situ X-ray absorption spectroscopy (XAS), together with other experiments powerfully reveal that the nitrogen vacancies produced by nitrogen leaching are stable and play a key role in boosting nitrate reduction to ammonia. Theoretical calculations confirm that Co4N with abundant nitrogen vacancies can optimize the adsorption energies of NO3- and intermediates, lower the free energy (ΔG) of the potential-determining step (*NH3 to NH3) and inhibit the formation of N-containing byproducts. In addition, we also conclude that the nitrogen vacancies can stabilize the adsorbed hydrogen, making H2 quite difficult to produce, and lowering ΔG from *NO to *NOH, which facilitates the selective reduction of nitrate. This study reveals significant insights about the in-situ nonmetal leaching to enhance the NITRR activity.

High-performance molecularly imprinted polymers grafted magnetic photonic crystal microspheres for selective enrichment of ochratoxin a

Development of selective enrichment materials for the accurate analysis of ochratoxin a (OTA) in environmental and food samples is an effective way to protect human health. Here, a molecularly imprinted polymer (MIP) known as plastic antibody was synthesized onto the magnetic inverse opal photonic crystal microsphere (MIPCM) using a low-cost dummy template imprinting strategy targeting OTA. The MIP@MIPCM exhibited ultrahigh selectivity with an imprinting factor of 130, high specificity with cross-reactivity factors of 3.3–10.5, and large adsorption capacity of 60.5 μg/mg. Such MIP@MIPCM was used for selective capture of OTA in real samples which was quantified in combination with high-performance liquid chromatography, giving a wide linear detection range of 5–20,000 ng/mL, a detection limit of 0.675 ng/mL, and good recovery rates of 84–116%. Moreover, the MIP@MIPCM can be produced simply and rapidly and is very stable under different environmental conditions and easy to store and transport, so it is an ideal substitute of biological antibody modified materials for the selective enrichment of OTA in real samples.

Highly selective and permeable SSZ-13 zeolite membranes synthesized by a facile in-situ approach for CO2/CH4 separation

High-quality tubular SSZ-13 zeolite membranes were fabricated by a facile in-situ approach for the first time. The in-situ approach requires only a single hydrothermal step for membrane growth, which is much simpler than the normal multi-step secondary-growth approach with seed preparation and seeding steps. The proper aging time and relatively high synthesis temperature provide sufficient nuclei for SSZ-13 growth, which further facilitates the in-situ formation of continuous membranes on the substrates. Three SSZ-13 zeolite membranes fabricated by the simple in-situ approach displayed ultrahigh average selectivity of (233 ± 46) and high average carbon dioxide permeance of (1220 ± 100) × 10−9 mol (m2 s Pa)−1 [∼3660 ± 300 Gas Permeation Unit (GPU), 1 GPU = 3.348 × 10−10 mol/(m2 s Pa)] at 298 K in the CO2/CH4 (50/50 in mol) mixture. The overall separation performance of the current membranes exceeded that of most reported zeolite membranes in the CO2/CH4 mixture. It indicated that the current in-situ synthesis approach had good reproducibility. The typical membrane also showed excellent separation performance in the CO2/N2 mixture toward the carbon capture from flue gas. The long-term stability of this membrane was investigated in the humidified CO2/CH4 mixture with a relative humidity close to 100%. This simple in-situ approach is suitable to prepare other zeolite membranes for gas separation after improving the gel nucleation.

Atomically Dispersed ZnN5 Sites Immobilized on g-C3 N4 Nanosheets for Ultrasensitive Selective Detection of Phenanthrene by Dual Ratiometric Fluorescence.

Ultrasensitively selective detection of trace polycyclic aromatic hydrocarbons (PAHs) like phenanthrene (PHE) is critical but remains challenging. Herein, atomically dispersed Zn sites on g-C3 N4 nanosheets (sZn-CN) are constructed by thermal polymerization of a Zn-cyanuric acid-melamine supramolecular precursor for the fluorescence detection of PHE. A high amount (1.6 wt%) of sZn is grafted in the cave of CN with one N vacancy in the form of unique Zn(II)N5 coordination. The optimized sZn-CN achieves a wide detection range (1 ng L-1 to 5 mg L-1 ), ultralow detection limit (0.35 ng L-1 , with 5-order magnitude improvement over CN), and ultrahigh selectivity toward PHE even among typical PAHs based on the built PHE-CN dual ratiometric fluorescence method. By means of in situ Fourier transform infrared spectroscopy, time-resolved absorptionand fluorescence spectroscopy, and theoretical calculations, the resulting superior detection performance is attributed to the favorable selective adsorption of PHE on as-constructed atomic Zn(II)N5 sites via the ionic cation-π interactions (Znδ+ C2 δ- type), and the fluorescence quenching is dominated by the inner filter effect (IFE) from the multilayer adsorption of PHE at low concentrations, while it is done by the protruded photogenerated electron-transfer process, as well as IFE from the monolayer adsorption of PHE at ultralow concentration.

Achieving Ultra-High Selectivity to Hydrogen Production from Formic Acid on Pd-Ag Alloys.

Palladium-silver-based alloy catalysts have a great potential for CO-free hydrogen production from formic acid for fuel cell applications. However, the structural factors affecting the selectivity of formic acid decomposition are still debated. Herein, the decomposition pathways of formic acid on Pd-Ag alloys with different atomic configurations have been investigated to identify the alloy structures yielding high H2 selectively. Several PdxAg1-x surface alloys with various compositions were generated on a Pd(111) single crystal; their atomic distribution and electronic structure were determined by a combination of infrared reflection absorption spectroscopy (IRAS), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT). It was established that the Ag atoms with Pd neighbors are electronically altered, and the degree of alteration correlates with the number of nearest Pd. Temperature-programmed reaction spectroscopy (TPRS) and DFT demonstrated that the electronically altered Ag domains create a new reaction pathway that selectively dehydrogenates formic acid. In contrast, Pd monomers surrounded by Ag are demonstrated to have a similar reactivity compared to pristine Pd(111), yielding CO and H2O in addition to the dehydrogenation products. However, they bind to the produced CO weaker than pristine Pd, demonstrating an enhancement in resistance to CO poisoning. This work therefore shows that surface Ag domains modified by interaction with subsurface Pd are the key active sites for selective decomposition of formic acid, while surface Pd atoms are detrimental to selectivity. Hence, the decomposition pathways can be tailored for CO-free H2 production on Pd-Ag alloy systems.

Regulating the activity of intrinsic sites in covalent organic frameworks by introducing electro-withdrawing groups towards highly selective H2O2 electrosynthesis

Oxidized carbon catalysts have shown the potential of producing H2O2 electrochemically, and the seeking of a champion active site is usually the primary concern. However, preparing an optimal catalyst requires more activation factors rather than identifying the only oxygen-containing group that activates the adjacent carbon atoms. In this work, we treat the commonly studied oxygenated groups as the main activation factor and introduce groups with varied electron-withdrawing abilities into the system additionally, attempting to break the catalytic limit imposed by a single factor. In detail, we designed dioxin-linked covalent organic frameworks (COFs) in which each structural unit contains four C-O-C groups as the main activation factor and two more functional groups (-CN, -COOH, or -CH2OH) as the additional regulation factors. The active carbon atoms are located between these chemical groups and thus their catalytic activities are impacted by them simultaneously. Results show that the catalytic activity is positively associated with the electron-withdrawing ability of the additional groups. The well-tailored COF-CN achieved an ultrahigh H2O2 selectivity of 97.2% and an outstanding H2O2 yield of 901 mmol g−1 h−1, allowing it to be directly used for wood pulping and waste paper recycling without extra separation processes. Further calculations and extended modeling of a nitrogen-dopant system suggest the universal potential of such an additional chemical influence design to go beyond the current electrocatalytic limit.

Ullmann-Like Covalent Bond Coupling without Participation of Metal Atoms.

Ullmann-like on-surface synthesis is one of the most appropriate approaches for the bottom-up fabrication of covalent organic nanostructures and many successes have been achieved. The Ullmann reaction requires the oxidative addition of a catalyst (a metal atom in most cases): the metal atom will insert into a carbon-halogen bond, forming organometallic intermediates, which are then reductively eliminated and form C-C covalent bonds. As a result, traditional Ullmann coupling involves reactions of multiple steps, making it difficult to control the final product. Moreover, forming the organometallic intermediates will potentially poison the metal surface catalytic reactivity. In the study, we used the 2D hBN, an atomically thin sp2-hybridized sheet with a large band gap, to protect the Rh(111) metal surface. It is an ideal 2D platform to decouple the molecular precursor from the Rh(111) surface while maintaining the reactivity of Rh(111). We realize an Ullmann-like coupling of a planar biphenylene-based molecule, i.e., 1,8-dibromobiphenylene (BPBr2), on an hBN/Rh(111) surface with an ultrahigh selectivity of the biphenylene dimer product, containing 4-, 6-, and 8-membered rings. The reaction mechanism, including electron wave penetration and the template effect of the hBN, is elucidated by combining low-temperature scanning tunneling microscopy and density functional theory calculations. Our findings are expected to play an essential role regarding the high-yield fabrication of functional nanostructures for future information devices.

Facile Synthesis of Hollow Fe3O4-rGO Nanocomposites for the Electrochemical Detection of Acetaminophen

Acetaminophen (AC) is one of the most popular pharmacologically active substances used as an analgesic and antipyretic drug. Herein, a new type of hollow Fe3O4-rGO/GCE electrode was prepared for electrochemical detection of AC through a three-step approach involving a solvothermal method for the synthesis of hollow Fe3O4 and the chemical reduction of graphene oxide (GO) for reduced graphene oxide (rGO) and Fe3O4-rGO nanocomposites modified on the glassy carbon electrode (GCE) surface. The as-prepared Fe3O4-rGO nanocomposites were characterized using a transmission electron microscope (TEM), X-ray diffraction (XRD), and a magnetic measurement system (SQUID-VSM). The magnetic Fe3O4-rGO/GCE electrodes were employed for the electrochemical detection of AC using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and square wave voltammetry (SWV) and exhibited an ultra-high selectivity and accuracy, a low detection limit of 0.11 µmol/L with a wider linear range from 5 × 10-7 to 10-4 mol/L, and high recovery between 100.52% and 101.43%. The obtained Fe3O4-rGO-modified GCE displays great practical significance for the detection of AC in drug analysis.

Rapid and selective removal of Pb ions by electroactive titanium Dioxide/Polyaniline ion exchange film

The slow accumulation of heavy metal in the sediment and aquatic food chain, leads to extremely bad health influence in human body. Most of the traditional adsorption materials have deficient adsorption capacity and selectivity. In this research, the TiO2/PANI composite material is synthesized successfully by intercalating 2HT (intercalating agent) and PANI into the interlayer of the TiO2 nanosheet for the separation of Pb2+. During this synthesis process, the layer spacing of TiO2/PANI can be controlled precisely by adjusting the concentration of 2HT and PANI. The rapid Pb2+ uptake/ release process is triggered through turning the redox states of composite film which can leads to the conversion between Ti4+ and Ti3+ and the conversion between –OH and -O-Pb covalent bond for maintaining the electrical neutrality. In addition, the directional H+ proton migration, fast electronic transporting network and superfast Pb2+ ion transport path both are benefit for the transmission and uptake of Pb2+. As a result, this composite film illustrates ultrahigh uptake capacity (1499.99 mg∙g−1) and selectivity (KD = 15.2 L·g−1). It can even treat real wastewater to a level lower than WHO. Hence, this composite film with superior electrochemical performance is a promising material, which could be used for uptake/release of Pb2+.

Enhancement in catalytic performance of HZSM-5 zeolite for glycerol dehydration after acidity regulation

HZSM-5 zeolites modified by simple and economical impregnation with phosphoric acid were applied to acrolein production from glycerol. After 68 h on stream, the glycerol conversion was still maintained at 100 % with an acrolein selectivity of 89.6 % on phosphorus modified nanosheet HZSM-5, which ranks among the best catalytic performance in glycerol dehydration catalyzed by zeolites. Besides, improvement in catalytic stability was further confirmed by the lowered deactivation rate on phosphorus modified HZSM-5 zeolite. Characterization results revealed that the acidity of HZSM-5 zeolite was adjusted by phosphorus incorporation. More importantly, the regulative mechanism was thoroughly discussed basing on a comprehensive consideration of the 27Al MAS NMR and Py-IR results. Further investigation with in situ FT-IR indicated that products or intermediates in glycerol dehydration could be more easily desorbed from phosphorus modified HZSM-5 zeolite with weaker acidity, which dramatically suppressed coke formation and greatly prolonged the lifetime of catalyst. Moreover, for the first time, diffusivity calculation and experimental results illustrated that product diffusion restriction played a crucial role in producing acrolein with ultrahigh selectivity over HZSM-5 apart from acidity.

Large surface-to-volume-ratio and ultrahigh selectivity SSZ-13 membranes on 61-channel monoliths for efficient separation of CO2/CH4 mixture

This monolithic configuration of support owns superior mechanical strength, high surface-to-volume ratio and largely reduced sealing points compared with the ceramic hollow-fiber and tubular ones. Intergrown and thin SSZ-13 membranes with surface-to-volume ratio of 680 m2/m3 were prepared the 61-channel monoliths via one-step secondary growth. The membrane thickness on the different channels was uniform. The typical membrane with efficient membrane area of ∼200 cm2 achieved ultrahigh selectivity of CO2/CH4 up to 280, which was higher than that of reported SSZ-13 membranes that always had area less than 20 cm2. The effects of temperature and pressure on separation performance of membranes on 61-channel monoliths were investigated. Our results suggest that the scalable SSZ-13 membrane on 61-channel monolith is a good candidate for natural gas sweetening.

Nitrogen Abundant Polyimide Covalent Organic Frameworks as Nanotraps toward Uranium Sequestration

The design and synthesis of efficient and highly selective UO22+ nanotraps still pose difficulties in the field of radionuclide removal. Herein, a stable polyimide covalent organic framework (PI-COF-6) was rationally synthesized for targeted uranium adsorption through the irreversible imidization reaction between nitrogen-rich monomer 5,5′,5″-(1,3,5-triazine-2,4,6-triyl)tris(pyridin-2-amine) (TTPA) and pyromellitic dianhydride (PMDA). The PI-COF-6 showed satisfactory uranium adsorption performance with high capacity (424.5 mg g–1), fast kinetics (98.0% removal rate in 50 min), ultrahigh selectivity among multiple metal ions, excellent stability, and outstanding recyclability. XPS characterization and DFT calculations identified that the uranium adsorption of PI-COF-6 mainly relied on the N–N–O nanotraps which were rationally constructed by pyridine nitrogen in TTPA coupling with the tertiary amine nitrogen and carbonyl oxygen in the imide ring. Moreover, the results of high-resolution U 4f XPS spectroscopy revealed that part of U(VI) was reduced into U(IV). Hence, according to the design of rational nanotraps for targeted radioactive nuclides, highly effective adsorbents for practical application (rare earth mining waste remediation) were successfully achieved.

Dislocated Bilayer MOF Enables High-Selectivity Photocatalytic Reduction of CO2 to CO.

The highly selective photoreduction of CO2 into valuable small-molecule chemical feedstocks such as CO is an effective strategy for addressing the energy crisis and environmental problems. However, it remains a challenge because the complex CO2 photoreduction process usually generates multiple possible products and requires a subsequent separation step. In this paper, 2D monolayer and bilayer porphyrin-based metal-organic frameworks (MOFs) are successfully constructed by adjusting the reaction temperature and solvent polarity with 5,10,15,20-tetrakis(4-pyridyl)porphyrin as the light-harvesting ligand. The bilayer MOF is a low-dimensional MOF with a special structure in which the upper and lower layers are arranged in dislocation and are bridged by halogen ions. This bilayer MOF exhibits 100% ultra-high selectivity for the reduction of CO2 to CO under simulated sunlight without any cocatalyst or photosensitizer and can be recycled at least three times. The intrinsic mechanism of this photocatalytic CO2 reduction process is explored through experimental characterization and density functional theory (DFT) calculations. This work shows that the rational design of the number of layers in 2D MOF structures can tune the stability of these structures and opens a new avenue for the design of highly selective MOF photocatalysts.

A new means of energy supply driven by terahertz photons recovers related neural activity

Continuous and efficient energy capture represents a long-sought dream of mankind. The brain is a major energy-consuming organ; an adult brain accounts for about 2% of the body weight but consumes about 20% of the body's energy. However, it is still unclear how the brain achieves efficient use of energy. Here, using nerve cells as test subjects, we found that THz photons with a specific frequency can effectively restore the reduced frequency of action potentials caused by inadequate ATP supply, which has been demonstrated as a novel mode of energy supply, present photons emission at a particular frequency from the breaking of the ATP phosphate bond. This energy supply mechanism may play a key biophysical basis for explaining how the body efficiently obtains energy, because the quantized chemical reactions could have a high energy efficiency and ultrahigh selectivity compared with the traditional thermochemistry and photochemistry.

Ultraselective Extraction Reprocessing of 99TcO4-/ReO4- with a Promising Carbamic Acid Extractant System.

With the development of nuclear energy, the reprocessing of 99TcO4-/ReO4- has become a very difficult problem due to environmental issues such as high output, long life, and easy leakage. In this study, three extraction systems containing carbamic acid were introduced into the reprocessing of 99TcO4-/ReO4- for the first time. The results involving one of the three results show that N-[N,N-di(2-ethylhexyl) aminocarbonylmethyl] glycine (D2EHAG) has ultrahigh selectivity for removal to 99TcO4-/ReO4-. When the extreme concentration ratio of SO42- and Cl- to ReO4- of D2EHAG is 10,000:1, the distribution coefficient of ReO4- still reaches 12.73 and 2.67, respectively. Additionally, the most hydrophilic NO3-, when the extreme concentration ratio of NO3- and ReO4- is 1000:1, still has a distribution coefficient close to 2.33, which is more than the most reported MOF adsorption materials. Moreover, the reaction kinetics, stripping rate, and reuse rate were studied. After five cycles, the removal rate is still 98.12%, with a decrease of less than 0.7%. The system containing carbamic acid is a potential extraction removal system to remove 99TcO4-/ReO4- from nuclear radioactive wastewater.

Rational Construction of Metal Organic Framework Hybrid Assemblies for Visible Light-Driven CO2 Conversion

Photocatalytic reduction of CO2 to value-added chemicals is known to be a promising approach for CO2 conversion. The design and preparation of ideal photocatalysts for CO2 conversion are of pivotal significance for the sustainable development of the whole society. In this work, we integrated two functional organic linkers to prepare a novel metal organic framework (MOF) photocatalyst {[Co(9,10-bis(4-pyridyl)anthracene)0.5(bpda)]·4DMF} (Co-MOF). The existence of anthryl and amino groups leads to a wide range of visible light absorption and efficient separation of photogenerated electrons. To extend the lifetime of photogenerated electrons in the photocatalytic system, we modified Co-MOF particles onto g-C3N4. As expected, Co-MOF/g-C3N4 composites exhibited an ultrahigh selectivity (more than 97%) in the photocatalytic process, and the highest CO production rate (1824 μmol/g/h) was 7.1 and 27.2 times of Co-MOFs and g-C3N4, respectively. What's more, we also discussed the reaction mechanism of the Co-MOF/g-C3N4 photocatalytic CO2 reduction, and this work paves the pathway for designing photocatalysts with ideal CO2 reduction performance.

Unveiling the impact of imidazole derivative with mechanistic insights into neutralize interfacial polymerized membranes for improved solute-solute selectivity

Domestic wastewater (DWW) contains a reservoir of nutrients, such as nitrogen, potassium, and phosphorus; however, emerging micropollutants (EMPs) hinder its applications in resource recovery. In this study, a novel class of nanofiltration (NF) membranes was developed; it enabled the efficient removal of harmful EMP constituents while preserving valuable nutrients in the permeate. Neutral (IM-N) and positively charged (IM-P) imidazole derivative compounds have been used to chemically functionalize pristine polyamide (PA) membranes to synchronously inhibit the hydrolysis of residual acyl chloride and promote their amination. Owing to their distinct properties, these IM modifiers can custom-build the membrane physicochemical properties and structures to benefit the NF process in DWW treatment. The electroneutral NF membrane exhibited ultrahigh solute-solute selectivity by minimizing the Donnan effects on ion penetration (K, N, and P ions rejection < 25%) while imposing remarkable size-sieving obstruction against EMPs (rejection ratio > 91%). Moreover, the hydrophilic IM-modifier synergistically led to enhanced water permeance of 9.2 L m−2 h−1 bar−1, reaching a 2-fold higher magnitude than that of the pristine PA membrane, along with excellent antifouling/antibacterial fouling properties. This study may provide a paradigm shift in membrane technology to convert wastewater streams into valuable water and nutrient resources.