engleski

Computational study of nitrogen-containing covalent organic polymers

Emissions of greenhouse gases have a global impact by contributing to climate change. New materials capable of facile CO2 capture have to be developed and porous materials are very promising candidates for the gas storage due to their low densities and high internal surface areas. Among different crystalline metal-organic (MOFs) and covalent- organic frameworks (COFs), many covalent-organic polymers (COPs), although lacking crystallinity thus making their pore size less uniform, show very similar behaviour toward binding of gases.[1, 2] We have synthesized and characterized a series of new azo-bridged COPs by condensation reactions between 1, 3, 5-tris(4-nitrophenyl)benzene and various aromatic diamino compounds acting as linkers between central units. A computational analysis was performed to give a better insight into selective binding properties of CO2/N2 and core functionalities of new azo-bridged COPs. In addition, a detailed conformational search was carried on (a) core functionalities like trifunctionalized pyridine, triazine and amine ; (b) linkers of variable length including biphenyl and those in which two phenyl rings were separated by one and two methylene groups, oxygen, sulphur, carbonyl and (c) different types of nitrogen- nitrogen linkages (azo, azoxy and azodioxy) connecting two phenyls. Binding energies were calculated to estimate the selectivity of different structural fragments toward selective binding of CO2 and N2. Although, the model is simple in comparison with the whole system, all the investigated fragments show a greater selectivity toward CO2 over N2. The calculated binding energy values may serve as a rough guideline for the design of better nitrogen-based COPs for the selective binding of CO2.

covalent organic polymers, nanoporous materials, molecular mechanics, DFT, binding energy, gas storage, gas separation

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