Organic/inorganic hybrid membranes have been proposed as promising materials for pervaporation in bioalcohol production.[1-4] However, achieving a uniform dispersion of nano-inorganic fillers in the polymer matrix is a primary challenge in the advancement of hybrid membranes.[5-7] Herein, we proposed two effective approaches to overcome nanoparticle (including porous MOF and nonporous silicon oxide) agglomeration during hybrid membrane formation. The first way is to prepare a homogeneous, nanodisperse MOF/polymer membrane by repeated immersion of a supporting membrane in a dilute MOF/polymer suspension and subsequent removal of defects using a concentrated polymer solution. To improve the nanoscale dispersion of MOF, the nascent MOF suspension was directly dispersed in a polymer solution without drying. This procedure avoids aggregation and re-dispersion of MOF nanoparticles after forming the powder. Analyses confirmed that such strategy effectively diminished aggregation between nanoparticles and led to the formation of a well-dispersed MOF/polymer membrane (see Fig. 1). The ZIF-8/PDMS hybrid membrane exhibited a high separation factor (52.81) and high flux (2800.5 g m-2 h-1) in the separation of 5.0 wt.% n-butanol¨Cwater solution (80 °C) (see Fig. 2). Besides, we performed sonication-enhanced in situ assembly to obtain a hybrid membrane with high degree of dispersion of silicon oxide nanoparticles. Characterizations suggested that through ultrasonic cavitation during assembly of the hybrid membrane, this method could effectively avoid nanoscale agglomeration and in turn uniformly disperse SiO2 nanoparticles within the polymer matrix (see Fig. 3). The prepared organic/inorganic hybrid membrane has a higher hydrophobicity and higher performance. For example, the contact angle of SiO2/PDMS hybrid membrane increased from 135.5° to 146.3º, and the separation factor for the pervaporation of 5 wt.% ethanol/water mixture increased from 7.3 to 12.5. Furthermore, this method could also be used to prepare a well-dispersed ZIF-8/PDMS hybrid membrane with higher performance in the pervaporation of alcohol/water mixtures. These results further suggest that in situ assembly via sonication is a promising approach to improve the dispersion of inorganic fillers and thus the membrane performance. As nanoscale dispersion of inorganic nanoparticles in the polymer matrix is one of the most difficult and important issues in the preparation of high performance hybrid membranes, these strategies we proposed above may contribute to the design and assembly of various hybrid membranes and thus extend the use of these membranes to different uses.
Keywords: Organic/inorganic hybrid membrane, Nanoscale dispersion, Sonication-enhanced in situ assembly, Pervaporation, Alcohol/water mixture
References
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Figure 1. Surface SEM images of suspension-dispersed ZIF-8/PDMS nanohybrid membrane
Figure 2. Pervaporation performance in the recovery of butanol from aqueous solutions reported in previous studies and in our study
Figure 3. Surface SEM images of the in situ sonication assembled SiO2/PDMS nanohybrid membrane