Redox‐Responsive Covalent Organic Nanosheets from Viologens and Calix[4]arene for Iodine and Toxic Dye Capture

Abstract

Owing to their chemical and thermal stabilities, high uptake capacities, and easy recyclability, covalent organic polymers (COPs) have shown promise as pollutant sponges. Herein, we describe the use of diazo coupling to synthesize two cationic COPs, COP1 and COP2 , that incorporate a viologen-based molecular switch and an organic macrocycle, calix[4]arene. The COPs form nanosheets that have height profiles of 6.00 nm and 8.00 nm, respectively, based on AFM measurements. The sheets remain morphologically intact upon one- or two-electron reductions of their viologen subunits. MD simulations of the COPs containing dicationic viologens indicate that the calix[4]arenes adopt a partial cone conformation and that, in height, the individual 2D polymer layers are 5.48 Å in COP1 and 5.65 Å in COP2 , which, together with the AFM measurements, suggests that the nanosheets are composed of 11 and 14 layers, respectively. Whether their viologens are in dicationic, radical cationic, or neutral form, the COPs exhibit high affinity for iodine, reaching up to 200 % mass increase when exposed to iodine vapor at 70 °C, which makes the materials among the best-performing nanosheets for iodine capture reported in the literature. In addition, the COPs effectively remove Congo red from solution in the pH range of 2-10, reaching nearly 100 % removal within 15 minutes at acidic pH.

Remarkably efficient removal of toxic bromate from drinking water with a porphyrin–viologen covalent organic framework

“…4a). The rate constant for the adsorption process was determined by tting the data to a pseudo-second order kinetic model 30,31 and an adsorption rate of 191.45 g mg À1 min À1 was calculated with a correlation coefficient of $1, which is a value higher than that of any other reported adsorbent (Fig. 4b, c and Table S2 †).…”

Macrocycle‐Based Porous Organic Polymers for Separation, Sensing, and Catalysis

“…On this account, Trabolsi and co‐workers have described two novel robust stimuli‐responsive azo‐linked cationic covalent organic polymers that are incorporated with CAs and two different positively charged viologen diamine, allowing the variation of molecular selectivity for specific separation of organic dyes ( Figure a). [ 68 ] By adding reductant sodium dithionate or bis(cyclopentadienyl)cobalt(II) (cobaltocene), dicationic polymer can transform to the corresponding radical cationic polymers and neutral polymers remaining the structure intact, which have been monitored by electron paramagnetic resonance (EPR) spectra. The adsorption performance of as‐synthesized dicationic polymer was investigated toward congo red, an anionic azo‐based dye with severe biotoxicity, which is effective in congo red removal within a broad spectrum of pH range from 2 to 10 and the dicationic state outperforms the radical and neutral counterparts.…”

Nitrogen-rich covalent organic frameworks: a promising class of sensory materials

“…On the other hand, neutral Red-PV-COF was obtained by room temperature stirring of PV-COF for 15 min where its bipyridinium units are chemically reduced using cobaltocene. The azo-bridged viologen-and calix [4]arene-based cationic covalent organic polymers (COPs) denoted as COP1 ++ and COP2 ++ were prepared by the formation of a diazo linkage between a nitro derivative of calix [4]arene (pTNC4A) and two different viologencontaining diamines in the presence of a strong base in a Schlenk tube at 150 °C for 1 d. 169 Oxazole and thiazole linkage. Two new covalently bonded frameworks with oxazole and thiazole-connected units were constructed by the linker exchange method under solvothermal conditions.…”