ATR-FTIR study of the interaction of CO2 with bacterial cellulose-based membranes

Bacterial cellulose (BC) was used as an active material for fabrication of the membrane for CO2 capture. The BC-membrane is further modified with silk fibroin protein and ZnO nanoparticles in order to increase the number of sites that may bind CO2. The interaction of the CO2 with the membranes was investigated by means of ATR-FTIR spectroscopy. The argon purged membranes were used as the control samples. After pressurizing the membranes in CO2 at 3 bar, FTIR spectra were recorded and compared to the spectra of the controls. The interaction of the membrane materials with CO2 were studied by examining two regions of the spectra: 740-610 cm−1 (bending vibrations of CO2) and 2400-2320 cm−1 (asymmetric stretching vibrations of CO2). The envelope of the bending mode peak in 740-610 cm−1 region is resolved into particular peaks and the appearance of the additional line at 654 cm−1 suggested that the absorption bands of CO2 alters because of the Lewis acid-base type of interaction with membranes. The changes in the region of asymmetric stretching vibrations of CO2 were even more pronounced after pressurization. The presence of the number of different sites (active groups) for the CO2 adsorption reflected in the appearance of several additional asymmetric stretching peaks. Also, due to the entrapment of the CO2 in the membrane, a typical CO asymmetric stretching vibration line at ∼2340 cm−1 is shifted towards lower frequencies. The analysis of the results suggested that there is a strong interaction of CO2 with BC membrane, which is additionally improved by its modification with silk fibroin and ZnO nanoparticles. From the results of CO2 permeation experiment, the basic BC membrane, silk fibroin-modified BC membrane and ZnO nanoparticles-modified BC membrane exhibited the CO2 permeability of 2.73, 2.69 and 2.66 Barrer, respectively.