Síntese de cofs assistida por micro-ondas: otimização do tempo e escalonamento

Abstract

Covalent Organic Frameworks (COFs) are materials with high specific surface area due to the pores formed by their structural organization, which allows them to be used in various applications — such as gas capture, catalysis and filtration. However, despite the good results in the applications, there is still a gap between the use of COFs in academic environments and their industrial implementation. One of the main obstacles is the long synthesis time, generally 72 hours, which results in a low rate of material formation due to the use of traditional methods. Thus, this work presents an optimization in the preparation of COFs aiming to reduce the reaction time while maintaining a yield equivalent to the traditional method. RIO-12 and TPB-DMTP-COF, chosen for their differences in pore size, were produced through microwave-assisted synthesis via condensation between the building blocks 1,3,4-triformylresorcinol and hydrazine hydrate or hydrazine hydrochloride for RIO-12; and between the blocks 1,3,5-Tris(4-aminophenyl)benzene and 2,5-dimethoxyterephthalaldehyde, in the case of TPB-DMTP. The COFs were characterized by powder X-ray diffraction (PXRD) and by N₂ (77 K) and Ar (87 K) adsorption-desorption using Pawley refinement; and the Brunauer–Emmett–Teller (BET), NL-DFT and Nguyen-Do methods in order to evaluate the structural and textural properties of the materials as a function of the reduction in reaction time, as well as to compare the different methodologies employed. In addition, this study evaluated the CO₂ adsorption capacity of RIO-12 synthesized under different conditions. Through this approach, it was possible to reduce the time of the reaction of TPB-DMTP from three days to 3 hours with a yield of 63 % and surface area of 2163 m²/g. In the case of RIO-12, the reduction was more significant: from three days with 901 m²/g of surface area and 77 % yield to 15 minutes, with 741 m²/g of surface area and a 60 % yield. The high CO₂ adsorption capacity shown by the RIO-12 synthesized in 15 minutes is also noteworthy. Thus, the results demonstrate the feasibility of obtaining COFs with high crystallinity and surface area through microwave-assisted synthesis, enabling a reduction of up to 99 % in reaction time without compromising yield — which represents an important step towards enabling large-scale production.