Novel Mixed Matrix Sodium Alginate–Fullerenol Membranes: Development, Characterization, and Study in Pervaporation Dehydration of Isopropanol

Abstract

Novel mixed matrix dense and supported membranes based on biopolymer sodium alginate (SA) modified by fullerenol were developed. Two kinds of SA–fullerenol membranes were investigated: untreated and cross-linked by immersing the dry membranes in 1.25 wt % calcium chloride (CaCl2) in water for 10 min. The structural and physicochemical characteristics features of the SA–fullerenol composite were investigated by Fourier-transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopic methods, scanning electron (SEM) and atomic force (AFM) microscopies, thermogravimetric analysis (TGA), and swelling experiments. Transport properties were evaluated in pervaporation dehydration of isopropanol in a wide concentration range. It was found that the developed supported cross-linked SA-5/PANCaCl2 membrane (modified by 5 wt % fullerenol) possessed the best transport properties (the highest permeation fluxes 0.64–2.9 kg/(m2 h) and separation factors 26–73,326) for the pervaporation separation of the water–isopropanol mixture in the wide concentration range (12–90 wt % water) at 22 °C and is suitable for the promising application in industry.

Novel Membranes Based on Hydroxyethyl Cellulose/Sodium Alginate for Pervaporation Dehydration of Isopropanol

“…Fullerenol decreased the cross-linking effect of CaCl 2 reducing the number of linked HEC/SA blocks (confirmed by FTIR and NMR data). This led to the more ordered and evenly roughened membrane structure with increased surface roughness (confirmed by SEM and AFM data), and surface hydrophilization (data of contact angle measurements), compared to the unmodified cross-linked HEC/SA membrane resulting in increased membrane permeability [ 63 ]. At the same time, it acted as a cross-linking agent due to bonding with polymer chains preventing a decrease in membrane selectivity to water.…”

“…It was shown that the cross-linking with CaCl 2 of the HEC/SA membrane led to maintaining the peak intensity at ~3280 cm −1 of hydroxyl groups, the peak shift from 1594, 1408, and 1316 cm −1 to 1590, 1412, and 1312 cm −1 , respectively, and the decrease of intensity of these peaks. These changes indicate the ionic interaction of HEC and SA with Ca 2+ forming the “egg box” structure, causing the cross-linking of polymer chains [ 63 , 75 , 76 ]. For the HEC/SA CA membrane, the broadening of the peak at 1600 cm −1 (C=O stretching) and the presence of peak at 1234 cm −1 (corresponding to ether linkage C-O-C between glucose rings in HEC backbone chains) indicate the cross-linking of the HEC/SA membrane with CA [ 87 ].…”

“…The comparison of FTIR spectra of the cross-linked HEC/SA CaCl2 and HEC/SA-5 CaCl2 membranes demonstrates that there are no significant changes in the structure of the 5 wt.% fullerenol modified membrane ( Figure 3 b and Figure 4 ). However, the decrease of peak intensity at ~3280 cm −1 , 1589, and 1411 cm −1 for the HEC/SA-5 CaCl2 membrane may be related to the leveling effect of fullerenol on the cross-linking with calcium chloride, which leads to the reduced cross-linking degree of polymer chains and the reduced linked polymer block number [ 63 ]. Namely, fullerenol modification led to the decrease of “crystallized” phase of the cross-linked membrane and the formation of a more amorphous structure (confirmed by NMR data below).…”

“…The transport properties of the developed membranes were evaluated in pervaporation dehydration of isopropanol in a steady-state regime with stirring, at ambient temperature (22 °C) and with a downstream pressure of 10 −1 mm Hg. The pervaporation setup was described in detail in the work [ 63 ]. The composition of the permeate and the feed was determined using a Chromatek Crystal 5000.2 chromatograph (Chromatec, Nizhny Novgorod, Russia) with a thermal conductivity detector and a “Hayesep R” column.…”

“…For example, the first approach can be the introduction of carbon nanoparticles in HEC/SA blend membranes. The modification of the polymer matrix with carbon nanoparticles, in particular, with water-soluble fullerene derivatives, is one of the perspective and relevant directions for improving the pervaporation performance of polymer membranes demonstrated in earlier studies [ 59 , 60 , 61 , 62 , 63 ]. Especially, the introduction of fullerenol into the polymer matrix leads to a more rigid structure, changes in inner morphology, and greater hydrophilization of the membrane surface, due to the presence of an increased number of polar groups [ 59 , 60 , 61 , 62 , 63 ].…”