An unprecedented fully reduced {MoV 60} polyoxometalate: from an all-inorganic molecular light-absorber model to improved photoelectronic performance.

Fully reduced polyoxometalates are predicted to give rise to a broad and strong absorption spectrum, suitable energy levels, and unparalleled electronic and optical properties. However, they are not available to date. Here, an unprecedented fully reduced polyoxomolybdate cluster, namely Na8[MoV 60O140(OH)28]·19H2O {MoV 60}, was successfully designed and obtained under hydrothermal conditions, which is rare and is the largest fully reduced polyoxometalate reported so far. The MoV 60 molecule describes one Keggin {ε-Mo12} encapsulated in an unprecedented {Mo24} cage, giving rise to a double truncated tetrahedron quasi-nesting architecture, which is further face-capped by another four {Mo6} tripods. Its crystalline stability in air, solvent tolerance, and photosensitivity were all shown. As a cheap and robust molecular light-absorber model possessing wide light absorption, MoV 60 was applied to build a co-sensitized solar cell photoelectronic device along with N719 dyes and the optimal power conversion efficiency was 28% higher than that of single-dye sensitization. These results show that MoV 60 polyoxometalate could serve as an ideal model for the design and synthesis of all-inorganic molecular light-absorbers for other light-driven processes in the future.

Porous Aromatic Framework Nanosheets Anchored with Lewis Pairs for Efficient and Recyclable Heterogeneous Catalysis.

Lewis pairs (LPs) with outstanding performance for nonmetal-mediated catalysis reactions have high fundamental interest and remarkable application prospects. However, their solubility characteristics lead to instability and deactivation upon recycling. Here, the layered porous aromatic framework (PAF-6), featuring two kinds of Lewis base sites (NPiperazine and NTriazine), is exfoliated into few-layer nanosheets to form the LP entity with the Lewis acid. After comparison with various porous networks and verification by density functional theory (DFT) calculations, the NTriazine atom in the specific spatial environment is determined to preferably coordinate with the electron-deficient boron compound in a sterically hindered pattern. LP-bare porous product displays high catalytic activity for the hydrogenation of both olefin and imine compounds, and demonstrates ≈100% activity after 10 successful cycles in hydrogenation reactions. Considering the natural advantage of porous organic frameworks to construct LP groups opens up novel prospects for preparing other nonmetallic heterogeneous catalysts for efficient and recyclable catalysis.

Porous Organic Frameworks Featured by Distinct Confining Fields for the Selective Hydrogenation of Biomass-Derived Ketones.

The asymmetric hydrogenation of biomass-derived molecules for the preparation of single enantiomer compounds is an effective method to reduce the rapid consumption of fossil resources. Porous organic frameworks (POFs) with pure organic surfaces may provide unusual confinement effects for organic substrates in chiral catalysis. Here, a series of POF catalysts are designed with chiral active centers decorated into sharply defined one-dimensional channels with diameters in the range of 1.2-2.9 nm. Due to the synergistic effect originating from the conjugated inner wall, the POF material (aperture size 2.4 nm) concentrates over 90% of aromatic species into the porous architecture, and its affinity is one or two orders of magnitude higher than those of classical porous solids. As determined by PBE+D3 calculation, the phenyl fragment reveals strong π-π interaction for steric hindrance around the metal active site to achieve stronger asymmetric induction. Therefore, this POF catalyst achieves high conversion (>99% yield) and enantioselectivity (>99% ee) for various substrates. The advantages of using the POF platform as a chiral catalyst can provide new perspectives on POF-based solid-state host-guest chemistry and asymmetric heterogeneous catalysis.

Harnessed Dopant Block Copolymers Assist Decorating Membrane Pores: A Dissipative Particle Dynamics Study.

Self-assembly of asymmetric block copolymers (BCPs) around active pore edges has emerged as an important strategy to produce smart membranes with tunable pathways for solute transport. However, thus far, it is still challenging to manipulate pore shape and functionality for directional transformation under external stimuli. Here, a versatile strategy by mesoscale simulations to design stimuli-responsive pores with various edge decorations in hybrid membranes is reported. Dopant BCPs are used as decorators to stabilize pore edges and extend their function in reconfiguring pores in response to repeated membrane stretching/shrinking caused by external stimuli. The decoration morphologies are predictable since the assemblies of dopant BCPs around pore edges are closely related to their self-assemblies in solution. The coassembly between different BCPs in the hybrid membrane for the control of pore morphology is featured, and the parameter settings, including block incompatibility and molecular architecture for the construction of a specific pore, are determined. Results show that harnessed dopant BCPs in the hybrid membrane can enhance pore formation and induce directional pore shape and functionality transformation. Diversified pore decorations exhibit potential that can be further explored in selective solute transport and the design of stimuli-responsive smart nanodevices.

A Molecular Coordination Template Strategy for Designing Selective Porous Aromatic Framework Materials for Uranyl Capture.

Uranium capture from seawater could solve increasing energy demand and enable a much needed relaxing from fossil fuels. Low concentration (∼3 ppb), competing cations (especially vanadium) and pH-dependent speciation prohibit highly efficient uranium uptake. Despite intensive research, selective extraction of uranyl ions over vanadyl units remains a tremendous challenge. Here, we adopted a molecular coordination template strategy to design a uranyl-specific bis-salicylaldoxime entity and decorated it into a highly porous aromatic framework (PAF-1) by programmable assembly. The superstructure (MISS-PAF-1) gives a strong affinity that removes 99.97% of uranium in 120 min. Notably, it binds to the uranyl ion at least 100 times more selectively than 14 different cations tested, including the vanadyl ion, in simulated seawater at ambient pH. Real seawater samples collected from the Bohai Sea achieve 5.79 mg g-1 of uranium capacity over 56 days without PAF degradation, exceeding a 4-fold higher amount than commercial adsorbents.

Surface Pore Engineering of Covalent Organic Frameworks for Ammonia Capture through Synergistic Multivariate and Open Metal Site Approaches.

Ammonia (NH3) is a commonly used industrial gas, but its corrosiveness and toxicity are hazardous to human health. Although many adsorbents have been investigated for NH3 sorption, limited ammonia uptake remains an urgent issue yet to be solved. In this article, a series of multivariate covalent organic frameworks (COFs) are explored which are densely functionalized with various active groups, such as -N-H, -C=O, and carboxyl group. Then, a metal ion (Ca2+, Mn2+, and Sr2+) is integrated into the carboxylated structure achieving the first case of an open metal site in COF architecture. X-ray photoelectron spectroscopy reveals conclusive evidence for the multiple binding interactions with ammonia in the modified COF materials. Infrared spectroscopy indicates a general trend of binding capability from weak to strong along with -N-H, -C=O, carboxyl group, and metal ion. Through the synergistic multivariate and open metal site, the COF materials show excellent adsorption capacities (14.3 and 19.8 mmol g-1 at 298 and 283 K, respectively) and isosteric heat (Qst) of 91.2 kJ mol-1 for ammonia molecules. This novel approach enables the development of tailor-made porous materials with tunable pore-engineered surface for ammonia uptake.

Atomistic modeling of La3+ doping segregation effect on nanocrystalline yttria-stabilized zirconia.

The effect of La3+ doping on the structure and ionic conductivity change in nanocrystalline yttria-stabilized zirconia (YSZ) was studied using a combination of Monte Carlo and molecular dynamics simulations. The simulation revealed the segregation of La3+ at eight tilt grain boundary (GB) structures and predicted an average grain boundary (GB) energy decrease of 0.25 J m-2, which is close to the experimental values reported in the literature. Cation stabilization was found to be the main reason for the GB energy decrease, and energy fluctuations near the grain boundary are smoothed out with La3+ segregation. Both dynamic and energetic analysis on the Σ13(510)/[001] GB structure revealed La3+ doping hinders O2- diffusion in the GB region, where the diffusion coefficient monotonically decreases with increasing La3+ doping concentration. The effect was attributed to the increase in the site-dependent migration barriers for O2- hopping caused by segregated La3+, which also leads to anisotropic diffusion at the GB.

A quantum chemistry study of curvature effects on boron nitride nanotubes/nanosheets for gas adsorption.

Quantum chemistry calculations were performed to investigate the effect of the surface curvature of a Boron Nitride (BN) nanotube/nanosheet on gas adsorption. Curved boron nitride layers with different curvatures interacting with a number of different gases including noble gases, oxygen, and water on both their convex and concave sides of the surface were studied using density functional theory (DFT) with a high level dispersion corrected functional. Potential energy surfaces of the gas molecules interacting with the selected BN surfaces were investigated. In addition, the charge distribution and electrostatic potential contour of the selected BN surfaces are discussed. The results reveal how the curvature of the BN surfaces affects gas adsorption. In particular, small curvatures lead to a slight difference in the physisorption energy, while large curvatures present distinct potential energy surfaces, especially for the short-range repulsion.

Large-scale fabrication of nanodimple arrays for surface-enhanced Raman scattering.

Here we report a simple bottom-up technology for scalably fabricating gold nanodimple arrays with tunable nanostructures for surface-enhanced Raman scattering (SERS). Double-layer silica colloidal crystal-polymer nanocomposites with an unusual non-close-packed structure created using a spin-coating technique are utilized as structural templates. A variety of nanodimple structures, including simple monolayer voids, nanoring-like nanodimples, and binary-void nanodimples, can be reproducibly templated over wafer-sized areas by simply controlling the conditions during an oxygen plasma etching process. Normal-incidence specular reflection measurements show that the resulting gold nanodimple arrays exhibit tunable surface plasmon properties. The efficient electromagnetic coupling between neighboring nanodimples and inner-outer walls of nanoring-like nanodimples leads to high SERS enhancement factors (>10(8)). Numerical simulations based on a finite-difference time-domain model complement the experimental measurements, showing the spatial distribution of electromagnetic "hot spots" surrounding the periodic gold nanodimple arrays.