Triazine functionalized porous covalent organic framework for photo-organocatalytic E–Z isomerization of olefins

Visible light-mediated photocatalytic organic transformation has drawn significant attention as an alternative process for replacing thermal reactions. Although precious metal/organic dyes based homogeneous photocatalysts have been developed, their toxic and nonreusable nature makes them inappropriate for large-scale production. Therefore, we have synthesized a triazine and a keto functionalized nonmetal based covalent organic framework (TpTt) for heterogeneous photocatalysis. As the catalyst shows significant absorption of visible light, it has been applied for the photocatalytic uphill conversion of trans-stilbene to cis-stilbene in the presence of blue light-emitting diodes with broad substrate scope via an energy transfer process

Pore engineering of ultrathin covalent organic framework membranes for organic solvent nanofiltration and molecular sieving

The advantages of two dimensional covalent organic framework membranes to achieve high flux have been demonstrated, but the capability of easy structural modification to manipulate the pore size has not been fully explored yet. Here we report the use of the Langmuir–Blodgett method to synthesize two ultrathin covalent organic framework membranes (TFP–DPF and TFP–DNF) that have a similar framework structure to our previously reported covalent organic framework membrane (TFP–DHF) but different lengths of carbon chains aiming to rationally control the pore size. The membrane permeation results in the applications of organic solvent nanofiltration and molecular sieving of organic dyes showed a systematic shift of the membrane flux and molecular weight cut-off correlated to the pore size change. These results enhanced our fundamental understanding of transport through uniform channels at nanometer scales. Pore engineering of the covalent organic framework membranes was demonstrated for the first time

Two-dimensional amine and hydroxy functionalized fused aromatic covalent organic framework

Ordered two-dimensional covalent organic frameworks (COFs) have generally been synthesized using reversible reactions. It has been difficult to synthesize a similar degree of ordered COFs using irreversible reactions. Developing COFs with a fused aromatic ring system via an irreversible reaction is highly desirable but has remained a significant challenge. Here we demonstrate a COF that can be synthesized from organic building blocks via irreversible condensation (aromatization). The as-synthesized robust fused aromatic COF (F-COF) exhibits high crystallinity. Its lattice structure is characterized by scanning tunneling microscopy and X-ray diffraction pattern. Because of its fused aromatic ring system, the F-COF structure possesses high physiochemical stability, due to the absence of hydrolysable weak covalent bonds

Ultra-stable imine-based covalent organic frameworks for sulfuric acid recovery: an effect of interlayer hydrogen bonding

Covalent Organic Frameworks (COFs) have convened inordinate scientific attention from last few years because of their unique tunable porosity and long range ordered structures with high atomic precisions. Although the high crystalline nature with considerable porosity fashioned these novel materials as an eligible candidate for diverse applications, the ordered nano-channels with controllable pore aperture, especially regarding membrane separations in extreme conditions, have been poorly explored. Herein, we have demonstrated rapid and scalable synthesis of six new imine-linked highly crystalline and porous COFs via salt (p-toluenesulfonic acid) mediated solid state crystallization approach. These as-synthesized materials show exceptionally high chemical stability in harsh environments including conc. H2SO4 (36 N), conc. HCl (12 N) and NaOH (9N). This is exclusivly because of the presence of strong interlayer C–H***N H-bonding interactions among the individual layers. This H-bonding reinforce interlayer stacking interaction and provides a steric hindrance and hydrophobic environ-ment around the imine (–C=N) bonds making it safe from hydrolysis, as confirmed by Density Functional Theory (DFT) calculations. By taking advantage of processability of COF powders in salt mediated synthesis approach, the continuous, porous, crystalline, self-standing and crack-free COF membranes (COFMs) with high chemical stability have been transmut-ed, for their potential applications to separate various environmentally toxic materials from drinking water with high water flux. Moreover, owing to its highly robust backbone, the COFM have showed unprecedented Sulfuric acid (12 N) permeance reflecting its potential applications for sulfuric acid purification. Also, the as-synthesized COFMs exhibit exceptionally high permeance of acetonitrile (380 Lm-2h-1bar-1) and acetone (340 Lm-2h-1bar-1)

Porous covalent organic nanotubes and their assembly in loops and toroids

Carbon nanotubes, and synthetic organic nanotubes more generally, have in recent decades been widely explored for application in electronic devices, energy storage, catalysis and biosensors. Despite noteworthy progress made in the synthesis of nanotubular architectures with well-defined lengths and diameters, purely covalently bonded organic nanotubes have remained somewhat challenging to prepare. Here we report the synthesis of covalently bonded porous organic nanotubes (CONTs) by Schiff base reaction between a tetratopic amine-functionalized triptycene and a linear dialdehyde. The spatial orientation of the functional groups promotes the growth of the framework in one dimension, and the strong covalent bonds between carbon, nitrogen and oxygen impart the resulting CONTs with high thermal and chemical stability. Upon ultrasonication, the CONTs form intertwined structures that go on to coil and form toroidal superstructures. Computational studies give some insight into the effect of the solvent in this assembly process

Zinc ion interactions in a two-dimensional covalent organic framework based aqueous zinc ion battery

The two-dimensional structural features of covalent organic frameworks (COFs) can promote the electrochemical storage of cations like H+, Li+, and Na+ through both faradaic and non-faradaic processes. However, the electrochemical storage of cations like Zn2+ ion is still unexplored although it bears a promising divalent charge. Herein, for the first time, we have utilized hydroquinone linked β-ketoenamine COF acting as a Zn2+ anchor in an aqueous rechargeable zinc ion battery. The charge-storage mechanism comprises of an efficient reversible interlayer interaction of Zn2+ ions with the functional moieties in the adjacent layers of COF (−182.0 kcal mol−1). Notably, due to the well-defined nanopores and structural organization, a constructed full cell, displays a discharge capacity as high as 276 mA h g−1 at a current rate of 125 mA g−1

Phosphoric acid loaded azo (-N=N-) based covalent organic framework for proton conduction

Two new chemically stable functional crystalline covalent organic frameworkds (COFs) (Tp-Azo and Tp-Stb) were synthesized using the Schiff base reaction between triformylphloroglucinol (Tp) and 4,4-azodianiline (Azo) or 4,4-diaminostilbene (Stb), respectively. Both COFs show the expected keto-enamine form, and high stability toward boiling water, strong acidic, and basic media. H3PO4 doping in Tp-Azo leads to immobilization of the acid within the porous framework, which facilitates proton conduction in both the hydrous (O= 9.9 × 10-4 S cm -1) and anhydrous state (O= 6.7 × 10-5 S cm -1). This report constitutes the first emergence of COFs as proton conducting materials