Schematic of analysis of the forces acting on a sand particle.

<p>Particles B and C are the supporting sand particles on the bed surface.</p

Tailor-Made Pore Surface Engineering in Covalent Organic Frameworks: Systematic Functionalization for Performance Screening

Imine-linked covalent organic frameworks (COFs) were synthesized to bear content-tunable, accessible, and reactive ethynyl groups on the walls of one-dimensional pores. These COFs offer an ideal platform for pore-wall surface engineering aimed at anchoring diverse functional groups ranging from hydrophobic to hydrophilic units and from basic to acidic moieties with controllable loading contents. This approach enables the development of various tailor-made COFs with systematically tuned porosities and functionalities while retaining the crystallinity. We demonstrate that this strategy can be used to efficiently screen for suitable pore structures for use as CO₂ adsorbents. The pore-surface-engineered walls exhibit an enhanced affinity for CO₂, resulting in COFs that can capture and separate CO₂ with high performance

The critical starting friction wind velocity for sand grains of different shape.

<p>(a). Comparison of the critical starting friction wind velocity of non-spherical particles with that of spherical particles (equivalent diameter ). (b). Comparison of the critical starting friction wind velocity of non-spherical particles with that of spherical particles (equivalent diameter ). The black solid line indicates the spherical sand grains, and represent two different ellipsoid-shaped sand particles, represents cube-shaped sand particles, and are two types of cylinder-shaped sand particles, and represents frustum-shaped sand particles.</p

The drag coefficient of sand particles as a function of the Reynolds number.

<p>The relationship of the drag coefficient of sand grains of different shape to the Reynolds number is shown. Here, the black solid line indicates spherical sand grains, and are two different ellipsoid-shaped sand particles, represents cube-shaped sand particles, and represent two types of cylinder-shaped sand particles, and represents frustum-shaped sand particles.</p

The sand transport rate per width for sand particles of different shape.

<p>(a). Comparison of calculated sand transport rates per width for different shapes sand particles with equivalent diameters of with experimental data. (b). Comparison of calculated sand transport rates per width for sand particles of different shape with equivalent diameters of with experimental data. The black solid line indicates spherical sand grains, and are two different ellipsoid-shaped sand particles, represents cube-shaped sand particles, and are two types of cylinder-shaped sand particles, and represents frustum-shaped sand particles.</p

Parameters of sand particles with different shapes.

<p>where and are two different ellipsoid-shaped sand particles, represents cube-shaped sand particles, and represent two types of cylinder-shaped sand particles, and represents frustum-shaped sand particles.</p><p>Parameters of sand particles with different shapes.</p

The drag force of different shaped particles with height.

<p>All the sand particles of different shapes take off with the same horizontal initial velocity of and vertical initial velocity of . The black solid line indicates spherical sand grains, and are two different ellipsoid-shaped sand particles, represents cube-shaped sand particles, and are two types of cylinder-shaped sand particles, and represents frustum-shaped sand particles.</p

The sand transport rates of sand particles with different shapes as a function of height.

<p>(a) and (b) show the sand transport rates of sand particles with the same equivalent diameter of as a function of height but at different friction wind velocities. (c), (d) and (e) represent the sand transport rates of sand particles with the same equivalent diameter of as a function of height but at different friction wind velocities. Here, the black solid line indicates the spherical sand grains, and are two different ellipsoid-shaped sand particles, represents cube-shaped sand particles, and are two types of cylinder-shaped sand particles, and represents frustum-shaped sand particles.</p

Carborane-Based Three-Dimensional Covalent Organic Frameworks

The predesignable porous structure and high structural flexibility of covalent organic frameworks (COFs) render this material desirable as a platform for addressing various cutting-edge issues. Precise control over their composition, topological structure, porosity, and stability to realize tailor-made functionality still remains a great challenge. In this work, we developed a new kind of three-dimensional (3D) carborane-based COF with a 7-fold interpenetrating dia topological diagram. The resulting COFs exhibited high crystallinity, exceptional porosity, and strong robustness. The slightly lower electronegativity of boron (2.04) than that of hydrogen (2.20) can lead to the polarization of the B–H bond into a Bδ+–Hδ− mode, which renders these COFs as high-performance materials for the adsorption and separation of hexane isomers through the B–Hδ−···Hδ+–C interaction. Significantly, the carborane content of obtained COFs reached up to 54.2 wt %, which gets the highest rank among all the reported porous materials. Combining high surface area, strong robustness, and high content of carborane, the obtained COFs can work as efficient adsorbents for the separation of the five hexane isomers with high separation factors. This work not only enhances the diversity of 3D functional COFs but also constitutes a further step toward the efficient separation of alkane isomers