Review: 117 refs.

Highly porous, strong aerogels with anisotropic structural properties are of great interest for multifunctional materials for applications including insulators in buildings, filters for oil cleanup, electrical storage devices, etc . Contemporary aerogels are mostly extracted from fossil resources and synthesized from bottom-up techniques, often requiring additional strategies to obtain high anisotropy. In this work, a universal approach to prepare porous, strong, anisotropic aerogels is presented through exploiting the natural hierarchical and anisotropic structure of wood. The preparation comprises nanoscale removal of lignin, followed by dissolution–regeneration of nanofibers, leading to enhanced cell wall porosity with nanofibrillated networks occupying the pore space in the cellular wood structure. The aerogels retain structural anisotropy of natural wood, exhibit specific surface areas up to 247 m 2 /g, and show high compression strength at 95% porosity. This is a record specific area value for wood aerogels/foams and even higher than most cellulose-based aerogels for its assigned strength. The aerogel can serve as a platform for multifunctional composites including scaffolds for catalysis, gas separation, or liquid purification due to its porous matrix or as binder-free electrodes in electronics. To demonstrate the multifunctionality, the aerogels are successfully decorated with metal nanoparticles (Ag) and metal oxide nanoparticles (TiO 2 ) by in situ synthesis, coated by the conductive polymer (PEDOT:PSS), and carbonized to yield conductive aerogels. This approach is found to be a universal way to prepare highly porous anisotropic aerogels.

Bismuth subgallate has been used in wound and gastrointestinal therapy for over a century. The combination of continuous rotation electron diffraction and sample cooling finally revealed its structure as a coordination polymer. The structure provides insight regarding its formula, poor solubility, acid resistance and previously unreported gas sorption properties.

No abstract

Zeolites with appropriately narrow pore apertures can kinetically enhance the selective adsorption of CO 2 over N 2 . Here, we showed that the exchangeable cations (e.g., Na + or K + ) on zeolite ZK-4 play an important role in the CO 2 selectivity. Zeolites NaK ZK-4 with Si/Al = 1.8–2.8 had very high CO 2 selectivity when an intermediate number of the exchangeable cations were K + (the rest being Na + ). Zeolites NaK ZK-4 with Si/Al = 1.8 had high CO 2 uptake capacity and very high CO 2 -over-N 2 selectivity (1190). Zeolite NaK ZK-4 with Si/Al = 2.3 and 2.8 also had enhanced CO 2 selectivity with an intermediate number of K + cations. The high CO 2 selectivity was related to the K + cation in the 8-rings of the α-cage, together with Na + cations in the 6-ring, obstructing the diffusion of N 2 throughout the zeolite. The positions of the K + cation in the 8-ring moved slightly (max 0.2 Å) toward the center of the α-cage upon the adsorption of CO 2 , as revealed by in situ X-ray diffraction. The CO 2 -over-N 2 selectivity was somewhat reduced when the number of K + cations approached 100%. This was possibly due to the shift in the K + cation positions in the 8-ring when the number of Na + was going toward 0%, allowing N 2 diffusion through the 8-ring. According to in situ infrared spectroscopy, the amount of chemisorbed CO 2 was reduced on zeolite ZK-4s with increasing Si/Al ratio. In the context of potential applications, a kinetically enhanced selection of CO 2 could be relevant for applications in carbon capture and bio- and natural gas upgrading.