Growth of High‐Quality,Thickness‐Reduced Zeolite Membranes towards N2/CH4 Separation Using High‐Aspect‐Ratio Seeds

Greatly improved zeolite membranes were prepared by using high‐aspect‐ratio zeolite seeds. Slice‐shaped seeds with a high aspect ratio (AR) facilitated growth of thinner continuous SAPO‐34 membranes of much higher quality. These membranes showed N₂ permeances as high as (2.87±0.15)×10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ at 22 °C while maintaining a decent N₂/CH₄ selectivity (9–11.2 for equimolar mixture). On the basis of these thinner high‐quality SAPO‐34 membranes, fine‐tuning the local crystal structure by incorporating more silicon further increased the N₂ permeance by 1.4 times without sacrificing the N₂/CH₄ selectivity. We expect that application of large AR zeolite seeds might be a viable strategy to grow thin high‐quality zeolite membranes. In addition, fine‐tuning of the crystal structure by changing the crystal composition might be a feasible way for further improving the separating performance of high‐quality zeolite membranes.     

Cesium's Off‐the‐Map Valence Orbital

The T_d ‐symmetric [CsO₄]⁺ ion, featuring Cs in an oxidation state of 9, is computed to be a minimum. Cs uses outer core 5s and 5p orbitals to bind the oxygen atoms. The valence Cs 6s orbital lies too high to be involved in bonding, and contributes to Rydberg levels only. From a molecular orbital perspective, the bonding scheme is reminiscent of XeO₄: an octet of electrons to bind electronegative ligands, and no low‐lying acceptor orbitals on the central atom. In this sense, Cs⁺ resembles hypervalent Xe.     

Understanding Hydrogen Bonding Interactions in Crosslinked Methylammonium Lead Iodide Crystals: Towards Reducing Moisture and Light Degradation Pathways

Methylammonium lead halide perovskite‐based solar cells have demonstrated efficiencies as high as 24.2 %, highlighting their potential as inexpensive and solution‐processable alternatives to silicon solar cell technologies. Poor stability towards moisture, ultraviolet irradiation, heat, and a bias voltage of the perovskite layer and its various device interfaces limits the commercial feasibility of this material for outdoor applications. Herein, we investigate the role of hydrogen bonding interactions induced when metal halide perovskite crystals are crosslinked with alkyl or π‐conjugated boronic acid small molecules (‐B(OH)₂). The crosslinked perovskite crystals are investigated under continuous light irradiation and moisture exposure. These studies demonstrate that the origin of the interaction between the alkyl or π‐conjugated crosslinking molecules is due to hydrogen bonding between the ‐B(OH)₂ terminal group of the crosslinker and the I of the [PbI₆]^4? octahedra of the perovskite layer. Also, this interaction influences the stability of the perovskite layer towards moisture and ultraviolet light irradiation. Morphology and structural analyses, as well as IR studies as a function of aging under both dark and light conditions show that π‐conjugated boronic acid molecules are more effective crosslinkers of the perovskite crystals than their alkyl counterparts thus imparting better stability towards light and moisture degradation.