Next-Generation Asymmetric Membranes Using Thin-Film Liftoff.

For the past 30 years, thin-film membrane composites have been the state-of-the-art technology for reverse osmosis, nanofiltration, ultrafiltration, and gas separation. However, traditional membrane casting techniques, such as phase inversion and interfacial polymerization, limit the types of material that are used for the membrane separation layer. Here, we describe a novel thin-film liftoff (T-FLO) technique that enables the fabrication of thin-film composite membranes with new materials for desalination, organic solvent nanofiltration, and gas separation. The active layer is cast separately from the porous support layer, allowing for the tuning of the thickness and chemistry of the active layer. A fiber-reinforced, epoxy-based resin is then cured on top of the active layer to form a covalently bound support layer. Upon submersion in water, the cured membrane lifts off from the substrate to produce a robust, freestanding, asymmetric membrane composite. We demonstrate the fabrication of three novel T-FLO membranes for chlorine-tolerant reverse osmosis, organic solvent nanofiltration, and gas separation. The isolable nature of support and active-layer formation paves the way for the discovery of the transport and selectivity properties of new polymeric materials. This work introduces the foundation for T-FLO membranes and enables exciting new materials to be implemented as the active layers of thin-film membranes, including high-performance polymers, two-dimensional materials, and metal-organic frameworks.

Three-dimensional holey-graphene/niobia composite architectures for ultrahigh-rate energy storage.

Nanostructured materials have shown extraordinary promise for electrochemical energy storage but are usually limited to electrodes with rather low mass loading (~1 milligram per square centimeter) because of the increasing ion diffusion limitations in thicker electrodes. We report the design of a three-dimensional (3D) holey-graphene/niobia (Nb2O5) composite for ultrahigh-rate energy storage at practical levels of mass loading (>10 milligrams per square centimeter). The highly interconnected graphene network in the 3D architecture provides excellent electron transport properties, and its hierarchical porous structure facilitates rapid ion transport. By systematically tailoring the porosity in the holey graphene backbone, charge transport in the composite architecture is optimized to deliver high areal capacity and high-rate capability at high mass loading, which represents a critical step forward toward practical applications.

Molecular ligand modulation of palladium nanocatalysts for highly efficient and robust heterogeneous oxidation of cyclohexenone to phenol.

Metallic nanoparticles are emerging as an exciting class of heterogeneous catalysts with the potential advantages of exceptional activity, stability, recyclability, and easier separation than homogeneous catalysts. The traditional colloid nanoparticle syntheses usually involve strong surface binding ligands that could passivate the surface active sites and result in poor catalytic activity. The subsequent removal of surface ligands could reactivate the surface but often leads to metal ion leaching and/or severe Ostwald ripening with diminished catalytic activity or poor stability. Molecular ligand engineering represents a powerful strategy for the design of homogeneous molecular catalysts but is insufficiently explored for nanoparticle catalysts to date. We report a systematic investigation on molecular ligand modulation of palladium (Pd) nanoparticle catalysts. Our studies show that ß-functional groups of butyric acid ligand on Pd nanoparticles can significantly modulate the catalytic reaction process to modify the catalytic activity and stability for important aerobic reactions. With a ß-hydroxybutyric acid ligand, the Pd nanoparticle catalysts exhibit exceptional catalytic activity and stability with an unsaturated turnover number (TON) >3000 for dehydrogenative oxidation of cyclohexenone to phenol, greatly exceeding that of homogeneous Pd(II) catalysts (TON, ~30). This study presents a systematic investigation of molecular ligand modulation of nanoparticle catalysts and could open up a new pathway toward the design and construction of highly efficient and robust heterogeneous catalysts through molecular ligand engineering.

Mechanically Shaped Two-Dimensional Covalent Organic Frameworks Reveal Crystallographic Alignment and Fast Li-Ion Conductivity.

Covalent organic frameworks (COFs) usually crystallize as insoluble powders, and their processing for suitable devices is thought to be limited. We demonstrate that COFs can be mechanically pressed into shaped objects having anisotropic ordering with preferred orientation between hk0 and 00l crystallographic planes. Five COFs with different functionality and symmetry exhibited similar crystallographic behavior and remarkable stability, indicating the generality of this processing. Pellets prepared from bulk COF powders impregnated with LiClO4 displayed room temperature conductivity up to 0.26 mS cm(-1) and high electrochemical stability. This outcome portends use of COFs as solid-state electrolytes in batteries.

Synthesis of Stable Shape-Controlled Catalytically Active ß-Palladium Hydride.

We have developed an efficient strategy for the production of stable ß-palladium hydride (PdH0.43) nanocrystals with controllable shapes and remarkable stability. The as-synthesized PdH0.43 nanocrystals showed impressive stability in air at room temperature for over 10 months, which has enabled the investigation of their catalytic property for the first time. The prepared PdH0.43 nanocrystals served as highly efficient catalysts in the oxidation of methanol, showing higher activity than their Pd counterparts. These studies opened a door for further exploration of ß-palladium hydride-based nanomaterials as a new class of promising catalytic materials and beyond.

Solution Processable Holey Graphene Oxide and Its Derived Macrostructures for High-Performance Supercapacitors.

Scalable preparation of solution processable graphene and its bulk materials with high specific surface areas and designed porosities is essential for many practical applications. Herein, we report a scalable approach to produce aqueous dispersions of holey graphene oxide with abundant in-plane nanopores via a convenient mild defect-etching reaction and demonstrate that the holey graphene oxide can function as a versatile building block for the assembly of macrostructures including holey graphene hydrogels with a three-dimensional hierarchical porosity and holey graphene papers with a compact but porous layered structure. These holey graphene macrostructures exhibit significantly improved specific surface area and ion diffusion rate compared to the nonholey counterparts and can be directly used as binder-free supercapacitor electrodes with ultrahigh specific capacitances of 283 F/g and 234 F/cm(3), excellent rate capabilities, and superior cycling stabilities. Our study defines a scalable pathway to solution processable holey graphene materials and will greatly impact the applications of graphene in diverse technological areas.

High Surface Area Tunnels in Hexagonal WO3.

High surface area in h-WO3 has been verified from the intracrystalline tunnels. This bottom-up approach differs from conventional templating-type methods. The 3.67 Å diameter tunnels are characterized by low-pressure CO2 adsorption isotherms with nonlocal density functional theory fitting, transmission electron microscopy, and thermal gravimetric analysis. These open and rigid tunnels absorb H(+) and Li(+), but not Na(+) in aqueous electrolytes without inducing a phase transformation, accessing both internal and external active sites. Moreover, these tunnel structures demonstrate high specific pseudocapacitance and good stability in an H2SO4 aqueous electrolyte. Thus, the high surface area created from 3.67 Å diameter tunnels in h-WO3 shows potential applications in electrochemical energy storage, selective ion transfer, and selective gas adsorption.

Metal-organic framework templated synthesis of ultrathin, well-aligned metallic nanowires.

With well-defined porous structures and dimensions, metal-organic frameworks (MOFs) can function as versatile templates for the growth of metallic nanostructures with precisely controlled shapes and sizes. Using MOFs as templates, metallic nanostructures can be grown without the need of bulky surfactants and thus preserve their intrinsic surface. Additionally, the high surface area of MOFs can also ensure that the surface of the template metallic nanostructures is readily accessible, which is critical for the proper function of catalysts or sensors. The hybrid metal@MOF structures have been demonstrated to exhibit useful properties not found in either component separately. Here we report the growth of ultrafine metallic nanowires inside one-dimensional MOF pores with well-controlled shape and size. Our study shows that solvent selection plays an important role in controlling precursor loading and the reduction rate inside the MOF pores for the formation of the nanowires. The growth of the well-aligned, ultrathin nanowires was monitored and characterized by transmission electron microscopy, X-ray diffraction, UV-vis spectroscopy, fluorescence studies, and Brunauer-Emmet-Teller surface area analysis.

A rational biomimetic approach to structure defect generation in colloidal nanocrystals.

Controlling the morphology of nanocrystals (NCs) is of paramount importance for both fundamental studies and practical applications. The morphology of NCs is determined by the seed structure and the following facet growth. While means for directing facet formation in NC growth have been extensively studied, rational strategies for the production of NCs bearing structure defects in seeds have been much less explored. Here, we report mechanistic investigations of high density twin formation induced by specific peptides in platinum (Pt) NC growth, on the basis of which we derive principles that can serve as guidelines for the rational design of molecular surfactants to introduce high yield twinning in noble metal NC syntheses. Two synergistic factors are identified in producing twinned Pt NCs with the peptide: (1) the altered reduction kinetics and crystal growth pathway as a result of the complex formation between the histidine residue on the peptide and Pt ions, and (2) the preferential stabilization of {111} planes upon the formation of twinned seeds. We further apply the discovered principles to the design of small organic molecules bearing similar binding motifs as ligands/surfactants to create single and multiple twinned Pd and Rh NCs. Our studies demonstrate the rich information derived from biomimetic synthesis and the broad applicability of biomimetic principles to NC synthesis for diverse property tailoring.

Novel epoxide formation in the reaction of 2-bromo-3-methyl-1,4-naphthoquinone with 1,3-propanedithiol.

A novel epoxide 2 was formed as the major product in the reaction of 2-bromo-3-methyl-1,4-naphthoquinone with 1,3-propanedithiol in the presence of triethylamine in 92% yield. Molecular oxygen is suggested to be the source of the added oxygen in 2, an oxidation product of its precursor 3. A strong base such as triethylamine is required to abstract the methyl hydrogen of 1,4-naphthoquinones, leading to the formation of 3 as well as 2.

Metal insertion in a microporous metal-organic framework lined with 2,2'-bipyridine.

Reaction of AlCl(3)·6H(2)O with 2,2'-bipyridine-5,5'-dicarboxylic acid (H(2)bpydc) affords Al(OH)(bpydc) (1, MOF-253), the first metal-organic framework with open 2,2'-bipyridine (bpy) coordination sites. The material displays a BET surface area of 2160 m(2)/g and readily complexes metals to afford, for example, 1·xPdCl(2) (x = 0.08, 0.83) and 1·0.97Cu(BF(4))(2). EXAFS spectroscopy performed on 1·0.83PdCl(2) reveals the expected square planar coordination geometry, matching the structure of the model complex (bpy)PdCl(2). Significantly, the selectivity factor for binding CO(2) over N(2) under typical flue gas conditions is observed to increase from 2.8 in 1 to 12 in 1·0.97Cu(BF(4))(2).

Ring-opening reactions within porous metal-organic frameworks.

Two new metal-organic framework (MOF) structures, IRMOF-3b and -3c, were prepared by ring-opening reaction of 1,3-propanesultone and 2-methylaziridine with an amine functionalized MOF, IRMOF-3. The new structures are permanently functionalized with covalently linked sulfonate and alkyamine units, respectively. The underlying framework structure is retained after reaction as confirmed by powder X-ray diffraction. The high porosity of IRMOF-3 is also maintained, as evidenced by nitrogen adsorption experiments, which yield Brunauer-Emmett-Teller (BET) surface areas of 1380 and 530 m(2) g(-1) compared to 2040 m(2) g(-1) in the parent material. Ring-opening reactions provide a versatile route to irreversible binding of a range of functionalities that are otherwise difficult to access in MOFs.