Ion-Selective Transport Promotion Enabled by Angstrom-Scale Nanochannels in Dendrimer-Assembled Polyamide Nanofilm for Efficient Electrodialysis.

The ion permeability and selectivity of membranes are crucial in nanofluidic behavior, impacting industries ranging from traditional to advanced manufacturing. Herein, we demonstrate the engineering of ion-conductive membranes featuring angstrom-scale ion-transport channels by introducing ionic polyamidoamine (PAMAM) dendrimers for ion separation. The exterior quaternary ammonium-rich structure contributes to significant electrostatic charge exclusion due to enhanced local charge density; the interior protoplasmic channels of PAMAM dendrimer are assembled to provide additional degrees of free volume. This facilitates the monovalent ion transfer while maintaining continuity and efficient ion screening. The dendrimer-assembled hybrid membrane achieves high monovalent ion permeance of 2.81 mol m-2 h-1 (K+), reaching excellent mono/multivalent selectivity up to 20.1 (K+/Mg2+) and surpassing the permselectivities of state-of-the-art membranes. Both experimental results and simulating calculations suggest that the impressive ion selectivity arises from the significant disparity in transport energy barrier between mono/multivalent ions, induced by the "exterior-interior" synergistic effects of bifunctional membrane channels.

Scalable Preparation of Ultraselective and Highly Permeable Fully Aromatic Polyamide Nanofiltration Membranes for Antibiotic Desalination.

Membranes are important in the pharmaceutical industry for the separation of antibiotics and salts. However, its widespread adoption has been hindered by limited control of the membrane microstructure (pore architecture and free-volume elements), separation threshold, scalability, and operational stability. In this study, 4,4',4'',4'''-methanetetrayltetrakis(benzene-1,2-diamine) (MTLB) as prepared as a molecular building block for fabricating thin-film composite membranes (TFCMs) via interfacial polymerization. The relatively large molecular size and rigid molecular structure of MTLB, along with its non-coplanar and distorted conformation, produced thin and defect-free selective layers (~27 nm) with ideal microporosities for antibiotic desalination. These structural advantages yielded an unprecedented high performance with a water permeance of 45.2 L m-2 h-1 bar-1 and efficient antibiotic desalination (NaCl/adriamycin selectivity of 422). We demonstrated the feasibility of the industrial scaling of the membrane into a spiral-wound module (with an effective area of 2.0 m2). This module exhibited long-term stability and performance that surpassed those of state-of-the-art membranes used for antibiotic desalination. This study provides a scientific reference for the development of high-performance TFCMs for water purification and desalination in the pharmaceutical industry.

Surface Activation by Single Ru Atoms for Enhanced High-Temperature CO2 Electrolysis.

Cathodic CO2 adsorption and activation is essential for high-temperature CO2 electrolysis in solid oxide electrolysis cells (SOECs). However, the component of oxygen ionic conductor in the cathode displays limited electrocatalytic activity. Herein, stable single Ruthenium (Ru) atoms are anchored on the surface of oxygen ionic conductor (Ce0.8 Sm0.2 O2-δ , SDC) via the strong covalent metal-support interaction, which evidently modifies the electronic structure of SDC surface for favorable oxygen vacancy formation and enhanced CO2 adsorption and activation, finally evoking the electrocatalytic activity of SDC for high-temperature CO2 electrolysis. Experimentally, SOEC with the Ru1 /SDC-La0.6 Sr0.4 Co0.2 Fe0.8 O3-δ cathode exhibits a current density as high as 2.39 A cm-2 at 1.6 V and 800 °C. This work expands the application of single atom catalyst to the high-temperature electrocatalytic reaction in SOEC and provides an efficient strategy to tailor the electronic structure and electrocatalytic activity of SOEC cathode at the atomic scale.

TiO2-Modified Montmorillonite-Supported Porous Carbon-Immobilized Pd Species Nanocomposite as an Efficient Catalyst for Sonogashira Reactions.

In this study, a combination of the porous carbon (PCN), montmorillonite (MMT), and TiO2 was synthesized into a composite immobilized Pd metal catalyst (TiO2-MMT/PCN@Pd) with effective synergism improvements in catalytic performance. The successful TiO2-pillaring modification for MMT, derivation of carbon from the biopolymer of chitosan, and immobilization of Pd species for the prepared TiO2-MMT/PCN@Pd0 nanocomposites were confirmed using a combined characterization with X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N2 adsorption-desorption isotherms, high-resolution transition electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. It was shown that the combination of PCN, MMT, and TiO2 as a composite support for the stabilization of the Pd catalysts could synergistically improve the adsorption and catalytic properties. The resultant TiO2-MMT80/PCN20@Pd0 showed a high surface area of 108.9 m2/g. Furthermore, it exhibited moderate to excellent activity (59-99% yield) and high stability (recyclable 19 times) in the liquid-solid catalytic reactions, such as the Sonogashira reactions of aryl halides (I, Br) with terminal alkynes in organic solutions. The positron annihilation lifetime spectroscopy (PALS) characterization sensitively detected the development of sub-nanoscale microdefects in the catalyst after long-term recycling service. This study provided direct evidence for the formation of some larger-sized microdefects during sequential recycling, which would act as leaching channels for loaded molecules, including active Pd species.

Effects of Nonhydroxyl Oxygen Heteroatoms in Diethylene Glycols on the Properties of 2,5-Furandicarboxylic Acid-Based Polyesters.

With regard to polyesters based on biobased 2,5-furandicarboxylic acid (FDCA), our work presents a new strategy, heteroatom substitution, to adjust the thermal and gas barrier properties. The effects of nonhydroxyl oxygen heteroatoms in the diols on the properties of FDCA-based polyesters were first investigated by a combination of an experiment and molecular simulation. The results demonstrated that the introduction of oxygen heteroatoms significantly influenced the thermal and gas barrier properties. As for the two model polymers with a very similar skeleton structure, poly(pentylene 2,5-furandicarboxylate) (PPeF) and poly(diethylene glycol 2,5-furandicarboxylate) (PDEF), their Tg exhibited an obviously increasing order. Moreover, they showed similar thermal stability and thermal oxidative stability. Dynamic mechanical analysis, positron annihilation lifetime spectroscopy, and molecular dynamics simulation indicated that the gas barrier properties followed the sequence of PDEF > PPeF mainly due to the decreased chain mobility and smaller fractional free volume. In-depth analysis of the effects of heteroatom substitution has an important directive significance for the design and preparation of new high glass transition temperature or novel excellent gas barrier materials. Through the manipulation of different heteroatoms in the diols, the polyesters with varied properties can be expected.

Boosting the Catalytic Performance of CeO2 in Toluene Combustion via the Ce-Ce Homogeneous Interface.

Catalytic combustion is an advanced technology to eliminate industrial volatile organic compounds such as toluene. In order to replace the expensive noble metal catalysts and avoid the aggregation phenomenon occurring in traditional heterogeneous interfaces, designing homogeneous interfaces can become an emerging methodology to enhance the catalytic combustion performance of metal oxide catalysts. A mesocrystalline CeO2 catalyst with abundant Ce-Ce homogeneous interfaces is synthesized via a self-flaming method which exhibits boosted catalytic performance for toluene combustion compared with traditional CeO2, leading to a ∼40 °C lower T90. The abundant Ce-Ce homogeneous interfaces formed by both highly ordered stacking and small grain size endow the CeO2 mesocrystal with superior redox property and oxygen storage capacity via forming various oxygen vacancies. Surface and bulk oxygen vacancies generate and activate crucial oxygen species, while interfacial oxygen vacancies further promote the reaction behavior of oxygen species (i.e., activation, regeneration, and migration), causing the splitting of redox property toward lower temperature. These properties facilitate aromatic ring decomposition, the important rate-determining step, thus contributing to toluene catalytic degradation to CO2. This work may shed insights into the catalytic effects of homogeneous interfaces in pollutant removal and provide a strategy of interfacial defect engineering for catalyst development.

Roles of Oxygen Vacancies in the Bulk and Surface of CeO2 for Toluene Catalytic Combustion.

Catalytic combustion technology is one of the effective methods to remove VOCs such as toluene from industrial emissions. The decomposition of an aromatic ring via catalyst oxygen vacancies is usually the rate-determining step of toluene oxidation into CO2. Series of CeO2 probe models were synthesized with different ratios of surface-to-bulk oxygen vacancies. Besides the devotion of the surface vacancies, a part of the bulk vacancies promotes the redox property of CeO2 in toluene catalytic combustion: surface vacancies tend to adsorb and activate gaseous O2 to form adsorbed oxygen species, whereas bulk vacancies improve the mobility and activity of lattice oxygen species via their transmission effect. Adsorbed oxygen mainly participates in the chemical adsorption and partial oxidation of toluene (mostly to phenolate). With the elevated temperatures, lattice oxygen of the catalysts facilitates the decomposition of aromatic rings and further improves the oxidation of toluene to CO2.

Adsorption and oxidation of SO2 on the surface of TiO2 nanoparticles: the role of terminal hydroxyl and oxygen vacancy-Ti3+ states.

Herein, the absorption and oxidation reactions of SO2 on TiO2 nanoparticles (TiO2 NPs) at 296 K under various environmental conditions (humidity, UV irradiation, and ozone copresence) were investigated by using a flow chamber reaction system, synchrotron X-ray absorption near-edge structure (XANES) and high resolution synchrotron X-ray photoelectron spectroscopy (XPS) measurements. The results showed that oxidation of SO2 to sulfate via TiO2 NP catalysis happened at a very rapid rate. The appropriate relative humidity, UV irradiation and co-presence of ozone all markedly promoted SO2 oxidation on TiO2 NPs. High resolution XPS unraveled that the terminal hydroxyl (OHt) and oxygen vacancy (VO)-Ti3+ states on TiO2 NPs were the active sites for SO2 adsorption and oxidation. The data of XPS measurements suggest that SO2 was adsorbed on a OHt next to a Ti3+ VO and reacted to form HSO3-. HSO3- can then transform into SO32-via transfer of a proton. The resulting adsorbed SO32- could bind to a surface bridging O (Ob) atom and transform into SO42-. A H2O molecule could dissociate on VO-Ti3+ into two bridging hydroxyl (OHb) groups, subsequently forming new Ob, which provides an active O site for the adsorbed HSO3-/SO32- and oxidizes them into HSO4-/SO42- on the surface of the TiO2 NPs. The copresence of O3 could promote H2O dissociation into OHb, promoting the formation of Ob. The copresence of O3 may also promote the dissociation of adsorbed H2O into TiO2-O2- and hydroxyl radicals (˙OH) on VOs, facilitating the oxidation of adsorbed HSO3-/SO32-. Under UV irradiation, new VOs were created via oxidation of lattice O by photo-generated holes, resulting in increased Ob and subsequently enhanced oxidation of adsorbed HSO3-/SO32- on TiO2 NPs.

A MOF Glass Membrane for Gas Separation.

Metal-organic framework (MOF) glasses are promising candidates for membrane fabrication due to their significant porosity, the ease of processing, and most notably, the potential to eliminate the grain boundary that is unavoidable for polycrystalline MOF membranes. Herein, we developed a ZIF-62 MOF glass membrane and exploited its intrinsic gas-separation properties. The MOF glass membrane was fabricated by melt-quenching treatment of an in situ solvothermally synthesized polycrystalline ZIF-62 MOF membrane on a porous ceramic alumina support. The molten ZIF-62 phase penetrated into the nanopores of the support and eliminated the formation of intercrystalline defects in the resultant glass membrane. The molecular sieving ability of the MOF membrane is remarkably enhanced via vitrification. The separation factors of the MOF glass membrane for H2 /CH4 , CO2 /N2 and CO2 /CH4 mixtures are 50.7, 34.5, and 36.6, respectively, far exceeding the Robeson upper bounds.

Highly Selective Photoreduction of CO2 with Suppressing H2 Evolution over Monolayer Layered Double Hydroxide under Irradiation above 600†nm.

Although progress has been made to improve photocatalytic CO2 reduction under visible light (λ>400 nm), the development of photocatalysts that can work under a longer wavelength (λ>600 nm) remains a challenge. Now, a heterogeneous photocatalyst system consisting of a ruthenium complex and a monolayer nickel-alumina layered double hydroxide (NiAl-LDH), which act as light-harvesting and catalytic units for selective photoreduction of CO2 and H2 O into CH4 and CO under irradiation with λ>400 nm. By precisely tuning the irradiation wavelength, the selectivity of CH4 can be improved to 70.3 %, and the H2 evolution reaction can be completely suppressed under irradiation with λ>600 nm. The photogenerated electrons matching the energy levels of photosensitizer and m-NiAl-LDH only localized at the defect state, providing a driving force of 0.313 eV to overcome the Gibbs free energy barrier of CO2 reduction to CH4 (0.127 eV), rather than that for H2 evolution (0.425 eV).

Generating Defect-Rich Bismuth for Enhancing the Rate of Nitrogen Electroreduction to Ammonia.

The electrochemical N2 fixation, which is far from practical application in aqueous solution under ambient conditions, is extremely challenging and requires a rational design of electrocatalytic centers. We observed that bismuth (Bi) might be a promising candidate for this task because of its weak binding with H adatoms, which increases the selectivity and production rate. Furthermore, we successfully synthesized defect-rich Bi nanoplates as an efficient noble-metal-free N2 reduction electrocatalyst via a low-temperature plasma bombardment approach. When exclusively using 1 H NMR measurements with N2 gas as a quantitative testing method, the defect-rich Bi(110) nanoplates achieved a 15 NH3 production rate of 5.453 µg mgBi -1 h-1 and a Faradaic efficiency of 11.68 % at -0.6 V vs. RHE in aqueous solution at ambient conditions.

Photocatalytic Properties Dependent on the Interfacial Defects of Intergrains within TiO2 Mesocrystals.

The regulation of interfacial defects of nanocrystals aligned orderly in a superstructured photocatalyst is an effective approach to improve the photocatalytic performance. However, the synthesis of ordered self-assemblies with abundant interfacial defects and reactive sites is hard to achieve, and applications are limited due to the unclear physicochemical properties, which result from the unique mesocrystalline microstructures. It is reported herein that the photocatalytic properties depend on the interfacial defects of intergrains in anatase TiO2 mesocrystals (TMCs). Research reveals that the photocatalytic activity largely depends on defects, such as lattice distortion and oxygen vacancies, which are located at highly aligned interfaces of intergrains within TMCs. Moreover, the mesocrystalline TiO2 photocatalysts exhibit higher photocatalytic performance in organic degradation and hydrogen evolution, compared with single crystals and polycrystals; this can be ascribed to an appropriate amount of interfacial defects at the intergrains and improved carrier separation efficiency through the highly oriented interfaces. In addition, the photocatalytic performance of the TMCs could be further improved through regulation of defects by undergoing an annealing process under a redox atmosphere. This work can provide an avenue to defect engineering for improved photocatalytic performance.

Localized Defects on Copper Sulfide Surface for Enhanced Plasmon Resonance and Water Splitting.

Surficial defects in semiconductor can induce high density of carriers and cause localized surface plasmon resonance which is prone to light harvesting and energy conversion, while internal defects may cause serious recombination of electrons and holes. Thus, it is significant to precisely control the distribution of defects, although there are few successful examples. Herein, an effective strategy to confine abundant defects within the surface layer of Cu1.94 S nanoflake arrays (NFAs) is reported, leaving a perfect internal structure. The Cu1.94 S NFAs are then applied in photoelectrochemical (PEC) water splitting. As expected, the surficial defects give rise to strong LSPR effect and quick charge separation near the surface; meanwhile, they provide active sites for catalyzing hydrogen evolution. As a result, the NFAs achieve the top PEC properties ever reported for Cux S-based photocathodes.

Probing sub-nano level molecular packing and correlated positron annihilation characteristics of ionic cross-linked chitosan membranes using positron annihilation spectroscopy.

Chitosan, CS, cross-linked with bivalent palladium has shown enhanced mechanical and thermal properties depending on the transformation of the structure at a microscopic scale. In the present study, CS directly cross-linked by palladium cation membranes (CS-cr-PM) was prepared through a solution-casting method. Mobility of chitosan chains were greatly reduced after crosslinking, making a great reduction in the swelling ratio studied by a water-swelling degree measurement, which led to an improvement in molecular chain rigidity. In order to investigate the chain packing at the molecular level in the ionic cross-linked CS system, the structure of chemically-crosslinked CS is investigated by means of the combined use of wide angle X-ray diffraction (WAXD) and infrared measurements, and a combination of positron annihilation lifetime spectroscopy (PALS) and simultaneous coincidence Doppler broadening (CDB) spectroscopy offers coherent information on both the free-volume related sub-nano level molecular packing and the chemical surrounding of free volume nanoholes in CS-cr-PM as a function of palladium salt loading. The variations in the free volume size and size distribution have been determined through the ortho-positronium (o-Ps) lifetime and its lifetime distribution. The studies showed that a strong interaction between CS molecules and palladium cations results in the change in crystallinity in formed CS-cr-PM leading to variational chain packing density. Meanwhile, significant inhibition effects on positronium formation due to doping are observed, which could be interpreted in terms of the existence of chloride ions. Applications of positron annihilation spectroscopy to study the microstructure and correlated positron annihilation characteristics of an ionic cross-linked CS system are systematically discussed.

Investigations on Zr incorporation into Li3V2(PO4)3/C cathode materials for lithium ion batteries.

Li3V2(PO4)3/C (LVP/C) composites have been modified by different ways of Zr-incorporation via ultrasonic-assisted solid-state reaction. The difference in the effect on the physicochemical properties and the electrochemical performance of LVP between Zr-doping and ZrO2-coating has also been investigated. Compared with pristine LVP/C, Zr-incorporated LVP/C composites exhibit better rate capability and cycling stability. In particular, the LVP/C-Zr electrode delivers the highest initial capacity of 150.4 mA h g-1 at 10C with a capacity retention ratio of 88.4% after 100 cycles. The enhanced electrochemical performance of Zr-incorporated LVP/C samples (LVZrP/C and LVP/C-Zr) is attributed to the increased ionic conductivity and electronic conductivity, the improved stability of the LVP structure, and the decreased charge-transfer resistance.

Microporous Polyamide Membranes for Molecular Sieving of Nitrogen from Volatile Organic Compounds.

Microporous polymer membranes continue to receive tremendous attention for energy-efficient gas separation processes owing to their high separation performances. A new network microporous polyamide membrane with good molecular-sieving performance for the separation of N2 from a volatile organic compound (VOC) mixture is described. Triple-substituted triptycene was used as the main monomer to form a fisherman's net-shaped polymer, which readily forms a composite membrane by solution casting. This membrane exhibited outstanding separation performance and good stability for the molecular-sieving separation of N2 over VOCs such as cyclohexane. The rejection rate of the membrane reached 99.2 % with 2098 Barrer N2 permeability at 24 °C under 4 kPa. This approach promotes development of microporous membranes for separation of condensable gases.

Contributions of Phase, Sulfur Vacancies, and Edges to the Hydrogen Evolution Reaction Catalytic Activity of Porous Molybdenum Disulfide Nanosheets.

Molybdenum disulfide (MoS2) is a promising nonprecious catalyst for the hydrogen evolution reaction (HER) that has been extensively studied due to its excellent performance, but the lack of understanding of the factors that impact its catalytic activity hinders further design and enhancement of MoS2-based electrocatalysts. Here, by using novel porous (holey) metallic 1T phase MoS2 nanosheets synthesized by a liquid-ammonia-assisted lithiation route, we systematically investigated the contributions of crystal structure (phase), edges, and sulfur vacancies (S-vacancies) to the catalytic activity toward HER from five representative MoS2 nanosheet samples, including 2H and 1T phase, porous 2H and 1T phase, and sulfur-compensated porous 2H phase. Superior HER catalytic activity was achieved in the porous 1T phase MoS2 nanosheets that have even more edges and S-vacancies than conventional 1T phase MoS2. A comparative study revealed that the phase serves as the key role in determining the HER performance, as 1T phase MoS2 always outperforms the corresponding 2H phase MoS2 samples, and that both edges and S-vacancies also contribute significantly to the catalytic activity in porous MoS2 samples. Then, using combined defect characterization techniques of electron spin resonance spectroscopy and positron annihilation lifetime spectroscopy to quantify the S-vacancies, the contributions of each factor were individually elucidated. This study presents new insights and opens up new avenues for designing electrocatalysts based on MoS2 or other layered materials with enhanced HER performance.

Facile Aluminum Reduction Synthesis of Blue TiO2 with Oxygen Deficiency for Lithium-Ion Batteries.

An ultrafacile aluminum reduction method is reported herein for the preparation of blue TiO2 nanoparticles (donated as Al-TiO2 , anatase phase) with abundant oxygen deficiency for lithium-ion batteries. Under aluminum reduction, the morphology of the TiO2 nanosheets changes from well-defined rectangular into uniform round or oval nanoparticles and the particle size also decreases from 60 to 31 nm, which can aggressively accelerate the lithium-ion diffusion. Electron paramagnetic resonance (EPR) and positron annihilation lifetime spectroscopy (PALS) results reveal that plentiful oxygen deficiencies relative to the Ti(3+) species were generated in blue Al-TiO2 ; this effectively enhances the electron conductivity of the TiO2 . X-ray photoelectron spectrometry (XPS) analysis indicates that a small peak is observed for the Al-O bond, which probably plays a very important role in the stabilization of the oxygen deficiencies/Ti(3+) species. As a result, the blue Al-TiO2 possesses significantly higher capacity, better rate performance, and a longer cycle life than the white pure TiO2 . Such improvements can be attributed to the decreased particle size, as well as the existence of the oxygen deficiencies/Ti(3+) species.

The role of Sn in enhancing the visible-light photocatalytic activity of hollow hierarchical microspheres of the Bi/BiOBr heterojunction.

Hollow hierarchical microspheres of Bi/BiOBr (SBB) with oxygen vacancies were prepared using a one step solvothermal method. It was found that the stannous chloride dihydrate played key roles in the formation of Bi, defects and the stacking mode of hierarchical construction units. Positron annihilation lifetime spectroscopy (PALS) was used to demonstrate the oxygen vacancies in Bi/BiOBr samples. The density of states (DOS) of the valence band of BiOBr can be modulated by the introduction of oxygen vacancies according to the valence band XPS and Density Functional Theory (DFT) calculations. Analyses of photoluminescence and BET demonstrated that SBB hollow hierarchical microspheres with higher specific surface area have a lower recombination rate of photo-generated electrons and holes. The photocatalytic and adsorptive performances showed that the samples exhibited stronger adsorption capacity toward rhodamine B (RhB) and highly efficient photocatalytic activity in the degradation of RhB, which were attributed to the higher adsorption ability and synergistic effect of oxygen vacancies and construction of the heterojunction structure (Bi/BiOBr).

The Influence of Rhenium Content on Helium Desorption Behavior in Tungsten-Rhenium Alloy.

To investigate the influence of different rhenium contents on the helium desorption behavior in tungsten-rhenium alloys, pure tungsten and tungsten-rhenium alloys were irradiated with helium under the same conditions. All irradiated samples were characterized using TDS and DBS techniques. The results indicate that the addition of rhenium can reduce the total helium desorption quantity in tungsten-rhenium alloys and slightly accelerate the reduction in the concentration of vacancy-type defects accompanying helium dissociation. The desorption activation energy of helium is approximately 2 eV at the low-temperature peak (~785 K) and about 4 eV at the high-temperature peak (~1475 K). An increase in rhenium content causes the desorption peak to shift towards higher temperatures (>1473 K), which is attributed to the formation of the stable complex structures between rhenium and vacancies. Besides, the migration of He-vacancy complexes towards traps and dynamic annealing processes both lead to the recovery of vacancy-type defects, resulting in a decrease in the positron annihilation S parameters.