Boosting Hydrostability and Carbon Dioxide Capture of Boroxine-Linked Covalent Organic Frameworks by One-Pot Oligoamine Modification.

Boron-based covalent organic frameworks (COFs) are susceptible to nucleophilic attack by water at the electron-deficient boron sites and even slightly humid air could destroy the integrity of their porous frameworks within hours. Such instability is a major limitation to the practical applications of boron-based COFs. Herein we report a significant enhancement of hydrostability of boroxine-linked COFs (COF-1 as representative) by modification with an oligoamine (tetraethylenepentamine, TEPA), which leads to survival of the modified COF in water and long-time stability under humid atmosphere. Meanwhile, the TEPA modification also results in a considerable increase in CO2 adsorption capacity up to 13 times and a dramatic improvement in CO2 /N2 selectivity in low pressure region, which make the modified COF suitable for capturing CO2 from flue gas. This work provides a facile, efficient, and scalable method to greatly improve hydrostability of boroxine-linked COFs and reshape them into high-performance CO2 adsorbents.

Two-dimensional covalent organic frameworks with hierarchical porosity.

Covalent organic frameworks (COFs) are a class of crystalline porous organic polymers assembled by connecting organic building units via covalent bonds. They are characterized as extended two-dimensional (2D) or three-dimensional (3D) frameworks with precise spatial structures and building block distribution. A key feature of COFs is their inherent porosity originating from their well-ordered nanopores which are designable, tunable and modifiable through pore engineering. This review describes the pore engineering of 2D COFs based on their framework topologies. It begins with a brief summary of the pore design principles of 2D COFs which are composed of uniform micropores or mesopores. Then the state-of-the-art progress achieved in a new branch of 2D COFs, that is, heteropore COFs, which possess multiple-pore skeletons and thus exhibit hierarchical porosity, is comprehensively reviewed, including their design strategies, synthesis, characterization, properties and applications. In the last part, personal perspectives on this emerging class of 2D polymers with complex structures and hierarchical porosity are discussed.

Aminal-Linked Covalent Organic Frameworks through Condensation of Secondary Amine with Aldehyde.

New linkage chemistry will endow covalent organic frameworks (COFs) with not only structural diversity but also fascinating properties. However, to develop a new type of linkages has been a great challenge. We herein report the first two COFs using aminal as the linkages. These two COFs have been synthesized by condensation of secondary amine and aldehyde. They crystallize in cpi net, which is a new topology for COFs. The aminal linkage is found to favor reservation of photophysical property of the monomers due to its tetrahedral geometry and nonconjugated feature. These aminal-COFs exhibit good thermal stability and high chemical stability under neutral and basic conditions.

Creating amphiphilic porosity in two-dimensional covalent organic frameworks via steric-hindrance-mediated precision hydrophilic-hydrophobic microphase separation.

Creating different pore environments within a covalent organic framework (COF) will lead to useful multicompartment structure and multiple functions, which however has been scarcely achieved. Herein we report designed synthesis of three two-dimensional COFs with amphiphilic porosity by steric-hindrance-mediated precision hydrophilic-hydrophobic microphase separation. Dictated by the different steric effect of the substituents introduced to a monomer, dual-pore COFs with kgm net, in which all hydroxyls locate in trigonal micropores while hydrophobic sidechains exclusively distribute in hexagonal mesopores, have been constructed to form completely separated hydrophilic and hydrophobic nanochannels. The unique amphiphilic channels in the COFs enable the formation of Janus membranes via interface growth. This work has realized the creation of two types of channels with opposite properties in one COF, demonstrating the feasibility of introducing different properties/functions into different pores of heteropore COFs, which can be a useful strategy to develop multifunctional materials.

A gaseous hydrogen chloride chemosensor based on a 2D covalent organic framework.

A tetraphenylethene-based 2D covalent organic framework (COF) has been synthesized. It exhibits a very fast response and high sensitivity to the presence of gaseous HCl by way of distinct changes in fluorescence emission and color, which makes the COF a good chemosensor for spectroscopic and naked-eye detection of gaseous HCl.