Modificação da argila montmorilonita sódica utilizando diferentes solventes orgânicos: uma nova metodologia

Abstract

Polar organic solvents have the ability to interact with and modify the structure of Montmorillonite (MMT), through solvation or complexation in the clay mineral gallery and/or on the MMT surface, involving certain atomic groups. In this paper, the interaction between MMT and four polar organic solvents - dimethylsulfoxide (DMSO), dimethylformamide (DMF), acetic acid (AA) and acetonitrile – was studied. A mixture of ethyl alcohol, MMT and organic solvent was kept under magnetic stirring in a reflux condenser for 1h. Statical analysis has been applied to evaluate the effects of the amount of DMSO, temperature and sonication time on the modified clay (DMSO-MSAT) basal plane (d001) distance trough a 23 factorial desing. An average increase of 0.57 nm for d001 distance has been found after swelling with DMSO interaction, as confirmed by FTIR analysis with the appearance of bands at 3017, 2931, 706, 1329, 1402 and 1432 cm-1 characteristics of DMSO molecules vibration. BET analysis revealed a decrease in the surface area (from 41.8933 m²/g to 2.1572 m²/g) for SMAT and DMSO-MSAT, respectively. The porosity increases from 1.74 to 1.87 nm for SMAT and DMSO-MSAT, respectively. Statistical analysis showed that only the effect of the amount of DMSO is significant for increasing the interlamellar distance. In addition, at room temperature, the drying time of the sample was only 30 minutes using this methodology. Afterwards, this study proceeded by testing the methodology and interactions that occurs between MMT with the other three solvents, and through XRD analyses revealed that reaction time of 4 hours and 5 mL of an organic solvent were necessary to achieve modifications, such as larger lamellar spacing, reduced delamination, improved structural organization, and interaction with the inner surface of MMT. The TG/DTG diagrams confirmed that the interaction of MMT with DMF occurs trough two different mechanism: free electron pair of the nitrogen or the carbonyl group. This is supported by two endothermic events observed at 202 and 303°C, indicating the release of DMF molecule. Additionally, FTIR spectra demonstrated the interaction between organic solvents and MMT, as the band at 3627cm-1 exhibited a significant decrease, with the MSAT+DMF sample showing the lowest intensity in this band. Notably, the FTIR spectra also suggested that the MMT’s structural decomposition was limited, as the reflected band for the octahedral cations showed a minimal displacement. Furthermore, it can be concluded that when following the methodology proposed in this paper, there is only a low degree of evaporation of the organic solvent molecules insert into the MMT gallery during the material’s drying stage. Consequently, this leads to an increase in the interlamellar space, with values of 0.11 nm for acetonitrile, 0.27 nm for AA and 0.85 nm for DMF.