Multi-Functional Polymer Membranes Enable Integrated CO2 Capture and Conversion in a Single, Continuous-Flow Membrane Reactor under Mild Conditions.

Herein, we present a membrane-based system designed to capture CO2 from dilute mixtures and convert the captured CO2 into value-added products in a single integrated process operated continuously under mild conditions. Specifically, we demonstrate that quaternized poly(4-vinylpyridine) (P4VP) membranes are selective CO2 separation membranes that are also catalytically active for cyclic carbonate synthesis from the cycloaddition of CO2 to epichlorohydrin. We further demonstrate that quaternized P4VP membranes can integrate CO2 capture, including from dilute mixtures down to 0.1 kPa of CO2, with CO2 conversion to cyclic carbonates at 57 °C and atmospheric pressure. The catalytic membrane acts as both the CO2 capture and conversion medium, providing an energy-efficient alternative to sorbent-based capture, compression, transport, and storage. The membrane is also potentially tunable for the conversion of CO2 to a variety of products, including chemicals and fuels not limited to cyclic carbonates, which would be a transformative shift in carbon capture and utilization technology.

Operando Surface-Enhanced Raman-Scattering (SERS) for Probing CO2 Facilitated Transport Mechanisms of Amine-Functionalized Polymeric Membranes.

This work describes a new operando surface enhanced Raman spectroscopy (SERS) platform that we developed for use with polymeric membranes that includes (1) a method for preparing SERS-active polymer membranes and (2) a permeation cell with optical access for SERS characterization of membranes under realistic operating conditions. This technique enables the direct correlation of membrane structure to its performance under realistic operating conditions by combining in situ SERS characterization of the molecular structure of polymer membranes and simultaneous measurement of solute permeation rates on the same sample. Using the new operando SERS technique, this work aims to clarify the unknown mechanisms by which reactive amines facilitate CO2 transport across polyvinylamine (PVAm), a prototypical facilitated transport membrane for CO2 separations. We show that a small amount of plasmonic silver particles added to the PVAm solution prior to knife-casting selectively enhances the sensitivity to detection of chemical intermediates (e.g., carbamate) formed in the PVAm film due to the surface-enhanced Raman scattering effect with only minimal effect on the CO2 permeance and selectivity of the membrane. Operando SERS characterization of PVAm during exposure to humidified CO2/CH4 biogas mixtures at room temperature shows that CO2 permeates across PVAm primarily as carbamate species. This work clarifies the previously unknown mechanism of CO2 facilitated transport across PVAm and establishes a new operando SERS platform that can be used with a wide range of polymer membrane systems. This technique can be used to elucidate fundamental transport mechanisms in polymer membranes, to establish reliable structure-performance relationships, and for real-time diagnostics of membrane fouling, among other applications.

Highly Active CuOx/SiO2 Dot Core/Rod Shell Catalysts with Enhanced Stability for the Reverse Water Gas Shift Reaction.

Cu-based catalysts are highly active and selective for several CO2 conversion reactions; however, traditional monometallic Cu-based catalysts suffer poor thermal stability due to the aggregation of copper particles at high temperatures. In this work, we demonstrate a crystal engineering strategy to controllably prepare copper/silica (CuOx/SiO2) catalysts for the reverse water gas shift reaction (RWGS) at high temperatures. We show that CuOx/SiO2 catalysts derived from the in situ reduction of pure copper silicate nanotubes in a CO2 and H2 atmosphere exhibit superior catalytic activity with enhanced stability compared to traditional monometallic Cu-based catalysts for the RWGS at high temperatures. Detailed structural characterization reveals that there is a strong interaction between Cu and SiO2 in CuOx/SiO2 catalysts, which produces more Cu+ sites and smaller CuOx nanoparticles. Moreover, CuOx/SiO2 catalysts possess a unique dot core/rod shell structure, which could prevent the aggregation of Cu particles. This structural confinement effect, enhanced CO2 adsorption by Cu+, and small CuOx nanoparticles presumably caused the catalyst's extraordinary activity with enhanced stability at high temperatures.

Low Temperature Oxidation of Ethane to Oxygenates by Oxygen over Iridium-Cluster Catalysts.

Direct selective oxidation of light alkanes, such as ethane, into value-added chemical products under mild reaction conditions remains a challenge in both industry and academia. Herein, the iridium cluster and atomically dispersed iridium catalysts have been successfully fabricated using nanodiamond as support. The obtained iridium cluster catalyst shows remarkable performance for selective oxidation of ethane under oxygen at 100 °C, with an initial activity as high as 7.5 mol/mol/h and a selectivity to acetic acid higher than 70% after five in situ recycles. The presence of CO in the reaction feed is pivotal for the excellent reaction performance. On the basis of X-ray photoelectron spectroscopy (XPS) analysis, the critical role of CO was revealed, which is to maintain the metallic state of reactive Ir species during the oxidation cycles.

Highly active and stable copper catalysts derived from copper silicate double-shell nanofibers with strong metal-support interactions for the RWGS reaction.

Highly active and stable copper catalysts were successfully achieved by in situ self-reduction treatment of hierarchical double-shell copper silicate hollow nanofibers. The coexistence of Cu0 and Cu+ species in the as-prepared catalysts demonstrated the strong metal-support interactions and endowed them with outstanding catalytic performance for the RWGS reaction.

Enantioseparation of Au20 (PP3 )4 Cl4 Clusters with Intrinsically Chiral Cores.

Au20 (PP3 )4 Cl4 (PP3 =tris(2-(diphenylphosphino)ethyl) phosphine), abbreviated as Au20 , is the only Au nanocluster with an intrinsically chiral core without a chiral environment (chiral ligands or Au-thiolate staples), making it a unique object to understand chiral evolution and explore chiral applications. Unfortunately, the synthesized Au20 is racemic, and its enantiomers have not yet been separated. Herein, we report a supramolecular assembly strategy with α-cyclodextrin (α-CD) to afford enantiopure Au20 in bulk, and an enantiomer excess (ee) value of as-separated Au20 of 97 %. As a result of its high purity, the distinctive optical activity of Au20 , which originates from electronic transitions confined in chiral cores, is fully explored. Theoretical studies reveals that the enantioseparation results from the preferential self-assembly of α-CD with organic ligands on the surface of right-handed Au20 .

Controlling Ag-doping in [AgxAu25-x(SC6H11)18]- nanoclusters: cryogenic optical, electronic and electrocatalytic properties.

Doping metal nanoclusters with a second type of metal is a powerful method for tuning the physicochemical properties of nanoclusters at the atomic level and it also provides opportunities for a fundamental understanding of alloying rules as well as new applications. Herein, we have devised a new, one-phase strategy for achieving heavy Ag-doping in Au25(SR)18 nanoclusters. This strategy overcomes the light doping of silver by previous methods. X-ray crystallography together with ESI-MS determined the composition of the product to be [AgxAu25-x(SC6H11)18]- with x ∼ 21. Cryogenic optical spectroscopy (80-300 K) revealed fine features in optical absorption peaks. Interestingly, the heavy doping of silver does not significantly change the electron-phonon coupling strength and the surface phonon frequency. DFT simulations reproduced the experimentally observed trend of electronic structure evolution with Ag doping. We further investigated the electrocatalytic performance of such heavily Ag-doped nanoclusters for oxygen reduction in alkaline solutions. The mass activity of ligand-off [AgxAu25-x(SC6H11)18]- nanoclusters (217.4 A g-1metal) was determined to be higher than that of ligand-on nanoclusters (29.6 A g-1metal) at a potential of -0.3 V (vs. Ag/AgCl). The rotating disk electrode (RDE) studies revealed the tunable kinetic features of the nanoclusters by ligand removal.

Atomically Precise Gold Nanoclusters Accelerate Hydrogen Evolution over MoS2 Nanosheets: The Dual Interfacial Effect.

Hydrogen generation via electrocatalytic water splitting holds great promise for future energy revolution. It is desirable to design abundant and efficient catalysts and achieve mechanistic understanding of hydrogen evolution reaction (HER). Here, this paper reports a strategy for improving HER performance of molybdenum disulfide (MoS2 ) via introducing gold nanoclusters as a cocatalyst. Compared to plain MoS2 nanosheets, the Au25 (SR)18 /MoS2 nanocomposite exhibits enhanced HER activity with a small onset potential of -0.20 V (vs reversible hydrogen electrode) and a higher current density of 59.3 mA cm-2 at the potential of -0.4 V. In addition to the interfacial interaction between nanoclusters and MoS2 , the interface between the Au25 core and the surface ligands (thiolate vs selenolate) is also discovered to distinctly affect the catalytic performance. This work highlights the promise of metal nanoclusters in boosting the HER performance via tailoring the interfacial electronic interactions between gold nanoclusters and MoS2 nanosheets, as well as the interface between metal core and surface ligands.

Electron localization in rod-shaped triicosahedral gold nanocluster.

Atomically precise gold nanocluster based on linear assembly of repeating icosahedrons (clusters of clusters) is a unique type of linear nanostructure, which exhibits strong near-infrared absorption as their free electrons are confined in a one-dimensional quantum box. Little is known about the carrier dynamics in these nanoclusters, which limit their energy-related applications. Here, we reported the observation of exciton localization in triicosahedral Au37 nanoclusters (0.5 nm in diameter and 1.6 nm in length) by measuring femtosecond and nanosecond carrier dynamics. Upon photoexcitation to S1 electronic state, electrons in Au37 undergo ∼100-ps localization from the two vertexes of three icosahedrons to one vertex, forming a long-lived S1* state. Such phenomenon is not observed in Au25 (dimer) and Au13 (monomer) consisting of two and one icosahedrons, respectively. We have further observed temperature dependence on the localization process, which proves it is thermally driven. Two excited-state vibration modes with frequencies of 20 and 70 cm-1 observed in the kinetic traces are assigned to the axial and radial breathing modes, respectively. The electron localization is ascribed to the structural distortion of Au37 in the excited state induced by the strong coherent vibrations. The observed electron localization phenomenon provides unique physical insight into one-dimensional gold nanoclusters and other nanostructures, which will advance their applications in solar-energy storage and conversion.

Oxidation-Induced Transformation of Eight-Electron Gold Nanoclusters: [Au23(SR)16]- to [Au28(SR)20]0.

Here we report an oxidation-induced transformation of [Au23(S-c-C6H11)16]-TOA+ (S-c-C6H11: cyclohexanethiolate; TOA: tetraoctylammonium) to the [Au28(S-c-C6H11)20]0 nanocluster by H2O2 treatment under ambient conditions. This is the first example of oxidation-induced transformation of one stable size to another with atomic precision. The product was crystallized and analyzed by X-ray crystallography. Further insights into the transformation process were obtained by monitoring the process with optical spectroscopy and also by electrochemical analysis. This work adds a new dimension to the recently established transformation chemistry of nanoclusters that involves size and structure transformations.

Gold Nanoclusters Promote Electrocatalytic Water Oxidation at the Nanocluster/CoSe2 Interface.

Electrocatalytic water splitting to produce hydrogen comprises the hydrogen and oxygen evolution half reactions (HER and OER), with the latter as the bottleneck process. Thus, enhancing the OER performance and understanding the mechanism are critically important. Herein, we report a strategy for OER enhancement by utilizing gold nanoclusters to form cluster/CoSe2 composites; the latter exhibit largely enhanced OER activity in alkaline solutions. The Au25/CoSe2 composite affords a current density of 10 mA cm-2 at small overpotential of ∼0.43 V (cf. CoSe2: ∼0.52 V). The ligand and gold cluster size can also tune the catalytic performance of the composites. Based upon XPS analysis and DFT simulations, we attribute the activity enhancement to electronic interactions between nanocluster and CoSe2, which favors the formation of the important intermediate (OOH) as well as the desorption of oxygen molecules over Aun/CoSe2 composites in the process of water oxidation. Such an atomic level understanding may provide some guidelines for design of OER catalysts.

Facile Fabrication of Well-Dispersed Pt Nanoparticles in Mesoporous Silica with Large Open Spaces and Their Catalytic Applications.

In this paper, a facile strategy is reported for the preparation of well-dispersed Pt nanoparticles in ordered mesoporous silica (Pt@OMS) by using a hybrid mesoporous phenolic resin-silica nanocomposite as the parent material. The phenolic resin polymer is proposed herein to be the key in preventing the aggregation of Pt nanoparticles during their formation process and making contributions both to enhance the surface area and enlarge the pore size of the support. The Pt@OMS proves to be a highly active and stable catalyst for both gas-phase oxidation of CO and liquid-phase hydrogenation of 4-nitrophenol. This work might open new avenues for the preparation of noble metal nanoparticles in mesoporous silica with unique structures for catalytic applications.

Controlling the Atomic Structure of Au30 Nanoclusters by a Ligand-Based Strategy.

We report the X-ray structure of a gold nanocluster with 30 gold atoms protected by 18 1-adamantanethiolate ligands (formulated as Au30 (S-Adm)18 ). This nanocluster exhibits a threefold rotationally symmetrical, hexagonal-close-packed (HCP) Au18 kernel protected by six dimeric Au2 (SR)3 staple motifs. This new structure is distinctly different from the previously reported Au30 S(S-(t) Bu)18 nanocluster protected by 18 tert-butylthiolate ligands and one sulfido ligand with a face-centered cubic (FCC) Au22 kernel. The Au30 (S-Adm)18 nanocluster has an anomalous solubility (it is only soluble in benzene but not in other common solvents). This work demonstrates a ligand-based strategy for controlling nanocluster structure and also provides a method for the discovery of possibly overlooked clusters because of their anomalous solubility.

In situ loading of Ag(2)WO(4) on ultrathin g-C(3)N(4) nanosheets with highly enhanced photocatalytic performance.

The g-C3N4 nanosheets (g-C3N4NS) exhibit more excellent property than common bulk g-C3N4 (g-C3N4-B) due to their large surface areas, improved electron transport ability and well dispersion in water. In this work, ultrathin g-C3N4NS with a thickness of about 2.7nm have been synthesized by a simple thermal exfoliation of bulk g-C3N4, and then Ag2WO4 nanoparticles are in situ loaded on their surface to construct the Ag2WO4/g-C3N4NS heterostructured photocatalysts. Due to their unique physicochemical properties, the as-prepared heterostructures possess a fast interfacial charge transfer and increased lifetime of photo-excited charge carriers, and exhibit much higher photocatalytic activity. Under visible light irradiation, the optimum photocatalytic activity of Ag2WO4/g-C3N4NS composites is almost 53.6 and 26.5 times higher than that of pure g-C3N4-B and Ag2WO4/g-C3N4-B heterostructures towards the degradation of rhodamine B, respectively, and is almost 30.6 and 9.8 times higher towards the degradation of methyl orange, respectively. In addition, the natural sunlight photocatalytic activities of the as-prepared samples are also investigated.

Tri-icosahedral Gold Nanocluster [Au37(PPh3)10(SC2H4Ph)10X2](+): Linear Assembly of Icosahedral Building Blocks.

The [Au37(PPh3)10(SR)10X2](+) nanocluster (where SR = thiolate and X = Cl/Br) was theoretically predicted in 2007, but since then, there has been no experimental success in the synthesis and structure determination. Herein, we report a kinetically controlled, selective synthesis of [Au37(PPh3)10(SC2H4Ph)10X2](+) (counterion: Cl(-) or Br(-)) with its crystal structure characterized by X-ray crystallography. This nanocluster shows a rod-like structure assembled from three icosahedral Au13 units in a linear fashion, consistent with the earlier prediction. The optical absorption and the electrochemical and catalytic properties are investigated. The successful synthesis of this new nanocluster allows us to gain insight into the size, structure, and property evolution of gold nanoclusters that are based upon the assembly of icosahedral units (i.e., cluster of clusters). Some interesting trends are identified in the evolution from the monoicosahedral [Au13(PPh3)10X2](3+) to the bi-icosahedral [Au25(PPh3)10(SC2H4Ph)5X2](2+) and to the tri-icosahedral [Au37(PPh3)10(SC2H4Ph)10X2](+) nanocluster, which also points to the possibility of achieving even longer rod nanoclusters based upon assembly of icosahedral building blocks.

Sandwich-structured graphene-nickel silicate-nickel ternary composites as superior anode materials for lithium-ion batteries.

We report the synthesis of sandwich-structured graphene-nickel silicate-Ni ternary composites by using the solvothermal method followed by a simple in situ reduction procedure. The composites show an interesting structure with graphene sandwiched between two layers of well-dispersed Ni nanoparticles (NPs) anchored on ultrathin nickel silicate nanosheets. These ternary composites exhibit enhanced performance as anode materials owing to the synergistic effect between the graphene matrix and electrochemically inert Ni nanoparticles, an effect that holds promise for the design and fabrication of other advanced electrode materials.

Facile Synthesis of Hierarchical Magnesium Silicate Hollow Nanofibers Assembled by Nanosheets as an Efficient Adsorbent.

Magnesium silicate double-walled hollow nanofibers (MSHNFs) with a hierarchical nanostructure have been successfully fabricated by combining the electrospinning technique with a hydrothermal method. The as-prepared MSHNFs are composed of numerous ultrathin nanosheets with a thickness of approximately 10 nm and have a high specific surface area (632.2 m2 g-1 ) and large pore volume (0.92 cm3 g-1 ). The MSHNFs exhibit high adsorption capacity and excellent stability in a purification test with organic molecules and a solution of heavy-metal ions. Moreover, the MSHNFs can be easily separated from solution by gravitational sedimentation owing to their unique structure.

Preparation and enhanced visible light photocatalytic activity of novel g-C3N4 nanosheets loaded with Ag2CO3 nanoparticles.

As a potential visible-light photocatalyst, the photocatalytic performance of the bulk g-C3N4 synthesized by heating melamine (denote as g-C3N4-M) is limited due to its low specific surface area and the high recombination rate of the photo-induced electron-hole pair. In this paper, a novel g-C3N4-M nanosheet (g-C3N4-MN) obtained from the bulk g-C3N4-M through a thermal exploitation method is employed as an excellent substrate and different amounts of Ag2CO3 nanoparticles are loaded at room temperature. The phase and chemical structure, electronic and optical properties of the Ag2CO3/g-C3N4-MN heterostructures are well-characterized. The photocatalytic activities of the as-prepared Ag2CO3/g-C3N4-MN are evaluated by the degradation of methyl orange (MO) and rhodamine B (RhB) pollutants under visible light irradiation. More importantly, the Ag2CO3/g-C3N4-MN heterostructure has been proved to be an excellent photocatalytic system with an enhanced specific surface area and charge separation rate compared with those of the Ag2CO3/g-C3N4-M system.

In situ assembly of well-dispersed gold nanoparticles on hierarchical double-walled nickel silicate hollow nanofibers as an efficient and reusable hydrogenation catalyst.

Highly dispersive and ultrafine Au nanoparticles were effectively immobilized on the surface of hierarchical double-walled nickel silicate hollow nanofibers assembled by ultrathin nanosheets, which showed remarkable catalytic performances as an efficient and reusable hydrogenation catalyst.

Facile synthesis and properties of hierarchical double-walled copper silicate hollow nanofibers assembled by nanotubes.

The hierarchical assembly of multilevel, nonspherical hollow structures remains a considerable challenge. Here, we report a facile approach for synthesizing copper silicate hollow nanofibers with an ultrasmall nanotube-assembled, double-walled structure. The as-prepared hollow fibers possess a tailored complex wall structure, high length-to-diameter ratio, good structural stability, and a high surface area, and they exhibit excellent performance as an easily recycled adsorbent for wastewater treatment and as an ideal support for noble metal catalysts. In addition, this strategy can be extended as a general approach to prepare other double-walled, hollow, fibrous silica-templated materials.