Hydrogen released from chemical hydride ammonia borane (AB, NH3BH3) can be greatly improved when AB is confined in metal–organic frameworks (MOFs), showing reduced decomposition temperature and suppressed unwanted byproducts. However, it is still debatable whether the mechanism of improved AB dehydrogenation is due to catalysis or nanosize. In this research, selected MOFs (IRMOF-1, IRMOF-10, UiO-66, UiO-67, and MIL-53­(Al)) were chosen to explore both catalytic effect of the metal clusters and the manipulation of pore size for nanoconfinement by variations in ligand length. When AB particle size was restricted by the controlled micropores of MOFs, we observed that the decomposition temperature was not correlated to the MOF catalytic environment, but inversely proportional to the reciprocal of the particle size. The results correspond well with the derived thermodynamic model for AB decomposition considering surface tension of nanoparticles.

Although there have been intense efforts to fabricate large three-dimensional photonic crystals in order to realize their full potential, the technologies developed so far are still beset with various material processing and cost issues. Conventional top-down fabrications are costly and time-consuming, whereas natural self-assembly and bottom-up fabrications often result in high defect density and limited dimensions. Here we report the fabrication of extraordinarily large monocrystalline photonic crystals by controlling the self-assembly processes which occur in unique phases of liquid crystals that exhibit three-dimensional photonic-crystalline properties called liquid-crystal blue phases. In particular, we have developed a gradient-temperature technique that enables three-dimensional photonic crystals to grow to lateral dimensions of ~1 cm (~30,000 of unit cells) and thickness of ~100 μm (~ 300 unit cells). These giant single crystals exhibit extraordinarily sharp photonic bandgaps with high reflectivity, long-range periodicity in all dimensions and well-defined lattice orientation.

Photonic nanostructures that realize ultrafast switching of light polarization are essential to advancements in the area of optical information processing. The unprecedented flexibility of metasurfaces in light manipulation makes them a promising candidate for active polarization control. However, due to the lack of optical materials exhibiting a fast as well as large refractive index change, photonic metadevices capable of ultrafast polarization switching remain elusive. Here, an ultrathin nonlinear chiral meta-mirror consisting of an array of amorphous silicon (α-Si) split-ring resonators on top of a silver backplane is demonstrated as a feasible platform for picosecond all-optical polarization switching of near-infrared light at picojoule-per-resonator pump energies. This success was made possible by the high-quality-factor resonances of the proposed meta-atoms that enable the mirror to exhibit strong chiro- and enantioselectivity. Experimental results confirm that our meta-mirrors can be used to facilitate high-speed and power-efficient polarization-state modulators.

The stability of three metal-organic frameworks (MOFs), namely IRMOF-8, Cu-TDPAT, and Cu-BTC, was tested after incorporation of Pt. Stability was assessed with powder X-ray diffraction (PXRD), physical (N 2 at 77 K) and chemical (H 2 at 300 K) adsorption, and thermogravimetric analysis in H 2 and N 2. Introduction of Pt via wet precipitation led to MOF degradation during the H 2 reduction step. Addition of pre-reduced Pt supported on activated carbon (Pt/AC) to MOFs via physical mixing also led to structural degradation. However, addition of Pt/AC via a "pre-bridge" (PB) technique led to high MOF stability, with retention of surface area, porosity, crystallinity, and thermal stability. The catalytically active surface area was assessed by hydrogen adsorption, and demonstrated extension of the catalytically active surface area to the MOF surface. High hydrogen uptake correlated with MOF particle size, due to the connectivity between Pt/AC and MOF, and the interpenetration of Pt/AC into the MOF crystal.