Rota alternativa para síntese de ZIF-7-III via conversão por solvente evaporado

Resumo

Zeolitic Imidazolate frameworks (ZIFs) has established itself as versatile materials for various applications. Usually, the synthesis of these materials uses organic solvents such as dimethylformamide (DMF), diethylformamide (DEF), methanol, and others, therefore, the synthesis free of these solvents is an advantageous option due to the reduction of steps, cost and pollution of the environment. However, syntheses in aqueous solutions tend to use a higher ligand/metal molar ratio or use of a deprotonator base for the synthesis of ZIFs, with its stoichiometric molar ratio. This work proposes the use of the evaporated solvent conversion method (SEC) as an alternative route for the synthesis of ZIF-7-III, aiming at a reduction in the number of steps in the synthesis process as well as the reduction of the number of reagents and production of residue since this method does not require the use of an ammonia atmosphere [2].

For the synthesis with the SEC route, benzimidazole (bIm) was used as the ligand and zinc acetate as the metal source, both were deposed in a 8 ml Teflon beaker supported on 40 g of 4A zeolite containing water, this system was sealed in a 250mL Teflon beaker in a stainless autoclave, which is maintained under thermal treatment at 100°C for 24h. Different Zn2+:bIm:H2O ratios were tested to evaluate the effects of these ratios on the crystallinity and purity of the obtained material. For comparison, an hydrothermal synthesis was made with zinc nitrate as the metal source and ammonium hydroxide as the deprotonate agent maintaining thec ondition of the thermal treatment. For the characterization of the materials obtained, theirt opologies were identified by XRD, their composition was analysed by FTIR, and theirm orphology was analysed by SEM without metallization of the samples.

Comparing the material obtained via SEC with the materials obtained by the hydrothermal method it was observed that theS EC method is quite promising, which is evidenced by the significant increase in the crystallinity of the material obtained, asw ell as the fact that the material obtained is dry, eliminating the need for separation by centrifugation or filtration, however, thes trict control of the amount of water and the bIm/Zn2+ ratio is the key to obtaining a pure and more crystalline phase.